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

ABSTRACT

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.

KEYWORDS:

• Arctic
• allochthony
• freshwater ecology
• Bayesian mixing models
• plankton
• stable isotope

Acknowledgments

We thank Tim Howe and Norma Haubenstock at the Alaska Stable Isotope Facility for their assistance with stable isotope analyses; Nils Willumsen for chemical analyses and assistance in the laboratory; as well as Nina Reuss, Jacob Yde, and Jasmine Saros for constructive comments on an earlier version of the manuscript.

Additional information

Funding

Funding was provided by the University of Copenhagen, NordSIR, Academy of Finland and the Canada Research Chairs Program.