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Longitudinal and Seasonal Variations in Amplitude and Phase of Diel Carbonate Cycling in Clear, Spring-Fed Rivers

Permanent Link: http://ufdc.ufl.edu/UFE0044431/00001

Material Information

Title: Longitudinal and Seasonal Variations in Amplitude and Phase of Diel Carbonate Cycling in Clear, Spring-Fed Rivers
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Ball, Carolyn Elizabeth
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: biogeochemical -- carbonate -- longitudinal -- river -- seasonal -- spring
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Photosynthesis and respiration cause diel cycles in water variables of karst river systems, including dissolved oxygen, pH, and the equilibrium state of calcite. Four 28-48-hr water-sampling surveys were completed at three locations on the Ichetucknee and Lower Santa Fe rivers, north-central Florida to understand controls on downstream variations in these diel cycles.  Diel cycles of water chemistry at different locations downstream of the headwaters of spring-fed streams were compared using calculated flow-weighted residence times. Diel cycles of carbonate-related variables pH, Ca2+ and DIC concentrations, alkalinity, d13CDIC, and SIcalcite increasingly lagged solar radiation, which drives the cycles, with increasing residence time (i.e. distance downstream). Amplitudes of cycles also decreased with increasing residence time.  Assuming that diel cycling of Ca2+ is related to calcite precipitation, the amount of Ca2+ lost to calcite precipitation decreased by about 0.32 mM/day after 9 hr of water travel time. The increased lag and decreased amplitude could be controlled by at least three processes, including downstream diagenetic reactions as flow is retarded by transient storage, limitation of biological productivity with decreased light availability, and downstream accumulation of reaction products of biological metabolism. The primary process appears to be asynchronous accumulation of metabolic reaction products as water flows downstream.  The longitudinal variations in amplitude and phase in diel cycles indicate that timing and location of water quality measurements need to be considered for long-term monitoring schedules designed to estimate fluxes of materials through watersheds.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Carolyn Elizabeth Ball.
Thesis: Thesis (M.S.)--University of Florida, 2012.
Local: Adviser: Martin, Jonathan B.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044431:00001

Permanent Link: http://ufdc.ufl.edu/UFE0044431/00001

Material Information

Title: Longitudinal and Seasonal Variations in Amplitude and Phase of Diel Carbonate Cycling in Clear, Spring-Fed Rivers
Physical Description: 1 online resource (53 p.)
Language: english
Creator: Ball, Carolyn Elizabeth
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2012

Subjects

Subjects / Keywords: biogeochemical -- carbonate -- longitudinal -- river -- seasonal -- spring
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Photosynthesis and respiration cause diel cycles in water variables of karst river systems, including dissolved oxygen, pH, and the equilibrium state of calcite. Four 28-48-hr water-sampling surveys were completed at three locations on the Ichetucknee and Lower Santa Fe rivers, north-central Florida to understand controls on downstream variations in these diel cycles.  Diel cycles of water chemistry at different locations downstream of the headwaters of spring-fed streams were compared using calculated flow-weighted residence times. Diel cycles of carbonate-related variables pH, Ca2+ and DIC concentrations, alkalinity, d13CDIC, and SIcalcite increasingly lagged solar radiation, which drives the cycles, with increasing residence time (i.e. distance downstream). Amplitudes of cycles also decreased with increasing residence time.  Assuming that diel cycling of Ca2+ is related to calcite precipitation, the amount of Ca2+ lost to calcite precipitation decreased by about 0.32 mM/day after 9 hr of water travel time. The increased lag and decreased amplitude could be controlled by at least three processes, including downstream diagenetic reactions as flow is retarded by transient storage, limitation of biological productivity with decreased light availability, and downstream accumulation of reaction products of biological metabolism. The primary process appears to be asynchronous accumulation of metabolic reaction products as water flows downstream.  The longitudinal variations in amplitude and phase in diel cycles indicate that timing and location of water quality measurements need to be considered for long-term monitoring schedules designed to estimate fluxes of materials through watersheds.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Carolyn Elizabeth Ball.
Thesis: Thesis (M.S.)--University of Florida, 2012.
Local: Adviser: Martin, Jonathan B.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2012
System ID: UFE0044431:00001


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1 L ONGITUDINAL AND SEASONAL VARIATIONS IN AMPLITUDE AND PHASE OF DIEL CARBONATE CYCLING IN CLEAR, SPRING FED RIVERS By CAROLYN BALL A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLME NT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2012

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2 2012 Carolyn Ball

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3 To my family and friends

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4 ACKNOWLEDGMENTS I thank my advisor Dr. Jon Martin and the members of my committee, Dr. Matt Cohen and Dr. Mark Brenner for offering their insight and advice. I acknowledge helpful discussion with fellow graduate students at the Department of Geological Sciences, University of Florida: Marie Kurz, Chad Foster, Bobby Hensley, Amy Brown, Kelly Deuerling, John Eze ll, Mitra Khadka, Pati Spellman, and Jason Gulley. Support for the project has come from the National Science Foundation through grants: EAR0853956 and EAR0910794. Most importantly, I thank my fianc and my parents for their support and encouragement.

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5 TA BLE OF CONTENTS ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREVIATIONS ................................ ................................ ............................. 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 12 Biogeochemical Cycling ................................ ................................ .......................... 12 Transient Storage ................................ ................................ ................................ ... 13 Light Limitations ................................ ................................ ................................ ...... 13 Hypothesis ................................ ................................ ................................ .............. 14 2 STUDY SITE ................................ ................................ ................................ ........... 16 Geology and Hydrogeology ................................ ................................ .................... 16 Hydrology ................................ ................................ ................................ ................ 17 Vegetation ................................ ................................ ................................ ............... 18 3 METHODS ................................ ................................ ................................ .............. 21 Sites ................................ ................................ ................................ ........................ 21 Field Sampling and Analytical Methods ................................ ................................ .. 21 Model Estimates and Diel Cycling ................................ ................................ .......... 24 Flow Weighted Resid ence Time ................................ ................................ ............. 24 4 RESULTS ................................ ................................ ................................ ............... 28 Flow Weighted Residence Time ................................ ................................ ............. 28 Diel C ycles ................................ ................................ ................................ .............. 28 5 DISCUSSION ................................ ................................ ................................ ......... 37 Estimates of Residence Time ................................ ................................ ................. 37 Seasonal Effects of Diel Cycles ................................ ................................ .............. 39 Residence Time Controls on Diel Cycles ................................ ................................ 40 Longitudinal Variations in Ca 2+ Concentrations and Carbonat e Mineral Diagenesis ................................ ................................ ................................ ........... 42 6 CONCLUSION ................................ ................................ ................................ ........ 47 LIST OF REFERENCES ................................ ................................ ............................... 48

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6 BI OGRAPHICAL SKETCH ................................ ................................ ............................ 53

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7 LIST OF TABLES Table page 4 1 Flow w eighted r esidence t ime r esults ................................ ................................ 31 4 2 pH c ross c orrelations ................................ ................................ .......................... 36 4 3 Ca 2+ c ross c orrelations ................................ ................................ ....................... 36 5 1 Comparison of estimated Ca 2+ lost to precipitation at the m onitoring sites. ........ 46

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8 LIST OF FIGURES Figure page 1 1 Diagram showing key diel biogeochemical processes affecting aqueous chemistry of streams. ................................ ................................ ......................... 15 2 1 Location maps of the Santa Fe and Ichetucknee rivers ................................ ...... 20 3 1 Conceptual figure for flow weighted residence time calculation .......................... 27 4 1 Ratio of cumulative spring discharge to river discharge ................................ ..... 31 4 2 Time series measurements ................................ ................................ ................ 32 4 3 A. W inter and B. summer diel cycles ................................ ................................ .. 33 4 4 Lag time from solar radiation versus flow weighted residence time. ................... 34 4 5 Average values and amplitudes ................................ ................................ .......... 35 5 1 Conceptual figure for the proposed processes controlling longitudinal variations in diel biogeochemical cycling with increasing res idence time ........... 45

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9 LIST OF ABBREVIATION S A S Area of n th segment A T Area at sampling site L S Length of n th segment Q S Discharge at n th segment Q T Total discharge at sampling site ] S Residence time of n th segment S,S Residence time of n th segment, occupying discharge from n th spring T Flow weighted residence time V S Volume of n th segment, occupying discharge from n th spring

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10 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science L ONGITUDINAL AND SEASONAL VARIATIONS IN AMPLITUDE AND PHASE OF DIEL CARBONATE CYCLING IN CLEA R, SPRING FED RIVERS By Carolyn Elizabeth Ball August 2012 Chair: Jonathan B. Martin Major: Geolog y Photosynthesis and respiration cause diel cycles in water variables of karst river systems, including dissolved oxygen, pH, and the equilibrium state o f calcite. Four 28 48 hr water sampling surveys were completed at three locations on the Ichetucknee and Lower Santa Fe rivers, north central Florida to understand controls on downstream variations in these diel cycles. Diel cycles of water chemistry at d ifferent locations downstream of the headwaters of spring fed streams were compared using calculated flow weighted residence times. Diel cycles of carbonate related variables pH, Ca 2+ and DIC concentrations, alkalinity, 13 C DIC and SI calcite increasingly lagged solar radiation, which drives the cycles, with increasing residence time (i.e. distance downstream). Amplitudes of cycles also decreased with increasing residence time. Assuming that diel cycling of Ca 2+ is relat ed to calcite precipitation, the amount of Ca 2+ lost to calcite precipitation decreased by about 0.32 mM/day after 9 hr of water travel time. The increased lag and decreased amplitude could be controlled by at least three processes, including downstream di agenetic reactions as flow is retarded by transient storage, limitation of biological productivity with decreased light availability, and downstream accumulation of reaction products of biological metabolism. The primary process

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11 appears to be asynchronous accumulation of metabolic reaction products as water flows downstream. The longitudinal variations in amplitude and phase in diel cycles indicate that timing and location of water quality measurements need to be considered for long term monitoring schedul es designed to estimate fluxes of materials through watersheds.

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12 CHAPTER 1 INTRODUCTION Biogeochemical Cycling Biogeochemical processes, such as photosynthesis and respiration, affect the chemical composition of streams at diel frequencies as a consequence of changes in sunlight and air temperature (Falkowski and Raven, 1997; Neal et al., 2002; Drysdale et al., 2003; Parker et al ., 2007; Nimick et al., 2010) (F igure 1 1 ). During the day, photosynthesis consumes CO 2 and produces O 2 whereas respiration cons umes O 2 and yields CO 2 Only respiration operates by night, consuming O 2 and producing CO 2 (Odum, 1956; Simonsen et al., 1978; Aucour et al., 1999; Clarke, 2002; Parker et al., 2007). Changes in CO 2 concentrations control pH, resulting in associated diel variations in the saturation states of minerals such as calcite (SI calcite ) ( Spiro and Pentecost, 1991; Hartley et al., 1996; Guasch et al., 1998; Cicerone et al., 1999; de Montety et al., 2011). Diel changes in dissolved oxygen (DO) concentrations control the redox potential of the water and thus concentrations of redox sensitive elements such as Fe (Stumm and Morgan, 1996; Loperfido et al., 2009; Nimick et al., 2010; Kurz, in review). Therefore, plant metabolism ultimately affects the chemical compositio n of stream water, the frequency of compositional variations, and equilibrium between stream water and mineral phases, particularly soluble minerals such as calcite (Findlay, 1995) Although these diel variations ultimately stem from variations in solar r adiation, not all cycles are in phase with solar radiation and the magnitude of chemical diel cycles may vary with longitudinal distance along the river channel. Diel variations of water chemical composition may also vary seasonally along stream channels because daylight hours and primary production are lower in winter and higher in summer.

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13 Transient Storage Longitudinal variations in magnitudes and phases of diel cycles may relate to the amount of time required for biological processes to alter stream w ater chemistry, which can be represented by the average residence time of water in the stream channel. Residence time is controlled by river velocity, channel size, and transient storage (Bencala and Walter, 1983). Transient storage occurs where flow is s tagnant relative to the flow in the main channel, for example where sub aquatic plants increase bottom roughness and within the hyporheic zone of the stream bed sediments. Transient storage would impact concentrations of bio reactive elements by increasin g the amount of time for biogeochemical reactions. A common reaction that may occur in the transient storage zone is remineralization of organic carbon (Boulton et al., 1998; Findlay, 1995), which increases concentrations of CO 2 thereby lowering pH and r educing the saturation state of carbonate minerals. Light Limitations Light limitation diminishes photosynthesis by sub aquatic vegetation and thus may contribute to changes in the magnitude of diel signals along the length of stream channels Light limit ation can result from riparian plants that shade the stream. Light limitation may also result from high concentrations of dissolved color (i.e. dissolved organic carbon[DOC]) and inorganic turbidity. Turbidity should increase downstream as increased amou nts of fine grained sediment are entrained in the water column. Thus, increased turbidity should correlate roughly with residence time (Brown and Ritter, 1986; Lenhart et al., 2010).

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14 Hypothesis Variations in diel cycles of dissolved solutes longitudinally along a stream could reflect the amount of carbonate minerals that precipitate or dissolve within a stream channel. Dissolution and precipitation may alter channel morphology (Pentecost, 1992) and play a role in the global carbon cycle (Berner et al., 1 983; Oki, 1999; Aucour et al., 1999; Brunet et al., 2005). Because of diel cycling, synoptic monitoring schemes for stream water chemistry are affected by the timing of sampling, and if longitudinal variations are large, the location of sampling sites alo ng the stream length will also affect sampling results. Differences in diel cycling with distance downstream have major implications for estimates of whole stream metabolism using diel cycling of metabolic products such as DO and NO 3 concentrations (Odum 1956; Heffernan and Cohen, 2010). This study focuses on how diel cycles vary downstream by comparison of diel cycles and estimates of water residence time in the stream channel. Understanding how diel cycles vary spatially and relate to residence time m ay improve the understanding of controls on the diel cycling of stream water chemistry and thus the ultimate composition of stream discharge. This work focuses primarily on the diel variations in factors related to carbonate mineral diagenesis in two river s, the Ichetucknee and the Lower Santa Fe, that flow across carbonate terrains in north central Florida.

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15 Figure 1 1 Diagram showing key diel biogeochemical processes affecting aqueous chemi stry of streams with neutral to alkaline pH. During the day photosynthesis (P) is a more important process than respiration (R), and at night the opposite is true, which alter CO 2 and O 2 concentrations at diel frequencies (modified from Nimich et al., 2010 ).

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16 CHAPTER 2 STUDY SITE Geology and Hydrogeology The Ichetucknee and Lower Santa Fe rivers are located in north central Florida, USA (F igure 2 1 ), which is underlain by the carbonate Floridan Aquifer of Eocene and Oligocene age (Lane, 1986; Scott, 1992). The Floridan Aquifer is confined where the Miocene Hawthorn Group is > 30 m thick and semi confined where the H awthorn Gp is 0 to 30 m thick (F igure 2 1 A). The Floridan Aquifer is unconfined and mantled by a thin veneer of undifferentiated Pleistocene san ds where the Hawthorn Gp is missing. The boundary between the confined and unconfined portions of the Floridan Aquifer is a marine terrace that represents the erosional edge of the Hawthorn Gp (Scott, 1992). This feature is called the Cody Scarp (Hunn and Slack, 1983) and trends northwest to southeast through north central Florida (F igure 2 1 A). The Ichetucknee and Lower Santa Fe rivers are located in the unconfined western portion of the watershed, whereas the Upper Santa Fe River is located in the confi ned to partly confined eastern portion of the watershed. The Upper Santa Fe River is completely captured by a sinkhole (the River Sink) at the Cody Scarp, and the Lower Santa Fe River reemerges as a 1 st magnitude spring called the River Rise approximately 6 km from the River Sink (Katz et al., 1997; Martin and Dean, 2001; Scott, 2004). The Upper Santa Fe River drains wetlands perched on the confining unit, and productivity of the wetlands and surrounding forests causes the river to contain elevated DOC co ncentrations, in the form of tannic, humic, and fulvic acids, which make the stream waters high in dissolved color. The Lower Santa Fe River differs from the Upper Santa Fe River because during baseflow, the Lower Santa Fe River originates

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17 from springs tha t discharge from the Floridan Aquifer, and thus has low DOC concentrations and clear water (Hunn and Slack, 1983). During flooding, DOC rich water passes through the sink rise system, increasing color in the Lower Santa Fe River. Hydrology The Santa Fe Ri ver flows 120 km west across north central Florida from its head waters in the Santa Fe Swamp to its confluence with the Suwannee River. Its watershed drains more than 3500 km 2 including the Ichetucknee Springshed (Hunn and Slack, 1983). The Ichetucknee River flows 8 km south from its head spring to its confluence with the Lower Santa Fe River. Unlike the Santa Fe River, the Ichetucknee River receives minimal surface runoff from the confining unit, but drains approximately 960 km 2 of the Floridan Aquifer (Champion and Upchurch, 2006). From 2007 2012, the Ichetucknee and Lower Santa Fe rivers discharged an average of 9 m 3 /s and 38 m 3 /s, respectively, according to data from USGS gauging sites 02322700 and 02322500, (U.S. Geological Survey, http://waterdata.usgs.gov2012 F igure 2 1 B). The Ichetucknee River has an average depth of 2.15 m (Hensley and Cohen, 2012) and an average width of 18 m (Google Earth, 2012). The Lower Santa Fe River has an average depth of 3 .04 m (Grubbs and Crandall, 2007) and an average width of 33 m (Google Earth, 2012). The Ichetucknee River receives hydrologic input from eight named springs and the Lower Santa Fe River receives inputs from 18 named springs. All springs discharge from th e Floridan Aquifer and the inter spring water discharge rates range from 0.27 to 6.29 m 3 /sec, making them 1 st to 3 rd magnitude springs (Meisner, 1927). First magnitude springs on the Ichetucknee River are Blue Hole and Mission springs, which had an

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18 annual mean discharge of 3.7 and 2.7 m 3 /s, respectively between 2002 and 2008 (U.S. Geological Survey, 2012). The Ichetucknee River is also sourced by several 2 nd rd magnitude sprin g s, including Cedar and Coffee (F igure 2 1 B; Scott, 2004). First July springs. These springs discharge an average 6.3, 5.9, and 2.8 m 3 /s, respectively (Scott, 2004). The Low er Santa Fe River also has numerous 2 nd magnitude springs including Deer, Dogwood, Ginnie, Gilchrist Complex, Pickard, Lilly, Poe, Darby, Columbia, and River Rise springs; and 3 rd magnitude springs including Twin, Sawdus t, Rum, Jonathan, and Hornsby (F igur e 2 1 B; Scott, 2004). In addition to the named springs, unnamed and ungauged springs, boils, and seeps contribute to the flow of both rivers, but the magnitude of those sources is unknown. During baseflow, the River Sink captures less water than discharge s from the River Rise (Martin and Dean, 2001; Screaton el al., 2004). During droughts, all flow in the Upper Santa Fe River is captured by a sinkhole approximately 1.5 km upstream from the River Sink, although water continues to discharge from the River R ise. At these dry times, the River Rise discharges water primarily from the Floridan Aquifer, including a source from around 400 m below the land surface that is enriched in Na + Mg 2+ K + Cl and SO 2 4 (Martin and Dean, 2001; Moore et al., 2009). Mass b alance calculations made by Moore et al. (2009) suggest that during baseflow >50% of the water discharging from River Rise is deep water upwelling from the Floridan Aquifer. Vegetation Subaquatic vegetation in the Ichetucknee River is mainly native submer ged C 3 macrophytes, such as strapleaf sagittaria ( Sagittaria kurziana ) and tapegrass or

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19 eelgrass ( Vallisneria americana ) (Heffernan et al., 2010). These taxa are common in Florida springs (Odum 1957). Other species such as wild rice ( Zizania aquatica ) and emergent ( Cicuta maculata ) and floating species (non native Pistia stratiotes ) are present in the Ichetucknee River (Heffernan et al., 2010). Epiphytic and benthic algal mats are also commonly observed in most springs in north central Florida (Frydenbourg, 2006; Heffernan et al., 2010).

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20 Figure 2 1 Location maps of the Santa Fe and Ichetucknee rivers. (A) Distribution of the confined and unconfined Floridan Aquifer in North Florida (from DEP, modified). (B) Detailed map of the Santa Fe and Ichetucknee rivers (white lines), the tributary springs (white dots), and the three sampling locations (red stars). The site at US 27 Bridge and site 2500 are the locations of USGS gauging stations 02322700 and 02322500.

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21 CHAPTER 3 METHODS To understand how longitud inal and seasonal changes control the magnitude and phase relationship of biogeochemical cycles with respect to solar radiation, four 28 to 48 hr water sampling surveys were completed at three locations, two on the Ichetucknee River and one on the Santa Fe River. Each site was located at a different different water residence times. Sites The farthest upstream site on the Ichetucknee River was at site US 27 Bridge, collo cated with USGS gauging station 02322700 (F igure 2 1 B). A second site, approximately 3 km downstream of site US 27 Bridge, was established at site Three Rivers Estates at the confluence of the Ichetucknee and Lower Santa Fe Rivers. A third site was estab lished on the Lower Santa Fe River (Site 2500) and is collocated with USGS gauging station 02322500. The sites at US 27 Bridge and Three Rivers Estates are located 5080 and 8065 m, respectively from the Head Spring on the Ichetucknee River. Site 2500 is located 21,513 m from River Rise, which we consider to be the headwater s of the Lower Santa Fe River (F igure 2 1 B). Field Sampling and Analytical Methods Samples were collected on four sampling surveys, once each at site Three Rivers Estates and Site 2500 and twice at site US 27 Bridge. While water samples were being collected, field data were recorded at 15 minute intervals using a YSI 6920 sonde, for temperature, specific conductivity (SpC), pH, and dissolved oxygen (DO). NO 3 concentrations were obtain ed with a SUNA in situ nitrate sensor.

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22 Stream discharge, solar radiation, precipitation, and evapotranspiration data were compiled for each sampling time. Information about discharge was compiled from the National Water Information System (NWIS), which i s maintained by the U.S. Geological Survey (USGS) at 15 minute resolution ( http://www.srwmd.state.fl.us/ ). Information about s olar radiation, precipitation, and evapotranspiration was compiled from data measur ed by the Florida Automated Weather Network (FAWN; http://fawn.ifas.ufl.edu) at 15 minute intervals in the town of Alachua, about 15 20 km from all study sites. Water samples were collected at site US 27 Bridge site on 2 November 2009 and 28 May 2010, at s ite Three Rivers Estates on 8 November 2011, and at Site 2500 on 1 June 2011. The sampling period in November 2009 was about 28 hours and all other sampling periods were more than 36 hours. Water samples were collected at least 1 m below the surface usin g an ISCO autosampler and 1 L bottles. After collection, samples were split and preserved for labor atory analyses. Samples for measurement of DIC 13 C DIC were collected unfiltered and preserved with mercuric chloride; samples for measurement of DOC concentration were filtered and preserved using hydrochloric acid; samples for measureme nt of major cations were filtered and preserved with nitric acid; and samples for measurement of major anions and alkalinity were filtered, but not preserved. Samples were kept on ice while in the field and either refrigerated at 4C or frozen (nutrient sa mples) until analyzed. All samples were analyzed at the Department of Geological Sciences, University of Florida for major element (Na + K + Mg 2+ Ca 2+ Cl and SO 4 2 ), nutrient, DOC, and DIC concentrations, 13 C DIC and alkalinity. Alkalinity was titrated to the second end point (i.e. pH=X.X) of the carbonate system within 36 hr of each survey, using 30 m L of

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23 sample and 0.1 N HCl, and calculated using the Gran function (Stumm and Morgan, 1996). Error in the alkalinity measurements was estimated to be 0.05 meq/L from measurement of a NaHCO 3 standard (n = 8). Major element concentrations were measured within 2 months of sampling using an automated Dionex DX500 Ion Chromatograph. Analyses had a precision of <3% i.e. the relative standard deviation of internal standards (n = 16) measured along with the samples. Charge balance errors were <5%, with the exception of two samples. DOC and DIC concentrations and 13 C DIC values were analyzed within 1 2 months of collection. DIC concentrations were measured with a UIC 5011 carbon coulometer coupled to an AutoMate Prep Device. Results were standardized by measurement of known concentra tions of dissolved KHCO 3 The average error was estimated to be 0.02 mM. Dissolved CO 2 in water was extracted with a Thermo Finnigan Gasbench II connected directly to a Thermo Finnigan Delta PlusXL isotopic ratio mass spectrometer, which was used to meas ure 13 C DIC values. Dissolved KHCO 3 13 C DIC value was used for standardization and PDB. Saturation indices (SI = log [IAP/K sp ], where IAP is the ion activity product and Ksp is the solubility constant for individual mineral phases) of the major carbonate minerals were calculated using the geochemical modeling program PHREEQC (Parkhurst and Appelo, 1999) with thermodynamic constants in the phreeqc.dat database.

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24 Model Estimates and Diel Cycling A model was developed to estimate if the observed data fit a sine function with a 24 hr periodicity (Kurz et al., in prep) (3 1) where C E is the concentration estimated by the model, M M is the mean of the measured data, A M is the amplitude of the diel cycle, P M is the phase of the measured diel cycle, and t is the time. The goodness of fit for this model was based on the Akaike Information Criterion, AIC (Akaike, 1974) according to (3 2) where K is the number of parameters, N D is the number of data points, C M is the measured concentration, and C E is either the concentration estimated by E quation 3 1 or the mean value of the data. I considered the measured values to be better represented by a sinusoidal cycle, if the AIC value fit the observed data better using C E based on the results of E quation 3 1 rather than C E based on the mean of the data. Phase shifts between site US 27 Bridge (May 2010), site US 27 Bridge (Novemb er 2009), Three River Estates (November 2011), and Site 2500 (June 2011) were compared through cross correlation analysis as an alternate approach to assess the lag between each site for the pH and Ca 2+ concentration cycles. Flow Weighted Residence Time M ean residence times at each sampling location were estimated by summing the fraction of discharge from each spring contributing to the di scharge at the sampling point (F igure 3 1 ). Cross sectional area of required flow from each spring discharge (A S ) was calculated by

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25 ( 3 3 ) where Q T is the total discharge at the sampling site, Q S is the discharge at an individual spring, and A T is the cross section area at the sampling site. A T was calculated using stream width measured with Google Earth and stream depth estimates found in Hensley and Cohen (2012) and Grubbs and Crandall (2007) for the Ichetucknee and Lower Santa Fe Rivers, respectively. Q T was acquired from USGS NWIS on the day of sampling. Values for Q S were average discharge val ues for the springs reported in Scott (2004). The springs are ungauged and thus their discharges are unknown for the sampling periods. The average discharges were normalized to the stream flow during each sampling period. Sampling occurred during low flow periods and thus typically the river discharges at the sampling sites were lower than average river flows and consequently, averages for each spring discharge were also proportionately lower. The volume of the channel occupied by discharge from each spri ng (V S ) was estimated by ( 3 4 ) where L S is the length of the channel from the spring to the sampling location. The length of each segment was measured using Google Earth. I ndividual reside nce times S ) was estimated by (3 5) The residence time for each spring discharge were then flow S,S ) by (3 6) and these weighted residence times were summed for each flow to estimate the flow T )

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26 ( 3 7)

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27 Figure 3 1 Conceptual figure for flow weighted residence time calculation

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28 CHAPTER 4 RESULTS Flow Weighted Residence Time Estimat ed residence times differ at each of the sampling locations because of differences in the distance between the head springs and sampling points and the number of springs and discharges. Most springs discharging to the Ichetucknee River occur near the head waters of the river. Nearly 40% of the Lower Santa Fe River flow originates from five springs about 15 km from Site 2500, which is almost twice the dist ance of the Ichetucknee River (F igure 4 1 ). No springs occur between site US 27 Bridge and site Three R ivers Estates, and thus site Three River Estates has a proportionately longer residence time than site US 27 Bridge. Based on the spring discharges and the distance between the springs and the sampling locations, flow weighted residence times for water at the sampling locations were found to be 5.2, 9.0, and 14.1 hrs for site US 27 Bridge, site Three Rivers Estates, and Site 2500, respectively. Site 2500 had a 60% and 271% longer residence time than at site Three Rivers Estate and site US 27 Bridge, respec tively (Table 4 1 and F igure 4 1 ). Diel Cycles Diel cycles occur in DO concentration, pH, Ca 2+ concentration, SI calcite 13 C DIC values at all sites ( F igure 4 2 ). These diel cycles decreased in amplitude fro m site US 27 Bridge to site Three Rivers Estates to Site 2500. At site US 27 Bridge and site Three Rivers Estates, pH, SI calcite and DO concentration diel cycles were asymmetrical and had constant values for about 6 and 3 hours during the night, respectiv ely. At Site 2500, the pH and SI calcite were symmetrical over the 24 hour cycle. The DO cycle was also asymmetrical at Site 2500,

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29 but never became constant at nighttime and instead displayed a gradual decrease through the night with a rapid rise during th e day. All diel cycles lagged solar radiation but by different amounts. All measured components, other than Cl concentrations, show signif icant diel cycles according to E quations 3 1 and 3 2 ( F igure 4 3 ). Diel cycles of DIC concentration, alkalinity, and Ca 2 + concentrations lag the solar radiation cycle by different amounts depending on the season they were collected. During winter (November 2009 and November 2011 sampling times), the diel cycles of DIC concentration, alkalinity, and Ca 2+ concentrations lag s olar radiation by 12 18 hrs (F igure 4 3 A). During summer (May 2010 and June 2011 sampling times), DIC concentration, alkalinity, and Ca 2+ concentrations lag solar radiation by 18 24 hrs, or about a 4 hours longer lag than in winter ( F igure 4 3 B). Regardle ss of these seasonal variations, diel cycles of all components consistently lag solar radiation with increased residence time ( F igure 4 4 ). Lag time in DO concentration, pH, Ca 2+ concentration, SI calcite temperature, alkalinity, DIC 13 C DIC values increased from site US 27 Bridge to site Three Rivers Estates to Site 2500. At site US 27 Bridge, with an estimated residence time of about 5.2 hrs, SI calcite DO concentration, temperature, and pH lag solar radiation by about 4.2 hrs in May 2010, while at Site 2500, with an estimated residence time of 14.1 hrs, the same components lag solar radiation by about 5.9 hrs in June 2011 (F igure 4 4 ). DIC and Ca 2+ concentrations at Site 2500 lag com ponents at site US 27 Bridge by about 1.8 hrs. SI calcite 13 C DIC value, and Ca 2+ concentration at site Three Rivers Estates in November 2011 lag these values at site US 27 Bridge in November 2009 by about 1 hr.

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30 Cross correlation values support the observati ons that lag times increase with increasing distance from the head springs. The cross correlation analyses, although limited to a resolution of 1 hr because of the sampling interval, indicate that pH has a 2+ concentrat

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31 Figure 4 1 Ratio of cumulative spring discharge to river discharge (at US 27 Bridge, Three Rivers Estates, and Site 2500 ) compared to the distance from each spring to the sampling location. US 27 Bridge and T hree Rivers Estates have identical slopes because they are located on the same river with identical spring inputs. Stars indicate sampling location distance for US 27 Bridge (light gray), Three Rivers Estates (dark gray), and Site 2500 (black). Table 4 1 Flow w eighted r esidence t ime r esults River Site Location Sampling Time Weighted Residence Time Ichetucknee US 27 Bridge May 2010 5.2 hr Ichetucknee US 27 Bridge November 2009 5.2 hr Ichetucknee Three Rivers Estates Novem ber 2011 9.0 hr Lower Santa Fe Site 2500 June 2011 14.1 hr

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32 Figure 4 2 Time series measurements of (A) DO concentration, (B) pH, (C) calcium concentration, (D) the saturation index of calcite, (E) temperature, (F) alkalinity, (G) DIC concentration and ( 13 C DIC values from all four sampling surveys. Open points were sampled during the summer; filled points were sampled during the winter. Triangles are data on the Ichetucknee River, and circle data are on the Santa Fe River.

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33 Figure 4 3 A. Winter and B. summer diel cycles. The upper vertical line represents the phase of solar radiation and all other data are plotted clockwise around the circle depending on their phase lags relative to solar radiation. The circles radiating out from the center ref lect the good ness of fit estimated based on E quation 3 2. Cl shows no significant diel variation as shown by its location at the center of the figure.

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34 Figure 4 4 La g time from solar radiation versus flow weighted residence time for (A) DO concentra tion, (B) pH, (C) calcium concentration, (D) the saturation index of calcite, (E) temperature, (F) alkalinity, (G) DIC concentration, and (H) 13 C DIC value. Open data were sampled during the summer, closed data were sampled during the winter, triangles ar e data on the Ichetucknee River, and circle data are on the Santa Fe River.

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35 Figure 4 5 Average values and amplitudes of DO concentration, pH, calcium concentration, and the saturation index of calcite compared to flow weighted residence time.

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36 Table 4 2 pH c ross c orrelations pH US 27 Bridge May (5.2h) US 27 Bridge Nov (5.2h) Three Rivers Estates Nov (9.0h) Site 2500 Jun (14.1h) US 27 Bridge May (5.2h) X 0.965 0.926 0.883 US 27 Bridge Nov (5.2h) 1 X 0.949 0.902 Three Riv ers Estates Nov (9.0h) 0 0 X 0.944 Site 2500 Jun (14.1h) 1 1 0 X Table 4 3 Ca 2+ c ross c orrelations Ca 2+ US 27 Bridge May (5.2h) US 27 Bridge Nov (5.2h) Three Rivers Estates Nov (9.0h) Site 2500 Jun (14.1h) US 27 Bridge May (5.2h) X 0.631 0.65 0.791 US 27 Bridge Nov (5.2h) 2 X 0.652 0.341 Three Rivers Estates Nov (9.0h) 0 2 X 0.463 Site 2500 Jun (14.1h) 1 2 1 X Bottom results are lag times and top results are r 2 values

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37 CHAPTER 5 DISCUSSION It is important to understand longitudinal variations in diel cycling because they affect whole stream estimates of metabolic products, such as DO and NO 3 concentrations. Depending on where measurements are taken along streams, estimates of whole stream metabolism may vary because of the downstream changes in amplitude and phase. In addition to DO and NO 3 concentrations, using whole stream estimates of calcite mineral precipitation may have major implications for estimates of short term climate change (Liu et al., 2010). Accurate quantification of calcite precipitation in streams is important because it effects the bicarbonate concentration within the river and thus affects atmospheric CO 2 Liu et al. (2010) argue that calcite precipitation can affect short term climate change as well, by the removal of CO 2 from the atmosphere. Consequently, we focus on how diel cycles vary downstream through a comparison of the diel cycles and estimates of residence time of water in the stream channel. Understanding how diel cycles var y spatially and relate to residence time may improve the understanding of controls on the diel cycling of stream water chemistry and thus the ultimate composition of stream discharge. Estimates of Residence Time Estima tes of residence time based on E quatio ns 3 3 through 3 7 match closely with results from a single tracer study of residence time on the Ichetucknee River reported in Hensley and Cohen (2012). This tracer study found residence time to be about 6 hrs from Blue Hole Spring to site US 27 Bridge when the river was discharging approximately 6.5 m 3 /s. This measured residence time is similar to our estimate of 5.2 hrs at site US 27 Bridge when discharge was 7.8 and 8.2 m 3 /s on November 2009 and

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38 May 2010, respectively. Residence time would be expected to be shorter during elevated flow, which may explain the difference between the residence time reported in Hensely and Cohen (2012) and my results. In addition, Hensley and Cohen (2012) suggested that approximately 20% of the residence time they measured re sulted from transient storage, including hyporheic exchange and retardation of flow by subaquatic vegetation. My estimates of residence time do not include transient storage and thus would be expected to be shorter than those found by tracer studies. Alt hough transient storage is neglected in my estimates of residence time presented here, similarity of my asured residence time suggests E quations 3 3 to 3 7 provide reasonable estimates for residence time. The residence t ime at the sampling location appears to control the asymmetry of diel cycles of DO concentration, pH, and SI calcite values at site US 27 Bridge and site Three River Estates (F ig ure 4 2 ). These solutes exhibit minima at night that remain constant for appro ximately 6 hrs at site US 27 Bridge and about 3 hrs at site Three Rivers Estate. These sites have residence times shorter than the length of night, thus allowing water to flow to the site from the springs before sub aqueous plants would begin photosynthes is and associated alteration to the stream water chemistry. Consequently, the water would retain the composition of the spring water, which has little DO, low pH and SI calcite values (Martin and Gordon, 2000; Champion and Upchurch, 2006; Heffernan et al., 2010). Similar periods of constant minima do not occur at Site 2500 because the residence time there allows at least a fraction of the water flowing past the site to have been modified by photosynthesis. This relationship between the constant minima in water composition and the residence time suggests

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39 that the shapes, and possibly the amplitudes, of diel cycles are impacted by the residence times of the water through accumulation of reaction products during flow from the head waters to the sampling sites Seasonal Effects of Diel Cycles Seasonal variations in precipitation or evapotranspiration could affect downstream variations in diel cycles by changing the water budget and thus the concentrations of solutes and lag in the cycle relative to solar radiat ion (e.g., Lundquist and Cayan, 2002; Czikowsky and Fitzjarrald, 2004). In the field area, precipitation is highly seasonal, with about 50% of the annual rainfall occurring during the months of June to September (Jordan 1985; Chen and Gerber 1990). Duri ng the rainy season, evapotranspiration is elevated and thus most high discharge events occur during the passage of cold fronts during the winter dry season and occasionally during the passage of tropical storms, most commonly in August and September (Jord an, 1985; Pentecost, 1992; Martin and Gordon, 2000). Seasonal differences in precipitation and evapotranspiration appear to have little effect on variations in chemical composition. No precipitation fell during May 14 th 2010, or November 2 nd 2009 samp ling trips, but evapotranspiration was 0.43 cm on May 14 th 2010, but only 0.08 cm in November 2 nd 2009. Regardless of the differences in evapotranspiration, Cl concentrations were constant at 0.3 mM during both sampling times. Because Cl is conservati ve in this setting (Martin and Gordon, 2000), its constant value indicates evapotranspiration has little to no impact on the concentration of water chemistry. DIC concentration, Ca 2+ concentration, and alkalinity lag solar radiation at site US 27 Bridge by ~4 hrs more in May 2010 than November 2009 sampling times (F igure 4

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40 3 ). This greater lag may result from seasonal variations in plant metabolic processes. The combination of vigorous growth of plants during the summer and the longer period of daylight during the summer could cause a greater lag than during winter because the timing of plant productivity. Seasonal variations in lag times of temperature, pH, SI calcite 13 C DIC values are minimal and less consistent than longitudinal variations. Residence Time Controls on Diel Cycles Longitudinal variations in phase and amplitude of diel carbonate cycling appear to be largely controlled by reside nce times (F igures 4 4 and 4 5 ). These changes could be controlled by at least three pr ocesses, including downstream diagenetic reactions as flow is retarded by transient storage, limitation of biological productivity with decreased light availability, and downstream accumulation of reaction products of biological metabolic processes ( F igure 5 1 ). Transient storage, including hyporheic exchange, has previously been proposed to cause a time lag in temperature with increasing residence time (Loheide and Gorelick, 2006; Vogt et al., 2010). Transient storage may be similar for both the Ichetuck nee and Lower Santa Fe rivers because they both flow over unconfined Ocala Limestone, which retains elevated primary depositional porosity (i.e. the eogenetic karst aquifers of Vacher and Mylroie, 2002) and thus has elevated hydraulic conductivity, allowin g extensive exchange between surface and groundwater (Martin and Dean, 2000; Screaton et al., 2004; Ritorto et al., 2009). The Ichetucknee River has a thicker layer of sediment overlying the Ocala Limestone than the Santa Fe River, which may enhance or li mit transient storage there. Transient storage should increase the lag of the diel cycles relative to solar radiation by increasing residence time of the water and thus

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41 changing the phase of the diel cycle. Transient storage could also either increase or decrease the amplitudes of the diel cycle with increasing residence time, depending on whether exchange acts as a source or sink of biogeochemical elements. In particular, remineralization of organic carbon within the hyporheic zone would increase the DIC concentration and decrease the DO concentrations of the pore water. The lag in diel cycles relative to solar radiation increases rather than decreases with distance downstream, indicating that transient storage is a minor effect on the diel cycles ( F igur e 5 1 A). Nonetheless, with hyporheic exchange this DO poor and CO 2 rich water would impact the CO 2 and O 2 concentrations within the water column, and the CO 2 concentration will alter the saturation state of the river with respect to carbonate minerals. Li ght limitations, resulting from turbidity, plant cover, or from increased concentrations of DOC, can decrease photosynthesis and thus decrease the reaction products from primary production as well as magnitudes of diel cycles (Tilzer, 1973; Jeydrysek, 1998 ; Loperfido et al., 2010; de Montety et al., 2011). Flow conditions were low during the three sampling periods and thus DOC concentrations were also low and unlikely to impact the diel cycles during this study. Although the water was clear, turbidity is known to increase with distance downstream ( Brown and Ritter, 1986; Lenhart et al., 2010). If a similar effect occurs in the Ichetucknee and Santa Fe rivers, the limitation of light may reduce diel variations downstream (F igures 4 4 and 4 5 ). Because of downstream reduction in light, in the magnitude of diel cycles should decre ase in a downstream direction (F igure 5 1 B). This process should not cause a shift in the phase of the signal.

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42 The most likely control on lag and the decrease in amplitude of the diel cycles is from downstream accumulation of reaction products of the biological metabolic processes. The timing of photosynthesis and respiration is controlled by the amount of solar radiation that hits the river surface. These metabolic processes var y with distance downstream causing longitudinal changes in whole stream ecology. The magnitude of these processes will occur simultaneously along the river channel but will depend on time of day. Water emerging from the springs will obtain a diel cycle in chemical composition that corresponds to the immediate variation in light. As water flows downstream, chemical changes caused by primary productivity will be out of phase with the cycle in the section of t he river immediately upstream (F igure 5 1 C). C onsequently, as water flows downstream, successive shifts in the timing of the metabolic cycle will continuously reduce the magnitude and increase the lag of the diel signal at the sampling location. The cumulative effect of these shifts results in the ob served decreases in amplitude (F igure 4 5 ) and increases in lag time (F igure 4 4 ) with increasing residence time ( F igure 5 1 C). Although each of these processes (i.e. transient storage, light limitation, and downstream accumulation) produces variations in the downstream variation in the diel cycles, none of them acts alone and combined they are likely to enhance the observed signal ( F igure 5 1 D). Longitudinal V ariations in Ca 2+ C oncentrations and C arbonate M ineral D iagenesis Average Ca 2+ concentration i ncreases with residence time in the Ichetuckn ee and Santa Fe rivers (F igure 4 5 ). The longitudinal increase in Ca 2+ may have implications for whole stream calcite precipitation budgets, and thus affect short term climate change predictions. This increase in Ca 2+ is somewhat surprising considering that water in both the Santa Fe and Ichetucknee rivers is continuously supersaturated with respect

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43 to calcite and raises the question of what could be the source of the Ca 2+ (F igure 4 2 ). Pore water in sediments in the channel of the Ichetucknee River has been found to have Ca 2+ concentrations of 1.40 mM, which is about 0.10 mM greater than the river water (Kurz et al., 2011). Pore water chemistry is dominated by the remineralization of organic carbon which in t urn drives changes in carbonate saturation state making the pore waters a potential source of calcite undersaturated water to the river. Hydraulic head gradients are oriented from the pore water to the stream suggesting the river gains Ca 2+ rich pore wate r (Kurz et al., 2011). Furthermore, hyporheic exchange would allow river water to react with the bottom sediments and increase its Ca 2+ concentration. Consequently, with increased residence times, more Ca 2+ rich water could enter the system, causing the o bserved relationship between increased Ca 2+ concentration and the es timated residence time (F igure 4 5 ). Regardless of the overall increase in Ca 2+ concentration with distance downstream, the diel decreases in Ca 2+ concentrations reflect precipitation of calcite (de Montety et al., 2011) considering the river water is continuously supersaturated w ith respect to calcite ( F igure 4 2 D). Whatever calcite precipitates is likely to be flushed from the system since no deposits of massive calcite occur in the riv ers. de Montety et al. (2011) suggests that fine grained authigenic calcite may remain in suspension and be exported out of the Ichetucknee River in colloidal or fine grained particulate form. High pH microenvironments, such as algae, are able to have lo calized carbonate precipitation due to small scale photosynthesis driven cycles (Hartley et al., 1996; Shiraishi et al., 2010). Consequently, calcite could also precipitate on subaquatic

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44 vegetation or on the surface of biofilms, which would also be export ed from the system (e.g., Hoffer French and Herman, 1989; de Montety et al., 2011). Assuming that the diel cycling of Ca 2+ results from calcite precipitation, we can estimate the amount of calcite precipitated longitudinally along the rivers based on the loss of Ca 2+ assuming the difference between peak Ca 2+ concentration and the measured Ca 2+ concentration over a 24 hour period at each sampling location represents the amount of calcite precipitated (de Montety et al., 2011). With this assumption, 0.66 mM/day of calcite precipitated on May 14 th 2010 at site US 27 Bridge, 0.60 mM/day of calcite precipitated on November 9 th 2011 at site Three Rivers Estates and 0.34 mM/day on June 1 st 2011 at Site 2500 (T able 5 1 ). This pattern suggests that less calc ite precipitates as residence time of the water increases. In contrast with this systematic change, only 0.16 mM/day of calcite precipitates at site US 27 Bridge on November 2 nd 2009.

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45 Figure 5 1 Conceptual figure for the proposed processes contro lling longitudinal variations in diel biogeochemical cycling with increasing residence time. (A) transient storage, (B) light limitation and (C) accumulation. Panel D shows the accumulative effects of all processes. The right hand side of the diagram shows the sum of the variations in cycles. The cumulative effect results in decreased amplitudes and increased lags relative to solar radiation downstream.

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46 Table 5 1 Comparison of estimated Ca 2+ lost to precipitation at the monitoring sites. US 27 Bridge May 2010 US 27 Bridge Nov. 2009 Three Rivers Estates Nov. 2011 Site 2500 June 2011 (Ca 2+ ) (Ca 2+ ) (Ca 2+ ) (Ca 2+ ) Loss to precip. (mM/day) 0.66 *0.16 0.60 0.34 *Possible outlier

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47 CHAPTER 6 CONCLUSION To understand the control of residence times on t he amplitude and timing of biogeochemical cycles, four 28 to 48 hr water sampling surveys were completed at three locations on the Ichetucknee and Lower Santa Fe rivers, north central Florida. Estimates of residence time at each of location increased with distance from the head springs from 5.2 to 14.1 hrs. Diel cycles of carbonate components, Ca 2+ concentrations, DIC concentrations, alkalinity, pH, 13 C DIC values, and SI calcite lagged solar radiation by more than 4 hours with increasing residence time. A dditionally, amplitudes of the diel cycles decreased with increasing residence time. Loss of Ca 2+ due to calcite precipitation decreased with increasing residence time. The observed lags, decreases in amplitude, and loss of Ca 2+ appear to result from sev eral processes in the river. The primary process appears to be the asynchronous accumulation of metabolic reaction products as water flows downstream. Decreasing amounts of light with increased turbidity limits the amount of photosynthesis and respiratio n, which decreases the amplitude of the diel cycles, but is unlikely to cause a lag relative to solar radiation. Transient storage, which will increase the residence time as well as alter the chemical composition of the water, but the changes in concentra tions could either increase or decrease depending on whether the pore waters represent a source or sink of material to the river. Observations of longitudinal variations in diel cycles may provide information on carbonate mineral diagenesis and its effect s on channel morphology and the global carbon cycle. In addition, differences in diel cycling with distance downstream have major implications for estimates of whole stream metabolism, shown by diel shifts in concentrations of metabolic products such as D O and NO 3

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48 LIST OF REFERENCES Akaike, H. 1974. A new look at the stat istical model identification. IEEE Transactions on Automatic Control 19:716 723 Aucour, A. M., Sheppard, S. M. F., Guyomar, O., Wattelet, J., 1999. Use of 13C to trace origin and cycling of inorganic carbon in the Rhone river system. Chemical Geology 159, 87 105. Berner RA, Lasaga AC, Garrels RM. 1983. The carbonate silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 millions years. American Journ al of Science 283 (7): 641 683. Boulton, A.J., Finlay, S., Marmonier, P., Stanely, E.H., and Valett, H.M. 1998. The functional significance of the hyporheic zone in streams and rivers. Annual Review of Ecology and Systematics. 29: 59 81 Brown, W.M., Ritt er, J.R. 1971. Sediment transport and turbidity in the eel river basin, California. Geological Survey Water Supply Paper Brunet, F., Gaiero, D., Probst, J. L., Depetris, P. J., Lafaye, F. G., Stille, P. 2005. delta 13C tracing of dissolved inorganic carbo n sources in Patagonian rivers (Argentina). Hydrological Processes 19, 3321 3344. Champion, K. M., Upchurch, S. B., 2006. Delineation of spring water source areas in the Ichetucknee springshed. Tampa, Florida, Report prepared for the Florida Department of Environmental Protection, SDII Global Corporation: 39. Chen, E., and Gerber, J.F. 1990. Ecosystems of Florida. Climate. University of Central Florida Press. P 11 34 Clark, I.D., Fritz, P., 1997. Environmental Isotopes in Hydrogeology. Lewis Publishers, New York. Clarke, S. J., 2002. Vegetation growth in rivers: influences upon sediment and nutrient dynamics. Progress in Physical Geography 26, 159 172. Czikowsky, M.J., Fitzjarrald, D.R., 2004. Evidence of seasonal changes in evapotranspiration in easter n U.S. hydrological records. J. Hydrometeorol. 5, 974 988. de Montety, V., J.B. Martin, M.J. Cohen, C. Foster, M.J. Kurz, 2011. Influence of diel biogeochemical cycles on carbonate equilibrium in a karst river. Chemical Geology 283(1 2), 31 43

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49 Kurz, M.J ., Martin, J.B., and Cohen, M.J., 2011. Pore Water Chemistry and Hydrology in a Spring Fed River: Implications for Hyporheic Control of Nutrient Cycling and Speleogenesis. American Geophysical Union, abstract. Kurz, M. J., de Montety, V., Martin, J. B., Cohen, M. J., Foster, C., in prep. Controls of diel variations in metal concentrations in a karst river at seasonal scales. Falkowski, P.G., Raven, J.A., 1997. Aquatic Photosynthesis. Blackwell Sciences, Malden. Findlay, S., 1995. Importance of surface s ubsurface exchange in stream ecosystems: the hyporheic zone. Limnology and Oceanography 40, 159 164. Gammons, C.H., Nimick, D.A., Parker, S.R., Cleasby, T.E., McCleskey, R.B., 2005. Diel behavior of iron and other heavy metals in a mountain stream with ac idic to neutral pH: Fisher Creek, Montana, USA. Geochim. Cosmochim. Acta 69, 2505 2516. Gippel, C.J. 2006. Potential of turbidity monitoring for measuring the transport of suspended solids in streams. Hydrological processes. DOI: 10.1002/hyp.3360090108 G oogle Earth, 2012. Grubbs, J.W., and Crandall, C.A., 2007. Exchanges of Water between the Upper Floridan Aquifer and the Lower Suwannee and Lower Santa Fe Rivers, Florida: U.S. Geological Survey PP 1656 C 83 p. Guasch, H., Armengol, J., Marti, E., Sabater, S., 1998. Diurnal variation in dissolved oxygen and carbon dioxide in two low order streams. Water Research 32, 1067 1074. Hartley, A. M., House, W. A., Leadbeater, B. S. C., Callow, M. E., 1996. The u se of microelectrodes to study the precipitation of calcite upon algal biofilms. Journal of Colloid and Interface Science 183, 498 505. Heffernan, J. B., Cohen, M. J., 2010. Direct and indirect coupling of primary production and diel nitrate dynamics in a large spring fed river.Limnol.Oceanogr. 55, 677 688. Heffernan, J. B., Liebowitz, D. M., Frazer, T. K., Evans, J. M., Cohen, M. J., 2010. Algal blooms and the nitrogen enrichment hypothesis in Florida springs: evidence, alternatives, and adaptive managem ent. Ecological Applications 20, 816 829. Hensley, R. and Cohen, M. 2012. Controls on solute transport in large spring fed karst rivers.

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50 Hoffer French, K.J. and Herman, J.S. 1989. Evaluation of hydrological and biological influences on CO2 fluxes from a karst stream. Journal of Hydrology 108, 189 212. Hunn, J.D., and Slack, L.J., 1983, Water resources of the Santa Fe River Basin, Florida, U.S. Geological Survey, Water Resources Inves tigations Report 83 4075, 105 climate: implications for water. Water resources atlas of Florida. Institute of Science and Public Affairs, Florida State University. p. 18 35 Katz, B.G., DeHan, R.S., Hirten, J.J., and Catches, J.S., 1997, Interactions between ground water and surface w ater in the Suwannee River Basin, Florida, Journal of the American Water Resources Association v. 33, p. 1237 1254. Lane, E. 1986.Karst in Florida, Special Publication No. 29, Florida Geological Survey, Tallahassee, Florida, 100 p. Langmuir, D. 1997. Aq ueous environmental chemistry. New Jersey, Prentice Hall, Inc. Lenhart, C., Brooks, K., Heneley, D., Magner, J. 2010. Spatial and temporal variation in suspended sediment, organic matter, and turbidity in a Minnesota prairie river: implications for TMDL. Environmental Monitoring Assessment. 165:435 447 Liu, Z., Liu, X., Liao, C. 2008. Daytime deposition and nighttime dissolution of calcium carbonate controlled by submerged plants in a karst spring fed pool: insights from high time resolution monitoring of physico chemistry of water. Environmental Geology 55, 1159 1168. Loheide, S.P., and Gorelick, S.M.2006. Quantifying stream aquifer interactions through the analysis of remotely sensed thermographic profiles and in situ temperature histories.Enviromental Science Technologies. 40, 3336 3341. Loperfido, J.V., Just, C.L. Schnoor, J.L., 2009. High frequency diel dissolved oxygen stream data modeled for variable temperature and scale. J. Environ. Eng. 135, 1250 1256. Loperfido, J.V., Just, C.L., Papanicolaou, A.N., Schnoor, J.L., 2010. In situ sensing to understand diel t urbidity cycles, suspended solids, and nutrient transport in Clear Creek, Iowa. Water Resour. Res. 46, W06525. doi10.1029/2009WR008293. Lundquist, J.D., Cayan, D., 2002. Seasonal and spatial patterns in diurnal cycles in streamflow in the Western United S tates. J. Hydrometeorol. 3, 591 603.

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51 Martin J.B., and Dean, R.W.2001.Exchange of water between conduits and matrix in the Floridan Aquifer, Chemical Geology, 179: 145 155. Martin, J.B., Gordon, S.L., 2000. Surface and ground water mixing, flow paths, and temporal variations in chemical compositions of karst springs. In: Sasowsky, I.E., Wicks, C. (Eds.), Groundwater Flow and Contaminant Transport in Karst Aquifers. A.A. Balkema, Rotterdam, pp. 65 92. Martin, J.B. and Screaton, E.J. 2000, Exchange of matri x and conduit water with examples from the Floridan Aquifer: U.S. Geological Survey Water Resources Investigations Report 01 4011, p. 38 44. Meisner, 1927. Spr ing discharge magnitude Moore, P.J., Martin, J.B., Screaton, E.J. 2009.Geochemical and statis tical evidence of recharge, mixing, and controls on spring discharge in an eogenetic karst aquifer. Journal of Hydrology 376 (2009) 443 455 Munn, N. L., andMeyer, J.L. 1988. Rapid flowthrough the sediments of a headwater stream inthe southern Appalachians Freshwater Biology20:235 240. Nimick, D.A.2010. Diel biogeochemical processes and their effect on the aqueous chemistry of streams: A review, Chem. Geol. doi:10.1016/j.chemgeo.2010.08.017 Odum, H. T. 1956. Primary Production in Flowing Waters. Limnolog y and Oceanography 1, 102 117. Oki, T. 1999. The global water cycle. In: Browning, K., Gurney, R. (Eds.), Global Energy and Water Cycles. Cambridge University Press, pp. 10 27. Park, C.C. 1977. World wide variations in hydraulic geometry exponents of str eam channels: an analysis and some observations. Journal of Hydrology 33:133 146. Parker, S. R., Gammons, C. H., Poulson, S. R., DeGrandpre, M. D. 2007. Diel variations in stream chemistry and isotopic composition of dissolved inorganic carbon, upper Cla rk Fork River, Montana, USA. Applied Geochemistry 22, 1329 1343. Parker, S. R., Gammons, C. H., Poulson, S. R., DeGrandpre, M. D., Weyer, C. L., Smith, M. G., Babcock, J. N., Oba, Y. 2010. Diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions, and in a mesocosm experiment. Chemical Geology 269, 22 32.

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52 Parkhurst, D. L., Appelo, C. A. J. 1999. User's guide to PHREEQC (Version 2) A computer program forspeciation, reactionpath, 1D tran sport, and inverse geochemical calculations., U.S. Geol. Survey Water Resour. Inv. Rep.: 99 4259. Pentecost, A., 1992. Carbonate chemistry of surface waters in a temperate karst region: the southern Yorkshire Dales, UK. Journal of Hydrology 139, 211 232. Ritorto, M., Screaton, E.J., Martin, J.B., Moore, P.J. 2009.Relative importance and chemical effects of diffuse and focused recharge in an eogenetic karst aquifer: an example from the uncon fi ned upper Floridan aquifer, USA. Hydrogeology Journal.DOI10.100 7/s10040 009 0460 0 Shiraishi, F., Okumura, T., Takahashi, Y., and Kano, A. 2010. Influence of microbial photosynthesis on tufa stromatolite formation and ambient water chemistry, SW Japan. Geochimica et Cosmochimica Acta 74, 5289 5304. Scott, T.M. 1992. A geological overview of Florida. Florida Geological Survey, Open File Report No. 50. Screaton, E.J., Martin, J.B., Ginn, B., Smith, L. 2004. Conduit properties and karstification in the unconfined Floridan Aquifer.Ground Water.Volume 42.No. 3. Simonsen, J. F., Harremoes, P. 1978. Oxygen and pH fluctuations in rivers. Water Research 12, 477 489. Spiro, B., Pentecost, A. 1991. One day in the life of a stream A diurnal inorganic carbon mass balance for travertine depositing stream (Waterfall Beck, Yorksh ire). Geomicrobiology Journal 9, 1 11. Stumm, W., Morgan, J.J., 1996. Aquatic Chemistry, Chemical Equilibria and Rates in Natural Waters, 3rd ed. John Wiley & Sons, Inc., New York. U.S. Geological Survey. 2012. Surface water data for Florida: USGS real t ime water data and daily statistics. Vogt, T., Schneider, P., Hahn Woernle, L., Cirpka, O.A.2010. Estimation of seepage rates in a losing stream by means of fiber optic high resolution vertical temperature profiling. Journal of Hydrology 380, 154 164.

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53 BIOGRAPHICAL SKETCH Carolyn Ball received her bachelor s degree in g eological s cience from the University of Florida in 2011 her s degree, in August 2012. She will be working for Shell O il Company in August 2012 as an Exploration GeoScientist in Houston, Texas