Changing land-use
The expansion of agriculture and pastoralism into natural lands, and the intensification of production, or changes in crop-species have become a major features of rural land-use in all areas, but particularly in developing regions. In many cases these changes can be linked to increases in the problems already discussed of toxin and nutrient pollution, and further problems of erosion. The conversion of forests, together with the draining of wetlands have led to very large-scale losses of standing biomass, which is a major contributor to global climate change.
Forest loss over the past 200 years has been exceptional, with perhaps half of the world's natural forests now removed. Quite apart from the impacts such losses may have to terrestrial ecosystems and biodiversity, in many areas this forest loss is leading to massive increases in sedimentation in rivers, which is deposited in coastal waters. The role of natural vegetation in mitigating flood- waters has also received considerable attention and there is good evidence that floods have become more devastating in some areas where vegetation cover is lower, and the soils and vegetation are less able soak up the rainfall from severe storms. This has led to increased pulses of freshwater into coastal waters following such events, and to occasional impacts on marine communities.