运用稳定同位素技术分析大宁河主要鱼类营养层级

运用氮稳定同位素技术分析了大宁河静水水域和流水河段主要鱼类的氮稳定同位素比值和营养层级,并对静水水域不同水文时期相同鱼类的营养层级进行了比较研究。结果表明, 颗粒有机物(POM)氮稳定性同位素变化幅度较大, 并存在季节差异。大宁河下游静水水域鱼类15N 值范围为4.5417.51, 营养级处于1.513.88, 平均营养层级为2.49;上游流水水域鱼类的15N 值范围为2.2510.81, 营养层级范围为1.494.01, 平均营养层级为2.87。大宁河上游鱼类的平均营养层级大于下游静水水域, 可能是由于上游底栖生物丰富, 鱼类倾向摄食适口性更高的动物性食物而导致。大宁河下游静水水域汛期的鱼类营养层级较非汛期的值显著降低, 可能是因为汛期的水文扰动影响鱼类摄食中间捕食者, 以及水位的降低导致鱼类食物竞争增加迫使其摄食低营养水平的食物。重复基准生物采样建立精确充足的基线值以及确定合适的富集度,是提高营养层级评估准确性的重要手段。  

THE ANALYSIS OF THE TROPHIC LEVELS OF THE MAJOR FISH SPECIES IN THE DANING RIVER USING STABLE ISOTOPE TECHNOLOGY

In this study, we measured the stable nitrogen isotope ratios of the major fish species in the lotic reaches and the impounded reaches of the Daning River to identify their trophic levels, and we compared the mean trophic levels of several conspecifics in lentic waters during different hydrological periods. The results showed that the 15N values of particulate organic matter (POM) fluctuated in a wide range and exhibited significant seasonal variation. The 15N values of species in the lentic downstream ranged from 4.54 to 17.51, and the trophic levels of these organisms were 1.513.88 with an average of 2.49. In the upstream, the 15N values of fish species varied between 2.25 and 10.81, and their trophic levels were in the range of 1.494.01 with an average of 2.87. The fact that the mean trophic levels were higher in the upstream than that in the downstream, which indicated that the fish tended to consume preferable invertebrate in the lotic areas probably due to their high diversity and abundant biomass. The mean trophic levels of conspecifics in the impounded waters were significantly lower in the flooding period than that in the non-flooding period. This is most likely because the hydrological disturbance affected the intermediate predators. Another possibility is that during the low-water period, the fish in the downstream need to forage for food at lower trophic levels because of the intense competition. To improve the assessment of the trophic levels, we will need to determine the appropriate trophic discrimination values and to establish an adequate isotopic baseline by repeated sampling of the baseline organisms.