The Beautiful and the Dammed: Defining Multi-Stressor Disturbance Regimes in an Atlantic River Floodplain Wetland

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.

Environmental filtering of macroinvertebrate traits influences ecosystem functioning in a large river floodplain

“…The resulting community subsequently possessed traits that influenced ecosystem function. Sheltered habitats with low connectivity showed higher levels of nutrients and niche diversity, as well as significant carbon stores (Rideout et al, 2021). This resulted in reduced dependency on allochthonous carbon inputs and increased functional evenness of the invertebrate community.…”

“…These wetlands are a vital reservoir for biodiversity (including rare and endangered species) and act as important nursery, flyway and nesting habitat for many migratory and transitional species, prompting the provincial and federal governments to protect them through the Grand Lake Meadows Protected Natural Area (GLM PNA) and the Portobello Creek National Wildlife Area (PC NWA), respectively. Despite its outstanding conservation value, however, the GLM complex has experienced substantial wetland habitat change in the last few decades, with an altered hydrologic regime, and subsequent sediment and nutrient deposition, into the floodplain due to significant anthropogenic alterations within the watershed (Rideout et al, 2021).…”

“…Supporting habitat data for this work are described in detail in Rideout et al (2021) and thus the methods employed are only summarized here.…”

“…In a previous paper focusing on disturbance regimes in the Wolastoq | Saint John River (Rideout et al, 2021), we identified connectivity and hydrology as the driving forces in the formation of floodplain wetland habitat patches, influencing shoreline change, temperature variation, nutrient and metal retention, macrophyte growth, and carbon storage. Our analysis described above has shown that habitat characteristics filter invertebrate traits, shaping the local community.…”

Plankton Diversity in Tropical Wetlands Under Different Hydrological Conditions (Lake Tana, Ethiopia)

“…Hydrological conditions, such as water availability and depth in wetlands affect the interchange of water, sediment, nutrients, organic matter, and organisms between the wetlands and their adjacent water bodies (i.e., river, river-lake, or lake; Chaparro et al, 2018;Feng et al, 2021;Rideout et al, 2021). During high water level periods, inputs from the river, and lake water can also modify local environmental conditions in wetlands by altering dissolved oxygen concentration, conductivity, turbidity, and nutrient levels (Alvarez-mieles et al, 2013;Castillo, 2020).…”