Water column nutrient processing rates in rivermouths of Green Bay (Lake Michigan)

Biogeochemistry
By: , and 

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Abstract

Understanding the quantity and form of nutrient loads to large lakes is necessary to understand controls over primary production, phytoplankton community composition and the production of phytotoxins. Nutrient loading estimates to large lakes are primarily made at stream gages that are deliberately placed outside the direct influence of lake processes, but these estimates cannot take into account processes that occur in the biologically active river-to-lake transition zone. These transition zones (rivermouths) sometimes alter nutrient concentrations and ratios substantially, but few studies have directly measured processing rates of nutrients within rivermouths. From April through September 2016, we conducted 23 water column incubation experiments to measure nutrient loss rates in four rivermouths. First order loss rates (K) for inorganic nitrogen (N) and phosphorus (P) indicated greater loss in light than in dark treatments, suggesting primary production increases N and P removal. Variability in K was high across both time and space, and the measured environmental parameters did not appear to be strongly associated with this variation in K for most N and P forms. If the measured Kvalues and water residence times are accurate, then between 0 and 99% of the inorganic P and nitrates entering the rivermouth would be lost (i.e., converted to organic or particulate P). In late summer, Fox River discharge is low and residence times are usually long, which allow for much higher proportional nutrient removal in the water column. Water column processing appears to be capable of transforming large quantities of dissolved N and P to particulate forms and thus altering its transport and presumably its bioavailability.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Water column nutrient processing rates in rivermouths of Green Bay (Lake Michigan)
Series title Biogeochemistry
DOI 10.1007/s10533-018-0517-z
Volume 142
Issue 1
Year Published 2019
Language English
Publisher Springer
Contributing office(s) Upper Midwest Environmental Sciences Center, Great Lakes Science Center
Description 21 p.
First page 73
Last page 93
Country United States
Other Geospatial Green Bay, Lake Michigan