Groundwater-induced redox-gradients control soil properties and phosphorus availability across four headwater wetlands, New York, USA

Abstract

Hydrochemical patterns across groundwater-fed wetlands, especially carbonate and redox gradients, can influence phosphorus (P) availability by controlling its distribution among different soil pools. We explored these linkages by comparing shallow (5-20 cm) soil properties along groundwater flowpaths in two rich fens, a marl fen, and a poor fen. Organic matter content, bulk density, and total elemental content varied more with depth to underlying drift materials than with water table fluctuation, but also were influenced by groundwater discharge, which stabilized water table elevations and controlled redox conditions. Total sulfur and calcium content increased where pore-water chemistry indicated active iron and sulfate reduction. Calcium mineral dynamics, however, did not appear to influence P availability: first, calcium carbonate (CaCO 3 ) accounted for \2% of the soil composition, except in the marl fen where it accounted for 20-25% of the soil composition. Second, Ca-bound P pools, determined from hydrochloric extraction of wet soil samples, accounted for \25% of the inorganic soil P pool. In contrast, iron-bound P determined from bicarbonate-buffered dithionite solution, accounted for 50-80% of the inorganic soil P, and increased where there was evidence of groundwater mixing, as did P release rates inferred from incubated anion resin bags. The total carbon and phosphorus content of organic-rich soils as well as available and labile P pools were strongly correlated with pore-water iron and alkalinity concentrations. Groundwater discharge and resulting hydrochemical gradients explained significant variation in soil composition and P availability across each site. Results highlight the importance of conducting biogeochemical studies in the context of a site's shallow geologic setting and suggest mechanisms supporting the diverse plant species unique to groundwater wetlands.

Environmental controls of plant species richness in riparian wetlands: Implications for restoration

“…Stable and high groundwater inflows are often considered a prerequisite for the development of species-rich fen vegetation in riparian areas (Almendinger & Leete, 1998;Boomer & Bedford, 2008). This is also consistent with our study since the sites with the highest species richness (i.e.…”

Local and regional impact of anthropogenic drainage on fen contiguity

“…Simultaneously, it prevents upwelling groundwater from entering the fen root zone, as a result of the immediate discharge of exfiltrated groundwater as surface water. These local hydrological consequences of anthropogenic drainage may have farreaching consequences for the suitability of fen habitat sites, because (1) base ions become leached from fens, instead of supplied to fens, when locally infiltrated precipitation percolates through the fen soil (Almendinger and Leete, 1998), and (2) oxic conditions, instead of anoxic or sub-oxic conditions, become established across the shallow subsurface when the groundwater supply of electron donors has ceased (Boomer and Bedford, 2008a) and aeration of the fen soil is enhanced (De Mars and Wassen, 1999). As the cumulative effects of these shifts in supply rates are thought to contribute to the acidification and eutrophication (Fojt and Harding, 1995;De Mars et al, 1996) of fens, the hydrological consequences of anthropogenic drainage may underlie the loss of fen plant species observed at drained fens in The Netherlands (Grootjans et al, 2005;Van der Hoek and Sykora, 2006) and Sweden (Malson et al, 2008).…”

“…In addition, dissolved minerals are transported by the groundwater to the fen surface. Both the shallow groundwater tables and the supply of dissolved minerals maintain the acidity of fens at a near-neutral pH level (Kemmers et al, 2003;Almendinger and Leete, 1998), and limit nutrient availability for plant growth provided the sulphate concentration of the groundwater is low (Boomer and Bedford, 2008a;Lamers et al, 1998).…”

Environmental predictors of shrubby cinquefoil (Dasiphora fruticosa) habitat and quality as host for Maine’s endangered Clayton’s copper butterfly (Lycaena dorcas claytoni)

“…Fluctuations in the water table can affect availability of nutrients in peat and pore water (Carter 1986;Boyer and Wheeler 1989;Smolders et al 2006;Fig. 3 Running mean inundation depth (cm) during Clayton's copper (CC) life history stages in representative wetland hydrological types during the 2010 Shrubby Cinquefoil (SC) growing season in Maine Boomer and Bedford 2008) and mineral and oxygen concentrations (Wassan et al 1990), which may affect wetland vegetation composition and productivity (Mitsch and Gosselink 2007). In Maine wetlands, pore water chemistry in the D. fruticosa rooting zone generally reflected the wetland's water source, whereas, peat chemistry was only weakly related to water source and hydrological types.…”