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Chemical compositions of rainwater collected in three stations in Taihu Lake in Jiangsu Province, China between March and May 2003 were analyzed through numerical simulations and field observation data. In terms of average ion deposition rate in spring at the air/water interface, of all anions, that of SO42− was the largest followed by NO3−, whereas among all cations, Ca2+ concentration and the rate was the largest, and then NH4+ was the next. The correlation of ion concentration indicated that the catchment of the lake has been artificially polluted considerably. Using backward trajectory analysis, the raining water in the stations in Taihu Lake was classified. In spring, marine-originated rain is the main contribution to this area, counting for 92.7% of the total precipitation, in which SO42−, NO3− and NH4− contributed 89.2%, 88.1%, and 88.3% respectively to the total spring-rain chemicals, whereas land-originated rains contributed in a small amount. However, the ion concentration in the land-originated rain was higher and acidic, causing considerable harm to local ecosystem. The analysis of backward trajectory analysis shows that three types of air masses influenced the chemical composition of the lake water, namely, air mass from NE direction, air mass from SW direction, and local air mass. Although the local air masses often produced small rainfall amount, but the nature of high ion concentration and high acidity impacted the local ecosystem rmmarkably. The ion concentration and rainfall from long-distance boreal air mass are clearly greater than those in austral air.

Chromophoric dissolved organic matter (CDOM) is the light absorption fraction of dissolved organic carbon (DOC) that absorbs light in both the ultraviolet and visible ranges. The spatial and temporal distribution of CDOM in aquatic ecosystems can have important effects on ecosystem productivity, negatively impacting primary productivity due to CDOM absorbs light at both ultraviolet and visible wavelengths while positively impacting secondary productivity by fueling of microbial respiration by photo-degraded CDOM. In water color remote sensing, o-verlaps of pigment absorption spectra with CDOM absorption at blue wavelength generally complicate the use of chlorophyll a retrieval algorithms that are based on remotely sensed ocean color and lead to overestimated chlorophyll a concentration. In addition, high concentrations of CDOM can also act as a photoprotectant against UV damage for aquatic organisms. However, the protection against UV radiation provided by dissolved humic material for a-quatic biota may be diminished if photodegradation of CDOM by UV radiation and acidification increase the UV transparency in lakes. CDOM absorption measurements and their relationship with DOC, and fluorescence are presented in Meiliang Bay of Lake Taihu based on a field investigation and lab analysis to show the spatial distribution of CDOM. Absorption spectral of CDOM was measured from 240 to 800 nm. Concentrations of DOC ranged from 10. 48 to 19. 72 mg/ L with an average of 13. 20±2. 78 mg/L. CDOM absorption coefficients at 280 nm and 355 nm were in the range 18.73-31.91 m-1(average 23. 19±4.36m-1) and 4. 63 -7. 14 m-1 ( average 5. 76±0. 90 m-1) , respectively. The values of the DOC-specific absorption coefficient at 355 nm ranged from 0. 34 to 0. 57 L/(mg·m). Fluorescence emission at 450 nm, excited at 355 nm, had a mean value of 1. 69±0. 77 nm-1. A significant lake zone difference is found in DOC concentration, CDOM absorption coefficient and fluorescence. This regional distribution pattern was in agreement with the location of sources of yellow substance; highest concentrations close to river mouth under the influence of river inflow, lower values in outlet of Meiliang bay. CDOM fluorescence and absorption coefficient were significantly and positively correlated. The results show a good correlation between CDOM absorption and DOC coefficients during 280 -500 nm short wavelength intervals. The coefficient of variation between CDOM absorption and DOC concentration decreased with the increase of wavelength from 280 to 500 nm. The linear regression equations between fluorescence, DOC concentration and absorption coefficients at 355 nm are: Fn(355) = 0.692(±0. 135)a(355) -2.297(±0.786), a(355) =0.233(±0.061)DOC +2.690(±0.816), respectively. The exponential slope coefficient ranged from 11.0 to 14.9μm-1 with a mean value 13. 86±0.91μm-1 , 15.8-20.7μm-1 with a mean value 18.54±1. 11μm-1 and 9.9-13.9μm-1 with a mean value 12.93±0.92μm-1 over the 280 -500 nm, 280 -360 nm and 360 -440 nm intervals. A significant negative linear correlation was found between spectral slope coefficient and DOC specific absorption coefficient, but a significant positive linear correlation for spectral slope coefficient and the ratio of a( 250)/a (365). Larger specific absorption coefficient corresponds to smaller a(250)/a(365) and spectral slope coefficient, which shows higher ratio humic in CDOM.

Lake Taihu is one of the five largest freshwater lakes and also one of the most-studied and better-understood water bodies in China. There have been many studies on nutrient distribution and concentrations in the water body; however, the amount and chemical forms of nutrients input from the atmosphere to Meiliang Bay are largely unknown. To fully understand and assess the impact of atmospheric P on water quality of Meiliang Bay, we have quantified the atmospheric input of P by measuring its concentrations in aerosols during spring of 2003. Aerosol samples were collected at eastern part of the lake for determination of phosphorus concentrations in the atmospheric aerosols. The aerosol P was speciated into soluble inorganic phosphorus, insoluble inorganic phosphorus, and organic phosphorus. The average concentrations of the total aerosol P in spring are 0. 157 μg/m3. And about 15. 6% - 51. 0% of atmospheric phosphorus is soluble inorganic phosphorus. Through estimating the flux of aerosol phosphorus to Meiliang Bay, we found that dry deposition of P has an important impact on the water quality of Meiliang Bay.

It has been observed and studied that the natural restoration process of aquatic vegetation in the experimental enclosure of northern lakeside, Lake Taihu, from 1997 to 1999 years. It is found that the local macrophytes, for example, the Nymphoides peltata, Trapa sp. and Potamogeton malainus Mig, can be naturally restored in the bare lakeside of big shallow eutrophication lakes by an enclosed protection methods. The cover area by species of Nymphoides peltata and Trapa sp. has taken up to 14.3% and 12.7% of the total enclosure area in the summer of 1998, respectively. The companion species of vegetation are Potamogeton malainus Mig, Hydrilla verticillata Royle and Vallisneria spiralis L. The affection to the natural restore of macrophytes by anthropologic readping and fish culture has also been discussed. According to the results of enclosure experiment, it has provided a strategy for control of eutrophication in big shallow lakes, for example, Taihu Lake.

It has been measured that the pH value and concentrations of nutrients such as N and P etc. in the rain and runoff at the mouth of Meiliang Bay, Lake Taihu, from January 1998 to June 2000. Due to the affection of rainfall, the TIN, PO 3- 4 and COD Mn are amounts to 10-15%, 2.0% and 4-6% of the total pollutes loads that was enter to the lake in the same period respectively. It was measured also that the total hard ions and alkalinity concentrations at the mouth of Meiliang Bay, Lake Taihu, in the March June of 1999. According to the analysis with historic dada, it has been found that the ratio of total hard ions over to the alkalinity in water of lake was raised with time. This phenomenon could reflect the response of aquatic ecosystem, Lake Taihu, to the deposition of acid rainfall in long term.

The contents of nitrogen and phosphorus and ferrous in the column sediments and their interstitial water were analyzed and compared in the main regions of Taihu Lake in 1998. The results show that the upper layer(0—10cm) contained higher contents in TN and TP and than the lower. And NH 4 N and PO 4 P in the interstitial water are a bit higher in the seriously polluted waters than those in the gently polluted waters. However, those of the lower layers are slightly higher in the gently polluted waters than those in the seriously polluted. It was indicated that there was no distinct corresponding relationships between NH 4 N/PO 4 P contents in the interstitial water and TN/TP contents in the sediments. The ferrous concentration in the interstitial water is distinctly in positive correlation with NH 4 N content ( R =0.9234).