lands, or pastures can be used to process runoff from croplands adjacent to surface waters (Table 3-2). While it is known that adopting different farm practices can make substantial reductions in nutrient runoff, the challenge is in having sufficient numbers of farmers adopt the practices to make widespread improvements in the environment.
3.1.1.2 Environmental consequences of pesticides and other agricultural chemical use
Pesticides are chemicals that target pests, weeds, or disease organisms and include veterinary products (see 3.1.2). Their potential toxic or other adverse effects on farm workers, persons handling pesticide containers, members of the public exposed to spray drift near farms and the issues of residues in food and drinking water are important topics, but are not addressed here. While pesticides are intended to control organisms that adversely affect crop and animal production, they can also affect non-target organisms, including beneficial ones (e.g., Somerville and Walker, 1990). For example, certain insecticides are toxic to honeybees and other pollinators of cultivated and wild plants and so their usage can result in both environmental and economic losses. Insecticide and herbicide run-off from farmers' fields may have direct toxic effects on aquatic organisms. Low-level exposure to pesticides through the food chain may affect certain organisms (Hinga et al., 2006). The case of the chlorinated, persistent pesticide DDT being concentrated in predatory birds and leading to reproductive failure is well known. Research is revealing other unpredicted effects from low-dose exposure. For example, the herbicide atrazine has been shown to feminize amphibians, with implications for reproduction in other species (Hayes et al., 2002, 2006). Endocrine disrupting and chronic effects of pesticides have been traced in mammals (Choi et al., 2004). The potential for effects that are not easy to predict or to identify is a continuing concern. Pesticides may change the availability of food sources for higher level organisms. For example, the control of insect pests can reduce insect prey populations, which in turn limits the size of a bird population feeding on the insect. Similarly, herbicides may change habitats or limit plants that are the foundation for specific food chains. Specific research projects have demonstrated that herbicide, insecticide and fungicide use has decreased the breeding success of several |
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farmland bird species, including grey partridge and yellow-hammer (Rands, 1986; Boatman et al., 2004; Hart et al., 2006). The unwanted effects of pesticides can be mitigated in a number of ways, including decreasing the intrinsic toxicity of the pesticides themselves. Modern pesticides are generally more environmentally benign than the older products that they have replaced. Good farming practices can also reduce unwanted exposures to pesticides. These practices include adoption of Integrated Pest Management (Kogan, 1998); treating pests when needed rather than as a preventive measure; timing spraying to avoid winds and rain; using appropriate and well-maintained machinery; training operators to reduce poor spray practices and disposing safely of waste. Use of biological controls agents, biopesticides and integrated pest management techniques, such as traps with chemical lures, may reduce pest damage sufficiently to avoid general treatment of the whole field, greatly reducing the amount of pesticide used.
3.1.1.3. Environmental consequences of increased field drainage
The land in many parts of NAE, especially the US and western Europe, has been drained with sub-surface tile drains or ditches, to allow lands that were wetlands (with standing water), or were frequently wet enough to preclude tillage, to provide suitable conditions for successful crop growth. However, artificial drainage also facilitates the transport of sediments (especially in the ditches), nutrients and pesticides from agricultural fields. Drainage also affects the hydrology of watersheds as the creation of drains and ditches results in less local water retention and increasing peak flows leading to increased risk of downstream flooding. In removing wetlands, where water may be retained, there is a loss of function of the wetland to act as a site of nutrient removal (see 3.1.1.1) and the degradation of agricultural chemicals. In the UK, over 300,000 ha of wet grassland were lost between 1970 and 1985 (Bradbury and Kirby, 2006). In the US, the conversion of wetlands, primarily for agricultural use, has resulted in the loss of approximately half of the original inventory. In recent decades US conservation policies have acted to reduce agricultural wetland loss and the total amount of wetlands on agricultural lands in the US has increased since the early 1990s (Wiebe and Gollehon, 2006). There are a number of practices which help mitigate the undesirable loss of sediment, nutrients and pesticides. Con- |