Nitrogen Concentrations In Water Research Articles

Do stable carbon and nitrogen isotope values of Nitella flexilis differ between softwater and hardwater lakes?

The composition of stable carbon and nitrogen isotopes (δ13C and δ15N) is widely used for tracking the origin of organic matter (OM) present in lacustrine sediments. These isotopes also define the evolution of OM in food web loops. Charophyte species Nitella flexilis C. Agardh, 1824 can be found in different aquatic environments where it contributes significantly to sediment formation and influences biota function. Therefore, it is crucial to study more about δ13C and δ15N in different lake types. Here, we present the results of the first comprehensive study of N. flexilis δ13C and δ15N, which add to the knowledge of the C and N isotope records of charophytes. We obtained the δ13C and δ15N records of N. flexilis OM from hardwater and softwater lakes and checked for differences between these records. We also analyzed the differences in physical and chemical parameters. Finally, we compared the δ13C and δ15N records with physical and chemical parameters to identify the variables that have the highest influence on N. flexilis δ13C and δ15N values. Our study showed that both δ13C and δ15N did not differ significantly in the two types of lakes, although the lakes had significant differences in several physical and chemical parameters (pH, Ca2+, dissolved inorganic carbon, total phosphorus, conductivity). However, we observed that δ13C values were influenced by light conditions (photosynthetic active radiation, depth, dissolved OM), while δ15N values were influenced by the total nitrogen concentration in water.

Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

Effects of Aeration on Surface Water Nutrient Dynamics and Greenhouse Gas Emission in Different Straw Returning Paddy Fields

Straw returning is of great significance for improving soil structure, soil fertility, crop yield, and quality. However, straw returning causes environmental problems such as increased methane emission and non-point source pollutant emission risk. How to reduce the negative effects of straw returning is an urgent problem to be solved.In this study, the effects of aerobic treatment on carbon and nitrogen concentration in surface water and greenhouse gas emissions in paddy fields with different treatments of straw returning were systematically compared.The results showed that different treatments of straw returning significantly increased chemical oxygen demand (COD) in the surface water of the paddy field and significantly promoted the methane emission of the rice field and the global warming potential (GWP), although it slightly reduced N2O emission. The increasing trends showed that wheat straw returning>rape straw>broad bean straw returning.Straw returning increased rice yield when compared with the control without straw returning, but the difference was not significant. Aerobic treatment reduced the COD in surface water by 15%-32%, the methane emission of the paddy field by 10.4%-24.8%, and the GWP of paddy field by 9.7%-24.4% under different straw returning treatments, without affecting the rice yield. The mitigation effect of aerobic treatment with wheat straw returning was the best. The results indicated the potential of oxygenation measures in greenhouse gas emission mitigation and COD emission risk reduction in straw returning paddy fields, especially in wheat straw returning paddy fields.

Removal of low concentration ammonia nitrogen enhanced by hydraulic cavitation combined with ozonation

The combination of hydraulic cavitation and ozone oxidation improves the removal efficiency of low concentration ammonia nitrogen. Focusing on the treatment of low concentration ammonia nitrogen wastewater (about 25mg/L), the study discusses the treatment effect of cavitation combined with different gases (O2, O3) on low concentration ammonia nitrogen. The treatment effect of ozone 3L/min combined with cavitation on ammonia nitrogen is 33.07%. The treatment effect of oxygen (3mg/L) combined with cavitation on ammonia nitrogen was 16.91%. At the same time, the treatment efficiency of ammonia nitrogen at different PH values was compared. When the initial concentration was adjusted from 7 to 10, the treatment efficiency increased from 33.07% to 84.55%. When PH=10, the ammonia nitrogen concentration in water finally dropped to 3.5mg/L, reaching the Chinese first-level emission standard (15mg/L). In addition, the mechanism of treating ammonia nitrogen in water by hydraulic cavitation combined with ozonation was discussed. The results show that ozone combined cavitation is very effective for the treatment of low concentration ammonia nitrogen wastewater.

Biochar as a water protection tool in peatland forestry – nutrient recovery from runoff water

Water quality is significantly affected by the forest logging activities that are carried out in drained peatlands, which causes a notable enhancement in sediment loading and nutrient export to water bodies. Furthermore, the seasonal fluctuations in nutrient concentrations in the runoff further underscore the need for efficient water protection tools in peatland forestry. To address these issues, biochar-based adsorption methods can potentially offer an effective alternative for water protection in peatland forestry. The current thesis investigates the potential for adsorption-based nutrient recovery from clear-cut peatland runoff water using Norway spruce and Silver birch biochars. In particular, the aim is to i) study the adsorption characteristics in relation to biochar properties and nutrient compounds in runoff waters in a small-scale laboratory experiment (Paper I); ii) investigate the adsorption characteristics of nitrogen (N) compounds from runoff water in a meso-scale laboratory experiment that utilises biochar reactors (Paper II); and iii) investigate the dynamics of biochar adsorption and desorption under fluctuating total nitrogen (TN) concentrations in runoff water (Paper III). Biochar made from birch and spruce were shown to efficiently adsorb N compounds from the water. Across all experiments, the TN content declined significantly, irrespective of the scale, or whether the runoff volume ranged from litres (I and III) to hundreds of litres (II). Furthermore, the TN content at the beginning of the experiment declined at the fastest rate. The results indicate that cases of relatively low adsorption capacity were attributed to the low initial TN concentrations in the water. In addition, TN adsorption occurs above a threshold concentration in natural runoff water. The spruce did not adsorb TN when the concentrations in the runoff water fell below 0.4 mg L-1. In this thesis, biochar emerges as a compelling water protection solution, particularly in regions where clear-cut peatlands release substantial quantities of nutrients.

Biochar as a water protection tool in peatland forestry – nutrient recovery from runoff water

Water quality is significantly affected by the forest logging activities that are carried out in drained peatlands, which causes a notable enhancement in sediment loading and nutrient export to water bodies. Furthermore, the seasonal fluctuations in nutrient concentrations in the runoff further underscore the need for efficient water protection tools in peatland forestry. To address these issues, biochar-based adsorption methods can potentially offer an effective alternative for water protection in peatland forestry. The current thesis investigates the potential for adsorption-based nutrient recovery from clear-cut peatland runoff water using Norway spruce and Silver birch biochars. In particular, the aim is to i) study the adsorption characteristics in relation to biochar properties and nutrient compounds in runoff waters in a small-scale laboratory experiment (Paper I); ii) investigate the adsorption characteristics of nitrogen (N) compounds from runoff water in a meso-scale laboratory experiment that utilises biochar reactors (Paper II); and iii) investigate the dynamics of biochar adsorption and desorption under fluctuating total nitrogen (TN) concentrations in runoff water (Paper III). Biochar made from birch and spruce were shown to efficiently adsorb N compounds from the water. Across all experiments, the TN content declined significantly, irrespective of the scale, or whether the runoff volume ranged from litres (I and III) to hundreds of litres (II). Furthermore, the TN content at the beginning of the experiment declined at the fastest rate. The results indicate that cases of relatively low adsorption capacity were attributed to the low initial TN concentrations in the water. In addition, TN adsorption occurs above a threshold concentration in natural runoff water. The spruce did not adsorb TN when the concentrations in the runoff water fell below 0.4 mg L-1. In this thesis, biochar emerges as a compelling water protection solution, particularly in regions where clear-cut peatlands release substantial quantities of nutrients.

GHG Emissions from Drainage Ditches in Peat Extraction Sites and Peatland Forests in Hemiboreal Latvia

We determined the magnitude of instantaneous greenhouse gas (GHG) emissions from drainage ditches in hemiboreal peatlands in Latvia during the frost-free period of 2021 and evaluated the main affecting factors. In total, 10 research sites were established in drained peatlands in Latvia, including active and abandoned peat extraction sites and peatland forests. Results demonstrated that in terms of global warming potential, the contribution of CO2 emissions to the total budget of GHG emissions from drainage ditches can exceed the CH4 contribution. The average CO2 and N2O emissions from drainage ditches in peatland forests were significantly higher than those from ditches in peat extraction sites, while there was no difference in average CH4 emissions from ditches between peatland forests and peat extraction sites. Emissions from ditches of all GHGs increased with increasing temperature. In addition, CO2 and N2O emissions from drainage ditches increased with decreasing groundwater (GW) level. They were also negatively correlated with water level in ditches, but positively with potassium (K) and total nitrogen (TN) concentrations in water. By contrast, CH4 emissions from drainage ditches increased with increasing GW level and water level in ditches but were negatively correlated with K and TN concentrations in water.

Nitrogen and phosphorus concentration zoning control method of surface water in the Haihe River Basin

Various uncertain influencing factors and incomprehensible mechanisms have posed daunting challenges to the management and treatment of regional surface water environment quality. The unified measures and the “one-size-fits-all” management approach limit the treatment effectiveness. Therefore, considering natural and human activities which are major factors affecting the surface water environment quality, the present study proposed a set of zoning management and control schemes for nitrogen and phosphorus concentrations in surface water based on its natural attributes. Selecting DEM, rainfall, vegetation type, soil type, and land use, and employing “grid transformation”, “data extraction”, “attribute superposition” of GIS software and “correlation analysis”, “cluster analysis”, and “principal component analysis” of SPSS software, the Haihe River Basin was divided into the prevention zone, the control zone, and the non-control zone with different natural attribute sets by the correlation coefficient R2 and the nitrogen and phosphorus pollution therein. Based on the nitrogen and phosphorus data of 276 surface water quality monitoring sites, the multiple nonlinear stepwise regression analysis was conducted to construct the relationship between a single water quality indicator and its natural attributes in the three zones. The results are of essential practical significance to surface water environment quality zoning management and survey in the Haihe River Basin. Meanwhile, it provides innovative insights into environmental zoning management in other regions.

Effects of Organic Fertilization Rates on Surface Water Nitrogen and Phosphorus Concentrations in Paddy Fields

Inappropriate organic fertilizer application may cause serious environmental risks, especially nitrogen (N) and phosphorus (P) losses. To achieve a win–win for high yield and environmental protection in organic agriculture, it was essential to demonstrate the relationship between the organic fertilizer input, rice yields, and risks of N and P losses. Based on a rice and green manure cropping rotation field experiment in the Yangtze River Delta of China, the effects of organic fertilization rates on the dynamics of surface water N and P concentrations and rice grain yields were determined. The results showed that the N (total N, ammonium-nitrogen, nitrate-nitrogen) and P (total P and dissolved P) concentrations in surface water immediately and greatly reached the highest values 1 day after basal fertilization and topdressing fertilization. Then, the N and P concentrations sharply decreased and were maintained at a relatively low level. The initial 3 and 7 days after organic fertilization were the high-risk periods for controlling N and P runoff losses. The surface water N and P concentrations had a positive correlation with the organic fertilization rate in high-risk periods. Besides, the effects of organic fertilization on surface water P concentrations existed longer than those of N concentrations. The rice grain yields increased with the increase in organic fertilization rates, but high organic fertilizer input (>225 kg N per hectare) did not increase the grain yield. Meanwhile, the high organic fertilizer input had the highest risks for N and P losses. Therefore, in organic rice farming, organic fertilization rates with 150~200 kg N per hectare are the optimal organic fertilizer input, with relatively high grain yields and low N and P losses.

Release of Endogenous Nutrients Drives the Transformation of Nitrogen and Phosphorous in the Shallow Plateau of Lake Jian in Southwestern China

Eutrophication remediation is an ongoing priority for protecting aquatic ecosystems, especially in plateau lakes with fragile ecologies and special tectonic environments. However, current strategies to control the phosphorus (P) and nitrogen (N) levels in eutrophication sites have been mainly guided by laboratory experiments or literature reviews without in-field analyses of the geochemical processes associated with the hydrological and eutrophic characteristics of lakes. This study analyzed the water quality parameters of 50 sites at Lake Jian in May 2019, a moderate eutrophication shallow plateau lake, based on dissolved/sedimentary nitrogen, phosphorous and organic matter, grain size, C/N ratios and stable isotope ratios of δ13C or δ15N in sediments. The results showed that the average total nitrogen (TN) and total phosphorus (TP) concentrations in the lake water were 0.57 mg/L and 0.071 mg/L, respectively. The TN and TP contents of surface sediment ranged from 2.15 to 9.55 g/kg and 0.76 to 1.74 g/kg, respectively. Stable isotope and grain source analysis indicated that N in sediments mainly existed in organic matter form and P mainly occurred as inorganic mineral adsorption. Endogenous pollution contributed to >20% of TN. Furthermore, our findings showed that phosphorus was the nutrient that limited eutrophication at Lake Jian, unlike other eutrophic shallow lakes. In contrast, the nutrient levels in the sediment and input streams belonged entirely to the N-limitation state. The distinctness in release intensity of N and P could modify the N/P limitation in the lake, which affects algae growth and nutrient control. These results demonstrated that reducing exogenous nutrients might not effectively mitigate lake eutrophication due to their endogenous recycling; thus, detailed nutrient monitoring is needed to preserve aquatic ecosystems.

Effects of tidal variations on total nitrogen concentration, speciation, and exchange flux in the Shuidong Bay coastal water, South China Sea

Nitrogen (N) plays an important role in marine ecosystems as a biogenic element for phytoplankton. The tidal cycle had major influence on various biogeochemical parameters of the bay and changed nutrients input with the ebb and flow of the tide. In this study, we collected samples from Shuidong Bay (SDB) in China, in August 2021, to explore the periodic variations in coastal waters during spring and neap tides. The effects of spring and neap tides on different speciation of nitrogen in the SDB and the exchange fluxes between the SDB and the South China Sea (SCS) were investigated. The results indicated that the concentrations of particulate nitrogen (PN) and N-NO2- were significantly different between the spring and neap tides (P < 0.05). The total nitrogen (TN) concentrations in SDB during the spring and neap tides were 258.12 ± 89.49 μmol/L and 231.77 ± 56.86 μmol/L. During the spring and neap tides, total dissolved nitrogen (TDN) accounted for 54.1% and 52.2% of TN, respectively. In addition, dissolved organic nitrogen (DON) accounted for 81.4% and 69.9% of the TDN during the spring and neap tides, respectively. Furthermore, the net exchange fluxes of different speciation of nitrogen showed that the net exchange fluxes of TN were transported from SDB to SCS during the spring and neap tide, with the net exchange fluxes of 37.7 t and 8.8 t, respectively. The net exchange flux of TN during spring tide was 4.3 times higher than that of neap tide. In addition, a significant negative correlation was observed between dissolved inorganic nitrogen (DIN) and salinity in SDB during the spring and neap tides (P < 0.001), indicated that DIN was mainly influenced by terrestrial sources inputs. A significant positive correlation (P < 0.01) was observed between PN and Chlorophyll-a in SDB during the spring and neap tides, implied that the assimilation of a large number of planktonic organisms promoted PN formation. The present results revealed that tidal variation played an important role in regulating N speciation and exchange flux in coastal waters, which had great implications for N biogeochemistry and water quality improvement in SDB.

A semi-empirical semi-process model of ammonia volatilization from paddy fields under different irrigation modes and urea application regimes

Both empirical models and process-based models of ammonia (NH3) volatilization simulation in paddy field have some disadvantages. This work describes a semi-empirical semi-process model, which combines the simplicity of empirical models with the precision of process-based models, and its combinatorial structure is sufficient for reproducing the characteristic course of NH3 volatilization in paddy fields under different irrigation modes and urea application regimes over time. A dataset consisting of seven rice seasons across three locations was used for model development. Performance indexes showed the model is good (R2 values ranged from 0.67 to 0.94). The influence of air temperature and wind speed on NH3 volatilization was not as great as our conventional understanding, and soil temperature was a more accurate indicator than air temperature for model development. Model performance was better where the less urea splits and the higher urea rate, but there was no significant difference between alternate wetting and drying (AWD) irrigation mode (average values of R2, IA, NSI, and RMSE were 0.82, 0.94, 0.96, and 0.53 kg ha-1 d-1) and flooding irrigation (FI) mode (average values of R2, IA, NSI, and RMSE were 0.86, 0.94, 0.96, and 0.58 kg ha-1 d-1). The ammonium nitrogen (NH4+-N) concentration and pH of surface water and soil water in paddy fields had the greatest impact on NH3 volatilization, and they were mainly related to the amount of urea applied. Splitting the urea application and delaying the first urea application are the fundamental countermeasures to reduce NH3 volatilization. The magnitude of developed model performance varied among rice cropping systems, irrigation modes, urea application regimes, and climatic regions, highlighting the need to understand why measured NH3 volatilization varies among locations. The new model may be a useful tool for predicting fertilizer efficiency of paddy fields applied urea, assessing NH3 volatilization factors, and reducing emission.

Nitrogen removal performance, and microbial community structure of water and its association with nitrogen metabolism of an ecological engineering pond aquaculture system

The ecological engineering pond aquaculture system was promoted in China in recent years as it can save water and reduce pollution. In the present study, an ecological engineering pond aquaculture system was established, consisting of a drainage ditch, a settling pond, an aeration pond, a filter dam, eco-ponds, and fish ponds for tilapia farming. Water from different ponds were sampled and sequenced by Illumina sequencing, and then the microbial communities were analyzed. The metabolic activity of bacteria in the water samples was tested using Biolog EcoPlates. The concentrations of total nitrogen (TN), ammonia-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), and total phosphorus (TP) in water after treatment by the system were 0.71 ± 0.19, 0.48 ± 0.15, 0.51 ± 0.21, 0.03 ± 0.01, and 0.04 ± 0.01 mg/L, respectively. All the units of the system could remove TN in water. Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Planctomycetes were the dominant phyla in the water of the system. The genera Candidatus Aquiluna and Dechloromonas positively correlated with the microbial metabolic activity of organic nitrogen and NH4-N concentrations in water, which could be the functional bacteria for nitrogen removal. Several genera showed positive correlation with the TN and NH4-N concentrations of water and were probably involved in nitrogen cycling of the system. Our data indicated that the ecological engineering pond aquaculture system notably improves water quality and alters the microbial populations. The results supply substantial information on the functional microbiota for nitrogen removal from freshwater aquaculture ecosystems.

Development of Solid-State Chemiresistive Devices for Simultaneous Detection of Nitrate, Nitrite and Ammonium Ions in Aqueous Solutions

The presence of various ions is an important factor in evaluating water quality. Nitrate, nitrite and ammonium in water can cause health issues and pose environmental concerns1,2. Some sources of the nitrogen species are from natural water and some of them arise from industrial and agricultural activities. Currently commercially available sensors for measuring nitrogen compounds in water are based on colorimetric techniques and potentiometric methods incorporating ion selective electrodes. Progress still needs to be made towards fabricating devices with less instrumentation costs, less complexity, less maintenance and without need for any reagents to facilitate measurement of species1. Chemiresistive sensors are solid-state devices which can be simply fabricated from two contacts and a conductive sensing material affixed on a suitable substrate. They operate by detecting modulations in resistance of the conducting film due to surface charge transfer as a result of interactions with the analyte(s)3.Here, we demonstrate chemiresistive devices capable of quantifying aqueous nitrate, nitrite and ammonium ions selectively. Due to challenges in the aqueous phase such as ionic strength effect, probability of side reactions, non-specific bonding on the surface, low interaction energy between analyte and surface, chemiresistive technology has not been developed extensively in water quality sensors4,5. In this study, we have overcome the issues in water by coating the chemiresistive devices with selective membranes. If the fabricated sensors are used as an array, the total nitrogen concentration in water can be measured online which is a significant advance since nitrate, nitrite and ammonium may interconvert and a single nitrate, nitrite or ammonium sensor by itself cannot give the total amount of nitrogen in a sample. For device fabrication, p-doped carbon nanotubes were selected as a sensitive conductive layer which were modified with selective membranes to improve the sensing performance. Nitrite sensors worked over a dynamic range of 67 ppb to 67 ppm with a 27.6% response at 67 ppm. Nitrate showed 13.2% response from 2.2 ppm to 220 ppm. Ammonium devices operated over a dynamic range of 10 ppb to 100 ppm with a 23.6% response at 100 ppm. The proposed response mechanism involves both an electrostatic gating effect and surface charge transfer. Compared with paper-based colorimetric sensors, the proposed devices perform better with a lower detection limit and the ability to perform continuous online measurements. Moreover, the chemiresistive responses of the devices were compared with their potentiometric responses and found to be equally sensitive but more selective. Unlike ion-selective electrodes, the resulting devices do not require the use of reference electrodes and are therefore potentially more robust for use in continuous water analyzers and in resource-poor settings. The chemiresistive devices showed low interferences and good reversibility. They were also tested in river water samples and showed satisfactory results. The fabricated devices are an advanced proof of concept and have the potential to replace the current technology. Nuñez, L., Cetó, X., Pividori, M. I., Zanoni, M. V. B. & del Valle, M. Development and application of an electronic tongue for detection and monitoring of nitrate, nitrite and ammonium levels in waters. Microchem. J. 110, 273–279 (2013).Li, D., Xu, X., Li, Z., Wang, T. & Wang, C. Detection methods of ammonia nitrogen in water: A review. TrAC - Trends Anal. Chem. 127, 115890 (2020).Choi, S. J. & Kim, I. D. Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electronic Materials Letters vol. 14 (The Korean Institute of Metals and Materials, 2018).Kruse, P. Review on water quality sensors. J. Phys. D. Appl. Phys. 51, (2018).Dalmieda, J., Zubiarrain-Laserna, A., Saha, D., Selvaganapathy, P. R. & Kruse, P. Impact of Surface Adsorption on Metal-Ligand Binding of Phenanthrolines. J. Phys. Chem. C 125, 21112–21123 (2021). Figure 1

Efficient Removal Technology of Ammonia Nitrogen by Membrane Separation

AbstractThe working principle, process flow, treatment effect, and application scope of ammonia nitrogen removal by membrane separation were investigated. The effects of initial ammonia nitrogen concentration, pH value, and flow rate of raw water on mass transfer coefficient and removal rate of ammonia nitrogen in the membrane separation process were evaluated, and the optimal operating conditions of membrane separation were assessed. In addition, several kinds of representative wastewaters were treated. Under the optimal operating conditions, the ammonia nitrogen removal rate can reach more than 99 % and the specific surface area can be up to 3000 m2m−3.

Effects of the non‐chlorine oxidizer potassium monopersulfate on the water quality, growth performance and microbial community of Pacific white shrimp ( Penaeus vannamei ) culture systems with limited water exchange

In this study, limited water exchange was used to simulate small earthen ponds equipped with greenhouses for Penaeus vannamei culture by laying sediment in tanks, and we investigated the effects of treatment with potassium monopersulfate compound (KMPC) in multiple low-dose (5 g/m3, three times every 2 weeks) and single high-dose (15 g/m3, once every 2 weeks) on the culture environment and shrimp performance. The application of KMPC significantly increased the dissolved oxygen and decreased the ammonia nitrogen and nitrite nitrogen concentration in water. Further analysis of water micro-organisms showed that the application of KMPC inhibited some micro-organisms with anaerobic denitrification, and prevented the excessive accumulation of ammonia nitrogen and nitrite nitrogen in water. Compared with two different KMPC application methods, multiple low-dose KMPC application improved water quality in a short time, and the growth state of shrimp perform better. However, the survival rate of shrimp was reduced under the single high-dose KMPC application. Therefore, the KMPC application mode of multiple low-dose is more suitable as a reference application method for daily cultural environment management. However, in this mode, micro-organisms in water may be inhibited to a certain extent. Therefore, it is recommended to supplement probiotics when managing the culture environment for a long period.

Physiological Response of the Freshwater Mussel Unio douglasiae in Microcystis aeruginosa Bloom Waters

In the present study, we evaluated the effects of different environments on the filtering rate (FR), mortality, and biodeposition (BD) of the freshwater mussel Unio douglasiae in bloom waters containing the toxic cyanobacterium Microcystis aeruginosa. The mean FR of 19 selected individuals (shell length, 5.0–9.8 cm) was 0.30 ± 0.03 L g−1 h−1 (range = 0.24–0.35 L g−1 h−1). Shell length was strongly correlated with both net and gross BD of mussels (P < 0.0001). The mean FR was higher in river water (0.405 ± 0.052 L g−1 h−1) than in lake water (0.304 ± 0.051 L g−1 h−1). In contrast, the BD of mussels was higher in RW (0.671 ± 0.609 mg g−1 h−1) than in LW (0.275 ± 0.027 mg g−1 h−1). For algal species, the FR of mussels ranged from 0.114 ± 0.024 to 0.553 ± 0.019 L g−1 h−1. The FR of U. douglasiae was higher in river water (mainly diatoms), whereas BD was higher in lake water (mainly Microcystis). U. douglasiae did not prefer toxic M. aeruginosa, which was significantly accumulated in pseudofaeces and faeces. The maximum FR of U. douglasiae in algal bloom water was recorded at a water temperature of 25°C and water depth of 50 cm. Moreover, the in situ mortality of U. douglasiae was strongly affected by water temperature and nitrogen concentration. Overall, U. douglasiae can enhance water quality in eutrophic areas by removing dominant cyanobacteria, although its removal efficiency depends on environmental parameters and site of introduction.

Impacts of land use and landscape pattern on water quality at multiple spatial scales in a subtropical large river

AbstractThe coupling between land use/landscape pattern and water quality in river systems varies across different spatial and temporal scales. It is important to understand the association between water quality and land use/landscape pattern across different spatial and temporal scales for the protection of water resources. Here, we measured seasonal water quality at 12 sub‐basins in the upper reaches of the Han River (UHR) between 2010 and 2018. We conducted factor analysis and redundancy analysis to determine the links between land use and water quality at multiple spatial scales and to identify the main factors influencing water quality. We found that the concentration of nutrients, including total nitrogen, total phosphorus, nitrate‐N and ammonium‐N, was higher during the wet season than the dry season. Total nitrogen was the main driver of nutrient pollution in the UHR, whereas total phosphorus was identified as another potential nutrient pollutant. We also found that water quality parameters were more strongly related to land use types during the wet season than the dry season. Croplands and urban lands increased phosphorus concentrations of river water, whereas forest and grasslands decreased the nitrogen concentrations of river water at the sub‐basin scale. Land use at the riparian zone scales better explained variations in water quality than land use at sub‐basin scales. The explained variations in landscape metrics were generally higher during the dry season than the wet season. The largest patch index and Shannon's diversity index were the main predictors of river water quality in the UHR.

Factores ambientales condicionantes del metabolismo de una laguna pampeana

Pampean shallow lakes naturally have water nitrogen and phosphorous concentrations that allow the development of dense beds of submerged aquatic vegetation, phytoplankton, or free-floating aquatic plants. In recent years, the eutrophication of these shallow lakes has increased due to the intensification of agriculture, use of fertilization and livestock. Phytoplankton- induced turbidity inhibits the growth of the submerged aquatic vegetation leading to phytoplankton dominance. This is the case of the Lobos shallow lake, which in a period greater than 20 years has remained as an organic turbid shallow lake, with cyanobacteria dominance. The study of the ecosystem metabolism can give relevant information about how the trophic state of a shallow lake drives production, respiration and net metabolism, and the potential consequences for aquatic biota. We evaluated the Lobos shallow lake metabolism using diel changes in dissolved oxygen concentrations during autumn and spring. Gross primary production showed lower values and variability in Autumn (1.57±1.33 g O2.m-2.día-1) than in Spring (20.45±18.00 g O2.m-2.día-1). Although there was high production during the day, respiration was also high, especially in Spring, where there was higher density of planktonic organisms principally cyanobacteria, exceeding net production in both seasons. Thus, we found mainly low or negative values for the net metabolism in Lobos shallow lake. A high oxygen consumption occurred during spring and at the lowest depth, coinciding with the highest chlorophyll-a concentrations, particulate matter, and lowest water transparency. We conclude that Lobos shallow lake was predominantly heterotrophic during study period. High nutrient concentrations will likely increase the factors that produce stress and negative impacts on aquatic fauna.

Nitrous oxide emissions from subtropical estuaries: Insights for environmental controls and implications

Estuaries are expected to contribute large nitrous oxide (N2O) emissions, however the environmental controls and implications of N2O emissions have not been well understood. Here we investigated water N2O concentrations, fluxes and sources in wet and dry seasons for 2019–2020 in five subtropical estuaries spanning hydrologic characteristics and nitrogen concentrations gradient. Water dissolved N2O concentrations and fluxes were in a range of 15.8–84.9 nmol L–1 and 0.66–22.2 µg m–2 h–1, respectively. These studied estuaries were oversaturated in N2O, with the saturations of 118–615%. Water dissolved N2O concentrations, saturations and fluxes increased significantly as nitrogen concentrations increase, whereas they did not differ significantly between the wet and dry seasons. Water N2O emissions, however, were also lower in the estuaries characterized by large discharge and water flow. N2O saturations and fluxes were determined directly by water nitrogen and oxygen concentrations and more indirectly by water temperature and velocity. The δ15N-N2O and site preference-N2O varied respectively from 2.86 to 11.31‰ and from 1.58 to 11.72‰, which overlapped the values between nitrification and denitrification. Nitrification and denitrification were responsible for 18.7–38.1% and 61.9–81.3% of N2O emissions, respectively. Indirect N2O emission factors were 0.08–0.14% and decreased with increasing total nitrogen concentrations. It is estimated that water N2O emissions in CO2 equiv could offset approximately 4.9% of average CO2 sink of China estuaries. Therefore, these results suggest that nitrogen concentrations and hydrologic characteristics together modify N2O emissions and that estuaries may be the important contributors to N2O emissions.