Pruell Richard J, Taplin Bryan K, Lake James L, Jayaraman Saro
US Environmental Protection Agency, National Health and Ecological Effects Research Laboratory, Office of Research and Development, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882, USA.
Mar Pollut Bull. 2006 Jun;52(6):612-20. doi: 10.1016/j.marpolbul.2005.10.009. Epub 2005 Nov 21.
Stable nitrogen isotope ratios were used to study the incorporation of anthropogenically-derived nitrogen into the food webs of salt marsh systems along a contamination gradient in Narragansett Bay. Nitrogen isotope ratios (delta(15)N) were measured in six estuarine species collected from three marshes along this gradient, monthly from June to October between 1997 and 1999. A significant decrease in delta(15)N was found with distance along the estuary for four of the six species. Significant differences were found among monthly isotope ratios for some species. Nitrogen isotope ratios in sea lettuce (Ulva lactuca) increased during the summer season with highest delta(15)N values measured during September and October. This trend was most pronounced at the station receiving the highest nutrient inputs. Elevated delta(15)N values at this station appeared to correlate with seawater ammonia/nitrate concentration ratios. The temporal variations in delta(15)N suggest that care should be taken in species selection and the design of sampling schemes of studies using delta(15)N for monitoring anthropogenic nutrients in aquatic systems. Sampling programs designed to determine long-term trends should consider species that do not show rapid fluctuations in isotope ratios. The mud snail, Nassarius obsoletus, responded this way in the present study. Studies designed to measure short-term changes should include species such as U. lactuca, which rapidly respond to isotope changes. The results from this study also help to establish a baseline for nitrogen isotope values in Narragansett Bay. This information can be used to monitor future trends in nitrogen inputs to this estuary.
利用稳定氮同位素比率研究了纳拉甘西特湾沿污染梯度的盐沼系统食物网中人为源氮的掺入情况。在1997年至1999年期间，于6月至10月每月从沿该梯度的三个沼泽地采集的六种河口物种中测量氮同位素比率（δ¹⁵N）。六种物种中的四种，其δ¹⁵N随沿河口距离的增加而显著降低。一些物种的月度同位素比率之间存在显著差异。海莴苣（Ulva lactuca）的氮同位素比率在夏季增加，9月和10月测得的δ¹⁵N值最高。这种趋势在接收营养输入最高的站点最为明显。该站点升高的δ¹⁵N值似乎与海水氨/硝酸盐浓度比率相关。δ¹⁵N的时间变化表明，在使用δ¹⁵N监测水生系统中人为养分的研究中，物种选择和采样方案设计应谨慎。旨在确定长期趋势的采样计划应考虑同位素比率不显示快速波动的物种。在本研究中，泥螺（Nassarius obsoletus）就是这样一种物种。旨在测量短期变化的研究应包括像海莴苣这样对同位素变化快速做出反应的物种。本研究结果也有助于建立纳拉甘西特湾氮同位素值的基线。该信息可用于监测该河口未来的氮输入趋势。
