standard Accumulation of small events creates a large environmental hazard: the case of diffuse pollution

Many environmental hazards are visually impressive including floods, landslides and volcanic eruptions. All of them have a wow factor in that they grab news headlines. However, other environmental hazards can pose a significant problem, but originate from the accumulation of many small events spread out over a huge landscape. These small events would not be a big problem if water didn’t move across the landscape concentrating the material into streams, rivers and lakes. Diffuse pollution (or non-point source pollution) is one of the widely distributed problems that is having a significant impact on the water quality of rivers and lakes, and leads to significant environmental hazard.

Excessive algae growing in the river as a result of an oversupply of nutrient. This algae causes ecological problems in the river. As the algae decompose it uses oxygen and the low oxygen levels in the water can kill fish.

Poor water quality causes deterioration in the health of rivers and lakes, reducing the ability of these waterbodies to provide water supply for consumption, food sources such as fish and impacts on the use of the waterways for cultural activities such as fishing and walking. The need to maintain and improve the ecological health of rivers and lakes has been recognised at both the national and EU levels and is enshrined within the EU Water Framework Directive. However, in 2012 in England only 28% of water bodies meet their ecological potential or good status and 67% of river water bodies cite phosphorus from diffuse pollution as a key pressure, which is preventing improvement of these waterbodies to achieve good ecological status (Figures from the EA).

Diffuse pollution can be defined as the contribution of many small, distributed pollutants (such as fine sediment, nitrogen, phosphorus, fecal indicator organisms and pesticides) from across the landscape which then enter lakes or river channels. The spatial pattern of contributions of polluting material from across the landscape are non-uniform and they also vary across the year and in response to storm events. This distributed and episodic characteristic of the problem means that it is difficult to assess where the sources of the problem originate. This physical complexity is coupled with the socioeconomic landscape of farm businesses producing food in challenging economic times. Therefore, it is important to understand that processes and hence mitigation measures can be targeted where they will be most effective and limit the impact on agricultural production.

Livestock in the landscape are a potential source of diffuse pollution. This pollution may be in the form of FIO or fine sediment.

The research framework that is often used to describe the diffuse pollution breaks the problem down into four components: Source, Mobilisation, Pathway and Impact:

Source: relates to the amount if nutrient or other pollutant that is stored in the landscape. This source may be from the application of fertiliser to agricultural land or the number of livestock in a field producing FIOs.

Mobilisation: relates to the material being detached from the land surface and is made available for transport. The erosion of soil by rainfall or the solution of nutrients from fertiliser are two key processes of mobilisation.

Pathways: are the different routes along which the material can travel. Different pollutants travel along different pathways, e.g. nitrates travel dissolved in the water and hence can travel through the soil whereas fine sediment will travel solely across the landscapes surface.

Impact: Once the material reaches the water body, it can have a range of impacts on the water quality, ecology and environment. The impact depends on the pollutant, for example:

  • Fine Sediment: Smothers salmon eggs, starves them of oxygen and leads to the eggs dying.
  • Nutrients (N and P): High nutrient levels can lead to eutrophication which reduces the oxygen levels in the water and leads to fish kills
  • FIOs: Fecal indicator organisms show that fecal material from livestock has entered the water course. FIOs include e coli bacteria and pose a direct hazard to human health
  • Pesticides: They are used to kill unwanted pests, weeds and moulds, so if not used properly have the potential to harm human health, wildlife and the environment, including direct impacts on the macro-invertebrates and fish within the water body.

IHRR researchers at Durham University have been investigating these problems, that cause water quality to be an environmental hazard, through the EdenDTC, NERC EVOp and SCIMAP projects. Each of these projects is tackling a different part of the problem from field monitoring (EdenDTC) to spatial modelling (SCIMAP and EVOp). The EdenDTC project is monitoring three river catchments in Cumbria using near continuous water chemistry measurements. These measurements are made using a field laboratory installed next to the river channel with the data being published daily to the internet at the project website. Below is an example graph of the water chemistry response to a storm event. This water chemistry information is supported by ecological samples by Lancaster University and engagement with the local farmers through the Eden River Trust. The aim of the project is to gain better understanding of the processes leading to degraded water quality and to test mitigation approaches to reduce the impacts of agriculture on water quality. This work is supported through the use of tools such as SCIMAP and these will be discussed in part two next week.

This graph shows the response of the stream water chemistry to a storm event at the beginning of Aug 2012 at the Morland EdenDTC site. The blue line shows the river level rising and falling, the green line shows the phosphate responding in sync with the level river. The red line show the two parts of the nitrate response, the first part is in response to the water flowing over the surface and transporting the nitrate, the second 18 hours later, relates to the water moving through the slow pathways in the soil. The graph shows the chemistry being measured every 15 minutes resulting in 240 measurements for each line. This level of detail contrasts with the previous approaches to water chemistry monitoring where a site would be measure 10 times in a year.


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