The state of things, part 1

I found a very useful dataset online that gives a good overview of long-term trends in the condition of British rivers. This is the fruits of the Harmonised Monitoring Scheme (HMS), a programme that has ensured the collection of comparable data from locations all over Great Britain (but not, it seems, from Northern Ireland).   The earliest data are from 1980, before the formation of the National Rivers Authority (predecessor to the Environment Agency), when water quality monitoring was the responsibility of ten separate Regional Water Authorities in England and Wales, so collection of comparable data would have required an enormous amount of effort, and this dataset represents a major achievement.

I am going to divide my discussion about this dataset across two posts: the first dealing with the good news and the second considering some aspects where the regulators have made some progress but perhaps not enough.   I am also going to relate the results from the HMS to the current UK environmental standards for each variable, as these give us a snapshot of what ecologists regard as acceptable concentrations for each pollutant.   The precise value of each standard varies depending on the type of river under consideration and, to make life easier, I have used the most lenient of the values for any particular standard.

The first variable I looked at was Biochemical Oxygen Demand (BOD) which is a good indicator of the level of organic (i.e. sewage) pollution in a river.   This measures the amount of oxygen needed by the various bugs involved in breaking the organic matter down to its constituent parts.   As I live in north-east England, I thought that it would be interesting to compare the average values for Great Britain as a whole with the averages for this region. These statistics are, however, not especially illuminating: although there is a downward trend, all values are below the threshold required to support high ecological status.   In this case, the “average” is pulled down by the large number of streams in rural areas with low population densities.   The maximum values recorded in NE England are, on the other hand, very interesting. Note the way that values first increase (suggesting a gradual deterioration in water quality), then decrease. And note the point at which this change starts: it is in the late 1980s.   The significant date here is 1989, when the then Conservative government split the regulatory functions of the old Water Authorities away from their duties to treat sewage.   Previously, the Water Authorities were both “poacher” and “gamekeeper”; from 1989 the National Rivers Authority had no conflicting interests and the effect is visible on this graph. In 1995, the NRA became the Environment Agency, which continues to be responsible in England. The overall impression here is that even the most polluted streams in NE England generally have BOD levels that should be of little concern to ecologists.


Trends in average Biochemical Oxygen Demand (BOD) in Great Britain (closed circles) and north-east England (open circles) between 1980 and 2012. The open squares show the maximum values of BOD recorded in NE England during the same period and the horizontal lines show the current UK standards required to support different classes of ecological status.

If the bugs responsible for breaking down organic matter in our rivers are not using so much oxygen then there should, in theory, be more in our rivers for fish and other wildlife to use.   This is borne out by the evidence, though the trends are not as strong as for BOD. Note that in this case we are most interested in the minimum concentrations available. There are UK standards for dissolved oxygen but these are expressed as percent saturation, rather than concentrations, so we cannot compare the HMS data with these.   One reason for the weak trend shown here is that the Environment Agency takes monthly “spot” measurements in the rivers it monitors and several factors including time of day can also affect the amount of oxygen present.   A river that is visited in on a summer morning will have much lower concentrations of oxygen than one that is scheduled for a visit late in the afternoon of the same day.


Trends in average dissolved oxygen concentrations in Great Britain and north-east England and minimum values in north-east England, between 1980 and 2012.   Legend as for previous graph. Note that UK standards for dissolved oxygen are not expressed as milligrams per litre.

Another measurement that gives us a very good indication of the scale of organic pollution in a river is the concentration of ammonium.   Proteins are broken down first to urea, which organisms excrete, and then, via the action of microbes, to ammonium.   If there is a general trend of better regulation and improved sewage treatment then we would expect a gradual fall in the concentrations of ammonium over the past thirty years and this is, indeed, what we see.

As was the case for BOD, ammonia concentrations show a steady downward trend. In this case, the decline only starts after the establishment of the NRA in 1989. Once again, the average state of our rivers looks promising and even the maximum values recorded are now mostly within the standard for “good ecological status”, which is the EU’s threshold for acceptable river conditions.

So at the end of the first part of my survey of river conditions everything seems to look promising, with concentrations of some of the main pollutants associated with organic pollution within the limits that should enable the UK to meet targets set by the EU.   The Environment Agency has a great deal of experience in managing sewage discharges and the technology for reducing concentrations of pollutants such as ammonium is well understood.   In the next post, I’ll move on to consider two other pollutants where the situation is not quite so optimistic and several challenges still remain.


Trends in average ammonia-N concentrations in Great Britain (closed circles) and north-east England (open circles), and maximum values in north-east England, between 1980 and 2012. The horizontal lines show the current UK standards required to support different classes of ecological status.

3 thoughts on “The state of things, part 1

  1. Pingback: Farewell to our “Green and Pleasant Land”? | microscopesandmonsters

  2. Pingback: (In)Competent Authority? – microscopesandmonsters

  3. Pingback: The challenging ecology of a freshwater diatom? – microscopesandmonsters

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