Biofloc application in carp polyculture: impacts on water quality, growth, and immune-antioxidant responses

The spatial response mechanism of hydrology and water quality of large river-connected lakes is very complicated. In this study, we developed a spatial response analysis method that couples wavelet correlation analysis (WTC) with self-organizing maps (SOM), revealing the spatial response and variation of water level and water quality in Poyang Lake, China's largest river-connected lake, over the past decade. The results show that: (1) there was significant spatial heterogeneity in water level and quality during the dry seasons (2010-2018) compared to other hydrological stages. (2) We identified a more pronounced difference in response of water level and quality between northern and southern parts of Poyang Lake. As the distance increases from the northern lake outlet, the impact of rising water levels on water quality deterioration intensified during the dry seasons. (3) The complex spatial heterogeneity of water level and quality response in the dry seasons is primarily influenced by water level fluctuations from the northern region and the cumulative pollutant entering the lake from the south, which particularly leads to the reversal of the response in the central area of Poyang Lake. The results of this study can contribute to scientific decision-making regarding water environment zoning management in large river-connected lakes amidst complex environment conditions.

Wildfires are landscape scale disturbances that can significantly affect hydrologic processes such as runoff generation and sediment and nutrient transport to streams. In Fall 2016, multiple large drought‐related wildfires burned forests across the southern Appalachian Mountains. Immediately after the fires, we identified and instrumented eight 28.4–344 ha watersheds (four burned and four unburned) to measure vegetation, soil, water quantity, and water quality responses over the following two years. Within burned watersheds, plots varied in burn severity with up to 100% tree mortality and soil O‐horizon loss. Watershed scale high burn severity extent ranged from 5% to 65% of total watershed area. Water quantity and quality responses among burned watersheds were closely related to the high burn severity extent. Total water yield (Q) was up to 39% greater in burned watersheds than unburned reference watersheds. Total suspended solids (TSS) concentration during storm events were up to 168 times greater in samples collected from the most severely burned watershed than from a corresponding unburned reference watershed, suggesting that there was elevated risk of localized erosion and sedimentation of streams. NO3‐N concentration, export, and concentration dependence on streamflow were greater in burned watersheds and increased with increasing high burn severity extent. Mean NO3‐N concentration in the most severely burned watershed increased from 0.087 mg L−1in the first year to 0.363 mg L−1(+317%) in the second year. These results suggest that the 2016 wildfires degraded forest condition, increasedQ, and had negative effects on water quality particularly during storm events.

To investigate the differences in water quality response to landscape features at multiple spatial and temporal scales for different lake types， the Dianchi Lake （Tectonic Lake） in Kunming， Yunnan Province and Fushun West Lake （Hecheng Lake） in Zigong， Sichuan Province were used as the objects of the study. Land use types and landscape pattern indices were extracted at five spatial scales of 200， 400， 600， 800， and 1 000 m buffer zones of the Dianchi Lake basin in Kunming and 20， 40， 60， 80， and 100 m buffer zones of the Fushun West Lake Basin. Combined with lake water quality data from the wet season （July 2022） and dry season （April 2023）， the correlation analysis and the redundancy analysis （RDA） were used to quantitatively compare the differences in the multi-temporal and spatial scale responses of water quality to landscape characteristics between two types of lakes. The results showed that： ① All land use types of Fushun West Lake were urban land， and the land use types of Kunming Dianchi were richer， in which urban land was dominant. The landscape fragmentation of both lakes decreased with the increase of spatial scale. Due to the different landscape characteristics of the two lake basins， their water quality was better in the dry season than in the wet season， and the water quality of Fushun West Lake was better than that of Kunming Dianchi. ② Fushun West Lake had the highest explanation rate of the landscape characteristics to the water quality at the scale of 60 m lakeshore buffer zone in the dry season， whereas Kunming Dianchi had the strongest response to the landscape characteristics in the wet season and 800 m lakeshore buffer zone. The response of water quality to the landscape characteristics of Kunming Dianchi was higher than that of Fushun West Lake. ③ There were significant differences in the response of water quality of varying lake types to different landscape features at different spatial and temporal scales. In this study， the urban land was a "sink" landscape of water quality in the Dianchi Lake basin in both dry and wet seasons， while the Fushun West Lake basin was a typical "source" landscape. Forest land was a "source" of polluted water quality at multiple spatial and temporal scales in the Kunming Dianchi basin， with a negative correlation between buffer scale and most water quality indicators at more distant lakeshore zones during the dry season. Patch density was the most critical indicator affecting water quality in Dianchi and Fushun West Lake watersheds. Moreover， the landscape shape index had a greater impact on the water quality of Fushun West Lake than that of Kunming Dianchi. By studying the differences in the response of water quality of different lake types at multiple spatial and temporal scales， this study helps to better predict and respond to the potential impacts of environmental changes on water resources and ecosystems. It also provides a scientific basis for the development of more precise and effective water resource management and protection policies by optimizing the allocation of water resources and strengthening ecological protection and environmental governance.

The article focuses on the problem of obtaining high-quality fish products, for which it is necessary to take into account the specific conditions of each water body. Ponds intensively exploited for fish farming suffer from the violation of the hydrochemical regime of water, accumulation of a significant mass of phytoplankton and increase of organic pollution, which results in fish illness and death. The issues of participation of hydrobionts in the processes of reservoir self-cleaning and the influence of fish-breeding processes on hydrochemical and microbiological characteristics of water in the fish farms are being investigated. The work was carried out on the basis of two fish hatcheries in the Saratov region: “Engels Fish hatchery” LLC and “Teplovsky Fish hatchery” FSUE. Water samples for the study were taken from ponds with uterine population of carp and nursery ponds with polyculture of carp and herbivorous fish, carp monoculture and carp and white carp polyculture. It has been noted that the examined nursery ponds belong to the type mesosaprobic reservoirs. They have a powerful potential for self-purification. With the increasing number of bacteria involved in recycling of dissolved organic matter there is a decrease in biochemical oxigen demand and chemical oxygen demand. In the fish pond microorganisms that provide the processes of water self-purification find favorable conditions for their development and reproduction, especially in polyculture environment. The best indicators of biochemical oxygen demand were observed in ponds with a polyculture of carp and silver carp, because silver carp is a biological ameliorator of the aquatic ecosystem. Maintaining optimal balance between all parts of the hydrobiocenosis of the fishpond and the biochemical processes occurring with the participation of hydrobionts, which contribute to the purification of water, has a positive effect on the quality of water in the reservoir.

Density-dependent water use in carp polyculture: Impacts on production performance and water productivity

To assess 12 years of pollution abatement efforts in all drain estuaries in Northern Egypt, which discharge to Northern Lakes and the Mediterranean Sea, this paper provides temporal trends in water quality indices from 2002 to 2013. For the estuary of 20 drains: one drain had insufficient data to analyze for trends (Burullus Drain), four drains had significant increase in water quality index (WQI) score (Bahr ElBaqar Drain, Drain No. 1, Tabia Drain and No. 11 Drain), one drain had significant declination in water quality score over the tested time period (Ramsis Drain). While the rest (14 drains) showed insignificant trend in either direction (improving or declining). Water quality fluctuated over that time period. On average, temporal changes in excursions of coliform count from their threshold can explain 83.3% of the temporal variability observed in water quality indicators monitored in all drain estuaries (38.9%% < R2 < 89.2%). Therefore, the most effective water quality variables among a set of variables affecting the WQI score was total coliform.

The content and calibration of the comprehensive generic 3D eutrophication model ECO for water and sediment quality is presented. Based on a computational grid for water and sediment, ECO is used as a tool for water quality management to simulate concentrations and mass fluxes of nutrients (N, P, Si), phytoplankton species, detrital organic matter, electron acceptors and related substances. ECO combines integral simulation of water and sediment quality with sediment diagenesis and closed mass balances. Its advanced process formulations for substances in the water column and the bed sediment were developed to allow for a much more dynamic calculation of the sediment-water exchange fluxes of nutrients as resulting from steep concentration gradients across the sediment-water interface than is possible with other eutrophication models. ECO is to more accurately calculate the accumulation of organic matter and nutrients in the sediment, and to allow for more accurate prediction of phytoplankton biomass and water quality in response to mitigative measures such as nutrient load reduction. ECO was calibrated for shallow Lake Veluwe (The Netherlands). Due to restoration measures this lake underwent a transition from hypertrophic conditions to moderately eutrophic conditions, leading to the extensive colonization by submerged macrophytes. ECO reproduces observed water quality well for the transition period of ten years. The values of its process coefficients are in line with ranges derived from literature. ECO’s calculation results underline the importance of redox processes and phosphate speciation for the nutrient return fluxes. Among other things, the results suggest that authigenic formation of a stable apatite-like mineral in the sediment can contribute significantly to oligotrophication of a lake after a phosphorus load reduction.

A review of the application of constructed wetlands (CWs) and their hydraulic, water quality and biological responses to changing hydrological conditions

We synthesize and summarize main findings from a special issue examining the origins, evolution, and resilience of diverse water quality responses to extreme climate events resulting from a Chapman Conference of the American Geophysical Union (AGU). Origins refer to sequences of interactive disturbances and antecedent conditions that influence diversification of water quality responses to extreme events. Evolution refers to the amplification, intensification, and persistence of water quality signals across space and time in watersheds. Resilience refers to strategies for managing and minimizing extreme water quality impacts and ecosystem recovery. The contributions of this special issue, taken together, highlight the following: (1) there is diversification in the origins of water quality responses to extreme climate events based on the intensity, duration, and magnitude of the event mediated by previous historical conditions; (2) interactions between climate variability and watershed disturbances (e.g., channelization of river networks, land use change, and deforestation) amplify water quality ‘pulses,’ which can manifest as large changes in chemical concentrations and fluxes over relatively short time periods. In the context of the evolution of water quality responses, results highlight: (3) there are high intensity and long-term climate events, which can generate unique sequences in water quality, which have differential impacts on persistence of water quality problems and ecosystem recovery rates; and (4) ‘chemical cocktails’ or novel mixtures of elements and compounds are transported and transformed during extreme climate events. The main findings regarding resilience to extreme climate events are that: (5) river restoration strategies for reducing pollution from extreme events can be improved by preserving and restoring floodplains, wetlands, and oxbow ponds, which enhance hydrologic and biogeochemical retention, and lengthen the distribution of hydrologic residence times; and (6) the biogeochemical capacity for stream and river ecosystems to retain and transform pollution from landscapes can become “saturated” during floods unless watershed pollution sources are reduced. Finally, the unpredictable occurrence of extreme climate events argues for wider deployment of high-frequency, in situ sensors for monitoring, managing, and modeling diverse water quality responses. These sensors can be used to develop robust proxies for chemical cocktails, detect water quality violations following extreme climate events, and effectively trace the trajectory of water quality recovery in response to managing ecosystem resilience.

River water quality is strongly affected by droughts and heatwaves worldwide. However, these effects have only been studied in a small number of river basins and regions, mainly in the US, Europe, or Australia. In this study, we analyse the large-scale responses in river water quality under droughts, heatwaves and compound events for 300,000+ water quality monitoring stations worldwide between 1980-2021. We include 16 water quality constituents in the analysis, grouped into general constituents (e.g. water temperature, salinity, dissolved oxygen), biological constituents (e.g. faecal coliform, biochemical oxygen demand) and emerging contaminants (e.g. pesticides and pharmaceuticals). Further, we assess the water quality responses to droughts and heatwaves in relation to climate, land use and level of wastewater treatment. We find a general deterioration in river water quality under droughts and heatwaves globally for most types of water quality constituents, with on average higher water temperatures (+27%), increases in salinity (+23%) and lower concentrations of dissolved oxygen (-17%). We also find that climate type, land use and level of wastewater treatment have a significant effect on the magnitude of water quality responses under droughts and heatwaves. The median increase in river temperature under compound drought-heatwaves strongly depends on climate, with for example higher increases in the Polar climate zone (+4.5&amp;#176;C) compared to the Tropical zone (+2.1&amp;#176;C). Increases in salinity under droughts are on average twice as large in irrigated regions compared to non-irrigated regions. Phosphorus and nitrogen concentrations in rivers can either increase or decrease during drought events, depending on the type of nutrient form (dissolved versus particulate) and land use (urban versus rural). Higher levels of wastewater treatment lead to a stronger reduction in faecal coliform (an indicator of pathogens) during droughts and heatwaves. Compared to previous local and regional-scale analyses, this study provides a more consistent and broader understanding of how droughts and heatwaves affect river water quality. In addition, the results from this study could be used to validate large-scale models of river water quality under droughts and heatwaves.

Understanding the response of water quality in lake to landscape pattern at different spatial scales in agricultural watershed is of great significance to water quality management. In this study, we classified seven riparian buffer zones of lakeside zone by ArcGIS and RS in the Honghu Lake, according to the five functional areas. The landscape metrics were analyzed at multiple buffer widths using Fragstats software. Mathematical statistical methods and models such as redundancy analysis were used to explore spatial relationship between water quality and landscape patterns. Results showed that: 1) The effect of landscape patterns on water quality was scale-dependent at multiple buffer widths. The highest total explanatory power between landscape characteristics and water quality was found at the 200 m buffer width, accounting for 86.1% of the total, which was the most effective spatial scale affecting water quality. 2) The landscape configuration (e.g., largest patch index, patch density) was more associated with water quality than landscape composition (e.g., the percent of landscape and evenness index). 3) The impacts of different landscape types on water quality varied. Agriculture land, affected by topography and cultivation mode, was the main influencing factor on the degradation of water quality at smaller buffer widths from 100 m to 500 m. Forests with higher density and area had more purification effect on water pollutants at the wider buffer widths from 1000 m to 5000 m. The impacts of grassland on water quality was similar with that of forests, but densely distributed urban land contributed to water quality degradation at the same buffer widths. This study could provide scientific reference for water quality management and landscape planning of lake basin in agricultural areas.

Exploring the type and strength of nonlinearity in water quality responses to nutrient loading reduction in shallow eutrophic water bodies: Insights from a large number of numerical simulations

Identification of the interactive responses of water quantity and quality to changes in nature and human stressors is important for the effective management of water resources. Many studies have been conducted to determine the influence of these stressors on river discharge and water quality. However, there is little information about whether sewage treatment plants can improve water quality in a region where river streamflow has decreased sharply. In this study, a seasonal trend decomposition method was used to analyze long-term (1996–2015) and seasonal trends in the streamflow and water quality of the Guanting Reservoir Basin, which is located in a semi-arid region of China. The results showed that the streamflow in the Guanting Reservoir Basin decreased sharply from 1996–2000 due to precipitation change and human activities (human use and reservoir regulation), while the streamflow decline over the longer period of time (1996–2015) could be attributed to human activities. During the same time, the river water quality improved significantly, having a positive relationship with the capacity of wastewater treatment facilities. The water quality in the Guanting Reservoir showed a deferred response to the reduced external loading, due to internal loading from sediments. These results implied that for rivers in which streamflow has declined sharply, the water quality could be improved significantly by actions to control water pollution control. This study not only provides useful information for water resource management in the Guanting Reservoir Basin, but also supports the implementation of water pollution control measures in other rivers with a sharp decline in streamflow.

River water quality has been increasingly deteriorated because of the influence of natural process and anthropogenic activities. Quantifying the influence of landscape metrics, namely topography and land use pattern, which encompass land use composition and landscape configuration, across different spatial and seasonal scales that reflect natural process and anthropogenic activities, is highly beneficial for water quality protection. In this study, we focused on investigating the effects of topography, landscape configuration and land use composition on water quality at different spatial scales, including 1-km buffer and sub-watershed, and seasonal scales, including wet and dry season, based on the monthly water quality data in 2016 of Dongting Lake in China. Multivariate statistical analysis of redundancy analysis and partial redundancy analysis was used to quantify the contributions of these factors under different scales. Our results showed that among the three environmental groups, topography made the greatest pure contribution to water quality, accounting for 11.4 to 30.9% of the variation. This was followed by landscape configuration, which accounted for 9.4 to 23.0%, and land use composition, which accounted for 5.9 to 15.7%. More specifically, water body made the greatest contribution to the water quality variation during dry season at both spatial scales, contributing 16.6 to 17.2% of the variation. In contrast, edge density was the primary interpreter of the variability in water quality during wet season at both spatial scales, accounting for 9.9 to 11.1% of the variation. The spatial variability in the influence of landscape metrics on water quality was not markedly distinct. However, these metrics have a minimal impact difference on water quality at the buffer scale and the sub-watershed scale. Moreover, the contribution of landscape configuration varied the most from the buffer to sub-watershed scales, indicating its importance for the spatial scale difference in water quality. The findings of this study offer useful insights into enhancing water quality through improved handling of landscape metrics.

Water quality and pollution source apportionment responses to rainfall in steppe lake estuaries: A case study of Hulun Lake in northern China