Influence of Nitrate and Phosphorus Loading on Denitrifying Enzyme Activity in Everglades Wetland Soils

Abstract

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

Comparative Study of Three Two-Stage Hybrid Ecological Wastewater Treatment Systems for Producing High Nutrient, Reclaimed Water for Irrigation Reuse in Developing Countries

“…The HF wetland systems typically have greater reduction rates for nitrate [19,20]. However, our system may have lacked sufficient organic carbon to stimulate denitrification [21]. The BOD was almost entirely removed in the first stage leaving little bioavailable carbon for denitrification in the second stage, having as a consequence a nitrate accumulation [8].…”

Modeling of denitrification rates in eutrophic wetlands by artificial neural networks

“…The reviews of Q 10 of the treatment wetlands near 1.0 [3,39] exhibited that temperature effect can be estimated to be too high. The effect of temperature was also often confounded with other seasonal effects [6,39] involving light intensity, vegetation growth, etc. Therefore, low contribution of temperature in the limited range indicates that denitrification is not highly sensitive to seasonal variables such as DOC supply, microbial activity or plant growth in this study.…”

“…Eutrophication was also influential in keeping DEA from contributing to denitrification. DEA is highly dependent on nitrate and carbon availability [6,10]. However, the nutrient sources such as nitrate or carbon could not be a limiting factor in eutrophication.…”

“…Denitrification has been considered as a major mechanism for N removal, and wetlands are known to be a hotspot of denitrification [5,6]. In a wetland where anaerobic conditions are easily introduced, many facultative microorganisms, called denitrifying bacteria, can use nitrate as an electron acceptor and remove the nitrogen from water [5,7].…”

“…High organic matter content, nitrate input and development of rhizosphere with anaerobic condition also induce high denitrification rate [4,[8][9][10]. Denitrifying Enzyme Activity (DEA) reflects the amount of denitrifying enzymes in soil, and it is often correlated with denitrification rate positively [6,11].…”