Mixing of floodwaters in a restored habitat wetland in northeastern Ontario

Abstract

Water levels, nutrient supplies, and vegetation cover are key issues in the successful management of wetland habitats. The Hilliardton Marsh Provincial Wildlife Area is a newly restored wetland in north eastern Ontario, Canada about 200 ha in size. It is entirely enclosed by a dike. To maintain water levels, water is pumped into Cell 1 from the adjacent Blanche River and is allowed to flow into Cell 2 and other cells in the wetland by water-control devices between the cells. This study explores the effectiveness of environmental isotopes, oxygen-18 (¹⁸O) and deuterium (²H), in tracing water circulation and mixing of isotopically depleted river water and isotopically enriched wetland water during two pumping events in two of the wetland cells. In Cell 1, water levels rose everywhere as a result of pumping. δ¹⁸O values at sampling stations closest to the inflow became isotopically depleted by river water almost immediately after the pump was turned on. Despite rising water levels, stations farthest away from the inflow did not show any initial change in the isotopic composition of the water for the duration of the period of this study. Stations in the center of the cell had intermediate isotopic values. The isotope data suggest that river water is only present in the cell portion closest to the inflow. River water and wetland water mix in the central part of the cell, and river water never reaches areas farthest from the inflow. It appears that wetland water is displaced by the pumped river water and is forced by hydrostatic pressure into areas farthest from the inflow. When Cell 1 waters are allowed to flow into Cell 2, there is mixing between river water and wetland waters. This study shows that environmental isotopes can be effective tracers for determining mixing and water-flow patterns in restored wetlands.