Widespread closures of COVID-19 resulted in favorable ecosystem effects for watershed, riverine, coastal, and SW Great Lake Michigan water. Between March and July aquatic resources had extended relief from inhibitory inputs and would have flushed existing dissolved and suspended materials of human origin. Dissolved Fe and Mn, crucial phytoplankton nutrients, remained elevated in the rivers and harbor, and declined slowly with distance from outflows within the first 5 km. Toxic or extreme micronutrient trace metals Mo, Zn, Cu, Cd, Se, As, and others were below detection (ca. 20nM) at all locations prior to reopening. Moving through the continuum, repeated expeditions from the lower rivers into Lake Michigan encountered unusually high proportions >30% of larger phytoplankton as far as 15km out; this anomalous size distribution was accompanied by extraordinary longevity of phytoplankton nearshore abundance into July following early stratification. Reversed seasonality of post-mussel diatom resurgence has additionally provided new high nutritional input into nearshore coastal ecosystems during late summer and fall. Robust biomass-specific productivity regime with maximum carbon dioxide fixation commonly 6-15 &microgC/ &microgCHLa/hour (PBm), was double or more previous coastal zone values. Projected dredging of river-harbor legacy sediments to remove particle-bound forever contaminants (PFAS, PCB, PAH) will unwittingly release porewater nutrients into the water column. These are mostly reduced, e.g., ammonium, Fe++, Mn++, and lead to potential eutrophication downstream into coastal areas.

Primary Presenter: Carmen Aguilar, University of Wisconsin - Milwaukee (aguilar@uwm.edu)

Authors:

Russell Cuhel, University of Wisconsin-Milwaukee School of Freshwater Sciences  (rcuhel@uwm.edu)