A New Methodology to Manage Anthropogenic Sources of Phosphorus Deposition to Lakes: Lake Simcoe Case Study

Abstract

Excessive phosphorus loading to inland freshwater lakes around the globe has resulted in nuisance plant growth along waterfronts, degraded habitat for cold water fisheries, and impaired beaches, marinas and waterfront property. The direct atmospheric deposition of phosphorus can be a significant contributing source to inland lakes. The atmospheric deposition monitoring program for Lake Simcoe, Ontario indicates roughly 20% of the annual total phosphorus load (2010 to 2014 period) is due to direct atmospheric deposition (both wet and dry deposition) on the lake. Bare soil exposure in the spring due to lack of vegetative cover, along with soil disturbance related to agricultural activities, results in higher susceptibility to wind erosion and dust emission. The objectives of this study were to develop a methodology to model the anthropogenic sources of atmospheric phosphorus deposition to an inland lake and provide land management guidance to reduce loading to the lake. The methodology was then implemented for Lake Simcoe. This was accomplished using the following research milestones: 1) quantifying seasonal variability of atmospheric TP deposition on Lake Simcoe and identifying spatial distribution patterns of atmospheric TP deposition on Lake Simcoe, 2) introducing the new concept of Dust Response Units (DRUs), which combine soil type and land use to determine the dust emission susceptibility based on the hourly variation of wind speed and monthly changes in soil cover due to crop growth, 3) developing an integrated PM10 emission, transport and deposition model which has been validated using monitored data, and 4) Developing a first-time application of the Genetic Algorithm (GA) methodology to optimize the application of best management practices (BMPs) related to agriculture and mobile sources to achieve atmospheric phosphorus reduction targets and restore the ecological health of the lake. The geospatial aspect to the optimization (i.e. proximity and location with respect to the lake) will help land managers to encourage the use of these targeted BMPs in areas that will most benefit from the phosphorus reduction approach.