Response of benthic and planktonic algal biomass to experimental water-level manipulation in a prairie lakeshore wetland

Abstract

The quantitative contribution of benthic (periphytic) and planktonic algae to primary production in prairie wetlands is largely unknown, as is their response to the fluctuations in water level that characterize such systems. We measured the biomass (chlorophyll-a m -2 of wetland area) of phytoplankton, epipelon, epiphyton, and metaphyton in Delta Marsh, Manitoba as part of a five-year study in which diked, drawn down cells were reflooded to ~e normal level of the wetland, or to a depth 30 cm or 60 cm deeper. Our objective was to investigate the effects of flooding depth on algal biomass and the relative contributions by each of the four algal assemblages. Floating metaphyton mats flourished in all cells after flooding, contributing about 87% of total algal biomass. Epiphytes contributed 11% of biomass, and epipeton and phytoplankton each contributed 1%. En-iergent macrophyte density was reduced by flooding, leading to increases in open water area. The wetland cells changed gradually over the study period from an early "'open wetland'" to a "sheltered wetland." in late stages of the study, phytoplankton became more abundant as the cells proceeded to a "lake wetland" state.

Net heterotrophy in productive prairie wetlands with high DOC concentrations

“…In more productive wetland systems, however, mid-summer, and even fall, maxima may occur (Crumpton 1989). In fact, the timing of biomass and production peaks reported here is similar to those recorded for productive wetlands at Delta Marsh, Manitoba (Robinson et al 1997). There are a number of possible explanations for this phenomenon.…”

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

“…and water depth was unexpected and suggested that relatively more light reached the sediments in deep than in shallow water. Profuse epiphyton, metaphyton, and macrophytes can reduce water transparency and we found that algal productivity (Figures 5, 6) and biomass (Robinson et al 1997) also varied inversely with water depth. Thus, high light extinction in shallow waters was probably a consequence of high macrophyte, metaphyton, and epiphyton biomass.…”

“…This procedure incorporated regular estimates of algal biomass expressed as area-based chlorophyll-a (Table 1; Robinson et al 1997), numerical relationships between biomass-normalized carbon assimilation rates (specific productivity) and irradiance, and measurements of ambient photosynthetically active radiation (PAR).…”

“…On each date and at each site, water samples were filtered (Whatman GF/C) and analyzed for chlorophyll-a (Chl-a) following Robinson et al (1997). Three aliquots of water were also dispensed into glass culture tubes for productivity experiments.…”

“…Details of data collection are presented in Robinson et al (1997). Biomass estimates were used to model the primary productivity of each assemblage in each cell.…”