Spatial heterogeneity of soil properties in relation to microtopography in a non-tidal rewetted coastal mire

Abstract

Over the past century, mires and peatlands have faced a wide range of degradation by artificial drainage, making them one of the most threatened ecosystems in Europe. However, restoration of drained peatlands has gained much importance over the last three decades, mostly due to the multiple ecosystem services they provide such as carbon storage, habitat provision and water flow regulation. Although there has been an increased focus on such ecosystems, spatial research on hydrophysical soil properties following rewetting in coastal mires is lacking. Therefore, the objectives of the study were to understand the spatial structures of hydrophysical properties of organic soils and spatial patterns of organic matter accumulation in relation to soil surface microtopography. Soil organic matter content (SOM) and hydraulic conductivity (Ks) of topsoils (0–28 cm), along with soil textures of the underlying mineral substrate, were investigated in a rewetted non-tidal coastal flood mire (Baltic Sea). The results indicate that the organic horizon with its relatively low Ks acts as a hydrological barrier to infiltration. Soil organic matter content (SOM), Ks and soil surface microtopography are all spatially auto-correlated within 100, 87 and 53 m, respectively. Bivariate Moran’s I revealed a positive but weak spatial correlation between SOM and Ks and a moderately strong negative spatial correlation between SOM and soil surface microtopography. A map of SOM was generated using simple kriging, which predicts higher SOM in the centre of the ecosystem, at lower elevations; and lower SOM at the edges of the study area, at higher elevations. Local depressions in the centre of the ecosystem provide a wetter and therefore more anaerobic environment, thereby decreasing carbon mineralisation rates and enabling peat accumulation. The low hydraulic conductivity of the degraded peat in the presence of lower micro-elevations in the centre of the ecosystem is likely to increase the residence time of floodwater and thus may enhance (new) peat accumulation. Thus, we conclude that, for the restoration of non-tidal coastal mires where flooding events are not as frequent, Ks and soil surface microtopography are even more important factors to consider than for tidal systems.

Keywords

• hydraulic conductivity
• peatland
• restoration
• soil organic matter
• spatial variability