Abstract
Natural hydrological fluctuations within river floodplains generate habitat diversity through variable connections between habitat patches and the main river channel. Human modification of floodplains can alter the magnitude and frequency of large floods and associated sediment movement by interrupting these floodplain connections. The lower Wolastoq | Saint John River and its associated floodplain wetlands are experiencing anthropogenic disturbances arising from climate change, increased urbanization in the watershed, changing upstream agricultural landscape practices, and, most notably, major road and dam construction. By comparing digitized aerial images, we identified key periods of change in wetland extent throughout an ecologically significant component of the floodplain, the Grand Lake Meadows and Portobello Creek wetland complex, with significant erosion evident in coves and backwater areas across the landscape following dam construction and significant accretion around the Jemseg River following highway construction. Connectivity and hydrological regime also influenced other habitat components, namely nutrients and metals retention, as well as the composition of the local macrophyte community. These findings address two key aspects of floodplain management: (1) understanding how hydrological alteration has historically influenced floodplain wetlands can inform us of how the ecosystem may respond under future conditions, such as climate change, and (2) the mechanisms by which habitat diversity and disturbance regimes filter biological communities, with the potential for patches to host a rich biodiversity continuously supporting critical ecosystem functions.
Highlights
River floodplains are subjected to habitat shaping disturbances, and as a result, spatiotemporal creation of patch diversity can promote high biodiversity through niche differentiation and environmental filtering (Ward et al, 1999; Amoros and Bornette, 2002; Tockner and Stanford, 2002)
It was historically thought that flooding was a stress, it is realized, on the contrary, that flood pulses are an essential ecological disturbance, hydrologically linking the river and its floodplain, and replenishing sediment, nutrients and biological propagules to floodplain wetlands (Tockner et al, 2010)
This study aimed to determine if there are areas that have experienced significant change to floodplain wetland extent associated with major anthropogenic disturbance within the Wolastoq | Saint John River watershed, and to determine if these areas are responding in terms of habitat structure and environmental stressors
Summary
River floodplains are subjected to habitat shaping disturbances, and as a result, spatiotemporal creation of patch diversity can promote high biodiversity through niche differentiation and environmental filtering (Ward et al, 1999; Amoros and Bornette, 2002; Tockner and Stanford, 2002). This reflects the Intermediate Disturbance Hypothesis (i.e., few taxa can survive in habitats with high disturbance and many taxa are outcompeted by competitive dominants in habitats with low disturbance; Connell, 1978). Varying degrees of hydrological connectedness of wetland patches creates spatial heterogeneity in water temperature, suspended solids and turbidity, nutrient content, and substrate composition, all of which can influence biodiversity patterns (Amoros and Bornette, 2002)
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