Stable isotope value and trophic position of fishes in Three Gorges Reservoir and Changshou Reservoir

Abstract

为探究人为活动对水库鱼类食物来源和营养级关系的影响，选择人为影响程度较低的三峡水库和影响程度较高的长寿湖水库为研究对象，应用碳、氮稳定同位素技术对两个水库鱼类δ¹³C值、δ¹⁵N值和营养级进行比较分析.结果显示：长寿湖水库鱼类δ¹³C平均值（-22.66‰±1.94‰）与三峡水库（-22.59‰±1.87‰）较为接近，但长寿湖鱼类的δ¹⁵N值（13.95‰ ±3.02‰）显著高于三峡水库鱼类的δ¹⁵N值（11.98‰ ±2.25‰）.根据δ¹⁵N值计算不同食性鱼类间的营养级，三峡水库营养级为肉食性鱼类 > 杂食性鱼类 > 浮游生物食性鱼类 > 草食性鱼类；而长寿湖中则表现为浮游生物食性鱼类 > 肉食性鱼类 > 杂食性鱼类 > 草食性鱼类，营养级出现了异常现象.这一结果表明，对于人为影响（如人工喂食鱼饲料等）较大的水体，采用δ¹⁵N值计算不同食性鱼类间的营养级存在不确定性.;To investigate the effect of the food sources and trophic position of fish in different anthropogenic interference of Three Gorges Reservoir (TGR) and Changshou Reservoir, we used stable isotopes analysis to investigate the δ¹³C and δ¹⁵N signatures of fish in these two reservoirs. Meanwhile, differences in isotopic values and trophic position of fish were also compared. The result showed that little variation in δ¹³C values of fish was observed between TGR and Changshou Reservoir. The average δ¹³C values of fish observed in Changshou Reservoir (-22.66‰±1.94‰) was similar to that in TGR (-22.59‰±1.87‰). While, the δ¹⁵N values of fish in Changshou Reservoir (13.95‰ ±3.02‰) were significantly higher than that in TGR (11.98‰ ±2.25‰). We calculated the trophic level among different fishes based on the value of δ¹⁵N. The trophic level decreased in order of carnivorous fish > omnivorous fish > planktivore fish > herbivorous fish in TGR. While, a relative difference was occurred at Lake Changshou in terms of the trophic level which was conducted as planktivore fish > carnivorous fish > omnivorous fish > herbivorous fish when compared with those in TGR. The result indicated the uncertainty of trophic level derived from value of δ¹⁵N for aqueous systems with intensive influences of human activities.