DETERMINATION OF HYDROLOGICAL CONTROLS ON BIOGEOCHEMICAL PROCESSES AT A WETLAND-AQUIFER INTERFACE USING MULTIVARIATE STATISTICS

Seasonal hydrological changes may influence biogeochemical cycling significantly in a wetland-aquifer system. Spatial and temporal variation of geochemical process indicators including, sulfate, sulfide, methane, ferrous iron, ferric iron, ammonium, and alkalinity, were evaluated from pore-water samples collected from a wetland-aquifer system. The system was studied during a wet and a dry period at three locations that exhibited 1) upward, 2) downward, and 3) negligent flow between the aquifer and wetland. Using multivariate statistics, the data were explored and reduced to factors which were interpreted as a dominant biogeochemical process. Analysis of Variance (ANOVA) was performed on factors obtained from Principal Component Analysis (PCA) to test significant differences in biogeochemical processes attributed to seasonal hydrological conditions. Seasonal differences in biogeochemistry were dominated by changes in water table and water flow paths. In the wet period the dominant process is methanogenesis, attributed to a high water table (which favors anaerobic conditions) and strongly associated with a site with negligible water flow. In the dry period, lowering of the water table oxidizes previously reduced sediments rich in iron sulfide minerals which contribute to the availability of electron acceptors, enhancing iron and sulfate reduction. The results illustrate the effects of seasonal hydrological changes on biogeochemical cycling in a linked wetland-aquifer system.