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Metal contamination in surface water is one of the major environmental risk factors contributing to the incidence and mortality of gastric cancer (GC) in rural China. In this study, the generalized additive model (GAM) was used to explore the single and interactive effects of metal elements in surface water on GC incidence on the watershed scale in Lujiang County, east of China. Spatially, the areas with a high incidence of GC were concentrated in the northwest watershed where the drainage system was relatively developed. Apart from Sr, the average concentrations of Al, As, Be, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, and Zn in the northern watershed were higher than those in the southern watershed. Among them, the average concentrations of Be (0.036 mg/L), Fe (1.539 mg/L), Mn (0.355 mg/L), and Ni (0.040 mg/L) well exceeded China's Grade III water quality standards. On the sub-watershed scale Be (F(5.130)), Pb (F(4.963)), As (F(3.508)), Cu (F(3.023)), Zn (F(2.922)), Cr (F(2.725)), Sn (F(2.588)), and Co (F(2.140)) in surface water were the main elements contributing to the high incidence of GC in Lujiang County, and the interaction effect mostly showed nonlinear enhancement. Especially, the nonlinear enhancement effect of Be with Cu (F(7.051)), Co (F(5.798)), Sn (F(5.328)), and Pb (F(5.193)) was more significant and had a greater effect on the incidence of GC. This study provides compelling direct evidence on the effects of metal contamination in surface water on the higher GC incidence in Lujiang County, China. It is recommended that there be routine monitoring of metal concentrations in surface water resources. [ABSTRACT FROM AUTHOR]

Background: Post-fire studies show that water repellency is limited by moisture conditions, but no existing study has examined this limiting effect at a watershed scale. Aims: This study aimed to identify the soil moisture threshold value at which wildfire-induced hydrophobic condition transitions back to hydrophilic condition at a watershed scale. Methods: The effect of moisture thresholds on post-fire water-repellent soil and hydrological variables including infiltration, runoff volume and peak flow are examined, using the post-wildfire hydrological model of the upper Arroyo Seco watershed, California, following the August 2009 Station Fire. Key results: As the moisture threshold value increased from wilting point towards field capacity, the wildfire's impact on runoff was greatest near the wilting point, and decreased sharply as the threshold increased. The percentage error in peak flow exponentially decreased as the moisture threshold increased and the corresponding Nash–Sutcliffe efficiency increased. Soil moisture threshold values >0.2 m3/m3 were significantly less sensitive to Nash–Sutcliffe efficiency, infiltration depth and percentage error in peak flow and runoff volume. Conclusion: At the soil moisture threshold value of 0.25 m3/m3, transition from hydrophobic to hydrophilic conditions occurred. Identification of this watershed-scale soil moisture threshold value allows inclusion of the wildfire-induced hydrophobic transition back to hydrophilic condition in post-fire hydrological modelling of watersheds. At a watershed scale, the impact of wildfires on runoff following a precipitation event is greatest when the soil is dry and decreases sharply as soil moisture increases. Once the post-wildfire soil moisture reaches the threshold value of 0.25 m3/m3, flooding due to water repellency is no longer significant. [ABSTRACT FROM AUTHOR]

Understanding the contributions of stream bank and bed erosion will allow us to implement the most effective management practices. The objective of this study was to assess different methods to measure bank and bed erosion at different scales, specifically the watershed, reach and plot. Innovative and traditional methods were utilized. At the watershed scale, indices based on free satellite images were used. For the reach scale, indices were used, but the images with higher accuracy were purchased and captured by unmanned aerial vehicles (UAVs). At the plot scale, erosion pins, cross-sections and laser scanning were applied. The watershed scale analysis showcased "hot spots". These "hot spots" were reaches vulnerable to erosion and deposition. The indices of the purchased images were applied to these "hot spots" and allowed us to narrow the length of the reaches where UAV flights took place. These flight images located where erosion and deposition occurred. Finally, at the plot scale, laser scanning provided more detailed and accurate data at a greater scale compared to the traditional methods. The implementation of these methods allows us to find the areas vulnerable to erosion and deposition. These are the areas where nature-based solutions should be implemented to effectively mitigate erosion problems. [ABSTRACT FROM AUTHOR]

● This study clarified the critical processes and major factors that nitrogen transport from farm fields to surface water bodies.● Soil storage, exogenous inputs and meteorological hydrology were found to influence nitrogen loss from farmland.● Hydrology, biogeochemistry and nitrogen inputs were found to influence the transformation of nitrogen in the ditches and rivers. Agricultural non-point source pollution is increasingly an important issue affecting surface water quality. Currently, the majority of the studies on nitrogen loss have focused on the agricultural field scale, however, the response of surface water quality at the watershed scale into the nitrogen loss at the field scale is poorly understood. The present study systematically reviewed the critical processes and major factors that nitrogen transport from farm fields to surface water bodies. The critical processes of farmland nitrogen entering surface water bodies involve the processes of nitrogen transport from farmland to ditches and the transformation processes of nitrogen during migration in ditches/rivers. Nitrogen transport from farmland to ditches is one of the prerequisites and critical processes for farmland nitrogen transport to surface water bodies. The transformation of nitrogen forms in ditches/rivers is an intermediate process in the migration of nitrogen from farmland to surface water bodies. Nitrogen loss from farmland is related to soil storage and exogenous inputs. Therefore, nitrogen input management should not only consider the current input, but also the contribution of soil storage due to the historical surpluses. Ditches/rivers have a strong retention capacity for nitrogen, which will significantly affect the process of farmland nitrogen entering surface water bodies. The factors affecting nitrogen transformation in river/ditches can be placed in four categories: (1) factors affecting hydraulic retention time, (2) factors affecting contact area, (3) factors affecting biological activity, and (4) forms and amount of nitrogen loading to river/ditches. Ditch systems are more biologically (including plants and microbes) active than rivers with biological factors having a greater influence on nitrogen transformation. When developing pollution prevention and control strategies, ecological ditches can be constructed to increase biological activity and reduce the amount of surplus nitrogen entering the water body. The present research should be valuable for the evaluation of environment impacts of nitrogen loss and the non-point source pollution control.

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. [ABSTRACT FROM AUTHOR]

Purpose: Nutrient and sediment pollution of surface waters remains a critical challenge for improving water quality. This study takes a user-friendly field-scale tool and assesses its ability to model at both the field and watershed scale within the Fox River Watershed (FRW), Wisconsin, USA, along with assessing how targeted vegetation implementation could attenuate nutrient and sediment exports. Methods: To assess potential load reductions, the nutrient tracking tool (NTT) was used with a scoring system to identify areas where vegetation mitigation could be implemented within three selected FRW sub-watersheds. A corn soybean rotation, an implementation of a 10-m-vegetated buffer, a full forest conversion, and tiling were modeled and assessed. The corn–soybean results were aggregated and compared to watershed level gauge data in two sub-watersheds. Edge-of-field data was compared to modeled results using multiple parameterization schemes. Results: The agricultural areas that scored higher and were untiled showed greater potential nutrient and sediment export reduction (up to 80 to 95%) when vegetation mitigation was implemented in the model. Field-scale results aggregated to the watershed scale showed disparities between modeled and measured phosphorus exports but modeled sediment exports fell within observed gauge data ranges. Field-specific parameter adjustments resulted in more accurate modeled results compared to measured edge-of-field export data but needed further refinement. Conclusion: Targeted mitigation using a vegetation-based scoring system with the NTT model was shown to be a helpful tool for predicting nutrient and sediment reductions. Using a field-scale model aggregated to the watershed scale presents tradeoffs regarding processes found beyond the edge of field. [ABSTRACT FROM AUTHOR]

A better understanding of diffuse pollution processes distressing surface water bodies is relevant to develop actions focused on the sustainable management of water resources. This research aims to identify relevant watershed variables that explain the spatial variability patterns of surface water quality in lotic mountain water bodies. Twenty-eight candidate variables (10 land cover and land use (LCLU), 6 pedo-topographic (PT), and 12 hydrometeorological (HM)) were defined to explain the concentration of six water quality parameters temperature (T), pH, dissolved oxygen (DO), chemical oxygen demand (COD), electrical conductivity (EC), and nitrates (NO3-)) in 76 surface water streams of the Andina region, Colombia. The selection of the explanatory variables was carried out by applying an iterative input selection (IIS) algorithm based on highly randomized tree models. The results show that the variability in the concentration of each water quality parameter is explained by a combination of LCLU, HM, and PT variables. LCLU was the most important group of explanatory variables in the selection, followed by HM variables group. This is not the case for DO, where the HM variables show the highest importance. In all the implemented models, the PT variables showed the lowest incidence. This research developed a success approach for identifying basin variables able to contribute to understand non-point sources of pollution, and thus it was not oriented to create a predictive model of water quality, but rather to use machine learning modeling to expose probable relationships between watershed attributes and the quality of surface water. These results can support other water quality studies and territorial planning instruments on the role of watershed-scale variables in diffuse pollution processes in surface water bodies. The implemented algorithm provided modeling flexibility, computational efficiency, and minimum redundancy, allowing a reasonable representation of the observational data set. [ABSTRACT FROM AUTHOR]

Understanding the contributions of stream bank and bed erosion will allow us to implement the most effective management practices. The objective of this study was to assess different methods to measure bank and bed erosion at different scales, specifically the watershed, reach and plot. Innovative and traditional methods were utilized. At the watershed scale, indices based on free satellite images were used. For the reach scale, indices were used, but the images with higher accuracy were purchased and captured by unmanned aerial vehicles (UAVs). At the plot scale, erosion pins, cross-sections and laser scanning were applied. The watershed scale analysis showcased “hot spots”. These “hot spots” were reaches vulnerable to erosion and deposition. The indices of the purchased images were applied to these “hot spots” and allowed us to narrow the length of the reaches where UAV flights took place. These flight images located where erosion and deposition occurred. Finally, at the plot scale, laser scanning provided more detailed and accurate data at a greater scale compared to the traditional methods. The implementation of these methods allows us to find the areas vulnerable to erosion and deposition. These are the areas where nature-based solutions should be implemented to effectively mitigate erosion problems.

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. • An innovative approach for assessing farmland nitrogen loss risk to surface waters was established. • The nitrogen surplus in wheat season had a legacy effect on nitrogen loss to surface waters. • Nitrogen surplus had a greater impact on nitrogen loss risk to the rivers than transport coefficient. • Transport factors had a greater influence on nitrogen loss risk to the lake than source factors. • The optimal scenario for reducing the farmland nitrogen loss to surface waters was a combination of factors. [ABSTRACT FROM AUTHOR]

This study aims to characterize the watershed-level distribution patterns of severely degraded alpine meadows commonly known as “heitutan” in the Yongqu River basin of the Source Zone of Yellow River. Topographic data were analyzed in ArcGIS to derive several variables and delineate multi-level watershed units. In addition, remotely sensed data were analyzed to map ground covers in two-level watershed units (i.e. first-level and second-level watershed units), including heitutan degraded grassland. The two sets of results were intersected to identify the correlation of land covers and spatial proximity with heitutan and their possible influences on it. The results show that the alpine meadow in the Yongqu watershed comprised 51.39 % of the total area, and shrub grassland accounted for 45.45 % of the total area. At the first-level tributary unit of the Yongqu watershed, heitutan-degraded grassland is the most common feature at 4.75 km2, accounting for 2.46 % of all alpine meadows. Heitutan patches on average have a minimal size of 1007 m2. Most heitutan patches are distributed on gentle, mainly sunny, and semi-sunny slopes of 7–18° in gradient. They are situated within 1000 m of roads, accounting for 90.53 % of total “heitutan”, while 96.56 % are distributed within 0–1500 m of settlements. At the second-level tributary unit of the Hallaqu and Chayangwa, heitutan is the most common at 1.23 and 0.41 km2, respectively, accounting for 0.79 % and 1.01 % of the total alpine meadows. However, the highest proportion in the Chayangwa River basin is in the 0–3° beach areas. The areas widely distributed with heitutan heavily overlap with those affected by overgrazing and rodent activities. Redundancy analysis and structural equation modeling indicate that slope exerts the greatest influence on the formation and distribution patterns of the heitutan degraded grassland, followed by slope aspect and distance to roads. In comparison, distance to river channels and settlements and the annual temperature has an insignificant influence on the heitutan degraded grassland.

Accurate quantification of evapotranspiration (ET) at the watershed scale remains an important research challenge for managing water resources in arid and semiarid areas. In this study, daily latent heat flux (LE) maps at the kilometer scale were derived from the two-source energy budget (TSEB) model fed by the MODIS leaf area index (LAI), land surface temperature (LST) products, and meteorological data from ERA-Interim reanalysis from 2001 to 2015 on the Tensift catchment (center of Morocco). As a preliminary step, both ERA-Interim and predicted LE at the time of the satellite overpass are evaluated in comparison to a large database of in situ meteorological measurements and eddy covariance (EC) observations, respectively. ERA-Interim compared reasonably well to in situ measurements, but a positive bias on air temperature was highlighted because meteorological stations used for the evaluation were mainly installed on irrigated fields while the grid point of ERA-Interim is representative of larger areas including bare (and hot) soil. Likewise, the predicted LE was in good agreement with the EC measurements gathered on the main crops of the region during 15 agricultural seasons with a correlation coefficient r = 0.70 and a reasonable bias of 30 W/m2. After extrapolating the instantaneous LE estimates to ET daily values, monthly ET was then assessed in comparison to monthly irrigation water amounts provided by the local agricultural office added to CRU precipitation dataset with a reasonable agreement; the relative error was more than 89% but the correlation coefficient r reached 0.80. Seasonal and interannual evapotranspiration was analyzed in relation to local climate and land use. Lastly, the potential use for improving the early prediction of grain yield, as well as detecting newly irrigated areas for arboriculture, is also discussed. The proposed method provides a relatively simple way for obtaining spatially distributed daily estimates of ET at the watershed scale, especially for not ungauged catchments. [ABSTRACT FROM AUTHOR]

Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bulk density (BD) is one of the most important soil physical properties in the hydrological processes of Earth's Critical Zone (CZ). The heterogeneity and related controlling factors of surface BD have received extensive research attention. However, it is unclear whether the effects of controlling factors on BD are homogeneous or vary spatially. This study quantified topsoil BD with a high‐density sampling strategy (10 m × 10 m; n = 1134) across the ShuangChaGou watershed in the critical zone of the Chinese Loess Plateau (CLP‐CZ). Stepwise multiple linear regression (SMLR), regression kriging (RK), random forest (RF) and geographically weighted regression (GWR) were established as modelling approaches to (i) compare the performance of these four models in explaining BD variation, (ii) assess the main factors driving BD, and (iii) evaluate the spatial non‐stationary relationship between BD and its explanatory variables. GWR explained the BD variation to the same extent as the RK model (35%), outperforming both the SMLR (15%) and RF models (19%). The variation in topsoil BD depended mainly on: soil organic carbon (SOC) content, normalised difference vegetation index (NDVI), plan curvature, and slope length. The spatial distribution of the local R2, regression coefficient magnitude, significance and sign calculated by GWR revealed that the effects of variables accounting for variation in BD varied spatially. The explanatory power of these variables in terms of BD variation was strongest in northern and northeastern areas of the watershed and weakest in southern areas of the watershed. Both significant negative and positive correlations between BD and silt content, NDVI, and plan curvature were found. This study enriched traditional research linked to the complicated relationships between BD and controlling factors by incorporating spatial non‐stationarity, which is useful for improving the accuracy of hydrological modelling in the CLP‐CZ and in similar CZs worldwide. Highlights: Non‐stationary relationships between BD (N = 1134) and its explanatory variables were captured at the watershed scale.GWR model performed on par with the RK and better than the SMLR or RF model.Silt content, NDVI, and plan curvature showed both significant negative and positive effects on BD.Spatial non‐stationarity of BD should be considered for improving the performance of hydrological modeling. [ABSTRACT FROM AUTHOR]

Sustainable stormwater management (SSM) has gained global interests to solve both on‐site and off‐site downstream water problems. However, current structural SSM practices are often limited to small scales and their impacts on river water quality have not been fully understood. In this study, we have quantified watershed responses to SSM via multiyear monitoring and integrated modeling in an urbanizing watershed in China, while five scenarios (baseline, current SSM, improved SSM, future traditional urban development, and future improved SSM scenarios) were comparatively analyzed. The results showed that water quality of ammonia nitrogen (NH3‐N), total phosphorus (TP), chemical oxygen demand (COD), and suspended solid (SS) would deteriorate by both traditional urban development and current SSM design. Compared to other pollutants, NH3‐N and TP showed greatest deterioration by current SSM due to disproportionate management of on‐site runoff quantity‐related and quality‐related problems. Comparatively, the improved SSM design, which incorporated watershed responses into consideration, would reduce current concentrations of NH3‐N, TP, COD, and SS by 0–53.85%, 8.16–38.84%, 23.07–61.03%, and 68.82–77.82%, respectively; and improve water quality by 60–80% in future SMM scenario. Priority management and stricter objectives should be given to those urbanizing regions at the watershed scale. The results of this study should be used as references for future SSM design as well as water resource protection. Plain Language Summary: Sustainable stormwater management (SSM) is vital for urban water resources and water quality protection. However, watersheds serve as the end of the SSM system, the related water quality benefits from SSM have not been fully quantified. To address this problem, five scenarios were evaluated via multiyear monitoring and integrated modeling in an urbanizing watershed. Water bodies in the urbanizing areas are more vulnerable, which would multiply several times in pollutant concentrations by traditional urbanization. However, unexpected deterioration of river quality occurred by current SSM, although local runoff and pollutant loads were controlled. The improved SSM was then given by incorporating watershed response into SSM design to handle water problems at different scales. The findings and approach could undoubtedly facilitate the SSM development and watershed management, and could be applied in other cities and countries because urban expansion has become a global issue. Key Points: Unexpected river quality deterioration was found in current sustainable stormwater management (SSM) due to the neglect of relative reduction proportions in runoff and pollutant loadsVulnerable water bodies were found in urbanizing period, during which NH3‐N and TP were more sensitive to urbanization and SSMImproved SSM design was put forward by considering watershed responses through an integrated model [ABSTRACT FROM AUTHOR]

The high spatial variability of the saturated soil hydraulic conductivity (Ksat) and the effort required for its data sampling have been a challenge for soil scientists to obtain its representativeness at a scale resolution required by watershed management. The objective of this work was to simulate the spatial variability of Ksat and evaluate its uncertainties through sequential Gaussian simulation (SGS) in a subtropical watershed, Southern Brazil. Ksat data were obtained in an experimental grid of 179 points established in a watershed with shallow soils and relief varying from undulating to strong undulating. Experimental and theoretical semivariograms were calculated and the SGS was used to generate 100 equiprobable fields. Local and spatial uncertainties of Ksat were assessed. Lower Ksat uncertainty estimates were found in densely sampled areas. Higher Ksat uncertainty estimates were obtained in soils located at steeper areas of the watershed and on soils formed alongside the main watercourse. Spatial variability maps of Ksat are quite useful for supporting hydrological simulation of the floods in watersheds, identifying areas more prone to groundwater recharge and the effects of different tillage systems on soil water dynamics at watershed scale as well. [ABSTRACT FROM AUTHOR]

Accurate quantification of evapotranspiration (ET) at the watershed scale remains an important research challenge for managing water resources in arid and semiarid areas. In this study, daily latent heat flux (LE) maps at the kilometer scale were derived from the two-source energy budget (TSEB) model fed by the MODIS leaf area index (LAI), land surface temperature (LST) products, and meteorological data from ERA-Interim reanalysis from 2001 to 2015 on the Tensift catchment (center of Morocco). As a preliminary step, both ERA-Interim and predicted LE at the time of the satellite overpass are evaluated in comparison to a large database of in situ meteorological measurements and eddy covariance (EC) observations, respectively. ERA-Interim compared reasonably well to in situ measurements, but a positive bias on air temperature was highlighted because meteorological stations used for the evaluation were mainly installed on irrigated fields while the grid point of ERA-Interim is representative of larger areas including bare (and hot) soil. Likewise, the predicted LE was in good agreement with the EC measurements gathered on the main crops of the region during 15 agricultural seasons with a correlation coefficient r = 0.70 and a reasonable bias of 30 W/m2. After extrapolating the instantaneous LE estimates to ET daily values, monthly ET was then assessed in comparison to monthly irrigation water amounts provided by the local agricultural office added to CRU precipitation dataset with a reasonable agreement; the relative error was more than 89% but the correlation coefficient r reached 0.80. Seasonal and interannual evapotranspiration was analyzed in relation to local climate and land use. Lastly, the potential use for improving the early prediction of grain yield, as well as detecting newly irrigated areas for arboriculture, is also discussed. The proposed method provides a relatively simple way for obtaining spatially distributed daily estimates of ET at the watershed scale, especially for not ungauged catchments.

The estimation of terrestrial carbon sinks in the Qinghai-Tibet Plateau (QTP) still faces significant uncertainties, and the spatiotemporal dynamics of terrestrial carbon sinks along altitudinal gradients remain unexplored. Moreover, the driving mechanisms of terrestrial carbon sinks at the watershed scale in the QTP continue to be lacking. To address these research gaps, based on multi-source remote sensing data and meteorological data, this study calculated the Net Ecosystem Productivity (NEP) in the QTP from 2000 to 2020 using the Modis NPP-soil respiration model. Through the coefficient of variation (CV), the Mann-Kendall test (MK), and the spatial autocorrelation methods, the spatial distribution pattern and spatiotemporal trends of NEP were investigated. Employing a pixel accumulation method, the variation of NEP along altitudinal gradients was explored. Grey relation analysis, Pearson correlation analysis, and Geographical detector (GD) were used to investigate the driving mechanisms of NEP at the watershed scale. Results showed that: (1) the terrestrial ecosystem in the QTP served as a carbon sink, which produced a total of 2.04 Pg C from 2000 to 2020, and the multi-year average of total carbon sinks was 96.92 Tg C; (2) the spatial distribution of NEP shows a decreasing change from southeast to northwest, and the clustering characteristic of NEP is significant at the watershed scale; (3) the elevation of 4507 m we proposed is likely to be a key threshold for biophysical processes of the terrestrial ecosystems in the QTP; (4) the fluctuation and change trend of carbon sources and carbon sinks show significant differences between the East and West; (5) at the watershed scale, precipitation and temperature play a dominant role in the variation of NEP, while the impact of human activities on NEP variation is weak. Our study aims to address the existing knowledge gaps and provide valuable insights into the management of terrestrial carbon sinks in QTP. [Display omitted] • The terrestrial ecosystem in the Qinghai-Tibet Plateau (QTP) shows a carbon sink. • The Net Ecosystem Productivity (NEP) of QTP decreased from Southeast to Northwest. • Climate, terrain, and vegetation factors are the main drivers of NEP. • The elevation of 4,507m is proposed as a key threshold for biophysical processes. [ABSTRACT FROM AUTHOR]

Excessive nutrient supply in agricultural regions has led to various environmental issues, thereby requiring concentrated management owing to its persistent upward trend. Nutrient budgets (NBs), a vital agricultural environmental indicator, are employed for nutrient management in agricultural areas, using data surveyed by administrative agencies. However, the spatial extent of nutrient data for nutrient budgeting is limited by administrative boundaries according to the surveying organization, posing challenges in interpreting spatial patterns at the watershed level. In this study, a novel approach was developed to identify priority nutrient management areas by applying hot spot spatial analysis to watershed-level NBs, considering hydrological characteristics. This method was applied to approximately 850 subwatersheds across the Republic of Korea, where land cover characteristics are complex. Reassessing nutrient budgets at the watershed scale, accounting for overlapping administrative boundary areas and crop cultivation ratios, indicated similar levels between the two methods. Hot spot analysis revealed that watersheds with elevated NBs mirrored the spatial patterns of livestock excreta and cropland. The spatial distribution characteristics of watersheds with high nutrient levels in rivers corresponded with the concentration characteristics of industrial and commercial areas. Therefore, applying watershed-level NBs based on land cover ratios that consider nutrient input characteristics in agricultural regions is deemed appropriate for selecting priority nutrient management areas. Collectively, this study presents a method for selecting nutrient management priority areas by simultaneously considering the spatial characteristics of various environmental factors, such as land cover, livestock excreta, river water quality, and land area-based watershed-specific NBs. The proposed approach, considering mixed land cover characteristics, is anticipated to be valuable for selecting priority management areas in watersheds with diverse pollution sources. Future research is needed to explore nutrient budgets within watersheds, the influence of land use on pollution sources, and their correlation with water quality. • Improving a watershed-scale nutrient budget incorporating cropland ratio • Presenting hotspots of nutrient budgets, livestock manure, cropland ratios, water quality • Identifying priority management watersheds in mixed land-use areas [ABSTRACT FROM AUTHOR]

Copyright of Journal of Remote Sensing is the property of Editorial Office of Journal of Remote Sensing & Science Publishing Co. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carinata (Brassica carinata) is an industrial oilseed feedstock for renewable fuels grown as a winter crop in the southeast US, which may provide a new rotation alternative and benefits for water quality. However, the effects of carinata on water quantity and quality at the watershed and local scales are unknown. In this study, we use the Soil and Water Assessment Tool (SWAT) to assess the potential influence of carinata on water balance components, nutrients and sediment loads under plausible future scenarios of land use change in the upper Suwannee River Basin in the Atlantic Coastal Plain Physiographic Region near Tifton in South‐Central Georgia. Three future scenarios are considered, including planting stand‐alone carinata in winter fallow land every third year, planting stand‐alone winter wheat in winter fallow land every third year, and carinata and winter wheat in rotation, one year of winter carinata followed by two years of winter wheat during simulation periods. The results show that under all three future scenarios, surface runoff, sediment, phosphorus, and nitrogen loadings decrease at both watershed and local scales, with higher average monthly reductions in the stand‐alone carinata scenario versus the stand‐alone winter wheat scenario. When carinata and winter wheat were planted over 36% of the total watershed area, reduction in total sediment, mineral phosphorus, and nitrate loads was ranging from 11.5% to 50.0%. However, when only 12% of the total watershed area was converted to carinata, the simulated reductions ranged from 3.8% to 14.0%. This suggests that the extent of carinata planting is crucial in assessing its hydrologic and water quality benefits. Overall, these results indicate that planting the biofuel carinata as a winter crop can reduce sediment and nutrient loading and provide water quality benefits to downstream waterbodies. [ABSTRACT FROM AUTHOR]

This study attempts to predict future landslide occurrence at watershed scale and calculate the potency of landslide for each sub-watershed at Lompobatang Mountain. In order to produce landslide susceptibility map (LSM) using the statistical model on the watershed scale, we identified the landslide with landslide inventories that occurred in the past, and predict the prospective future landslide occurrence by correlating it with landslide causal factors. In this study, six parameters were used namely, distance from fault, slope, aspect, curvature, distance from river and land use. This research proposed the weight of evidence (WoE) model to produce a landslide susceptibility map. Success and predictive rate were also used to evaluate the accuracy by using Area under curve (AUC) of Receiver operating characteristic (ROC). The result is useful for land use planner and decision makers, in order to devise a strategy for disaster mitigation.

Modelling the linkage between physical habitat and aquatic organisms on multiple spatial scales has become an important tool in the management of rivers. The mesoscale (100–102 m) represents an intermediate resolution in modelling that bridges the gap between available resources and conservation efforts for riverine species. However, existing mesohabitat classification schemes for lotic systems vary significantly in the definition of habitat types as well as in their application in the field. This article aims to provide an overview of current attempts to model the mesoscale pattern of physical habitats with a focus on fish. First, we outline descriptive, qualitative as well as objective, quantitative classification methods that are available in the literature. Next, the ecological relevance of the mesohabitat concept is being discussed, using single‐species and community‐level approaches as examples. Different modelling approaches that describe and quantify riverine mesohabitats are presented, and finally, limitations and uncertainties in the modelling process are discussed, followed by an outline of future perspectives in mesohabitat modelling. [ABSTRACT FROM AUTHOR]

A total of 1165 samples were collected from the topsoil at a depth of 20 cm to explore the effect of soil material and topography on the variation of soil texture classification over a basin of Pengshui in Chongqing, southwest China. Classification and regression tree （CART）method was applied to class the soil texture based on parent materials and terrain indicators（elevation, slope, slope height, slope length, flow accumulation, SAGA topographical wetness index, flow path length, vector ruggedness, measure multi-resolution index of valley bottom flatness, multi-resolution index of the ridge top flatness, diffuse insolation, wind effect, wind exposition index）. The major influencing factors on soil texture class variability were investigated by the CART model. The results showed that：Parent material and topographic factors both had important effects on soil texture class variations, the factors with higher relative importance were parent material （PAR）>wind effect（WindEff）>SAGA topographic wetness index（SAGATWI）; The relative importance of terrain attributes to soil texture class variations varied with parent materials, wind effect（WindEff）and diffuse insolation（DiffuseIns）were the most essential variables for the Ordovician and the Silurian. The CART model produced a good accuracy with 86.3%（P<0.05）for the watershed. The results could provide a scientific basis for the rational planning and management of soil utilization in this area. [ABSTRACT FROM AUTHOR]

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• δ18O P and DGT techniques was synchronously used in lake systems for the first time. • Sediments had lighter δ18O P values than agricultural soils due to the biotic reactions. • Sediments conserved the isotopic signal of terrigenous source. • Terrigenous input still prominently contributed to the P load in lake sediments. The reduction of exogenous emissions of phosphorus (P) is a crucial measure for resolving eutrophication in lakes. However, the input of terrigenous materials still potentially contributes to an increase of P load in lake systems. In this study, we examined the phosphate oxygen isotope (δ18O P) of various P fractions in soils and sediments in a small lake watershed, namely, Shijiuhu watershed. The high-resolution in-situ diffusive gradients in thin films (DGT) technology was also used to survey the dynamic processes of P diffusion from sediment particles to the water. The results demonstrated that lighter δ18O P values (16.2–19.5‰) for individual P fractions in lake sediments were detected compared to other land-use patterns, indicating the cumulative biological P recycling on anaerobic condition. Fe bound P (Fe-P) overall had heavier δ18O P values (17.3–24.8‰) than some of Ca bound P (Ca-P) and equilibrium values, suggesting that Fe-P conserved the parental isotope signatures from terrigenous source and could act as the ideal tracer for the lake sediments. The mixing effect of terrigenous detrital input and biological mineralization made the source identification uncertain by using Ca-P, which had a wider range of δ18O P values (13.0–26.6‰). Additionally, significantly positive correlation (r = 0.551–0.913, p <0.05) between soluble reactive P (SRP) and Fe2+ in interstitial water obtained using DGT measurement revealed the conspicuous release and desorption of solid Fe-P toward the water. High diffusion fluxes from the sediments toward the overlying water further demonstrated that the desorption of Fe-P in the soil-originated sediments toward the solution conspicuously facilitated the accumulation of SRP in lake water. The first-time application of δ18O P isotope combined with in-situ DGT techniques certified that it's feasible for the contribution confirmation from terrigenous to lacustrine environments, and presented the direct evidence for management strategy making about P control and eutrophication restoration at the catchment scale of lakes. [Display omitted] [ABSTRACT FROM AUTHOR]

Pressures on the Brazilian Amazon forest have been accentuated by agricultural activities practiced by families encouraged to settle in this region in the 1970s by the colonization program of the government. The aims of this study were to analyze the temporal and spatial evolution of land cover and land use (LCLU) in the lower Tapajós region, in the state of Pará. We contrast 11 watersheds that are generally representative of the colonization dynamics in the region. For this purpose, Landsat satellite images from three different years, 1986, 2001, and 2009, were analyzed with Geographic Information Systems. Individual images were subject to an unsupervised classification using the Maximum Likelihood Classification algorithm available on GRASS. The classes retained for the representation of LCLU in this study were: (1) slightly altered old-growth forest, (2) succession forest, (3) crop land and pasture, and (4) bare soil. The analysis and observation of general trends in eleven watersheds shows that LCLU is changing very rapidly. The average deforestation of old-growth forest in all the watersheds was estimated at more than 30% for the period of 1986 to 2009. The local-scale analysis of watersheds reveals the complexity of LCLU, notably in relation to large changes in the temporal and spatial evolution of watersheds. Proximity to the sprawling city of Itaituba is related to the highest rate of deforestation in two watersheds. The opening of roads such as the Transamazonian highway is associated to the second highest rate of deforestation in three watersheds.

Landslides represent a serious hazard, particularly in the mountainous area currently. This recent study attempts to predict future landslide occurrence at watershed scale and to calculate the potency of mass movements for each sub-watershed at Lompobatang Mountain. In order to produce landslide susceptibility map (LSM) using the statistical model, we identified landslide inventories that occurred in the past, and predicted the prospective future landslide occurrence by correlating it with causal factors. In this study, six parameters were used namely, distance from fault, slope, aspect, curvature, distance from river and land use. This research proposed the Weight of Evidence (WoE) model to produce a landslide susceptibility map. Success and predictive rate were also used to evaluate the accuracy by using Area Under Curve (AUC) of Receiver Operating Characteristic (ROC). The result would be useful for land use planner and decision makers, in order to devise a strategy for disaster mitigation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • We created an intermediate complexity model for simulating channel evolution at watershed scales. • The model matches physical understanding of channel change. • It can also predict erosion processes in accordance with field data sets. • The model is useful for predicting channel evolution and answering relevant management questions. Abstract Excessive river erosion and sedimentation threatens critical infrastructure, degrades aquatic habitat, and impairs water quality. Tools for predicting the magnitude of erosion, sedimentation, and channel evolution processes are needed for effective mitigation and management. We present a new numerical model that simulates coupled river bed and bank erosion at the watershed scale. The model uses modified versions of Bagnold's sediment transport equation to simulate bed erosion and aggradation, as well as a simplified Bank Stability and Toe Erosion Model (BSTEM) to simulate bank erosion processes. The model is mechanistic and intermediate complexity, accounting for the dominant channel evolution processes while limiting data requirements. We apply the model to a generic test case of channel network response following a disturbance and the results match physical understanding of channel evolution. The model was also tested on two field data sets: below Parker Dam on the lower Colorado River and the North Fork Toutle River (NFTR) which responded dramatically to the 1980 eruption of Mount St. Helens. It accurately predicts observed channel incision and bed material coarsening on the Colorado River, as well as observations for the upstream 18 km of the NFTR watershed. The model does not include algorithms for extensive lateral migration and avulsions and therefore did not perform well in the lower NFTR where the channel migrated across a wide valley bottom. REM is parsimonious and useful for simulating network scale channel change in single thread systems responding to disturbance. [ABSTRACT FROM AUTHOR]

Source-sink theory is an ecological framework that describes how site and habitat-specific demographic rates and patch connectivity can explain population structure and persistence across heterogeneous landscapes. Although commonly used in conservation planning, source-sink theory has rarely been applied to the management of invasive species. This study tested whether the common carp, one of the world’s most invasive species, exhibits source-sink dynamics in a representative watershed in the Upper Mississippi River Basin comprised of a dozen interconnected ponds and lakes. To test for source-sink population structure, we used standard fish sampling techniques, tagging, and genetic assignment methods to describe habitat-specific recruitment rates and dispersal. Five years of sampling revealed that while adult carp were found across the entire watershed, reproductive success (the presence of young carp) was restricted to shallow ponds. Additionally, nearly a third of the carp tagged in a representative pond dispersed into the connected deeper lakes, suggesting that ponds in this system serve as sources and lakes as sinks. This possibility was confirmed by microsatellite analysis of carp tissue samples (n = 1041) which revealed the presence of two distinct strains of carp cohabitating in the lakes, whose natal origins could be traced back to one of two pond systems, with many adult carp attempting to migrate back into these natal ponds to spawn. We conclude that the distribution and persistence of invasive carp in complex interconnected systems may often be driven by source-sink dynamics and that their populations could be controlled by suppressing reproduction in source habitats or by disrupting dispersal pathways, instead of culling individuals from sink habitats. [ABSTRACT FROM AUTHOR]

Sediment connectivity has been shown in recent years to explain how the watershed configuration controls sediment transport. However, we find no studies develop a watershed erosion modeling framework based on sediment connectivity, and few, if any, studies have quantified sediment connectivity for gently rolling systems. We develop a new predictive sediment connectivity model that relies on the intersecting probabilities for sediment supply, detachment, transport, and buffers to sediment transport, which is integrated in a watershed erosion model framework. The model predicts sediment flux temporally and spatially across a watershed using field reconnaissance results, a high-resolution digital elevation models, a hydrologic model, and shear-based erosion formulae. Model results validate the capability of the model to predict erosion pathways causing sediment connectivity. More notably, disconnectivity dominates the gently rolling watershed across all morphologic levels of the uplands, including, microtopography from low energy undulating surfaces across the landscape, swales and gullies only active in the highest events, karst sinkholes that disconnect drainage areas, and floodplains that de-couple the hillslopes from the stream corridor. Results show that sediment connectivity is predicted for about 2% or more the watershed’s area 37 days of the year, with the remaining days showing very little or no connectivity. Only 12.8 ± 0.7% of the gently rolling watershed shows sediment connectivity on the wettest day of the study year. Results also highlight the importance of urban/suburban sediment pathways in gently rolling watersheds, and dynamic and longitudinal distributions of sediment connectivity might be further investigated in future work. We suggest the method herein provides the modeler with an added tool to account for sediment transport criteria and has the potential to reduce computational costs in watershed erosion modeling. [ABSTRACT FROM AUTHOR]

Knowledge of the environmental chemistry of antimony (Sb) in aquatic systems is limited, and a better understanding of its geochemical behaviour is needed. Based on a fourteen-year survey (2003-2016) with monthly measurements of dissolved and particulate Sb at five sites in the Lot-Garonne river system, combined with daily measurements of water discharge and suspended particulate matter, this work characterises Sb behaviour in the upstream major river watershed of the Gironde Estuary. The survey provides a first regional geochemical Sb background in the Garonne River watershed for dissolved (~0.2 µg L-1) and Th-normalised particulate Sb (Sbp/Thp ~0.25) concentrations. Observed decreasing temporal trends (<1 ng L-1 in dissolved and <0.02 mg kg-1 in particulate concentrations per month) at sites representing natural concentrations probably reflect global atmospheric Sb dynamics at the watershed scale. Regular seasonal cycles of solid/liquid partitioning, with higher solubility in summer (matching high dissolved and low particulate concentrations), reflect water-discharge and suspended particulate matter transport dynamics and possibly seasonal (bio)geochemical processes. Furthermore, this coefficient decreases from the river to the estuarine reaches (from average log10Kd 4.3 to minimum 3.7 L kg-1), suggesting an increased solubility of Sb in estuarine systems. Flux estimates indicate the relevance of the dissolved fraction in Sb transport (with negligible influence of the colloidal fraction) and a total flux (dissolved +; particulate) entering the Gironde Estuary of 5.66 ± 2.96 t year-1 (~50 %; particulate). These results highlight the importance of timescales and environmental parameters for understanding and prediction of future Sb biogeochemistry. [ABSTRACT FROM AUTHOR]

We evaluated the impacts of domestic and agricultural rainwater harvesting (RWH) systems in three watersheds within the Albemarle-Pamlico river basin (southeastern U.S.) using life cycle assessment (LCA) and life cycle cost assessment. Life cycle impact assessment (LCIA) categories included energy demand, fossil fuel, metals, ozone depletion, global warming, acidification, smog, blue and green water use, ecotoxicity, eutrophication, and human health effects. Building upon previous LCAs of near-optimal domestic and agricultural RWH systems in the region, we scaled functional unit LCIA scores for adoption rates of 25%, 50%, 75%, and 100% and compared these to conventional municipal water and well water systems. In addition to investigating watershed-scale impacts of RWH adoption, which few studies have addressed, potential life cycle cost savings due to reduced cumulative energy demand were scaled in each watershed for a more comprehensive analysis. The importance of managing the holistic water balance, including blue water (surface/ground water), green water (rainwater) use, and annual precipitation and their relationship to RWH are also addressed. RWH contributes to water resource sustainability by offsetting surface and ground water consumption and by reducing environmental and human health impacts compared to conventional sources. A watershed-wide RWH adoption rate of 25% has a number of ecological and human health benefits including blue water use reduction ranging from 2–39 Mm3, cumulative energy savings of 12–210 TJ, and reduced global warming potential of 600–10,100 Mg CO2 eq. Potential maximum lifetime energy cost savings were estimated at $5M and $24M corresponding to domestic RWH in Greens Mill and agricultural RWH in Back Creek watersheds.