Search

Several studies have demonstrated the great range of possibilities offered by remote sensing in identifying, estimating and mapping biological soil crust (BSC) patterns, i.e. a feature recognised to play major functions in drylands. However those techniques are suitable mainly where BSC patterns are abundant (> 30%) and vegetation cover low (< 10%), otherwise reflectance values matched different levels of BSCs mixed with vegetation and bare soil surfaces. This study developed an alternative methodology in mapping BSC presence in areas with a wide range of BSC cover associated with different mosaics encompassing vegetation and bare surfaces in the Sahel. Data were collected during intensive field surveys and remote sensing imagery of two typical Sahelian watersheds in western Niger (Banizoumbou and Tamou). Statistical methods were used to explore relationships between BSC occurrence and abundance and key environmental factors (rainfall, land use, land cover, vegetation, physical crusts). A predictive model of BSC spatial distribution was developed based on logistic regressions. This model allowed predicting and mapping BSC occurrence in areas where BSC cover ranged from 0 to 65% at Tamou (15% in average) and 1 to 48% at Banizoumbou (4% in average) and where vegetation cover ranged from < 1% to > 75%. Predicted values were obtained with an overall accuracy of 77.7% (kappa = 0.54), classifying the model as good and discriminant. This work is the first step in assessing the local scale ecological functions of BSC. Further work is needed for extrapolation at the regional scale in order to provide a useful tool for ecological surveys and for predictions of soil surface dynamics related to global changes in dryland areas. [ABSTRACT FROM AUTHOR]

• Two contrasting years of monitoring of an agricultural tile-drained catchment. • Water and suspended particle transfers displayed high temporal variability. • Two transfer pathways to tile drains were observed. • Suspended particle dynamics in tile drains may be controlled by sediment storage and exhaustion. Soil erosion, runoff and sediment connectivity are strongly impacted by anthropogenic features in lowland agricultural catchments. Among these landscape features, the role played by tile drainage on water and sediment transfers and hillslope-to-river connectivity in drained catchments remains poorly understood. This study quantified water and sediment transfers in a tile drained catchment of central France by combining high frequency rainfall, discharge and sediment concentration measurements at the outlet of a set of 10 tile drained plots (34 ha) and at the medium-sized (120 km2) catchment scale. Over the monitoring period, including a dry and a wet year compared to average conditions (one year with 112% of the mean annual rainfall and one year with 64% of the mean annual rainfall), 36 rainfall-flood events were recorded and analyzed. The high frequency analysis of water and sediment transfers in tile-drained plots showed a high seasonal variability and the occurrence of two transfer pathways in the soil column including the slow drainage of saturated soils and the occurrence of preferential flow pathways through the soil column. Indeed, 13 of the 36 recorded flood events showed hydrographs with two components, reflecting these two pathways: slow transfers in the soil columns and fast transfers through soil macropores and/or cracks. Indeed, at the beginning of the flood event, a high-magnitude peak overlaid on the hydrograph. On average, this fast peak contributed 15% of the water and sediment fluxes. The sediment dynamics in tile drains was suggested to depend on sediment storage and exhaustion processes occurring in the tile drain network. [ABSTRACT FROM AUTHOR]