Denitrification Potential In Sediments Research Articles

Catchment topography and the distribution of electron donors for denitrification control the nitrate concentration in headwater streams of the Lake Hachiro watershed

ABSTRACT We examined the linkages between topography and electron donors for denitrification on in-stream NO3 − concentration in headwater catchments in the Lake Hachiro watershed having marine sedimentary rock, Japan. In 35 headwater catchments (0.07–16.9 km2), we sampled stream water every season in 2 years. The water samples were analyzed for NO3 –, dissolved nitrous oxide (dN2O), and SO4 2 – concentrations. Stream sediment was sampled once for the measurement of denitrification potential (DP). Water-extractable soil organic carbon (WESOC) and easily oxidizable sulfide (EOS) in the sediment, which can be considered the principal potential electron donors for denitrification, were measured. The topographical features of each catchment were calculated using a digital elevation model with 10-m grid cells. Stream NO3 – concentrations displayed large spatial variation among catchments, ranging from 0.06 to 0.52 mg N L–1, and were negatively correlated with topographic wetness index (TWI) (P < 0.01) and were positively correlated with catchment slope (P < 0.01), indicating that NO3 – concentrations decreased in wetter and gentle slope catchments. Sediment DP and the WESOC content in sediments were positively correlated with TWI, significantly. These results suggested denitrification was likely to occur in higher TWI catchments. Generalized linear model showed that TWI, slope aspect, and sediment DP significantly affected in-stream NO3 – concentration and WESOC was a significant explanatory variable for sediment DP. EOS content in riverbed sediments was not selected as a significant explanatory variable for either in-stream NO3 − concentrations or sediment DP. But higher soil DP with higher EOS was detected in the stream bank subsoil at the catchment where the higher EOS content in the riverbed sediment was observed, which suggested EOS in riverbed sediments can contain site-specific information about denitrification hotspot driven by sulfides. We conclude that catchment topography and the distribution of electron donors in riverbed sediment can be important factors to explain the spatial variation in in-stream NO3 – concentration and sediment DP.

Excess N2 and denitrification in hyporheic porewaters and groundwaters of the San Joaquin River, California

The San Joaquin River (SJR) in California is purported to receive high nitrate loadings from surrounding agricultural lands through both surface and groundwater inputs. To investigate the potential removal of nitrate (NO3−) from surface and ground water sources, the spatial variations in dinitrogen (N2) gas concentrations and direct measurements of sediment denitrification potential (DNP), with amended NO3− and carbon (C) treatments, were investigated in the summer along a 95-km reach of the San Joaquin River. Excess N2 in hyporheic porewaters ranged from <0.1 to 8.65 mg L−1 and was significantly higher in porewaters from the 1.3 m (ground water source) versus 0.3 m (mixed surface and ground water) depths. In deep groundwater wells (3–7 m), median excess N2 concentration was 5.39 mg L−1 (range = <0.1–14.6 mg L−1). Excess N2 concentrations were inversely correlated with dissolved oxygen and NO3− concentrations suggesting denitrification as an important process in the dominantly anaerobic sediments. Hyporheic porewater NO3− concentrations exceeded the detection limit of 0.01 mg L−1 in only 20% of the hyporheic porewaters, in spite of high NO3− concentrations measured in both surface waters (mean = 2.25 mg N L−1) and surrounding groundwaters. Sediment DNP rates averaged 253 and 297 μg N kg−1 hr−1 for NO3− amended, and NO3− + C amended sediments, respectively, supporting the prevalence of denitrification in hyporheic sediments. Our results indicate that the hyporheic/riparian zones act as an anoxic barrier to nitrate transport from regional groundwater and as a location to remove NO3− from surface waters exchanging with the hyporheic zone.

Nitrate removal in deep sediments of a nitrogen‐rich river network: A test of a conceptual model

Many estimates of nitrogen removal in streams and watersheds do not include or account for nitrate removal in deep sediments, particularly in gaining streams. We developed and tested a conceptual model for nitrate removal in deep sediments in a nitrogen‐rich river network. The model predicts that oxic, nitrate‐rich groundwater will become depleted in nitrate as groundwater upwelling through sediments encounters a zone that contains buried particulate organic carbon, which promotes redox conditions favorable for nitrate removal. We tested the model at eight sites in upwelling reaches of lotic ecosystems in the Waupaca River Watershed that varied by three orders of magnitude in groundwater nitrate concentration. We measured denitrification potential in sediment core sections to 30 cm and developed vertical nitrate profiles to a depth of about 1 m with peepers and piezometer nests. Denitrification potential was higher on average in shallower core sections. However, core sections deeper than 5 cm accounted for 70% on average of the depth‐integrated denitrification potential. Denitrification potential increased linearly with groundwater nitrate concentration up to 2 mg NO3‐N/L, but the relationship broke down at higher concentrations (&gt;5 mg NO3‐N/L), a pattern that suggests nitrate saturation. At most sites groundwater nitrate declined from high concentrations at depth to much lower concentrations prior to discharge into the surface water. The profiles suggested that nitrate removal occurred at sediment depths between 20 and 40 cm. Dissolved oxygen concentrations were much higher in deep sediments than in pore water at 5 cm sediment depth at most locations. The substantial denitrification potential in deep sediments coupled with the declines in nitrate and dissolved oxygen concentrations in upwelling groundwater suggest that our conceptual model for nitrate removal in deep sediments is applicable to this river network. Our results suggest that nitrate removal rates can be high in deep sediments of upwelling stream reaches, which may have implications for efforts to understand and quantify nitrogen transport and removal at larger scales.

Microbial biomass and activity in geomorphic features in forested and urban restored and degraded streams

Geomorphic spatial heterogeneity affects sediment denitrification, an anaerobic microbial process that results in the loss of nitrogen (N), and other anaerobic microbial processes such as methanogenesis in urban streams. We measured sediment denitrification potential (DEA), net nitrification, methanogenesis, and a suite of ancillary microbial variables in geomorphic stream features (organic debris dams, pools, riffles, and sloughs) in forested, urban degraded and urban restored streams in the Baltimore, MD, USA metropolitan area, between June 2005 and November 2006. DEA was higher in organic debris dams (2783 ± 1405 ng N g −1 h −1, mean ± standard error) than in pools (505 ± 144), riffles (360 ± 78), and sloughs (270 ± 106), and was higher in forest (1439 ± 613) than in urban degraded (442 ± 98) and restored sites (391 ± 116), but the differences were not statistically significant. DEA was positively related to microbial biomass N (MBN) ( p < 0.0001) and percent sediment organic matter (SOM) ( p = 0.006). DEA and MBN were significantly higher in June 2005 and August 2006 than in November 2006, a temporal pattern that may have been driven by changes in microbial biomass. Methanogenesis was active in all stream geomorphic features across all study sites. Reach scale estimates of nitrification ranged from 157 to 344 mg N m −2 d −1 and were similar to reach scale DEA rates (97–230 mg N m −2 d −1), with no significant differences between restored and unrestored reaches. These results suggest that in-stream geomorphic features in urban restored and degraded sites have the potential to function as N sinks by maintaining anaerobic conditions and microbial biomass and activity that stimulate denitrification.

Denitrification Potential in Lake Sediment Increases Across a Gradient of Catchment Agriculture

Intensification of catchment agriculture has increased nutrient loads and accelerated eutrophication in some lakes, often resulting in episodic harmful algal blooms or prolonged periods of anoxia. The influence of catchment agriculture on lake sediment denitrification capacity as a nitrogen (N) removal mechanism in lakes is largely unknown, particularly in contrast to research on denitrification in agricultural streams and rivers. We measured denitrification enzyme activity (DEA) to assess sediment denitrification potential in seven monomictic and three polymictic lakes that range in the proportion of agriculture in the catchment from 3 to 96% to determine if there is a link between agricultural land use in the lake catchment and sediment denitrification potential. We collected sediment cores for DEA measurements over 3 weeks in austral spring 2008 (October–November). Lake Okaro, with 96% catchment agriculture, had approximately 15 times higher DEA than Lake Tikitapu, with 3% catchment agriculture (232.2 ± 55.9 vs. 15.9 ± 4.5 μg N gAFDM−1 h−1, respectively). Additionally, sediment denitrification potential increased with the proportion of catchment in agriculture (R 2 = 0.85, P < 0.001). Our data suggest that lakes retain a high capacity to remove excess N via denitrification under increasing N loads from higher proportions of catchment agriculture. However, evidence from the literature suggests that despite a high capacity for denitrification and longer water residence times, lakes with high N loads will still remove a smaller proportion of their N load. Lakes have a denitrification potential that reflects the condition of the lake catchment, but more measurements of in situ denitrification rates across lake catchments is necessary to determine if this capacity translates to high N removal rates.

Denitrification characteristics of pond sediments in a Chinese agricultural watershed

Ponds are widely distributed in rice-based agricultural watersheds, particularly in southern China, and may play an important role in nitrate (NO- 3) removal. However, the denitrification rate of pond sediment, measured using the acetylene (C2H2) inhibition technique, indicated that the amount of nitrogen removed by denitrification accounted for <1% of the total nitrogen applied. The present study was undertaken to determine the effects of sediment depth and temperature on denitrification of pond sediment using the C2H2 inhibition technique. The highest denitrification potential was found in the upper 5 cm of sediment, but this only accounted for approximately 34% of the total denitrification of the upper 0–30 cm of sediment, suggesting that sediment denitrification potential would be underestimated if only the upper 5 cm of sediment was measured. The denitrification potential was low and showed a weak response over a temperature range of 6–18°C, whereas denitrification increased significantly from 18 to 30°C, indicating that denitrification may play an important role in the removal of NO- 3 in warm seasons. A comparison of the NO- 3 disappearance and C2H2 inhibition methods showed that they were significantly (P < 0.01) and positively correlated. However, the C2H2 inhibition method gave only approximately 25% of the values determined by the NO- 3 disappearance method.

Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland, USA

There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was low in the restored streams during summer baseflow conditions. Uptake length of NO3−–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3−–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary, however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in response to the “flashy” hydrologic flow conditions during storms common in urban streams.

Denitrification in cypress swamp within the Atchafalaya River Basin, Louisiana

Nitrogen has been implicated as a major cause of hypoxia in shallow water along the Louisiana/Texas, USA coasts. Excess nitrogen (mainly nitrate) from Mississippi and Atchafalaya River drainage basins may drive the onset and duration of hypoxia in the northern Gulf of Mexico. Restoring and enhancing denitrification have been proposed to reduce and control coastal hypoxia and improve water quality in the Mississippi River Basin. Sediments were collected from six baldcypress restoration sites within the Atchafalaya River Basin, Louisiana, USA. The acetylene blockage technique was used to measure background and potential sediment denitrification rates. Denitrification fluxes were measured before nitrate addition (background rates) and after nitrate addition of 100 mg N l −1 (potential denitrification) at three seasonal temperatures. Background denitrification was low across all cypress swamp sites ranging from 0.9 to 8.8, 0.6 to 28.5 and 8.8 to 47.5 g N evolved ha −1 d −1 at water/sediment column temperatures of 8, 22 and 30 °C, respectively. After nitrate addition, temperature had a significant effect on sediment denitrification potential. Maximum rates measured at 8, 22 and 30 °C were approximately 250–260, 550 and 970 g N ha −1 d −1, respectively. Most of the added nitrate in water columns, incubated at 8 °C, was removed after 65 d compared to 32 d and 17 d at 22 and 30 °C, respectively. These results indicate cypress swamps have the potential to assimilate and process elevated levels of floodwater nitrate with denitrification being a major removal mechanism.

Nitrogen removal capacity of wetlands: sediment versus epiphytic biofilms

Wetlands are important sinks for nutrients and constructed wetlands are current practice for stormwater treatment. For nitrogen, the main removal process is denitrification (microbial reduction of nitrate to nitrogen gas). The bacteria responsible for this process are mostly found in the sediments and in epiphytic biofilms growing on wetland macrophytes. This paper reports on a project which aimed at measuring denitrification potential in sediments and epiphyton in urban wetlands. This study showed that wetland sediments could support high rates of denitrification. Interestingly, the most polluted of the wetlands studied had the highest denitrification potential. The management implication from this result is that indicators of pollution, such as hydrocarbon levels, will not necessarily reflect the ability of a wetland to denitrify. Two of the wetlands were studied in more detail. Here the denitrification potential of the epiphyton on dominant macrophytes and sediments were measured. The results indicated that the potential denitrification activity of the epiphyton was comparable to those measured in the sediments. Hence, biofilms could play a significant part in removing nitrogen loads. This work contributes to a better knowledge of the functioning of wetlands. This will lead to improved design and management of wetlands used for treating stormwater.

Factors affecting denitrification rates in experimental wetlands: Field and laboratory studies

To identify the conditions that promote high rates of denitrification we systematically investigated the interactions of wetland age, water temperature, organic carbon, macrophytic type and density, hydraulic conditions on denitrification rates in field and laboratory experiments. In the field, nitrate removal was consistently greater in a shallow, young, well-mixed constructed wetland, regardless of temperature and despite lower sediment denitrification potential (DNP), than in mature, more diverse, less well-mixed wetlands. We believe the presence of a benthic mesh, which supported a dense periphytic biofilm, to be partly responsible for the unexpectedly high observed rates. We measured the DNP of wetland sediments and periphyton in the laboratory with the acetylene block method under different temperatures, nitrate concentrations, and carbon sources. The overall DNP of periphyton was greater than the corresponding sediment samples on a per cell basis. We hypothesize that the organic carbon produced by the periphytic algae is readily degradable and promoted the higher denitrification rates. We found a positive relationship between DNP and biodegradable organic carbon concentration and identified chemical markers illustrating that biodegradability is promoted by a combination of polyhydroxyaromatic and polysaccharide parent structures. These findings highlight the importance of organic quality and the role of periphyton in accelerating the rates of denitrification in wetlands.

Denitrification potential in sediments of headwater streams in the southern Appalachian Mountains, USA

We investigated variations in resource availability (NO3-N and labile organic C [LOC]) as determinants of potential denitrification in stream sediments in the southern Appalachian Mountains, USA. Stream water and sediments were sampled seasonally in 2 streams of contrasting NO3-N availability, Noland Creek (high NO3-N) and Walker Branch (low NO3-N). Eight additional streams with varying NO3-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, NO3-N and LOC amendments indicated that denitrification potential in Walker Branch sediments was NO3-N limited, whereas temperature had no effect on rates. Denitrification potential in Noland Creek sediments was not limited by NO3-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. NO3-N in the 10 surveyed streams ranged from 10 to 549 μg/L, with the highest NO3-N levels and denitrification rates generally occurring in the higher-elevation streams of Great Smoky Mountains National Park. Our results suggest that NO3-N availability is the primary factor limiting potential denitrification 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 the Noland Divide Watershed).

A spatial study of denitrification potential of sediments in Belfast and Strangford Loughs and its significance

The C 2H 2 inhibition technique was employed to study seasonal denitrification potential rates in sediment slurries from tidal and subtidal sites in Belfast and Strangford Loughs, Northern Ireland. A comparison of denitrification rates obtained from this method with those obtained from the 15N-gas flux method generally showed good agreement. Depth profiles measured up to 1 m showed that denitrification decreased with depth, with highest values in the 0–5-cm fraction. For the Belfast Lough tidal system a multiple regression model was developed which explained 83% of the variation in denitrification potential. The independent variables were water content, sediment temperature, total oxidizable N in porewater and total organic N. The highest rate of denitrification potential, 2100 μmol N m −2 h −1, was found in areas where there was a high anthropogenic input of nutrients. Denitrification in sediments in both loughs can play a potentially significant role in removal of NO 3 − from the overlying water. In Belfast Lough the overall denitrification potential rate matched the external NO 3 -N inputs, whilst in Strangford Lough it exceeded it by sixfold, which suggests a potential to remove future additional anthropogenic inputs to the Lough.

Organic Matter Dynamics in the West Fork of Walker Branch, Tennessee, USA

Previous articleNext article No AccessStream Organic Matter BudgetsOrganic Matter Dynamics in the West Fork of Walker Branch, Tennessee, USAP. J. MulhollandP. J. Mulholland Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 16, Number 1Mar., 1997 Article DOIhttps://doi.org/10.2307/1468235 Views: 7Total views on this site Citations: 17Citations are reported from Crossref Journal History This article was published in the Journal of the North American Benthological Society (1986-2011), which is continued by Freshwater Science (2012-present). Copyright 1997 The North American Benthological SocietyPDF download Crossref reports the following articles citing this article:J. David Allan, Maria M. Castillo, Krista A. 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