Brian Morgan – How are our rivers being polluted – Nov 21

In my last blog I described how you can locate data about the levels of pollution in your local water bodies. Here in this blog, I am showing you how to access current information on local pollution.

So, let us look at the main types of pollution in those water bodies, at their sources and at the monitoring.

A major problem is unwanted over-growth in streams, a process called eutrophication. This is where some types of plant take over to form floating blankets of algae and cyanobacteria (single celled blue-green algae) which take the form of dense growth below the surface. These plants not only block the light necessary for photosynthesis in submerged plants but some of them, notably the blue-green cyanoalgae, also emit toxins which cause the death of fish and invertebrates.

The two main causes of eutrophicationeutrophic Water (freshwater or saline) is said to be eutrophic when all normal life in it has died due to oxygen starvation. The process is usually caused by excess nutrients present in the water which causes an explosion in algal species (known as an algal bloom). As this algal bloom dies the decaying plant material (algae) falls to the bed of the watercourse where it is consumed by bacteria. This abundance of decaying material in turn causes a population explosion in the bacteria. However, bacteria (unlike plants) consume oxygen and the population explosion of bacteria strips all the dissolved oxygen out of the water with the result that all other aquatic species who are reliant on the dissolved oxygen for breathing (e.g. fish, larvae, insects) are asphyxiated and die. When this process occurs, a body of water is said to eutrophic. A body of water that is partially eutrophic is where this process (oxygen starvation) has fallen short and/or not yet reached its fullest extent. are the powerful nutrient compounds of phosphorus and nitrogen which increase growth rates.

In the long term phosphorus and nitrogen compounds (largely in the form of phosphates and nitrates) can build up naturally in water bodies, especially in lakes. However nowadays these two compounds mostly come from agriculture and the ‘run-off’ from modern methods of fertilizing fields; and also from the use of sewage sludge waste — created by aeration treatment at sewage treatment works — which is applied as a fertilizer on fields; and additionally, from the direct discharges to rivers of poorly or untreated sewage.

The incidence of this form of pollution will be indicated in the Catchment Data Explorer described in the previous blog : How polluted is your river? How to find out and how to access the data.

Overall information on the behaviour of these chemicals in rivers, along with basic scientific data, is available at:

Defra-stats-observatory-indicators-da3-120224.pdf
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/162164/defra-stats-observatory-indicators-da3-120224.pdf

Indicators: Da1 Biological quality of rivers.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/160780/defra-stats-observatory-indicators-da1-120224.pdf

Indicators: Da2 Chemical quality of rivers.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/160781/defra-stats-observatory-indicators-da2-120224.pdf

Indicators: Da3 Nitrates and phosphates levels in rivers.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/162164/defra-stats-observatory-indicators-da3-120224.pdf

Indicators: Da4, Pesticides in water.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/162165/defra-stats-observatory-indicators-da4.-120224.pdf

Government guidance on the level of nitrate and phosphate in rivers is as follows: recommended level does not exceed 30mg of NO₃ per litre (legal limit of 50mg of NO₃ per litre) and phosphate recommended level should not exceed 0.1 mg per litre.

In 2000 39% of English rivers exceeded 30mg of NO₃ per litre, and in 2009 this figure was 29%. And in respect of phosphates, in 2000 62% of English rivers exceeded 0.1 mg per litre whilst in 2009 the figure was 50%.

The above are average figures for English rivers and there are considerable regional differences. To identify these, view: Indicators: Da3 Nitrates and phosphates levels in rivers, link above.

All the above Indicators show the regional differences that exist in pollution levels, and also indicate differences in the performance of regional water companies.

For the situation in Europe as a whole, see EEA Nutrients in Freshwater in Europe: Indicator Assessment. This gives good information on phosphates and nitrates in lakes and rivers in Europe, with concentrations and trends. After years of decline, some pollutants are increasing again. https://www.eea.europa.eu/data-and-maps/indicators/nutrients-in-freshwater/nutrients-in-freshwater-assessment-published-10

For your particular local catchment, the streams and rivers affected are shown in the Catchment Data Explorer, as explained in my blog 1 (October 2021). These identify continuous and spasmodic discharges, from Sewage Treatment Works, and from agricultural runoff.

Sewage Treatment in England

There are over 7,000 Sewage Treatment Works (STWs) in England. Each person produces about 150 litres of waste water per day, amounting to about 8 million tons per day, countrywide. Much of this ends up in inland waterways, on the way to the sea.

There are three main levels of sewage treatment: — Primary, Secondary and Tertiary, with one extra high level, UV, at less than 3% of STWs, but this is highly restricted, to shellfish areas, and a very few seaside resorts. Most treatment is Secondary, a level of treatment which still leaves much to be desired. If the Catchment Data Explorer indicates sewage discharges into your stream, then it will come from an STW or its pipework. They are subject to permissions to discharge, and this data is available, see: environment.data@gov.uk

To find out what is happening at your local sewage treatment works, first identify it by name, on the river or stream.

Mine is Blackburn Meadows. So, for example:

Google:

Blackburn Meadows STW, then go down the page and open the European Commission Page.

There you will find the total load by population, and the types of treatment given. Whether or not phosphorus or nitrogen are removed, whether it is subjected to oxygenation, chlorination, or sand or microfiltration, or UV treatment, whether different treatment parameters are met, etc. In most cases they are not.

Brian Morgan