Denitrification In Lake Research Articles

Influence of Denitrification on Cyanobacterial Blooms Trends in Lake Taihu, China

Denitrification is a major process in aquatic ecosystems, and it competes with cyanobacterial growth for nitrogen. However, the effect of denitrification on cyanobacterial blooms under the background of climate change remains unclear. This study explored the interaction between lake denitrification and formation of cyanobacterial blooms, using the historical water quality monitoring data of North Lake Taihu over five years from 2017 to 2021 and via incubation experiments of cyanobacteria and sediment denitrification. The monitoring data showed that algal biomass (Chla as a proxy) primarily peaked during summer and autumn. The seasonal variations in total N concentration showed a completely opposite trend than that of algal biomass, which peaked in winter and spring. Nitrate was the major component of dissolved inorganic nitrogen, and the nitrate concentration was approximately zero in summer and autumn. The total phosphorus concentration varied in the same way as the Chla concentration. The experimental results showed that Cyanobacteria did not grow when the temperature was below 20℃. In comparison, denitrification showed a significant linear relationship with temperatures between 10-25℃ (R2=0.99) and reached the maximum value of (62.98±21.36) μmol·(kg·h)-1 in Lake Taihu at 25℃. Additionally, the nitrate concentration threshold at the maximum denitrification rate was 4 mg·L-1. Cyanobacteria assimilate nitrate for growth, thereby reducing the concentration of nitrate required for denitrification. This study indicated that the advance in lake temperature warming due to climate change may result in earlier growth of cyanobacteria, thereby leading to large amounts of N being assimilated by algae before denitrification, further affecting the dynamics of cyanobacterial blooms. The present results are scientifically important for explaining the mechanism of cyanobacterial bloom rebound in Lake Taihu under the background of recent climate changes.

Community structure and functional diversity of epiphytic bacteria and planktonic bacteria on submerged macrophytes in Caohai Lake, southwest of China

Epiphytic bacteria on the surfaces of submerged macrophytes play an important role in lake biodiversity and ecological processes. However, compared with planktonic bacteria, there is poor understanding of the community structure and function of epiphytic bacteria. Here, we used 16S rRNA gene high-throughput sequencing and functional prediction analysis to explore the structural and functional diversity of epiphytic bacteria and planktonic bacteria of a typical submerged macrophyte (Potamogeton lucens) in Caohai Lake. The results showed that the species composition of epiphytic and planktonic bacteria was highly similar as 88.89% phyla, 77.21% genera and 65.78% OTUs were shared by the two kinds of samples. Proteobacteria and Bacteroidetes were dominant phyla shared by the two kinds of communities. However, there are also some special taxa. Furthermore, the epiphytic bacterial communities exhibited significantly different structures from those in water, and the abundant OTUs had opposite constituents. The explained proportion of the planktonic bacterial community by aquatic environmental parameters is significantly higher than that of epiphytic bacteria, implying that the habitat microenvironment of epiphytic biofilms may be a strong driving force of the epiphytic bacterial community. Functional predictive analysis (Functional Annotation of Prokaryotic Taxa, FAPROTAX) found that epiphytic bacteria and planktonic bacteria are dominated by heterotrophic functions, but epiphytic bacteria have more prominent fermentation and denitrification functions (nitrate reduction, nitrate respiration, and nitrite respiration) than planktonic bacteria. This study has increased our understanding of the communities and functions of epiphytic bacteria on submerged macrophyte leaves, and their role in lake denitrification cannot be ignored.

Comparison of heterotrophic and autotrophic denitrification processes for nitrate removal from phosphorus-limited surface water

Phosphorus (P) limitation has been demonstrated for micro-polluted surface water denitrification treatment in previous study. In this paper, a lab-scale comparative study of autotrophic denitrification (ADN) and heterotrophic denitrification (HDN) in phosphorus-limited surface water was investigated, aiming to find out the optimal nitrogen/phosphorus (N/P) ratio and the mechanism of the effect of P limitation on ADN and HDN. Furthermore, the optimal denitrification process was applied to the West Lake denitrification project, aiming to improve the water quality of the West Lake from worse than grade V to grade IV (GB3838-2006). The lab-scale study showed that the lack of P indeed inhibited HDN more greatly than ADN. The optimal N/P ratio for ADN and HDN was 25 and a 0.15 mg PO43--P L−1 of microbial available phosphorus (MAP) was observed. P additions could greatly enhance the resistance of ADN and HDN to hydraulic loading shock. Besides, The P addition could effectively stimulate the HDN performance via enriching the heterotrophic denitrifiers and the denitrifying phosphate-accumulating organisms (DNPAOs). Additionally, HDN was more effective and cost-effective than ADN for treating P-limited surface water. The study of the full-scale HDBF (heterotrophic denitrification biofilter) indicated that the denitrification performance was periodically impacted by P limitation, particularly at low water temperatures.

The effects of temperature and resource availability on denitrification and relative N2O production in boreal lake sediments

Anthropogenic environmental stressors (like atmospheric deposition, land use change, and climate warming) are predicted to increase inorganic nitrogen and organic carbon loading to northern boreal lakes, with potential consequences for denitrification in lakes. However, our ability to predict effects of these changes is currently limited as northern boreal lakes have been largely neglected in denitrification studies. The aim of this study was therefore to assess how maximum potential denitrification and N2O production rates, and the relationship between the two (relative N2O production), is controlled by availability of nitrate (NO3−), carbon (C), phosphorus (P), and temperature. Experiments were performed using the acetylene inhibition technique on sediments from a small, nutrient poor boreal lake in northern Sweden in 2014. Maximum potential denitrification and N2O production rates at 4°C were reached already at NO3− additions of 106–120μg NO3−–N/L, and remained unchanged with higher NO3 amendments. Higher incubation temperatures increased maximum potential denitrification and N2O production rates, and Q10 was somewhat higher for N2O production (1.77) than for denitrification (1.69). The relative N2O production ranged between 13% and 64%, and was not related to NO3− concentration, but the ratio increased when incubations were amended with C and P (from a median of 16% to 27%). Combined, our results suggests that unproductive northern boreal lakes currently have low potential for denitrification but are susceptible to small changes in NO3 loading especially if these are accompanied by enhanced C and P availability, likely promoting higher N2O production relative to N2.

Human land uses enhance sediment denitrification and N<sub>2</sub>O production in Yangtze lakes primarily by influencing lake water quality

Abstract. Sediment denitrification in lakes alleviates the effects of eutrophication through the removal of nitrogen to the atmosphere as N2O and N2. However, N2O contributes notably to the greenhouse effect and global warming. Human land uses (e.g. agricultural and urban areas) strongly affect lake water quality and sediment characteristics, which, in turn, may regulate lake sediment denitrification and N2O production. In this study, we investigated sediment denitrification and N2O production and their relationships to within-lake variables and watershed land uses in 20 lakes from the Yangtze River basin in China. The results indicated that both lake water quality and sediment characteristics were significantly influenced by watershed land uses. N2O production rates increased with increasing background denitrification rates. Background denitrification and N2O production rates were positively related to water nitrogen concentrations but were not significantly correlated with sediment characteristics and plant community structure. A significant positive relationship was observed between background denitrification rate and percentage of human-dominated land uses (HDL) in watersheds. Structural equation modelling revealed that the indirect effects of HDL on sediment denitrification and N2O production in Yangtze lakes were mediated primarily through lake water quality. Our findings also suggest that although sediments in Yangtze lakes can remove large quantities of nitrogen through denitrification, they may also be an important source of N2O, especially in lakes with high nitrogen content.

Sediment denitrification and nitrous oxide production in Chinese plateau lakes with varying watershed land uses

Denitrification in lake sediments removes nitrogen and releases N2O to the atmosphere, contributing to global warming. However, the rates and controls of sediment denitrification and N2O production are still poorly understood in lakes. In this study, we measured potential denitrification, unamended denitrification and N2O production rate in sediments which were collected from 68 sites in 20 Chinese plateau lakes of varying watershed land uses. The result showed that potential denitrification rate of human-dominated lakes (37.94 ± 8.91 ng N g−1 h−1) was significantly higher than that of reference lakes (18.50 ± 3.22 ng N g−1 h−1). In addition, potential denitrification rate was positively related to the proportion of human land uses in watersheds. At the lake level, unamended denitrification and N2O production rates were significantly related to water chemistry or sediment properties (e.g., conductivity and sediment total nitrogen). Water chemistry and sediment properties together accounted for 0–69 % of the variance in denitrification and N2O production rates. Variance partitioning showed that unamended denitrification and N2O production rates in human-dominated lakes were controlled primarily by sediment properties, while in reference lakes were generally controlled by water chemistry. Our findings suggest that Chinese plateau lakes can remove large quantities of nitrogen through sediment denitrification and produce small amounts of N2O. The relative contributions of water chemistry and sediment properties to the lake denitrification and N2O production vary widely.

DENITRIFICATION ACROSS LANDSCAPES AND WATERSCAPES: A SYNTHESIS

Denitrification is a critical process regulating the removal of bioavailable nitrogen (N) from natural and human-altered systems. While it has been extensively studied in terrestrial, freshwater, and marine systems, there has been limited communication among denitrification scientists working in these individual systems. Here, we compare rates of denitrification and controlling factors across a range of ecosystem types. We suggest that terrestrial, freshwater, and marine systems in which denitrification occurs can be organized along a continuum ranging from (1) those in which nitrification and denitrification are tightly coupled in space and time to (2) those in which nitrate production and denitrification are relatively decoupled. In aquatic ecosystems, N inputs influence denitrification rates whereas hydrology and geomorphology influence the proportion of N inputs that are denitrified. Relationships between denitrification and water residence time and N load are remarkably similar across lakes, river reaches, estuaries, and continental shelves. Spatially distributed global models of denitrification suggest that continental shelf sediments account for the largest portion (44%) of total global denitrification, followed by terrestrial soils (22%) and oceanic oxygen minimum zones (OMZs; 14%). Freshwater systems (groundwater, lakes, rivers) account for about 20% and estuaries 1% of total global denitrification. Denitrification of land-based N sources is distributed somewhat differently. Within watersheds, the amount of land-based N denitrified is generally highest in terrestrial soils, with progressively smaller amounts denitrified in groundwater, rivers, lakes and reservoirs, and estuaries. A number of regional exceptions to this general trend of decreasing denitrification in a downstream direction exist, including significant denitrification in continental shelves of N from terrestrial sources. Though terrestrial soils and groundwater are responsible for much denitrification at the watershed scale, per-area denitrification rates in soils and groundwater (kg N x km(-2) x yr(-1)) are, on average, approximately one-tenth the per-area rates of denitrification in lakes, rivers, estuaries, continental shelves, or OMZs. A number of potential approaches to increase denitrification on the landscape, and thus decrease N export to sensitive coastal systems exist. However, these have not generally been widely tested for their effectiveness at scales required to significantly reduce N export at the whole watershed scale.

Denitrification rates in the sediments of Lake Memphremagog, Canada–USA

Denitrification is the most important mechanism of nitrogen retention in aquatic systems. Research into the spatial variability of sediment denitrification has been relatively rare. Here, we use the N2 flux technique to measure sediment denitrification rates at 19 littoral and 1 profundal site in Lake Memphremagog. Littoral denitrification rates were highly variable with an average rate of 111μmolNm−2h−1. Littoral denitrification rates were positively related to temperature (r2=0.66,p<0.01), % organic matter (r2=0.31,p<0.05) and macrophyte biomass density and negatively related to depth. These results in combination with an analysis of the literature and a predictive model created from literature data relating site depth and denitrification rates show that the littoral zone dominates whole lake denitrification.

Nitrogen mass balances and denitrification rates in central Ontario Lakes

Nitrogen mass balances for seven unproductive lakes and 20 forested catchments in central Ontario were measured between 1977 and 1989. Average annual lake denitrification rates calculated with the N/P ratio method were strongly correlated with summer anoxic factor (extent of surficial sediment anoxia) whereas denitrification rates calculated with a210Pb sediment N accumulation method were poorly correlated with the anoxic factor suggesting that the N/P method is superior. Substantial denitrification occurred in all lakes — an average of 36% of TN inputs or 75% of the net gain. On a regional area-weighted basis, 67% of bulk atmospheric TN deposition was stored or denitrified terrestrially, 12% was denitrified in lakes, 4% was stored in lake sediments, and 17% was exported from lakes. N/P ratios were generally less in streams than in precipitation suggesting preferential N retention in catchments, whereas the N/P ratios in lake outputs were slightly higher than lake input ratios, suggesting preferential P retention in lakes. This is consistent with the notion that P-limited lakes can exist adjacent to N-limited forests.

Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15 N Dilution Technique and Isotope Pairing

The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained NO(3), and by determination of the isotopic composition of the N(2), NO(3), and NH(4) pools in the outflowing water, it was possible to quantify the following reactions: total NO(3) uptake, denitrification based on NO(3) from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO(3) and NH(4) for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO(3) originating from the overlying water accounted for 91 to 171 mumol m h in the lake sediments and for 131 to 182 mumol m h in the estuarine sediments, corresponding to approximately 100% of the total NO(3) uptake for both sediments. It seems that high NO(3) uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process.

Denitrification in freshwater and coastal marine ecosystems: Ecological and geochemical significance

Denitrification occurs in essentially all river, lake, and coastal marine ecosystems that have been studied. In general, the range of denitrification rates measured in coastal marine sediments is greater than that measured in lake or river sediments. In various estuarine and coastal marine sediments, rates commonly range between 50 and 250 µmol N m−2 h−1, with extremes from 0 to 1,067. Rates of denitrification in lake sediments measured at near‐ambient conditions range from 2 to 171 µmol N m−2 h−1. Denitrification rates in river and stream sediments range from 0 to 345 µmol N m−2 h−1. The higher rates are from systems that receive substantial amounts of anthropogenic nutrient input. In lakes, denitrification also occurs in low oxygen hypolimnetic waters, where rates generally range from 0.2 to 1.9 µmol N liter−1 d−1. In lakes where denitrification rates in both the water and sediments have been measured, denitrification is greater in the sediments.The major source of nitrate for denitrification in most river, lake, and coastal marine sediments underlying an aerobic water column is nitrate produced in the sediments, not nitrate diffusing into the sediments from the overlying water. During the mineralization of organic matter in sediments, a major portion of the mineralized nitrogen is lost from the ecosystem via denitrification. In freshwater sediments, denitrification appears to remove a larger percentage of the mineralized nitrogen. N2 fluxes accounted for 76–100% of the sediment‐water nitrogen flux in rivers and lakes, but only 15–70% in estuarine and coastal marine sediments. Benthic N2O fluxes were always small compared to N, fluxes.The loss of nitrogen via denitrification exceeds the input of nitrogen via N2 fixation in almost all river, lake, and coastal marine ecosystems in which both processes have been measured.Denitrification is also important relative to other inputs of fixed N in both freshwater and coastal marine ecosystems. In the two rivers where both denitrification measurements and N input data were available, denitrification removed an amount of nitrogen equivalent to 7 and 35% of the external nitrogen loading. In six lakes and six estuaries where data are available, denitrification is estimated to remove an amount of nitrogen equivalent to between 1 and 36% of the input to the lakes and between 20 and 50% of the input to the estuaries.

Denitrification in Lake 227 During Summer Stratification

In situ denitrification in Lake 227 was assayed by using 15N-labeled NO3− during summer stratification periods in 1973, 1974, and 1975. Dissolved oxygen and NO3− concentrations were the main factors controlling denitrification in the water column and in sediments. The epilimnetic sediment–water interface was a more significant site of natural denitrification when compared to the oxygen-limiting (dissolved oxygen less than 0.2 mg/L) thermocline and the anoxic hypolimnion. Epilimnetic sediment denitrification rates averaged about 15 mg N∙m−2∙d−1. Nearly all of the NO3− that mixed into the surficial sediments was denitrified. Alone, epilimnetic denitrification removed 1.4% of the NO3− added annually. Below the euphotic zone, sediments would provide an efficient sink for NO3−-N without simultaneous initiation of eutrophication.Key words: denitrification, nitrogen sink, nitrate in lakes, experimental lakes, summer stratification

Factors Influencing Nitrate Transformations in Sediments

AbstractThe effects of environmental and procedural factors (e.g., aeration, size of sample, water/sediment ratio, nitrate concentration, glucose addition, temperature, and sterilization) on denitrification in lake and reservoir sediments were evaluated by incubating nitrate‐amended natural sediments in the laboratory. The standard laboratory procedure adopted for denitrification studies involved the incubation of small samples of sediment (undried) after addition of a nitrate solution. Incubations were conducted at 15C in polypropylene centrifuge tubes. Denitrification in sediment‐water samples was not enhanced by continuously purging samples with helium to create artificial anaerobic conditions. Experiments showed that denitrification rates in sediments could be satisfactorily measured using wet sediment (0.5 g solids) treated with 5 ml of 100 ppm nitrate‐15N solution and incubated for 5 to 10 days. The small sample size facilitated sample preparation, extraction of inorganic forms of N and micro‐Kjeldahl analysis of sediment.Even though glucose additions enhanced denitrification by 25 to 30%, unamended sediments contained sufficient available organic‐C for near maximal rates of denitrification. Denitrification in sediments increased with increasing temperature over the range of 5 to 23C. However, significant denitrification occurred at temperatures as low as 5C. Nitrate was not lost from sterilized sediment samples, therefore, the nitrogen transformations observed in unsterilized sediment samples were mediated by biological mechanisms.The evaluation of factors affecting denitrification in sediment shows that the environmental conditions likely to exist in natural sediments are suitable for denitrification. Anaerobiosis and the high organic matter of most sediments create an ideal environment for microbial denitrification. The levels of nitrate in surface water may in part be controlled naturally by denitrification in sediments.

ESTIMATES OF THE RATES OF DENITRIFICATION IN A SUBARCTIC LAKE1

Experimental data were collected which give direct evidence that 15N‐labeled nitrate added to lake water can be converted to molecular nitrogen during anoxic periods. The rate of denitrification measured by the 15N method agrees with the rate calculated from the disappearance of nitrate. The end product of denitrification in lakes appears to be N2. There was no evidence of N2O or NO production.