Heterogeneity of soil carbon pools and fluxes in a channelized and a restored floodplain section (Thur River, Switzerland)

Abstract

Due to their spatial complexity and dynamic nature, floodplains provide a wide range of ecosystem functions. However, because of flow regulation, many riverine floodplains have lost their characteristic heterogeneity. Restoration of floodplain habitats and the rehabilitation of key ecosystem functions has therefore become a major goal of environmental policy. Many important ecosystem functions are linked to organic carbon (C) dynamics in riparian soils. The fundamental understanding of the factors that drive the processes involved in C cycling in heterogeneous and dynamic systems such as floodplains is however only fragmentary. <br><br> We quantified soil organic C pools (microbial C and water extractable organic C) and fluxes (soil respiration and net methane production) in functional process zones of adjacent channelized and widened sections of the Thur River, NE Switzerland, on a seasonal basis. The objective was to assess how spatial heterogeneity and temporal variability of these pools and fluxes relate to physicochemical soil properties on one hand, and to soil environmental conditions and flood disturbance on the other hand. <br><br> Overall, factors related to seasonality and flooding (temperature, water content, organic matter input) affected soil C dynamics more than soil properties did. Coarse-textured soils on gravel bars in the restored section were characterized by low base-levels of organic C pools due to low TOC contents. However, frequent disturbance by flood pulses led to high heterogeneity with temporarily and locally increased pools and soil respiration. By contrast, in stable riparian forests, the finer texture of the soils and corresponding higher TOC contents and water retention capacity led to high base-levels of C pools. Spatial heterogeneity was low, but major floods and seasonal differences in temperature had additional impacts on both pools and fluxes. Soil properties and base levels of C pools in the dam foreland of the channelized section were similar to the gravel bars of the restored section. By contrast, spatial heterogeneity, seasonal effects and flood disturbance were similar to the forests, except for indications of high CH<sub>4</sub> production that are explained by long travel times of infiltrating water favouring reducing conditions. Overall, the restored section exhibited both a larger range and a higher heterogeneity of organic C pools and fluxes as well as a higher plant biodiversity than the channelized section. This suggests that restoration has indeed led to an increase in functional diversity

Carbon dioxide and methane fluxes in variably-flooded riparian forests

“…This interpretation would explain the delayed response of soil respiration to flood events, as well as the trend in CO 2 emission in relation to flood frequency (Table 3). Similar to the trend observed in the present investigation, a study conducted in the Thur River watershed (Switzerland) found higher rates of CO 2 emission in riparian buffers along flood-affected sections of the river compared to riparian areas near channelized sections of the river (Samaritani et al, 2011).…”

Seasonal variability of soil CO2 flux and its carbon isotope composition in Krakow urban area, Southern Poland

“…The values of Q 10 coefficients reported for Fluvisols are higher than the value obtained for the urban meadow (site B-2.98). In Switzerland, Samaritani et al [26] obtained Q 10 values of 3.6 for grass, 3.4 for pasture and 3.2 for mixed forest. Awasthi et al [27] report Q 10 values in a range from 2.5 to 5.0 for mixed Fluvisols, Cambisols, Rigosols and Luvisols in Nepal.…”

The impact of a pulsing groundwater table on greenhouse gas emissions in riparian grey alder stands

“…3b). Samaritani et al (2011) have shown that frequent disturbance by flood pulses of a floodplain forest led to high heterogeneity with temporarily and locally increased C pools and soil respiration but also higher CH 4 fluxes.…”