88 | North America and Europe (NAE) Report

farming systems, assisted by increasing mechanization, has led to reductions in non-grass biodiversity in pastures and meadows (Johnson and Hope, 2005).
     Intensive, industrial production systems have evolved from the less intensive mixed farming systems in response to increased demand for meat, resulting in animal concen­trations that are greater than the waste absorptive and feed supply capacity of nearby available land and which can cause major pollution problems and human health risks. Indoor production systems are now predominant for pigs, poultry and veal cattle. These agricultural systems have be­come increasingly controversial because of the amount of waste produced, odor problems, the potential for surface and groundwater contamination and animal welfare con­cerns. In intensive livestock farming areas excessive loss of nutrients and farm effluents in surface runoff and/or leach­ing, are the principal causes of degradation of water quality (Hooda et al., 2000; Tamminga, 2003). Environmental effects of manures produced by animal production
Awareness of the environmental impacts of some animal production systems, especially in relation to phosphorus and nitrogen pollution of water and the presence of anti­biotics, pesticides and micro-organisms in manures, has re­sulted in the development of more sustainable management practices. Increased mechanization has enhanced efficiency of management of animal waste, resulting in reduced poten­tial for negative affects on the environment, but the use of mechanization to increase intensity of production can coun­teract these benefits, by producing much greater quantities. In some European countries changes in management have been supported by legislation restricting the way manures are processed. An evaluation in 2003 of the Danish Na­tional Action Plan for the Aquatic Environment showed that nitrogen leaching (primarily from intensive pig farms) had declined by 50% since 1989 (Grant et al., 2006). A range of measures have also been introduced in The Netherlands, including a manure phosphorus quota which has been al­located to every farm, limiting the amount of P that can be applied to the land (Kuipers and Mandersloot, 1999). In the UK a range of management options have been intro­duced to encourage reductions in water pollution from live­stock farms (Hooda et al., 2000). Further legislation on the impact of nutrients on water is included in the EU's Water Framework Directive (http//ec.europa.eu), currently being promulgated across Europe. All countries in the NAE are endeavoring to reduce the effects of animal manures on the wider environment. A range of new technologies are also being developed and adopted, especially in the USA, to min­imize the environmental impact of animal production, such as optimized feeding strategies and the identification of feed additives that could improve the efficiency of utilization forages and crop residues, while reducing methane emis­sion (Makker and Viljoen, 2006). However, manure from industrial livestock systems and its impact on water systems remains a significant concern in some areas of NAE. Animal husbandry and methane
Husbandry of ruminant animals is the major source of in­creased agricultural emissions of CH4 (including lagoon-


ing and management of waste) (Prather et al., 2001). It is estimated that ruminant livestock production (including cattle and sheep) accounts for 90% of agricultural methane because of their unique digestive system allowing them to digest coarse plant material. The most recent UK estimates are that 80% of emissions are from enteric fermentation and 20% from animal waste (Anon, 2006). Beef and dairy cattle combined account for over 90% of the CH4 enteric emissions in the USA (Table 3-3). In the UK cattle alone account for 75% of these enteric emissions. Manipulation of the diet in these concentrated animal feeding operations (CAFO's) is one of the major methods available to manage these emissions (MAFF, 2000).
     Whereas methane can be collected from manure, the methane can be used as an energy source to generate heat and electricity (e.g., Williams and Gould-Wells, 2004). Extrac­tion energy from the conversion of methane to CO2 reduces the greenhouse effect, as CO2 is not as strong a greenhouse gas as is methane. Such manure management also reduces potential for runoff pollution from manure wastes and may also reduce odor problems. Environmental consequences of the use of veterinary medicines
Animal husbandry in industrialized systems often requires the use drugs to keep animals healthy or stimulate growth. Residues of such pharmaceuticals are excreted and may es­cape through runoff to be dispersed in the environment. Of particular concern is the routine use of antibiotics for growth promotion or prophylaxis rather than disease control. It is a near certainty that microbes will develop a tolerance if given steady exposure to low levels of antibiotics, eventually rendering the antibiotics ineffective for treatment of disease (Cohen and Tauxe, 1986). Administered hormones may be excreted by livestock, especially those held in dense popula­tions and can affect other organisms at very low concentra­tions. Estrogenic compounds may affect growth, behavior and sexual development and hence breeding ability. Prac­tices that control agricultural runoff, such as buffer zones and wetlands, are effective in retaining and degrading ag­ricultural pharmaceuticals to prevent release into the wider environment (Lorenzen et al., 2005; Shappell et al., 2007).
     Current FAO studies of the influence of livestock devel­opment practices on the natural resource base will provide information to predict and prevent possible negative affects of intensified production and enhance positive ones. These livestock studies involve feed quality, use of biomass for ani­mal fodder, avoidance of overgrazing, manure management, animal waste disposal, domestic animal genetic diversity, plant and animal wildlife diversity and integration of crop­ping and livestock systems (FAO/IAEA, 2006).

3.1.3 Environmental impacts of a larger aquaculture sector
The different types of aquaculture have very different po­tentials for impacts on the environment and it is useful to divide aquaculture into three major categories in order to address their risks.
     Substantial increases in the production of caged aqua­culture in open ecosystems (e.g., salmon culture in coastal ecosystems or tilapia in caged cultures in parts of fresh wa-