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To study the potential effects of climate change on water quality in a shallow reservoir in China, the field data analysis method is applied to data collected over a given monitoring period. Nine water quality parameters (water temperature, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, total nitrogen, total phosphorus, chemical oxygen demand, biochemical oxygen demand and dissolved oxygen) and three climate indicators for 20 years (1992-2011) are considered. The annual trends exhibit significant trends with respect to certain water quality and climate parameters. Five parameters exhibit significant seasonality differences in the monthly means between the two decades (1992-2001 and 2002-2011) of the monitoring period. Non-parametric regression of the statistical analyses is performed to explore potential key climate drivers of water quality in the reservoir. The results indicate that seasonal changes in temperature and rainfall may have positive impacts on water quality. However, an extremely cold spring and high wind speed are likely to affect the self-stabilising equilibrium states of the reservoir, which requires attention in the future. The results suggest that land use changes have important impact on nitrogen load. This study provides useful information regarding the potential effects of climate change on water quality in developing countries.

This study presents the Yuqiao Reservoir Water Quality Model (YRWQM), a three-dimensional hydrodynamic and water quality model of the Yuqiao reservoir, China. The YRWQM was developed under the environmental fluid dynamics code (EFDC) model and was calibrated and verified to hydrodynamic and water quality data, using two sets of observed data from January 1 to December 31, 2006 and from May 1 to October 31, 2007, respectively. The primary hydrodynamic and transport driving forces are inflows/outflows and surface wind stresses. Considering effects of water transfer and wind on the advection-dispersion processes, the model results showed better agreements with observed data in the reservoir. The YRWQM predicted the variations of water quality resulting from agricultural pollution which flowed into the reservoir with floods lasting for 12 days in 2009. The results indicated that the concentrations of chemical oxygen demand and total nitrogen were increased 225 and 314%, respectively. Considering the interactions between chlorophyll-a and nitrogen in the model, the results indicated the reservoir was not a nitrogen-limited environment. We suggest the management should focus on agricultural pollution strategies for the reservoir during the flood period. The YRWQM could be a useful tool for water sources management in the reservoir.

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To improve water quality aiid construct a landscape lagoon in China, an ecological reconstruction plan for the Qilihal Lagoon (Changli County, Hebei) is proposed. A three-dimensional numerical model (EFDC) was used to study the water renewal capacity in the reconstructed lagoon by using residence time, exposure time and connectivity as timescales. The influences of wind and the depth of the tidal inlet of the lagoon on water renewal capacity were also investigated. The results show that the transport and diffusion processes in the lagoon were strongly influenced by wind and the modification of the tidal inlet. The lagoon under a no wind condition exhibited a low water renewal capacity, especially at the end areas (exposure time, 700-1,000 days). The wind action notably enhanced the water renewal capacity in the lagoon, and the exposure times were all lower than 400 days in the whole region. The optimal inlet depth for the water renewal in the lagoon was predicted to be 4.0 m. The connectivity matrices identified which areas of the domain would be most affected by a pollution source under different conditions. This study examines transport and diffusion processes in a reconstructed lagoon, which could be informative for ecological reconstruction planning.

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