The erosional response of calcareous soils along a climatological gradient in Southeast Spain

doi:10.1016/S0169-555X(97)00097-4

Geomorphology

Volume 24, Issue 1, July 1998, Pages 3-16

https://doi.org/10.1016/S0169-555X(97)00097-4 Get rights and content

Abstract

The erosional response of calcareous soils along a climatological gradient in Alicante, SE Spain was studied. The erosional response was defined in terms of indicators obtained from field rainfall simulation experiments and laboratory studies of soil aggregation. Measurements were made at seven sites on limestones and marls between Benidorm with an annual average rainfall of 400 mm yr⁻¹ and Coll de Rates (annual rainfall 900 mm yr⁻¹). The sites were on matorral vegetation affected to varying intensities by grazing and fire. At the seven locations, soil aggregation was studied by sieving, by the single water drop test and by a Microscan particle-sizer. Rainfall simulation experiments were made on circular 55-cm diameter target area plots using the Calvo simulator at an intensities between 35 and 59 mm h⁻¹. On limestone, it was found that on bare surfaces, the coarse soil aggregation increases with depth at the highest sites and decreases at the lower sites. The Benidorm surface soil has the highest erodibility. The least stable soils are at the lower intermediate sites. On marls, the aggregate stability is generally high in contrast to those under cultivation. Simulated runoff from the wetter limestone sites is very low. The driest areas have the highest runoff and sediment yields. Trends with climate suggest that the erosional responses of the soils indeed increase with aridity and temperature but local factors have a large effect, particularly at intermediate altitudes. A clear relationship like that found in Israel by Lavee on a similar lithology does not exist.

Introduction

Relationships between climatic conditions and geo-ecological processes are central to understanding the nature of past and future environmental change. Such relationships are of both scientific and practical interest. Available information concerning the impact of projected climate change on soil erosion and ecosystem degradation enables only simplified generalisations to be made. One reason for this is the lack of field data with respect to the influence of climate on a number of critical processes of land degradation. Such information is needed to calibrate and validate models that predict the geomorphological impact of climate change.

In order to analyse relationships between climate and ecosystem behaviour, an analysis of geo-ecological processes along climatological gradients has been applied at several locations in the Mediterranean basin. In many parts of the Mediterranean, sharp climatic gradients on rather uniform geological parent materials are quite common. The objective of this paper is to present the results from one such study along a climatological gradient in SE Spain between Benidorm and the Coll de Rates, where the annual precipitation increases from about 300 to above 950 mm over a distance of approximately 30 km (Fig. 1).

Rainfall simulation experiments and studies of soil characteristics are used to determine the erosional response of the soil. Measurements are obtained of runoff and soil loss, and basic information acquired about the infiltration characteristics of the site and the erodibility of the soil. Soil samples to study soil aggregation and obtain erodibility parameters were collected.

In the Eastern Mediterranean, Lavee et al. (1991)found a clear relationship between climate and almost all of the erosional response parameters that they measured. On south-facing slopes composed of chalk of the Menuha Formation (Cretaceous), infiltration rates increased with altitude and annual precipitation, while soil erosion and soil erodibility decreased. The authors reported, however, that different processes dominated the erosional response at different climatological positions and that the sites studied did not form a continuum.

Section snippets

Field site selection and criteria

When applying the climate gradient approach to isolate the effect of climate on geo-ecological processes, the factors such as time, parent material, land use and slope gradient need to be kept as uniform as possible. Few locations were found suitable due to large contrasts in parent material and land-use. The coastal area, stretching from Benidorm to Coll de Rates in the Mediterranean crosses one of the most marked climatic gradients in Spain (Fig. 1). In this area there are two contrasting

Soil aggregation characteristics

Soil aggregation parameters were obtained in several ways. Soil samples were collected and sieved gently into different size fractions (>4.8 mm, 4–4.8 mm, 2–4 mm and <2 mm). Stones and soil aggregates were separated by hand. The 4–4.8-mm soil aggregates were used for the determination of aggregate stability by means of the water-drop test as described by Imeson and Vis (1984). This involved either measuring the amount of material eroded by 10 drops of 0.1 g impacting on each of the 10

Description of field sites

Basic plot characteristics of topography, climate, vegetation and cover can be found in Table 1. This section briefly describes the vegetation and soil conditions specific to each of the locations from high to low along the gradient.

Limestone sites

The aggregate size distributions plotted in Table 2 show that the proportion of aggregated material coarser than 4.8 mm increases with depth at the two wettest sites, is constant in depth at Callosa and decreases with depth at the driest sites at Finestrat and Benidorm. The amount of fine material <2 mm shows the opposite trend. For example, it is highest in the top 5 cm of soil at Rates and at the deepest sampled horizon at Benidorm. The very low amounts of fine material below the surface soil

Conclusion

It can be concluded that there is a trend along the climatological gradient whereby the erosional response of the soil increases with decreasing altitude. This relationship is, however, far less clear than reported on similar lithologies in Israel (Lavee et al., 1991). Parameter values found along the gradient seem to be much more variable than in Israel. This is thought to be due to the effects of fire, grazing or other disturbance. Also all of the sites studied had a high organic matter

Acknowledgements

We wish to thank all those who have contributed to the work reported in this paper in Amsterdam, Valencia and Bar-Ilan Universities. We gratefully acknowledge support from the UNEP (Mediterranean Action Plan) who supported an early phase of this research. Later work was supported under Project EV 012 of the Europe Environment Programme. A. Cerdà's work leading to this paper was supported by a Conselleria d'Educació i Ciencia grant and the Ministerio de Educación y Ciencia fellowship of

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