Journal
LIMNOLOGY AND OCEANOGRAPHY
Volume 60, Issue 3, Pages 856-871Publisher
WILEY
DOI: 10.1002/lno.10076
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Funding
- Alberta Water Research Institute
- Alberta Environment
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- NSERC
- Alberta Ingenuity Fund
- University of Alberta
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Several lines of evidence from a eutrophic lake show how polymixis enables phosphorus (P) released from anoxic, iron (Fe)-poor sediments to lower nitrogen-to-phosphorus (N : P) ratios and stimulate cyanobacterial blooms. Detailed sediment analyses revealed extensive formation of Fe sulfides, which suppressed porewater Fe levels and prevented sequestration of P in Fe minerals. Experimental additions of Fe significantly decreased the flux of dissolved P from warm, anoxic sediments, increasing N : P ratios in porewater and overlying water. The net midsummer effect of polymixis and P release from Fe-poor sediments quickly doubled the total P in the euphotic zone during a period of very low external P loading. This internal nutrient pump decreased N : P in surface waters and led to a cyanobacterial bloom comprised primarily of diazotrophic Anabaena and Aphanizomenon spp. along with nonheterocystous and potentially toxic Microcystis icthyoblabe and Woronichinia naegelianum. Concentrations of the cyanotoxin, microcystin, in this lake were typically elevated during, or shortly after, episodes of internal P loading. Our study demonstrates an important mechanism underlying the increasing cyanobacterial dominance of weakly stratified eutrophic north temperate lakes, and warns of further increases under a warming climate.
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