There have been recent concerns about the anthropogenic phosphorus (P) loading to the naturally oligotrophic Everglades ecosystem. We investigated the effect of P loading on the biogeochemical cycling of nitrogen (N). We investigated the distribution of the potentially mineralizable N (PMN) rate as an indicator of the influence of P loading on selected microbial activities in soil and detritus layers. Soil characteristics measured included bulk density; total C, N, and P; microbial biomass C; and N and extractable NH|. PMN rates ranged from 10.4 to 325 mg N kg" 1 d" 1. The highest values of microbial biomass C and N, total P, extractable NH|, and PMN were observed in the detrital layer, and rates decreased with increasing soil depth. An increase in the size of the microbial pool and heterotrophic activity (organic N mineralization) was found to be related to the P-loading rate and related to the distribution of total P content in the soil and detrital layers. Extractable NHJ was a good indicator of PMN rates and total P was found to be significantly correlated to microbial biomass C and N. The stimulatory effect of P enrichment on microbial activity, overall size of the microbial biomass pool, and the PMN rate has led to an increased availability of inorganic N, which could potentially affect macrophyte growth and water quality of the northern Everglades system.
There has been recent concern about the impact of increased nutrient loading on the northern Everglades ecosystem. We investigated the spatial and temporal distribution of denitrifying enzyme activity (DEA) along a P-enrichment gradient in the Water Conservation Area 2A (WCA-2A) and determined the effects of added P and NO., on DEA. The DEA in soil and detritus layers was measured under anaerobic conditions four times during 2 yr, using the acetylene blockage technique. The DEA ranged from 0.004 to 7.75 mg NjO-N kg" 1 h~'. Highest rates of DEA were found in the detritus and surface (0-10 cm) soils, and rates decreased exponentially with increasing distance from the surface-water inflow point, where nutrients are loaded to the wetland. Nitrate was found to be limiting, while the addition of P had no effect on the distribution of DEA in these soils. There was a seasonal effect on DEA, with higher activity observed during the summer when temperatures and hydraulic and nutrient loading were highest. Soils from outside the impacted zone demonstrated denitrifying potentials, within 10 h when spiked with inflow concentrations of NOf, similar to DEA of soils from within the impacted zone. This suggests that soils from outside the impacted zone can increase denitrification rates when exposed to higher NOf concentrations in a relatively short time. Agricultural drainage water discharge, and consequent NOr loading, has created a zone of elevated DEA proximal to the S-lOCsnrface-water inflow point in WCA-2A. N ITRATE REDUCTION is the major N removal mechanism in wetlands. Among NO 3~ reduction processes, denitrification is the dominant NO 3~ removal process. Denitrification is a microbially mediated process whereby facultative anaerobic bacteria use NO 3~ (or NOr) in the absence of O 2 as the terminal electron acceptor during the oxidation of organic C (microbial respiration), resulting in the production of gaseous end products, N 2 O and N 2. The denitrification enzyme assay is used as a means to eliminate all other regulating factors of denitrification in order to quantify the amount of active denitrifying enzymes present in soil (Smith and Tiedje, 1979; Smith and Parsons, 1985; Groffman, 1987; Schipper et al., 1993). The enzyme assay is the shortterm (2 h) rate of N 2 O production and is indicative of the size and activity of the denitrifying enzyme pool present in soil. The assay reflects the immediate biological effect of changes in redox conditions attributed to changes in soil O 2 levels (Martin et al., 1988). Several studies of DEA have focused on upland soils
Future conditions of coastal Louisiana are highly uncertain due to the dynamic nature of deltas, climate change, tropical storms, and human reliance on natural resources and ecosystem services. Managing a system in which natural and socio-economic components are highly integrated is inherently difficult. Sediment diversions are a unique restoration tool that would reconnect the Mississippi River to its deltaic plain to build and sustain land. Diversions are innately adaptable as operations can be modified over time. An expert working group was formed to explore how various operational strategies may affect the complex interactions of coastal Louisiana's ecological and social landscape and provide preliminary recommendations for further consideration and research. For example, initial operations should be gradually increased over 5 to 10 years to facilitate the development of a distributary channel network, reduce flood risk potential to communities, limit erosion of adjacent marshes and reduce stress to vegetation and fish and wildlife species. Diversions should operate over winter peaks to capture the highest sediment concentration, reduce vegetation loss while dormant, and reduce detrimental effects to fish and wildlife. Operations during the spring/summer should occur over shorter periods to capture the highest sediment load during the rising limb of the flood peak and minimize impacts to the ecosystem. Operational strategies should strive to build and sustain as much of the coastal landscape as possible while also balancing the ecosystem and community needs.
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.
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