Watershed Management Strategies Research Articles

Watershed Management for Sustainable Livelihoods: Integrating Local Pond Ecosystems in Malda, West Bengal

This research article explores the intricate relationship between watershed management, local pond ecosystems, and sustainable livelihoods in the Malda district of West Bengal. The study investigates the potential of integrating local pond ecosystems into watershed management strategies as a means to enhance economic prosperity, ecological resilience, and community well-being. Through a multidisciplinary approach, combining ecological assessments, socioeconomic surveys, and participatory engagement, the research aims to provide insights into the synergies that exist between watershed management practices and the sustainable livelihoods of the local villagers. The research methodology involves field studies encompassing hydrological analysis, biodiversity assessments, and community consultations, aimed at understanding the dynamics of local pond ecosystems and their interconnectedness with the broader watershed. Special attention is given to the diverse ecosystem services provided by these ponds, such as water provisioning, nutrient cycling, and supporting aquatic biodiversity, and how they contribute to the overall resilience of the watershed. The findings of this study are expected to contribute valuable information for policymakers, environmental practitioners, and local communities in Malda district, offering a comprehensive understanding of how the integration of local pond ecosystems into watershed management plans can foster sustainable livelihoods. The article discusses potential strategies for optimizing the co-management of these resources, balancing the ecological health of the ponds with the socioeconomic needs of the local population. Ultimately, this research aims to provide a blueprint for sustainable watershed management practices that prioritize the conservation and utilization of local pond ecosystems, fostering a harmonious balance between ecological integrity and the livelihood aspirations of the communities in Malda, West Bengal.

Accelerated export and transportation of heavy metals in watersheds under high geological backgrounds

The geological background level of metals plays a major role in mineral distribution and watershed diffuse heavy metal (HM) pollution. In this study, field research and a distributed hydrological model were used to analyze the distribution, sources, and pollution risk of watershed HMs in sediments with high geological HM backgrounds. Study showed that the mineral distribution and landcover promoted the transport differences of watershed HMs from upstream to the estuary. And the main sources of Co, Ni, and V in the estuarine sediments were natural sources. Sources of Pb and Zn were dominated by anthropogenic sources, accounting for 76% and 64% of their respective totals. The overall ecological risk of anthropogenically sourced HMs was dominated by Pb (46.6%), while the contributions of Co and Ni were also relatively high, accounting for 35.70% and 33.40%. Moreover, redundancy analysis showed that HM variations in the sediments were most sensitive to soil erosion and mineralizing rock distribution. The spatial patterns of watershed HMs from natural sources were significantly influenced by P loading, precipitation, and forest distribution. This combination of experiments and model improves the understanding of watershed HM variation and provides a new perspective for formulating effective watershed HM management strategies.

Watershed management in Ethiopia and its effects on soil quality and productivity

Indigenous peoples have utilized watershed management techniques for ages. It has substantial ramifications for improved productivity and improved soil management. This essay examined Ethiopia’s soil quality and production improvements as they relate to watershed management strategies. In particular, the roles of the government and other partners who started soil and water conservation initiatives are described. These initiatives had unsatisfactory or unsuccessful results because the community was not involved, the land was held insecurely, there were disincentives, and the planning units were too large. Ethiopia’s Federal Democratic Republic has copied community-based participatory watershed management. It has had a great impact on the restoration of highly damaged areas and provided local populations with a source of income. For instance, Amhara, the Oromia, and Tigray Regional States’ well-managed watersheds of the Abraha Atsbaha, Gerebshelela, Bechyti, Goho Cheri, Kereba, and Bedesa Kela rivers have boosted agricultural incomes and food security. Additionally, the environmental soundness, commercial feasibility, and social acceptability of watershed management must be assessed.

Evolving environmental awareness and shifts in management priorities: a socioeconomic lens on the min river basin, China

Watersheds have experienced economic and demographic development for decades. In China, this development has been associated with environmental degradation, including water quality deterioration, abnormal stream flow, and biotic resource depletion. Effective watershed management incorporates sustainability and public involvement, enabling the long-term security of the human and natural world. Management strategies however need to take into account local conditions, as every watershed is unique. This paper adopts the analytic hierarchy process (AHP) combined with the random forest model to investigate the shift in participants’ environmental awareness across different socioeconomic groups over the past 15 years. Additionally, it scrutinizes the changing public perceptions on the management priorities and areas requiring enhancement. The AHP index highlighted the importance of environmental behavioral intentions (EBI) as a component of environmental awareness (EA). Between 2006 and 2021, significant changes occurred in public environmental awareness (perception, knowledge, behavioral intention) and perceived management priorities, stressing the need for timely adjustment of management policies. Notably, environmental concern (EC) appears to have decreased over time, reflecting effective management and increased governmental attention. Emphasis on the recreational ecosystem services offered by watershed forests has increased. Males, individuals aged over 40-years-old, and individuals located in the upper reaches possessed higher risk perceptions than other groups. These findings may help policymakers to adjust management priorities based on geographic region and may assist them in promoting more effective measures to communicate watershed sustainable management goals and strategies to the public.

Effect of Land Use on Stream Water Quality and Biological Conditions in Multi-Scale Watersheds

Understanding the relation between watershed land use and stream conditions is critical for watershed planning and management. This study investigated the effects of land use on stream water quality and biological conditions in sub-watersheds and micro-watersheds across the Han River watershed in South Korea. We developed random forest models for each water quality and biological indicator using the proportions of urban, agricultural, and forested areas. Our results indicate that water quality and biological indicators were significantly affected by forest area at both scales, and the sub-watershed models performed better than the micro-watershed models. Accumulated local effects were used to interpret the effect of each explanatory variable on the response variable. The plots for water quality and biological indicators with proportions of watershed land use demonstrated similar patterns at both scales, although the relation between land use and stream conditions was slightly more sensitive in micro-watersheds than in sub-watersheds. Urban and agricultural areas showed a lower proportion of water quality and biological condition variability in the micro-watersheds than in the sub-watersheds, while forests showed the opposite results. The findings of this study suggest that different spatial scales should be considered when developing effective watershed management strategies to maintain stream ecosystems.

Simulation of sediment yield and evaluation of best management practices in Azuari watershed, Upper Blue Nile Basin

Abstract This study was conducted to simulate the sediment yield and evaluate best management practices (BMPs) for sediment control in the Azuari watershed, Upper Blue Nile basin, Ethiopia using the Soil and Water Assessment Tool (SWAT) model. As inputs for the model, 30 years (1991–2020) of daily values of meteorological data were used. For model simulation, daily stream flow and sediment data were collected for the periods from 1988 to 2012. The study area was delineated into 19 subwatersheds and the sediment yield was estimated in each subwatershed using the modified universal soil loss equation. The average simulated sediment yield in the watershed was found to be 10.81 t/ha/yr. Six subwatersheds were identified to have high to severe sediment yields and are considered hotspot areas which require prior mitigation measures to control sediment. Four soil and conservation measures were evaluated in SWAT as BMPs namely filter strip, terracing, strip cropping, and contouring. Filter strip was found to reduce sediment by 35.61%, terracing by 20.44%, strip cropping by 44.12%, and contouring by 43.6%. Thus, the implementation of strip cropping resulted in maximum sediment yield reduction. The findings of the study would help to make informed decisions on best watershed management strategies.

The role of integrated watershed management in climate change adaptation for small-scale farmers in Southwest Ethiopia

Climate change severely affects smallholder farmers in developing countries such as Ethiopia. To overcome the impacts, the government of Ethiopia has been undertaking a massive adaptation programs including integrated watershed management practices. However, there is a limited understanding of climate change, adaptation strategies, and the effect and acceptance of the implemented techniques. The objective of this study was to assess climate variability, farmers’ climate change adaptation strategies, and the role of watershed management in climate change adaptation. A multi-stage sampling technique was used to select 255 household heads from three rural kebeles (lowest administrative unit of government) in high, mid, and low-elevation areas. The household survey, focus group discussion, and key informant interview record were used to collect data. In addition, long term meteorology record was used. Data were analyzed using descriptive statistics and a multinomial logit model. The results showed that more than 80% of the farmers, in each elevation, perceived climate variability such as increasing temperature and rainfall fluctuations. The perceived variability is more pronounced in the low-elevation areas. The meteorology record also showed fluctuation in rainfall. About 90% of respondents in each elevation area perceived population pressure, cultivation, and deforestation as the major causes of climate variability. About 90% of respondents perceived crop yield decline due to climate variability. In drought years, crop yield and livestock production decline by ∼50% compared to the average year. Adjustment of crop planting time, crop diversification, selling household assets, participating in off-farm activities, and using government aid were practiced as climate change adaptation measures. About 70% of farmers perceived the positive role of watershed management in climate change adaptation. On average, 36–43% of the farmers in the study area participated in watershed management activities such as the construction of bunds and tree planting, which assist in coping with climate variability impacts. Farm size, sex, education, and farming experience positively and significantly affect the adaptation practices of the farmers. Policymakers and practitioners need to consider the issues related to climate variability and watershed management as a strategy for climate change adaptation. Policy intervention by the Federal government on sustainable watershed management and rural livelihood strategies could assist in sustainable environmental management and climate change adaptation.

Spatial and Temporal Variations of Land Use and Land Cover In Kadiri Watershed Using Rs & Gis Techniques

The change detection and land use and land cover (LULC) maps are more important powerful forces behind numerous ecological systems and fallow land. It is widely known that land use/land cover (LULC) changes significantly alter watershed hydrology and sediment yields. The impact, especially on erosion and sedimentation, is likely to be exacerbated in regions dominated by high rainfall patterns such as monsoons. RS & GIS technologies are very useful to determine the LULC changes. Present research area Kadiri Watershed of Anantapur district of Andhra Pradesh, India, drains an area about 240 km2 including 15 villages. The average annual rainfall in this area varies between 600mm to 700mm in which 60%, 35% and 5% of total rainfall occurs in South-West (S-W),North-East (N-E) and in Summer seasons respectively. The current research focuses on demarcating the spatiotemporal LULC changes. These effects directly affect the ecosystem, land resources, cropping pattern and agriculture. LULC assessment and surveillance are essential for long-term planning and sustainable use of natural resources. The LULC maps were prepared for the study area using Landsat-5, Senthinel 2 images pertaining to pre-monsoon and post-monsoon seasons of 2013, 2017 and 2021. Variations in the extents of agriculture, plantations, scrubs, water bodies, open lands, and built-up areas were noted during these years in the pre-monsoon season, and they ranged from 22 to 35 and 43%, 2 to 3 and 5%, 22 to 28%, 1 to 4%, 52 to 29 and 15%, as well as 1 to 5%, respectively. Similar fluctuations were seen in the post-monsoon season, where they ranged from 29 to 40 and 47%, 3 to 7%, 33 to 30%, 2 to 4%, 32 to 20 and 7%, as well as 1 to 5%. Kadiri watershed, an agriculturally dominant area, has seen an increase in cultivated land due to the conversion of fallow land and open scrub into cropland as a result of good rainfall received during the south-west monsoon during in assessment years and implementation of watershed development activities. These findings highlight the potential impacts of LULC changes in a monsoon-dominated watershed and may contribute to the development of successful LULC-based watershed management strategies for prevention of flooding and sediment loss.

Biomonitoring for Watershed Protection from a Multiscale Land-Use Perspective

The types and intensification of land use in the watershed affect the living organisms in aquatic ecosystems differently; this impact will also vary according to temporal and spatial scales. Understanding these interactions is crucial in the design of biomonitoring programs to detect the effect of different pollutants in freshwater ecosystems and improve watershed management and conservation strategies. Therefore, this paper qualitatively reviews biomonitoring studies in freshwater ecosystems to evaluate the impact of different land use types on multiple scales in watersheds. The paper is organized into four sections. The first section presents biomonitoring in different freshwater systems (streams, rivers, lakes, and reservoirs). In the second section, we describe the biomonitoring characteristics of the main land use types. In the third section, we explain how spatial and temporal scales affect biomonitoring. Finally, in the fourth section, we focus on biomonitoring planning and future prediction and discuss how to design biomonitoring programs and how to use models and eDNA in biomonitoring. Our review will assist in decision-making regarding biomonitoring programs in watersheds and will guide future studies on the different bioindicators for various land use types in diverse ecosystems worldwide.

Identification of Watershed Conditions and Formulation of Watershed Management Strategies

In Indonesia, 39 watersheds were deemed essential in 1994, and the importance of watersheds grew in 2000. The existence of a watershed has the role of being able to sustain water availability, maintain the balance of the ecosystem and as a container for flowing water. The Musi-Sugihan-Banyuasin-Lemau River Area (WS MSBL), which has an area of 86680 km2 and is made up of 23 primary watersheds, is one of the largest watersheds in the Sumatra region. Research was done to determine the state of the watershed so that a strategy for watershed conservation could be chosen. In-depth interviews with stakeholders in the form of focus group discussions (FGD) were utilized as the study method to collect both secondary and primary data about the circumstances of the watershed as well as to gain in-depth management outcomes. The study's findings demonstrate that managing the WS MSBL watershed involves more than only technical issues; it also necessitates involving associated institutions and stakeholders, necessitating the creation of operational watershed management strategies.

MODELLING THE IMPACTS OF SELECTED WATERSHED MANAGEMENT STRATEGIES ON SEDIMENT REDUCTION UPSTREAM OF SHIRORO DAM, NIGERIA

This research utilized a regulated hydrological model, Soil and Water Assessment Tool (SWAT) interfaced with Geographical Information System (GIS), in studying the effectiveness of the chosen watershed management strategies on sediment reduction upstream of Shiroro dam, Nigeria. Selected management approaches were modelled while calibration and validation of the model were achieved using observed streamflow data. Findings indicated a good correlation during calibration and validation period. Application of reforestation, vegetative filter strips and stone bunds in the watershed reduces sediment production by 27 %, 39 %, and 15 % respectively. Thus, the sediment management scenarios depicted within this research are considerably sustainable and effective.

Identification of groundwater potential zones in the Rabigh-Yanbu area on the western coast of Saudi Arabia using remote sensing (RS) and geographic information system (GIS)

The groundwater potential zones in the Rapigh-Yanbu area, on the west coast of Saudi Arabia, were evaluated using remote sensing and geographic information system data leading to the establishment of major watershed development and management strategies. Many factors, including slope, drainage density, land use, geology, lineament density, elevation, yearly precipitation, and soil type distribution, affect the hydrogeological characteristics of coastal aquifers. The Rabigh-Yanbu coastline groundwater potential zones were located and mapped using these characteristics. The annual precipitation rate is categorized into 2–28 mm, 29–52 mm, 53–76 mm,77–107 mm, and 108–164 mm within the study area. The highest elevation was ordered with the lowest rank of 1, while the lowest elevation was given the highest rank of 5. Slopes of 0°–9° were present in the majority of the study region, while slopes of 9°–63° were present in the northwest. Based on the slope, the research area was separated into five classes; 0-3o; 4-9o; 10–16o; 17–25o; 26–63o. Based on the drainage density map; 0–0.36 km2, 0.37–0.53 km2, 0.54–0.73 km2, 0.74–1.32 km2, 1.33–3.31 km2. The majority of the fractures trended NE–SW and NW–SE. A map of lineament density was made using the line density method. This map makes it obvious that the region was divided into five classes; 0–0.02 km2, 0.03–0.08 km2, 0.09–0.13 km2, 0.14–0.2 km2, and 0.21–0.34 km2. The classification of soil types in the study region into four classes such as clay loam, clay, sandy clay, and loam. Accordingly, the clay soil was ranked 1, while the loam soil was given the highest rank of 4. The Precambrian rocks had low groundwater potential because of their reduced porosity and were ranked 1, while Quaternary deposits had a high porosity and good groundwater potential and were given a high rank of 3. According to the likelihood of groundwater supply, the area is divided into four categories: very good, good, moderate, and poor. The area with very good groundwater potential covered 1,384 km2, while the area with good groundwater potential covered 30,498 km2, according to the findings. The study area had 34,412 km2 of somewhat appropriate land for groundwater development. In contrast, 1,734 km2 of the study area is scarce. The best zones featured the lowest slopes, the least number of lineaments, and the most drainage. The lineaments, which serve as the main conduits for groundwater flow and storage, have significant levels of groundwater recharge capacity in the study area. Managing groundwater according to these identified potential zones will maximize their benefits and increase the groundwater yield. This will help in creating new agricultural, urban, and industrial communities in this strategic area and contribute toward achieving the goals of Saudi Vision 2030.

ANALYSIS OF WATER QUALITY AND QUALITY STATUS IN ACEH RIVERS BASED ON ENVIRONMENTAL POLLUTION INDEX

The rapid development of industrialization and urbanization in the world impact increased water pollution. Human activities, such as dam constructions, excessive water consumption, severance of river flows, compaction of riverbanks, and excessive use of riverbed vegetation, disrupt river flow and alter the original hydrological cycle. In response to these conditions, this study aims to analyze water quality and river quality status to set up a watershed environmental management strategy in Aceh Province as a case study. River water quality was analyzed descriptively by comparing the results of laboratory tests with parameters, namely TSS, pH, BOD, COD, DO, total phosphate, nitrate, and fecal coli. These parameters were then transformed into the environmental index (Water Quality Index and Pollution Index). It was found that Water Quality Index (WQI) results are shown from 50 to 70. WQI with the Good category is at Kr. Weh which is in the Central Aceh city. The medium-less type is found in 10 watersheds. The water quality with the category of Less is found at 3 points, namely Kr. Aceh, Cr. Doy, and Cr. Daroy. The quality of the river water in the Aceh region, from upstream to downstream, has decreased in quality with a lightly polluted status based on the Minister of Environment and Forestry of the Republic of Indonesia No. 27 of 2021 for class II.

Landscape dependency of land-based salmon farming under climate change

The success of Chilean salmon farming’s early cultivation stages is largely facilitated by access to high-quality water, which is provisioned by watersheds dominated by native forests and defined by high precipitation levels. In recent decades, human activities have increasingly affected both attributes. This study analyzed the risk of climate change in 123 watersheds that supply water to land-based salmon farms in south-central Chile (36.5−43°S). The risk was calculated based on exposure (fingerling and smolt production), sensitivity (land cover maps for three time periods), and hazard indicators (four climate change indicators). The results show a disturbing reality: under a high emissions scenario (RCP 8.5), more than 50% of the current fingerling and smolts production would be located in high or very high-risk areas. These projections are the result of both a drier and warmer climate as well as the continued processes of deforestation and fragmentation of native forests, a spatio-temporal combination which could limit the availability and quality of the water needed for optimal aquaculture production. The risk analysis suggests that landscape configuration may be a potential alternative to mitigate the consequences of climate change on Chilean salmon farming. This is particularly important in areas such as south-central Chile, where the current watershed management and/or conservation strategies do not ensure landscapes resilient to projected hydroclimatic changes.

Long-term trends of streamflow, sediment load and nutrient fluxes from the Mississippi River Basin: Impacts of climate change and human activities

Under the influences of global climate change and intense human activities, the hydrological and biogeochemical processes have been undergoing profound changes in most of the world's watersheds. However, the long-term changes in streamflow, sediment load, and nutrient fluxes, and quantitative attribution of these changes from a basin-wide perspective are incompletely understood. Here we examined the trends of streamflow, sediment load, and total nitrogen (TN), total phosphorus (TP), and dissolved inorganic carbon (DIC) fluxes in the Mississippi River Basin (MRB) and its four major tributary basins during the 1930s-2010s, and major causes for streamflow, sediment load and nutrient fluxes changes were quantified. The streamflow increased significantly (p < 0.05) in the entire basin except for the Arkansas River Basin, while the sediment load significantly decreased except in the Arkansas River Basin and Upper MRB. Generally, the TN flux reduced except for an increasing trend in the Upper MRB. While the TP flux rose except for a decrease in the Ohio River Basin, and the DIC flux increased significantly. The strength of the relationship between nutrient flux and streamflow/sediment load showed four binary patterns, and in general the nutrient fluxes were more strongly correlated with streamflow compared to sediment load. Over the past 80 years, the increasing precipitation in the MRB has made the most contribution (67 % on average) to the river discharge increase, whereas human activities contribute the most (>58 %) to the changes in the sediment load and nutrient fluxes. The sediment yield coefficient decreased linearly with the increasing impermeable area proportion, river revetment length, and dam storage capacity (p < 0.05) in the MRB. The decrease in TN flux probably resulted from sedimentation and denitrification in reservoirs and wetlands, and increases in farm fertilizer and manure use were the two main factors contributing to the increased TP flux. In addition, the agricultural practices, increased precipitation, and raised temperature jointly led to an increase in the DIC flux. This study provides quantitative results of water–sediment-nutrient variations in the entire watershed system, which facilitates development of watershed management strategies.

Effects of Dynamic Land Use/Land Cover Change on Flow and Sediment Yield in a Monsoon-Dominated Tropical Watershed

It is widely known that land use/land cover (LULC) changes significantly alter watershed hydrology and sediment yields. The impact, especially on erosion and sedimentation, is likely to be exacerbated in regions dominated by high rainfall patterns such as monsoons. This study analyzed the hydrological responses of LULC changes in terms of streamflow (SF) and sediment yield (SY) in a monsoon-dominated tropical watershed, the Periyar River Watershed (PRW) in Kerala, India. This watershed drains an area of 4793 km2 characterized by an average monsoon rainfall of 2900 mm from June to November. The watershed hydrology and sediment dynamics were simulated using the Soil and Water Assessment Tool (SWAT) model for the impact assessment at the watershed outlet and the sub-watershed level. Historical LULC data were analyzed for 1988, 1992, 2002, and 2016 using the maximum likelihood method, and future LULC changes were projected for 2030, 2050, 2075, and 2100 using the Markov chain–cellular automata technique. Between 1988 and 2016, the urban area increased by 4.13 percent, while plantation and forest coverage decreased by 1.5 percent. At this rate, by 2100, the urban area is expected to grow by 16.45% while plantations and forest area will shrink by 13.7% compared to 1988. The effects of these changes on SF and SY were found to be minimal at the watershed outlet; however, at the spatial scale of sub-watersheds, the changes varied up to 70% for surface runoff and 200% for SY. These findings highlight the potential impacts of LULC changes in a monsoon-dominated watershed and may contribute to the development of successful LULC-based watershed management strategies for prevention of flooding and sediment loss.

Dam construction reshapes sedimentary pollutant distribution along the Yangtze river by regulating sediment composition

Dam construction has far-reaching impacts on pollutant accumulation and the pollutant-induced quality of aquatic environments. Nonetheless, its large-scale effects on pollutant distribution in sediments, which greatly contribute to the environmental impacts of coexisting pollutants, remain poorly understood. We collected sediments from the Yangtze River during the dry and normal seasons (with ‘normal’ defined in terms of precipitation level), and examined how dam construction alters the spatial trajectories of both inorganic and organic pollutants in the sediments. Sediment composition exhibited linear variation from the upper to the lower reaches, with clay and silt particles dominating the sediment in the Three Gorges Reservoir and sand particles dominating in the middle–lower reaches. Accordingly, upstream of the Three Gorges Dam (TGD), sedimentary carbon, nitrogen, phosphorus, heavy metal, polycyclic aromatic hydrocarbons (PAHs), and oxygenated PAHs (OPAHs) contents increased toward the TGD owing to its regulation of the spatial variation in sediment particle size. The TGD caused upstream sedimentary accumulation of pollutants to be higher nearer to the TGD than in the upper reaches by 17%–129% for carbon, nitrogen, and phosphorus, 7%–51% for heavy metals, 30% for PAHs, and 140% for OPAHs. Pollutant content was sharply lower below the TGD, by 0.58–11.15 times for carbon, nitrogen, and phosphorus, 0.1–2.6 times for heavy metals, 1.7 times for PAHs, and 5.6 times for OPAHs. Upstream of the TGD, levels of NH4+-N, the main form of N in the interstitial water of the Yangtze River, increased lineary toward the TGD, whereas those of NO3−-N and NO2−-N decreased. Sedimentary organic matter source contributions were consistent along the Yangtze River, being on an average 46% for C3 plants and 28% for soil organic substances, further confirming the dam's regulatory effect on pollutants. These findings provide a foundation for future assessments of the environmental impact of dam-induced river fragmentation and hydrological alterations, and for developing advanced watershed pollutant management strategies.

Quantify soil erosion and sediment export in response to land use/cover change in the Suha watershed, northwestern highlands of Ethiopia: implications for watershed management

Soil erosion accelerated by human activities is a critical challenge affecting soil health, agricultural productivity, food security and environmental sustainability in the highlands of Ethiopia. The aim of this study was to examine the dynamics of soil loss and sediment yield potential, and identify soil erosion hotspots using RUSLE with GIS in the Suha watershed, north western highlands of Ethiopia. Digital Elevation Model, LU/LC, rainfall, soil, and conservation practice were used as input data for RUSLE model. The estimated total annual soil loss for the entire watershed increased from 1.22 million tons in 1985 to 2.43 million tons in 2019, with average annual soil loss rates of 15.2 t ha−1 yr−1 and 31.4 t ha−1 yr−1 respectively. Total sediment yield also increased from 317.52 to 630.85 thousand tons over the past 35 years. In addition, the area of soil erosion hotspots changed from 15.2% (12,708 ha) to 32% (25,660 ha) during the same periods. Sub watershed 1, 2, 15, 17, 18, and 23 are severely degraded parts of the watershed. Expansion of agriculture and bare land as the expenses of other land use types over the past 35 years could be the major causes of extensive soil erosion risk in the watershed. Besides its temporal variability, soil loss and sediment export also showed variation between land use/cover classes. The estimated results of soil loss and sediment yield as well as soil erosion hotspots revealed that the soil erosion risk is progressively increasing during the study periods. Unless action is taken and the current condition is reversed, it will critically threat the livelihoods of the community in the watershed. Generally, the results underscore urgent demand for integrated and effective watershed management strategies.

Spatiotemporal differences in riverine nitrogen and phosphorus fluxes and associated drivers across China from 1980 to 2018

Increases in nutrient loadings to waterways over the past four decades have led to widespread eutrophication and water quality impairments across China. Understanding the spatial, interannual and long-term variations in nutrient loadings and associated drivers at the national scale is crucial for developing effective nutrient reduction strategies. However, the controls on, and spatiotemporal variations in, nutrient fluxes remain a problem from both an academic and management perspective. This study provides spatially extensive and temporally contiguous estimates of changes in riverine total nitrogen (TN), ammonia nitrogen (NH3–N) and total phosphorus (TP) fluxes for continental area of China based on machine learning stack models and empirical modeling over the period from 1980 to 2018. Results reveal considerable spatial, interannual and long-term variability in annual TN, NH3–N and TP fluxes, with spatial variations in average TN and NH3–N fluxes primarily driven by net anthropogenic nitrogen inputs. Interannual variability is dominated by precipitation across continental areas of China. Spatial variability in the estimated average annual TP flux in the undeveloped western and the developed middle east regions of China are primarily controlled by net anthropogenic phosphorus inputs and precipitation, respectively. We found that TN, NH3–N and TP fluxes increased from 1980 to 2018 in watersheds in East China; the national mean annual TN, NH3–N and TP fluxes increased before 2015 and decreased after 2015. This study illustrates the important role of precipitation and temperature variability in controlling the spatial, interannual and long-term variability of nutrient fluxes, and indicates that the influence of the meteorological conditions on annual loadings is needed when designing watershed nutrient reduction or management strategies.

Comparison of multi-objective evolutionary algorithms applied to watershed management problem

Simulation-based optimization (S–O) frameworks are effective in developing cost-effective watershed management strategies, where optimization algorithms have substantial effect on the quality of strategies. Despite the development and improvement of multi-objective evolutionary algorithms (MOEAs) provide more robust alternatives for optimization, they typically have limited applications in real-world decision contexts. In this study, three advanced MOEAs, including NSGA-II, MOEA/D and NSGA-III, were introduced into the S–O framework and applied to a real-world watershed management problem, and their performance and characteristics were quantified through performance metrics. Results show that a higher crossover or mutation probability do not necessarily promote convergence and diversity of solutions, while a larger generation and population size is helpful for MOEAs to find high-quality solutions. Compared to the other two MOEAs, NSGA-II consistently exhibits robust performance in finding solutions with good convergence and high diversity, and provides more options at the same computational cost, while the degenerate Pareto front of the proposed watershed management problem may account for the poor performance of MOEA/D and NSGA-III in terms of diversity. For a 10% TN or TP reduction target, the average cost of the NSGA-II optimized strategies is 32.22% or 47.83% of the commonly used strategies. In addition, this study also discussed the development of resilient watershed management to buffer the impacts of climate change on aquatic system, the incorporation of fuzzy programming into the S–O framework to develop robust watershed management strategies under uncertainty, and the application of machine learning-based surrogate models to reduce computational cost of the S–O framework. These results can contribute to the understanding of MOEAs and provide useful guidance to decision makers.