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MODELING LONG-TERM DYNAMICS OF LITTER ACCUMULATION IN RESPONSE TO STATIC AND VARIABLE HYDROPERIODS
Citation:
CHRISTENSEN, J. R., W. G. Crumpton, AND A. G. van der Valk. MODELING LONG-TERM DYNAMICS OF LITTER ACCUMULATION IN RESPONSE TO STATIC AND VARIABLE HYDROPERIODS. Presented at 8th INTECOL International Wetlands Conference, Cuiaba, BRAZIL, July 20 - 25, 2008.
Impact/Purpose:
Presentation
Description:
Accumulated litter from emergent species like the cattail hybrid (Typha glauca Godr.) can influence local abiotic conditions, other biota, and ecosystem processes. Litter accumulation results from high production coupled with slow breakdown rates. Wetland managers regularly manipulate wetland hydrology via drawdowns to increase production and extent of emergent species but it is unclear how these drawdowns influence litter dynamics. A model was developed to investigate the long-term dynamics of litter in response to multiple scenarios involving spatial extent, production, and water level manipulations. This model is the first attempt to investigate long-term litter dynamics in hydrologically variable wetlands and is needed to understand the impact of hydrological events on litter, local conditions, and biogeochemical processes. The Marsh Ecology Research Program (MERP) at Delta Marsh, Canada monitored emergent biomass and litter mass following an experimental high water and drawdown event that reset the plant community and litter levels. This model uses data and breakdown and distribution models derived from the MERP study to investigate long-term litter dynamics. Under stable distributions, stable annual biomass (500 g/m2), and stable water levels, the litter levels off after 3-4 yrs at ~200 g/m2 at a water depth of 1-20 cm where the majority of Typha is located. These litter values are comparable with observed litter mass values taken in Delta Marsh after 20 years of stable conditions. Under increasing distribution and increasing biomass but stable water levels, such as what occurred in MERP following the high water- drawdown event, the litter levels stabilize after 12 years once extent and production stabilize. This represents a substantial lag time for the recovery of wetlands that experience extreme events and has implications for wetland restoration and creation projects. Drawdowns decrease the litter mass considerably during the year of drawdown due to higher breakdown rates. With drawdowns every 5 or 10 years, litter levels return to pre-drawdown levels after 2-3 yrs if production and extent remain unchanged. Drawdowns every other year keep litter very low and do not allow for litter levels to stabilize. The model indicates that drawdowns can heavily influence litter accumulation of Typha spp. with significant consequences for local conditions, nutrient budgets, and biogeochemical processes within the marsh.