Determining a measure of biogeochemical structure relevant to denitrification in six central Pennsylvania wetlands

Background/Question/Methods 

Wetlands are recognized for providing valuable ecosystem functions, including denitrification.  Management of wetlands often assumes that degradation of ecosystem structure leads to a reduction in function.  Since management needs often require large-scale prediction of N-processing, ecosystem structure has been described using site-scale parameters such as vegetation and hydrology. This approach has proven inadequate in accurately predicting denitrification.  We hypothesize that measurement of process-scale biogeochemical parameters, such as nitrate and DOC concentrations in groundwater, can be used to construct functional habitats relevant for prediction of denitrification and can provide a more accurate measure of ecosystem structure. We measured a number of descriptors of biogeochemical structure for shallow groundwater in a case study of three good-condition and three poor-condition headwater riparian wetlands in central Pennsylvania. In each wetland, twenty shallow groundwater piezometers were located in a 400m²plot, and a suite of variables known to be important for denitrification were analyzed.  The results were used in a cluster analysis to identify distinct “functional habitats” for denitrification. These functional habitats were then compared with denitrification model results using the denitrification subroutine of the Created Wetlands Model #1 (CWM1), and with potential denitrification rates determined at the wetlands using the push-pull method.

Results/Conclusions 

Utilizing the results of water samples gathered in May, early October, and late October of 2012 and analyzed for pH, temperature, DO, DOC, ammonia, and nitrate, a total of four distinct functional habitats were identified across the six wetlands using the cluster analysis. Initial analyses of the clusters shows that multiple functional habitats are present at most sites, and that functional habitats for denitrification are spatially heterogeneous within a wetland. Functional habitat distribution within each wetland also differs between spring and fall. Pairing the initial CWM1 denitrification model results with the functional habitats revealed that the functional habitats may be useful for identifying areas of high and low denitrification. Potential denitrification results determined via push-pull are forthcoming. The initial results indicate that functional habitats may be a more accurate descriptor of ecosystem structure relevant to the wetland function of denitrification.