DECOMPOSITION OF LITTER OF 3 MUDFLAT ANNUAL SPECIES IN A NORTHERN PRAIRIE MARSH DURING DRAWDOWN

The loss of dry mass, nitrogen and phosphorus from shoot and root litt er of mudflat annuals was examined in a series of experimental marshes in the Delta Marsh, Manitoba, Canada. Litter bags containing shoot ma terial of three mudflat annuals (Aster laurentianus Fern., Atriplex pa tula L., and Chenopodium rubrum L.) were placed on the sediment surfac e of the marshes under drawdown conditions. In addition, litter bags c ontaining root material of these three species were shallowly buried. Approximately 70% and 50% of both shoot and root litter, respectively, was still present after one year in the field. During the second year when the marshes were flooded, shoot and root litter lost an addition al 20% and 0% of their mass, respectively. Except for Chenopodium root s, which accumulated nitrogen and phosphorus during both years, shoot and root litter lost from 0 to 50% of their nitrogen and phosphorus ea rly in the first year, with levels generally remaining constant throug h the remainder of the study period. Our results indicate that mudflat annual litter decomposed slowly and would provide abundant habitat fo r aquatic invertebrates when these marshes were reflooded, However, mo st nutrient loss took place in the first year when the litter was unfl ooded, with little loss occurring in the second year when flooded.