As well as the strong link between erosion and vegetation, a theme that has in the past been championed by John Thornes, it is also clear that erosion interacts with a much wider range of ecosystem services, and this session provides an opportunity to explore these links, building on previous successful EGU sessions on 'vegetation and erosion'. For example, erosion degrades the natural capital represented by the mineral soil, soil organic matter and soil nutrients, leading to reductions in crop productivity and the biodiversity of semi-natural vegetation. In turn, reductions in vegetation cover accentuate erosion, potentially leading to an irreversible decline in the soil resource, with associated increases in surface runoff and reduced recharge. Although the reduction of erosion to ‘tolerable levels’ may allow maintenance of soil organic matter, it provides no protection against the progressive stripping of shallow soils, at rates generally far in excess of replacement by weathering.

Soil erosion and ecology interact to determine how and where sediment is redistributed at pedon, plot, slope and watershed scales. Vegetation is widely recognized as one key factor controlling soil erosion. When vegetation is absent, or is removed by fire and/or for cultivation, erosion rates are generally significantly higher than in the undisturbed state. Vegetation is, however, only the most visible component of the ecological system that supports soil structure and soil nutrients. The earthworms, gophers and tree-throws that turn over the soil are all part of the bioturbation that aerates the near-surface soil, bringing minerals to the surface, increasing infiltration rates and sequestering carbon by burying organic matter. Sediment carried down the hillside and redeposited at the base, either by water or tillage erosion, also buries carbon. Conditions that permit or promote the breakdown of organic matter by fungi and soil organisms provide an essential foundation for further plant growth that in turn promotes soil conservation.

Although re-afforestation has been the most widespread measure used to control erosion, the last two decades have seen a wider appreciation of the interaction of the vegetation and erosion, showing for example how plant distribution is also modified by the erosion processes acting on slopes and watershed. Moreover the erosion processes are also relevant for the subsequent distribution of water and nutrients, for example determining the spatial distribution of seeds and their germination, often with a key role played by soil fauna. Thus, not only does ecology control erosion, but erosion also modifies the vegetation and the ecology. The interaction between vegetation and erosion is also a key issue on agricultural land where management can control the timing and pattern of vegetation cover and the resulting soil losses. This is because soil development is highly dependent on vegetation cover and type. Catch crops, wood and straw mulches, weeds and organic geotextiles are among the measures being used to control soil losses through modifying surface cover.

We welcome submissions that enhance our understanding of the functional relationships between erosion and ecology in both directions, together with field studies that provide insights into the processes and rates involved. Improved understanding of soil erosion is seen as one important facet of the need to move towards more sustainable management of land for both agriculture and a wider spectrum of ecosystem services.

During the EGU 2012 an special attention will be paid to the interaction of the biotic and abiotic world within the soil. Soil aggregation and soil aggregate stability are key to understand the soil processes and properties, which are the key factor for soil erosion.
Soil aggregation can be defined as any stable association of individual particles of the same or different nature, as a result of granulometric composition, soil biology and soil physic-chemical properties. Soil aggregates are the result of the organization of soil mineral and organic particles. Therefore, both the inorganic and organic soil components influence aggregate formation and stabilization. Aggregate stability refers to soil resistance in maintaining its own structure when it is subjected to external forces, particularly those resulting from moisture, impact of raindrops, or a particular dispersive process. Therefore, this property can be used as an indicator of soil structure and physical stability. In fact, it has been used as a parameter indicative of soil system perturbation, and potential erodibility since the 1940.
Biotic and abiotic factors determine the complexity of the study of soil structure. Soil aggregation can be therefore considered a parameter indicative of soil health. Moreover, aggregate stability is one of the main factors controlling topsoil hydrology, crust development and erodibility, and can be affected by different perturbation agents such as forest fires, and soil use and management practices. All of these things make this property as a very valuable parameter in soil science studies.
This session aims to provide the opportunity for broad international scientific exchange and cross-fertilisation between researchers concerned with soil aggregate stability. Contributions are therefore invited from all fundamental and applied aspects of aggregate stability, ranging from preliminary results from small studies to the final outcomes of large studies carried out by major research teams. Examples of methodologies, factors and related properties to include in future studies, human perturbation impacts on aggregate stability, or studies linking aggregate stability with other different scale levels; from small plots to catchments are examples of topic that will be very welcome to the session.