Accounting for Lags, Inertia and Cross Scale Dynamics in Sustaining Freshwater Lakes

While a growing body of modeling and experimental research in sustainability and environmental sciences has identified the importance of cross-scale dynamics, many issues about modeling cascades of lags, inertia and thresholds (phase transitions) in coupled natural and human systems remain unresolved. Situated in a Social Ecological Systems (SES) theoretical and empirical framework, this paper addresses the following question: How do lags, inertia and thresholds affect the evolution of state variables in SES that interact across multiple spatial and temporal scales? We investigate this question in the context of modeling the cascading impacts of global climate change and local land and nutrient management across a river-lake continuum within the Lake Champlain Basin in North America from 2000 through 2050.Twelve future climate simulations (4 global climate models (GCMs) x 3 emissions scenarios), 4 land use land cover change (LULCC) forecast scenarios and 6 early versus delayed nutrient reduction scenarios drive a distributed hydrological model (RHESSys) that simulates 288 daily time series of riverine discharge and nutrient loads entering Missisquoi Bay of Lake Champlain. A high-resolution system of biogeochemistry and hydrodynamic lake models simulates water quality, including four phytoplankton groups, in the shallow bay. Simulations suggest that moderate and high emission scenarios will trigger, irrespective of LULCC changes, phase transitions in summer and shoulder season months (eutrophic to hyper-eutrophic and mesotrophic to eutrophic respectively) due to sustained high water temperatures above thresholds that promote cyanobacteria dominance. Achieving low-emission greenhouse gas trajectories at the planetary scale is necessary but not sufficient for avoiding undesirable trophic state shifts in shallow freshwater bays and lakes. Watershed management implications of early versus delayed actions for sustaining freshwater lakes will be discussed.