Carbon cycling in boreal wetlands: A comparison of three approaches

Three independent methods were used to measure net ecosystem production (NE P) in four wetlands near Thompson, Manitoba, Canada. The first method calcu lated NEP by subtracting heterotrophic respiration from net primary product ivity, using both measurements and estimates derived from the literature. T he second method used radiocarbon data from cores to derive long-term NEP a veraged over the past several decades. The third method used direct measure ment of NEP combined with a model to fill in for days with no data. The thr ee methods, with their independently derived uncertainties, ail show the sa me magnitude and pattern of NEP variation across four different wetland typ es. However direct measurement yielded distinctly lower estimates of NEP in the most productive sites. Highest NEP (31 - 180 gC m(-2) yr(-1)) was obse rved in the two wetlands with the highest proportion of sedge vegetation. A bog collapse scar and a nutrient-rich fen had NEP values not significantly different from zero. The maximum NEP at sites with intermediate nutrient s tatus is due to slower overall decomposition and is likely associated with greater allocation of production below ground by sedges. The three methods for estimating NEP differ in the effort required, the sources of error, and in the timescale over which they apply. Used in combination, they allow es timation of parameters such as belowground production and the contribution of heterotrophic decomposition to total soil respiration. Using the radioca rbon method, we also derived estimates of the rate of N accumulation in the four wetland types.