Author: Russell  Cuhel,  DR COOL (School of Freshwater Sciences)

Description:
20 years of year-around offshore sampling in Southwestern Lake Michigan have provided for assessment of episodic events vs. chronic change sufficient to effect basin-scale anomalies. From our ice-free upwind base, Fox Point time series expeditions 25 km ENE of Milwaukee Harbor (100 m depth) include deep winter mixing, the day after first stratification, event-driven perturbations, fall cooling, and onset of winter deep mixing. Harbor to offshore transects provide dilution gradient observations, and north-south transects across Mid-Lake Reef Complex seamount-like structures offer insight into physical hydrodynamics of abrupt bathymetric features. Dissolved and particulate components, optical characterization, hydrographic profiling, and PvsI analysis of primary productivity are rare in winter and crucial to process interpretation. Additional consistent measurements of physical, chemical, and biological processes suggest differences between timing and consequences of nutrient management and biological invasions. Using establishment of quagga mussel (QM) ecosystem engineers as an example, changes in many aspects of large phytoplankton communities occurred within 2 years, while broader phytoplankton indices like surface extracted chlorophyll a were virtually unperturbed for over a decade. However, areally integrated chlorophyll decreased quickly, and the seasonality of inventory cycles was reversed. Surface concentration, areal inventory, and speciation of phosphorus, silicate, and nitrogen demonstrate favorable outcomes for management but also show likely stable endpoints.

Category: Scientific Program Abstract > Special Session > SS50 The importance of long-term monitoring for detecting and understanding human impacts on aquatic systems from past and emerging environmental issues