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 a re poorly utilized by breeding waterfowl in spite of generally reliabl e water conditions during spring and summer. Nutrient additions were m ade 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 d uring the summer of 1988 at target rates of 0 and 0, 30 and 800, and 6 0 and 1600 mug l-1 (P and N respectively). Algal and invertebrate comm unities were monitored from mid-June to September, 1988. Phytoplankton , epiphytic periphyton and metaphyton communities demonstrated signifi cant increases in biomass over the treatment period. No significant di fferences in epipelon community biomass were noted. An examination of several indicators of nutrient deficiency indicated that algal product ivity was moderately to severely limited in all enclosures, with littl e or no mitigative effects noted due to nutrient addition treatment. N o significant differences in numbers or biomass of total invertebrates or invertebrate functional groups attributed to fertilization were ob served. Nutrient additions did increase community productivity, howeve r the levels used in this study were insufficient to yield a sustained increase in primary or secondary productivity.