ESTIMATING THE BREAKDOWN AND ACCUMULATION OF EMERGENT MACROPHYTE LITTER: A MASS-BALANCE APPROACH

Litter accumulation within emergent macrophyte marshes may significantly influence abiotic conditions and biota but litter is rarely considered in emergent macrophyte Studies. Litter is defined here as the standing and fallen dead plant material that can be collected using harvest methods in the field. Litter accumulation can be predicted by combining annual production with litter breakdown rates. Breakdown rates are typically measured using litter bag studies but these rates may also be measured using a mass-balance approach. A five year study conducted in Delta Marsh, Manitoba measured annual standing crop and harvested accumulated litter of Phragmites australis (Cav.) Trin., Typha glauca Godr., and Scolochloa festucacea (Willd.) Link. These species differ in their level of refractory material and hence the amount of litter that is expected to accumulate. Using annual estimates of standing crop and litter mass, a mass-balance model was used to estimate the litter breakdown rate for each species at three water levels. Mass-balance derived rates for Phragmites and Typha were significantly different (F-1,F- 14 = 5.07, p = 0.03) and also differed across water depths (F-2,F- 14 = 4.35, p = 0.04). For both species, predicted annual accumulations of litter tracked observed litter Values. The mass-balance approach, however, was not suitable for Scolochloa because there is no litter carry over from year to year. When compared to observed litter accumulations, estimates of litter accumulation made using litter bag breakdown rates consistently overestimated annual litter accumulation. In short, breakdown rates can be estimated using a mass-balance approach and can then provide more accurate estimates of annual litter accumulations emergent species With recalcitrant litter.