Impacts of water level fluctuation on mesotrophic rich fens: acidification vs. eutrophication

Abstract

Summary1. Water levels in areas with intensive agriculture have often been strictly controlled for decades. Recently, more natural fluctuating water levels have been propagated to improve the ecological quality of wetlands in these areas. This study investigated the effects of water levels on protected base-rich mesotrophic fens during winter and summer. 2. We used a mesocosm approach to simulate water level fluctuations under winter and summer conditions (light and temperature) to test the effects of water level on the biogeochemistry and vegetation of two highly endangered fen types with the brownmosses Scorpidium scorpioides and Hamatocaulis vernicosus as dominant mosses. 3. Both species showed decreased photosynthetic capacity at lower water levels. These levels also resulted in decreased alkalinity due to oxidation processes in the moss layer. High water levels led to increased pH and alkalinity, due to reduction processes and infiltration of baserich water. 4. For the P-limited S. scorpioides mesocosms, high water levels did not lead to P mobilization or to significant changes in biomass production, P uptake and N:P ratios. However, for the mesocosms with H. vernicosus, where P limitation was not obvious, high water levels did result in P mobilization and increased P availability due to iron reduction. The lower P mobilization for S. scorpioides appeared to be related to lower total soil P content and higher Fe:P and Ca:P ratios. Although high water levels resulted in the accumulation of ammonium under winter conditions, this did not happen under summer conditions, making ammonium toxicity unlikely. 5. Synthesis and applications. Our results suggest that low water levels could hamper protected brownmosses in rich fens, especially during the summer. In contrast, inundations may have a positive effect on rich fens by increasing the alkalinity. However, inundations may lead to eutrophication due to internal P mobilization in soils with a high total P content and low Fe:P ratio. Therefore, we recommend that soils with high total P content and low Fe:P ratios should not be flooded.

Impacts of short-term droughts and inundations in species-rich fens during summer and winter: Large-scale field manipulation experiments

“…However, longer-term inundations during winter can lead to both forms of ANC-increase in waterlogged rich fen soils, as demonstrated in a mesocosm experiment (Cusell et al, 2013a). 2 weeks of winter inundation in 2011 did lead to an increase in alkalinity and Ca-concentration in soil pore water by 50-100%, but only in Scor-and Call-soils.…”

“…This clear seasonal difference may be explained by higher evapotranspiration in summer, which facilitates the infiltration of base-rich inundation water (Cusell et al, 2013a).…”

“…Raised surface water levels may lead to increased alkalinity, pH, and/or Ca-concentrations in soil pore waters (Loeb et al, 2008a,b;Cusell et al, 2013a). Additionally, the acid neutralizing capacity (ANC) may be increased during inundation by microbial reduction of Fe(III), SO 4 and/or NO 3 (Gambrell and Patrick, 1978;Baker et al, 1986), or, more permanently, infiltration of base-rich surface water (Cusell et al, 2013a). Inundation may, however, also result in eutrophication due to higher P-and N-inputs (Wassen et al, 1996) or internal P-mobilization (Patrick and Khalid, 1974;Lamers et al, 1998a).…”

Understanding the Long Term Ecosystem Stability of a Fen Mire by Analyzing Subsurface Geology, Eco-Hydrology and Nutrient Stoichiometry – Case Study of the Rospuda Valley (NE Poland)

“…In the lower basin, where water level stayed close to the surface during the whole season, N and P inputs from peat mineralisation are very low, whereas low redox potential make P freely available (cf. Cusell et al 2013).…”

Mapping wetland loss and restoration potential in Flanders (Belgium): an ecosystem service perspective.

“…Nicholls 2004. The combination of increased evapotranspiration and more extreme weather events will probably challenge the restoration of specific wetland types that depend on more or less stable, high water levels, especially those of oligo-mesotrophic conditions (e.g., Cusell et al 2013). Of course, restoration success will also depend on how the local geographical location is impacted by climate change (Čížková et al 2013).…”