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

S. E. Bayley,J. E. Thompson,A. S. Wong

doi:10.1007/s13157-012-0349-x

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.

Highlights

Conversion of native landscapes for agriculture has resulted in extensive loss of wetlands globally and in Canada (Turner et al 1987; Watmough et al 2002; Zedler and Kercher 2005; Dahl and Watmough 2007) as well as increased runoff of nutrients from agricultural lands (Harmel et al 2006)
We examined the effect of agricultural encroachment, year sampled and sampling region on concentrations of total phosphorus (TP), total nitrogen (TN) and chla, maximum depth, secchi depth, submersed aquatic vegetation (SAV), conductivity and silica
Numerous studies have detected increased nutrient concentrations associated with increased agricultural land use (Egertson et al 2004) and even isolated depressional lakes with little surface runoff show increased nutrient concentrations in water and sediment (Neely and Baker 1989; Whigham and Jordan 2003)

Summary

Introduction

Conversion of native landscapes for agriculture has resulted in extensive loss of wetlands globally and in Canada (Turner et al 1987; Watmough et al 2002; Zedler and Kercher 2005; Dahl and Watmough 2007) as well as increased runoff of nutrients from agricultural lands (Harmel et al 2006). The Boreal Transition Zone (BTZ), generally defined as the southern tier of ecoregions in the Boreal Plains (Fig. 1), has suffered extensive wetland losses in recent decades (Watmough and Schmoll 2007). Much of this loss has occurred as forest land has been converted into production of annual crops, hayland, and improved pasture. The region is unique in that background levels of nutrients are high in soils

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