Application of integrated hydrological models to manage a watershed’s water resources are increasingly finding their way into the decision-making processes. The Soil and Water Assessment Tool (SWAT) is a multi-process model integrating hydrology, ecology, agriculture, and water quality. SWAT is a continuation of nearly 40 years of modeling efforts conducted by the United States Department of Agriculture (USDA) Agricultural Research Service (ARS). A large number of SWAT-related papers have appeared in ISI journals, building a world-wide consensus around the model’s stability and usefulness. The current issue is a collection of the latest research using SWAT as the modeling tool. Most models must undergo calibration/validation and uncertainty analysis. Unfortunately, these sciences are not formal subjects of teaching in most universities and the students are often left to their own resources to calibrate their model. In this paper, we focus on calibration and uncertainty analysis highlighting some serious issues in the calibration of distributed models. A protocol for calibration is also highlighted to guide the users to obtain better modeling results. Finally, a summary of the papers published in this special issue is provided in the Appendix.

https://www.mdpi.com/2073-4441/10/1/6/pdf

A Guideline for Successful Calibration and Uncertainty Analysis for Soil and Water Assessment: A Review of Papers from the 2016 International SWAT Conference

Understanding the drivers and implications of anthropogenic disturbance of ecological connectivity is a key concern for the conservation of biodiversity and ecosystem processes. Here, we review human activities that affect the movements and dispersal of aquatic organisms, including damming of rivers, river regulation, habitat loss and alteration, human-assisted dispersal of organisms and climate change. Using a series of case studies, we show that the insight needed to understand the nature and implications of connectivity, and to underpin conservation and management, is best achieved via data synthesis from multiple analytical approaches. We identify four key knowledge requirements for progressing our understanding of the effects of anthropogenic impacts on ecological connectivity: autecology; population structure; movement characteristics; and environmental tolerance/phenotypic plasticity. Structuring empirical research around these four broad data requirements, and using this information to parameterise appropriate models and develop management approaches, will allow for mitigation of the effects of anthropogenic disturbance on ecological connectivity in aquatic ecosystems.

Human effects on ecological connectivity in aquatic ecosystems: Integrating scientific approaches to support management and mitigation ; Science of the Total Environment

Total nitrogen removal in biochar amended non-aerated vertical flow constructed wetlands for secondary wastewater effluent with low C/N ratio: Microbial community structure and dissolved organic carbon release conditions

Anthropogenic reactive nitrogen deposition and associated nutrient limitation effect on gross primary productivity in inland water of China

Enhanced denitrification and power generation of municipal wastewater treatment plants (WWTPs) effluents with biomass in microbial fuel cell coupled with constructed wetland.

Effects of different covering systems and carbon nitrogen ratios on nitrogen removal in surface flow constructed wetlands

The Sichuan Basin is the main agricultural production area of the upper reaches of the Yangtze River and is also an extremely important ecological area because it is rich in biodiversity and has complex and diverse landscape types. The dominant soil type, purple soil, is prone to rapid soil erosion and weathering processes because it is shallow and rich in phosphorus and other nutrients. Field experiments were conducted to reveal the effects of precipitation and topography characteristics on nonpoint source pollutants from purple soil. The results showed that total phosphorus (TP) load and TP concentration both increased with increasing rainfall amount, and there was an initial time of runoff and sediment yield before runoff generation. Moreover, the TP load generally increased with precipitation intensity as setting a coincident value of rainfall amount; however, the difference between TP load at 30 and 60 mm/h was minimal as was the difference between 90 and 120 mm/h. Similarly, TP concentration increased with increasing precipitation intensity. In terms of topographical conditions, TP load increased with increasing gradient, but began to decline when the gradient was about 20°, which indicates that 20° is the critical gradient for TP loss. There was a significant positive correlation between gradient and TP concentration when the gradient was <15°, whereas the increase in TP concentration slowed as the gradient increased.

https://www.mdpi.com/2073-4441/9/5/315/pdf

Effects of Precipitation and Topography on Total Phosphorus Loss from Purple Soil

The upper reach of the Yangtze River is an ecologically sensitive region where water loss, soil erosion, and nonpoint source (NPS) pollution are serious issues. In this drainage area, regosol is the most widely distributed soil type. Cultivation on regosol is extensive and total nitrogen (TN) has become a common NPS pollutant. Artificial rainfall experiments were conducted to reveal the influence mechanisms of rainfall and terrain on TN losses from regosol. The results showed that there were positive correlations between precipitations and TN loads but negative ones between precipitations and TN concentrations. Furthermore, negative correlations were more obvious on fields with slopes of 5° and 25° than on other slopes. With increasing rainfall intensity, TN loads rose simultaneously. However, TN concentration in runoff-yielding time presented a decline over time. As far as terrain was concerned, TN loads grew generally but not limitlessly when slopes increased. Similarly, TN concentrations also rose with rising slopes; upward trends were more obvious for steeper slopes. Furthermore, the initial runoff-yielding time became longer for steeper slopes and the differences under various rainfall intensity conditions diminished gradually.

https://www.mdpi.com/2073-4441/9/3/167/pdf

Influence Mechanisms of Rainfall and Terrain Characteristics on Total Nitrogen Losses from Regosol

Visual platform for water quality prediction and pre-warning of drinking water source area in the Three Gorges Reservoir Area

Nowadays, cleaner production is getting more and more attention, and nuclear power has been widely used due to its low energy consumption and lower pollution. Most nuclear power plants in China, including those under construction and constructed ones, are coastal. For a nuclear power plant, however, its large amount of water consumption and high guarantee rate of water quality will have impacts on the regional water-resource allocation in the site area. During the water-discharge process, low-level radioactive wastewater and warm water will be discharged, while medium or even highly radioactive wastewater will be generated in an accident, both of which will affect the environment of the receiving water. In 2016, the Chinese government began to work on the Guidelines for Water Resources Assessment of Coastal Nuclear Power Plant Projects. The compilation work, led mainly by the Ministry of Water Resources, focused on analyzing key technical points of the impacts of water intake, wastewater discharge, and their reduction measures, as well as water-protection measures. In this study, the technical requirements for impact analysis of water-draw, wastewater discharge, and their remedial measures for coastal nuclear power construction projects in different periods were put forward. Lastly, the measures for water conservation, protection, and management were given. All the technical requirements and measures gave a research basis and technical support for the formulation of the guidelines.

https://www.mdpi.com/2071-1050/13/11/6308/pdf

Xiaowen Ding

Papers

Effects of different covering systems and carbon nitrogen ratios on nitrogen removal in surface flow constructed wetlands

Effects of Precipitation and Topography on Total Phosphorus Loss from Purple Soil

Influence Mechanisms of Rainfall and Terrain Characteristics on Total Nitrogen Losses from Regosol

Visual platform for water quality prediction and pre-warning of drinking water source area in the Three Gorges Reservoir Area

Technical Points of Water-Draw and Discharge Impact Analysis in Guidelines for Water Resource Assessment of Coastal Nuclear Power Plants