Changes of nutrients and phytoplankton chlorophyll-α in a large shallow lake, Taihu, China:: an 8-year investigation

Inter-annual changes of total nitrogen (TN) and total phosphorus (TP) and phytoplankton chlorophyll-a (Chla) in a large shallow lake, Taihu China, were analysed using the monthly monitoring data covering the period of 1991-1999. The concentrations of TN, TP and Chla showed marked gradients in the lake from high values near the northern river input in the inner Meiliang Bay towards lower concentrations the lake centre. TN was always much greater than TP (>>7:1 by weight) indicating that nitrogen was not a limiting factor in the lake. Annual averages of TN, TP and Chla increased until 1996 declining thereafter possibly because of the controlling of wastewater discharged from the catchment area by the local government. The internal nutrient loading in the lake was low because of the well-mixed condition and the low organic content of superficial sediment. Our results suggest that the recovery process in the lake might have started in 1996.