Nutrient additions to wetlands in the Interlake region of Manitoba,Canada: effects of periodic additions throughout the growing season

The Interlake region of central Manitoba is characterized by numerous shallow, relatively unproductive wetlands. Typically, these wetlands are poorly utilized by breeding waterfowl in spite of generally reliable water conditions during spring and summer. Nutrient additions were made throughout the growing season to 18 PVC enclosures installed in a low productivity wetland near Lundar, Manitoba. Inorganic phosphorus (as H₃PO₄) and nitrogen (as NH₄NO₃) were added at bi-weekly intervals during the summer of 1988 at target rates of 0 and 0, 30 and 800, and 60 and 1600 µg 1^–1 (P and N respectively). Algal and invertebrate communities were monitored from mid-June to September, 1988. Phytoplankton, epiphytic periphyton and metaphyton communities demonstrated significant increases in biomass over the treatment period. No significant differences in epipelon community biomass were noted. An examination of several indicators of nutrient deficiency indicated that algal productivity was moderately to severely limited in all enclosures, with little or no mitigative effects noted due to nutrient addition treatment. No significant differences in numbers or biomass of total invertebrates or invertebrate functional groups attributed to fertilization were observed. Nutrient additions did increase community productivity, however the levels used in this study were insufficient to yield a sustained increase in primary or secondary productivity.