Relative Importance Of Denitrification Research Articles

Factors controlling dissimilatory nitrate reduction processes in constructed stormwater urban wetlands

Water treatment wetlands are increasingly being used to reduce pollutant loads including nitrogen (N) in urban runoff. Processes such as denitrification (DNF) and anaerobic ammonium oxidation (anammox), which remove N, and dissimilatory nitrate reduction to ammonium (DNRA), which recycles N, play an important role in controlling NOx (NO3− + NO2−) removal versus recycling in wetlands. The relative importance of DNF, anammox and DNRA was investigated in four constructed stormwater urban wetlands in Melbourne, Australia. Rates of DNF and DNRA were variable and did not differ significantly among wetlands. However, rates of DNF and DNRA were significantly different (p < 0.05) in different seasons. The relationship between NOx reduction processes and measured concentrations of water column NOx, chlorophyll a (chl-a), sediment organic carbon (OC), porewater ferrous iron (Fe2+) and sulfide (S2−) and water column temperature were examined using multiple regression analysis (MRA). Anammox was an insignificant pathway (< 0.05% of total nitrate reduction). During winter when average water column temperatures were 12 °C, DNRA was consistently higher than DNF averaging 67 ± 23% of total NOx reduction. The MRA revealed that DNF was positively associated with NOx concentration whereas DNRA was negatively associated with temperature, and porewater Fe2+, and positively associated with chl-a. The ratio between DNF and DNF:(DNF + DNRA) showed a positive correlation with both temperature and NOx concentration in the MRA. At higher temperatures and higher NOx concentrations, DNF increased over DNRA. Overall, this study suggests that at low NOx concentrations, N is recycled internally in these urban stormwater wetlands, but the portion of N removed by DNF increases as NOx concentrations increase.

Biogeochemical Controls on the Relative Importance of Denitrification and Dissimilatory Nitrate Reduction to Ammonium in Estuaries

AbstractThe balance between estuarine denitrification and dissimilatory nitrate reduction to ammonium (DNRA) is critical for determining nitrogen loads received by oceans from inland waters. We aimed to determine the factors controlling the ratio between these processes and determining whether nitrogen was generally removed or recycled in estuaries. Rates of denitrification and DNRA with depth were measured in intact sediment cores in 11 estuaries along the coast of Victoria, Australia. The estuaries studied represent a range of biogeochemical conditions, land use, and catchment size. At a pore water profile scale, the ratio of denitrification to DNRA was well predicted by a multiple regression model with nitrate concentration in the overlying water, dissolved pore water iron, and ammonium as the predictor variables. Areal denitrification rates varied from 4 to 150 μmol · m−2 · hr−1, and DNRA rates varied from 2 to 30 μmol · m−2 · hr−1, with the ratio of denitrification to DNRA spanning a range from denitrification‐dominated (denitrification/DNRA = 8.4) to DNRA‐dominated (denitrification/DNRA = 0.3). DNRA dominated at sites with high iron pools and high organic carbon to nitrate ratios. We conclude that low nitrate and high Fe2+ availability generally enhances DNRA and drives an estuary toward being N recycling, rather than N removing.

Microbial nitrogen processing in hard clam ( Mercenaria mercenaria ) aquaculture sediments: the relative importance of denitrification and dissimilatory nitrate reduction to ammonium (DNRA)

As bivalve aquaculture expands worldwide, an understanding of its role in nutrient cycling is necessary to ensure ecological sustainability and determine the potential of using bivalves for nutrient mitigation. Whereas several studies, primarily of epifaunal bivalves, have assessed denitrification, few have considered nutrient regeneration processes such as dissimilatory nitrate reduction to ammonium (DNRA), which competes with denitrification for nitrate and results in nitrogen retention rather than loss. This study compares sediment nitrogen cycling including mineralization, DNRA, and denitrification within U.S. clam aquaculture sediments to nearby uncultivated sediments, seasonally. Clam aquaculture significantly increased sediment ammonium and phosphate effluxes relative to uncultivated sediments. Both DNRA and denitrification were significantly enhanced at clam beds compared to uncultivated sediments in July and November, while in May only DNRA was increased. The ratio of DNRA to denitrification was significantly higher at clam beds compared to uncultivated sediments, demonstrating that DNRA may be favored due to a ready supply of labile organic carbon relative to nitrate and perhaps sulfidic conditions. Functional gene abundances, nrfA (DNRA) and nirS (denitrification) followed similar patterns to nitrate respiration rates with highest nrfA abundances in the clam sediments and similar nirS abundances across seasons and sediment type. Ultimately clam sediments were found to be a significant source of nutrients to the water column whereas uncultivated sediments retained ammonium produced by microbial mineralization. Thus, clam cultivation may promote local eutrophication (i.e., increased primary production) by facilitating nutrient regeneration and retention of ammonium in the sediments.

남해안 주요 하구 갯벌 퇴적물의 탈질소화를 통한 질소 영양염 제거

남해안의 주요 하구 4곳(순천만, 섬진강, 고성천, 마산만)과 서해안의 태안 근소만 갯벌에서 2009년 3월부터 2010년 5월까지 유기물 정화능력을 파악할 수 있는 퇴적물 산소요구량(Sediment Oxygen Demand; SOD)과 탈질소화(Denitrification)를 측정하였다. 퇴적물 산소요구량은 퇴적물 배양 중 시간당 용존산소감소율로 부터 추정되었으며, 탈질소화 측정에는 질소 안정동위원소를 추적자로 이용하는 isotope paring technique이 사용되었다. 조사지역의 퇴적물 산소요구량과 탈질소화율은 각각 -5.1~24.6 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>와 0.0~3.9 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>의 범위를 보였다. 퇴적물 산소요구량이 가장 높은 곳은 마산만(평균 = 10.2(범위 =-2.2~19.2 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>)이었으며, 순천만, 고성, 태안, 섬진강 순으로 나타났다. 탈질소화율도 마산만(평균 = 1.0(범위 =0.0~3.9) mmole <TEX>$N_2 m^{-2}d^{-1}$</TEX>이 가장 높았으며, 고성, 섬진강, 순천만, 태안 순으로 나타났다. 태안, 섬진강, 마산 지역에서는 계절적으로 저서미세조류에 의한 광합성이 탈질소화에 뚜렷한 영향을 미쳤는데 광합성 동안 생성된 산소는 혐기성과정인 탈질소화를 저해하기 보다는 질산화를 원활하게 하여, 질산화-탈질소화 연계과정을 촉진시켰다. 남해안 허구에서 탈질소화의 계절변화 유형(봄철 최대 유형과 여름철 최대 유형)의 지역적 차이는 탈질소화에 사용되는 두 질산원(<TEX>$D_w$</TEX>; 강을 통해 공급된 질산과 <TEX>$D_n$</TEX>; 질산화-탈질소화 연계과정에 의해 생성된 질산)의 상대적 중요성에 따라 결정되었다. 즉 봄철에 탈질소화가 높게 나타난 순천만, 고성, 마산은 여름철에 비해 봄철 수층 질산염이 풍부하였고, 이를 통해 <TEX>$D_w$</TEX>가 증가되었다. 태안과 섬진강 지역이 여름철에 탈질소화 최대값을 보인 이유는 수층의 질산염이 고갈되지 않은 상태에서 여름철 수온의 증가로 <TEX>$D_w$</TEX>가 증가하였고, 이와 더불어, 산소고갈이 나타나지 않아 질산화에 좋은 환경이 조성되었으며, 결과적으로 <TEX>$D_n$</TEX>이 증가되었기 때문이다. Sediment oxygen demand(SOD) and denitrification rates were measured in four major estuaries(Suncheon Bay, Seomjin river estuary, Goseong stream estuary and Masan Bay) in south coast of Korean peninsula from March of 2009 to May 2010 to estimate organic matter cleaning capacity. SOD was estimated from the temporal dissolved oxygen concentration change and isotopic pairing technique was employed to measure denitrification. Sediment oxygen demand(SOD) was ranged from -5.1 to 24.6 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX> and denitrification rate was ranged from 0.0 to 3.9 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>in the study area. SOD was the highest in Masan Bay(-2.2 to 19.2, average = 10.2 mmole <TEX>$O_2m^{-2}d^{-1}$</TEX>) and Suncheon, Goseong, Tae-an and Seomjin followed. Denitrification was also the highest in Masn Bay(0.0 to 3.9, average = 1.0 mmole <TEX>$N_2m^{-2}d^{-1}$</TEX>) and Goseong, Seomjin, Suncheon and Taean followed. The effect of benthic photosynthesis by microphytobenthos on denitrification was evident in some season of Tae-an, Seomjin, and Masn Bay. The increased oxygen level produced by photosynthesis stimulated nitrification without severe adverse effect on denitrification and, as a result, coupled nitrification and denitrification was enhanced in these areas. A difference of seasonal patterns of denitrification at each site depended on relative importance of denitrification on different nitrate source(<TEX>$D_w$</TEX>: nitrate from water column and <TEX>$D_n$</TEX>: nitrated produced during nitrification). Denitrification was maximum during spring in Goseong, Suncheon and Masan Bay. On the contrary, denitrification was the highest during summer in Tae-an and Seomjin estuary.

Plant–microbe interactions and nitrogen dynamics during wetland establishment in a desert stream

In late-successional steady state ecosystems, plants and microbes compete for nutrients and nutrient retention efficiency is expected to decline when inputs exceed biotic demand. In carbon (C)-poor environments typical of early primary succession, nitrogen (N) uptake by C-limited microbes may be limited by inputs of detritus and exudates derived from contemporaneous plant production. If plants are N-limited in these environments, then this differential limitation may lead to positive relationships between N inputs and N retention efficiency. Further, the mechanisms of N removal may vary as a function of inputs if plant-derived C promotes denitrification. These hypotheses were tested using field surveys and greenhouse microcosms simulating the colonization of desert stream channel sediments by herbaceous vegetation. In field surveys of wetland (cienega) and gravelbed habitat, plant biomass was positively correlated with nitrate (NO3 −) concentration. Manipulation of NO3 − in flow-through microcosms produced positive relationships among NO3 − supply, plant production, and tissue N content, and a negative relationship with root:shoot ratio. These results are consistent with N limitation of herbaceous vegetation in Sycamore Creek and suggest that N availability may influence transitions between and resilience of wetland and gravelbed stable states in desert streams. Increased biomass in high N treatments resulted in elevated rates of denitrification and shifts from co-limitation by C and NO3 − to limitation by NO3 − alone. Overall NO3 − retention efficiency and the relative importance of denitrification increased with increasing N inputs. Thus the coupling of plant growth and microbial processes in low C environments alters the relationship between N inputs and exports due to increased N removal under high input regimes that exceed assimilative demand.

The relative importance of denitrification and nitrate assimilation in midcontinental bogs

Denitrification rates measured in a Minnesota bog and a bog in western Ontario were similarly low (&lt;0.20–2.28 µg m‒2 h‒1 as N). Nitrate addition stimulated denitrification at the Minnesota bog, but &lt;1% of added NO3‒‐N (0.01–0.1 g m‒2) was denitrified in 24 h. In the Ontario bog, denitrification was not stimulated by NO3‒‐N application (0.08 g m‒2). Rates of NO3‒‐N uptake by Sphagnum, measured by nitrate reductase activity assays and NO3‒ disappearance from cultures, were much higher, 100–24,000 µg m‒2 h‒1 (0.57–48.7 µg g‒1 h‒1), than rates of denitrification at comparable NO3‒ loadings. Measurements of NO3‒ in pore water and moss throughfall confirm that NO3‒ disappears in the top 5–10 cm of moss. Plant uptake appears to be the dominant sink for NO3‒ in midcontinental bogs.

The relative importance of denitrification and nitrate assimilation in midcontinental bogs

The relative importance of denitrification and nitrate assimilation in midcontinental bogs

An experiment on the relative importance of denitrification, nitrate reduction and ammonification in coastal marine sediment

Simultaneous determinations of 15N-nitrogen gas production, 15N-ammonia formation by nitrate reduction and ammonia production from organic nitrogen were carried out after addition of 15N-nitrate to anaerobically incubated sediment slurries from a location in the Dutch Wadden Sea. The rate of nitrogen gas production was 1.57 μmol N·cm −3 wet sediment·d −1, nitrate reduction to ammonia occurred at a rate of 0.79 μmol N·cm −3·d −1 and ammonification at 1.17 μmol N·cm −3·d −1. At the end of the incubation experiment (after 30 h) 63% of the originally added 15N-nitrate was present as nitrogen gas, 32% ended up as ammonia and ∼4% as particulate organic nitrogen. Ammonia production by degradation of organic nitrogen compounds was the most important process in building up the ammonia pool in the anaerobic sediment incubation.