Water quality and biotic community response to an urban – rural land-use gradient in the Lake Simcoe watershed

Abstract

Most research in the Lake Simcoe watershed (LSW) has focused on how the lake has responded to changes in nutrients sourced by agriculture, particularly after mitigation measures have been put in place to remedy the lake’s water quality. Nutrient sources from urban areas are not well understood, yet 31% of phosphorus originates from urban tributaries, despite urban land-use accounting for only 12% of total watershed area. Since many urban areas are seeing drastic human population growth and intensification, the impact urban derived stressors have on water quality and biotic communities requires further investigation. The research presented here explored the links between land-use, periphyton nutrient content and biomass, and invertebrate response in lotic surface waters in the LSW. To infer the contribution of cosmetic fertilizer use in the LSW, a community survey was conducted to assess lawn care and fertilizer choices by residents. Overall, the survey results confirmed that cosmetic fertilizer application posed a significant issue in the LSW. The effects of land-use, season, and abiotic parameters on periphyton biomass, nutrient content, invertebrate abundance and biotic composition were investigated using artificial and natural substrates at 14 field sites that represent a gradient from reference to agriculture to urban land-uses. Two consecutive years of sampling found that water quality, particularly nitrate and chloride, from urban land-uses was the same or worse as compared to reference and agriculture land-uses. There was not an increase in periphyton biomass nor change in indicator taxa at urban sites, potentially due to light availability and/or chloride. There was a periphyton nutrient content response between land-uses, however, potential drivers varied. Exploring relationships between established periphyton and invertebrate abundance determined that herbivores exhibited negative relationships with abiotic and biotic predictors, however these varied with season and land-use. The results did highlight that periphyton studies require investigation throughout the complete ice-free year in temperate climates because single season sampling may yield incorrect or incomplete conclusions.