MEASURING RESILIENCE AND STABILITY WITH DISSOLVED OXYGEN AND PH DATA FROM WHOLE LAKE NUTRIENT ADDITIONS

Dissolved oxygen (DO) concentrations and pH are commonly measured in situ with sensors and are sensitive to changes in primary production and phytoplankton biomass. We evaluated the potential use of DO and pH to distinguish alternate states of high and low phytoplankton using data from whole lake nutrient manipulations designed to promote blooms. These manipulations were conducted in five different years with differential responses including no blooms and substantial blooms related to environmental and ecological conditions. When phytoplankton increased in response to nutrient additions, dissolved oxygen saturation (DOsat) increased to above 120% and pH often exceeded 9. Daily average DOsat and pH data were fit with b-splines, and from these relationships, stability basins and unstable thresholds (= loss of resilience) for low and high biomass states were derived. In manipulations where only modest or temporary changes in DOsat and pH occurred, stability conditions and thresholds were not well resolved. Overall, the approach distinguishes important properties of stability and resilience while requiring much less data than more established methods.

Presentation Preference: Oral

Primary Presenter: Michael Pace, University of Virginia (mlp5fy@virginia.edu)

Authors:

Stephen Carpenter, University of Wisconsin  (steve.carpenter@wisc.edu)

Dat Ha, University of Virginia  (dh3dv@virgiinia.edu)

Moira McCarthy, University of Wisconsin  (moira.mccarthy@wisc.edu)

Daniel Szydlowski, University of Wisconsin  (dszydlowski@wisc.edu)

Grace Wilkinson, University of Wisconsin  (gwilkinson@wisc.edu)