The Panjiakou and Daheiting Reservoir system of northern Hebei Province has problems with eutrophication related to phosphorus input. The main source of phosphorus is the load from the Luan He River due to a combination of runoff from agricultural lands and untreated sewage from an upstream city with a population of over 3 million people, as well as numerous sources of untreated sewage in the rural villages. A study was conducted during a period of extended low rainfall and stream flow on the causes of eutrophication and the relationship between chlorophyll-a concentration and total phosphorus load. Annual phosphorus loads and reservoir chlorophyll-a concentrations of the Panjiakou/Daheiting Reservoir system are similar to those reported for other eutrophic lakes, and follow the trend of worldwide lakes described by the Vollenweider-OCED model.
This model can therefore be used to guide load reduction strategies in northern China. Concentrations of total nitrogen and molar ratios of total nitrogen to phosphorus in the input streams are typical to those observed in agricultural landscapes, suggesting that fertilization of crops is a primary source of nutrients to the reservoirs; however, measurements of nitrogen and oxygen isotopes in nitrate indicate that human and animal waste must also contribute to the nutrient inputs and that treatment of wastewater must be considered in a load reduction strategy. Three main strategies for phosphorus load reduction for this reservoir system are: (1) decreasing the amount of untreated domestic and industrial sewage volumes from an upstream urban area; (2) control of soil erosion in areas with highly erodible soil or soils with high soluble phosphorus levels; and, (3) management of the lake aquaculture to limit the production of bait-eating fish.