Assessment of Runoff and Sediment Yields Using the AnnAGNPS Model in a Three-Gorge Watershed of China

Soil erosion has been recognized as one of the major threats to our environment and water quality worldwide, especially in China. To mitigate nonpoint source water quality problems caused by soil erosion, best management practices (BMPs) and/or conservation programs have been adopted. Watershed models, such as the Annualized Agricultural Non-Point Source Pollutant Loading model (AnnAGNPS), have been developed to aid in the evaluation of watershed response to watershed management practices. The model has been applied worldwide and proven to be a very effective tool in identifying the critical areas which had serious erosion, and in aiding in decision-making processes for adopting BMPs and/or conservation programs so that cost/benefit can be maximized and non-point source pollution control can be achieved in the most efficient way. The main goal of this study was to assess the characteristics of soil erosion, sediment and sediment delivery of a watershed so that effective conservation measures can be implemented. To achieve the overall objective of this study, all necessary data for the 4,184 km2 Daning River watershed in the Three-Gorge region of the Yangtze River of China were assembled. The model was calibrated using observed monthly runoff from 1998 to 1999 (Nash-Sutcliffe coefficient of efficiency of 0.94 and R2 of 0.94) and validated using the observed monthly runoff from 2003 to 2005 (Nash-Sutcliffe coefficient of efficiency of 0.93 and R2 of 0.93). Additionally, the model was validated using annual average sediment of 2000–2002 (relative error of −0.34) and 2003–2004 (relative error of 0.18) at Wuxi station. Post validation simulation showed that approximately 48% of the watershed was under the soil loss tolerance released by the Ministry of Water Resources of China (500 t·km−2·y−1). However, 8% of the watershed had soil erosion of exceeding 5,000 t·km−2·y−1. Sloping areas and low coverage areas are the main source of soil loss in the watershed

Calibration and Evaluation of Phosphorus Loss in Surface Runoff and Subsurface Drainage Using APEX

Modeling phosphorus (P) loss through surface runoff and subsurface drainage is essential because it helps understand how P transfers to the water bodies in an inexpensive and feasible way. P loss into the Great Lakes leads to eutrophication. APEX (Agriculture Policy/Environmental eXtender) is extended from EPIC (Environmental Policy Integrated Climate model) and can simulate management practices and land use impacts for various land sizes from a field to a small watershed. However, APEX has not been tested in Lake Erie Region. This research, therefore, represents the first effort to use APEX to simulate P loss in this area. Field data were obtained from experiments conducted at the Agriculture and Agri-Food Canada\u27s Whelan experimental farm in Woodslee, ON, Canada, with corn-soybean rotation. Calibration and evaluation of APEX was executed to test its capability in simulating the impacts of chemical fertilizers and cattle manure on P loss. Different potential evapotranspiration equations (PET) and curve number (CN) equations were used to determine the most suitable one for this study area. Statistical analysis was used to assess the model performance. Satisfactory results were obtained from the simulation of APEX in the Brookstone clay loam soil

Soil Nitrogen in Response to Interseeded Cover Crops in Maize–Soybean Production Systems

Improved agronomic management strategies are needed to minimize the impact that current maize (Zea mays L.) and soybean (Glycine max (L.) Merr.) production practices have on soil erosion and nutrient losses, especially nitrogen (N). Interseeded cover crops in standing maize and soybean scavenge excess soil N and thus reduce potential N leaching and runoff. The objectives were to determine the impact that pennycress (Thlaspi arvense L.) (PC), winter camelina (Camelina sativa (L.) Crantz) (WC), and winter rye (Secale cereale L.) (WR) cover crops have on soil N, and carbon (C) and N accumulation in cover-crop biomass. The cover crops were interseeded in maize at the R5 growth stage and in soybean at R7 in four replicates over two growing seasons at four locations. Soil and aboveground biomass samples were taken in autumn and spring. Data from the maize and soybean systems were analyzed separately. The results showed that cover crops had no effect on soil NH4+-N under both systems. However, winter rye decreased soil NO3−-N up to 76% compared with no-cover-crop treatment in the soybean system. Pennycress and WC scavenged less soil N than WR. Similarly, N and C accumulation in PC and WC biomass were less than in WR, in part because of their poor growth performance under the interseeding practice. Until PC and WC varieties with improved suitability for interseeding are developed, other agronomic practices may need to be explored for improving N scavenging in maize and soybean cropping systems to reduce nutrient leaching and enhance crop diversification

Advancing understanding of development policy impacts on transboundary river basins: Integrated watershed modelling of the Lower Mekong Basin.

The management of transboundary river basins across developing countries, such as the Lower Mekong River Basin (LMB), is frequently challenging given the development and conservation divergences of the basin countries. Driven by needs to sustain economic performance and reduce poverty, the LMB countries are embarking on significant land use changes in the form hydropower dams, to fulfill their energy requirements. This pathway could lead to irreversible changes to the ecosystem of the Mekong River, if not properly managed. This thesis aims to explore the potential effects of changes in land use —with a focus on current and projected hydropower operations— on the Lower Mekong River network streamflow and instream water quality. To achieve this aim, this thesis first examined the relationships between the basin land use/land cover attributes, and streamflow and instream water quality dynamics of the Mekong River, using total suspended solids and nitrate as proxies for water quality. Findings from this allowed framing challenges of integrated water management of transboundary river basins. These were used as criteria for selecting eWater’s Source modelling framework as a management tool that can support decision-making in the socio-ecological context of the LMB. Against a combination of predictive performance metrics and hydrologic signatures, the model’s application in the LMB was found to robustly simulate streamflow, TSS and nitrate time series. The model was then used for analysing four plausible future hydropower development scenarios, under extreme climate conditions and operational alternatives. This revealed that hydropower operations on either tributary or mainstream could result in annual and wet season flow reduction while increasing dry season flows compared to a baseline scenario. Conversely, hydropower operation on both tributary and mainstream could result in dry season flow reduction. Both instream TSS and nitrate loads were predicted to reduce under all three scenarios compared to the baseline. These effects were found to magnify under extreme climate conditions, but were less severe under improved operational alternatives. In the LMB where hydropower development is inevitable, findings from this thesis provide an enhanced understanding on the importance of operational alternatives as an effective transboundary cooperation and management pathway for balancing electricity generation and protection of riverine ecology, water and food security, and people livelihoods

Modelling of Hydrological and Non-Point Source Pollution Regimes in Big Creek Watershed

The hydrological and non-point source loading processes of the Big Creek Marsh and Big Creek Watershed were investigated in this study. The Big Creek Watershed in south-western Ontario was modelled with AnnAGNPS (Annualized AGricultural Non-point Source). The AnnAGNPS model was first calibrated and validated with observed streamflow data in the neighbouring Canard River Watershed. Nash-Sutcliffe model efficiencies for monthly streamflow predictions were 0.75 and 0.72, for the calibration and validation periods. In the Big Creek Watershed the north-eastern and south-eastern regions were found to produce the highest sediment and nutrient loads. A water budget model for the Big Creek Marsh was developed to investigate hydrologic historic processes in the wetland. In the model assessment three potential wetland operating plans were reviewed and compared to the observed pumping data. A sensitivity analysis of the water budget model was performed. An investigation of Lake Erie\u27s influence on the Marsh was also included