人为营养物质输入对汉丰湖不同营养级生物的影响--稳定C、N同位素分析

Effects of anthropogenic nutrient input on organisms from different trophic levels in Hanfeng Lake:evidence from stable carbon and nitrogen isotope analysis

以长江一级支流小江上游的汉丰湖为研究对象,设置了4个采样点(影响组:A,B;对照组:C,D),应用碳、氮稳定性同位素探讨人类生活污水和农业面源污染对汉丰湖水生生态系统中不同营养级水平生物类群的影响。结果表明:影响组POM(颗粒有机物)和螺类碳、氮稳定性同位素比值范围分别为-25.93‰—-24.63‰、4.12‰—9.86‰,-14.28‰—-21.60‰、7.97‰—19.99‰;对照组POM(颗粒有机物)和螺类碳、氮稳定性同位素比值范围分别为-25.62‰—-22.51‰、0.01‰—6.56‰,-22.96‰—-19.21‰、6.75‰—8.89‰;不同组间POM和初级消费者螺类碳同位素比值无明显空间变化(P>0.05),而氮稳定性同位素比值空间变化显著(P<0.05)。因此,在汉丰湖食物网中,氮稳定性同位素特征更好地反应了营养物质(人为输入)吸收和富集的信息。与固着藻类、鱼类等相比,POM和软体动物螺类更适合作为环境评价的指示物。影响组A、B样点的部分生物类群已经受到了人为营养物质输入的影响,影响强度B样点区域>A样点区域。结果建议加强汉丰湖水环境保护,控制污水排放量及提高污水处理水平,对于保护小江和三峡库区水质具有十分重要的意义。

The carbon and nitrogen stable isotope analysis have been used to study the aquatic ecological system and trophic ecology since the early 1970s. With the increasing of human activities, many kinds of pollution, such as industrial waste water, widespread pollution from the overuse of fertilizers, and domestic sewage and rubbish, were discharged into rivers and lakes, causing aquatic eutrophication, which has resulted in many severe ecological consequences like the disappearance of aquatic plants and the decrease in biodiversity. Therefore, it is vital to monitor the eutrophication as early as possible. The carbon and nitrogen stable isotope analysis are a good method of checking and evaluating the trophic conditions of aquatic ecology. Moreover, many studies were conducted with regard to the organic materials in human sewage as well as the influences of the input of nutrient materials on the aquatic ecology environment. And the organisms of the Hanfeng Lake have been also faced with the threats of domestic sewage water and widespread pollution from the overuse of fertilizers produced by surrounding residents. In the present study, the stable isotope approach was used and we compared the difference of isotopic signatures of the same species between the impacted areas （A and B sites） and the control areas （C and D sites）.. So the aims of the present study were trying to investigate the effects of human sewage and agricultural non-point source input in organisms from the different trophic levels （primary producers and primary consumers） in the Hanfeng Lake, an upper reaches of the Yangtze River. The results showed that the carbon and nitrogen stable isotope values of POM and sanil samples were various in different groups. In impact groups, the values of POM samples were -25.93‰ --24.63‰ forδ13C and 4.12 ‰ -9.86‰ for δ15N, the values of snail samples ranged from -14.28‰ - -21.60 ‰ （δ13C） and 7.97 ‰ - 19.99‰ （δ15N）; In control groups, the values of bothe POM and snails samples were -25.62- -22.51‰ （δ13C）、0.01-6.56‰ （δ15N）,-22.96--19.21‰ （δ13C）、6.75-8.89‰ （δ15N）, respectively;.The δ13C values for either POM and snails （primary consumers） were not significantly different between different sampling groups （P〉0.05）, while the change of δ15N in different sampling groups varied greatly （P〈0.05）. The relative trophic position of primary producer, such as periphytic algae, POM （mainly composed of phytoplankton） and primary consumers （snails）, are higher in impact groups than in those of control groups, whereas there is no significant difference in the relative trophic levels of the other higher trophic level consumers, such as carp （Cyprinus carpio）, crucian （Carassius auratus） and Amur catfish （Silurus asotus）. Therefore, the nitrogen stable isotope signature was proved to better describe the information on the absorption and enrichment of anthropogenically derived material in food webs of the Hanfeng Lake. Compared with the other organisms（e.g. periphytic algae and fish）, POM and snails were more sensitive to pollution than other species, and could be more appropriate to serve as an indicator of assessing the quality of environment. Moreover, the organisms from both impacted groups （site A and site B） in the Hanfeng Lake have been profoundly influenced by anthropogenic inputs of nutrient matter, and site B received a more stronger interference than site A. In conclusion, it has important significance to strengthen the protection of the environment of the Hanfeng Lake, and control the effluent discharge amount for protecting the water quality of the Xiaojiang River and even the Three Gorges Reservoir Area.