Watershed Water Quality Research Articles

Systematic evaluation of management measure effects on the water environment based on the DPSIR-Tapio decoupling model: A case study in the Chaohu Lake watershed, China

Watershed management measures have been widely implemented worldwide to reduce the water quality deterioration in rivers and lakes, which continue to face increasing stresses from human activities. Due to the complexity of influential factors within watersheds, systematic and reliable approaches are urgently needed to evaluate the effects of watershed managerial practices on scientific applications. In this study, the driving force-pressure-state-impact-response (DPSIR) model integrated by Tapio decoupling analysis was established using 30 quantitative indicators to systematically evaluate their effects on overall watershed water environmental health of Chaohu Lake watershed, China, which was under intensive management practices during 2000–2019. The DPSIR model outcomes revealed that the driving force subsystem with 7 indictors accounted for 34.2% of the watershed water environmental health, in which gross domestic product (GDP), gross industrial output value, crop planting and urbanization contributed a larger proportion. Management measure implementation positively improved the watershed water environmental health, with the second largest proportion being 23.4%. During the study period, a trend of simultaneous improvement in the water quality of the rivers and lakes existed. The Tapio decoupling analysis indicated that watershed water quality was weakly decoupled with socioeconomic development and related pressures, and management responses. The response strategy is the main force in alleviating the pressure from socioeconomic development on the watershed water quality. Overall, the method proposed in this study would improve the understanding of watershed management practice effects and provide guidance for future management measure applications.

Relating land-use/land-cover patterns to water quality in watersheds based on the structural equation modeling

Understanding the relationships between land-use/land-cover (LULC) patterns in watersheds and water quality is of great significance for exploring the causes of non-point source pollution and scientific planning of land use. Multivariate regression methods have often been used to examine the response of specific water contaminants to LULC patterns. However, this also resulted in overlooking the ecological process and biased parameter estimates caused by redundancy where some landscape metrics are strongly correlated. In this study, based on “source-sink” landscape theory, Redundancy Analysis (RDA) and Partial Least Squares Structural Equation Modeling (PLS-SEM) were used to investigate the relationship between LULC patterns and water quality in the surrounding sub-watersheds of the Danjiangkou Reservoir in the dry and rainy seasons. The results showed that water quality parameters were characterized by seasonal differences. In the dry season, only the proportion of the watershed occupied by urban landscapes (P_Urban) had a significant impact on water quality in watersheds (β = 0.835, p < 0.001), so the water quality was only affected by point source pollution in the dry season. In the rainy season, specific water contaminants were categorized as organic and inorganic pollutants. The “sources” of organic and inorganic pollutants were agricultural and urban land, respectively. However, natural vegetation was not only a “sink” of inorganic pollutants, but also a “source” of organic pollutants. Furthermore, agriculture and natural vegetation mediated the effects of landscape spatial configuration on the water quality, yet landscape aggregation negatively moderated the relationship between urban and organic pollution. Therefore, watersheds with high landscape aggregation have small agricultural landscapes and large natural vegetation landscapes where water quality is affected by low levels of inorganic pollution and high levels of organic pollution. However, organic pollution from urban sources was aggravated by watersheds with low landscape aggregation. This study revealed the relationships between LULC patterns and water quality in watersheds and reflected the ecological process to a certain extent.

Assessing the effects of climate change on urban watersheds: a review and call for future research

Considerable efforts have been made to control and manage the hydrology and water quality of watersheds impacted by urban development through the construction of stormwater control measures (SCMs). Climate change (CC) could, however, undermine these efforts by intensifying precipitation and hydrologic extremes. Although the impact of CC on water resources has been well-documented, its impact on urban hydrology remains less studied. CC may complicate sustainable urban hydrology, which can cause a reduction in the efficiency of SCMs with changes in precipitation patterns (i.e., changes in duration, frequency, depth, and intensity). More intense precipitation may result in reduced runoff reduction and treatment efficiency, given that SCMs have a finite surface storage volume and surface infiltration capacity. Determining the functionality of various SCMs under future climate projections is important to better understand the impact of CC on urban stormwater and how well these practices can build resiliency into our urban environment. The purpose of this review is to provide the needs and opportunities for future research on quantifying the effect of CC on urban SCMs and to characterize the performance and effectiveness of these systems under existing and projected climate scenarios. A summary of the modeled constituents as well as the stormwater and climate models applied in these studies is provided. We concluded that there are still limitations in exploring the impact of future changes in meteorological variables that will influence the operation of SCMs in the long-term. Previous studies mostly focused on the impacts of CC on urban runoff quantity, and only a handful of studies have explored water quality impacts from CC, such as potential changes in water temperature, metals, and pathogens. Assessing the pollutant-removal efficiency of SCMs, such as bioretention, infiltration trenches, dry and wet swales, rooftop disconnections, and wet and dry ponds, which are common practices in urban watersheds, also needs more attention. Analysis of the cost of adapting SCMs for CC to maintain the same performance as current climate conditions is also recommended for future research.

Integrated assessment modeling reveals near-channel management as cost-effective to improve water quality in agricultural watersheds

Despite decades of policy that strives to reduce nutrient and sediment export from agricultural fields, surface water quality in intensively managed agricultural landscapes remains highly degraded. Recent analyses show that current conservation efforts are not sufficient to reverse widespread water degradation in Midwestern agricultural systems. Intensifying row crop agriculture and increasing climate pressure require a more integrated approach to water quality management that addresses diverse sources of nutrients and sediment and off-field mitigation actions. We used multiobjective optimization analysis and integrated three biophysical models to evaluate the cost-effectiveness of alternative portfolios of watershed management practices at achieving nitrate and suspended sediment reduction goals in an agricultural basin of the Upper Midwestern United States. Integrating watershed-scale models enabled the inclusion of near-channel management alongside more typical field management and thus directly the comparison of cost-effectiveness across portfolios. The optimization analysis revealed that fluvial wetlands (i.e., wide, slow-flowing, vegetated water bodies within the riverine corridor) are the single-most cost-effective management action to reduce both nitrate and sediment loads and will be essential for meeting moderate to aggressive water quality targets. Although highly cost-effective, wetland construction was costly compared to other practices, and it was not selected in portfolios at low investment levels. Wetland performance was sensitive to placement, emphasizing the importance of watershed scale planning to realize potential benefits of wetland restorations. We conclude that extensive interagency cooperation and coordination at a watershed scale is required to achieve substantial, economically viable improvements in water quality under intensive row crop agricultural production.

Water Quality Trading Framework with Uncertainty for River Systems Due to Climate and Population Characteristics

Climate change and population growth serve as fundamental problems in assessing potential impacts on future surface water quality. In addition to uncertainties in climate depicted in various representative concentration pathway (RCP) scenarios, futuristic population growth mimicking historical conditions is subject to uncertainties related to changing development patterns. The combination of climate change and population characteristics exacerbates concerns regarding the future water quality performance of river systems. Previous studies have established linkages among future climate, population impacts and watershed water quality performance. However, these linkages have not been specifically incorporated into water quality trading programs. Rather than temporally-variant adjustment factors, WQT programs use constant margins of safety for pollutant reduction credits resulting in trade ratios that do not explicitly account for futuristic climate and population uncertainties. Hence, this study proposes a conceptual framework for water quality trading establishing adjustment factors as margins of safety on trade ratios for pollutant reduction credits examining climate and population characteristics separately followed by evaluating them combined. This new framework is demonstrated using a programming script that calculates the margins of safety based on simulation results conducted through a water quality model of the Jordan River in Salt Lake City, UT, USA over a 3-year timeframe. With margins of safety over magnitudes of ±2 over the Jordan River simulations, this research introduces the framework as a foundation for developing adjustment factors for addressing climatic and population characteristics upon river systems.

Impact of Agricultural Practices on Water Quality of Old Woman Creek Watershed, Ohio

The effect of agricultural practices on water quality of Old Woman Creek (OWC) watershed was evaluated in a hydrological model using the Parameter-elevation Regressions on Independent Slopes Model (PRISM) climate data and 20 different global circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). A hydrological model was set up in the Soil and Water Assessment Tool (SWAT), while calibration was done using a Multi-Objective Evolutionary Algorithm and Pareto Optimization with PRISM climate data. Validation was done using the measured data from the USGS gage station at Berlin Road in the OWC watershed and water quality data were obtained from the water quality lab, Heidelberg University. Land use scenario simulations were conducted by varying percentages of agricultural land from 20% to 40%, 53.5%, 65%, and 80% while adjusting the forest area. A total of 105 simulations was run for the period 2015–2017: one with PRISM data and 20 with CMIP5 model data for each of the five land use classes scenarios. Ten variables were analyzed, including flow, sediment, organic nitrogen, organic phosphorus, mineral phosphorus, chlorophyll a, CBOD, dissolved oxygen, total nitrogen, and total phosphorus. For all the variables of interest, the average of the 20 CMIP5 simulation results show good correlation with the PRISM results with an underestimation relative to the PRISM result. The underestimation was insignificant in organic nitrogen, organic phosphorus, total nitrogen, chlorophyll a, CBOD, and total phosphorus, but was significant in CMIP5 flow, sediment, mineral phosphorus, and dissolved oxygen. A weak negative correlation was observed between agricultural land percentages and flow, and between agricultural land percentages and sediment, while a strong positive correlation was observed between agricultural land use and the water quality variables. A large increase in farmland will produce a small decrease in flow and sediment transport with a large increase in nutrient transport, which would degrade the water quality of the OWC estuary with economic implications.

Effect of Projected Land Use and Climate Change on Water Quality of Old Woman Creek Watershed, Ohio

The separate and synergistic effects of land use and climate change on water quality variables in Old Woman Creek (OWC) watershed were evaluated using a hydrological model set up in Soil and Water Assessment Tool (SWAT) for the OWC watershed. Model calibration was done using a multi-objective evolutionary algorithm and pareto optimization. The Parameter-Elevation Regressions on Independent Slopes Model (PRISM) climate data and the 20 different Global Circulation Models (GCMs) developed by the Coupled Model Intercomparison Project Phase five (CMIP5) were used. Validation was done using the streamflow data from USGS gaging station and water quality data from the water quality lab, Heidelberg University. The simulation was divided into two land use scenarios: Scenario 1 for constant land use and Scenario 2 where land use was varied. Both land use simulations were run in four time periods to account for climate change: historical (1985–2014), current to near future (2018–2045), mid-century (2046–2075), and late-century (2076–2100) climate windows. For the historical period, the average of all the simulations made from the 20 different CMIP5 GCMs shows good agreement with the PRISM results for flow and the water quality variables of interest with smaller inter-model variability compared to PRISM results. For the other three climate windows, the results of Scenario 1 show an increase in flow and eight water quality variables (sediment (total suspended sediment), organic nitrogen, organic phosphorus (particulate p), mineral phosphorus (soluble reactive p), chlorophyll a, carbonaceous biochemical oxygen demand (CBOD), dissolved oxygen, total nitrogen) across the climate windows but a slight decrease in one water quality variable, mineral phosphorus in the mid-century. The results of Scenario 2 show a greater increase in flow, and the eight water quality variables across the climate windows show a relatively larger decrease in one water quality variable (mineral phosphorus). The projected land use change has little impact compared to the projected climate change on OWC watershed in the 21st century.

Teleconnection between climate oscillations and riverine nutrient dynamics in Southeast China based on wavelet analysis.

Nonpoint source (NPS) pollution is mainly driven by hydrological processes; climate oscillation can affect regional water cycle processes. However, the relationship between climate oscillation and NPS pollution is still unclear, which increases the difficulty of water quality prediction and management. In this study, Mann-Kendall test and wavelet transform were adopted to investigate the teleconnection between ENSO (El Niño-Southern Oscillation) phenomenon and riverine NPS load dynamics in an agricultural watershed of Southeast China from 2003 to 2016. Results showed that annual precipitation, streamflow, and riverine nutrient load increased significantly during the study period. The change point for long-term riverine TN load and TP load appeared in 2009 and 2007, respectively. Rainfall, streamflow, nutrient loads, and Niño 3.4 sea temperature (SST) shared a common periodicity of 10-16 months. The southern oscillation index (SOI) and Niño 3.4 SST shared a common periodicity of 28-36 months. Moreover, Niño 3.4 SST showed a positive correlation with riverine nutrient loads at a periodicity of 10-16 months, while SOI showed a weakly negative correlation with riverine nutrient loads at a periodicity of 28-36 months. These findings indicate that the increasing frequency of warm ENSO events would enhance the risk of nutrient export to rivers in Southeast China and more attention should be paid to large-scale climate oscillation in the prediction of agricultural nutrient pollution and management of water quality in agricultural watersheds.

Effects of land use configuration, seasonality and point source on water quality in a tropical watershed: A case study of the Johor River Basin.

Land use plays a significant role in determining the spatial patterns of water quality in the Johor River Basin (JRB), Malaysia. In the recent years, there have been several occurrences of pollution in these rivers, which has generated concerns over the long-term sustainability of the water resources in the JRB. Specifically, this water resource is a shared commodity between two states, namely, Johor state of Malaysia and Singapore, a neighbouring country adjacent to Malaysia. Prior to this study, few research on the influence of land use configuration on water quality have been conducted in Johor. In addition, it is also unclear how water quality varies under different seasonality in the presence of point sources. In this study, we investigated the influence of land use and point sources from wastewater treatment plants (WWTPs) on the water quality in the JRB. Two statistical techniques - Multivariate Linear Regression (MLR) and Redundancy Analysis (RA) were undertaken to analyse the relationships between river water quality and land use configuration, as well as point sources from WWTPs under different seasonality. Water samples were collected from 49 sites within the JRB from March to December in 2019. Results showed that influence from WWTPs on water quality was greater during the dry season and less significant during the wet season. In particular, point source was highly positively correlated with ammoniacal‑nitrogen (NH3-N). On the other hand, land use influence was greater than point source influence during the wet season. Residential and urban land use were important predictors for nutrients and organic matter (chemical oxygen demand); and forest land use were important sinks for heavy metals but a significant source of manganese.

Evaluation of Kalibomo watershed water quality using the storet method

The Kali Bomo watershed has a length of ± 7,417 km and passes through Rogojampi District, Banyuwangi Regency. Rogojampi sub-district consists of 10 villages, including Aliyan Village, Powder Village, Gitik Village, Gladak Village, Karangbendo Village, Kedaleman Village, Lemahbangdewo Village, and Mangir Village. The area of Rogojampi District is 102.25 km2 with a population of 94,268 people. There are 4 watersheds (DAS) in Rogojampi District, namely Binau, Tambong, Bomo and Lumbun which irrigate 11,819 hectares of rice fields and 1,113 hectares of land for corn cultivation. The main problem in watersheds in general is the occurrence of changes in land use due to development both upstream, middle and downstream as well as the conversion of forests into cultivated agricultural land. This has an impact on reduced water absorption function, increased erosion, sedimentation and river water quality. Based on the above conditions, it is very important to conduct water quality analysis, especially in the Kali Bomo watershed so that its sustainability can be maintained. The results of the water quality analysis using the STORET method show that the water quality of the Kali Bomo watershed in the 2017 period from January to April for class I, II, III and IV quality is poor, bad, moderate and moderate, respectively.

Analysis of time-space varying relationship between land use and water quality in a tropical watershed

Over the years, studies have been conducted to examine not only the relationship between land use and water pollution using ordinary least square (OLS) regression but also their spatially varying relationships using geographical weighted regression (GWR). However, the relationships between land use and water quality indicators may vary not only spatially but also over time. Therefore, this study was conducted to analyse the spatiotemporal variations in land use-water quality relations over time within a tropical watershed. To achieve this goal, land use data for 2006, 2010, and 2015 and the corresponding years of frequently sampled water quality data were utilised. The kriging interpolation technique was applied to estimate the unknown water quality values at 12 unmonitored sampling points using the measured values from the 9 monitored sites that were used for the regression analyses. Both OLS and GWR were applied using four groups of land use and seven water quality variables. The study found better performances of GWR models over OLS models throughout these investigation periods. The GWR results indicated that the ability of land use indicators to explain water quality change is not the same with time and space and neither the same among the different water quality parameters. For examples, in 2015, agricultural land most predicted the change in most water quality variables compared with its prediction proportion in 2010 and 2006, while urban land most predicted the change in most water quality variables in 2010 compared to other years. However, other groups of lands were more positively associated with most of the water pollutants compared to forest, agricultural, and urban areas. Therefore, this study suggests that control and management policies be adjusted to different periods and areas according to the time-space varying sources of pollution and good predictors of water quality. Although the approach used in this study tends to reveal the complex spatiotemporal relationships between land use and water quality over different time periods, it should be noted that this approach is more appropriate for comparative analysis to understand the implication of the land use chance pattern into surface water pollution

The effect of landscape complexity on water quality in mountainous urbanized watersheds: a case study in Chongqing, China

The most significant feature of the landscape of mountainous urbanized watersheds is complexity. The geomorphology, composition, and configuration have strong ties with river water quality. In this study, through redundancy analysis, we examined how landscape complexity measured at both landscape and class levels related to water quality within watersheds. The results indicate that water quality is closely associated with both the relief degree of the land surface and patch density at the landscape level. The river water quality of mountainous watersheds is better if the relief degree of the land surface is larger, though river water quality degradation is associated with higher fragmentation of the landscape. At the class level, a greater proportion of non-urban land use may contribute to better river water quality, as do better connectivity and moderate degrees of aggregation. Water quality is more likely to be degraded when the shape of residential land, public service, and commercial land is more complex. We conclude that, in mountainous urbanized watersheds, river water quality can be protected through land use planning and management by regulating a set of landscape metrics for complexity measures.

Impacts of soil erosion and forest quality on water quality in Samanalawewa watershed, Sri Lanka

Soil erosion is one of the serious environmental concerns in Sri Lanka which affects on water quality of watersheds. Forest quality is an important indicator of the healthiness of forests which often contribute to mitigate the adverse impacts resulting from watershed disturbances and to improve water quality in river watersheds. Thus, the prime aim of this study is to evaluate and map the rate of soil erosion and forest quality of the Samanalawewa watershed and to establish their relationship with water quality of the watershed. Soil erosion and forest quality of 12 sub-watersheds of Samanalawewa watershed were evaluated using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST), InVEST Sediment Delivery Ratio (SDR) and Carbon models developed by the NatCap-Project, Sanford University-USA and also using the Normalized Difference Vegetation Index (NDVI), respectively. Water quality parameters viz. temperature, pH, electrical conductivity, total dissolved solids, dissolved oxygen, biochemical oxygen demand, alkalinity, hardness, nitrate–N, phosphate-P were analyzed in monthly basis for water samples collected from 12 sampling locations (n = 12) in the sub-watersheds within month of May–July 2019. Pearson correlation was conducted to establish the relationships between water quality parameters and soil erosion and forest quality/NDVI of each sub-watershed. The results of the study indicated that the soil erosion of the watersheds ranges from 0 to 3555.7 t/ha/yr with an annual average of 139.9 t/ha/yr, which is ~ 28 times greater than the soil loss tolerance (T) in Sri Lanka. The average NDVI values (forest quality) of the sub-watersheds varied between − 0.2907 and 0.4628. All the water quality parameters in the study area were within the standards limits of SLS (614:2013). Estimation of vegetation cover of the study area using the InVEST Carbon model revealed that the above ground biomass is the dominant carbon storage among the other carbon pools. No significant correlation (p < 0.05) was found between the water quality parameters and the soil erosion rates in the watershed possibly attributed to the mitigation effects of the healthy forest cover within the study catchment. This was further confirmed by the significant negative correlation (r2 = 0.521, p = 0.008) established between the average NDVI values and nitrate–N levels of the river water of the catchment. The findings of the study provided the empirical evidence of the contribution of the healthy forest cover on the improvement of watershed water quality. The outcome of the research is useful for formulating watershed management policies and planning for watershed management

Response of non-point source pollution to landscape pattern: case study in mountain-rural region, China.

Landscape patterns have a substantial effect on non-point source (NPS) pollution in watersheds. Facilitating sustainable development of mountain-rural areas is a major priority for China. Knowledge of the impacts of various landscapes on water quality in these areas is critical to meeting environmental goals. This study applied the Soil and Water Assessment Tool (SWAT) to create a hydrologic and water quality model of the study watershed; then, the relationship between water quality and landscape patterns was investigated using multiple linear regression and redundancy analysis. The results show that the western sub-basins had higher nitrogen pollution loads, and the total nitrogen concentration reached a maximum value of 3.91 mg/L; the eastern sub-basins had a higher pollution load of phosphorous featured by maximum total phosphorous concentration of 2.15 mg/L. The water quality of the entire watershed in all scenarios tended to deteriorate over time. Landscape metrics accounted for 81.7% of the total variation in pollutant indicators. The percentage of forest landscape was negatively correlated with NPS pollution, while other types of landscape showed a positive correlation. The patch density, landscape shape index, and largest patch index of urban and agricultural lands were negatively correlated with pollutant concentrations. Upland landscapes contributed more pollutants than paddy fields. Some measures, e.g., returning grassland and farmland to forest in steep regions and replacing upland crops with paddy fields, were recommended for mitigating NPS pollution in the study watershed.

Water quality in Cidurian watershed, Indonesia

Studies about river water quality are essential since the decreasing of water quality could threaten hydrology watershed function. The objective of this study was to identify water quality in rainy and dry seasons of Cidurian watershed. Water quality data were obtained from Main River Basin Organization Territory Cidanau – Ciujung – Cidurian for 2018 and 2019. The parameters of water quality consist of total suspended solids (TSS), pH, dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), phosphate (PO4), nitrite (NO2 – N), electrical conductivity (EC), temperature, Ca, and Mg. Water sampling location were in Jasinga (upstream), Neglasari (middle stream), Rancasumur (middle stream), and Tanara (downstream). The result showed that TSS concentration showed higher in rainy season than dry season in all sampling points with values higher than river water quality standard 50 mg/L. Therefore, need attention to adopt soil conservation practices in mixed tree crops, dry cultivation land, and crop plantation to decrease soil erosion. Downstream had values of pH, DO, COD, and BOD outside of water quality standards. Accordingly, government should issue some policies to protect from decreasing water quality. The information on river water quality in Cidurian watershed could support better watershed management for sustainable hydrology watershed function.

Evaluation of Water Quality in the Lower Huallaga River Watershed using the Grey Clustering Analysis Method

Currently, the evaluation of water quality is a topic of global interest, due to its socio-cultural, environmental and economic importance, but in recent years this quality is deteriorating due to inadequate management in the conservation, disposal and use of water by the competent authorities, private-state entities and the population itself. An alternative to determine the quality of a water body in an integrated manner is the Grey Clustering Method, which was used in this study taking as an indicator the Prati Quality Index, with the objective of making an objective analysis of the quality of the water bodies under study. The case study is the Lower Watershed of the Huallaga River, located between the region of Loreto and San Martin, along which 12 monitoring stations were established to evaluate its surface water quality, through the analysis of 7 parameters: pH, BOD, COD, Total Suspended Solids (TSS), Ammonia Nitrogen, Substrates and Nitrates. Finally, it was determined that the water quality of eleven monitoring stations in the Lower Huallaga River Watershed are within the "Uncontaminated" category, while one monitoring station is within the "Highly Contaminated" category of the Prati Index, this due to its proximity to a landfill. The results obtained in this study, could be useful for the authorities responsible for the protection and sustainable conservation of the Huallaga River Watershed, in order to propose appropriate measures to improve its quality, additionally, this study could be a reference for future studies since the proposed method allowed to prioritize the quality level of the water bodies and identify critical areas.

Watershed Water Quality Management Plan Using SWAT and Load Duration Curve

Watershed Water Quality Management Plan Using SWAT and Load Duration Curve

Solid Waste Management in Urban and Rural Communities of Santa Cruz Watershed, Laguna, Philippines

Solid waste management (SWM) has become a continuing hurdle for governments and communities because of its multi-faceted nature. With the worsening SWM problem, the Philippines enacted Republic Act 9003, the Ecological Solid Waste Management (SWM) Act 2000, instituting SWM Program. Water quality in water bodies and watersheds is adversely affected by pollution, exacerbated by increasing population and urbanization. This study examined RA 9003 implementation in urban and rural communities of Santa Cruz Watershed (SCW) which drains into Laguna Lake. Knowledge, awareness, and perceptions (KAPs) of communities were elicited using focused group discussions, interviews, and surveys in barangays within the watershed. Municipalities have completed respective10- year SWM Plans, organized SWM Boards, and SWM committees in villages. Communities showed satisfaction with SWM implementation and monitoring but rural communities had higher overall SWM effectiveness ratings. Both communities were willing to pay for a cleaner environment. Challenges that hamper better implementation of RA 9003 include non-segregation of solid waste by residents attributed to lack of awareness and discipline; irregular garbage collection; inadequate garbage trucks; lack of functional materials recovery facilities; and limited government resources. Addressing these concerns will further boost RA 9003 compliance and enhance the effectiveness of implementation and monitoring in the communities.

Environmental and spatial factors affecting surface water quality in a Himalayan watershed, Central Nepal

Various spatial interrelationships among sampling stations are not well explored in the spatial modeling of water quality literature. This research explores the relationship between water quality and various social, demographic, and topographic factors in an urbanizing watershed of Nepal with a comparison of different connectivity matrices to conceptualize spatial interrelationships. We collected electrical conductivity and dissolved oxygen data from surface water bodies using a handheld probe and used the data to establish relationships with land use, topography, and population density-based explanatory variables at both watershed and 100-m buffer scales. The linear regression model was compared with different eigenvector-based spatial filtering models. These spatial filtering models were constructed using five different spatial conceptualizations based on different graph types generated from the geographic coordinates of the sampling sites. Population density, elevation, and percentage of sand in the watershed and riparian regions are most important in explaining dissolved oxygen concentration and electric conductivity. A human signature as population density and increased sand and gravel cover can be detected in this watershed impacting water quality. Among different graph types compared, the relative graph type provided the highest model strength signifying a stronger upstream-downstream relationship of dissolved oxygen, while k-nearest graph types with four neighbors provided the strongest model performance, indicating the impact of local factors on electrical conductivity. The relationships between socio-environmental factors and water quality and their spatial interrelationships identified in this work shed light on the source, mobilization, and transport of dissolved oxygen and electrical conductivity and can assist the water quality management endeavor.

Assessing land use change impact on stream discharge and stream water quality in an agricultural watershed

Land use and land cover (LULC) change impacts on hydrology and water quality are of critical importance in regions where water quality is degraded. One such location is the Mississippi Delta in the United States, where widespread agriculture across the landscape is a major contributing source to sediment- and nutrient-heavy runoff. To address how the landscape has changed in the recent past and consider how it may continue to change in the future, we analyzed the temporal and spatial variability of the LULC changes (e.g. forest, cropland, corn and soybean) in the Big Sunflower River Watershed. We applied these LULC changes in the Soil and Water Assessment Tool (SWAT) model to demonstrate the impacts on stream discharge, total suspended sediments (TSS) concentrations, total nitrogen (TN), and total phosphorus (TP) yields. Model performance was considered satisfactory to good (R2 = 0.46–0.88, NSE = 0.34–0.64) for all simulated water quantity and water quality parameters. TSS concentrations increased 1.9%, while TN and TP yields increased by 12.7%, and 10.2%, respectively as the area of the cropland increased. Stream discharge was unchanged. Moreover, TN yield increased as the percentage of land occupied by cornfields increased while TP yield increased as the percentage of land occupied by soybean increased, due to differences in crop management practices such as fertilization and tillage.