Water Quality Response Research Articles

Use of multispecies (Nannochloropsis oceanica, Artemia franciscana, and Arbacia nigra) approach to assess the quality of marine water from Callao Bay, Peru

Multi-species tests in bioassays offer a holistic view of the ecosystem’s response to toxicity, as different species display varying sensitivities to pollutants. This research aimed to assess the ability of toxicity tests’ to distinguish contamination levels, examine site-specific effects, and investigate seasonal variability. Using a multispecies approach (Nannochloropsis oceanica, Artemia franciscana, and Arbacia nigra), bioassays evaluated marine water quality from Callao Bay in Peru across four sampling areas (Naval School: PA1, Peruvian Marine Institute: PA2, Callao Pier: PA3, and San Lorenzo Island: PA4). These species, with varying sizes and morphologies, are relevant to marine systems and ideal for multispecies toxicity testing, contributing to broader environmental impact discussions. To conduct toxicity bioassays, seasonal evaluations were performed in fall, winter, spring, and summer. Brine shrimp displayed seasonal variations in toxicity values, with notable mortality rates during winter. Nannochloropsis oceanica was the most sensitive species, showing moderate toxicity across seasons. Areas impacted by pollution sources, such as wastewater and maritime traffic, exhibited the highest toxicity levels (PA3 and PA4). These fluctuations underscore the need to consider seasonal and local conditions when assessing organism sensitivity to seawater contaminants. Additionally, they reveal the complex interplay between environmental factors, water quality, and organism responses in marine ecosystems.

The competing controls of glaciers, precipitation, and vegetation on high-mountain fluvial sediment yields.

Investigating erosion and river sediment yield in high-mountain areas is crucial for understanding landscape and biogeochemical responses to environmental change. We compile data on contemporary fluvial suspended sediment yield (SSY) and 12 environmental proxies from 151 rivers in High Mountain Asia surrounding the Tibetan Plateau. We demonstrate that glaciers exert a first-order control on fluvial SSYs, with high precipitation nonlinearly amplifying their role, especially in high-glacier cover basins. We find a bidirectional response to vegetation's influence on SSY in the Eastern Tibetan Plateau and Tien Shan and identify that the two interacting factors of precipitation and vegetation cover explain 54% of the variability in SSY, reflecting the divergent roles of vegetation in promoting biogenic-weathering versus slope stabilization across bioclimatic zones. The competing interactions between glaciers, ecosystems, and climate in delivering suspended sediment have important implications for predicting carbon and nutrient exports and water quality in response to future climate change.

Optimization Model for Climatic Change Impact on the Water Quality of Al-Hilla River, Iraq

This study presents an advanced optimization model to assess the impacts of climate change on water quality in the Al-Hilla River. To reduce uncertainties associated with climate change projections and quantify the river's water quality response, a novel model of the river system is developed, with the objective function integrated into optimization theory. Water quality simulations for different regions of the river system are performed using the QUAL2K model, while the Ant Colony Optimization (ACO) method is applied to optimize the model. Additionally, the study investigates the effects of temperature and DO variations on microbial populations and the self-purification capacity of the water body. The results indicate that all climate change scenarios lead to a decline in water quality, with significant reductions in dissolved oxygen (DO) levels, even under safe discharge conditions. The study demonstrates that the proposed technique can identify optimal solutions more efficiently, contributing to faster and more reliable decision-making in water quality management. Also, the findings reveal that both temperature and DO significantly influence microbial composition and self-purification processes, with higher temperatures and DO levels improving self-purification efficiency. These insights enhance our understanding of the complex interactions between environmental factors and water quality, offering a valuable foundation for future water management strategies aimed at mitigating the effects of climate change.

Source–Sink Structural Coupling Within Forest-Clustered Landscapes Drives Headstream Quality Dynamics in Mountainous Sub-Watersheds: A Case Study in Chongqing, China

Water environment quality is profoundly driven by a series of landscape characteristics. However, current knowledge is limited to the independent response of water quality to single landscape elements; this has led to poor knowledge of the potential role of structural coupling within landscapes in driving water quality changes, especially in those agroforestry-mixed mountainous watersheds with highly embedded forest-clustered landscapes and abundant headstreams. Given this fact, this study aims to evaluate whether and how the source–sink coupling structure of forest-clustered landscapes systematically drives headstream quality dynamics. We first systematically assessed the association pattern of source and sink structures within forest-clustered landscapes, and then innovatively proposed and constructed a functional framework of source–sink coupling structure of landscapes across 112 agroforestry-mixed mountainous sub-watersheds in Chongqing, China. On this basis, we further evaluated the driving pattern and predictive performance of the source–sink coupling structure of landscapes behind headstream quality dynamics. We report three findings: (1) headstream quality varied across agroforestry-mixed sub-watersheds, mapping out the source–sink structures and functions of landscapes; (2) there was significant functional coordination between source–sink structures of the forest-clustered landscapes, which significantly drove headstream quality dynamics; (3) the structural positioning and differences of the forest-clustered landscapes along the multivariate functional axes directly corresponded to and predicted headstream quality status. These findings together highlight a key logic that the response of water quality dynamics to landscapes is essentially that to the functional coupling between the source–sink structures of landscapes, rather than the simple combination of a single landscape contribution. This is the first study on the landscape–runoff association from the perspective of source–sink structural coupling, which helps to deepen understanding of the correlation mechanism between water dynamics and landscape systems, and provides a new functional dimension to the development of future landscape ecological management strategies from a local to a global scale.

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

Hulun Lake, the largest inland steppe lake in China, is encountering severe water quality degradation. Estuaries play important roles in material and energetic exchange between rivers and lakes. The water quality at the estuaries of Hulun Lake directly reflects the impact of both human activities and natural factors on the lake’s overall water quality, especially during rainfall events. From July 28, 2021, to August 4, 2021, water samples from 62 sites were collected in the three estuaries of Hulun Lake before and after a moderate rainfall event. 13 water parameters, including dissolved oxygen (DO), Turbidity (Tur), Total Nitrogen (TN), Total Phosphorus (TP), Total Organic Nitrogen (TON), and Total Organic Phosphorus (TOP) were measured. The spatio-temporal distribution of water quality in the estuaries was assessed based on water quality index (WQI). Besides, an improved approach integrating stepwise linear regression (SLR) and principal component analysis (PCA) was utilized to construct a WQImin model for an effective assessment of water quality in these estuaries. Furthermore, the absolute principal component scores-multiple linear regression (APCS-MLR) model was employed to identify and quantify the environmental drivers underlying the water quality in the estuaries. The results of WQI indicated that the water quality of the sites in the estuaries of Hulun Lake was “medium” or “poor”, both before and after the rainfall, with a general deterioration in water quality in response to the rainfall. The simplified WQImin model consisted of 5 crucial parameters (i.e., TN, TP, ammonium (NH4+-N), Tur, and permanganate index (CODMn)), and it performed well without parameter weights. Spatial differences in some water parameters among the estuaries were detected, which were attributed to the natural factors and human activities upstream. The principal environmental factors affecting the water quality in the estuaries consisted of hydrodynamic processes, internal phosphorus release, external phosphorus input, external nitrogen input, nitrification in the estuaries, and external organic input and internal organic release. Therefore, we propose basin management strategies such as limiting grazing pressure, adopting enclosed pasture, wetland restoration, optimizing water renewal cycle in Hulun Lake, and transboundary water quality management to tackle water contamination in Hulun Lake.

Combined impacts of climate and land use scenarios on sediment loads in small agricultural watershed in Tunisia

This study investigates the impact of conservation practices, specifically mulching and terracing, on soil erosion in the Kamech watershed (2.6 km²) situated in the Cap Bon region of northeastern Tunisia, under both current and future climate scenarios. Utilizing the Soil and Water Assessment Tool (SWAT) model, the research evaluates the effectiveness of these Best Management Practices (BMPs) in reducing soil loss, revealing significant reductions of 1.5 t ha⁻¹ yr⁻¹ for mulching and 2 t ha⁻¹ yr⁻¹ for terracing. The findings indicate that these practices play a crucial role in enhancing soil conservation amidst climate change challenges, including altered precipitation patterns and increased temperatures. Additionally, the study highlights a notable decline in average monthly rainfall projected for the period 2051 to 2100 under the RCP8.5 scenario, further emphasizing the importance of implementing effective soil management strategies. This paper indicates that both methods, mulching and terracing, significantly contribute to reducing soil erosion under future scenarios (2051-2100). Their implementation proves essential for effective soil conservation, helping to mitigate the impacts of climate change and maintain soil health in the Kamech watershed. The results contribute to a better understanding of BMP performance in addressing soil erosion, water quality, and hydrological responses in the face of evolving environmental conditions. By enhancing our understanding of these interactions, this research aims to provide valuable insights for sustainable watershed management, particularly in regions prone to water scarcity and land degradation.

Combined effects of flood, drought and land use dominate water quality and nutrient exports in Jialing River basin, SW China

Climate change and the associated increase in hydroclimatic extremes necessitate a deeper understanding of the resulting water quality responses. This study investigates the combined impacts of hydroclimatic extremes and land uses on water quality of the Chinese Jialing River, of which the middle and downstream areas experienced a flood in 2021 and a severe drought in 2022. Water Quality Index (WQI) and nutrient loads were assessed using daily data from 22 monitoring stations across the Jialing River and its two tributaries, the Qujiang River and Fujiang River, over 2021–2022. The results indicate a slight upward trend in water quality, as reflected by the WQI, for the tributaries from 2021 to 2022, while a declining trend was observed in the mainstream. Floods had a more pronounced impact on water quality than droughts, particularly on nutrient concentrations, and both dilution and flushing effects were observed as discharge increased in the Jialing River and its tributaries. Notably, water quality deterioration was most pronounced in the downstream areas with land uses dominated by cropland and built-up area, where intensified rainfall distributed and exacerbated nutrient losses in the rainy seasons. Nutrient fluxes, including Chemical Oxygen Demand (COD), Total Phosphorus (TP), and Total Nitrogen (TN), were closely linked to discharge, with hydroclimatic extremes therefore significantly affecting nutrient exports. This study elucidates the complex interactions between land use, extreme weather and water quality in the Jialing River Basin. Our findings underscore the need to strengthen the management of non-point source pollutants in the downstream areas of the Jialing River to address the challenges posed by anticipated increases in extreme rainfall in the near future.

Response of Water Quality to Land Use and Landscape Pattern in the Ganjiang River Watershed.

Analysing the impact of landscape composition and structure on water quality at different scales is of great significance to water quality protection. The aim of this study was to determine scale-dependent impacts of land use/landscape patterns on water quality. The Ganjiang River, the largest water system in the Poyang Lake watershed, the largest freshwater lake in China. The response of water quality to land use and landscape patterns in the Ganjiang River watershed was explored based on land use and water quality data using redundancy and Spearman correlation analyses. Considering upstream monitoring of the entire Ganjiang River watershed; watersheds at the county level administrative region; and 1, 2, 5, 10, 15, 20, and 30 km-radius circular buffer zones, a total of nine scales of land use/landscape patterns that influence water quality in the Ganjiang River watershed were analysed. Results indicated that the county-level scale and the land use type of the 20 km-radius buffer zone upstream of the monitoring site were closely linked to water quality (96.28% and 93.23%, respectively). Among the land use types, construction land and cultivated land were the main output sources of pollutants. Regarding landscape pattern index, the greater the fragmentation of the landscape, the heavier was the water pollution load; the more the patches per unit area, the more stable was the ecosystem and the lower was the pollutant concentration. In addition, the eco-hydrological system of the Ganjiang River watershed was revealed to some extent through multi-angle analysis. These conclusions can serve as a reference for government departments to formulate land management and water quality protection measures.

Forest Dieback Alters Nutrient Pathways in a Temperate Headwater Catchment

ABSTRACTForested headwater catchments ensure good water quality for downstream ecosystems and human consumption. Climate change and the exacerbating likelihood of extreme events elevate the risk of severe forest dieback. However, the effects of forest dieback on the quantity and quality of stream water are not fully understood. Here, we analyse high‐frequency observations of discharge, electrical conductivity (EC), dissolved organic carbon (DOC) and nitrate (NO3N) obtained before, during and after a drought‐induced forest dieback in a headwater stream in the German Harz Mountains. We focus on the characteristics of concentration‐discharge (C‐Q) relationships at the scale of runoff events to assess the effects of forest dieback on the sources, mobilisation and pathways of EC, DOC and NO3N. When comparing pre‐ and post‐dieback conditions, we found a significant increase in runoff efficiency and a doubling of DOC loads exported from the catchment, while DOC concentrations increased only moderately and their C‐Q patterns did not change. EC exhibit no changes in concentrations but a steepening of C‐Q dilution patterns. We explain these findings with a dieback‐induced decrease in evapotranspiration, which leads to more intensive drainage of the upper organic soil layers in the riparian zone. In contrast, we observed a strong increase in NO3N concentrations and fluxes by a factor of ~5, while C‐Q patterns at the event scale changed from enrichment to dilution. We argue that the dieback led to an excess of NO3N on the hillslopes that connect to the stream via surficial flowpaths. In this way, NO3N bypasses the riparian zone, reducing the catchment's efficiency in attenuating this nutrient. Our study emphasises the pivotal role of riparian zones in mediating water quality in headwater streams. Different configurations of the riparian zone and its connection to the hillslopes and the stream network may be a missing piece in explaining differences in water quality responses of catchments to forest dieback.

Response of water quality in major tributaries to the difference of multi-scale landscape indicators in Dongting Lake basin, China.

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 wetland vegetation responses to water level variations in a university stormwater reuse reservoir: Nature-based approaches to campus water sustainability

In response to climate-driven water shortages, Duke University in 2014 constructed a water reuse reservoir and wetland complex (Pond) to capture urban stormwater and recycle water to provide campus cooling and reduce downstream loading of nutrients and sediment into Jordan Lake, a regional water supply. We postulated that even with significant water level changes due to withdrawals, the Pond would function to reduce downstream nutrients and sediment once wetland plants became established in the littoral zone. Throughout the project (2015–2021), baseflow nutrient concentrations downstream decreased, with Unfiltered Total Nitrogen (UTN) falling by 44 % and Unfiltered Total Phosphorus (UTP) by 50 %. Storm mean concentrations decreased by 31 % for UTN, 54 % for UTP, and 72 % for Total Suspended Solids (TSS). The annual reductions in mass fluxes (UTN, UTP, and TSS) were between 58 and 85 % across a range of storm intensities. Regardless of water level, temperature, pH, and oxygen concentrations downstream were not significantly changed. Between 2015 and 2020, a littoral survey of planted and naturally introduced species showed that wetter years resulted in a greater number of species across a gradient of three inundation zones (i.e., moist, wet, and aquatic). Conversely, dryer years resulted in fewer species across overlapping zones. The dominant plants that successfully colonized the Pond are all obligate wetland species despite the Pond's highly variable water depths and periods of inundation. The final plant populations were dominated by invasive native species supporting the self-design theory of plant succession as nearly half of the original planted species died. The reuse Pond design (pond-wetland complex) showed the capability of using stormwater runoff for campus cooling while improving water quality services and providing habitat for wetland plants. Thus, campuses with watershed runoff capture capability should consider a nature-based recycling approach as part of their water sustainability program.

Mountainous Floodplain Connectivity in Response to Hydrological Transitions

AbstractIn mountainous watersheds, floodplain sediments are typically characterized by gravel bed layers capped by an overlying soil unit that serves as a hotspot for biogeochemical reactivity. However, the influence of soil biogeochemistry on gravel bed underflow composition remains unclear, especially during hydrological transitions that alter the vertical connectivity between overlaying soils and the underlying gravel bed. This study investigates these dynamics by measuring hydraulic gradients and water compositions over three hydrological years in a typical mountainous, low‐order stream floodplain in the Upper Colorado River Basin. Results indicate that the timing of hydrological conditions strongly influences the vertical exchanges that control water quality. Specifically, during flooding events such as beaver ponding, that induce downward flushing of the soil, anoxic conditions prevalent in the biogeochemically active soil are transferred downstream via gravel bed underflow. Conversely, snowmelt and drought conditions increase oxic conditions in the gravel bed due to diminished hydrological connectivity with the overlying soil. To compare water quality response to hydrological transitions across similar floodplain environments, we propose a conceptual model that quantifies the inundation‐induced flushing of soil porewater to measure solute exchange efficiency with the gravel bed solute convergence efficiency (SCE). This model provides a framework for quantifying biogeochemical processes in hydrological underflow systems, which is critical for water and elemental budgets in these globally important mountainous ecosystems.

Enhanced Hydrologic Connectivity and Solute Dynamics Following Wildfire and Drought in a Contaminated Temperate Peatland Catchment

AbstractIntact peatlands provide hydrological ecosystem services, such as regulating water regimes and immobilizing pollutants within catchments. Climate change impacts including drought and wildfire may impair their functioning, potentially impacting ecosystem service delivery. Here we investigate stream water quality changes following the combined impacts of a summer drought and wildfire in a peat‐dominated catchment in the UK during 2018. The study catchment stores legacy pollutants (i.e., metals) due to past industrial activity, thus making it particularly susceptible to pollutant release during wildfires. We quantified changes in water chemistry during five storm events over a 9‐month period following the wildfire. Concentration‐discharge (C‐Q) relationships for nine solutes were analyzed to explore changes in activation and connectivity of solute source zones. Hysteresis and flushing indices of C‐Q responses further described solute dynamics during storm events. We found that most nutrient and base cation concentrations in the stream discharge were highest in the immediate post‐fire storm events and decreased during subsequent autumn and spring storms. Metal concentrations increased during autumn and spring storms, indicating delayed mobilization from within‐peat or distal headwater sources. Our findings suggest that seasonal re‐wetting and hydrologic connectivity following disturbance influenced solute source zone activation and transport in the study catchment. Water quality responses associated with wildfire and drought were primarily observed in the months following the wildfire, suggesting mobilization of pollutants peaks shortly after fire. Our results contribute to a critical understanding of the future of water quality risks in temperate peatland catchments subject to disturbances exacerbated by climate change.

Reversibility of seawater intrusion in a coastal aquifer: Insights from long-term field observation and numerical modeling

It is essential to understand basis processes affecting the reversibility of seawater intrusion (SWI) and the related timescale after groundwater pumping stopped for coastal groundwater management. Groundwater salinity variations presented by previous studies showed a fast SWI process and the following seawater retreat (SWR) process indicated by overall salinity decrease in the coast karst aquifer in the Dalian Peninsula, northeast China. Cross-sectional variable-density flow and transport simulations using equivalent porous medium (EPM) model, dual-domain (DDM) model and the EPM with a single discrete feature representative of conduit flow (EPM-DF) are conducted to understand the SWI reversibility related to the characteristics of the flow system, including aquifer parameters and seaside boundary conditions. Large dispersity combined with a low salinity concentration at the sea boundary are necessary in the EPM and DDM models to produce a fast SWI and low salinity concentration as observed. The enhanced dispersion in the DDM model enhances the mixing in the transition zone (TZ) and produces more obvious seasonal variation but longer SWR process compared to the EPM model. The EPM-DF model produces significant salinity seasonal variation during the SWI process and a fast decrease in the SWR process. The overall fast system response but low peak concentration during the SWI might be attributed to the highly heterogeneous characteristics of the karst aquifer system, which produces a wide front edge of TZ as observed. The dispersion-dominated EPM and DDM models produced higher degree of SWI reversibility compared to the EPM-DF model, as indicated by the weaker lag effects between groundwater levels and salinity concentration. Moreover, the SWI reversibility may arise not only from the heterogeneous characteristics of the karstic aquifer system but also from the rate for rise in the inland groundwater level during the seasonal variation cycle. An overall SWR process can be divided into two stages: the first stage with rapid decrease in salinity concentration but small changes in toe associated with TZ widening and the second stage with rapid toe retreat during aquifer flushing. The flushing of the brine leakage from the solar salt field may extend the SWR process. Considering this relatively longer water quality response time than the time span in general groundwater management plans, a reasonable objective and how maintain the hydraulic head during the SWI controlling have been of a great concern to the coastal groundwater management.

Persistent and lagged effects of fire on stream solutes linked to intermittent precipitation in arid lands

Increased occurrence, size, and intensity of fire result in significant but variable changes to hydrology and material retention in watersheds with concomitant effects on stream biogeochemistry. In arid regions, seasonal and episodic precipitation results in intermittency in flows connecting watersheds to recipient streams that can delay the effects of fire on stream chemistry. We investigated how the spatial extent of fire within watersheds interacts with variability in amount and timing of precipitation to influence stream chemistry of three forested, montane watersheds in a monsoonal climate and four coastal, chaparral watersheds in a Mediterranean climate. We applied state-space models to estimate effects of precipitation, fire, and their interaction on stream chemistry up to five years following fire using 15 + years of monthly observations. Precipitation alone diluted specific conductance and flushed nitrate and phosphate to Mediterranean streams. Fire had positive and negative effects on specific conductance in both climates, whereas ammonium and nitrate concentrations increased following fire in Mediterranean streams. Fire and precipitation had positive interactive effects on specific conductance in monsoonal streams and on ammonium in Mediterranean streams. In most cases, the effects of fire and its interaction with precipitation persisted or were lagged 2–5 years. These results suggest that precipitation influences the timing and intensity of the effects of fire on stream solute dynamics in aridland watersheds, but these responses vary by climate, solute, and watershed characteristics. Time series models were applied to data from long-term monitoring that included observations before and after fire, yielding estimated effects of fire on aridland stream chemistry. This statistical approach captured effects of local-scale temporal variation, including delayed responses to fire, and may be used to reduce uncertainty in predicted responses of water quality under changing fire and precipitation regimes of arid lands.

Multidimensional water level and water quality response to severe drought in Xingyun Lake

Drought stress has a significant impact on the quality and quantity of lake water. Understanding this impact is crucial for preventing water security risks and pollution recovery. However, there is a lack of systemic understanding of how drought affects water quality and quantity, and how they change in multiple dimensions. This manuscript established a synthesized methodology with the principles to judge the applicability and three steps of application to detect the change in water quality and water level under severe drought in Xingyun Lake, China. Results show that (1) The water level and water quality of Xingyun Lake have a synchronous and evident response to drought during 2009–2014. The rainfall during 2008–2015 declined by 22.9 % to normal, and the inundated area and lake water depth in 2012 decreased by 10.50 % from 2002 to 1.38 m to the average depth, respectively. The pollution index climbed above 1.21 after 2008, fluctuating around 1.42. (2) Under drought, the water quality indicators significantly changed in the terms of the overall feature, trend, eigenvalue, and morphological characteristics. The water quality indicators of Set2008-2015 are significantly different from set2000-2007 and not in the groups of set1994-2000. The morphological characteristics of water quality indicators in set2008-2015 differs significantly from that in set2000-2007 shown by the minimum, maximum, median, quartiles, and extreme values. (3) Although NH3–N showed no significant change, the water quality deteriorated in the physical, chemical, and biological aspects. The TP, IMN, and BOD5 changed more evidently than DO and NH3–N. (4) Water quality grade and indicator concentration deteriorated significantly and sharply under severe drought and are threatened deeply by TP and TN. The synthesized methodology is scientifically constructed and canbe employed in the characteristics cognition of water quality and water level to severe drought in and out of this research. And the intervention time and various regulating measures for pollution degradation and water quality recovery canbe constructed based on the multi-dimensional analysis of water quality change under drought evolution.

Areal artificial recharge has changed the interactions between surface water and groundwater

Artificial groundwater recharge is increasingly utilized globally for addressing regional groundwater issues due to its effectiveness and ease of application. However, due to the complexity of the interaction of groundwater systems with the external environment and its inherent latency, governance effects are difficult to quantify and are not fully understood yet. In this study, the efficiency of areal artificial groundwater recharge was determined and the interactions with surface water were analyzed by field surveys, sample analysis, water balance reconstruction, and model simulation. A typical groundwater recharge region in the Beijing-Tianjin-Hebei region, China, was focused. Additionally, the response of groundwater flow and water quality to areal artificial groundwater recharge was quantified. Results showed that areal artificial groundwater recharge changes the relationship between surface water and groundwater, with an efficiency of 70 % under high recharge and fluctuation, and decreasing to 20–30 % after the groundwater level was stabilized. The impact on the hydrodynamic field were primarily manifested as the formation of water mounds near river channels, which expand laterally up to 9.2 km from the recharging river channel one year after implementation.Then the impact increases to 14.9 km and continues to expend a year after cessation. The areal artificial groundwater recharge has simultaneously improved the water quality by 23 % in monitoring wells within a 10 km distance from the river channel. The results of this study quantify the impacts of area artificial recharge on groundwater and provide references for the improvement of water resources and water environment in those similar regions.

Difficulties in using land use pressure and soil quality indicators to predict water quality

Intensive agriculture can impair river water quality. Soil quality monitoring has been used to measure the effect of land use intensification on water quality at a point and field scales but not at the catchment scale. Other farm scale land use pressures, like stocking rate and the value of land, which relate to land use intensity are now publicly available, nationally. We therefore tested whether point scale soil quality measures, together with newly available farm scale land use pressures (land valuation and stocking rate) and existing catchment and climatic characteristics could help predict the behaviour of water quality data across 192 catchments in New Zealand. We used a generalised additive model to make predictions of the change in nitrogen fractions (r2 = 0.65–0.71), phosphorus fractions (r2 = 0.51–0.70), clarity and turbidity (r2 = 0.42–0.46), and E. coli (r2 = 0.35) over 15 years. The state and trend of water quality was strongly related to a refined farm scale land use classification, and to catchment and climatic characteristics (e.g. slope, elevation, and rainfall). Relationships with point scale soil quality measures and the land use pressures were weak. The weak relationship with land use pressures may be caused by using a single snapshot in time (2022), which cannot account for lag times in water quality response but leaves room for additional temporal data to improve predictive power. The weak relationship to soil quality measures was probably caused by limited data points (n = 667 sites) that were unrepresentative of land use, and areas of catchment subject to processes like runoff or leaching. While national soil quality measures might be useful for evaluating environmental risk at the field or farm scale, without a large increase in sampling, they were not relevant at the catchment scale. Additional analyses should be performed to determine how many samples would be needed to detect a change using an environmentally focused soil test that can guide water quality management.

Effects of a forested state park on stream nutrient concentrations in an agriculturally dominated watershed in the U.S. Midwest

AbstractAgricultural land cover in the U.S. Midwest is a major source of nutrient pollution that has led to impairment of stream water quality. This study examines the impact of a forested state park on nutrient concentrations within an agriculturally dominated watershed. Water samples were collected over a 2‐year study period from eight stream sampling sites along four creeks and processed for total nitrogen (TN), nitrate (), total phosphorus (TP), and orthophosphate (). Hydrology, channel morphology, and remotely sensed land cover and vegetation data were also collected and analyzed within the study area. Results indicate that water quality responses to a forested state park vary between TN, , TP, and , and water quality variables are uniquely influenced by watershed and stream characteristics. The greatest water quality benefits most frequently occurred within the two smallest study streams with the greatest residence times and proportion of watershed areas within the forested state park. Overall, the greatest improvements to water quality occurred during periods of low stream discharge and when riparian vegetation was greenest. The results of this study suggest that conservation of forested areas within agriculturally dominated watersheds can provide water quality improvements in the U.S. Midwest. Targeting watersheds that drain small streams with long residence times for conservation may be most beneficial to improving water quality.

Response of a source water quality through a heavy precipitation event: Nutrients, dissolved organic matter and their DBPs formation

To better understand the influence of heavy precipitation event on water supply security, the change of nutrients, dissolved organic matter (DOM) and their corresponding disinfection by-products (DBPs) generation in river were investigated through a heavy precipitation event. The results show that short-term sustained heavy precipitation causes additional load on the river. Significant temporal variations and increases in dissolved oxygen (DO), turbidity, dissolved organic carbon (DOC) and molecular weight of raw water were observed during the heavy precipitation, and dissolved organic nitrogen (DON) showed a remarkably decline with the continuation of precipitation. The molecular weight and aromaticity of DOM increased dramatically with the continuous superposition of precipitation and flow, and the proportion of hydrophobic fraction increased during the study period. Four different fluorescent components were identified, including humic-like (C1, C2 and C3), and protein-like fluorophore C4. Heavy precipitation events affected the mobilization of DOM, while the generation of DBPs increased by 4%–47% during the chlorination, and the elevated river level further increased the DBPs formation. In particular, the HOA fraction was the main contributor of DBPs (up to 70%). The risk of haloacetic acids (HAAs) generation caused by heavy rainfall was concentrated in the river runoff producing and regression periods for both hydrophobic and hydrophilic fractions of DOM. Humification index (HIX) was positively correlated with the yield level of TCM, DCAA, TCAA, and DCAN during chlorination. Chlorination disinfection of raw water during river runoff producing and regression period is likely to increase the haloacetonitriles formation potential (HANsFP), thus posing a vital threat to water supply safety, while chloramination disinfection may significantly relieve the threat. This study provides a theoretical basis for the direct/indirect link between short-term precipitation events and their impact on water quality.