Manipulative lowering of the water table during summer does not affect CO₂emissions and uptake in a fen in Germany

Abstract

We simulated the effect of prolonged dry summer periods by lowering the water table on three manipulation plots (D(1-3)) in a minerotrophic fen in southeastern Germany in three years (2006-2008). The water table at this site was lowered by drainage and by excluding precipitation; three nonmanipulated control plots (C(1-3)) served as a reference. We found no significant differences in soil respiration (R(Soil)), gross primary production (GPP), or aboveground respiration (R(AG)) between the C(1-3) and D(1-3) plots in any of the measurement years. The water table on the control plots was naturally low, with a median water table (2006-2008) of 8 cm below the surface, and even lower during summer when respiratory activity was highest, with median values (C(1-3)) between 11 and 19 cm below the surface. If it is assumed that oxygen availability in the uppermost 10 cm was not limited by the location of the water table, manipulative lowering of the water table most likely increased oxygen availability only in deeper peat layers where we expect R(Soil) to be limited by poor substrate quality rather than anoxia. This could explain the lack of a manipulation effect. In a second approach, we estimated the influence of the water table on R(Soil) irrespective of treatment. The results showed a significant correlation between R(Soil) and water table, but with R(Soil) decreasing at lower water tables rather than increasing. We thus conclude that decomposition in the litter layer is not limited by waterlogging in summer, and deeper peat layers bear no significant decomposition potential due to poor substrate quality. Consequently, we do not expect enhanced C losses from this site due to increasing frequency of dry summers. Assimilation and respiration of aboveground vegetation were not affected by water table fluctuations between 10 and >60 cm depth, indicating the lack of stress resulting from either anoxia (high water table) or drought (low water table).

Short-Term Effects of Drying and Rewetting on CO2 and CH4 Emissions from High-Altitude Peatlands on the Tibetan Plateau

“…A similar lack of effect from drying and rewetting has been found in northern [10] and German peatlands [17]. The drop in the water table did not affect CO 2 emissions from the soil, possibly because labile organic matter was primarily distributed in surface soils [17] rather than in deeper soils [17,18]. Moreover, soil respiration occurring in peatland ecosystems includes both autotrophic and heterotrophic respiration.…”

“…In our study, alternate drying and rewetting had little impact on CO2 release. A similar lack of effect from drying and rewetting has been found in northern [10] and German peatlands [17]. The drop in the water Researchers have drawn different conclusions about the effects of alternate drying and rewetting on CO2 release from the soil in wetlands.…”

Comparison of performance of tile drainage routines in SWAT 2009 and 2012 in an extensively tile-drained watershed in the Midwest

“…Tile drainage systems can cause water table recession in tile-drained soil. Water table was lower when respiratory activity was highest in summer (Muhr et al, 2011), which may be lower than the depth of subsurface tiles during long dry summer periods. Water table depth calculation based on change in the soil water for the whole soil profile tended to overestimate the distance between water table and the soil surface when long-term simulations were performed, most commonly in cases where days without rainfall dominated (Moriasi et al, 2013).…”

Partitioning of soil CO<sub>2</sub> efflux in un-manipulated and experimentally flooded plots of a temperate fen

“…Water level quickly recovered after ending the drainage in October of each year through lateral water inflow and natural precipitation (see Muhr et al, 2011 for more details). In a second experiment, reported here, the D1-3 plots were permanently flooded during the growing seasons of 2009 (14 May-30 October) and 2010 (10 May-9 November) using water from a creek directly beside the fen (Table 1).…”

“…However, not all peatlands seem to respond to water table drawdown. Muhr et al (2011) reported no increase of the soil CO 2 efflux in a minerotrophic fen, although the water table was permanently lowered during growing seasons. In the long run, peatlands may adapt to the new hydrological regime and constrain or compensate C losses by changing the vegetation community and plant productivity (Laiho, 2006;Strack and Waddington, 2007;Weltzin et al, 2000).…”