Reflections on water

Chapter 6 of Farming with the Environment covers the aquatic side of things. Some of it is about how nutrients behave in water and how aquatic invertebrate communities are affected by them. But the fact is that what goes on in water is influenced massively by the management of the land draining into it.

Our research over the years has improved our understanding of sediment movement to and within water, and the strong association with phosphorus in particular. We have shown how invertebrate species diversity is negatively affected by phosphorus concentrations and how the fine particles associated with our clay soils are held in suspension and provide the main mechanism for phosphorus transport from agricultural land to water. Chapter 3 of the book covers this from a soil management perspective. We discovered that, on our clay soils, sediment traps were not effective at reducing movement of sediment to water, but some of the soil management practices described in Chapter 3 can help to do so.

The other important source of phosphorus in water is us. Sewage treatment works are the major source of phosphorus in summer and early autumn when the ecological impact is greatest, even if the overall annual load is greatest from agricultural land. Domestic sources of P have the greatest impact on aquatic wildlife, but losses from farmland represent the greatest loss of nutrients from the system. We need to address both sources to protect both wildlife and finite nutrient resources.

We have shown that, for aquatic wildlife, it is also possible to ‘escape’ catchment scale nutrient enrichment by creating small clean water ponds in micro-catchments which are not affected by domestic or agricultural sources of nutrients. This is particularly relevant as ponds are inherently more species-rich than other forms of water body.

We have also shown that the installation of simple permeable timber dams in headwaters can reduce downstream flood risk. This is a relatively simple measure which complements traditional engineered flood risk management downstream, although as our results also show, there is a limit to which we can protect ourselves from the impact of climate change. What we can do about climate change is discussed in Chapter 9.