Relationships between Wetland Macroinvertebrates and Waterfowl along an Agricultural Gradient in the Boreal Transition Zone of Western Canada

Abstract

We examined 14 wetlands in the Boreal Transition Zone (BTZ) of western Canada to investigate the effects of agricultural encroachment on aquatic macroinvertebrate communities and the response of waterfowl communities to these changes. The amount of agriculture within a 1.6-km buffer around wetlands was quantified primarily by remote imagery, and a sample of relatively similar wetlands was selected along an encroachment gradient from 0 to 90% agriculture. Species dominance showed temporal shifts during spring and summer. In May, 3 primary macroinvertebrate-dominated community types were present: 1) Amphipoda, 2) Diptera, and 3) Sigara. In August, 3 community types were present: 1) Amphipoda, 2) Notonecta, and 3) Chaoborus–Sigara. Environmental conditions were not distinct in every community type; however Sigara-dominated communities occurred in significantly shallower wetlands with greater concentrations of total inorganic nitrogen, total dissolved solids, and salinity than did Diptera dominated communities. Agricultural intensity was positively associated with phosphorus concentration. Phosphorus was likely an important factor in determining macroinvertebrate community composition with Sigara and Chaoborus–Sigara communities occurring in wetlands with very high concentrations of phosphorus (average >800 µg/L), and Diptera and Notonecta communities occurring in wetlands with lower phosphorus (average <160 µg/L). Amphipoda-dominated communities tended to occur in larger and deeper basins than Sigara-dominated communities. Waterfowl abundance was significantly and positively associated with macroinvertebrate abundance; however, occurrence of most waterfowl species did not correspond well with specific macroinvertebrate community types.