Forrest E. Dierberg

Nitrogen and Phosphorus Mass Balances in Natural and Sewage-Enriched Cypress Domes

(1) Nitrogen and phosphorous mass balances were determined on two small cypress swamps in Florida. Nutrient inputs from secondary sewage effluent applied to one swamp for a 3-year period (1975-77) were 14-9 g m-2 y- for total nitrogen (TN) and 11.4 g m-2 y- for total phosphorus (TP). These values represent 90 and 99% of the TN and TP inputs to this system. Input rates measured on an undisturbed swamp were 0.051 g P m-2 y-1 and 2.19-4-26 g N m-2 yel, of which bulk precipitation contributed 67% of the P and 20-39% of the N. Runoff from uplands supplied an additional 33% of the P and 14-26% of the N. (2) Nitrogen fixation was an important source of nitrogen to the natural dome: 34-66% of the TN input, or 0.75-2.81 g m-2 y-1 (depending on the significance of nitrogenase activity measured on excised roots of woody species). Mass balance calculations indicate that without N2-fixation there would be inadequate nitrogen to support measured growth rates of woody biomass. Application of effluent inhibited N2-fixation; less than 2% of the TN loading to the sewage-enriched dome was accounted for by this process. (3) Denitrification was more prominent in the sewage-enriched dome than in the natural dome both in absolute amount (2.01 v. 0.15 g N m-2 y-1) and percentage of input N (13% v. 4-7%). Higher nitrate-nitrite loadings in the effluent accounted for this trend. Both domes are capable of denitrifying most of the input nitrate and nitrite. (4) Because of higher nutrient levels in shallow groundwater and higher infiltration rates, the sewage-enriched dome lost six times more TN and sixteen times more TP by infiltration than did the natural dome. Nonetheless, infiltration losses in the fortier dome were only 8% and 2% of the annual inputs of TN and TP, respectively. Losses from surface overflow were minor (1-6%) for both domes. (5) Higher uptake rates of N and P into above-ground cypress trees were calculated for the sewage-enriched dome than for the natural dome, but the fraction of nutrient inputs stored in the above-ground cypress biomass was much higher in the natural dome than in the sewage-enriched dome. (6) Annual inputs exceeded outputs by 11.fi0 g N m-2 y-1 and 10.4 g P m-2 y-1 in the sewage-enriched dome, indicating 74% retention of TN inputs and 92% retention of TP inputs. Most of the nutrients remaining in the dome were retained in below-ground biomass and peat (90% of the TP input and 56% of the TN input). (7) It is concluded that cypress domes can serve as efficient natural tertiary treatment systems, and they should be considered as alternatives to conventional tertiary treatment methods and to other wetland and upland disposal sites.

Biological uptake vs. coprecipitation of soluble reactive phosphorus by ‘P-enriched’ and ‘P-deficient’ Najas guadalupensis in hard and soft waters

In addition to direct assimilation and storage by submersed photosynrhetic communities, phosphorus (P) can also be adsorbed to and incorporated inro precipitating calcium carbonate (CaC03) crystals as they nucleate in hardwater environmenrs (ÜTSUKI & WETZEL 1972, MuRPHY et al. 1983). Since a photosynrhetically induced pH elevation is critical for attaining the supersaturated conditions that lead to CaC03 precipitation, al! submersed photosynrhetically active communities have the potenrial to precipitate CaC03 (and thus coprecipitate P) in a hardwater environment. Calcareous deposits are frequently observed in periphyton mats (BROWDER et al. 1994) and on the thalli, stems, and leaves of submersed aquatic vegetation (SAV) (WETZEL 1960, MICKLE & WETZEL 1978, McCONNAUGHEY et al. 1994) growing in hardwater habitats, verif}ring that CaC03 precipitation does occur on the planr surfaces. This formation implies that P may be coprecipitated in these deposits, eventually being either assimilated by the above-ground parts of the planr o r deposited in the sedimenr after planr senescence. The importance of this mechanism within SAV communities is somewhat harder to documenr than in phytoplankton and periphyton communities. Light limitation is more likely to have an effect on reducing diurnal pH values within SAV than phytoplankton because SAV does not have the same opportunity as phytoplankton to be recirculated to the euphotic zone. In addition, most SAV species are rooted and therefore can obtain a significanr amounr o f their P needs from the interstitial water ( GRANÉLI & SoLANDER 1988, WuzEL 2001). This complicates the determination of how much P is assimilated from the water column by the leaves and stems. Finally, SAV communities often support significanr quanrities of periphyton, which can also conrribute to the P removal from the water column, either by direct uptake or by coprecipitation. This paper presents the results of an experimenr where Najas guadalupensis was pre-conditioned in soft waters under P-enriched and P-deficienr culture conditions, and then exposed to a modest P amendment (125 flg/L) under both high and low calcium and alkalinity concenrrations. The purpose of the study was to separate the effects and idenrif}r the importance of direct planr uptake vs. P coprecipitation in P-enriched and P-deficient N. guadalupensis.

Nitrifying population densities and inhibition of ammonium oxidation in natural and sewage-enriched cypress swamps

Abstract The occurrence of autotrophic nitrifiers in the peat from the floors of a natural cypress dome, a cypress dome receiving deep artesian groundwater, and two cypress domes amended with secondary treated sewage effluent, were assessed by surveying their population densities. The absence of ammonium oxidation in the surface waters of the natural dome was due to the low pH and not to any toxic organic chemical effects present in the humic-colored water. This probably explains the low density (0–56 cells cm−3) of autotrophic nitrifiers found associated with the peat from that dome.

Temporal and spatial patterns of internal phosphorus recycling in a South Florida (USA) stormwater treatment area.

Large constructed wetlands, known as stormwater treatment areas (STAs), have been deployed to remove phosphorus (P) in drainage waters before discharge into the Everglades in South Florida, USA. Their P removal performance depends on internal P cycling under typically hydrated, but with occasionally desiccated, conditions. We examined the spatial and temporal P removal capacity under different hydrologic conditions along a STA flow path. While inflow soils are P enriched, the outflow region of the wetland contained P-unsaturated soils with minimal net recycling of bound soil P to the water column as plant-available P. The outflow-region soils were characterized by low porewater soluble reactive P (SRP) (≤40 μg L) and high total sulfide (TS) (2-9 mg L) concentrations, and total ammoniacal nitrogen (TAN) and SRP flux rates that averaged 1.51 and 0.002 mg m d, respectively. Pronounced increases in porewater and surface-water concentrations of SRP, dissolved organic P (DOP), and TAN were observed immediately after rehydration of the cell after an extended drought. Elevated total P concentrations persisted at the outfall of the cell for several months thereafter, resulting in an annual outflow total P concentration nearly threefold higher than the long-term mean. Relative to processes that can occur during extended periods of inundation, such as sulfate-enhanced P release from organic matter mineralization or iron sulfide formation, aerobic oxidation of organic matter during prolonged dryout periods is a more significant biogeochemical process in compromising soil P retention in STAs.

An assessment of iron and calcium amendments for managing phosphorus release from impacted Everglades soils

The recent implementation of agricultural best management practices (BMPs) and treatment wetlands called stormwater treatment areas (STAs) have reduced phosphorus (P) concentrations and loadings to the Everglades Protection Area (EPA) in Florida (USA). There is a concern that despite reductions in external P loadings, internal loading from the legacy P enrichment of the EPA wetland soils will continue to elevate water column P concentrations, and may impede restoration outcomes. In an effort to explore ways to reduce soil P efflux, we retrieved intact, vegetated (cattail, Typha domingensis) soil monoliths from two P-enriched areas of the EPA and deployed them at a location where they received pre-treated (low P) surface water as ex situ flow-through mesocosms for 21xa0months with a mid-study 7-week dry down to mimic natural hydroperiod conditions. Two treatments were tested for soils from both sites, using triplicate mesocosms for each treatment. After applying a herbicide (glyphosate) to eliminate the cattail vegetation, iron (Fe as liquid FeCl3) amendments provided no P retention benefits in the organic soils from the two sites, and did not yield significantly (Pxa0>xa00.05; nxa0=xa043) lower flux rates (6.1 and 3.5xa0mg Pm−2 d−1) than the herbicide/no soil amendment control (3.9 and 2.1xa0mg Pm−2 d−1), as was expected. A combination of low oxidation–reduction potential, heightened organic matter P mineralization, high pH, and sulfide production acted interactively to enhance Fe and P mobilization in the Fe-amended mesocosms. The herbicide/limerock (CaCO3)-amended soils exhibited significantly lower (Pxa0≤xa00.05; nxa0=xa043) P flux (1.3 and 1.1xa0mg Pm−2 d−1) than the herbicide/no soil amendment control soils, but it remains unknown whether the observed reduction in P efflux (ranging from 48 to 67%) would justify the expense and potential environmental impacts of applying a surficial limerock amendment to large regions of the P-enriched wetlands.