The primary productivity of benthic and planktonic algae in a prairie wetland under controlled water-level regimes

Abstract

There have been few measurements of primary productivity by benthic (periphytic) and planktonic algae in prairie wetlands so their quantitative importance relative to other primary producers is largely unknown. We measured the daily productivity (inorganic carbon assimilation per m2 of wetland area) of phytoplankton, epipelon, epiphyton, and metaphyton in ten wetland cells in Delta Marsh, Manitoba over a five-year period. Water levels in the cells were manipulated so that some cells had normal water levels for the wetland, while water depths increased 30 cm or 60 cm in other treatments. With increasing water depth, phytoplankton productivity increased while that of epipelon, epiphyton, and metaphyton decreased. Metaphyton was the largest contributor to total algal productivity (70%), followed by epiphyton (23%), phytoplankton (6%), and epipelon (1%). Phytoplankton had the highest photosynthetic efficiency (C assimilated per unit chlorophyll), despite being a minor contributor to total productivity. Variations in P-I parameters (α, β, Ik, and Pmax) were considerable, possibly due to temporal and spatial fluctuation in the abiotic environment. Algal productivity was comparable to that of submersed and emergent macrophytes, suggesting that algae are probably important resources in supporting food webs in prairie wetlands.