Agriculture

Large populations need large food supplies and ultimately increasing populations will mean an increase in land devoted to agriculture. By the coast this land will often be watershed habitat. Agriculture is the greatest consumer of both ground and surface waters. Thus, agriculture can profoundly affect the hydrological cycles of the watersheds in which it is practised, and, consequently, the quantity and timing of available water resources. Physically, watershed ecosystems, such as saltmarsh or coastal forests, are drained and cleared to be used as agricultural land. This alters water flow through the region as a watershed usually acts like a sponge, retaining water that will now flow straight through the area. This change in flow effects the physical shape of waterways and the biology of communities in and around these waterways. Downstream and out to sea the effects of agriculture can also be felt. Increased flow over the newly cleared land (where vegetation used to slow the water passage) mean faster flowing rivers and more sedimentation; the effects of which can be devastating for marine ecosystems, such as coral reefs and seagrass meadows, that rely on clear, substrate-free water.

Photo courtesy of Topham, UNEP.

Chemically, water can be polluted by agricultural treatments. Pesticides, insecticides and fertilisers, if used in excess, can have dramatic effects on flora and fauna in surrounding waterbodies and in coastal ecosystems. Animal-based agriculture creates manure and pathogens that can potentially damage water quality too.

The loss of different habitats means a loss of biodiversity. Loss of habitat to agriculture accounts for the endangerment of a disproportionately high number of species as watersheds are naturally very biodiverse ecosystems. However, agriculture is conserving biodiversity in some respects as alternatives, urbanisation for example, would result in an even greater losses.

Adopting Good Agricultural Practices (GAPs) includes measures that reduce water pollution via run-off and seepage into groundwater supplies. Farmers need cost- effective measures to prevent soil loss and conserve moisture without excessive losses of crop area. Undisturbed riparian corridors are a particularly valuable asset towards the conservation of biodiversity around waterways.