The impact of lake discontinuities on nitrogen biogeochemistry in river networks

Grefe, Imke; Mackay, Eleanor B. ORCID: https://orcid.org/0000-0001-5697-7062; Wynn, Peter M.; Barker, Phil A.; Grant, Helen K.; Gloria Pereira, M. ORCID: https://orcid.org/0000-0003-3740-0019; Maberly, Stephen C. ORCID: https://orcid.org/0000-0003-3541-5903; Surridge, Ben W.J.. 2024 The impact of lake discontinuities on nitrogen biogeochemistry in river networks. Inland Waters. https://doi.org/10.1080/20442041.2024.2379149

Before downloading, please read NORA policies.

Preview

Text The impact of lake discontinuities on nitrogen biogeochemistry in river networks.pdf - Accepted Version Available under License Creative Commons Attribution 4.0. Download (1MB) | Preview

Abstract/Summary

River networks connect terrestrial and marine ecosystems through transport of pollutants and nutrients. Lakes represent discontinuities within these river networks, which can be important biogeochemical hotspots, introducing substantial changes to the aquatic environment. Nitrogen is a key macronutrient that can potentially limit or co-limit primary production, but the processes that determine the fate of nitrogen during transport through river-lake networks are poorly understood. We studied three river systems and their lake discontinuities, spanning a range of trophic states and average water residence times, to understand the changes introduced to riverine nitrogen biogeochemistry by lake discontinuities. In-lake processes noticeably altered the concentration and speciation of nitrogen. Annually, lakes reduced up to 44% of nitrate compared to main inflow concentrations, while there was large variability in nitrate dynamics seasonally. The drawdown in surface nitrate concentrations resulted at times in phytoplankton co-limitation by nitrogen in-lake, as well as in the downstream river, where altered nitrogen patterns could persist for several kilometers. However, lakes occasionally subsidized N to downstream rivers as ammonium or dissolved organic nitrogen. Assimilation of nitrate in lake surface waters was one of the dominant processes impacting nitrogen availability; however, stable isotope data revealed an unexpected contribution of nitrification on nitrogen cycling in the epilimnion throughout the year and across trophic gradients. These changes in nitrogen concentration, as well as speciation introduced by lake discontinuities have potentially important consequences for the composition and metabolism of communities in downstream rivers and contribute to our fundamental understanding of freshwater processes.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1080/20442041.2024.2379149
UKCEH and CEH Sections/Science Areas:	Pollution (Science Area 2017-) Water Resources (Science Area 2017-) UKCEH Fellows
ISSN:	2044-2041
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	river-lake networks, nitrogen cycle, nitrate stable isotopes, nutrient limitation, ammonium, nutrient biogeochemistry
NORA Subject Terms:	Ecology and Environment Hydrology
Date made live:	24 Jul 2024 10:07 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537756

Actions (login required)

View Item

Document Downloads

More statistics for this item...