Study Of Source Of Particulate Organic Matter In Migratory Bird Habitat In Poyang Lake

The edge lakes of Poyang Lake are low-lying lands when water levels decline,where water flow slow and nutritive salt are easily accumulated.We analyzed the physicochemical characteristic and trophic states using the evaluation standard of entrophication and the experience frequency of the water quality index,and compared water quality types with surface water environmental quality standards in different months and water levels in Dahuchi Lake and Shahu Lake,Poyang Lake’s Migratory bird Reserve in Jiangxi Province.We discriminated the origins of suspended organic matters in different seasons and water levels by carbon and nitrogen stable isotopes(δ¹³C andδ¹⁵N)and ratio（C/N）in Dahuchi Lake and Shahu Lake.The results showed that concentrations of COD_Mn,TP and NH₄⁺-N were high in Oct.and Dec.,however low when water level rise in May.NO₃^--N concentration was high in May but a little different in other months.TN concentrations were highest in Dec.（2.7±0.4and 2.4±0.5 mg/L）.In Oct.after water declined,TN concentrations were not high but TP concentrations were high（0.27±0.0 and 0.33±0.02 mg/L）,and Chl-a concentrations were highest（10.4±1.2 and 15.6±1.7μg/L）.Water quality isⅢtype and middle trophic state when water level rise in May,andⅢ^Ⅳtype and primary entrophication in wet season in Aug,howeverⅤtype and entrophication in dry season in the two lakes.Theδ¹³C orδ¹⁵N had significant differences in different water levels.When the water level flowing in May,theδ¹³C were the most positive,average-26.4±0.9‰;when the dry season in Oct.,theδ¹³C were the most negative,average-31.2±1.1‰.Theδ¹⁵N were lower in flooding seasons,however relativity high in dry seasons.The C/N in Oct.was lowest,average 6.5±0.6 less than 7.The variation trend of carbon or nitrogen stable isotope or C/N ratio in each months was similar between Dahuchi Lake and Shahu Lake,and there wasn’t significant difference forδ¹³C,δ¹⁵N or C/N in same month between Dahuchi Lake and Shahu Lake.However,theδ¹³C andδ¹⁵N in Dahuchi Lake were more than 0.1⁰.5‰and C/N were lower than 0⁰.4 than those of Shahu Lake.At high water levels of May and Aug.,the suspended organic matters were mainly from soil organic matter through rivers transportation in May;the suspended organic matters in Oct.were mainly from algas,and the surface sediment had some contributions;at lower water levels of Dec.,Mar.and Apr.,the suspended organic matters were mainly from surface sediments and the excrement of migratory bird in Dec..The phytodetritus in wetland had more much contribution in Mar.and Apr.