C. Kosmas

The effect of land use on runoff and soil erosion rates under Mediterranean conditions

Abstract The effect of land use and precipitation on annual runoff and sediment loss was investigated in eight different sites along the northern Mediterranean region and the Atlantic coastline located in Portugal, Spain, France, Italy and Greece. These sites represent a variety of landscapes and are under a number of land-uses representative of the Mediterranean region, such as agricultural land with rainfed cereals, vines, olives, eucalyptus plantation or natural vegetation (shrubland). It was found that land use can greatly affect runoff and soil erosion. The greatest rates of runoff and sediment loss were measured in hilly areas under vines (average sediment loss 142.8 t km −2 yr −1 ). Areas cultivated with wheat are sensitive to erosion, especially during winter, generating intermediate amounts of runoff and sediment loss (17.6 t km −2 yr −1 ) especially under rainfalls higher than 280 mm per year. Olives grown under semi-natural conditions, as for example with an understory of vegetation of annual plants greatly restrict soil loss to nil values (0.8 t km −2 yr −1 ). Erosion in shrublands increased with decreasing annual rainfall to values in the range 280–300 mm and then it decreased with decreasing rainfall (average sediment loss 6.7 t km −2 yr −1 ).

The effect of land use change on soils and vegetation over various lithological formations on Lesvos (Greece).

Abstract The effect of land use change, from arable to abandoned pasture, on soil properties and vegetation establishment was studied in hilly areas of the island of Lesvos. The main purpose of this study was to establish key indicators or land parameters that can be used for defining environmentally sensitive areas to desertification. 106 soil sites were selected in fields cultivated or non-cultivated for 40–45 years and measurements related to protection from land degradation after abandonment, such as fertility status (organic matter content, pH, cation exchange capacity (CEC), exchangeable potassium and sodium), water storage capacity (soil water retention characteristics, soil depth), erosion resistance (soil aggregate stability), and vegetation characteristics (plant species, extent of vegetation cover) were conducted. The selected sites were located on a variety of parent materials such as volcanic lava, pyroclastics, ignimbrite, schist-marble, and shale. The obtained data indicated that soil pH, and CEC were slightly affected after abandonment as compared to the cultivated soils. Levels of exchangeable sodium and potassium were higher in cultivated soils. Organic matter content and soil aggregate stability were greatly enhanced in most of the abandoned soils. Physical characteristics of the parent material greatly influenced the establishment of the natural vegetation. A critical minimum soil depth of 25–30 cm was measured. On more shallow soils, the associated natural perennial vegetation cover was rapidly reduced, under the prevailing climatic conditions of the study area. Reduction of vegetation cover was related to the parent material. Perennial vegetation was not supported at all on soils below a crucial depth, ranging from 4 to 10 cm, depending on the parent material. This study showed that soil depth is the most important parameter which has to be considered in planning land use change from arable to unmanaged pasture under the soil and climatic conditions of the study area.

The effect of land parameters on vegetation performance and degree of erosion under Mediterranean conditions

Important land parameters such as soil texture, soil depth, topography, parent material, and climatic conditions were studied in a semi-detailed soil survey conducted in the island of Lesvos, and were related to the vegetation performance and degree of erosion. Rainfall data indicated that . the island could be divided into two major climatic zones: a semi-arid western part and a dry . sub-humid eastern part . A 45% rainfall gradient has been recorded in the above two climatic zones. The great reduction in rainfall combined with the higher evapotranspiraton demands in the semi-arid zone has significantly affected vegetation performance and degree of erosion in the area. Due to the general lack of available water, the semi-arid part of the island is dominated by poor maquis vegetation, while olive trees, oak and pine forests prevail in the dry sub-humid part under similar topographical and geomorphological conditions. Vegetation cover increases with increas- ing rainfall and soil depth. Slope grade has a variable effect on soil erosion in the various climatic zones. Erosion is decreasing with increasing rainfall for the same slope classes. Severely eroded soils prevail in the semi-arid zone with slopes greater than 12%, while slightly to moderately eroded soils are found in the dry sub-humid zone under similar slope classes. The highest rates of land degradation have been measured in areas with soils formed on pyroclastic formations. Areas with soils formed on basic igneous rocks, shale and lava are well vegetated and protected from

The effects of tillage displaced soil on soil properties and wheat biomass

Tillage operations transport large amounts of soil from convex slopes and deposit on concavities in hilly cultivated areas. Field experiment was conducted to assess tillage induced soil displacement and its effects on soil properties and wheat (Triticum aestivum L.) biomass production. The study was done on 3.5 ha fertilized and wheat seeded hillslope (14‐21% slope) located 100 km north of Athens, Greece. Numbered aluminum cylinders (700), each 10 mm diameter by 10 mm height, were buried in soil as soil movement tracers (SMTs) to estimate soil displacement as a function of moldboard plowing with two depths in up-slope and down-slope directions. Furthermore, clay, organic matter, rock fragment content, phosphorus and 137 Cs were determined on 81 soil bulk cores to estimate soil redistribution rates along the study hillslope. Soil depth and soil water storage were measured in 81 soil sites and related to the wheat biomass production. The mean SMT displacement distance due to 25-cm plow depth on 21% slope was 42 cm for down-slope tillage and 16 cm for up-slope tillage. Comparable values were 31 cm for down-slope and 14 cm for up-slope tillage on 14% slope gradient. The SMT distance for both tillage directions on 21% slope was about 60% less for 18-cm plow depth compared with 25-cm plow depth. Shallow soil (depth 70 cm) was found on lower concavities where displaced soil was deposited. The spatial pattern of 137 Cs inventories suggests that tillage erosion is a major erosion process in the study area. The maximum leaf area index of wheat was 2.8 for convex slope and 3.6 for concave slope. Wheat biomass, ranging from 0.2 to 1.2 kg m ˇ2 , increased logarithmically with increased soil depth. Moldboard plowing displaced large amounts of soil from convex slope which changed soil properties to less favorable for wheat production. Application of the obtained empirical functions showed that under the existing climatic conditions and management practices, the unprofitably productive area will increase from 4.1 to 6.8% in a period of 7 years. # 2001 Elsevier Science B.V. All rights reserved.

SOIL EROSION AT THREE EXPERIMENTAL SITES IN THE MEDITERRANEAN

The results of erosion studies carried out at three representative sites in the European Mediterranean basin are discussed. The objectives of the study are to clarify the underlying processes affecting soil erosion and to quantify erosion and runoff in the framework of mitigation of land degradation. The study was carried out at three instrumented field stations using similar layouts and experimental set-ups and harmonized field procedures. Runoff and sediment yield from bounded plots were measured for different types of land use for longer periods. The runoff and sediment values were found to be relatively low, and showed average annual values between 2·0 and 8·9 1 m−2 for runoff, and between 20·2 and 28·1 g m−2 for sediment yield. The results show that the individual plot response on an event basis shows no relationship between runoff and sediment yield for two of the three sites. On an annual average basis a significant relationship is found between the runoff and sediment yield. Significant differences were observed between different types of land use, especially between semi-natural vegetation, burned and abandoned field cover types on the one hand, and agricultural fields on the other hand. The runoff and erosion values were lowest for the semi-natural fields. It was found that in non-cultivated fields the bounded plots might suffer from depletion of available sediment. It can be concluded that erosion figures are very low for the sites studied, and that the maintenance of semi-natural vegetation may help in the prevention of runoff generation and erosion. It can be concluded that the use of bounded plots may not be as ideal as might be expected from its wide application. In some cases open plots, especially under semi-natural land use, may produce much better results, especially when measuring over longer periods. Copyright

Land-use evolution and degradation in Lesvos (Greece): a historical approach

An analysis has been undertaken of the land-use evolution in the island of Lesvos for the last 5000 years, based on historical and archaeological documents and recent soil and vegetation survey data. A series of maps were compiled using historical documents for the period from 3300 bc to 1886 bc and vegetation field survey data for the period from 1886–1996. A soil survey (scale 1:50 000) was conducted in 1996 in order to relate the land-use changes to the present physical environment. Cultivation of the land started around 3300 bc and intensified during the 18th century bc. During the Roman period forests were already significantly reduced to satisfy the increasing demands for agricultural products, timber and heating. In the Byzantine period (4th–15th century), vineyards and pastures expanded, mainly by clearing the forests. Olive plantations increased during the 13th century, motivated by the allocation of subsidies. During the first centuries of the Ottoman period, there was a further expansion of olive groves and pastures by reducing forests, while vineyards declined. Great changes occurred in the last century in the geographical distribution and the total area occupied by the various types of land use. Olive groves significantly expanded and were redistributed covering more fertile and productive land on hilly areas by clearing mainly pine forests. Oak forests increased on previous pasture areas. Today, pasture is the main type of land use in hilly areas. These previously forested areas have been cleared without any accompanying measures against soil erosion. This highly degraded land with shallow and severely eroded soils is not able to sustain any profitable agricultural use or natural forest. However, areas cultivated with olives remained sustainable for more than seven centuries without being significantly degraded. Copyright

Cracking patterns, bypass flow and nitrate leaching in Greek irrigated soils

Abstract Bypass flow of water during irrigation by flooding, and associated leaching of nitrates, were investigated in sixty-three, 40 cm high undisturbed cores of nineteen calcareous alluvial Greek soils. Cracks conducting bypass water formed a network of polygons on the soil surface. The sizes of the polygons increased curvilinearly with clay content. Large polygons were associated with deeper cracking of the soil mass than the small polygons did. The size of the polygons decreased with depth in the profile. Upon irrigation cracks developed in dry soil were closed by swelling and by soil material falling from their walls. The closing was either complete or incomplete, the latter leaving a shallow U-shaped trace. Upon drying, cracks reformed along the U-shaped traces. Elsewhere, cracks developed at new places. The volume of bypass water showed a sharp initial decrease with time because of filling of the cracks and swelling, but remained significant even after 2 hours (the usual irrigation time) suggesting that a significant amount of the applied water may move to the subsoil without wetting the surface soil. Bypass flow showed a marked decrease with increasing initial soil moisture. The amounts of nitrate leached by bypass water were rather small, ranging from 0.01 to 1.8% of nitrates present in the soil cores.

Estimation of the draining soil moisture characteristic from standard data as recorded in routine soil surveys

Abstract An analytical expression describing the moisture retention characteristic was tested using multiple regression on 105 horizons in 34 representative soils from Greece, with textures from loamy sand to heavy clay. All samples were analyzed for particle size distribution, organic carbon content, carbonates content and dry bulk density. It was found that soil moisture retention by the studied soils can satisfactorily be described using a logarithmic model that incorporates simple soil properties such as saturation moisture content, clay and silt contents, and bulk density. The applicability of a simplified model (with saturation moisture content and clay content as the only soil parameters) to small watersheds and considering groups of soil horizons was apparent from the improved coefficients of determination. Homogeneity tests showed, however, that only 2 major groups of soil horizons could be distinguished, namely well-structured horizons and structureless to weakly structured horizons. Incorporating other soil properties in the regression analyses of these soil horizon groups produced only a slightly higher R 2 -value.

The effect of rock fragments on wheat biomass production under highly variable moisture conditions in Mediterranean environments

Abstract The effects of soil properties that affect water availabilty to plants such as soil depth, rock fragments, parent material and degree of erosion on biomass production of rainfed wheat were studied on hilly soils under different weather conditions. Total above ground biomass production (TAGBP) of wheat was measured along catenas of marl and shale-sandstone formations in two successive growing periods. During the first growing period which was extremely dry (total amount of rainfall R = 95 mm versus 370 mm in an average year), the soils on marl, free of rock fragments, produced an average TAGBP of 1100 kg ha−1 despite their great soil depth, whereas on shoulders and footslopes of the stony soils on shale-sandstone formations TAGBP values of 4620 and 11,100 kg ha−1 were measured, respectively. The opposite occurred the following growing period which was exceptionally wet (R = 663 mm). Soils on marls were more productive due to the higher fertility status than the soils on shale-sandstone formations. Rock fragments, more responsible for the lower exploitable soil volume and the generally lower biomass production under wet climatic conditions, play an important role on soil water conservation under dry climatic conditions.

An evaluation of the pesera soil erosion model and its application to a case study in Zakynthos, Greece

The Pan-European Soil Erosion Risk Assessment (PESERA) model was evaluated using existing soil erosion data collected under various types of climate, vegetation, landscape and soil conditions. The data used represent a variety of typical Mediterranean land uses such as winter wheat, vines, olives and bare, stony land prevailing in hilly areas. Using this data, the model was calibrated for sediment transport by overland flow and results compared to measured soil erosion values from runoff plots and a watershed on a monthly basis. The performance of the model was assessed statistically, showing that it can be satisfactorily used for predicting soil erosion rates under the conditions included in the study. The overall model estimate including all the available experimental data was 0.69 t ha -1 yr -1 with a maximum error of 1.49 t ha -1 yr -1 . After validation, the model was applied to a small watershed (60 ha) of great ecological importance for the sea turtle Caretta caretta. For this purpose, soil and vegetation maps were compiled from all the necessary data for applying the model. The model was run for three years using daily data from an existing nearby meteorological station. The predicted and measured soil erosion rates for a 7-month period were 0.31 t and 0.18t, respectively. Application of the model to each mapping unit showed the over-riding importance of land use for sediment generation under the given climatic conditions. Bare land, occupying 5.5% of the watershed area, generated up to 69% of the total sediments estimated for the watershed. It is concluded that the PESERA model can be used as a regional diagnostic tool under a range of soil, topographic and climatic conditions for identifying the best land use type and vegetation cover to protect hilly areas from soil erosion. The calculated overall root mean square error for the model is 0.06 t ha -1 yr -1 , compared to a soil erosion rate of 0.04 t ha -1 yr -1 , which can be tolerated for protecting the area for the sea turtle.