Permanent Link: http://ufdc.ufl.edu/IR00003120/00001
 Material Information
Title: Phosphorus Cycling in Wetlands
Physical Description: Fact Sheet
Creator: DeBusk, William F.
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication: Gainesville, Fla.
Publication Date: 1999
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status: Published
General Note: "Published: July 1999."
General Note: "SL170"
 Record Information
Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00003120:00001

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SL 170 Phosphorus Cycling in Wetlands1 William F. DeBusk2 1. This document is SL170, a fact sheet of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published: July 1999. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. 2. William F. DeBusk, assistant professor and extension specialist, Soil and Water Science Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611-0510. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity Affirmative Action Employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Larry R. Arrington, Interim Dean Phosphorus (P) is an essential nutrient for plants and animals; however, excessive accumulation of nutrients can represent too much of a good thing, especially in water bodies such as lakes, streams and estuaries. Loading of nutrients to surface waters causes changes in ecological function, and often has undesirable environmental and economic consequences. Effective nutrient management, whether directed toward nutrient supply or abatement, requires a working knowledge of biogeochemical cycling; that is, the distribution and cycling of nutrients among living and non-living components of an ecosystem. Wetlands perform many important biogeochemical functions in watersheds. Among these are sediment trapping; nutrient removal, storage and release; and transformation of inorganic nutrients to organic forms. The P cycle in wetlands plays an important role in transport, storage and biological availability of P in the surrounding watershed. An overview of the key physical, chemical and biological processes associated with P cycling in wetlands is presented here (refer to Figure 1). Phosphorus can enter a wetland in several forms; for example, P carried in surface water may be in dissolved or particulate (suspended sediment) form, and may exist as organic or inorganic compounds. Organic P compounds are in either dissolved or particulate form, while inorganic P occurs primarily in solution as orthophosphate (HPO42-) or as phosphate-containing minerals suspended in the water column. Following is a summary of some major processes affecting retention, cycling and release of P in wetlands: Diffusion: Dissolved forms of P can be transferred from surface water to soil solution (porewater) and vice versa, through the process of diffusion. The driving force behind diffusion is the concentration gradient: a dissolved compound in the soil or water will diffuse from a region of high concentration to regions of lower concentration. Plant uptake: Inorganic P, primarily orthophosphate (HPO42and H2PO4-) is taken up by plants rooted in the soil or floating in the water (including algae). Litterfall: Dead plant tissue (e.g., leaves and stems) falls from the live plants and collects at the soil surface to form a litter layer, also known as detritus.


Phosphorus Cycling in Wetlands 2 Figure 1. Summary diagram of the fate of phosphorus entering a wetland. Sedimentation: Particulate matter (inorganic and/or organic sediment) entrained in the water column settles out, due to the reduced water velocity, shallow water depth and filtering action of emergent vegetation, and collects on the soil surface. Decomposition: Organic matter, including plant detritus, organic sediments and peat is broken down by a variety of microorganisms that utilize organic carbon as a source of energy. Organic P compounds are broken down to smaller organic molecules, both particulate and dissolved, and ultimately to orthophosphate, which may be utilized as a nutrient by the microorganisms or diffuse back into the soil or water. Sorption: This general term is applied to the processes of (1) adsorption of the orthophosphate ion by clays and iron or aluminum oxides (chemisorption) in the soil, and (2) precipitation of PO43with either iron and aluminum oxides or dissolved calcium, to form solid compounds (Feand Al-phosphates or Ca-phosphates) in the soil or water column. These phosphate minerals are potentially very stable in the soil, affording long-term storage of phosphorus. Burial and peat accretion: Partially decomposed plant detritus and other organic matter is gradually buried and incorporated into the soil profile. The buried material represents the portion of organic matter that is more resistant to decomposition. As this material ages, it becomes highly decomposed and compressed, forming peat (peat accretion). The capacity of wetlands for P removal is limited compared with their N removal capacity. There is no "permanent" loss mechanism for P in wetlands that is analogous to denitrification; therefore, P tends to accumulate in wetlands at a higher rate than does N. Precipitation of phosphate minerals can provide a significant sink for P in wetlands with large stores or inputs of iron and aluminum (low-pH wetlands) or calcium (high-pH wetlands). Although wetlands may remove and store substantial quantities of P, they also potentially release a significant amount of P to downstream ecosystems. Most of the P in wetlands is in organic form, contained either in the vegetation (live plants), plant detritus, macrofauna, microorganisms, soil (soil organic matter or peat) or water (dissolved organic compounds or suspended sediments). Peat accretion potentially affords long-term storage of P in wetlands, although it is a relatively slow process and generally fails to offset high rates of P loading to a


Phosphorus Cycling in Wetlands 3 wetland. Living components of the wetland also provide storage of P, but subsequently release a large portion of this P during death and decomposition. Plants turn over their stores of P in a matter of months to years, while the turnover time for microorganisms, which may account for up to 5 to 10% of the soil organic matter, is substantially shorter. Phosphorus released from the biota is either recycled within the wetland or exported to downstream waters. Due to the rapid biological uptake of nutrients and extensive production of organic matter, wetlands generally export more organic P than inorganic P, even though nutrient inputs are often largely in inorganic form. Biogeochemical cycling in wetlands represents an important function with respect to nutrient flow in watersheds. The transformation of inorganic nutrients to organic forms results in a more gradual release of P, and a general decrease in bioavailability in downstream waters, thus reducing the likelihood of algae blooms and other abrupt ecological changes. Coupled with their ability to buffer pulses of nutrients in the watershed by storing and slowly releasing nutrients to downstream waters, wetlands provide a significant amount of ecological stability to associated aquatic systems.