Responses of a prairie wetland to press and pulse additions of inorganic nitrogen and phosphorus: production by planktonic and benthic algae
McDougal, Rhonda L.; Goldsborough, L. Gordon; Hann, Brenda J .
published: Sep 25, 1997
ArtNo. ESP141014002001, Price: 29.00 €
Enclosures deployed in Delta Marsh, Canada, were treated with inorganic N and P either as two discrete additions (pulse) or as 29 smaller additions (press) comprising the same cumulative nutrient load over a three-month period. No effects on photosynthesis by phytoplankton, epiphyton or epipelon were detected. Similarly, phytoplankton and epipelon biomass was unaffected by any treatment. However, epiphyton and metaphyton biomass increased significantly. Absent from controls except after macrophyte senescence, metaphyton represented >80 % of total algal biomass and total algal P in treated enclosures. No differences in metaphyton biomass between press and pulse treatments were observed although its composition varied; diffuse masses of Cladophora developed in pulse enclosures whereas floating carpets of Enteromorpha occurred in press enclosures. The latter decreased water column irradiance markedly, leading to premature macrophyte senescence. Sediment and metaphyton were probably the primary sinks for added nutrients. These results illustrate that nutrient enrichment can shift a stable epiphyton-dominant system (open wetland) to metaphyton dominance (sheltered wetland) if macrophytes remain sufficiently abundant to provide substratum for metaphytic algae. Development of the phytoplankton-dominant lake wetland state presumably occurs only when there are few other algal and macrophytic competitors for nutrients.