Organic matter distribution in floodplains can be predicted using spatial and vegetation structure data

Abstract

Riparian forest ecosystems play a significant role in the storage of organic carbon. However, the knowledge on the spatial patterns of organic matter distribution which is crucial to the assessment of the C sequestration potential of riparian ecosystems is still lacking. The aim of our study was to identify predictors of organic matter distribution in floodplain soils and vegetation. We analysed the depth distribution of soil horizons to 1 m below the surface, calculated the organic C content and quantified living biomass and woody debris at 67 sampling plots in the Donau-Auen National Park (Austria) along principle spatial gradients (longitudinal, lateral and vertical to river direction). Multiple regression models were fitted using hierarchical partitioning of spatial information, which was supplemented by forest stand parameters as possible predictors of soil C. The concentration of organic C in the subsoil horizons increased significantly with distance to the main channel. In addition, the thickness of soil horizons enriched with organic matter increased downstream which probably indicates the effect of riverbed changes over the last two centuries. Model prediction of soil parameters was improved with the inclusion of vegetation structure variables which are a consequence of local river dynamics. Highly dynamic locations indicated by higher stem numbers, greater understory vegetation cover, lower mean stem diameter and lower canopy cover showed significantly lower concentrations of soil organic C and lower total organic C stocks. We conclude that spatial information and vegetation structure can indicate gradients of geomorphic floodplain dynamic, which is the main driver of organic matter storage.

Spatial distribution of organic carbon and nitrogen in soils related to flood recurrence intervals and land use changes in Southern Qubec, Canada

“…Similar results were also observed for the flooded or unflooded soils (Cierjacks et al, 2010;Myster, 2015). These authors find that soils are more fertile in less frequently flooded areas and contain more organic matter.…”

“…For instance, the soil organic carbon and nitrogen content can vary considerably based on river flows and the flood regime. Cierjacks et al (2010) have shown that soil organic content in riparian areas increases further away from the main channel. Also, the phenomenon of vertical aggradation (that is, accumulation of flood sediment) maintains the soil in an immature state and inhibits the mineralization and humification processes essential to biogeochemical cycles (Bayley and Guimond, 2011;Gervais-Beaulac et al, 2013).…”

“…Bedison et al (2013) showed that about 70% of the forest sites that were studied in flood zones had no organic horizons and that the mineral matrix had low organic carbon and nitrogen contents. Although numerous studies have been done on the relationship between soil use and soil organic carbon and nitrogen (Don et al, 2007;Li et al, 2013;Schilling et al, 2009), there are few detailed studies on the effects of successive floods on CO and N content in alluvial soils (Bayley and Guimond, 2009;Bedison et al, 2013;Cierjacks et al, 2010). Recent works (Gervais-Beaulac et al, 2013 have led to the determination that frequent floods can result in soil depletion and that organic carbon and nitrogen contents are significantly lower in frequent-flood zones than in areas prone to less flooding.…”

Distribution of Soil Organic Carbon in Riparian Forest Soils Affected by Frequent Floods (Southern Québec, Canada)

“…([25], p. 1243). Lastly, the study by Cierjacks et al [18] showed that "The concentration of organic C in subsoil horizons increased significantly with the distance to the main channel." ( [18], p. 1), although some soils close to the river may contain high SOC concentrations.…”

“…Lastly, the study by Cierjacks et al [18] showed that "The concentration of organic C in subsoil horizons increased significantly with the distance to the main channel." ( [18], p. 1), although some soils close to the river may contain high SOC concentrations. In other words, the impact of flooding on soils is complex and difficult to predict [25], and the conditions specific to each site must be taken into account.…”