Anita Veihe

The spatial variability of erodibility and its relation to soil types: a study from northern Ghana

In many parts of Africa, where regional mapping of soil erosion risk or related land-use planning exercises take place, existing soil maps are the only sources of information available when estimating erodibility. The current study examines the spatial variability of erodibility and the extent to which it is related to soil types based on a case study from northern Ghana. Soil samples from 136 test sites were analysed to determine erodibility parameters and surface characteristics were described in the field. Through ANOVA analysis, the intraclass correlations and within-class variations related to soil types were examined which showed an overall poor relationship. The fraction of sand was found to be the best indicator of erodibility due to its low spatial heterogeneity and determined the friability of water-stable aggregates. Further studies investigating the uncertainty associated with the use of soil maps in erosion studies should be carried out with the aim of producing soil maps with statistical information relevant for land resource studies.

The Power of Models in Planning: The Case of DaisyGIS and Nitrate Leaching

Abstract Spatial deterministic simulation models such as DaisyGIS are increasingly being used for decision‐making in European planning. In Denmark specifically, there is an increasing interest at the regional level to use DaisyGIS as an administrative tool. There are, however, uncertainties associated with the use of these deterministic models, partly due to the spatial variation in input parametres. This study evaluates the use of DaisyGIS for nitrate leaching assessments based on nitrate leaching experiments carried out at the Marbjerg experimental site at Roskilde University. The study includes geostatistical analysis of soil and hydraulic variables and the use of remote sensing for deriving spatial information about the Leaf Area Index. It is found that the model predicts nitrate leaching well when using site‐specific input data but it is quite sensitive to the parameterization of carbon, the C/N ratio and variations in the Leaf Area Index (LAI). With the increasing use of Daisy in the counties, there is a need to find better ways of handling uncertainties in model output which can be used by decision‐makers and to study further the impact of spatial LAI assimilation on catchment scale nitrate leaching processes.

Pedogenesis and Root Development in a Complex Geomorphologic Setting of the Faroe Islands

Abstract Studies of pedogenesis in basaltic soils within the cool, temperate zone were fairly limited. This study looked at pedogenesis and root development in Norðradalur of the Faroe Islands. To a large extent, soil physical and chemical characteristics were determined by sedimentological rather than pedological processes. Wind erosion plays an important role, and in spite of the homogeneity of the parent material, soil pedogenesis is highly varied. Soils were high in cation exchange capacity (CEC) and generally have a low base saturation, and the major soil‐forming processes were strong weathering, intensive leaching, gleying, and humification. Decomposition of the organic material was good overall. Nitrogen content was low to medium in the mineralogic horizons but high in the peaty horizons. Total phosphorus was within the range typical of soils with a high organic fraction, and previous theories explaining the low carrying capacity regarding grazing as a result of a low nutrient content do not seem to apply. Root densities were as expected for grazing areas, but there was a huge variation in the root diameters as a consequence of microclimatic differences and associated differences in vegetation.

Sensitivity of DaisyGIS to LAI: Implications for land use based modelling of nitrate leaching

Abstract Geografisk Tidsskrift, Danish Journal of Geography 106(2): 75–85, 2006 Scaling is an important issue when measuring, modelling and understanding coupled socio-environmental terrestrial systems. Scaling may be enhanced through the incorporation of remotely sensed data. This paper assesses the sensitivity of DaisyGIS to changes in the Leaf Area Index (LAI) and discusses the implications for land use based modelling of nitrate leaching using remote sensing based LAI estimates. It is shown how DaisyGIS simulates nitrate leaching quite well over the period 2001 to 2004 except for one plot during a season with winter rape. It was found that the model is sensitive to changes in LAI with increases of up to 262% on nitrate leaching rates when reducing LAI by 15%. At the same time, the nitrate leaching rates at the field level vary considerably due to local changes in the water balance determined by soil profile characteristics. DaisyGIS is already an important tool for aiding decision makers and this study has shown how remote sensing based LAI estimates may be a valuable tool for model parameterisation and potentially for model validation.

Classification of debris flow phenomena in the Faroe Islands

Landslides and debris flow phenomena in particular constitute a threat to human activities in the Faroe Islands. As a contribution to ongoing landslide risk management research, this paper proposes a classification scheme for debris flow phenomena in the Faroe Islands. The scheme, produced through a multidisciplinary study involving geomorphological fieldwork and qualitative collection of indigenous landslide knowledge, presents physical characteristics to classify debris flow phenomena into groups named with Faroese terms. The following landslide definitions are proposed. Brekku-skriðulop (English translation: hillslope debris flow): a very rapid to extremely rapid non-channelised downslope movement of remoulded colluvium and eventually fragmented rock, initiated as a debris slide in colluvial soil (type 1) or from rock fall (type 2). Áar-skriðulop (English translation: channelised debris flow): a very rapid to extremely rapid channelised downslope movement of remoulded colluvium and/or talus/fluvial material and eventually fragmented rock, initiated as a debris slide in colluvial soil (type 1), from rock fall (type 2) or from mobilisation of talus/fluvial material (type 3). The scheme, which is compatible with international landslide classification systems, significantly increases the knowledge of debris flow phenomena and promotes a consistent terminology of these within the Faroe Islands.

Young dry grassland ecosystems in Denmark: development in soil nutrient pools and root characteristics

Abstract Dry grassland ecosystems are listed habitats in the EU Habitats Directive due to their high biodiversity. Such areas have declined drastically over the last 200 years but set-aside of agricultural areas in recent years has increased the extent of grassland areas with secondary succession. This paper explores the soil nutrient pools of 14 young dry grasslands and compares them to the nutrient pools on heathlands, forested and agricultural land. On two sites, the plant species composition is compared to characteristic species for the EU Habitats Directive in Denmark and the relationship between soil nutrient pools and underground biomass development is investigated. It was found that soil nutrient content was lower as compared to agricultural land but generally higher as compared to forested areas and heathland. The organic matter on the grassland sites after they have been laid fallow is becoming less decomposed and this indicates that an O horizon will eventually develop and hence provide an important nutrient pool as a replacement for the decline in nutrient content in the subsoil. Root density was high in this study and soil nutrient content appeared to be an important parameter determining root development.