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Sustainable operation of a treatment wetland depends on its continued treatment of influent water to achieve desired outflow water quality targets. Water treatment or nutrient reduction is attained by a combination of biotic and abiotic processes. We studied one of the world's largest treatment wetlands established to revive the Florida Everglades from impacts of excessive phosphorus (P) inputs. Phosphorus retained in the treatment wetlands is sequestered within the accumulated material via biotic and abiotic pathways that are influenced by the existing wetland vegetation. Recently accreted soils (RAS) provide a major sink for stored P, and long-term P removal efficiency of treatment wetlands is governed by the stability of accreted P because more stable P pools are less susceptible to mobilization and loss. We quantified reactive P (extracted with acid and alkali) and nonreactive P (not extracted with acid and alkali) pools in wetland soils by using an operationally defined P fractionation scheme and assessed the effect of emergent vs. submerged vegetation communities on stability of sequestered P. Reactive P comprised 63 to 79% of total P in wetland soils without a clear difference between two vegetation groups. The quantities of reactive P forms (inorganic vs. organic P) were significantly different between two vegetation types. A higher proportion of reactive P was stored as organic P in flocculent detrital organic matter (floc) and RAS under emergent vegetation (46-47% total P) in comparison with submerged vegetation (21-34% total P). The dominant P removal pathway in the submerged vegetation system was associated with calcium whereas plant uptake and peat burial appeared to be the main pathway in the emergent vegetation system., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

To better manage legacy phosphorus (P) in watersheds, reliable techniques to predict P storage and release from uplands, ditches, streams, and wetlands must be developed. Techniques such as the P saturation ratio (PSR) and the soil P storage capacity (SPSC), originally developed for upland soils, are hypothesized to be applicable to wetland soils as well. Surface soils were collected from eight beef ranches within the Lake Okeechobee Watershed, FL, to obtain a threshold PSR value and to evaluate the use of PSR and SPSC for identifying legacy P storage and release from wetland soils. Water-soluble P (WSP) was determined for all soils; the equilibrium P concentration (EPC) was determined for selected soils through the generation of Langmuir isotherms. The threshold PSR for wetland soils, calculated from P, Fe, and Al in a Mehlich 1 solution, was determined to be 0.1; SPSC, calculated using the threshold PSR, was found to be related to WSP. When SPSC was positive, WSP and EPC were minimal. However, both WSP and EPC increased once SPSC became negative. Organic matter (OM) varied from 0.4 to 90 g kg for both positive and negative SPSC, suggesting that OM in wetland soils does not have any effect on P retention and release below the threshold PSR. Moreover, when a wetland or drainage ditch is heavily P impacted, it could be a P source; wetland vegetation may no longer be able to assimilate additional P, resulting in P loss from the soil. This study suggests that the PSR-SPSC concept could be a valuable tool for evaluating legacy P release from wetlands., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Newly created and restored wetlands play an important role in sequestering excess nutrients at the landscape scale. In evaluating the long-term efficacy of nutrient management strategies to increase wetland capacity for sequestering P, information is needed on the forms of P found across the upland-wetland transition. To assess this, we studied soils (0-10 cm) from four wetlands within cow-calf pastures north of Lake Okeechobee, FL. Wetlands contained significantly (P < 0.05) greater concentrations of organic matter (219 g C kg(-1)), total P (371 mg P kg(-1)), and metals (Al, Fe) relative to surrounding pasture. When calculated on an aerial basis, wetland surface soils contained significantly greater amounts of total P (236 kg ha(-1)) compared with upland soils (114 kg ha(-1)), which was linked to the concomitant increase in organic matter with increasing hydroperiod. The concentration of P forms, determined by extraction with anion exchange membranes, 1 mol L(-1) HCl, and an alkaline extract (0.25 mol L(-1) NaOH and 50 mmol L(-1) ethylenediaminetetraacetic acid [EDTA]) showed significant differences between uplands and wetlands but did not alter as a proportion of total P. Speciation of NaOH-EDTA extracts by solution 31P nuclear magnetic resonance spectroscopy revealed that organic P was dominated by phosphomonoesters in both wetland and pasture soils but that myo-inositol hexakisphosphate was not detected in any sample. The tight coupling of total C and P in the sandy soils of the region suggests that the successful management of historically isolated wetlands for P sequestration depends on the long-term accumulation and stabilization of soil organic matter.

The U.S. Environmental Protection Agency created the Clean Water Action Plan to develop nutrient criteria for four water body types: lakes and reservoirs, rivers and streams, estuaries, and wetlands. Significant progress has been made in open water systems. However, only areas in and around the Florida Everglades have had numeric nutrient criteria set, due to the complexity, heterogeneity, and limited information available for wetlands. Our objective was to evaluate various soil tests to predict significant P release potential of soil in wetlands. A total of 630 surface soil samples (0-10 cm) were collected for this study from four southeastern states: Florida, Alabama, Georgia, and South Carolina. Soil samples were collected from the center of wetlands, the edge of the wetlands, and from adjacent uplands. The phosphorus saturation ratios (PSR), calculated using P, Fe, and Al molar concentrations from Mehlich 1 (M1-PSR), Mehlich 3 (M3-PSR), and oxalate (Ox-PSR) extractions and the amount of P extracted by different extractants were used to predict P loss potential from a soil. Total phosphorus (TP) concentration in wetland soils, estimated as the 75th percentile of the distribution of least impacted wetland soils as an example, was approximately 550 mg kg(-1). Based on this reference background condition, procedures for obtaining threshold values for P release to the surrounding water bodies were developed and threshold values calculated: M1-P = 24 mg kg(-1), M3-P = 44 mg kg(-1), Ox-PSR = 0.079, M1-PSR = 0.101, and M3-PSR = 0.067.

Phosphorus (P) can be an important nutrient in regulating primary productivity in lakes. The ability of lake sediments to retain P from external sources depends on the physiochemical characteristics of the sediment. To assess the P dynamics in Lake Istokpoga and the upper chain of lakes that drain into Lake Okeechobee, Florida, USA, sorption properties of batch sediment samples for Lakes Tohopekaliga, Cypress, Hatchineha, Kissimmee, and Istokpoga were characterized under aerobic and anaerobic conditions. Langmuir model parameters fit the experimental data well (in general, r(2) > 0.70). There were strong correlations between P sorption and total C, total P, Ca, Mg, Fe, and Al (r = 0.83-0.97). Equilibrium P concentration values ranged between 0.001 and 0.192 mg L(-1) for aerobic conditions. A single-point isotherm (initial concentration, 5 mg L(-1)) was found for a wide range of sediment types, which allows estimation of the maximum potential sorption (S(max)) as 1.7 times the sorption (S(max) = 1.7 S(5)). Results suggest that although these sediments have high P sorption capacities, the lake sediments may release P into the water column by desorption under aerobic conditions if water-column P concentrations are low enough (<0.036 mg L(-1) for Lake Tohopekaliga and <0.003-0.027 mg L(-1) for the other four lakes). Current watershed management strategies must balance efforts to reduce P inputs into the lakes from point and nonpoint sources against lowering the water-column P concentration to such a low level that the lake sediments become a source of P to downstream Lake Okeechobee.

The effectiveness of various management practices to reduce phosphorus (P) loss from soil to water can potentially be improved by using by-product materials that have the capacity to sorb phosphorus. This study evaluated the P sorption and desorption potential, and the physicochemical characteristics of various phosphorus sorbing materials. Twelve materials were selected and P sorption potentials ranged between 66 and 990 mg kg(-1). Iron, and calcium drinking water treatment residuals (DWTRs), a magnesium fertilizer by-product, aluminum, and humate materials all removed substantial amounts of P from solution and desorbed little. Humate had the highest maximum P sorption capacity (S(max)). Materials which had a low equilibrium P concentration (EPC(0)) and a high S(max) included aluminum and humate by-products. In a kinetic study, the Fe-DWTR, Ca-DWTR, aluminum, and magnesium by-product materials all removed P (to relatively low levels) from solution within 4 h. Phosphorus fractionation suggests that most materials contained little or no P that was readily available to water. Sand materials contained the greatest P fraction associated with fulvic and humic acids. In general, materials (not Ca-DWTR) and magnesium by-product were composed of sand-sized particles. There were no relationships between particle size distributions and P sorption in materials other than sands. The Ca- and Fe-DWTR, and magnesium by-product also contained plant nutrients and thus, may be desirable as soil amendments after being used to sorb P. Further, using Ca-DWTRs and Fe-DWTRs as soil amendments may also increase soil cation exchange and water holding capacity.

Constructed treatment wetlands are a relatively low-cost alternative used for tertiary treatment of wastewater. Phosphorus (P) removal capacity of these wetlands may decline, however, as P is released from the accrued organic soils. Little research has been done on methods to restore the treatment capacity of aging constructed wetlands. One possibility is the seasonal addition of alum during periods of low productivity and nutrient removal. Our 3-mo mesocosm study investigated the effectiveness of alum in immobilizing P during periods of reduced treatment efficiency, as well as the effects on soil biogeochemistry. Eighteen mesocosms were established, triplicate experimental and control units for Typha sp., Schoenoplectus californicus, and submerged aquatic vegetation (SAV) (Najas guadalupensis dominated). Alum was slowly dripped to the water column of the experimental units at a rate of 0.91 g Al m(-2) d(-1) and water quality parameters were monitored. Soil cores were collected at experiment initiation and completion and sectioned into 0- to 5- and 5- to 10-cm intervals for characterization. The alum floc remained in the 0- to 5-cm surface soil, however, soil pH and microbial parameters were impacted throughout the upper 10 cm with the lowest pH found in the Typha treatment. Plant type did not impact most biogeochemical parameters; however, data were more variable in the SAV mesocosms. Amorphous Al was greater in the surface soil of alum-treated mesocosms, inversely correlated with soil pH and microbial biomass P in both soil layers. Microbial activity was also suppressed in the surface soil of alum-treated mesocosms. This research suggests alum may significantly affect the biogeochemistry of treatment wetlands and needs further investigation.

Florida Everglades restoration plans are aimed at maintaining and restoring characteristic landscape features such as soil, vegetation, and hydrologic patterns. This study presents the results from an exhaustive spatial sampling of key soil properties in Water Conservation Area 1 (WCA 1), which is part of the northern Everglades. Three soil strata were sampled: floc, upper 0- to 10-cm soil layer, and 10- to 20-cm soil layer. A variety of properties were measured including bulk density (BD), loss on ignition (LOI), total phosphorus (TP), total inorganic phosphorus (TIP), total nitrogen (TN), total carbon (TC), total iron (TFe), total magnesium (TMg), total aluminum (TAl), and total calcium (TCa). Interpolated maps and model prediction uncertainties of properties were generated using geostatistical methods. We found that the uncertainty associated with spatial predictions of floc, particularly floc BD, was highest, whereas spatial predictions of soil chemical properties such as soil Ca were more accurate. The resultant spatial patterns for these soil properties identified three predominant features in WCA 1: (i) a north to south gradient in soil properties associated with the predominant hydrological gradient, (ii) areas of considerable soil nutrient enrichment along the western canal of WCA 1, and (iii) areas of considerable Fe enrichment along the eastern canal. By using geostatistical techniques we were able to describe the spatial dynamics of soil variables and express these predictions with an acceptable level of uncertainty.

Phosphorus (P) has been identified as the key constituent defining wetland productivity, structure, and function. Our goal was to investigate the spatial patterns of total P and three labile forms of P (labile organic, inorganic, and microbial biomass P) across a subtropical wetland located in east-central Florida, the Blue Cypress Marsh Conservation Area (BCMCA), and link spatial patterns to ecosystem processes. The wetland received a continual input of nutrients primarily from the south and intermittently from the west and east, respectively, which ceased in the mid-1990s. Since then the marsh system has been undergoing natural succession. We used (i) ordinary kriging to characterize the spatial patterns of total P and labile P forms across the wetland, (ii) local, moving spatial correlations to investigate relationships between total P and labile P forms, and (iii) a clustering technique to link the identified spatial patterns to biogeochemical processes. The spatially explicit analyses revealed patterns of total P and labile P forms as well as changing relationships between variables across the marsh. We were able to distinguish P-enriched areas from unaffected ("natural") areas and intermediate zones that are currently undergoing change as P is mobilized and translocated. We also identified areas that are at risk, showing a shift toward a more P-enriched status. Our results improve our understanding of P and its labile components within a spatially explicit context.

The release of P from lake sediments, which occurs as a part of internal loading, may contribute a significant portion of the total P load to a lake. Phosphorus release rates from sediments in Spring Lake, Michigan, and the degree to which alum reduces P release from these sediments, were investigated during the summer of 2003. Triplicate sediment cores were sampled from four sites in the lake, and exposed to one of four treatments in the laboratory: (i) aerobic water column/alum, (ii) aerobic water column/no alum, (iii) anaerobic water column/alum, or (iv) anaerobic water column/no alum. Total P (TP) release rates were virtually undetectable in the alum treatments (both aerobic and anaerobic). Low, but detectable, release rates were measured in the aerobic/no alum treatment. The highest release rates were measured in the anaerobic/no alum treatments, and ranged from 1.6 to 29.5 mg P m(-2) d(-1) depending on how the calculations were derived. These fluxes translated to mean internal loads that ranged between 2.7 (low range) and 6.4 (high range) Mg yr(-1) when extrapolated to a whole-lake basis. Internal P loads accounted for between 55 and 65% of the total P load to Spring Lake. Although alum is a potentially effective means of reducing the sediment source of P, there is considerable uncertainty in how long an alum treatment would remain effective in this system given the current rates of external loading and the lack of information on wind-wave action and bioturbation in Spring Lake.

Temporal oscillations in hydrology are a common occurrence in wetlands and can result in alternating flooded and drained conditions in the surface soil. These oscillations in water levels can stimulate microbial activities and result in the mobilization and redistribution of significant amounts of carbon (C), nitrogen (N), and phosphorus (P). The goal of this study was to experimentally simulate a drawdown and reflood of marsh soil from a nutrient-enriched site and a reference site of a wetland (Blue Cypress Marsh Conservation Area, Florida). The goal was to better understand the changes in biogeochemistry and microbial activities present in these soils as a result of hydrological fluctuations. Measurements of dissolved reactive phosphorus (DRP), ammonia, and nitrate in the floodwater indicated significantly higher (alpha = 0.05) NH(4)(+) and DRP fluxes from the nutrient-enriched site; floodwaters in the cores from both sites contained significant NO(3)(-) concentrations (9.6 mg N L(-1)), which was rapidly consumed over the core incubation period (30 d). Water level drawdown and reflooding initially stimulated the soil microbial biomass, methanogenic rates, and extracellular enzyme activities (acid phosphatase and beta-glucosidase). The anaerobic microbial metabolic activities (CO(2)) where initially significantly (alpha = 0.05) enhanced by the reflood, resulting in roughly equivalent rates as the aerobic respiratory activities (CO(2)), presumably as a function of the high water column NO(3)(-) levels. This study illustrates that the reflood event in the hydrological cycles in a wetland can significantly stimulate the activities of hydrolytic enzymes and microbiological communities in these soils.

Internal cycling of nutrients from the sediment and water column can be an important contribution to the total nutrient load of an aquatic ecosystem. Our objective was to estimate the internal nutrient loading of the Lower St. Johns River (LSJR). Dissolved reactive phosphorus (DRP) and ammonium (NH(4)-N) flux from sediments were measured under aerobic and anaerobic water column conditions using intact cores, to estimate the overall contribution of the sediments to P and N loading to the LSJR. The DRP flux under aerobic water column conditions averaged 0.13 mg m(-2) d(-1), approximately 37 times lower than that under anaerobic conditions (4.77 mg m(-2) d(-1)). The average NH(4)-N released from the anaerobic cores (18.03 mg m(-2) d(-1)) was also significantly greater than in the aerobic cores for all sites and seasons, indicating the strong relationship between nutrient fluxes and oxygen availability in the water column. The mean annual internal DRP load was estimated to be 330 metric tons (Mg) yr(-1), 21% of the total P load to the river, while the mean annual internal load of NH(4)-N was determined to be 2066 Mg yr(-1), 28% of the total N load to the LSJR estuary. As water resource managers reduce external loading to the LSJR the frequency of anaerobic events should decline, thereby reducing nutrient fluxes from the sediment to the water column, reducing the internal loading of DRP and NH(4)-N. Results from this study demonstrate that the internal flux of nutrients from sediments may be a significant portion of the total load and should be accounted for in the total nutrient budget of the river for successful restoration.

Little information is available on the effect of phosphorus (P) enrichment on nitrogen (N) biogeochemical cycling in wetland soil. Of particular importance are the coupled nitrification-denitrification reactions that regulate the microbially mediated loss of N from wetland systems. Soils from the northern Florida Everglades have been affected by P loading from surface waters over the past 40 years. Elevated P levels have been show to have an effect on the size and activity of the microbial pool and a decrease in the N to P ratio of the microbial biomass. The objective of the study was to determine if P enrichment in soils affected microbial activities related to nitrification and denitrification in these flooded, peat soils. Potential nitrification rates of soil and detritus were determined using constantly stirred reactors under aerobic conditions while denitrification rates were determined from anaerobic incubations of slurry. Nitrification rates showed two distinct linear phases, a slower initial rate, signifying activity of nitrifiers present, followed by a sharp increase in the NH4+ conversion rate indicative of maximum potential rates. Initial rates of nitrification were highest in the surficial detrital layer decreasing with soil depth and did not correlate to soil total P. The potential rates of nitrification were 13 times greater than the initial rates. Potential denitrification rates were highest in the detritus and 0- to 10-cm soil interval with significantly lower values in the 10- to 30-cm soil interval, significantly correlated to total P of the soil. A significant (P < 0.01) relationship was seen between potential denitrification rates and soil total P suggesting an increased rate of N removal from P-enriched regions of the northern Everglades.

Microbial respiration in peat and overlying plant litter, as influenced by water level and phosphorus enrichment, was evaluated for an Everglades (Florida, USA) marsh ecosystem by measuring CO2 and CH4 release from soil-water microcosms. Intact cores of peat, overlying plant litter, and surface water were collected at seven locations in cattail (Typha domingensis Pers.) and sawgrass (Cladium jamaicense Crantz) stands along a phosphorus (P) enrichment gradient in Water Conservation Area 2A (WCA-2A). Each soil-water microcosm was outfitted with a controlled air circulation system whereby outflow gas from the headspace could be analyzed for CO2 and CH4 to determine flux of C from the soil-water column to the atmosphere. Gaseous C flux was determined for flooded conditions (10-cm water depth) and for water levels of 0, 5, 10, and 15 cm below the peat surface. Overall, decreasing water level resulted in significantly increased C flux, although rates were significantly higher under flooded conditions than under nonflooded, saturated-soil conditions, presumably due to O2 availability associated with algal photosynthesis within the litter layer in the water column. Carbon flux decreased significantly for sites increasingly distant from the primary hydrologic and nutrient inflows to WCA-2A. The microcosm study demonstrated that the C turnover rate was significantly increased by accelerated nutrient loading to the marsh, and was further enhanced by decreasing water level under drained conditions. Our results also demonstrated that photosynthesis within the water column is a potentially important regulator of C mineralization rate in the litter layer of the marsh system.

Enzymatic hydrolysis and mineralization of organic phosphorus (P) were determined in surface water samples collected from inflow and outflow of a submerged aquatic vegetation (SAV)-dominated treatment wetland of the Florida Everglades. Water samples were fractionated into three size fractions (> 0.4 micron, < 0.4 to > 0.05 micron, and < 0.05 micron) with a sequential flow filtration technique. The fractionated water samples were incubated to hydrolyze with alkaline phosphatase (APase) and phosphodiesterase (PDEase), and to mineralize at different redox and pH. Unlike APase, which hydrolyzed < or = 10% of organic P, PDEase hydrolyzed > or = 71% of organic P in unfiltered water from both inflow and outflow waters, suggesting the domination of bioavailable diester P in the water. Phosphodiesterase completely hydrolyzed organic P in the < 0.4- to > 0.05-micron and < 0.05-micron fractions, as compared with < or = 35% in the > 0.4-micron fraction. However, the P mineralization in inflow and outflow waters at different redox and pH showed that P associated with particulate > 0.4 micron had been mineralized the most. Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy showed that surficial sediments from the inflow region contained a high proportion of polynucleotides, nucleoside monophosphates, and previously unreported glycerophosphoethanolamine and phosphoenolpyruvates. However, at the outflow, the relative proportion of polynucleotides and nucleoside monophosphates was reduced substantially. This suggests that the SAV wetland may sequester P via accretion of organic matter.

Tailoring nitrogen (N) fertilizer applications to cotton (Gossypium hirsutum L.) in response to leaf N status may optimize N use efficiency and reduce off-site effects of excessive fertilizer use. This study compared leaf and canopy reflectance within the 350 to 950 nm range in order to identify reflectance ratios sensitive to leaf chlorophyll (Chl), and hence N status, in cotton. Plants were grown outdoors in large pots using half-strength Hoagland's (control) solution until some three-row plots received a restricted supply of N. Treatments comprised control, 20% of control N at first flower bud (square) onward; 0 and 20% of control N at first flower onward; and 0% of control N at fruit-filling onward. Despite leaf N values ranging from 51 to 19 g kg-1 across treatments and sampling dates, a weak correlation was obtained between Chl and N (r2 = 0.32, df = 70). In general, N stress led to increased reflectance at 695 +/- 2.5 nm (R695) and decreased reflectance at R410, and changes in leaf N were best correlated with either R695 or R755 in leaves and either R410 or R700 in canopies. The strongest associations between leaf constituent and canopy reflectance ratio were Chl vs. R415/R695 (r2 = 0.72), carotenoids vs. R415/R685 (r2 = 0.79), and N vs. R415/R710 (r2 = 0.70). The R415 measure appears to be a more stable spectral feature under N stress, as compared with more pronounced changes along the reflectance red edge (690-730 nm). Multiple regression identified a three-waveband canopy reflectance model that explained 80% of the variability in leaf N. Results indicate that remote sensing of N status in cotton is feasible using narrow-waveband reflectance ratios that involve the violet or blue region of the spectrum (400 to 450 nm) and the more commonly featured red-edge region.

Agricultural lands are often used for constructing stormwater treatment areas (STAs) to abate nutrient loading to adjacent aquatic systems. Flooding agricultural lands to create STAs could stimulate a significant release of phosphorus (P) from soil to the water column. To assess the suitability of agricultural lands, specifically those impacted by animal operations, for the construction of STAs, soils from different components of the New Palm-Newcomer dairies (Nubbin Slough Basin, Okeechobee, Florida, USA) were collected by horizon and their P retention and release capacities estimated. In general, P released from A-horizon soil under flooded (anaerobic) conditions was greater than under drained (aerobic) conditions due to redox effect on iron (Fe) and consequent P releases. However, the P released from Bh-horizon soil was greater under aerobic conditions than under anaerobic conditions, possibly due to excessive aluminum (Al) content in the horizon. Double acid-extractable calcium (Ca), magnesium (Mg), Al, and P explained 87% of the variability in P release under aerobic conditions, and 80% of that under anaerobic conditions. The P release maxima indicated a high solubility of P in A-horizon soil from both active and abandoned dairies (13 and 8% of the total P, respectively), suggesting that these soils could function as potential sources of P to the overlying water column when used in STA construction. Preestablishment of vegetative communities or chemical amendment, however, could ameliorate high P flux from soil to the water column.

Phosphorus (P) plays a major role in eutrophication of aquatic systems. Estuarine sediments could function as sources or sinks for P to the overlying water column depending upon their physico-chemical characteristics. Understanding of P sorption phenomena in estuarine sediments is important in regulating the P availability in estuaries. Phosphorus sorption characteristics of sediments from the Indian River Lagoon, Florida, USA, were determined to examine the role of selected physico-chemical properties of the sediments on soluble reactive P status in estuary water. Mean equilibrium P concentrations (EPCo) of 0.75 mg L(-1) and mean P sorption maxima (Smax) of 32.2 mg kg(-1) were obtained under anaerobic conditions, compared with EPCo of 0.05 mg L(-1) and Smax of 132.7 mg kg(-1) under aerobic conditions. The higher EPCo values under anaerobic conditions and the greater Smax values under aerobic conditions were associated with amorphous and poorly crystalline iron. These results suggest that sediments enriched with amorphous and poorly crystalline forms of iron act as an excellent reservoir for P by adsorbing excessive P in aerobic sediment zones and releasing it upon burial under anaerobic conditions. This study also indicates that P compounds in sediments independently maintain equilibrium with P in solutions. Thus, heterogeneous systems like soil and sediment simply behave as a mixture of homogeneous surfaces as far as their P sorption characteristics are concerned, and hence can be successfully described by the Langmuir and Freundlich models.

The Florida Everglades have undergone significant ecological change resulting from anthropogenic manipulation of historical regimes of hydrology, nutrient loading, and fire. Water Conservation Area 2A (WCA-2A) in the northern Everglades has been a focal point for the study of ecological effects of nutrient loading, especially phosphorus (P), from the nearby Everglades Agricultural Area (EAA). The overall objective of our study was to evaluate recent (1990 to 1998) changes in the spatial extent and patterns of soil P enrichment in Everglades WCA-2A. Surface soil was sampled to a depth of 10 cm at 62 sites within WCA-2A during 1998 for analysis of total phosphorus (TP) content. Geostatistical methods were used to create an interpolated grid of soil TP values across WCA-2A. Comparison of the results of this study with a similar study performed in 1990 showed that the extent of soil P enrichment in surface soil and sediments increased between 1990 and 1998, as evidenced by increased coverage of highly P-enriched soil near the primary surface inflows and a general increase in the concentration of soil TP in the interior regions of WCA-2A. Approximately 73% (31 777 ha) of the total land area of WCA-2A was considered P-enriched (soil total P > 500 mg kg(-1)) in 1998, compared with 48% of the land area (20,829 ha) in 1990, an average increase of 1,327 ha yr(-1). Study results indicate that the soil P enrichment "front" has advanced further into the relatively unimpacted interior of WCA-2A during the past several years.

Accretion of organic matter in wetlands provides long-term storage for nutrients and other contaminants. Water-table fluctuations and resulting alternate flooded and drained conditions may substantially alter the stability of stored materials including phosphorus (P). To study the effects of hydrologic fluctuation on P mobilization in wetlands, recently accreted detrial material (derived primarily from Typha spp.) was collected from the Everglades Nutrient Removal Project (ENRP), a constructed wetland used to treat agricultural drainage water in the northern Everglades. The detrital material was subjected to different periods of drawdown and consecutive reflooding under laboratory conditions. The 31P nuclear magnetic resonance (31P NMR) spectroscopy analysis revealed that sugar phosphate, glycerophosphate, polynucleotides, and phospholipids (glycerophosphoethanolamine and glycerophosphocholine) were the major forms of P in the detrital material. After 30 d of drawdown, polynucleotides were reduced to trace levels, whereas sugar phosphate, glycerophosphate, and phospholipids remained the major fractions of organic P. Microorganisms seemed to preferentially utilize nucleic acid P, perhaps to obtain associated nutrients including carbon and nitrogen. At the end of the 30-d reflooding period, cumulative P flux from detritus to water column accounted for 3% of the total P (< or = 15 d of drawdown) and further decreased to 2% at 30 d of drawdown, but increased to 8% at 60 d of drawdown. The drawdown (< or = 30 d) not only reduced P flux to the water column, but also increased the humification and microbial immobilization of P. Excessive drawdown (60 d), however, triggered the release of P into the water column as the water content of detritus decreased from 95 to 11%.

Wetland soils play a key role in the cycling of nutrients within an ecosystem. Since soils are potentially a source or a sink for inorganic nutrients, it is important to quantify their influence on overlying water quality in order to understand their importance in overall ecosystem nutrient budgets. Laboratory and field studies were performed in the northern Everglades (WCA-2A) to determine the magnitude of phosphorus (P) flux between the soil and the overlying water column, under various redox conditions. The P flux was estimated using three techniques: intact soil cores, in situ benthic chambers, and porewater equilibrators. There was reasonable agreement between the P flux estimated using intact soil cores and benthic chambers; however, P flux estimates using the porewater equilibrators were considerably lower than the other two techniques. Models of solute flux, based solely on soil physico-chemical characteristics, may substantially underestimate soil-water nutrient exchange processes. Phosphorus flux measured with the intact soil cores varied from 6.5 mg m(-2) d(-1) near nutrient inflow areas to undetectable flux 4 km away from the inflow. Oxygen consumption varied from 4 mg m(-2) d(-1) near the inflow to a constant 1 to 2 mg m(-2) d(-1) at a distance of 4 km from the inflow. Rate of consumption of NO3- -N and SO4(2-) showed no significant trend with respect to distance from inflow. Nitrate N and SO4 consumption rates averaged 120 and 130 mg m(-1) d(-1), respectively. Consumption of O2 was correlated with P flux, whereas NO3- -N and SO4(2-) consumption were not.

A recently constructed marsh from previously drained agricultural land currently receives nutrient-laden water from adjacent hypereutrophic Lake Apopka, located in central Florida. Lake water is allowed to cycle through the marsh, allowing settlement of participate organic matter, which forms a floc sediment layer on the native peat soil surface. The water leaving the marsh is returned to the lake after a retention time of 3 to 12 d. This study determined changes in temporal and spatial distribution of selected nutrients in the soil-water column of the marsh during the first 13 mo of operation. In situ distribution of selected chemical species (H + , NH + 4 , soluble P, SO 2- 4 , dissolved organic C, dissolved inorganic C, CH 4 , Ca, Mg, Fe, Mn, Al) were measured using soil pore water equilibrators at 3, 8, and 13 mo after marsh creation. Initial flooding of the agricultural soils resulted in high concentrations of NH + 4 (11 mg N L -1 ) and soluble P (31 mg P L -1 ) as a result of solubilization and anaerobic decomposition. Initially rapid soluble P flux (mean = 2.4 mg P m -2 d -1 ) occurred from soil to the water column, although lower flux (mean = 0.8 mg P m -2 d -1 ) occurred after 10 additional months of operation. In contrast, initial flux of NH + 4 into the water column was generally lower (mean = 3.4 mg N m -2 d -1 ) than observed after 10 additional months (mean = 8.2 mg N m -1 d -1 ). Microbial degradation and nutrient regeneration from settled labile organic matter appeared to support nutrient flux to the water column. After 13 mo of flooding, 75% of the variability of NH + 4 -N and 65% of the variability of soluble P contained in the water and floc sediment was explained by (DIC + CH 4 )-C mineralized from settled organic matter. Anaerobic conditions in both the floc sediment and peat soil layers (indicated by increased amounts of dissolved CH 4 and Fe, and by SO 2- 4 reduction) had significant effects on nutrient retention and release in the soil-water column., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Constructed marshes are currently being used as a low-cost alternative for treatment of nutrient-enriched waters. These marshes may function as net sinks for nutrients, especially for particulate organic forms of N and P. However, decomposition of organic matter and nutrient release may influence the ability of the marsh to function for this purpose. One of the main factors affecting decomposition is the availability of inorganic electron acceptors (e.g., O 2 , NO - 3 , and SO 2- 4 ). The role of electron acceptor consumption on N and P regeneration and release was investigated using batch incubation experiments with recently deposited organic matter (floc sediment) and peat soils collected from the constructed marsh. In electron acceptor-amended soil cores, electron acceptor consumption proceeded rapidly in the order O 2 > NO - 3 > SO 2- 4 . Mean oxygen reduction rate (OR) was 1.6 g O 2 m -2 d -1 (2025 g O 2 m -3 d -1 ), with corresponding values for NO - 3 and SO 2- 4 of 0.23 g N m -2 d -1 (60 g N m -3 d -1 ) and 0.086 g S m -2 d -1 (5.4 g S m -3 d -1 ), respectively. If electron acceptor consumption was coupled to decomposition of organic matter in floc sediment with a C/N/P ratio of 190:14:1, aerobic catabolism accounted for 92% of NH + 4 , and soluble P regenerated in the soil, with anaerobic activity (NO - 3 - and SO 2- 4 -reduction) accounting for the remaining 8%. In the constructed marsh receiving allochthonous inputs of labile organic matter, however, anaerobic decomposition was expected to be the dominant mechanism for nutrient regeneration. Under SO 2- 4 -reducing conditions, net rates of organic N and P mineralization were 3.3 to 14 mg N L -1 sediment d -1 and 0.5 to 0.6 mg P L -1 , respectively, and were highly correlated to production of dissolved inorganic C plus CH 4 -C. Once released to the soil porewater, nutrients were available for transport to the water column by diffusion and advection (e.g., gas ebullition), thus impacting water quality., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Field and laboratory experiments were conducted to measure forms, storages, and flux of C in the water-sediment colunm of a shallow, subtropical, hypereutrophic lake. High gross primary productivity in the lake (1.4 ± 0.3 kg C m -2 yr -1 ) was not significantly correlated with any water chemistry parameters measured. This suggested that the phytoplankton community was functioning at maximum levels and under nutrient nonlimiting conditions. Major C input to the lake is through gross primary productivity, of which 90% is lost through heterotrophic and microbial respiration processes within the water column. Resuspension of the bottom sediments was a major input of C into the water column, contributing 720 g C m -2 yr -1 . In comparison, diffusive flux of dissolved organic C from the sediment was minimal (1.2 g C m -2 yr -1 ), as were external inputs into the water column (20 g C m -2 yr -1 ). High productivity of this system has resulted in a net accumulation of C (as sediments) of 118 g C m -2 yr -1 ., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Increases in total P levels in Lake Okeechobee, Florida, have given rise to concern over eutrophication. The objective of this study was to evaluate the effects of redox potential and pH on the solubility of P in lake sediments. Bulk sediment samples were obtained from the mud zone of Lake Okeecbobee and were equilibrated under controlled conditions at fixed Eh and pH levels. The pH levels evaluated were 5.5, 6.5, 7.5, and 8.5; the Eh levels studied were 500, 250, 0, and -250 mV. Redox reactions were very important in the regulation of P in Lake Okeechobee sediments. Under oxidized conditions, soluble reactive P (SRP) concentrations were low (≈ 0.1 mg P L -1 ), whereas under reducing conditions SRP increased to over 1 mg P L -1 . Soluble reactive P was extremely high (18 mg P L -1 ) under acidic (pH 5.5), reducing (Eh < 0 mV) conditions. Water soluble Fe was highly correlated to water soluble P, implicating it as a possible agent governing P behavior. Sodium hydroxide-extractable P (Fe and Al bound) increased with increases in Eh, which indicated Fe phosphate precipitation or adsorption of P by Fe oxides or hydroxides. This was supported by mineral equilibria calculations, which showed porewaters were supersaturated with respect to strengite under oxidized conditions. Calcium-bound P was higher under reducing conditions. The results suggest that Fe phosphate precipitation controls the behavior of P in Lake Okeechobee sediments under oxidizing conditions, whereas Ca phosphate mineral precipitation governs P solubility under reducing conditions. These results also suggest that large fluxes of P from the sediment could occur if the lake water column were to experience low dissolved O 2 levels, due to the reduction and subsequent solubilization of ferric phosphate minerals in surficial sediments. Measurements of P fluxes from intact sediment cores and porewater SRP profiles taken in situ supported this hypothesis., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Wetlands are ecotones that buffer the interactions of terrestrial and aquatic systems. Considered wastelands until relatively recently, their value is currently being recognized with greater public awareness and development of a national policy. Wetlands protect aquatic systems from upland environments through sedimentation and filtration of runoff and providing environments for nutrient assimilation. Likewise, wetlands can protect uplands from aquatic systems by diverting and dissipating floodwater volume and energy. Major research needs in the area of wetland science include: (i) wetland delineation, (ii) characterization of wetland soils, and (iii) biogeochemical processes in soil and water column regulating the water quality. This overview provides a brief introduction to the papers presented at a symposium entitled "Wetland Processes and Water Quality" sponsored by Division A-5 of the American Society of Agronomy and S Divisions within the Soil Science Society of America., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Manure-derived P can jeopardize surface water quality in regions dominated by sandy soils, due to low P retention capacity of these soils. Surface (Ap) horizons from dairy-intensive areas in the Lake Okeechobee Basin were recently found to release P readily, despite abundant Ca and high pH. The purpose of this study was to determine the inorganic components that influence or reflect the stability of P in these horizons and in a related stream sediment that released much less P than soil material, despite comparable total P. Coarse fragments (>2 mm), sand, silt, and clay were separated by sieving and centrifugation. Whole soil material and coarse fragments were examined using a dissecting microscope. Crystalline and noncrystalline components were identified using a combination of optical microscopy, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, electron microprobe analysis, thermogravimetry, density separation, and selective dissolution techniques. The >2-μm fraction of Ap horizons was dominated by quartz, but appreciable biogenic opal was present in the silt. Clay from these horizons was mainly noncrystalline Si (opal A), which persisted after Ca and P were removed via selective dissolution. The clay-fraction Si had high CEC, abundant adsorbed water, amorphous morphology, and low affinity for P. It was probably a degradation product of opaline forage phytoliths, since dried manure contained Si bodies similar in morphology to those found in silt and clay. Lack of Ca-P minerals suggests that manure components (i.e., organic acids, Mg, Si, etc.) inhibited crystallization of stable Ca-P, thereby maintaining high P solubility. The stream sediment contained a calcium phosphate mineral resembling poorly crystalline apatite, and a ferrous phosphate mineral (vivianite). The flux of P from dairy to aquatic systems in regions of dominantly sandy soils could be markedly reduced if the barrier to the crystallization of Ca-P could be eliminated., (© 1994 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)