Agriculture and Water Quality
Agriculture is one of the main sources of diffuse water pollution, this is pollution that cannot be pinpointed to one specific location. There are a range of pollutants that enter our river from agriculture including sediment, nitrates, phosphates, metaldehydes, pesticides and herbicides. All of these pollutants have varying effects on the biodiversity and health of the Thame, but there are also other factors to consider. More than ever, food production is very high priority and we therefore need to work on ways where we can work with farmers and landowners to ensure a more sensitive approach to farming where possible.
Nutrient Run Off
In order to get the highest yield, many farmers use fertilisers to enrich the soil. These fertilisers come in many varieties but all of them contain phosphates and nitrates. To save money, most farmers will calculate the exact amount of fertiliser needed by their crop, the idea being that this is then all used up and none of it is wasted. Unfortunately, in reality this rarely happens; rain is a big factor in this! If fertilisers are applied and then there is heavy rainfall, much of this fertiliser is leached from the soil and enters groundwater, ditches, streams, ponds and rivers. Over more recent years, sporadic weather conditions (potentially a factor of climate change) have made this issue even worse. As we already know, the Thame catchment is dominated by farmland, which means that this is a major problem for us.
Although we may not be able to time the rainfall, there are many ways that we can work to reduce the impact of fertiliser run-off. Buffer strips are sections of land, usually 5m in width, that are left between the crop land and the river; these strips of natural vegetation draw in the extra nutrients and help to prevent as much entering our rivers. Another technique that can be used is to plough at 90 degrees to the gradient of the land, this slows the run-off of water and allows more of the fertiliser to be retained. There are many other techniques that we can advise on and you can find out more about this here.
Alongside fertilisers, other chemicals are also used in order to improve crop yield. Using herbicides and pesticides to prevent competition and predation is common. These chemicals can have varied impacts on our river, but very harmful and persistent chemicals cannot be used in the UK currently.
One pesticide that is currently under the spot light is metaldehyde, a type of slug pellet. This compound is highly restricted in drinking water, which means that Thames Water must ensure that it does not exceed 1 microgram per litre. Unfortunately metaldehyde is very difficult to remove from drinking water and therefore Thames Water is working hard to reduce its use; you can find out more about this here.
Sediment from our agricultural land has detrimental impacts on our rivers, resulting in vital habitats being lost and smothered, some of the impacts of sediments can be found in our section on habitat loss.
Although sediments can come from recently ploughed crop land, much of the sediment comes from livestock farms. Where livestock are found in high densities, large muddy areas are common as the animals congregate, this encourages sediment run off. Riparian land used for grazing provides benefits to landowners as there is a constant water supply for their animals. Uncontrolled access to the river, by large numbers of animals, causes bank degradation, slumping and loss which all encourages sediments to enter the river. In smaller densities, livestock can actually have positive impacts as they encourage varying habitats and plant communities. Unfortunately this is relatively uncommon.
In some places, livestock do have controlled access to the river, but even this can have negative impacts. Our image shows a cattle drink area where large numbers of cattle must access in order to drink. This sort of problem can be fixed simply by providing a more solid substrate which does not encourage sediment mobilisation and smothering of nearby habitat.
Although it may seem that there is a simple solution to this problem, such as fencing the river, it is very important for us to consider long term impacts of our work. Fencing the whole of the river would cause further issues in the future as dense scrub and trees would be allowed to grow, therefore causing much of our river to become shaded. We will work with livestock farmers to provide cost effective solutions which will provide long term protection for our rivers, as well as ensuring business as usual for the farmers that we depend on.
You can find out a lot more about the impact of agriculture on water quality in this report. If you are a landowner or farmer then you can find advice here, we would also love to hear from you if you wish to work with us to make positive changes for wildlife.
We are always looking for volunteers to help us with our work, so why not get involved?