Understanding Human-Water-Nitrogen Relationships: Using System Dynamics to Study Missisquoi Bay, Québec, Canada

Human alteration of the nitrogen cycle, through the use of fertilizers and fossil fuels, has intensified the flows of reactive nitrogen to the hydrosphere and degraded the quality of water resources. Imbalanced levels of nitrogen in surface water impact both ecological and human wellbeing, promoting the eutrophication of rivers and lakes and subsequently contributing to losses of wildlife, contaminated drinking water sources, increased health risks and water treatment costs, as well as decreased recreational activities and tourism revenue for local economies.

In order to protect water resources and the communities that rely upon them, approaches capable of understanding the complex interactions between humans and water are needed. System dynamics (SD) is a modelling method that maps, quantifies, and simulates the feedbacks that exist between the causes and consequences of an issue, such as surface water pollution. By capturing the long-term behaviour of non-linear systems and identifying potential leverage points, SD provides a holistic perspective that traditional modelling approaches frequently lack.

In this research, SD is employed to study Missisquoi Bay, a culturally significant waterbody located on the border of Québec, Canada and Vermont, USA, that is experiencing counterintuitive nitrogen trends. Over the last 30 years, levels of nitrogen in Missisquoi Bay have remained stable while loads from the Bay’s tributaries, namely the agriculturally intensive Pike River watershed, have increased, highlighting an existing knowledge gap in the region. Understanding and preventing nitrogen pollution is critical as nitrogen can exacerbate the toxicity of harmful algae blooms, which are already a consistent issue in Missisquoi Bay. Nitrogen loadings are also anticipated to increase in the area with future changes to land use and climate.

A quantitative SD model is being developed for the Pike River-Missisquoi Bay system at a monthly timestep to capture the seasonal variabilities of nitrogen dynamics. The resultant model will be used to evaluate: 1) What biogeochemical or socioeconomic processes are the most influential in governing the levels of nitrogen in the Pike River and Missisquoi Bay; 2) How will these processes change over the period of 2025 – 2050 given different climate, land use, and management scenarios; and 3) What pollution prevention strategies would be most effective in protecting the Bay and its surrounding communities?

Stakeholders and decision makers in the region will be able to use the final SD simulation model as a reliable decision support tool to examine the long-term outcomes of their proposed solutions, select strategies capable of reducing stresses on water quality, and answer “what-if” questions. By disseminating this model, other watersheds in Canada seeking to better understand their nitrogen dynamics will be able to use a consistent framework to improve their policy development and management strategies.