饶河枯水期主要鱼类营养级位置及其影响因素

Trophic position and its impact on fish in Raohe River during the dry season,Jiangxi Province

稳定同位素技术已经越来越多地被用来研究淡水生态系统的结构与功能。利用氮稳定同位素技术测定了枯水季节饶河鱼类等消费者的营养级位置,比较上、中、下游及入湖口鱼类营养级的空间差异,并分析了影响饶河鱼类营养级位置的主要因素。研究结果表明,饶河鱼类的δ15N值范围为4.7‰—15.6‰,大部分鱼类的δ15N值集中在10‰—14‰之间,其中鄱阳湖间下鱵的δ15N值最大,为(15.6±1.6)‰;乔木湾鲫的δ15N值最小值,为(4.7±0.9)‰。根据δ15N值计算可知,饶河鱼类占有3—4个营养等级。75%的鱼类种类所占的营养级大于3,而营养级小于2的鱼类种类不到10%,可能与枯水期鱼类活动范围受限,种间捕食作用增强,肉食性或饥饿现象增加有关。另外,饶河鱼类的营养级也存在着空间差异,表现为鄱阳湖湖区和入湖口处的鱼类营养级比上、中、下游的鱼类营养级要大。该结果与颗粒有机物POM的δ15N值呈现一致的变化,反映了饶河鱼类的营养级位置主要受到食物来源的影响,与鱼类的个体大小无明显相关。

Stable isotope techniques have been increasingly used to assess the structure and function of freshwater ecosystems. In this study, we used stable nitrogen isotope analysis to determine the trophic position of fish in Raohe River during the dry season. Then we estimated the relationships between body length and trophic position of Pseudobagrus fulvidraco and Hemiculter bleekeri and the δ15N values of POM, respectively. Spatial variation in trophic position of fish was compared among the upper, middle, and lower areas and estuary of the Raohe River, and the main impacts of the trophie position were also analyzed. The results showed that δ15N values of fish in Raohe River ranged from 4.7‰-15.6‰, and for most of the fish species δ15N values were concentrated from 10‰ to 14‰. The values of δ15N in Hemiramphus intermedius were highest （（15.6＋1.6）‰） , which was collected in Lake Poyang. However, crucian carp collected in Qiaomuwan had the minimum values of δ15N （（4.7±0.9）‰）. From the δ15N values of consumers, we estimated that fish occupied 3 to 4 trophic levels in Raohe River; 75% of fish species had a high trophic position of more than 3, and the trophie position of almost 10% of fish species was less than 2, which might be related to the increase in predation and starvation because of enhanced predator-prey interactions during the dry season. In addition, spatial variation in the trophic position of fish also occurred in Raohe River, reflecting that fish in Lake Poyang and its estuary had a higher trophic position than those in the upper, middle, and lower areas. That results were consistent with variation in δ15N values of POM, which were strongly affected by intensity of N input from the catchment, revealing that the trophic position of fish in Raohe River was largely affected by food sources but not by body size. Consequently, this study may add to the knowledge of the structure of the food web in Raohe River.