Quantifying nitrogen loading and corresponding eutrophication symptoms in 7 bays in eastern New Brunswick, Canada

Abstract

Anthropogenic nitrogen loading has been identified as a significant cause of seagrass decline worldwide. In the Southern Gulf of St. Lawrence, eelgrass (Zostera marina) is the dominant macrophyte in shallow coastal bays and designated an ecologically significant species, yet is increasingly threatened by eutrophication. This thesis applied a Nitrogen Loading Model (NLM) to estimate the magnitude and sources of nitrogen loading in 7 bays in eastern New Brunswick and linked model outputs to eutrophication symptoms and eelgrass bed structure in each bay. Nitrogen loading rates and the proportion of wastewater loading were significantly correlated with eelgrass tissue nitrogen content and isotope signatures. Additionally, higher nitrogen loading rates and longer bay flushing time were linked to elevated eutrophic symptoms, including epiphyte cover and microphytobenthos concentrations, and differences in eelgrass bed structure. This research can inform effective and targeted nutrient management and land-use planning in the region.