University of Florida College of Agriculture and Life Sciences Honors Thesis Using Properties of D issolved O rganic M atter to Trace Phosphorus Sources, Flows and Transformations in the Everglades S tormwater T reatment A rea s By: Isabella Fernandez Thesis Advisor: Patrick W. Inglett Natural Resources and Environment University of Florida, Gainesville, FL 32611
Acknowledgements: Thank you to Dr. Patrick Inglett for his help and guidance along the way, as well as to Sophia Carman and Devin Leon ard in the Wetland Biogeochemistry Laboratory for their assistance in teaching me to use the necessary equipment and complete the necessary analysis. Thank you to Mr. Steven Foster, who encouraged me to complete research and fueled my interests in the subj ect.
Introduction: The Florida Everglades is an interconnected system of wetlands whose nutrient cycles support a highly diverse community including many endangered and threatened species (Mitsch et al., 2014; Guardo et al., 1995). The Everglades wetland system also aids in the provision of clean water, recreation, enhances the commercial fishing industry and has benefits such as carbon sequestration (Richardson et al., 2014). Stormwater runoff rich in nutrients from the Everglades Agricultural Area (EAA) and Lake Okeechobee watershed poses a threat to the unique habitat through alterations of the natural nutrient profiles (Mitsch et al., 2014). This flow of stormwater is mainly contro lled by a system of canal implemented by the South Florida Water Management District (Guardo et al., 1995). Prior to the intensive agricultural development in the EAA north of t he Everglades, the system traditionally had oligotrophic conditions, partial to a community with dense sa wgrass (Mitsch et al., 2014; Guardo et al ., 1995). The ability of natural wetlands to reduce nutrient loads without costly treatment facilities led to the construction of manmade wetland systems for the inflow of nutrients to the Everglades syste m from th e EAA and Okeechobee watershed ( Pietro and Ivanoff 2015; Kadlec 2016 ). These constructed wetlands are referred to as Stormwater Treatment Areas or STAs (Pietro and Ivanoff 2015 ) and are used primarily to reduce phosphorus ( P ) loads, through storage, transformation sorption and precipitation with calcium carbonate (Pietro and Ivanoff 2015; Guardo et al., 1995). As of 2014, there were six STAs in The Everglades used for this purpose, with government regulations limiting the tot al P (TP) contained in outflow to approximately 10 p arts p er b illion (ppb) (Mitsch et al., 2014). While there are numerous instances of constructed wetlands and STAs reducing the nutrient loads associated with inflow s the goal of 10 ppb reliably over long periods of time is not
easily achieved (Mitsch et al., 2014). T here are various means by which P is removed, including accumulation in floc and litter layers, biological utilizatio n, and bio accretion (Kadlec, 2016). However, b ased on the biota involved in some P cycling mechanisms, namely the vegetation which takes up P and incorporates it into biomass s ome of the P in the outflow may have originated within the system itself through plant decompos ition (Chan et al., 2015). I n order for a system to remain effective it must be maintained in such a way that peat accumulatio n, and the build up of decaying biota present in the system do not contribute to higher TP levels in the water as this results in lowe r removal efficiency (Kadlec, 2016). The sediments which accumulate in the system increase the P found in floc and soil, which in turn can be released to the water when the concentration of P in the water is reduced so that it is below that of the soil sediments present (Diaz et al., 2006). Outflow P is composed of more organic than inorgani c P which may be the result of transformations to soluble reactive phosphorus ( SRP ) through biomass uptake or simply because it has not yet been removed by the associated processes (Dierberg & Dusk 2008). SRP is generally the first form of P to be assimilated into by biomass, while dissolved organic P ( DOP ) is generally a long term source of P in the system (Dierberg & Dusk 2008). Similarly variations in vegetation types, such as submerged aquatic vegetation (SAV) or emergent aquatic vegetation (EAV) may also result in differences in DO P due to light availability and differences in plant type and composition (Dierberg & Dusk, 2008). These two factors combined may be able to determine the p otential sources of P in outflow water which may be tracked through the system (Larsen et al., 2009) Along with P removal other functions and parameters such as dissolved organic matter (DOM) and dissolved organic carbon ( DO C) or total dissolved nitrogen ( T D N) can be indicators
of transformations of P and organic matter ( OM ) DOM is produced through the decomposition of organic material, including roots, leaf lit ter microbes and other living sources in the system and includes DOC dissolved organic nitrogen ( DON ), as well as DOP and other components (ElBislawi and Jaffe 2015). DOC specifically, is frequently produced during the treatment process of constructed wetlands as nutrients fuel plant growth and development which ultimately leads to decay again reintroducing C and nutrients back into the system (Villa et al., 2014). Starting in 1934 with Redfield, it was determined that species have a giv en C:N:P ratio which can be used to determine the levels of decomposition of DOM (Sardans, Rivas Ubach & Penuelas 2012 ; Redfield, 1934 ). DOM can be tracked through the system because there are structural differences in various organic molecules, which absorb and reflect light in different, measurable ways (Weishaar et al., 2003). Additionally, DOM can be used to determine flow patterns and concentrations at locations further along the system flow path (Noe et al., 2007). Determining the composition of DOM can reveal potential sources of the material, and how it is able to interact in the environment based on the concentration of bioavailable forms and decomposition stages (Hansen et al., 2016). Using known optical properties of DOM and thus through dete rmining the levels of specific ultraviolet absorbance and various wavelengths DOM can be traced through systems (Hansen et al., 2016). The optical properties determined from spectral analysis can be used to establish relationships b etween DOM and nutrient content as well as bioavailability of specific compounds (Stedmon et al. 2003). Relating DOM to the P concentrations in oligotrophic environments such as the natural Everglad es, is key to understanding vital biogeochemcial transformations which occur. Util izing the information from UV absorbance and optical properties and C:N:P ratios this study will
explore the dif ferences between EAV and SAV constructed wetlands throug h the treatment process to determine the sources and transformations of P in the Everglades STAs Light availability between EAV and SAV systems vary which influences the processes which occur, the microbes present and the hydrolysis or photolysis of P compounds (Moore et al., 2010). EAV dominated wetlands, have less light availability than SAV systems, which may impact the DOM and nutrient ratios present in each system (Moore et al., 2010). Analyses of the DOM components in the STA systems will potentially lead to a better understanding of how to reliably reduce outflow P concentrations to ensure they are below the current guidelines. It is expected that the optical properties of DOM and the DOM nutrient ratio stoichiometry will demonstrate a decrease in bioavailable P from inflow to outflow and an increase in organic P which is less bioavailable. Methods: Water Sampling and Processing Surface water samples were obtained from STA Cells 1 and 3 on October 11, 2017. STA Cell 1 contains predominantly EAV while Cell 3 is comprised predominantly of SAV the locations of these cells can be se en in I mages 1 and 2 below which describes where the samples were collected from The samples obtained fro m both cells were collected at three different points, the inflow, mid flow and outflow sections of the associated cells this is outlined below in T able 1 Inflow points, represent area s where stormwater is flowing into the cells, the mid flow points are located at approximately the midpoint of the flowpath, and the outflow reflects the location where water exit s the cell. The pH of the water samples was recorded and the samples
were stored in refrigerated conditions of approximately 2 5 o C until being processed for nutrient analysi s which occurred in stages over a 6 week period Table 1 Descriptions of the s ample site identification including STA cell, which is described in the images 1 and 2 The site ID which includes the position of the s ample site along the flowpath, a s well as the sample name as referenced for the completion of this research are also determined. Sampling Date STA Cell Site ID Sample Name 10/10/2017 1 Inflow C1 17 1347 10/10/2017 1 Mid flow C1 17 1348 10/10/2017 1 Outflow C1 17 1349 10/10/2017 3 Inflow C3 17 1350 10/10/2017 3 Mid Flow C3 17 1351 10/10/2017 3 Outflow C3 17 1352 Image 1 This image reflects the location and orientation of STA 2 Cell 1 from which three water samples were obtained. The stars indicate the sites from which water samples were taken and the blue indicates the location of the transect within the STA cell.
Image 2 This image reflects the location and orientation of STA 2 Cell 3 from which three water samples were obtained. The stars indicate the sites from which water samples were taken and the blue indicates the location of the transect within the STA cell. Nutrient Analys i s The samples were analyzed for their concentrations of TP, total organic carbon ( TOC ) total nitrogen ( TN ) as well as SRP. S amples were filtered through a 0.2 m membrane filter to ensure the nutrients present were within the dissolved size fraction (Larsen et al., 2010; Twardoswski et al., 2004). TP was measured using a persulfate block digestion while S RP was measured using the ascorbic acid method and color reagents (Pant et a l, 2002; USEPA 1 993) TOC and TN were determined using color reagents and absorbance measurements as were the SRP analyses (USEPA 1993) Dissolved organic phosphorus, (DOP), was then calculated by subtracting SRP from TP. Due to the filter used, the TOC, and TN represent the dissolved portions of C and N respectively, and are sh own as dissolved organic carbon (DOC) and total dissolved nit rogen (TDN). These values were then used to determine the C:N:P ratios of each of the samples being analyzed.
DOM Spectral Analysis The DOM spectral analysis was conducted using a S himadzu UV 1800 Spectropotometer using standard preparations (Hansen et al., 2016; Helms et al., 2008; Yamin et al., 2017 & Li & Hur, 2017). Hansen (2016) outlines specific wavelengths which should be analyzed. T he absorption coefficient (a) was calculated as : a=2.303A/l, where A = absorbance, and l = path length in meters (Helms et al., 2008). The path length in this case is 2 cm, or 0.02 m. T he specific absorbance or SUVA was then calculated for each wavelength using the following calculation ; L*mg C 1 m 1 = (a )/(TOC concentration in mg/L) (Helms et al., 2008). Specifically, SUVA 254 is frequently associated with aromaticity of carbon compound s (Weishaar 2003) and values for the samples are provided in Table 2 Table 2 Basic absorbance data which was calculated using the formulas described in the text above in the process of initial data processes for the DOM sample analysis Sample Absorption Coefficient (m 1 ) SUVA 254 (L*mg C 1 *m 1 ) EAV cell 1 inflow 399.34 10.75 EAV cell 1 mid flow 342.57 9.33 EAV cell 1 out flow 374.81 12.5 S AV cell 1 inflow 354.20 9.36 S AV cell 1 mid flow 359.95 9.87 S AV cell 1 out flow 375.38 9.95 S pectral slopes (S 275 295 S 350 400 ) were also calculated for wavelengths between 275 295 nm, and 350 400nm (Helms et al., 2008). Before the spectral slope can be determined, the log transformed absorption coefficients must be calculated, then the slope of the linearly fitting formula may be determined These values were the n used to create spectral slope ratios as S 275 295 to S 350 400 (S R ) (Helms et al., 2008 ; Sihi et al., 2016 ) as shown in Table 3
Table 3 The values of spectral slope and slope ratios calculated using the formulas provided by (Helms et al., 2008). Sample S 275 295 S 350 400 S R EAV cell 1 inflow 0.02423 0.01971 1.229 23 EAV cell 1 midflow 0.02163 0.01893 1.142599 EAV cell 1 outflow 0.0227 0.02011 1.128903 SAV cell 3 inflow 0.01789 0.0195 0.917391 SAV cell 3 midflow 0.02484 0.0195 1.273599 SAV cell 3 outflow 0.02021 0.01894 1.067159 Results and Discussion : DOP is the portion of dissolved P exclusive of SRP, which is readily assimilated by various species of plants and algae Understanding how DOP is transformed and how it moves through STA systems is key to understanding how to bet ter reduce the P present in outflow waters. One way to do so, is to track DOM and compare these values to th e nutrient ratios at different points along the flow paths of the STA SUVA 254 SUVA 254 is used to determine the DOM aromatic content as well as the estimated molecular weight of the DOM and is therefore commonly used to determine the properties of DOM (Hansen et al. 2016 ; Helms et al., 2008; Weishaar et al., 2003 ). As SUVA 254 increase s the aromatic content of the carbon molecules increases and therefore the reactivity of the molecule decreases (Helms et al., 2008; Larson et al., 2009). Microorganisms utilize non aromatic carbon first, and often transform non aromatic forms of ca rbon into aromatic forms as part of their metabolic processes (Hur et al., 2011). The SUVA 254 values for cell 1, w hich is dominated by EAV initially decreased between inflow and midflow, then increased between midflow to outflow regions. However, for cell 3 which contains mostly SAV the SUVA 254 values changed minimally along the flowpath as described in Images 1 and 2 As organic carbon compounds are decomposed and broken down the recalcitrance increases, which then increases the stability of these residual molecules (Hur et
al., 2011). Therefore, since the SUVA 254 values are increasing across the flowpath meaning outflow values were higher than inflow it likely indicates that decomposition is occurring along the flowpath as well. Since SAV cells showed a smaller increas e in SUVA values there is potentially more OM being put into the system which reduces the overall concentration of recalcitrant or aromatic C This could be further supported with information from the nutrient concentrations present in each of the two cells. Specifically, the ratios of C:N:P as well as the concentrations of each of these nutrients which can be used to further evaluate the differences between the cells based on the concentration of recalcitrant materials present in EAV and SAV. Figure 1 D ifferences in SUVA values between EAV in Cell 1 and SAV in Cell2, across the transect at three points; inflow, midflow and outflow. Spectral Slope Similar to the SUVA 254 values, spectral slope is commonly used to determine properties of DOM as it changes depending on the molecular weight characteristics of the organic matter (Roccaro et al., 2015; Helms et al., 2008). Specifically, spectral slope exam ines the effects of level of humification or potential ages of the DOM (Hansen et al., 2016). Spectral slope values are different across various sample types since t he starkest differences occur between 275 295 nm wavelengths and 350 400 nm wavelengths it is common to determine slope, and slope ratios between these wavelengths (Helms et al., 2008). Slopes in the se ranges generally have a more negative relationship or slope with increasing molecular weight of the DOM in the sample 0 2 4 6 8 10 12 14 SUVA254 (L*mg C 1 m 1 ) Inflow Midflow Outflow Cell 1 Cell 3
(Roccaro et al., 2015). According to Hur (2011), this indicates that as slopes decrease, the DOM contains a higher concentration of higher molecular weight or more humified, and older molecules. The log transformed absorbance co efficients have variations present in the slope values between wavelengths of 275 295nm, and between 350 400nm as seen in F igure 2 T he spectral slope values at those wavelengths are generally used to determine differences in the molecular weights of the DOM which can be indicators of photobleaching and the breakdown of OM (Helms et al. 2008) Figure 2 T he spectral slope values found at each site, across the flow path for 275 295 nm wavelengths (top) as well as 350 400 nm wavelengths (bottom) Higher spectral slopes between 275 and 295 nm signal the effects of photobleaching, which results in low molecu lar weight molecules (Helms et al., 2008) In cell 1, with EAV 0.017 0.018 0.019 0.02 0.021 0.022 0.023 0.024 0.025 0.026 Spectral Slope S 275 295 (nm 1 ) Inflow Midflow Outflow Cell 1 Cell 3 0.0188 0.019 0.0192 0.0194 0.0196 0.0198 0.02 0.0202 Spectral Slope S 350 400 (nm 1 ) Inflow Midflow Outflow Cell 1 Cell 3
species, there is a decrease in slope between inflow and midflow as well as a slight increase between midflow and outflow. However, there is relatively little change here. On the contrary, high er spectral slopes between 350 and 400 nm indicate humification (Helms et al., 2008) Cell 1 shows a steep decline in slope between inflow and midflow and steep increase from midflow to outflow. These points suggest that there is more humification in cell 1 than photobleaching and light degradation. Since the cell has emergent vegetation with little light penetration, this determination is representative. However, the opposite is shown in cell 3 with SAV spec ies. In regard to wavelengths between 275 and 2 95 nm there is a steep increase in slope indicating high photobleaching between inflow and midflow and a smaller decrease between midflow and outflow. Additionally, within the wavelengths between 350 400 nm, there is a relatively little change between inf low and midflow and a small decrease from midflow to outflow. This indicates that there is more photobleached material in cell 3 which considering the high light conditions is representative as cell 1. Spectral Slope Ratios In addition to the calculation of the spectral slopes, the ratio between S 275 295 and S 350 400 was calculated as it is relevant in determining the level of humification in the samples, based on molecular weight (Helms et al., 2008; Chow et al., 2013 ; Twardowski et al., 2004 ). In cell 1, the spectral slope ratio of DOM decreased between all transect points, however the decline was minimal between midflow and outflow as shown in figure 3 In contrast, f or cell 3, there was an increase between inflow and midflow followed by a decre ase between midflow and outflow. This was similar to the previous DOM measures regarding the molecular weight of the carbon molecules present.
Figure 3 V ariations in spectral slope ratio between the two cells over the three sites, inflow, midflow and outflow Stoichiometry Nutrient ratios can also be used to determine the source of DOM (Chow et al., 2013). When comparing the concentration of D OC, T D N and D O P over the inflow, midf l ow and outflow regions, the SAV cell remained relatively constant o r even increased in nutrient concentration s while the EAV cell showed a more typical constructed wetland pattern of decrease in concentration of nutrients as the water progressed along the cell flowpath seen in Table 4 Table 4 The nutrient concentrations present in the DOM as measured in order to determine the nutrient ratios present in the DOM. DOC, TDN, TP and SRP were measured and DOP was calculated by subtracting SRP from TP. This was calculated for each of the sample sites Nutrient Concentration (mg/L) inflow EAV midflow outflow inflow SAV midflow outflow Dissolved Organic Carbon DOC 37.14 36.7 29.92 37.83 36.45 37.69 Total Dissolved Nitrogen TDN 2.408 1.974 1.803 3.318 2.79 2.812 Total Dissolved Phosphorus T D P 0.129 0.117 0.045 0.119 0.136 0.137 Soluble Reactive Phosphorus SRP 0.093 0.088 0.028 0.099 0.096 0.111 Dissolved Organic Phosphorus DOP 0.036 0.029 0.017 0.02 0.04 0.026 0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 Spectral Slope Ratio (S R ) Inflow Midflow Outflow Cell 1 Cell 3
While these values indicate changes in nutrient concentrations along the flowpaths of both cells, the changes in proportions are easier to understand using figure 4 Figure 4 shows that i n the EAV cell the first two sites, inflow and midflow experience d relatively little change in the proportion of SRP and DOP (figure 4) Within t he third site however, the outflow point showed an increase in proportion of DOP and showed less SRP. Therefore, as P is transformed across the system, it increases in recalcitrant or nonbioavailable forms. This could be do to further decomposition and a lack of inputs of new material. However, the SAV cell showed an increase in the proportion of DOP from inflow to midflow, then a decrease from midflow to outflow site s. This demonstrates an increase in nonbioavailable P from inflow to midflow followed by an increase in bioavailable P. Therefore, this shows there is an increase in fresh OM between the midflow and outflow of cell 3 generating more SRP. Dierberg and Debusk ( 2008) provide results similar to that of cell 1 as the proportion of SRP decreases from inflow to outflow. The C:N:P ratios present in OM vary based on species, whether they are living or non living specimens (Scharler et al., 2015 ; Di Palo ). Rati os between SAV and EAV species have been shown to vary, where the C:N and C:P ratios are higher for the EAV and the N:P ratio is Figure 4 T he transformations of the proportions of SRP and DOP across the sample sites for the two cells. The dark grey indicates the percentage or SRP and the light grey indicates DOP a) EAV cell inflow d) SAV cell inflow b) EAV cell midflow e) SAV cell midflow c) EAV cell outflow f) SAV cell outflow
relatively similar (Xia et al., 2014). The changes in concentration of nutrients which occurred indicate that there are changes to the composition of OM. This is supported by the DOM calculations as well. Increases in ratios of dissolved nutrients in the middle of the flowpath indicates that the nutrients are being transformed or added from the biota within the system itself. When there are small changes in ratios it may indicate that decomposition is not occurring as quickly, or that inputs from the system match what is being decomposed 10 12 14 16 18 20 C:N ratio Inflow Midflow Outflow Cell 1 Cell 3 900 1100 1300 1500 1700 1900 C:P ratio Inflow Midflow Outflow Cell 1 Cell 3 60 80 100 120 140 160 N:P ratio Inflow Midflow Outflow Cell 1 Cell 3 Figure 5 These graphs indicate the ratios of nutrients present in DOM, over the inflow, midflow and outflow sites of the two cells being studied.
The EAV cell, cell 1, showed an increase from 15 to 19 in C:N ratio from inflow to midflow but then showed a decrease from 19 to 17 from midflow to outflow. However, for the C:P and N:P ratios, this cell showed an increase along all points, however a more drastic increase is seen between midflow and outflow in both. I n cell 3 there was less c onsistency The C:N ratio increased from 11 to 13 between inflow and midflow then remained constant between midflow and outflow. However, the C:P ratio decreased by more than half, from 1892 to 911, between inflow and midflow, then increased to 1450 betwee n midflow and outflow. The N:P ratio acted similarly to the C:P, in both cases although it increased from midflow to outflow, the final ratio was still lower than that of the inflow site. Conclusions: Constructed wetlands are often used to reduce P and other nutrients in runoff and wastewater directed into the Florida Everglades. H owever they are often unable to consist e n tly reach the goal of 10 ppb of T P in outflow waters (Mitsch et al., 2014). Understanding the processes which transform and remov e P from the system is vital to understandi ng how P can better be removed from the system. By investigating the optical properties of DOM in water samples collected along the flowpath of two cells, as well as the nutrient ratios of C, N and P, it was possi ble to determine likely sources of the nutrients in outflow waters. The two cel ls examined were an EAV cell and a SAV cell. There were clearly differ en ces in the effectiv e ness and traits of these two cells. EAV cells g enerally, have an increase in heavy weight molecules between inflow and midflow and an increase in low molecular weights from midflow to outflow (Hansen et al., 2016) In contrast, the SAV cell showed an increase in low molecular weight from inflow to midflow and an in crease in weight from midflow to outflow (Hansen et al., 2016). Therefore, in the EAV cell, the material showed an increase in
humification initially, followed by a decrease after midflow. While, in the SAV cell humified material was either lost or maintai ned, then increased after midflow. Similarly, the photobleaching and photolysis increased in the SAV cells than in the EAV cells due to the increase in light availability. The SUVA 254 values calculated also showed differences between the cells and along the flow path. In the EAV cell, SUVA 254 values decreased between inflow and midflow and increased between midflow and outflow. In contrast, the SUVA 254 values for the SAV cell remained relatively stable. This indicates that the EAV cell experienced a decrease in aromatic carbon initially, followed by an increase in aromatic compounds (Weishaar et al., 2003). More aromaticity means less biologically active carbon, showing that as treatment progressed carbon became less biologically active (Helms et al., 2009 & Weishaar et al., 2003). The SAV cell however, showed increases and then decreases in SUVA 254 values from inflow to midflow and from midflow to outflow respectively. This suggests that there is an increase i n biologically active carbon, followed by a decrease in these molecules (Weishaar et al., 2003). The nutrient values and ratios indicate similar findings. For all sites along the EAV cell flow path, DOC, TDN, and DOP decreased in concentration, though to varying amounts. However, the SAV cell showed a decrease initially, followed by an increase in nutrients for all except DOP. DOP in the SAV cell increased from inflow to midflow and decreased from midflow to outflo w. This increase suggests that in the SAV cells, there is a n input of nutrients from the system itself This w as not expected Due to the increased light availability it was expected that the S AV cells would more e fficiently remove nutrients. However due to the increased microbial and plant life in this cell, it is possible that the concentration of n utrients in the cell was impacted by this life.
In conclusion, the optical properties and nutrient ratios i ndicate that there is an addition of fresh organic matter along the flow path, especially notable in the SAV cells, which decreases the aromaticity of the carbon present and increases the biologically active portions of carbon. Similarly through the tracking of DOM, the data indicates that the P p resent in the outflow likely comes from, in part, the system itself Based on the data collected, it appears as though there is an input of P from within the system itself. There are differences in the nutrient transformations between each of the cells, du e to the differences in vegetation types between SAV and EAV properties. Additionally, the presence of microbial decomposition compared to light decomposition through photolysis is also different between the cells. More research is necessary into how the P can be better removed from the system, however changing the EAV an d SAV properties of the cells with different areas along the flow path may be part of a solution. R eferences : Chen, H.; Ivanoff D. & Pietro, K. 2015. Long term phosphorus removal in the Everglades stormwater treatment areas of South Florida in the United States. Ecological Engineering. 79:(158 168). Chow, A. T.; Dai, J.; Conner, W. H.; Hitchcock, D. R. & Wang, J. 2013. Dissolved organic matter and nutrient dynamics of a coastal freshwater forested wetland in Winyah Bay, South Carolina Biogeochemistry. 112:(571 587). Diaz, O.A.; Daroub, S.H.; Stuck, J.D.; Clark, M.W.; Lang, T.A. & Reddy, K.R. 2006. Sediment inventory and phosphor us fractions for water conservation area canals in The Everglades. Soil Science Society of America. 70:(863 871). Dierberg, F. E. & Debusk, T. A. 2008. Particulate phosphorus transformation in south Florida stormwater treatment areas used for Everglades pr otected areas Ecological Engineering.
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