Water Quality Management in the Holland Marsh, Ontario

Abstract. The Holland Marsh is an intensive ‘muck‘ farming area, north of Toronto, Canada, whose drainage is artificially managed for agriculture production. With the high intensity of intensive vegetable production there is growing concerns about non-point source (NPS) water pollution into the West Holland River which drains the cultivated area into Lake Simcoe. The Lake Simcoe Regional Conservation Authority has had multiple plans to reduce Nitrogen (N) and Phosphorus (P) loading. One NPS mitigation method being investigated is controlled drainage. In this study, two water management structures were installed at tile drain outlets to control the water table level in the field. The water table was set post growing season to allow the processes of mineralization of P and denitrification to occur. Analysis of the water quality in the water management structures during the peak outflow events over a two-year period (2014-15), showed that the total P concentration in the water is above the Provincial Water Quality Objectives (PWQO) of 0.03 mg/L. Furthermore, the nitrate concentration is significantly below the Canadian Water Quality Guidelines (CWQG) of 13 mg/L at all sites.