In many of the previous posts, there is a lot that is mentioned regarding water pollution as a result of intensified agriculture. This post will be focussed on a possible solution that could minimise the risk of water pollution.
One approach to solving the water pollution problem is the creation of buffer zones between the polluting farms and receiving waters. A buffer zone refers to a permanently vegetated area of land which is roughly 5-100m in width, preferably placed adjacent to a watercourse. The buffer zone works by providing a biochemical and physical barrier between the pollution source and the receiving water body.
The working mechanism of the buffer zone is relatively simple. The buffer zone spreads and separates the incoming flow of pollutants, minimising its fluid velocity. This increases infiltration and subsequently reduces the water depth on the surface. Huge particles fall to the bottom as sediments while suspended particles get filtered through leaf litter and soil. The remaining pollutants get trapped in the soil of the buffer zone, which allows for decay and subsequent absorption by plant roots or adsorption onto soil particles. The removal of pollutants transported in particulate form varies according to the buffer zone’s capacity of reducing energy of the incoming flow to allow pollutant particle settling. On the contrary, the removal of pollutants transported in dissolved form depends on the ability of the buffer zone to stall the runoff long enough to facilitate the pollutants breaking down, for subsequent absorption by plants.
The effectiveness of a buffer zone is determined by a number of factors. We must consider its physical structure, the type of pollutants it must handle and the closeness of the buffer zone to the pollution source. As for agricultural catchments, they are usually located in areas of low slope where the uplands were already cleared without any buffer. Such runoff from the uplands gets channelled away in the upper catchment and could flow out of the catchment without passing through the buffer downstream. This results in a huge loss of nutrients, which in this case are pollutants, that ultimately enters water bodies and causes water pollution.
In order to ensure the effectiveness of buffering for agricultural catchments, the buffer zones should ideally extend along tributary streams, so that none of the polluting sources will be left out and allowed to channel away. Hence, all polluting sources have to pass through buffer zones to trap the pollutants, as represented in the figure below.
Ideal agricultural catchment buffer zone
Regarding the effectiveness of buffer zones towards pesticides in agriculture, it has shown commendable results. In a study conducted by Asmussen et al. (1997), it was reported that herbicide 2,4-D were reduced along a buffer zone by 77% and 69% in wet and dry conditions. In a similar study by Rohde et al. (1980), there was evidence of trifluralin loss of 96% and 86% in wet and dry conditions. The large reduction of pesticide loss can be attributed to water infiltration, sediment deposition and attachment on vegetative and organic matter.
References:
Muscutt, A., Harris, G., Bailey, S. and Davies, D., 1993. Buffer zones to improve water quality: a review of their potential use in UK agriculture. Agriculture, Ecosystems & Environment, 45(1-2), pp.59-77.
Norris, V., 1993. The use of buffer zones to protect water quality: A review. Water Resources Management, 7(4), pp.257-272.
