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Abstract

Phosphorus (P) has been identified as the main cause of eutrophication in the Missisquoi Bay of Lake Champlain, of waterbody shared by the Province of Quebec (Canada) and State of Vermont (United States). The Pike River is one of the main water- courses contributing P to the bay, frequently at levels exceeding a bilaterally-imposed water quality stan- dard (25 μg P/l), designed to address multiple-use issues such as fishing, recreation, aquatic biodiversifi- cation and aesthetic value of the bay. The overall an- nual P flux contributed to the bay by the Pike River watershed (28 Mg per year) exceeds target levels by 3.5-fold. Consequently, daily and seasonal variability in P flux from the Pike River watershed were moni- tored and analysed to provide a sound basis for the holistic development of a P reduction and manage- ment plan. Mean daily P flux at the watershed outlet ranged from 130 kg/day in spring to 22 kg/day in sum- mer. Spring snowmelt and rainfall-generated runoff, along with that arising from rainfall on bare land after fall harvest, contributed 82% of the watershed’s annual P discharge. Thus, roughly three-fifths of the P contributed to the bay was discharged over only one- fifth of the hydrological year. This clearly indicates that a more stringent and targeted P pollution reduc- tion plan must be devised and implemented to achieve the water quality goals set for the bay.