Because current production is based principally on agriculture, bioenergy tends to have similar environmental impacts, particularly on water resources. Agriculture accounts for more than 70% of total water used in most countries, so cultivating energy crops can put further pressure on scarce water resources.
Farmers may pump 250 billionlitres of underground water to raise the corn feedstock for an ethanol production facility. If managed poorly, energy crops can lower sub-surface water tables, as well as rivers and lakes, particularly if these crops are irrigated. To avoid this potential problem, particularly in countries with scarce water resources, crops need to be carefully matched to available water resources. Efficient irrigation and rainwater harvesting can help reduce negative impacts.
Considerable amounts of water are also required to convert bioenergy feedstocks into fuels. A 200 million-litre ethanol plant, for example, might use 600 million-litres of water to make fuel - more water than some small towns use in a developed country. Hence, the choice of the end product should be influenced also by the considerations on water availability, e.g. straight vegetable oil requiring less water than biodiesel.
Bioenergy can also improve water resources. For example, the roots of some energy crops can reduce rainwater run off, and the energy 'harvested' can be used to power pumps and purifying water.
As with all agriculture production, growing bioenergy feedstocks can degrade soil fertility if not managed sustainably, particularly tilled monoculture that can leach and acidify soils.
There are some plants, however, that may help to recover degraded land, or improve marginal lands by reducing wind and water erosion.
Some forms of bioenergy can help improve air quality during the use phase, depending on feedstocks and combustion methods. Just a 20% blend of biodiesel can reduce asthma causing particulate matter by 30% and acid-rain forming sulphur dioxide by virtually 100%.
However, during the production of some forms of bioenergy, air pollution can be increased. The burning of cane fields for harvesting and the burning of crop wastes, for example, can increase local air pollution.