Nutrient limitation of pelagic bacteria and phytoplankton in four prairie wetlands

The prairie pothole region of Saskatchewan is characterized by many shallow, highly productive wetlands which support a diverse floral and faunal assemblage. Although assumed to be detritally driven, recent research has revealed that algal communities, both pelagic and attached, may be of great importance in these systems. Bacteria may also be significant. Consequently, studies of factors, for example nutrients, which control microbial growth are needed but lacking. In this study, a suite of physiological tests, including nutrient enrichment bioassays, sestonic ratios, protein to carbohydrate ratios, alkaline phosphatase activity and P-32 (phosphorus) uptake and turnover times, were utilized at four prairie wetland sites to assess nutrient status of algal and bacterial communities. The results indicated that the communities were nutrient sufficient in all ponds for the majority of the ice free season. Sestonic and protein to carbohydrate ratios were within the nutrient sufficient range, alkaline phosphatase activity was low and P-32 uptake and turnover times were slow for the majority of the year. Only in October did P-32 uptake and turnover times indicate P-deficiency. The abundance of biologically available nutrients may be linked to pond hydrology and ability of sediments to sequester and subsequently release nutrients. It is also hypothesized that a number of mechanisms including competition for P and P bound to dissolved organic carbon, may be responsible for the P-deficiency noted in October.