Dajingshan,Fenghuangshan and Meixi reservoirs are located in Zhuhai,a coastal city in southern China,and they function to supply drinking water to Zhuhai and Macau.For eff ectively supplying waster,they are hydrologically connected and Dajingshan Reservoir first receives the water pumped from the river at Guangchang Pumping Station,and then feeds Fenghuangshan Reservoir,and the two well-connected reservoirs are mesotrophic.Meixi Reservoir is a small and oligotrophic water body and feeds Dajingshan Reservoir only in wet seasons when overfl ow occurs.Particulate organic matter(POM)was collected from three hydrologically connected water supply reservoirs,and seasonal variations of POM were ascertained from stable carbon and nitrogen isotopes in wet and dry seasons,and the ef fects of pumping water and reservoir connectivity on POM variations and composition were demonstrated by the relationships of the stable isotope ratios of POM.Seasonality and similarity of stable carbon and nitrogen isotopes of POM varied with hydrodynamics,connectivity and trophic states of the four studied water bodies.The two wellconnected reservoirs displayed more similar seasonality for δ~(13)C_(POM) than those between the river station and the two reservoirs.However,the opposite seasonality appeared for δ~(15)N_(POM) between the above waters and indicates dif ferent processes aff ecting the stable carbon and nitrogen isotopes of POM.δ~(13)C_(POM) and δ~(15)N_(POM) changed little between wet and dry seasons in Meixi Reservoir-a low productive and rain-driven system,suggesting little POM response to environmental changes in that water system.As expected,connectivity enhanced the similarity of the stable isotope ratios of POM between the water bodies. Dajingshan, Fenghuangshan and Meixi reservoirs are located in Zhuhai, a coastal city in southern China, and they function to supply drinking water to Zhuhai and Macau.For eff ectively supplying waster, they are hydrologically connected and Dajingshan Reservoir first receives the water pumped from the river at Guangchang Pumping Station, and then feeds Fenghuangshan Reservoir, and the two well-connected reservoirs are mesotrophic.Meixi Reservoir is a small and oligotrophic water body and feeds Dajingshan Reservoir only in wet seasons when overfl ow occurs. Particulate organic matter (POM) was collected from three hydrologically connected water supply reservoirs, and seasonal variations of POM were ascertained from stable carbon and nitrogen isotopes in wet and dry seasons, and the ef fects of pumping water and reservoir connectivity on POM variations and compositions were demonstrated by the relationships of the stable isotope ratios of POM. Seasonal and similarity of stable carbon and nitrogen i sotopes of POM varied with hydrodynamics, connectivity and trophic states of the four studied water bodies. Two well connected reservoirs displayed more similar seasonality for δ ~ (13) C_ (POM) than those between the river station and the two reservoirs. Still, the (15) N_ (POM) between the above waters and indicates dif ferent processes aff ecting the stable carbon and nitrogen isotopes of POM.δ ~ (13) C_ (POM) and δ ~ (15) N_ POM) changed little between wet and dry seasons in Meixi Reservoir-a low productive and rain-driven system, suggesting little POM response to environmental changes in that water system. As expected, connectivity enhanced the similarity of the stable isotope ratios of POM between the water bodies.