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

Abstract

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, many of them linked to organic carbon (C) dynamics in riparian soils, has therefore become a major goal of environmental policy. 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.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.Correspondence to: J. Luster (joerg.luster@wsl.ch) 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 C 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 baselevels 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 4 production that are explained by long travel times of infiltrating water favoring 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.

Toward the use of testate amoeba functional traits as indicator of floodplain restoration success

“…Further information on this site is given in Woolsey et al [23]. We selected six habitats based on the functional process zones (FPZ) [24] proposed by Samaritani et al [25] to represent the different post-restoration successional stages present at the site. These zones represent a gradient of decreasing flood mechanical impact.…”

Patterns of earthworm communities and species traits in relation to the perturbation gradient of a restored floodplain

“…Bare gravels with patches of poorly developed soil -FLUVIOSOLS BRUTS -and pioneer vegetation constituted the first habitat (GRAVELS). The second habitat (HERBS) was an area with more developed soils -FLUVIOSOLS JUVENILES -but showing high spatial and temporal heterogeneity (Samaritani et al, 2011) and dominated by tall herbs (Phalaris arundinacea). The third habitat (WILLOW BUSH) was characterised by soils of average depth (FLUVIOSOLS TYPIQUES) and patches of planted willow bushes.…”

“…1). Six different habitats were selected based on elevation and distance to the river, soil type, vegetation structure, and impact of restoration (Samaritani et al, 2011). The French soil classification (Baize and Girard, 2009) was preferred over the FAO World Reference Base for Soil Resources (IUSS Working Group WRB, 2006) because the latter does not dis-criminate different types of Fluvisols (the dominant soil taxon within the study site).…”

“…For organic (OC), total carbon (C) and total nitrogen (N) measurements, three cores of 10 cm depth and 6 cm diameter were extracted at each sampling site, homogenised and sieved at 2 mm, and measured following the methods of Walthert et al (2010). The minimum flow rate required to flood each habitat was determined by Samaritani et al (2011) from inundation maps produced by digital terrain modelling based on river cross section measurements. The average num-ber of floods per year was calculated for each habitat using river flow measurement data covering the period from 2003 to 2008 (www.hydrodaten.admin.ch/d/2044.htm).…”

Analysis of carbon and nitrogen dynamics in riparian soils: Model validation and sensitivity to environmental controls

“…These samples were analysed for NH 4 (flow injection 141 analysis based on alkalinisation and diffusion of NH 3 into an acid carrier followed by 142 colorimetric detection of an indicator dye), NO 3 (direct colorimetry, Navone 1964) and non-143 purgeable organic C (elemental analyser, Skalar Formacs HT and TN). 144 Samaritani et al (2011) presented a study relating variability of C pools and fluxes (CO 2 ) to 145 soil properties, environmental conditions and flood disturbance in a revitalized section of the 146 Thur River. They found that, overall, environmental conditions driven by seasonality and 147 flooding affected soil C dynamics more than soil properties did.…”