Benthic nitrogen regeneration, fixation, and denitrification in a temperate, eutrophic lake: Effects on the nitrogen budget and cyanobacteria blooms. (14th May 2016)

• Record Type: Journal Article
• Authors: McCarthy, Mark J.; Gardner, Wayne S.; Lehmann, Moritz F.; Guindon, Alexandre; Bird, David F.
• Is Part Of: Limnology and oceanography. Volume 61:Number 4(2016)
• Page Start: 1406
• Page End: 1423
• Publication Date: 2016-05-14
• Subjects: Limnology -- Periodicals; Oceanography -- Periodicals; Océanographie; Limnologie; Limnology; Oceanography; Computer network resources; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); Periodicals; 551.4805
• DOI: 10.1002/lno.10306
• Languages: English
• ISSNs: 0024-3590

Abstract

Abstract: Nitrogen (N) transformations and fluxes at the sediment‐water interface (SWI) were measured in Missisquoi Bay, Lake Champlain, to clarify the role of N in cyanobacterial blooms in temperate, eutrophic lakes. N sources (e.g., N fixation and tributary inputs), sinks (e.g., denitrification/anammox), and internal "links" (e.g., dissimilatory NO 3 − reduction to NH 4 + ; DNRA) were evaluated at a river discharge (PRM) and in the central basin (MB). Sediments were a more effective NO 3 − sink at PRM than MB. Sediments at both sites were a net NH 4 + source to the water column, but DNRA was not a consistent NH 4 + regeneration pathway. Net N2 production at PRM in summer reversed to net N2 consumption/fixation in fall. MB sediments produced N2 at lower rates than PRM; these rates also reversed late in the season. Denitrification was limited by NO 3 −, especially at MB, and anammox may have contributed up to 10% of total N2 production. Sediment N2 fixation occurred simultaneously with denitrification throughout the ice‐free season and, on average, compensated 25–30% of total microbial N losses. A bottom‐water hypoxia event at MB in early July 2009 altered the N cycle, with lower actual denitrification rates and higher NH 4 + effluxes (not from DNRA), while phosphorus (P) flux was unaffected. The hypoxia‐altered N transformation pathways enhanced N bioavailability (but not P) and may have contributed to a non‐N‐fixing cyanobacterial bloom ( Microcystis ) observed 5 d later. A preliminary N budget incorporating sediment and water column sources and sinks and external loads suggested an ecosystem‐wide N deficit.