From field soil sampling to watershed model: Upscaling by integrating information entropy and interpolation method.

Soil property data plays a crucial role in watershed hydrology and non-point source (H/NPS) modeling, but how to improve modeling accuracy with affordable soil samplings and the effects of sampling information on H/NPS modeling remains to be further explored. In this study, the number of sampling points and soil properties were optimized by the information entropy and the spatial interpolation method. Then the sampled properties were parameterized and the effects of different parameterization schemes on H/NPS modeling were tested using the Soil and Water Assessment Tool (SWAT). The results indicated that the required sampling points increased successively for soil bulk density (SOL_BD), soil saturated hydraulic conductivity (SOL_K) and soil available water capacity (SOL_AWC). Compared to the traditional database (Harmonized world soil database), the NSE and R2 performance by new scheme increased by 22.8% and 10.5%, respectively. The entropy-based optimization reduced the sampling points by 13.2%, indicating a more cost-effective scheme. Compared to hydrological simulation, sampled properties showed greater effects on NPS modeling, especially for nitrogen. This proposed method/framework can be generalized to other watersheds by upscaling field soil sampling information to the watershed scale, thus improving H/NPS simulation.

Pesticide fate at watershed scale: A new framework integrating multimedia behavior with hydrological processes.

Pesticide pollution has been one serious ecological and environmental issue due to its wide application, high toxicity, and complex environmental behavior. The fugacity model has been widely used to quantify biogeochemical cycles of pesticides due to its clear compartments, simple structure, and easy-accessible data. However, the lack of detailed hydrological processes limits its application for large and heterogeneous watershed. In present study, a new framework was proposed through integration of hydrological processes of SWAT and pesticide fate of fugacity model, and was applied into a typical watershed in the Three Gorges Reservoir Area, China. The results showed that surface runoff, soil erosion, and percolation varied spatiotemporally, which highlighted the importance of considering regional and seasonal heterogeneity of pesticide transport variables in the fugacity model. The amount of dichlorvos (DDV) and chlorpyrifos (CHP) in air, water, soil, and sediment phase were estimated as 0.26 kg, 19.77 kg, 1.06 × 104 kg, and 0.55 kg, respectively. Spatiotemporally, pesticide concentrations in water phase peaked in summer, while the middle and southwest regions of the watershed were identified as the hotspots for pesticide pollution. Compared with the classical model, the new framework provided technical support for the pesticide assessment at watershed scale with heterogeneous hydrological conditions, which can be easily extended to other watersheds, and integrated with other models for comprehensive agricultural management.

Nitrogen removal enhanced by benthic bioturbation coupled with biofilm formation: A new strategy to alleviate freshwater eutrophication.

Excessive nitrogen input into the water caused eutrophication thereby reducing biodiversity and degrades freshwater function. Nitrogen pollution in sediments is one key reason that makes eutrophication difficult to control. The physicochemical technologies such as dredging and coverage for sediment pollution easily destroyed and homogenized aquatic habitats. To alleviate freshwater eutrophication in ecological way, this work combined the functions of bioturbation and biofilm to test their effect on the removal of nitrogen from sediment and water. The total nitrogen removal by employing the coupled function (bioturbation + biofilm, SCB) was greater than that of the single function (bioturbation or biofilm). The mean efficiency of total nitrogen removal in SCB treatment was 3.19 times that of the control without chironomids nor biofilm medium. Chironomid bioturbation promoted nitrogen release from sediments to the overlying water. Biofilm enhanced the conversion and removal of nitrogen stirred up by chironomids, resulting the lowest concentration of total nitrogen in overlying water of SCB treatment. The enhancement of nitrogen removal may be due to the coupled function increased the abundance of denitrifying and anammox functional bacteria in sediment and biofilm. Therefore, the method of combining benthic animals with biofilm medium is not only a viable solution for reducing sedimentary nitrogen loading in freshwater ecosystems, but also a solution to mitigate eutrophication in the overlying water. The restoration and management for aquatic ecosystems should consider protecting habitat for benthic organisms while maintaining heterogeneity for biofilm.