Comparing shallow groundwater hydrodynamics in reference peatlands and the ditched Big Meadow Bog complex on Brier Island, Nova Scotia

Abstract

Understanding characteristic hydrology is the first step toward assessing the degree of impairment in any wetland, including peatlands, and developing an effective approach for restoration. Pre-disturbance datasets are usually unavailable to use as a basis for establishing restoration targets, and there is limited research on peatlands in the province of Nova Scotia to serve as a reference for developing meaningful hydrologic performance measures on which to evaluate success. In the Big Meadow Bog wetland complex on Brier Island, Nova Scotia, a drainage ditch was excavated to increase arable land in 1958 and 1959. This study characterized the hydrodynamics of two Horizontal Fens, three Basin Bogs and a Domed Bog-Fen Complex to compare water level dynamics in different wetland types and to quantify the degree of hydrologic impairment of the ditched Big Meadow Bog complex. This study was also designed to examine relationships between hydrodynamics in the Big Meadow Bog complex and in the reference peatlands in relation to the known distribution of populations of the endangered Eastern Mountain Avens on the island. All analyses completed for this study were based on hourly water level data collected by pressure transducer-based data loggers installed by Nova Scotia Department of Natural Resources. Water levels were used to characterize water table depths, monthly fluctuations, water table depth durations and the water table response to individual rainfall events. Horizontal Fens were characterized by a water table close to ground level and small fluctuations. The Domed Bog-Fen had a low water table, and was quite stable which was different from the higher water table and larger fluctuations observed in Basin Bogs. Consistent similarities in hydrologic characteristics led to the reclassification of one of the reference Basin Bogs as a Horizontal Fen. Disturbance associated with drainage ditches resulted in a lowered water table, larger amplitude of water level fluctuations, and greater frequency of water levels in dryer depth strata. Hydrodynamic results suggest that Eastern Mountain Avens is most successful when water levels are concentrated in the shallow root zone, with regular fluctuations into the dryer depth stratum (20-40 cm below ground) for approximately 20-25% of the growing season. The results from this study characterize the typical hydrodynamics of peatlands on Brier Island and should be useful for developing targets to guide successful restoration of the Big Meadow Bog complex and increase the likelihood of sustaining populations of Eastern Mountain Avens in Nova Scotia.