Impacts of urbanization and climate change on water quantity and quality in the Carp River watershed

Pressure on water resources has reached unprecedented levels during the last decades because of climate change, industrialization, and population growth. As a result, vulnerability to inappropriate water availability and/or quality is increasing worldwide. In this paper, a Soil & Water Assessment Tool (SWAT) model of the Carp river watershed located in the city of Ottawa, Ontario was calibrated and validated. The model was then used to evaluate the individual and coupled impacts of urbanization and climate change on water quantity (discharge) and quality (nitrogen and phosphorus loads). While most of the watershed is currently rural, the headwaters will undergo rapid urbanization in the future, and there are concerns about possible negative impacts on water quantity and quality. Seven scenarios were developed to represent various watershed configurations in terms of land use and climate regime. Future climate time series were obtained by statistically downscaling the outputs of nine regional climate models, ran under representative concentration pathways (RCP)4.5 and RCP8.5. The impacts were evaluated at the main outlet and at the outlet of an upstream sub-watershed that would be most affected by urbanization. Results show that climate change and urbanization's impacts vary greatly depending on the spatial scale and geographic location. Globally, the annual average discharge will increase between 6.75 and 9.34% by 2050, while changes in annual average nitrogen and phosphorus loads will vary between −1.20 and 24.84%, and 19.15 and 23.81%, respectively. Local impacts in sub-watersheds undergoing rapid urbanization would be often much larger than watershed-scale impacts.

Evaluating the influence of hydrological condition on the phosphorus loads in an agricultural river basin using the SWAT model

Excessive phosphorus is an important cause of eutrophication. For river basin management, source identification and control of nonpoint source (NPS) pollution are difficult. In this study, to explore influences of hydrological conditions on phosphorus, the Soil and Water Assessment Tool (SWAT) model is applied to the Luanhe River basin in North China. Moreover, influences of the spatial scale of the livestock and poultry amount data on estimations of phosphorus loads are also discussed. The results show that applying town-level livestock and poultry amount data allows the model to perform better when estimating phosphorus loads, indicating that using data at a finer administrative level is necessary. For the typical wet year, the estimated annual phosphorus load was 2.6 times that in the typical dry year. Meanwhile, the contribution of pollution in summer to the annual load is greater in the wet year than that in the dry year. The spatial distributions of subbasins with high unit loads of phosphorus differ under different hydrological conditions, meaning that critical areas for pollution control vary with the wetness of each year. All these findings indicate that for pollution control at basin scale, considering the seasonal and interannual variabilities in hydrological conditions is highly demanded.

Water Resource Risk Assessment Based on Non-Point Source Pollution

As one of the most important causes of water quality deterioration, NPS (non-point source) pollution has become an urgent environmental and livelihood issue. To date, there have been only a few studies focusing on NPS pollution conforming to the estimation, and the pollution sources are mainly concentrated in nitrogen and phosphorus nutrients. Unlike studies that only consider the intensity of nitrogen and phosphorus loads, the NPS pollution risk for the China’s Fuxian Lake Basin was evaluated in this study by using IECM (Improve Export Coefficient Model) and RUSLE (Revised Universal Soil Loss Equation) models to estimate nitrogen and phosphorus loads and soil loss and by using a multi-factor NPS pollution risk assessment index established on the basis of the data mentioned above. First, the results showed that the load intensity of nitrogen and phosphorus pollution in the Fuxian Lake Basin is low, so agricultural production and life are important sources of pollution. Second, the soil loss degree of erosion in the Fuxian Lake is mild, so topography is one of the most important factors affecting soil erosion. Third, the risk of NPS pollution in the Fuxian Lake Basin is at a medium level and its spatial distribution characteristics are similar to the intensity characteristics of nitrogen and phosphorus loss. Nitrogen, phosphorus, sediment, and mean concentrations are important factors affecting NPS pollution. These factors involve both natural and man-made environments. Therefore, it is necessary to comprehensively consider the factors affecting NPS in order to assess the NPS risk more accurately, as well as to better solve the problem of ecological pollution of water resources and to allow environmental restoration.