Eutrophication is an increase in chemical nutrients -- compounds containing nitrogen or phosphorus -- in an ecosystem, and may occur on land or in water. However, the term is often used to mean the resultant increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.
The Sahel or Sahel Belt (from Arabic shore, border or coast of the Sahara) is a semi-arid tropical savanna ecoregion in Africa, which forms the transition between the Sahara to the north and the slightly less arid savanna belt to the south, known as the Sudan (not to be confused with the country of the same name).
Hachures are an older mode of representing relief. They show orientation of slope, and by their thickness and overall density they provide a general sense of steepness. Being non-numeric, they are less useful to a scientific survey than contours, but can successfully communicate quite specific shapes of terrain. They are a form of shading, although different from the one used in shaded maps.
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