Temporal and spatial changes in nutrients and chlorophyll-α in a shallow lake, Lake Chaohu, China: An 11-year investigation

Temporal and spatial changes of total nitrogen (TN), total phosphorus (TP) and chlorophyll-a (Chl-a) in a shallow lake, Lake Chaohu, China, were investigated using monthly monitoring data from 2001 through 2011. The results showed that the annual mean concentration ranges of TN, TP, and Chl-a were 0.08–14.60 mg/L, 0.02–1.08 mg/L, and 0.10–465.90 μg/L, respectively. Our data showed that Lake Chaohu was highly eutrophic and that water quality showed no substantial improvement during 2001 through 2011. The mean concentrations of TP, TN and Chl-a in the western lake were significantly higher than in the eastern lake, which indicates a spatial distribution of the three water parameters. The annual mean ratio of TN:TP by weight ranged from 10 to 20, indicating that phosphorus was the limiting nutrient in this lake. A similar seasonality variation for TP and Chl-a was observed. Riverine TP and NH4+ loading from eight major tributaries were in the range of 1.56 × 104−5.47 × 104 and 0.19 × 104−0.51 × 104 tons/yr over 2002–2011, respectively, and exceeded the water environmental capability of the two nutrients in the lake by a factor of 3–6. Thus reduction of nutrient loading in the sub-watershed and tributaries would be essential for the restoration of Lake Chaohu.