Characteristic Of Stable Isotopic Composition In Lake Taihu And Calculate The Water Evaporation

The compositions of hydrogen and oxygen stable isotopes in lake water are important to the research in hydrology, meteorology and paleoclimatology. In this study, long-term and continuous measurement on the compositions of HDO and H₂¹⁸O in lake water （δDL and δ18OL） were conducted over Lake Taihu, the deuterium excess （d_L） was calculated, the temporal variability and controlling factors were analyzed, and calculated on the basis of water evaporation and water residence time. The results indicated:（1） The variation of isotopic enrichment in lake water were significant, ranging from -59.8‰ to -24.2‰ for δDL from-8.6‰ to -2.6‰ for δ18OL, and from -7.9‰ to 12.9‰ for d_L, respectively. With comparison to cold season,δDL and δ18OL were higher and d_L was lower during warm season. For the whole lake, δ18O ranged from-6.50‰ to -3.54‰, which variation is 2.96‰;ranged from -41.73‰--25.11‰, variation is 16.62‰; The range variation of d_L is from-1.98‰ to 6.29‰, which variation 8.27‰。（2） Changes in spatial scale, the lake of HDO and H₂¹⁸O components with the lake in the direction of flow are gradually enriched d_L instead. The space distribution features in different seasons, however, as the movement direction of the lake cumulative evaporation, water of HDO and H₂¹⁸O components gradually enrichment.（3） On monthly time-scale, lake evaporation and the ratio of total water inputs lost by evaporation controlled the isotopic enrichment in lake water. When lake evaporation or the ratio increased,δ5DL and δ18OL increased, but d_L decreased. Over Lake Taihu, the isotopic composition in precipitation and water temperature did not control the isotopic enrichment.（4） From Oct.2013 to Sep.2014, two kinds of method to calculate the water evaporation were small difference,that using isotopic method is 842.99mm less than Priestley-Taylor 863.06mm. If our residence time calculations were based on the isotopic data collected at the single site （MLW）, the residence time was reduced to 42 ±7 and 24±7 days using HDO and H₂¹⁸O as tracer respectively.