Hydroerosion in foothills of the coastal plain of cozoaltepec, oaxaca, Mexico

Since the last century, edaphic disruption by techno genic activities has been constant. The FAO,1 indicates that 33% of the planet’s soils are moderately to highly degraded by erosion, salinization, acidification, compacting and chemical contamination. Water erosion alone, has removed approximately between 25,000 and 40,000 million of Mg from the arable layer of farming soils, which are transported into the oceans.2 This is a limiting factor for production of agricultural crops, given the world food demand. Soil degradation inevitably leads to famine, poverty, migration, and the destruction of ecosystems, mainly in developing countries.3 Forecasts in this matter are hardly encouraging. Should this continue, by the year 2050 an approximate surface of 1.5 million hectares of agricultural lands will be lost. The destruction and loss of soils are a result of population growth, urbanization, and climate change, which act with a negative synergy in food production and the conservation of biodiversity. Water erosion is the removal of soil caused by runoff water, generally from the higher to the lower areas of a basin. Natural erosion occurs with the flow of rivers, streams and runoffs caused by rainfall, which has modelled the reliefs of the Earth’s surface with the passage of geological time. On the other hand, erosion induced by human activity is due to deforestation, the clearing of lands for agriculture, soil compacting, mining, and urban settlements. In all cases the loss of vegetation cover and deforestation leaves the soil naked and at the mercy of hydrodynamic processes which produce the migration of their particles in the runoff water. This removal affects both the areas from which the substrate is removed and those that receive the deposit of sediments.4 More than 75% of the surface of the Mexican territory is vulnerable to water erosion; the uneven relief, the weather, the destruction of vegetation, and the increasing population are all factors that contribute to this. The erosion process progresses faster than the technology necessary to control it. It is estimated an average of 365 million Mg of productive soil are lost every year, out of which 31% remains in the superficial bodies of water, and the remaining 69% is discharged into the ocean.5 In the state of Oaxaca, the erosive phenomenon is explained by deforestation, which affects 30% of the total surfaces of forests and jungles, which have been removed to give way to agricultural and livestock farming activities. The naked surface, steep slopes, and intense rains are factors that induce the removal of a large amount of sediments that migrate from higher lands, and in their descent, deposit sediments in rivers and roads, and cause accidents due to landslides in meso and bas relief areas. In coastal areas, they accumulate or discharge into the ocean.6 The coastal plain of Oaxaca is not exempt to this problem, since it shows signs of erosion, sedimentation, and salinization. For the specific case of the coastal valley near the Cozoaltepec River, there is no knowledge on the scale of the current erosion caused by water, or of the amounts of the sediments deposited in low flatlands. The aim of this investigation was to quantify the mass of soil lost during a rainfall in an agricultural plot in “Barra del Potrero”, Cozoaltepec, Oaxaca, using a runoff plot and its comparison with the universal soil loss equation. This will help evaluate the impact of deforestation on runoff and the amount of sediments removed from the experimental plot to the coastal plain. The results will allow to propose alternatives of sustainable management of the soils to revert the erosive process.