An Analysis of Phosphorus Loading and Trophic State in Fletchers Lake, Nova Scotia

Abstract

Fletchers Lake, Fall River, Nova Scotia, is located within a diverse watershed, and is influenced by urban stormwater runoff, wastewater discharge and on-site septic systems. Due to the lake’s multi-uses and more planned development within the watershed, the Halifax Regional Municipality has identified accelerated eutrophication as a critical issue. With limited historical data on Fletchers Lake trophic parameters, there is a need for baseline data to identify future changes. A mass balance model identified the largest phosphorus (P) sources: headwaters and on-site septic systems. Baseline P export from the lake’s tributaries was measured, and P export coefficients were calculated for forested and low-density residential land use. Forested export coefficients varied between subwatersheds. The lowdensity residential coefficient was lower than an urban export coefficient widely applied in P prediction models. Trophic parameters, total phosphorus, nitrogen, chlorophyll a, measured as oligotrophic. Secchi depth measured as mesotrophic likely due to high humic contents.