In situ measurement of denitrification in agricultural streams (original) (raw)
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Journal of Soil and Water Conservation, 2018
A griculture accounts for 34% of land use in Wisconsin (USDA NASS 2012), and nonpoint source pollution plays a significant role in water quality impairment (WDNR 2016). Out of 2,400 water bodies assessed by the Wisconsin Department of Natural Resources, 1,294 were considered impaired, 74% of which were impaired by either phosphorus (P) or sediment, which are typically contributed by agricultural fields (WDNR 2016). In 2010, revisions to Wisconsin's Phosphorus Water Quality Standards created water quality standards for P in surface waters. To implement these standards, permit holders and agricultural producers were encouraged to work together through the compliance options called Water Quality Trading and Adaptive Management (WDNR 2012). These options allow point sources to offset their pollution load by taking credit for other P reductions in the watershed. The implementation of an enhanced regulatory package raises questions about the best way to engage with farmers in a watershed in order to document current practices and make improvements in water quality through installation of best management practices. Farmers are the focal point of many water quality improvement projects and efforts (Woods et al. 2014). The focus on farms is in part because nonpoint source pollution from agriculture contributes FEATURE
Denitrification Bioreactor in Northeast Iowa
2010
Denitrification bioreactors for removal of nitrate in tile drainage are new water quality technology that has rapidly gained interest in Iowa. A bioreactor is composed of an excavated trench filled with woodchips that are colonized by denitrifying bacteria. As drainage waters containing nitrate flow by these "good" bacteria, they convert the nitrate in the water to nitrogen gas. A critical component in evaluating the performance of these treatment systems is the documentation not only of nitrate concentrations in the drainage water, but also the flow rate and volume of the water treated in the bioreactor.
Environmental Pollution, 2010
Denitrification is a process that reduces nitrogen levels in headwaters and other streams. We compared nirS and nirK abundances with the absolute rate of denitrification, the longitudinal coefficient of denitrification (i.e., Kden, which represents optimal denitrification rates at given environmental conditions), and water quality in seven prairie streams to determine if nir-gene abundances explain denitrification activity. Previous work showed that absolute rates of denitrification correlate with nitrate levels; however, no correlation has been found for denitrification efficiency, which we hypothesise might be related to gene abundances. Water-column nitrate and soluble-reactive phosphorus levels significantly correlated with absolute rates of denitrification, but nir-gene abundances did not. However, nirS and nirK abundances significantly correlated with Kden, as well as phosphorus, although no correlation was found between Kden and nitrate. These data confirm that absolute denitrification rates are controlled by nitrate load, but intrinsic denitrification efficiency is linked to nirS and nirK gene abundances.
Whole-system estimation of denitrification in a plains river: a comparison of two methods
Biogeochemistry, 2005
Whole-system denitrification in the South Platte River was measured over a 13-month period using an open-channel N2 method and mass-balance measurements. Concentrations of dissolved N2 were measured with high precision by membrane-inlet mass spectrometry and estimates of denitrification were based on the mass flux of N2, after correction for reaeration and groundwater flux. Open-channel estimates of denitrification ranged from 0 to 3.08 g N m−2 d−1 and the mean annual rate was 1.62 g N m−2 d−1, which corresponds to removal of approximately 34% of the nitrate transported by the river over a distance of 18.5 km. Over the same period of time, estimates of denitrification based on mass-balance measurements ranged from 0.29 to 5.25 g N m−2 d−1 and the mean annual rate was 2.11 g N m−2 d−1. The two methods revealed similar seasonal patterns of denitrification the highest rates were measured from late April to August and the lowest rates were in winter. Both methods provide whole-system estimates of denitrification in running waters; where reaeration rate coefficients are low and flux of groundwater is well quantified, the open-channel method has fewer sources of uncertainty and is easier to implement.
Journal of The North American Benthological Society, 2001
V\fe investigated variations in resource availability (NO 3 -N and labile organic C [LOG]) as determinants of potential denitrih'cation in stream sediments in the southern Appalachian Mountains, USA. Stream water and sediments were sampled seasonally in 2 streams of contrasting NO 3 -N availability, Noland Creek (high NO 3 -N) and Walker Branch (low NO 3 -N). Eight additional streams with varying NO 3 -N levels were sampled once during summer. Stream sediments were incubated at ambient stream temperatures, and nitrous oxide accumulation was quantified following acetylene inhibition of nitrous oxide reduction. Denitrification potential was greater in Noland Creek than Walker Branch. In autumn and spring, NO 3 -N and LOC amendments indicated that denitrification potential in Walker Branch sediments was NO 3 -N limited, whereas temperature had no effect on rates. Denitrification potential in Noland Creek sediments was not limited by NO 3 -N or LOC, but was significantly affected by season and temperature. However, no differences in denitrification potential were detected when Noland Creek seasonal data were adjusted to a common temperature. NO 3 -N in the 10 surveyed streams ranged from 10 to 549 u.g/L, with the highest NO 3 -N levels and denitrification rates generally occurring in the higher-elevation streams of Great Smoky Mountains National Park. Our results suggest that NO 3 -N availability is the primary factor limiting potential denirrification in Southern Appalachian streams. Despite the ideal conditions of slurry studies, extrapolation of potential rates to estimate denitrification loss in the catchment channels indicates that the process is an insignificant N sink (1.7% of stream N export in Walker Branch and 1.5% of N export in thes Noland Divide Watershed).
Ecological Engineering, 2015
The transport of nitrate (NO 3 -N) from agricultural lands to surface waters is a complex and recalcitrant problem. Subsurface drainage systems that are especially prevalent in the corn-growing regions of the Midwestern USA facilitate NO 3 -N transport. Several conservation practices, including fertilizer and manure management, cover crops, natural and installed wetlands, and wood-chip denitrification bioreactors are options that can mitigate NO 3 -N losses from agricultural lands. Using simple methods of estimation we examine the cumulative volume of denitrification bioreactors required to treat various amounts of NO 3 -N in base flow, a proxy for tile drainage, at the watershed scale. The use of load duration curves from three different watersheds shows that NO 3 -N transport is disproportionately skewed toward larger daily base flows. Approximately 50% of the annual NO 3 -N is transported in largest 30% of daily base flows. Using previous estimates of NO 3 -N removal by wood-chip bioreactors, we calculated cumulative bioreactor volumes needed to achieve a range of hydraulic residence times (HRT) given rates of base flow observed in three agricultural watersheds. These analyses suggest that cumulative watershed bioreactor volumes sufficient to achieve an HRT of 0.5 days will reduce at least 20% of the total annual NO 3 -N loss in one watershed and 30% in the other two watersheds. The area required for wood-chip bioreactors would be at most 0.27% of the watershed area.