Critical Source Areas Research Articles

A novel framework reveals anthropogenic stressors of phosphorus polluted river-lake connection water system in Poyang lake basin of China

Poyang lake (PYL), as China's largest freshwater lake, has been suffering from increasing total phosphorus (TP) pollution associated with rapid basinal socio-economic development. However, anthropogenic phosphorus stressors were rarely examined in PYL basin due to its large-scale and complex river-lake connection water system, hampering phosphorus pollution control efforts. In this study, water pollution stress from multiple anthropogenic activities is quantitatively examined in PYL basin based on a newly developed framework coupling grey water footprint (GWF) analysis with the SPARROW model. Results show that the phosphorus source-sink process in PYL basin has been well simulated by SPARROW model quantifying an overall TP delivery rate of 0.39, with catchments closer to PYL showing higher delivery rate of phosphorus (up to over 0.8). The GWF analysis demonstrates that anthropogenic phosphorus sources have imposed much higher pollution stress on PYL than its inflowing rivers, with twelve catchments nearby PYL identified as critical source areas of TP contamination. Agricultural farming, livestock & poultry production, and urban household are recognized as the dominant anthropogenic stressors burdening water environment of PYL. Based on these, policy recommendations are provided for advancing control of the phosphorus pollution stressors. The methodology is effective in refined examination of water pollution sources, which is expected to be applied in other watersheds providing informative diagnosis of water issues especially in lakes.

Evaluation of Minnesota Phosphorus Loss Index performance.

Supported by the National Phosphorus (P) Research Project led by Dr. Andrew Sharpley, Minnesota developed its statewide P-Index, the Minnesota P Loss Index (MNPI), to manage critical source areas of agricultural P. The MNPI has remained unchanged since its last revision in 2006. The overall goal of this study was to critically evaluate the MNPI to determine, in the parlance of Sharpley, if the MNPI remains "directionally and magnitudinally correct." Observed P loss from 67 site-years of annual edge-of-field data was compared with MNPI-predicted P loss. Our assessment indicates that MNPI performance is directionally correct: it correctly ranks fields that are more at risk than others. The MNPI performed better in years with high-intensity rainfall events. Averaging MNPI assessment across multiple years of data input, along with minor adjustments to the calculation algorithm, improved the robustness of MNPI estimates. Continued re-evaluation of the MNPI will ensure that this important tool for nutrient management is properly evaluating P loss potential. This study reflects Dr. Sharpley's decades-long effort to improve and revise P indices so that they reflect advances in the science and management of agricultural P.

Innovative approach for assessing nitrogen loss risk to surface waters from crop production in a watershed scale through nitrogen surplus index method

Although various measures are applied to control farmland nitrogen loss at the field scale, effective control strategies at the watershed scale are still lacking due to poor understanding of nitrogen loss risks across different scales. Therefore, an innovative approach to assess the risk of nitrogen loss to surface waters from crop production at the watershed scale was established, with nitrogen surplus, a more accurate indicator, as a major source factor introduced to the traditional index method. Furthermore, this approach was applied in the Baiyangdian Lake Watershed, a typically agricultural-dominated watershed in China, and the control strategies for farmland nitrogen loss reduction were investigated with scenario analysis. The major results included: (1) Areas with high (2–4 for risk to river, 1.6–3.2 for risk to lake) and very high (>4 for risk to river, >3.2 for risk to lake) risks of nitrogen loss in crop production were relatively small. For example, in the wheat-maize rotation system, these areas accounted for only 2.1–3.5 % and 0.9–1.8% of the total study area, respectively. Additionally, the critical source areas of nitrogen loss were concentrated around the receiving water bodies. (2) The nitrogen surplus in wheat season increased the nitrogen loss to surface waters. Compared to the maize season, the area with high and very high risk for nitrogen loss to the nearby river in wheat-maize rotation system increased by 58.3% and 141.4%. Furthermore, the areas with high and very high risk for nitrogen loss to the lake in wheat-maize rotation system were 129.6% and 220.6% more than that during maize season. (3) Nitrogen loss risk to the nearby rivers was correlated with nitrogen surplus, but nitrogen loss risk to the lake was related to the transport coefficient. (4) The optimized scenario for nitrogen loss reduction in crop production was the combination of nitrogen surplus being less than 20 kg/ha and 500 m banning area around the river with no fertilizer application, which reduced the nitrogen loss risk to the nearby river and to the lake by 94–95% and 89–95%. The results of this study provide a scientific basis for nutrient resource management and non-point source pollution control.

Spatial distribution of available phosphorus in surface road and trackway surface materials on a sheep farm in Ireland

Farm roadway runoff is a high-risk source of pollution when connectivity with waters occurs. Nutrients in this runoff are dominated by fresh animal deposits, but recent dairy and beef farm studies showed that available phosphorus (P) accumulates in roadway surface material and can be lost in runoff. A current knowledge gap is to examine available P concentrations in unsealed roadway and trackway (non-maintained) network of a lowland sheep farm. The present study focused on a 45 ha farm stocked with 544 sheep in south-east Ireland. Ten locations were sampled along with the adjacent fields for available P (i.e., Morgan’s P) and ancillary parameters (e.g., pH, total P and heavy metals) in December 2022. The first sampling location was on an aggregate roadway and the other nine were on trackways representing an older aggregate roadway network used by the flock but now covered with soil and grass. Results showed a distinct difference in surface material pH between roadway and trackway locations. Trackways had a pH that mimicked adjacent fields around the agronomic optimum for grassland of ∼6.2. All sampling locations had elevated available P concentrations, ranging from 26.3 to 111.0 mg L−1 (mean 62.8 mg L−1), similar to the spatial distribution for dairy farms but above those found at beef farms previously studied. The highest available P concentrations were found in roadway and trackway sections adjacent to the farmyard. Other elevated sampling areas were on trackways (87.3 or 97.7 mg P L−1) away from the farmyard where sheep are funnelled to pasture, stop to seek shade, urinate and defecate but do not graze. By contrast the average available P concentration for the surrounding fields was 8.4 mg L−1 with a range of 2.7–15.9 mg L−1. Two sampling areas combine to create a critical source area where a high available P source becomes visibly mobilised as runoff during rainfall, discharges into an open drainage ditch, which is then connected to a local stream. Breaking the pathway before runoff enters the open ditch could be a cheap and effective way of mitigating nutrient losses at these two locations.

Application of fallout radionuclide—137Cs for estimating soil erosion in steep hillslopes with diverse land use of North-western Indian Himalayas

Hilly and mountainous regions are significantly impacted by soil erosion, primarily due to rainfall-runoff processes occurring on the hillslope scale. Assessing soil erosion is crucial for quantifying the loss of soil carbon and nutrients, which diminishes the potential of soil ecosystem services and is critical for mitigating the impacts of climate change on food security. However, the Himalayan landscape poses serious challenges for assessing soil erosion due to its steep and rugged terrain, which hinders the use of conventional and modelling methods. The fallout radionuclide—137Cs has been extensively utilized as an environmental marker for investigating soil redistribution processes. Despite its potential, there is a notable lack of 137Cs-based soil erosion studies in the Himalayan region. In this context, we assessed the applicability of the fallout radionuclide—137Cs method in quantifying soil erosion rates and identifying erosion hotspots on two hillslopes of the Higher Himalayas. On the hillslope scale, we observed that soil erosion rates vary based on slope gradient and land use/land cover. Forested areas exhibited the lowest soil erosion rates compared to cultivated areas, while flat hillslope positions experienced lower erosion rates than steeper positions. The average net erosion rate for the Harsil hillslope varied among different hillslope positions, ranging from – 2.9 to – 15.6 t ha−1 yr−1. Similarly, in the Gangnani hillslope, the net erosion rates varied across different positions, ranging from – 5.6 to – 39 t ha−1 yr−1. Our findings confirm that the middle and lower hillslope positions are the most critical source areas with higher soil erosion rates, while hillslope positions with forest cover demonstrate the lowest erosion rates, identified as helpful in controlling soil erosion. The study has demonstrated the applicability of FRN as a soil erosion measurement method in the complex, rugged, and steep terrain of the Himalayas, highlighting the need for targeted conservation efforts to mitigate soil erosion and preserve ecosystem integrity.

Improving the identification of pollution source areas with catchment-resolution sensitivity analysis

The significant impacts of total nitrogen (TN) and total phosphorus (TP) on riverine ecosystems underscores the critical need to identify the primary nutrient source areas in watersheds. This study aims to unravel the influences of terrain and land use types on mean monthly TN (TNM) and mean monthly TP (TPM) export across varying catchment resolutions in the Qiantang River Watershed of China. The findings of this study illuminated the critical role of topography in understanding nutrient dynamics, wielding a profound influence over water flow patterns and nutrient dispersion. Both land slope and Stream Power Index (SPI) displayed substantial negative correlations (r < −0.6) with TNM and TPM concentrations, whereas the Topographic Wetness Index (TWI) showed positive correlations with the nutrient indexes. In addition to terrain characteristics, impervious land surfaces had a positive correlation with nutrient concentrations, while grassland and forest areas exhibited negative correlations. Results further underscored the substantial influence of catchment resolution on correlations between watershed properties and riverine nutrient concentrations. It was imperative to choose an effective catchment resolution in watershed delineation – not too coarse, nor too fine – to accurately capture the topographic and land use impacts on nutrient dynamics. With the most appropriate catchment size (Catchment 700 km2), the critical pollution source areas for TN and TP pollution were identified, and thus could be used to guide future pollution reduction efforts. The study not only highlights the importance of identifying an appropriate catchment size for water pollution, but also emphasizes the necessity of effectively extracting critical pollution source areas to mitigate water nutrient pollution and increase the ecological integrity of the Qiantang River Watershed.

Phosphorus in farm roadway substrates: contrasting spatial and temporal patterns in dairy and beef farms

The mobilisation and impact of roadway runoff on dairy farms has been established as a sub-component of the nutrient transfer continuum. It is acknowledged that fresh nutrient sources deposited on roadways dominate runoff and recent work has shown that available phosphorus (P) in roadway substrates is also an important source component. The objectives of this study were to understand spatial and temporal available P concentrations in roadway substrate (aggregate and soil mix) across dairy and beef farms during the open (February–October, when cows use the roadway network and fields) and closed (November–January, when cows were housed) periods and identify locations which could be considered critical source areas (CSA). For the study, roadway substrate samples were taken at 18 locations on each farm, across eight sampling periods, and were analysed for available P. Results showed that mean available P concentrations (Morgan’s P) in the sampling locations ranged from 15.9 to 101.4 mg L-1 for the Dairy Farm, from 4.1 to 59.4 mg L-1 for Beef Farm 1 and from 6.3 to 23.2 mg L-1 for Beef Farm 2. In open period, the results showed that mean available P concentrations were 75.4 ± 30.9, 14.9 ± 3.2 and 13.4 ± 2.5 mg L-1 for the Dairy Farm, Beef Farm 1 and Beef Farm 2, respectively. In closed period, the mean available P were 40.3 ± 17.2, 10.4 ± 1.0 and 9.8 ± 0.2 mg L-1 for Dairy Farm, Beef Farm 1 and Beef Farm 2, respectively. Overall, P concentrations on the Dairy Farm roadways was up to 4 times greater than that in the Beef Farms’ roadways. Compared to soils in adjacent fields, P concentrations in the Dairy and Beef Farms roadways was up-to 7 and 2 times higher, respectively. Critical roadway sections that required mitigation were two in the Dairy Farm, one in Beef Farm 1 and two in Beef Farm 2. In addition to fresh faeces and urine (i.e., dominant source of nutrients in farm roadways), this study showed that nutrient enriched roadway materials are a labile P source. Thus, future mitigation of roadway runoff must consider all roadway nutrient sources, including livestock fresh excreta as well as used roadway surface materials.

Application of improved risk assessment methods to best management practices research for non-point source pollution: From a hilly mountainous-dominated region of Southern China

Non-point source pollution (NPSP) significantly affects regional water environments worldwide. Identifying critical source areas (CSAs) and implementing best management practices (BMPs) are essential to prevent and control NPSP. This study used the Soil and Water Assessment Tool model to simulate and evaluate the characteristics of NPSP in the Gongjiang Watershed, a typical, hilly mountainous area in Southern China. The study identified CSAs of NPSP using total nitrogen (TN), total phosphorus (TP), water quality level, and population density factors. The reduction effect of different BMPs on the NPSP load was evaluated, and the cost-effectiveness (CE) of various BMPs was evaluated for the control of NPSP in the watershed. The interannual variation in NPSP load was high from 2013 to 2018, with the largest pollution load in 2016 (wet year) and the smallest in 2018 (dry year). The pollution load fluctuated throughout the year and was related to fertilization and precipitation runoff. The spatial heterogeneity of NPSP was large, with TN and TP losses showing a spatial pattern of high in the south, low in the north, and highest in the center. The CSAs of the NPSP covered 1566.66 km2, representing 9.77 % of the total watershed area. However, TN and TP loads accounted for 19.39 % and 23.53 % of total watershed production. The order of effectiveness of individual management measures in reducing TN was stubble coverage (SC) > vegetative buffer strips (VBS) > terrace engineering (TE) > grassed waterways (GW) > 20 % fertilizer reduction (FR20) > 10 % fertilizer reduction (FR10). The order of effectiveness of TP reduction was SC > VBS > TE > FR20 > GW > FR10. Combined management measures were much more effective in reducing TN and TP than individual measures, with an average increase in TN and TP reduction of 20.59 % and 25.23 %, respectively. Based on the results of the CE evaluation of BMPs, a combination of FR20, GW, and VBS was more effective than individual measures. We suggest a combination of FR20, GW, and VBS measures for effective NPSP prevention and control in Southern China’s typical, hilly mountainous areas.

Simulating the land use change effects on non-point source pollution in the Duliujian River Basin.

The uncertainty in the generation and formation of non-point source pollution makes it challenging to monitor and control this type of pollution. The SWAT model is frequently used to simulate non-point source pollution in watersheds and is mainly applied to natural watersheds that are less affected by human activities. This study focuses on the Duliujian River Basin (Xiqing section), which is characterized by a dense population and rapid urbanization. Based on the calibrated SWAT model, this study analyzed the effects of land use change on non-point source pollution both temporally and spatially. It was found that nitrogen and phosphorus non-point source pollution load losses were closely related to land use type, with agricultural land and high-density urban land (including rural settlements) being the main contributors to riverine nitrogen and phosphorus pollution. This indicates the necessity of analyzing the impact of land use changes on non-point source pollution loads by identifying critical source areas and altering the land use types that contribute heavily to pollution in these areas. The simulation results of land use type changes in these critical source areas showed that the reduction effect on non-point source pollution load is in the order of forest land > grassland > low-density residential area. To effectively curb surface source pollution in the study area, strategies such as modifying urban land use types, increasing vegetation cover and ground infiltration rate, and strictly controlling the discharge of domestic waste and sewage from urban areas can be implemented.

Grazing strategies for reducing contaminant losses in surface runoff from winter forage crop fields located in hill country and grazed by sheep

ABSTRACT A paired catchment study approach was used to quantify fluxes of Nitrogen (N), Phosphorus (P), sediment and Escherichia coli (E. coli) in surface runoff from fields where sheep were wintered on swede (Brassica napus) and kale (Brassica oleracea) crops. The effectiveness of a strategic grazing approach that protected critical source areas (CSAs) was examined to determine if these fluxes could be reduced. Averaged over two years, estimated fluxes of N, P and sediment in surface runoff recorded in winter and early spring (June-September) were up to 0.64, 0.22 and 51 kg ha−1, respectively, and up to 2 × 1011 MPN ha−1 for E. coli. With the exception of E. coli, these fluxes were low compared to those reported in other studies and largely attributed to the low amounts of surface runoff recorded. This, in turn, can be explained by relatively benign weather conditions recorded during the study period and the relatively light grazing pressures imposed by sheep. Compared to standard grazing practice, protection of CSAs reduced N, P, sediment, and E. coli fluxes by 38%, 48%, 55% and 63%, respectively. These reductions can largely be attributed to lower concentrations of contaminants in surface runoff when the CSA was protected.

“Period-area-source” hierarchical management for agricultural non-point source pollution in typical watershed with integrated planting and breeding

Agricultural non-point source (NPS) pollution threatens the aquatic environments significantly. Insufficient attention to the migration characteristics of multiple sources of pollution as well as the variability of anthropogenic interference hinders effective pollution control, particularly in watersheds with integrated planting and breeding (IPB). In this study, we proposed a distributed dual-structure empirical export model for IPB (DSEEM-IPB) that optimizes hydrological processes in pollutant transport and refines NPS load estimation from animal breeding sources to simulate agricultural NPS pollution in a typical IPB watershed. Based on the estimated NPS load, a “period-area-source” management approach for NPS pollution is proposed with a co-analysis of critical periods (CPs), critical source areas (CSAs), and critical source types (CSTs). The results show that (1) the CPs of only two months (June and July) contributed 62.9% and 56.2% of the total nitrogen (TN) and total phosphorus (TP) load respectively; (2) the CSAs in the CPs contributed 17.6% of the TN load within 14.0% of the area and 16.2% of the TP load within 13.4% of the area; (3) planting (74.4%) is the primary source of nitrogen loss while breeding (58.3%) is the primary source of phosphorus loss; and (4) optimal control measures should target planting sources in CSAs and sub-CSAs within CPs (yielding 32.4% of annual TN loads) and breeding sources in CSAs within non-CPs (yielding 22.1% of annual TP loads). This study indicates that prioritizing pollution management of critical sources from critical areas or periods can achieve efficient and targeted control of agricultural NPS pollution.

Toward better targeting of mitigation measures for reducing phosphorus losses from land to water: Andrew Sharpley's legacy in Norway and Sweden.

Nordic agriculture faces big challenges to reduce phosphorus (P) loss from land to water for improving surface water quality. While understanding the processes controlling P loss and seeking for P mitigation measures, Norwegian and Swedish researchers have substantially benefited from and been inspired by Dr. Andrew Sharpley's career-long, high-standard P research. Here, we demonstrate how Sharpley and his research have helped the Nordic researchers to understand the role of cover crops in cold environmental conditions, best manure P management practices, and ditch processes. His work on critical source area (CSA) identification and site assessment tool development have also greatly inspired our thinking on the targeting of mitigation measures and the contextualizing tools for Nordic climate, landscape, and soils. While reflecting on Sharpley's legacy, we identify several needs for Norwegian and Swedish P research and management. These include (1) tackling the challenges caused by local/regional unevenness in livestock density and related manure management and farm P surpluses, (2) identifying CSAs of P loss with high erosion risk and high P surplus, (3) obtaining more high-resolution mapping of soils with low P sorption capacity both in the topsoil and subsoil, (4) improving cross-scale understanding of processes and mitigation measures and proper follow-up of applied mitigation measures, and (5) increasing collaborations of researchers with farmers and farmers' advisory groups and watershed groups by developing high-quality educational courses and extension materials. The needs should be addressed in the context of the challenges and opportunities created by climate change.

A review of the development and implementation of the critical source area concept: A reflection of Andrew Sharpley's role in improving water quality.

Critical source areas (CSAs) are small areas of a field, farm, or catchment that account for most contaminant loss by having both a high contaminant availability and transport potential. Most work on CSAs has focused on phosphorus (P), largely through the work in the 1990s initiated by Dr. Sharpley and colleagues who recognized the value in targeting mitigation efforts. The CSA concept has been readily grasped by scientists, farmers, and policymakers across the globe. However, experiences and success have been mixed, often caused by the variation in where and how CSAs are defined. For instance, analysis of studies from 1990 to 2023 shows that the proportion of the annual contaminant load coming from a CSA decreases from field to farm to catchment scale. This finding is consistent with increased buffering of CSAs and greater contribution of other sources with scale, or variation in the definition of CSAs. We therefore argue that the best application of CSAs to target mitigation actions should be at small areas that truly account for most contaminant loss. This article sheds light on the development and utilization of CSAs, paying tribute to Dr. Sharpley's remarkable contributions to the improvement of water quality, and reflecting upon where the CSA concept has succeeded or not in reducing contaminant (largely P) loss.

Revealing the Sources of Nutrients in the Surface Waters of the Selenga River Watershed Using Hydrochemical and Geospatial Data

This study was the first attempt to identify the sources of total oxidized nitrogen (TON) and inorganic phosphorus (IP) in the water of the Selenga River—the main tributary of Lake Baikal. To identify TON and IP sources, the data on nutrient concentrations in water of Selenga River and its tributaries as well as the data on river runoff were collected and mapped. On the basis of the obtained data, the values of TON and IP exported from different parts of Selenga watershed were evaluated and mapped using geospatial techniques. In addition, critical source areas (CSAs) which accumulate soil pollutants from nonpoint pollution sources and release them into the surface water during storm events were identified in most polluted watershed areas. It was found that the values of TON exports in most parts of the Selenga watershed varied in the range 0–50 kg/km2/yr, whereas the values of IP exports varied in the range 0–5 kg/km2/yr. Obtained data on TON export were in agreement with those obtained earlier by foreign researchers using global models of nutrient export, whereas data on IP exports were two times higher than those previously modelled.

Balancing agriculture and environment: Andrew Sharpley's nutrient, soil, and water management legacy

AbstractManaging agricultural phosphorus (P) to balance food security and water quality priorities is a massive challenge fraught with uncertainty and competing interests. Throughout his career, Andrew Sharpley addressed this challenge by building our understanding of the fundamental principles and processes that control P behavior in agricultural land, developing tools to assess P losses, and then evaluating and refining nutrient, soil, and water beneficial management practices (BMPs). Together with an exceptionally large and diverse group of collaborators, Sharpley developed, tested, refined, calibrated, and validated management practices and risk assessment tools to develop site‐specific recommendations for the right practices, in the right places, and at the right times. This approach has resonated globally, with the strategic use of BMPs in “critical source areas” widely implemented in an effort to improve the effectiveness of BMPs while reducing implementation costs. Additional contributions to nutrient management include determining environmental thresholds for soil test P and measuring the risk of P loss from different sources of P (e.g., various manures and commercial fertilizers). Sharpley's work was also distinctly realistic, ensuring that strategies for mitigating P loss were critically evaluated so that not only were the benefits highlighted, but also that trade‐offs were measured. Nowhere is this better illustrated than with trade‐offs in particulate P loss and dissolved P loss with conservation tillage. This review summarizes Sharpley's enormous contributions to our knowledge of agricultural P stewardship as well as his model of collaborative, multi‐disciplinary leadership, helping the world to maintain agricultural productivity and protect water quality.

Identifying critical source areas of non-point source pollution to enhance water quality: Integrated SWAT modeling and multi-variable statistical analysis to reveal key variables and thresholds

By integrating soil and water assessment tool (SWAT) modeling and land use and land cover (LULC) based multi-variable statistical analysis, this study aimed to identify driving factors, potential thresholds, and critical source areas (CSAs) to enhance water quality in southern Alabama and northwest Florida's Choctawhatchee Watershed. The results revealed the significance of forest cover and of the lumped developed areas and cultivated crops ("Source Areas") in influencing water quality. The stepwise linear regression analysis based on self-organizing maps (SOMs) showed that a negative correlation between forest percent cover and total nitrogen (TN), organic nitrogen (ORGN), and organic phosphorus (ORGP), highlighting the importance of forests in reducing nutrient loads. Conversely, Source Area percentage was positively correlated with total phosphorus (TP) loads, indicating the influence of human activities on TP levels. The receiver operating characteristic (ROC) curve analysis determined thresholds for forest percentage and Source Area percentage as 37.47 % and 20.26 %, respectively. These thresholds serve as important reference points for identifying CSAs. The CSAs identified based on these thresholds covered a relatively small portion (28 %) but contributed 47 % of TN and 50 % of TP of the whole watershed. The study underscores the importance of considering both physical process-based modeling and multi-variable statistical analysis for a comprehensive understanding of watershed management, i.e., the identification of CSAs and the associated variables and their tipping points to maintain water quality.

Identification of critical source areas and delineation of management subzones of non-point source pollution in Jing River Basin

Identification of critical source areas and delineation of management subzones of non-point source pollution in Jing River Basin

Evaluation of ecological buffer zone based on landscape pattern for non-point source pollution control: A case study in Hanjiang River basin, China

The deterioration of ecological environment caused by non-point source pollution (NPS) has seriously threatened human health and socioeconomic development. Effective identification of critical source areas and selecting appropriate best management practices (BMPs) for watersheds are the keys to controlling NPS. This paper, using Hanjiang River basin, the vital water source for the South-to-North Water Division, China, as a case study, presents a method for accurate critical source areas dentification according to the spatial distribution characteristics of underlying surface and pollution load by coupling NPS risk index (NPPRI), Minimum Cumulative Resistance (MCR) Model, and Soil and Water Assessment Tool (SWAT). In this research, ten single and three combined scenarios are set up in the critical source areas, including three non-engineering management practices, two engineering management practices, and five ecological buffer zones. Finally, the effect of BMPs for non-point source pollution is assessed by using landscape pattern theory and information entropy method. Furthermore, the influences of the five ecological buffer zones on the characteristics of landscape in watershed and the response relationship between the landscape pattern and NPS are analyzed. The following findings are obtained: (1) The critical source areas were mainly located in the south-central and southeastern part of the study area, accounting for 35.9 % of the total watershed area, and yielding 54.2 % and 60.7 % of the total nitrogen(TN) and total phosphorus(TP) loads in the watershed; (2) All ecological buffer zones play a positive role in NPS control with an average reduction rate of 32.1 % for TN and 46.7 % for TP, and the control effectiveness for TP are better than that for TN; (3) The deployment of the five ecological buffer zones have a significant impact on the interspersion juxtaposition index (IJI), the connectivity of the “sink” landscape is enhanced, the diversity of the “source” landscape is reduced and the “sink” landscape’s ability of interception is boosted; (4) The calculation result of information entropy shows the highest attribute value of practices in the ecological buffer zones is Buffer 200 m. Overall, the findings serve as a reference for NPS control and water environment management in the watershed and strengthen the feasibility of implementing of BMPs in the watershed.

Quantifying Soil Erosion and Identifying Critical Source Areas Under Current Management in the Holeta Watershed, Awash Basin, Ethiopia

Quantifying Soil Erosion and Identifying Critical Source Areas Under Current Management in the Holeta Watershed, Awash Basin, Ethiopia

An integrated watershed modelling framework to explore the covariation between sediment connectivity and soil erosion

AbstractQuantitative identification of the covariation between sediment connectivity and soil erosion can contribute to provide the key information for watershed sediment management. However, this covariation and its spatiotemporal response mechanisms are still unclear, especially whether this covariation can be used as a basis for identifying critical source areas of sediment in large‐scale ecological restored watersheds. In this study, an integrated methodology framework by the revised universal soil loss equation (RUSLE), index of connectivity (IC) and sediment delivery ratio (SDR) was proposed to visually assess the spatiotemporal characteristics of erosion and sediment yield processes in the Yanhe Watershed with large‐scale ecological restoration from 1985 to 2020 and to identify the covariation between sediment connectivity and erosion in subbasins. The soil erosion estimated by RUSLE has decreased by over 80% since 1985 owing to increased vegetation cover and the effective implementation of soil conservation measures, but the upper reaches still have high erosion intensity due to differences in specific controlling factors such as topographic conditions and land cover, requiring focused soil conservation practice. The IC results showed that as the vegetation restoration and soil conservation measures in the Yanhe Watershed varied from year to year, their spatial and temporal patterns had a strong influence on the distribution of sediment connectivity, and some local areas in the middle reaches showed local minima of IC in 1995, 1998 and 2010 mainly due to the implementation of long‐term ecological restoration project. The developed IC‐Erosion maps indicated that areas with high connectivity but low erosion accounted for over 60% of the total watershed area from 1985 to 1999, demonstrating a reverse correlation between sediment connectivity and erosion. Meanwhile, over 40% of the erosion occurred in a few areas (approximately 20%) with high connectivity and high erosion from 2000 to 2004, which can be characterized as the critical areas of erosion. The methods and results of this study provide ideas for separately defining both erosion and connectivity and quantifying bi‐variable erosion–connectivity classification, which can be easily viewed on a scatterplot.