Water Quality Response Research Articles

A Bayesian Modelling Framework for Integration of Ecosystem Services into Freshwater Resources Management

Models of ecological response to multiple stressors and of the consequences for ecosystem services (ES) delivery are scarce. This paper describes a methodology for constructing a BBN combining catchment and water quality model output, data, and expert knowledge that can support the integration of ES into water resources management. It proposes “small group” workshop methods for elucidating expert knowledge and analyses the areas of agreement and disagreement between experts. The model was developed for four selected ES and for assessing the consequences of management options relating to no-change, riparian management, and decreasing or increasing livestock numbers. Compared with no-change, riparian management and a decrease in livestock numbers improved the ES investigated to varying degrees. Sensitivity analysis of the expert information in the BBN showed the greatest disagreements between experts were mainly for low probability situations and thus had little impact on the results. Conversely, in our applications, the best agreement between experts tended to occur for the higher probability, more likely, situations. This has implications for the practical use of this type of model to support catchment management decisions. The complexity of the relationship between management measures, the water quality and ecological responses and resulting changes in ES must not be a barrier to making decisions in the present time. The interactions of multiple stressors further complicate the situation. However, management decisions typically relate to the overall character of solutions and not their detailed design, which can follow once the nature of the solution has been chosen, for example livestock management or riparian measures or both.

Exploring the pivotal response relationship between landscape composition–configuration–intensity metrics and water quality in Taihu basin, China

Declining water quality has exacerbated water scarcity worldwide, and effective water quality management requires a solid understanding of the factors of water quality. The response of water quality to landscape composition and configuration has been extensively studied, but landscape intensity has been disregarded. Therefore, constructing a comprehensive impact factor indicator and determining the pivotal factors are essential. This study focused on the response relationship of landscape composition, configuration, and intensity metrics to water quality. Water quality index included total nitrogen (TN) and total phosphorus (TP) from 43 monthly sites in the main rivers of the Taihu Lake Basin (TLB) in 2017. The TN:TP index was calculated. We used the partial least squares regression (PLS) method to explore the response strength between each index at different temporal and spatial scales, and the coefficient of determination (R2) calculated based on PLS was 0.4677 to 0.9039, in which the simulation effect was acceptable. In terms of pivotal influenced factors, industrial and domestic effluents for TN and TP showed a major effect in crop (CDR) and forest dominated region (FDR). For the TN:TP index, the pivotal influencing factors was merely industrial waste water discharge. In the fitting based on the pivotal factors of polynomial regression (PR), the landscape threshold of industrial and domestic effluents intensities to TN in CDR were higher than FDR, and landscape threshold substantially exceeded the water quality standard lines in CDR. This research can provide a reference for water quality precision management, distribution of pollutant emissions, and regional sustainable planning from the perspective of landscape regulation in TLB.

Pi-VAT: A web-based visualization tool for decision support using spatially complex water quality model outputs

Effective watershed management and protection of water resources from non-point source pollution require identification, prioritization, and targeting of pollutant source areas. Process-based hydrology and water quality models are powerful heuristic tools for land and water resources managers. However, because of their complexity, such models are often under-utilized as management prioritization and planning tools. In this paper, we present a prioritization, interactive visualization, and analysis tool (Pi-VAT) that is programmed to synthesize multi-scenario, multi-watershed outputs from process-based geospatial models. We demonstrate the utility of Pi-VAT to examine simulated hydrologic, sediment, and water quality response at the hillslope/hydrologic response unit (HRU) scale. We apply Pi-VAT to output from multiple watersheds and for multiple management scenarios and treatments from two geospatial models for watershed management: Water Erosion Prediction Project (WEPP) and Soil & Water Assessment Tool (SWAT). Pi-VAT was developed using the Shiny web application framework for the R programming language. In a matter of minutes, Pi-VAT can synthesize overwhelming amounts of output from process-based models into information useful for land and water resources managers. We illustrate the use of Pi-VAT to interactively identify, quantify, and visualize areas that are most susceptible to disturbance under different scenarios and provide a synthesis approach based on land use, soil type, and slope steepness. This approach guides land and water resources managers in prioritizing the areas of the watershed that provide the maximum reduction in pollutant loads while treating the least amount of area. Pi-VAT provides a flexible reactive platform for the development of decision support tools based on process-based models intended for watershed management and research applications.

Field scale discharge and water quality response, to drainage water management

Subsurface (tile) drainage, while necessary for viable agricultural crop production in the humid, poorly drained regions of the world, has been linked to offsite nutrient transport, culminating in harmful algal blooms and hypoxia in downstream waterbodies. Drainage water management (DWM), also known as controlled drainage, has been promoted as a method to reduce nitrogen (N) and phosphorus (P) loss from field scale tile drainage; however, subsequent changes in surface runoff and associated water quality have not been explored. Four years of surface and subsurface discharge, N, and P loss from two sets of paired field sites in northwest Ohio, USA were evaluated using a before-after control-impact (BACI) design to quantify the impact of DWM. Mean event surface runoff was greater (significant at one site) under DWM while tile drainage discharge was less at both sites but not significant. There was no significant difference in surface nitrate-N (NO3--N) loss; however, significant reductions in tile NO3--N loss under DWM were measured at both sites. Similar to discharge, dissolved reactive P (DRP) loss measured in surface runoff was greater under DWM (significant at one site), while no significant differences were noted in mean event tile drainage DRP loss. Total P (TP) surface runoff losses were significantly greater under DWM at the site with significantly greater surface runoff, while DWM reduced tile drainage TP loss at only one site. These findings suggest that DWM reduced tile NO3--N loss, while also highlighting that any benefit from DWM with respect to tile DRP or TP loss could be negated in part by increased surface losses. Furthermore, these findings emphasize the need to understand the natural resource concern to which the practice is targeted and also call for additional research on DWM implementation that includes surface runoff across a range of soil textures, cropping management, and climates.

Monitoring water transparency, total suspended matter and the beam attenuation coefficient in inland water using innovative ground-based proximal sensing technology

Long-term and high-frequency observations are vital to reveal water quality dynamics and responses to climate change and human activities. However, the datasets collected from traditional in situ and satellite observations may miss the rapid dynamics of water quality in the short term due to low temporal-spatial monitoring frequency and cloudy or rainy weather. To address this shortage, innovative ground-based proximal sensing (GBPS) technology was proposed to monitor water quality and identify emergencies with a wavelength range of 400–1000 nm, a spectral resolution of 1 nm and a minimal observation interval of 30 s. The GBPS was equipped with a hyperspectral imager placed 4–5 m above the water surface to minimize the impacts of the atmosphere and clouds. In this study, combined with 583 water samples obtained from four field samplings, GBPS datasets were first applied to estimate the total suspended matter (TSM), Secchi disk depth (SDD) and beam attenuation coefficient at 550 nm (C(550)) in Taihu Lake (TL), Liangxi River (LR) and Funchunjiang Reservoir (FR). The results demonstrated good performance with the TSM (R2 = 0.83, RMSE = 8.35 mg/L, MAPE = 24.0%), SDD (R2 = 0.88, RMSE = 0.09 m, MAPE = 14.7%), and C(550) (R2 = 0.79, RMSE = 3.55 m-1, MAPE = 35.8%). The time series of TSM and C(550) at the second-minute level showed consistent changes, but they were opposite to those of SDD. Taking TSM as an example, the datasets captured two mutations in TL with an 853.6% increase in 65 min and a rapid change from 40.3 mg/L to 256.9 mg/L and then to 51.0 mg/L in 224 min on November 1 and 3, respectively. Meanwhile, a significant decreasing trend (r = −0.83, p < 0.01) in LR from November 7 to 9 and a periodic diurnal increasing trend of TSM in FR during November 11 to 13 (0.46 ≤ R2 ≤ 0.70, p < 0.01) were observed. GBPS, with the advantages of high-frequency observations and the applicability of complex weather conditions, compensates for the in situ, aircraft and satellite observation deficiencies. Therefore, GBPS allows us to capture more detailed water quality information and episodic events, which is an important part of an integrated air-space-ground monitoring system in the future.

Effects of the addition of Calanopia elliptica, Artemia franciscana, and Brachionus rotundiformis in a nursery biofloc system on water quality, growth, gut morphology, health indices, and transcriptional response of immune and antioxidant-related genes in Penaeus vannamei

Effects of the addition of Calanopia elliptica, Artemia franciscana, and Brachionus rotundiformis in a nursery biofloc system on water quality, growth, gut morphology, health indices, and transcriptional response of immune and antioxidant-related genes in Penaeus vannamei

Progress of hydrological process researches in lake wetland: A review

湖泊湿地是世界上最重要的生态系统之一，在调蓄洪水、净化环境、保护生物多样性以及为人类提供淡水和食物等方面发挥着不可替代的作用.然而，受气候变化和人类活动叠加影响，湖泊湿地水文过程发生了剧烈变化，湖泊湿地面临着面积萎缩、质量下降和服务功能退化等风险.本文总结了原位观测、数值模拟和遥感技术在获取湖泊湿地关键水文要素方面的优势及不足；从辩证的角度探讨了气候变化和人类活动对湖泊湿地水文过程的双重影响；结合洪水和水文连通性等研究热点分析了水文过程的典型表现形式；从正反两方面揭示了湖泊湿地植物、动物和水质对水文过程改变的响应.本研究最终提出未来应该将遥感技术与数值模拟方法相结合，建立多目标-多要素-多尺度-多过程的湖泊湿地监测体系；定量评价多维度水文连通的转化方式及其对生态系统的阈值效应；加强研究地下水驱动下湿地植被演变的非线性动力学机制；综合考虑栖息地的面积和质量评价水鸟种群的弹性力和恢复力，为湖泊水位调控和退化湿地的恢复提供科学依据.;As one of the most important ecosystems in the world, lake wetlands are irreplaceable in flood regulation, environment decontamination, biodiversity conservation, and in the provision of freshwater and food resources. However, lake wetlands hydrological processes have changed drastically as a result of anthropogenic activities and climate change in combination, evidenced by shrinking wetland areas, declining wetland quality, and degraded wetland service functions. Here we summarized the merits and drawbacks of field observations, numerical simulations and remote sensing in deriving key hydrological elements of lake wetlands. The dual effects of human and climate on hydrological processes were discussed dialectically, and typical forms of hydrological processes were analysed incorporating the current hotspot flood and hydrological connectivity issues, and both positive and negative responses of plants, animals and water quality to changing hydrological processes were reviewed. In the forthcoming years, a combination of remote sensing and numerical simulation will lead to a multi-objective, multi-factor, multi-scale and multi-process lake wetland monitoring system. Based on extensive observational data, the conversion paths of multi-dimensional hydrological connectivity and their thresholding effects on ecosystem will be quantified. The investigation of nonlinear driving mechanisms behind wetland vegetation-groundwater dynamics will be strengthened. The elasticity and resilience of waterfowls' population will be evaluated considering both habitat area and quality. The ultimate goal is to provide a scientific basis for lake-level regulation and wetland restoration.

A review of simulation experiment techniques used to analyze wildfire effects on water quality and supply.

This review addresses the critical knowledge gap of techniques simulating combustion and heating characteristics present in natural wildfires and their use in assessing postfire impacts on water quality and quantity. Our assessment includes both laboratory and plot-scale techniques with burn and rainfall simulation components. Studies included focus on advancing understanding of changes in chemical and physical properties of soil, as well as subsequent runoff changes. Advantages of simulation experiments include: overcoming logistical challenges of collecting in situ wildfire data, reducing the high spatial variability observed in natural settings (i.e., the heterogeneity of burn intensity and the underlying vegetation and soil properties), and controlling the magnitude of key drivers of wildfire impacts. In sum, simulation experiments allow for more direct attribution of water quality and quantity responses to specific drivers than experiments conducted in situ. Drawbacks of simulation techniques include the limitation of observing only local-scale processes, the potential misrepresentation of natural settings (i.e., lack of spatial variability in vegetation, soil structure, burn intensity, etc.), uncertainty introduced through experimental error, and subsequent challenges in upscaling results to larger scales relevant for water management. This review focuses primarily on simulation techniques, with the goal of providing a foundation of knowledge for the design of future simulation experiments.

Precipitation-Driven Anthropogenic Pollutant Fluctuations Within Standing Water Sources of the Edwards Aquifer Region, Texas

The objective of this study was to assess the contribution of urban runoff in pollutant delivery to standing water pools within the Edwards Aquifer region of Texas. Grab samples of water were collected weekly over 5 months at one urban pool, one undeveloped pool, and one control pond that received minimal runoff. Samples were tested for nitrates, total dissolved phosphorus, Escherichia coli, and other coliform bacteria. The urban site had higher nitrate, E. coli, and other coliform bacteria concentrations than the undeveloped site. Significant positive linear relationships between weekly antecedent rainfall and both nitrate and E. coli were found at the urban site but not the undeveloped site. Water quality parameters at the control site remained stable, suggesting increases in nitrate and E. coli at the urban site were caused by runoff. Using publicly available data, relationships between water quality and weekly antecedent discharge were tested at 24 additional sites varying in land use. Positive relationships for E. coli were found at several urban sites, supporting runoff as a contributor to bacterial loading. Relationships for nitrate were variable, but all additional sites had flowing water, suggesting a unique response of water quality to urban runoff at the sampled urban pool.

Lake Water Quality Response to Upland Conservation Practices Assessment Using an Integrated Watershed and Water Quality Modeling System

Lake Water Quality Response to Upland Conservation Practices Assessment Using an Integrated Watershed and Water Quality Modeling System

Research on water environmental capacity accounting of the Yongzhou Section of Xiangjiang River Basin based on the SWAT-EFDC coupling model

Abstract In this paper, a coupling model of SWAT (Soil and Water Assessment Tool) and EFDC (Environmental Fluid Dynamics Code) was established, and the relationship between the pollution source and water quality response was identified. Based on the hydrodynamic water quality simulation results and the one-dimensional WEC (water environmental capacity) theoretical formula, the total nitrogen and total phosphorus WEC and the remaining WEC of the Yongzhou Section of Xiangjiang River Basin under the guaranteed rate of 90% and in 2017 were calculated, respectively. It can be seen from the results that the total nitrogen WEC of the Yongzhou Section of Xiangjiang River Basin in 2017 is 27,673.04 t, the total nitrogen WEC under the guaranteed rate of 90% is 19,497.61 t/a and the total phosphorus WEC of the Yongzhou Section of Xiangjiang River Basin in 2017 is 4,877.22 t. The total phosphorus WEC under the guaranteed rate of 90% is 2,936.64 t/a; in 2017, the remaining WECs of total nitrogen and total phosphorus in the entire basin are 14,646.69 and 3,358.67 t, respectively.

Study of water quality response to water transfer patterns in the receiving basin and surrogate model.

The spatio-temporal response of water quality in the receiving basins to water transfer remains unclear when considering more practical factors. Moreover, a much fast surrogate model is highly required to realize the purpose of rapid prediction of water quality. In this study, a two-dimensional hydrodynamic and water quality model was primarily established by considering the most comprehensive important pollution sources so far to investigate the water quality variation in Baiyangdian Lake, China. The pollution sources include atmospheric deposition, sediment release, village and tourism domestic sewage, livestock breeding, rainfall runoff, aquatic plants, and animals. The water quality at different sample sites was assessed using the water quality index (WQI). Subsequently, a surrogate model was proposed using the nonlinear autoregressive network with exogenous inputs (NARX), and the NARX model can realize fast prediction of the annual time series of water quality in a few seconds. The results showed that there are significant differences in water quality at different sample sites in each season. The highest WQI value occurred in autumn (65.46), and the average values at different sample sites were between 47.54 and 58.22 in this season. The water quality at Nanliuzhuang site and Caiputai site was significantly affected by water transfer patterns. In addition, the correlation coefficient R2 between the predicted results and the simulated ones except that of parameter TP was larger than 0.90. The prediction performance of surrogate model was shown to be very high efficiency and accurate. The proposed models and the results of this approach are guiding significance for lake management.

New framework for managing the water environmental capacity integrating the watershed model and stochastic algorithm

Integrated calculations of pollution load and water environmental capacity (WEC) are essential for effective water quality management. However, few studies have focused on the dynamic WEC and pollution load in a nonpoint source pollution (NPS)-dominant temperate monsoon watershed under changing rainfall conditions. In this study, a new framework based on the watershed model and WEC calculation with stochastic rainfall input (SR-WEC), was proposed to reveal the dynamic WEC and pollution load under changing rainfall conditions. Stochastic rainfall series was generated by a first-order Markov chain and gamma distribution, and further input into the Soil and Water Assessment Tool (SWAT) to explore the dynamic response of water quality to rainfall. The framework was applied to the Daning River watershed, Three Georges Reservoir Region, China. The results suggested that compared with the new SR-WEC, the traditional return period method with limited observed rainfall input would result in an underestimation of ideal WEC and NPS pollution load by 23% and 48% for TN and 48% and 51% for TP, respectively. Approximately 46% of the annual TN reduction and 51% of the annual TP reduction were concentrated from April to June in a relatively small area. The regression relationships between rainfall and the ideal WEC, pollution load and remnant WEC obtained by the SR-WEC were superior to those of the traditional method, with R2 values increasing from 0.005–0.797 to 0.718–0.989. Specific threshold (120 mm/month for the study area) was observed for the effect of rainfall on water quality, beyond which the remnant WEC of organic N would change from decreasing to increasing. The new framework proposed identifies the key periods and areas with consideration of uncertainty of rainfall on water quality, and provides basis for NPS pollution management.

Characteristics of water quality response to hypolimnetic anoxia in Daheiting Reservoir

Abstract Anoxia is a common phenomenon at the bottom of large reservoirs during thermal stratification. In an anoxic environment, an increasing amount of reducing substances and nutrients are released and settle at the hypolimnion of the reservoir, leading to water quality deterioration and eutrophication. This work presents a case study on Daheiting Reservoir, a part of the Water Diversion Project from the Luanhe River to Tianjin city. With the monitored data of the water temperature and dissolved oxygen content in the reservoir, and based on the mechanism of redox reactions, the water quality response to the hypolimnetic anoxia in Daheiting Reservoir was systematically analyzed. It was found that the release of total phosphorus from the sediments in Daheiting Reservoir was a joint effect of the biological and chemical processes, and the redox reaction in the anoxic zone boosted release of phosphorus. Anoxia in the reservoir caused the ammonia nitrogen released from sediments in the reservoir to accumulate at the hypolimnion, which increased the concentration of ammonia nitrogen in the water. Anoxia in the reservoir led to an increase in the concentration of iron and manganese, which accounts for the major driving factor of release of iron and manganese.

Linking flow alteration with fish assemblage structure in a river regulated by a small hydropower project in the Western Ghats of Karnataka, India

AbstractSmall hydropower projects (SHPs) are promoted as low‐impact alternatives for large hydropower. SHPs are generally commissioned on small‐ to medium‐sized mountainous rivers, often in biodiverse regions, with backing in the form of subsidies, facultative policies and exemption from impact assessments as they are considered ‘green’. However, the ecological impacts of SHPs are understudied especially in highly seasonal tropical streams of Western Ghats of India, a global biodiversity hotspot and a distinct freshwater fish eco‐region. We compared SHP‐affected segments of a dammed and an undammed river in the Western Ghats of Karnataka, to assess how altered flow regime affects seasonal variability in habitat and water quality, and influences fish assemblage structure. We found that flow alteration by the SHP varied between different segments of the dammed river and with season. Furthermore, the nature of flow alteration influenced habitat variability, water quality and fish assemblage response in the dammed river. We observed that the dewatered segment of the dammed river experienced a lotic to lentic shift in habitat and water quality, which favoured fish species with eurytopic affinities. Fluctuating flows in the downstream segment subdued natural variability in flow regime and created novel habitats and water‐quality conditions, affecting fish assemblages. The upstream segment of the dammed river retained natural variability in habitat and water quality, but did not mimic the undammed river in terms of fish composition. We also observed potential constraints on recruitment for migratory species of fish in the dammed river. Based on our results, we suggest how the placement of dewatered segment, and timing the closure of SHP operation in dry season based on ecological thresholds are potential solutions to mitigate the impacts of the SHPs. Furthermore, we recommend effective impact assessments, and adaptive management with active interventions to maintain genetic and ecological connectivity, as key to enhance the sustainability of the SHPs.

Seasonal Water Quality and Algal Responses to Monsoon-Mediated Nutrient Enrichment, Flow Regime, Drought, and Flood in a Drinking Water Reservoir.

Freshwater reservoirs are a crucial source of urban drinking water worldwide; thus, long-term evaluations of critical water quality determinants are essential. We conducted this study in a large drinking water reservoir for 11 years (2010–2020). The variabilities of ambient nutrients and total suspended solids (TSS) throughout the seasonal monsoon-mediated flow regime influenced algal chlorophyll (Chl-a) levels. The study determined the role of the monsoon-mediated flow regime on reservoir water chemistry. The reservoir conditions were mesotrophic to eutrophic based on nitrogen (N) and phosphorus (P) concentrations. An occasional total coliform bacteria (TCB) count of 16,000 MPN per 100 mL was recorded in the reservoir, presenting a significant risk of waterborne diseases among children. A Mann–Kendall test identified a consistent increase in water temperature, conductivity, and chemical oxygen demand (COD) over the study period, limiting a sustainable water supply. The drought and flood regime mediated by the monsoon resulted in large heterogeneities in Chl-a, TCB, TSS, and nutrients (N, P), indicating its role as a key regulator of the ecological functioning of the reservoir. The ambient N:P ratio is a reliable predictor of sestonic Chl-a productivity, and the reservoir was P-limited. Total phosphorus (TP) had a strong negative correlation (R2 = 0.59, p < 0.05) with the outflow from the dam, while both the TSS (R2 = 0.50) and Chl-a (R2 = 0.32, p < 0.05) had a strong positive correlation with the outflow. A seasonal trophic state index revealed oligo-mesotrophic conditions, indicating a limited risk of eutrophication and a positive outcome for long-term management. In conclusion, the Asian monsoon largely controlled the flood and drought conditions and manipulated the flow regime. Exceedingly intensive crop farming in the basin may lead to oligotrophic nutrient enrichment. Although the reservoir water quality was good, we strongly recommend stringent action to alleviate sewage, nutrient, and pollutant inflows to the reservoir.

Identification of the Relative Importance of Factors Affecting the Spatial Variability of River Water Quality

Understanding the temporal and spatial variability of water quality is important in order to establish effective customized management strategies for polluted aquatic ecosystems. Although various water quality management methods have been proposed based on insights into river water pollution factors through physically based modeling or statistical techniques, it is difficult to find studies that analyze the relative importance of these water pollution factors in a relatively large watershed using a step-by-step methodology. In this study, the spatial variability of river water quality is analyzed using time-averaged river water quality data collected from 40 sites in the Nakdong river basin, located on the Korean Peninsula. We focused on biological oxygen demand, total suspended solids, total nitrogen, and total organic carbon. A two-step exhaustive search approach was used to find a linear model that best links the various factors of the watershed with the average river water quality. The optimal model was selected by applying cross-correlation analysis and Bayesian inference. Through the process of finding the optimal statistical model, the major factors that have the most influence on river water quality were identified by analyzing the factors affecting river water quality, their levels of influence, and their levels of uncertainty. Identifying a set of processes provides insight into the key factors influencing spatial variability in average stream water quality conditions. We were able to identify the relative influences and uncertainties of the hydrological, climatic, topographical, and geological characteristics of the watershed on the spatial variability of river water quality. The proposed spatial variability model of average river water quality can be used to predict river water quality responses to future climate change, land use pattern change, and soil management strategy change.

Optimal allocation of best management practices based on receiving water capacity constraints

Best management practices (BMPs) are generally considered the most economical and effective methods to control nonpoint source pollution (NPS). However, the existing research on BMPs does not consider the local receiving water capacity, and, thus, may not yield much practical guidance for controlling local NPS. In order to improve the practical function of BMP schemes, load reduction and BMP implementation cost optimization under receiving water capacity constraints were considered to provide a new optimization methodology for BMPs in this study. The Soil Water and Assessment Tool (SWAT) was used to simulate the temporal and spatial distribution of nutrient load and identify priority management areas (PMAs). A multi-objective, non-dominated sorting genetic algorithm-II (NSGA-II) was used to explore optimal BMPs with tradeoffs between economic cost and water quality responses. This optimization methodology is applied to the Chao River watershed (CRW), north China. The main results are as follows. A total nitrogen (TN) priority management area (PMA) was mainly located in the upstream areas of the CRW, while a total phosphorus (TP) PMA was mainly located in the middle of the CRW. Terrace and contour planting were the most effective BMP measures to reduce TN and TP loads from the CRW, and filter belts played an important role in reducing the TN and TP loads. The allocation scheme of BMPs with TN as the control index could meet the receiving water capacity constraints for the CRW. The optimal allocation method yielded a significantly different BMP allocation from the previous objective of a total control strategy, which fully considered the receiving water capacity of the Miyun Reservoir. The new method has been successfully applied in the Miyun Reservoir watershed, and the BMP configuration schemes with practical guidance values were obtained. The applied methodology can be a good alternative for controlling agricultural NPS in other reservoir water source areas.

Impacts of water additives on water quality, production efficiency, intestinal morphology, gut microbiota, and immunological responses of Nile tilapia fingerlings under a zero-water-exchange system

The impacts of commercial probiotics as water additives to the zero-water exchange system on water quality, production efficiency, gut microbiota, antioxidant, and immunological responses of Nile tilapia (Oreochromis niloticus) were investigated. Five treatments, with three triplicates, were randomly designed, where in each replicate 150 fish (100 ± 4.5 g) were stocked in 20-m3 concrete ponds. Different water probiotics were added to ponds' water as follows: T1 (Control: no probiotic added); T2 (Prozym powder Ultra ® at 0.002 g/ m3/ day); T3 (Microban aqua ® at dose 0.002 g/ m3/ day); T4 (Aquastar ® at dose 0.0015 g/ m3/ day); and T5 (Sanolife PRO-W ® at dose 0.0010 g/ m3/ day). For eight weeks, fish in each group were fed a commercial feed (30% crude protein) up to satiety three times a day. After the experimental period, dissolved oxygen in ponds' water was significantly improved, while ammonia, nitrite, and nitrate levels were significantly lowered by water additives as compared to the control group. Compared to the control group, yield, specific growth rate, and total feed intake were significantly improved, while feed conversion ratio was not significantly changed among different treatments. Significant (p < 0.05) increases in villus height/width, and the absorption area was observed in groups that received water additives. Total Vibrio spp. counts in fish guts and ponds' water were significantly lower, while the total Bacillus spp. counts in both ponds' water and fish guts were significantly higher in probiotic-treated groups. Hematological parameters (counts of white blood cells and red blood cells as well as hemoglobin and hematocrit levels) significantly (p < 0.05) increased in probiotic-treated groups. In similar trends, antioxidant (superoxide dismutase and catalase activities) and immunity (total protein, globulin, immunoglobulin, and lysozyme activity as well as activities and index of phagocytes) were significantly enhanced in the groups treated with water probiotics. Overall, our results show that water probiotics in the current study were beneficial for reducing the nitrogenous compunds in ponds'water and improving the production efficiency, gut microbiota, antioxidant and immunological responses of Nile tilapia.

Is water quality better in wet years or dry years in river-connected lakes? A case study from Dongting Lake, China

Water quality is essential for lake systems, which are not only influenced by climate change and human activities but are also controlled by high-frequency hydrological rhythms. However, the differences in water quality during different hydrological periods have not been addressed in detail. Here, a 15-year water quality dataset (2004–2018) was selected to explore the variation trends and their relationship with water level in different hydrological periods in Dongting Lake, a typical river-connected lake in China. The hydrological periods were classified into hydrological years and hydrological phases based on the characteristics of water level fluctuations. The results showed that annual variation in the water level in Dongting Lake fluctuated between 23.63 and 25.81 m from 2004 to 2018, and also displayed considerable water level differences ranging from 7.66 m (dry years) to 9.97 m (wet years) within a year. The water level of the lake phase showed significant differences among the different hydrological years. The concentration of TP, CODMn, and NH3-N showed significant decreasing trends, whereas that of TN showed a significant increasing trend from 2004 to 2018. The TN concentration in wet years was significantly higher than that in dry years, which could be attributed to sewage discharge and hydrological conditions. The contributions of the lake phase to the total sewage discharge successively decreased from 64.54% in wet years to 59.47% in dry years, while the river phase showed the opposite trends, ranging from 35.46% to 40.53%, reflecting the strong relationship between water regimes and pollutant fluxes. A regression analysis indicated the different responses of water quality to water level fluctuations over hydrological years, and water quality in different hydrological phases clearly separated the lake and river phases, highlighting the influence of water level fluctuations on water quality within a year. To maintain the water quality of Dongting Lake, the control of external load should not be relaxed, and hydrological regulation should be actively carried out within each year.