Temporal And Spatial Variation In Carbon And Nitrogen Stable Isotope Of Particulate Organic Matter In Liuxihe Reservoir

Temporal and spatial variations ofδ¹⁵N andδ¹³C of particulate organic matter were investigated in Liuxihe reservoir,a subtropical oligo-mesotrophic reservoir during May-December in 2008.δ¹³C_POM varied from -23.6‰to -31.8‰,with an average of -26.5‰,close toδ¹³C terrestrial C₃ plants with an average -27‰.The mean ofδ¹³C_POM indicate that terrestrial detritus dominated POM.No spatial variation inδ¹³C andδ¹⁵N values was found for surface samples of POM.However,δ¹³C_POM decreased lightly from summer to winter.The average ofδ¹³C_POM in rain season(-24.9‰) was significantly different from dry season(-28.1‰). Hydrology had a great effect to composition of POM.During rain season reservoir received a lot of terrestrial detritus,but phytoplankton made large contribution to POM in dry season.The magnitude ofδ¹³C_POM variation was smaller than temperate and subarctic lake,but bigger than trophic water.It can be explained by lower production and terrestrial detritus dominating POM.δ¹⁵N_POM of Liuxihe reservoir varied from 3.8‰to 8.3‰.The minimumδ¹⁵N_POM(3.8‰) may be attributed to the occurrence of nitrogen fixation.δ¹³C of zooplankton more depleted than POM in all samples.Theδ¹³C amplitude between zooplankton and POM indicated composition of POM in my study.A response of phytoplanktonδ¹³C to eutrophication was studied through nutrient addition enclosure experiments.Results show that high nutrient addition(eutrophication) decreased phytoplankton carbon isotope fractionation,increasedδ¹³C.Theδ¹³C of zooplankton was increased from control enclosure to high trophic state enclosures consistent withδ¹³C of phytoplankton.An inverse relationship betweenδ¹⁵N of zooplankton and trophic state,because of adding nitrogen nutrition with a lowδ¹⁵N.