Effects of Agricultural Encroachment and Drought on Wetlands and Shallow Lakes in the Boreal Transition Zone of Canada

Abstract

The ecoregions along the southern edge of the Boreal Plains have experienced rapid and extensive agricultural encroachment over the last 60 years. Over 200 wetlands and shallow lakes in central and northern Alberta and northeastern British Columbia, Canada were surveyed along an agricultural encroachment gradient to investigate the effect of land use on water quality between 2005 and 2007. Study wetlands were typically small (median 29.8 ha), shallow (median 0.8 m) and highly eutrophic (median 148 μgTP∙L−1). Wetlands in the southern Boreal Plains were regionally variable and dynamic. Drought in 2006 caused significant increases in TP, TN, chlorophyll a (chla), conductivity, silica and significant decreases in maximum depth and light penetration. Increased agricultural activity within a 1.6 km buffer surrounding wetlands enhanced nutrients but not chla concentrations or submersed aquatic vegetation (SAV) coverage. Wetlands with higher amounts of agriculture in the buffer zone tended to be shallower with decreased secchi depths. Due to shallow depths, SAV thrived even under hypereutrophic conditions with high agricultural encroachment in the buffer zone. Our study suggests that SAV has a significant role in maintaining clear water states in Boreal Transition Zone wetlands and shallow lakes through its ability to suppress concentrations of chla and TP.