Changes in food web dynamics of low Arctic ponds with varying content of dissolved organic carbon

An influx of terrestrial dissolved organic carbon (DOC) into freshwater habitats can regulate a range of ecosystem characteristics, from water clarity to productivity. To understand the extent to which DOC can regulate ecosystem functioning, we conducted a survey to determine the source of DOC in low Arctic ponds close to the Arctic Circle (Kangerlussuaq, Greenland), including its role in food web dynamics. We used a multiple element (carbon, nitrogen, and hydrogen) stable isotope approach to examine the proportional contribution of different sources to aquatic consumers in nine arctic ponds that spanned a broad gradient of DOC (6.6–60.1 mg^L-1). Our results show that benthic and pelagic primary production decreased along a gradient of increasing DOC content. Additionally, the changes in the organic matter pool with increasing DOC translated into changes in consumer resource use. We found significant differences in resource use between species. All consumers relied on benthic autotrophic material when DOC was low; but when DOC was high some consumers changed their diet. Collectively, our findings demonstrate how the concentration of DOC influences aquatic production and our study can be used as a baseline to predict how the aquatic food web may respond to regionally changing DOC concentrations.

陆地溶解性有机碳（dissolved organic carbon, DOC）向淡水生境的输入，可调控从水体透明度到初级生产力等一系列生态系统特征。为明确DOC对生态系统功能的调控程度，我们开展了一项调查，以解析北极圈附近（格陵兰岛康克鲁斯瓦格，Kangerlussuaq）低北极池塘中DOC的来源，及其在食物网动态中的作用。我们采用多元素（碳、氮、氢）稳定同位素分析法，对覆盖6.6~60.1 mg·L⁻¹ DOC浓度梯度的9个北极池塘中的水生消费者的不同食物来源贡献比例进行了测算。结果显示，底栖与浮游初级生产力随DOC浓度升高的梯度呈下降趋势。此外，伴随DOC浓度升高而发生的有机质库变化，也导致了消费者的资源利用模式发生改变。我们发现不同物种间的资源利用模式存在显著差异：当DOC浓度较低时，所有水生消费者均依赖底栖自养物质；而当DOC浓度较高时，部分消费者的食性发生了改变。综合来看，本研究结果阐明了DOC浓度如何影响水生生产过程；本研究可作为基准，用于预测水生食物网如何响应区域尺度上DOC浓度的变化。