Do rural impoundments in coastal Bay of Fundy, Canada sustain adequate habitat for wildlife?

In Canada and elsewhere in North America, impoundments are created in compensation for historic wetland loss and for habitat loss due to development projects, but these new sites are infrequently evaluated to determine how effectively they function. The Cumberland Marsh Region (CMR), located at the head of the Bay of Fundy, Canada, is of importance to migratory birds and has been subject to 300+ years of anthropogenic alteration, including impoundment creation on diked and drained tidal marsh in the last five decades. Wetland managers have noticed a pervasive decline in impoundment productivity leading to reduced waterbird usage (senescence). To understand factors that promote senescence, we analyzed abiotic and biotic proxies in sediment archives from six freshwater impoundments in two coastal watersheds to assess spatial trends across the CMR within recent decades. Our results demonstrate that impoundment productivity is driven by autochthonous nutrient sources (C/N between 7.7 and 14.4), but biogeochemical conditions can be highly variable among impoundments despite their proximity. Biogeochemical variation among top-of-core sediment samples from each impoundment was generally minimal, and thus we believe that the aging of impoundments has resulted in low productivity and organic matter accumulation due to dike stabilization and declines in nutrient loading. We conclude that these freshwater impoundments (in the CMR and likely other similar settings) are not highly productive, and may not provide abundant forage and optimal wildlife habitat which is expected of these systems; adaptive management strategies and hydrologic rehabilitation merit consideration to enhance ecological functioning. Understanding landscape attributes, hydrologic dynamics, and conditions prior to and after major human alterations should be a priority in future compensation projects.