ABSTRACT:One component of the filamentous algal community of a northern fen ecosystem in central Michigan was studied under conditions of nutrient enrichment by secondarily treated sewage effluent during one growing season. The productivity ofCladophoraspp. measured by continuous flow bioassay was 2.6 g dry weight m day at the site of effluent addition compared to 0.085 g m day at the control site. Under conditions of nutrient enrichment, uptake by bioassayCladophoraspp. averaged 12 mg m−2day−1for phosphorus and 55 mg m−2day−1for nitrogen, compared to 0.01 mg m−2 day−1and 0.16 mg m−2day−1for phosphorus and nitrogen, respectively, in the control area. At the end of the growing season approximately 4.3 g N m−2 and 0.96 g P m−2were immobilized inCladophoraalgal biomass. Algal growth temporarily immobilized 3.0 percent of the nitrogen and 1.0 percent of the phosphorus added as sewage effluent. Gross productivity of surface water in the fen averaged 1.5 g O2m−2day−1at the nutrient enriched site, compared to 0.5 g O2m−2day−1at the control area. Gross productivity, community respiration and reaeration constant values in the fen were similar to data collected by other researchers in shallow water aquatic systems, but o
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