Absorption characteristics, major elements and chl a content of samples from Pond 19 at Zackenberg, NE Greenland

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic-pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C-enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton.
2. The cladoceran Daphnia middendorffiana responded to the 13C-enrichment of benthic mats with progressively increasing d13C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter.
3. Daily net production by phytoplankton in the pond (18 mg C/m**2/day) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C/m**2/day), whereas benthic primary production alone (145 mg C/m**2/day) was more than sufficient.
4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient-limited high arctic ponds.

1. 北极浅湖与浅塘拥有结构简洁的短食物网，但此类生态系统中的底栖-浮游层联系（benthic-pelagic links）仍存在大量不确定性。本研究以格陵兰东北部的一处池塘为研究对象，通过对池塘本体及13C富集围隔实验（13C-enrichment enclosure experiment）开展碳、氮稳定同位素分析（stable isotope analysis），验证底栖来源有机物是否能够支撑浮游动物（zooplankton）的生物量。在本次围隔实验中，我们通过调控底栖藻类（benthic algae）的碳同位素特征，以增强其与浮游动物其他潜在食物源之间的同位素分馏（isotopic discrimination）差异。
2. 枝角类（cladoceran）米氏溞（Daphnia middendorffiana）对底栖藻垫的13C富集产生响应，其d13C值随处理进程逐步升高，提示该物种以底栖食物为食。稳定同位素分析结果同样表明，陆源碳（terrestrial carbon）在米氏溞的食物组成中占比可忽略不计。这一结论与通过有色溶解有机物（coloured dissolved organic matter）分析所揭示的，该池塘内自生源溶解有机物（autochthonous dissolved organic matter）占据绝对优势的结果相一致。
3. 本池塘浮游植物（phytoplankton）的日净生产量（daily net production）为18 mg C/m²·d，仅能满足米氏溞测算得到的最低能量需求（35 mg C/m²·d）的一半；而仅底栖初级生产（benthic primary production）的日生产量（145 mg C/m²·d）便已远超其能量需求。
4. 本研究结果凸显了底栖初级生产作为该生态系统中米氏溞主要食物来源的核心地位，并表明在这类养分限制型（nutrient-limited）高北极池塘（high arctic ponds）中，底栖有机物可能在维持浮游层次级生产（pelagic secondary production）方面发挥关键作用。