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Cyanobacterial blooms in Lake Taihu occurred at the end of April 2007 and had crucial impacts on the livelihood of millions of people living there. Excessive nutrients may promote bloom formation. Atmospheric nitrogen (N) and phosphorus (P) deposition appears to play an important role in algal bloom formation. Bulk deposition and rain water samples were collected respectively from May 1 to November 30, 2007, the period of optimal algal growth, to measure the bulk atmospheric deposition rate, wet deposition rate, and dry deposition rate for total nitrogen (TN; i.e., all species of nitrogen), and total phosphorus (TP; i.e., all species of phosphorus), in northern Lake Taihu, China. The trends of the bulk atmospheric deposition rate for TN and the wet deposition rate for TN showed double peaks during the observation period and distinct influence with plum rains and typhoons. Meanwhile, monthly bulk atmospheric deposition rates for TP showed little influence of annual precipitation. However, excessive rain may lead to high atmospheric N and P deposition rates. In bulk deposition samples, the average percentage of total dissolved nitrogen accounting for TN was 91.2% and changed little with time. However, the average percentage of total dissolved phosphorus accounting for TP was 65.6% and changed substantially with time. Annual bulk atmospheric deposition rates of TN and TP during 2007 in Lake Taihu were estimated to be 2,976 and 84 kg km(-2) a(-1), respectively. The results showed decreases of 34.4% and 78.7%, respectively, compared to 2002-2003. Annual bulk deposition load of TN for Lake Taihu was estimated at 6,958 t a(-1) in 2007 including 4,642 t a(-1) of wet deposition, lower than the values obtained in 2002-2003. This may be due to measures taken to save energy and emission control regulations in the Yangtze River Delta. Nevertheless, high atmospheric N and P deposition loads helped support cyanobacterial blooms in northern Lake Taihu during summer and autumn, the period of favorable algal growth.

Nitrogen dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km2), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system nitrogen dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake nitrogen limitation by removing excess nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and nitrogen fixation was observed only in the main lake. Reflecting nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake. [ABSTRACT FROM AUTHOR]

Identification of sources of nutrient pollution is a first step towards remediation of eutrophication in aquatic ecosystems. The stable isotope nitrogen-15 (15N) is a natural indicator of nitrogen (N) source and biogeochemistry. We sampled Lake Taihu, a hyper-eutrophic lake in eastern China, and major inflow rivers during winter and spring of 2004 to determine concentration and δ15N of nitrate (NO). Nitrate concentrations in rivers and the lake were higher, in most cases, in spring than in winter. δ15N of NO was not correlated with NO concentration, indicating that concentrations alone are insufficient to describe N sources. Results show that riverine N inputs in winter are influenced by discharge of human sewage into rivers and the lake. In spring, however, wastewater inputs to the lake appear to be balanced by fertilizers, atmospheric, and/or N2 fixation sources. Rain NO concentrations were seasonally high and isotopically enriched compared to potential sources, indicating that rain may be a significant or even dominant source of N to the lake during the rainy season. δ15N values show that urbanized areas of the lake have more sewage-derived N than those areas dominated by agriculture, aquaculture, or industry. This observation has important implications for human health, since Lake Taihu is a source of drinking and irrigation water as well as fish for human consumption. [ABSTRACT FROM AUTHOR]

To evaluate seasonal and regional variations in precipitation chemistry in Lake Taihu Basin, 5 cities around the lake were selected for monthly collection of rainfall samples from July 2002 to June 2003. The analytical parameters included pH, cations (K+, Na+, Ca2+, Mg2+, ), anions (F−, Cl−, ), total nitrogen (TN) and total phosphorus (TP). In descending order, concentrations (in meqL−1) of the ions in wet deposition can be ordered as >Cl−>Na+>Mg2+>K+>F− with concentratin percentages of 48. 7%, 19. 1%, 11. 6%, 8. 1%, 5. 6%, 2. 6%, 1. 7%, 1. 6% and 1%, respectively. Rainfall was seasonally variable, with high rates in spring and summer but low rates in autumn and winter, while ion concentrations followed the reverse seasonal cycle. To evaluate deposition rates (DR) of different elements, average DR of each ion was calculated from a simple model. Most of the highest DRs of these substances occurred in Suzhou and Wuxi, located east and north of Lake Taihu, which shows there was considerable variation over the 5 stations. This regional pattern reflects local emissions from industry and agriculture, and suggests that steps need to be taken by local governments for particle emission reductions. The estimated annual inputs of TN and TP over the lake are 4722 and 75t, respectively, which accounts for around 16. 5% and 7. 3% of the annual total external inputs of these nutrients. Primary productivity in Lake Taihu associated solely with wet deposition of nitrogen to the lake was estimated to be 7. 03×106 mol Cday−1. These results suggest that wet deposition can have significant impacts on the trophic status of Lake Taihu and that attention to nutrients in precipitation should be included in the management of external nutrient loads to the lake. [Copyright &y& Elsevier]