Nutrient uptake controls and limitation dynamics in north-east Greenland streams

ABSTRACT

Permafrost thaw induced by climate change will cause increased release of nutrients and organic matter from the active layer to Arctic streams and, with increased water temperature, will potentially enhance algal biomass and nutrient uptake. Although essential for accurately predicting the response of Arctic streams to environmental change, knowledge of nutrient release on current Arctic in-stream processing is limited. Addressing this research gap, we quantified nutrient uptake of short-term releases of NO₃⁻, PO₄^3- and NH₄⁺ during peak snowmelt season in five streams of contrasting physiochemical characteristics (from unstable, highly turbid to highly stable, clear-water systems) in north-east Greenland to elucidate the major controls driving nutrient dynamics. Releases were plus or minus acetate to evaluate uptake dynamics with and without a dissolved organic carbon source. To substantiate limiting nutrients to algal biomass, nutrient-diffusing substrates were installed in the five streams for 16 days with NH₄⁺, PO₄^3- or NH₄⁺ + PO₄^3- on organic and inorganic substrates. Observed low uptake rates were due to a combination of low nutrient and DOC concentrations, combined with low water temperature and primary producer biomass, and substantial variation occurred between streams. N was found to be the primary limiting nutrient for biofilm, whilst streams displayed widespread PO₄^3- limitation. This research has important implications for future changes in nutrient processing and export in Arctic streams, which are predicted to include increased nutrient uptake rates due to increased nutrient availability, warmer water temperatures and increased concentration of labile carbon. These changes could have ecosystem and landscape-wide impacts.

KEYWORDS:

• Arctic
• river
• biofilm
• biogeochemistry
• climate change
• freshwater

ABBREVIATIONS:

• ANOVA: analysis of variance
• chl a: chlorophyll a
• DO: dissolved oxygen
• DOC: dissolved organic carbon
• FBOM: fine benthic organic matter
• NDS: nutrient-diffusing substrates
• TOC: total organic carbon

Acknowledgements

Precipitation data from the Greenland Ecosystem Monitoring Programme were provided by Asiaq – Greenland Survey, Nuuk, Greenland. Other climate data from the Greenland Ecosystem Monitoring Programme were provided by the Department of Bioscience, Aarhus University, Denmark, in collaboration with Department of Geosciences and Natural Resource Management, Copenhagen University, Denmark. The authors thank two anonymous reviewers for their comments that have helped improve this manuscript. The authors thank Biobasis, Geobasis and Zackenberg logistics for all of their field assistance. We thank Chantal Jackson for Fig. 1.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

CD was funded through a Natural Environment Research Council studentship under grant agreement number NE/L501712/1. Fieldwork was funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 262693 (INTERACT) and the Carlsberg Foundation under grant 2013-01-0258.