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.