Changes in water chemistry associated with beaver-impounded coastal marshes of eastern Georgian Bay

Abstract

Coastal marshes of eastern Georgian Bay contain unique water chemistry that reflects mixing between the relatively ion-rich waters of Georgian Bay and the relatively ion-poor water draining the Canadian Shield landscape. These unique chemical characteristics may be dramatically altered when wetlands become hydrologically disconnected from Georgian Bay through beaver activity. We sampled 35 coastal marshes in Georgian Bay, 17 of which had beaver impoundments built at the outlet of the coastal wetland. Impounded marshes had significantly higher total phosphorus (30.2 versus 15.3 μg·L-1, p = 0.0015), soluble reactive phosphorus, (13.33 versus 3.7 μg·L-1, p ≤ 0.0001), total suspended solids (15.5 versus 2.1 mg·L-1, p ≤ 0.0001), turbidity (5.4 versus 1.6, p = 0.0004), and chlorophyll (6.2 versus 1.9 μg·L-1, p = 0.0004), but significantly lower pH (5.57 versus 6.95, p ≤ 0.0001), nitrates (0.03 versus 0.04 mg·L-1, p = 0.0416), and conductivity (47 versus 134 μS·cm-1, p ≤ 0.0001), indicative of reduced mixing with Georgian Bay. The mosaic of chemical conditions and altered hydrological connectivity associated with beaver impoundments in coastal marshes of Georgian Bay may affect the distribution of other wetland biota, and further studies should be conducted to ascertain these impacts.