Extreme variability of water table dynamics in temperate calcareous fens: Implications for biodiversity

Abstract

Abstract:Calcareous fens are minerotrophic peatlands with very high species diversity, and maintenance of the water table is assumed to be a key contributor to this diversity. However, this assumption is based on limited study of fen water table dynamics. Here we monitor water table fluctuation in distributed locations across three calcareous fens differing in hydrogeomorphic setting for three growing seasons. Water table position was extremely variable with absolute ranges of 89, >100, and >118 cm in the Riparian, Trough and Basin Fens, respectively, and was controlled by landscape position and weather variability. Areas adjacent to a second-order stream experienced the least water table fluctuation, while the Basin Fen, at >75 m from a surface water connection, was very prone to year-to-year precipitation differences. Mean and median water table values were found to be poor indicators of biologically relevant hydroperiods. We introduce the term 'duration of initial growing season saturation' as a potentially more useful statistic to relate to plant species distribution. Across the studied fens, this duration ranged from 1 to 14 weeks from the start of the growing season. The water table resided below the ground surface for between 0 and 22 weeks of the growing season across the calcareous fens and study period. These findings impart great differences in the development of oxidized rooting depths. Our results demonstrate that there is much more variation in calcareous fen hydrology than previously reported, and this variability has important implications for fen vegetation patterning and management.

Water and nutrient discharge to a high‐value terrace–floodplain fen: resilience and risk

“…Based on our study, in the absence of irrigation-induced impacts, the hydrologic status of fens located along the Cedar River terrace boundary appears to be resilient to current climate perturbations, but recognition is growing that fens may be particularly vulnerable to future climate change (Duval and Waddington, 2011;Herrera-Pantoja et al, 2012). Climate projections for the central United States suggest that the region including southeast Iowa is projected to experience increasing trends in rainfall, with precipitation projected to increase 20% in the next 50 years (Villarini et al, 2013).…”

Hydro-ecology of groundwater-dependent ecosystems: applying basic science to groundwater management

“…For the former, there is a large and robust literature quantifying the water depth adaptations of many different peatland plant species (e.g. Amon et al 2002, Duval andWaddington 2011), and the response time of wetland plants to water depth change is relatively rapid (i.e. one to several years).…”

Beaver‐mediated water table dynamics in a Rocky Mountain fen

“…Then, data sets were further divided into groups based on their shared proximity to beaver dams and the stream (i.e., Bateman Creek). The reason for this was to parse out the hydrologic influence of each as studies have shown that streams can influence water table position and stability in fens (Duval & Waddington, ). Beaver dam proximity was determined as the distance of a well from the location where each dam intersects the stream and impedes the main vector of streamflow.…”

“…Thus, we use the median absolute deviation (MAD) of Δ WT i,j values for each well because distributions are nonnormal and MAD is more robust to outliers than the standard deviation. Numerous studies have shown that peatland form and function is impacted when annual water tables fluctuate >20 cm (e.g., Breeuwer et al, ; Duval & Waddington, ; Granath, Strengbom, & Rydin, ; Whittington & Price, ). For example, Menberu et al () showed that the optimum fluctuation for rich fens is ~8 cm.…”

“…In contrast to mineral soil environments, peatlands tend to have shallow water tables that are spatially/temporally variable and vulnerable to climatic variation (Duval & Waddington, 2011). Such variation has not only hydrological implications but also ecological, as spatial patterns of vegetation are affected (Sulman et al, 2010).…”