The way things were …

Writing the previous post led me to contemplate how much things had changed over the time that I have been working in this field.  Back in the early 1990s when I first set out to look at the response of diatoms to nutrients in streams, few in the National Rivers Authority (NRA, predecessor to the Environment Agency) regarded phosphorus as a serious pollutant in rivers, and most biologists thought about ecological quality solely in terms of organic pollution and invertebrates.   In order to investigate the effect of nutrients, I wanted to visit sites where organic pollution was not a problem.

I was helped in this task by the work done by biologists at the then Institute for Freshwater Ecology (now Centre for Ecology and Hydrology) who had just developed the early versions of RIVPACS (“River Invertebrate Prediction and Classification System”) which established the principle of expressing ecological quality as the observed quality / expected quality.  This, in turn, required an ability to predict the “expected” condition for any stream.   The work that had developed these equations started from a dataset of invertebrate and environmental data collected from a wide range of “unpolluted” running water sites which, in those far off days, was compiled by asking biologists working for the Regional Water Authorities (predecessors to the NRA) for their recommendations of sites that were of “good” or “fairly good” quality.  Nowadays, screening sites to be used for calibrating ecological methods is a much more rigorous procedure but this was the first tentative step on a long journey and “expert judgement” was as good a place to start as any.

The paper that emerged from this exercise (see reference below) analysed data from these “unpolluted” sites and classified them into eight groups.  Each of these groups consisted of sites that shared similar invertebrate assemblages which reflected similarities in the habitat, from upland, fast flowing becks to deep, wide slow-flowing rivers in the lowlands.  The authors included a useful table that listed the physical and chemical characteristics of each of these groups and I noticed that the phosphorus concentrations reported for these spanned a very wide range.   This meant that I could use these as the basis for putting together a sampling program that spanned a long gradient of nutrient pressure without the complications of organic pollution.   The outcome of that work was the first of the two papers referenced in my previous post.

Time has moved on and I thought it would be interesting to revisit these “unpolluted” sites to see how they would be classified using the UK’s current standards for phosphorus.  This highlights a striking difference between the prevailing idea of “unpolluted” in the early 1980s and the present day, as all of these groups had average concentrations that equate to substantial enrichment by modern standards; in half the groups this average concentration would be classified as “poor status” whilst the maximum concentrations in three groups equates to “bad status”.   Whatever way you look at it now, these sites were far from “unpolluted”.

Classification of TWINSPAN end-groups of unpolluted river sites in Great Britain based on Armitage et al. (1984) along with average and maximum phosphorus concentrations recorded in each group and the phosphorus status based on current environmental standards.  M = moderate status; P = poor status; B = bad status.

I am not being critical of the approach taken by Patrick Armitage and colleagues.  In many ways, I regard the work of this group as one of the most significant contributions to the science of ecological assessment in my lifetime.   I am just intrigued to see how the thinking of ecologists and regulators has moved on in the thirty years or so since this paper was published.  I know from my own early conversations with NRA biologists that inorganic nutrients were not perceived as a problem in rivers until the early 1990s.   It was probably the European Community’s Urban Wastewater Treatment Directive (UWWTD) that started to draw the attention of biologists in the UK to these problems, and which led to the development of stricter environmental standards for nutrients, though not without opposition from several quarters.

This, then is a situation where good legislation provided the impetus needed to start the process.  There were places in the UK – rivers in the Norfolk Broads, for example – where nutrients were already being regulated, but these were special circumstances and nutrient problems in most rivers were largely ignored. Indeed, as I said in my previous post, phosphorus was not even measured routinely in many rivers.   I heard via my professional grapevine that it was the Netherlands who had made the case for the clauses in the UWWTD concerning regulating nutrients, as their stretches of the lower Rhine were subject to numerous problems caused by unregulated inputs of nutrients from countries upstream.   I do not know if this is true, but it is certainly plausible.   However, once the need to control eutrophication in rivers was codified in UK law, then the debate about how to evaluate it started, one of the outcomes of which was more funding for me to develop the Trophic Diatom Index (referenced in the previous post).  And, gradually, over time, concentrations in rivers really did start to fall (see “The state of things, part 2”).   I’d like to think the TDI played a small part in this; though this might also mean that I am partially responsible for the steep increase in water charges that everyone endured in order to pay for better water quality …


Armitage, P.D., Moss, D., Wright, J.F. & Furse, M.T. (1984).  The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running-water sites.  Water Research 17: 333-347.

An embarrassment of riches …

A couple of years ago, on a snowy day in January, I gave a talk and ran a practical on algal-based ecological assessment for an MSc class at the University of Bristol. As part of the practical class, I asked my colleague, Marian Yallop, who organised the session, if she could set some algal cultures growing a few days ahead of my arrival, in order to stimulate some discussion amongst the students on what we understood by “eutrophication”.

I asked for four flasks, each with a standard algal growth media, into which an inoculum of algae was pipetted. I can’t remember what species of algae we used, except that it was a common green algae.   The growth medium was naturally low in nutrients, so Marian augmented the media in two of the flasks with an extra squirt of nutrients, so we had two with “background” nutrients and two with high nutrients.   Then she placed one of each pair on a windowsill, and the other in a refrigerator and left them for a few days.


Our eutrophication “thought experiment” in Bristol in January 2013

I had given the students the following definition of eutrophication, used in a key EU Directive (the Urban Waste Water Treatment Directive): “the enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned.”

My question to the students was simple.   Which of the four flasks is “eutrophic”?   The first part of the definition says “the enrichment of water by nutrients …”, so we could have argued that both of the “plus nutrient” treatments were eutrophic. However, the definition then goes on to say “… causing accelerated growth of algae ….”.   The plus nutrient treatment that was kept in the refrigerator did not fulfil this criterion; however, the one kept on the window ledge is the greenest of all the flasks. So could we claim that only the “plus nutrient, window ledge” flask was eutrophic?

What about the “minus nutrient window ledge” flask?   That looked quite green, even though the nutrient levels were low.   This illustrates a further important point: the quantity of phosphorus, in particular, that a plant needs to grow is very small and if other conditions are right (i.e. a windowsill in a centrally-heated laboratory), then you can get high biomasses of algae, even without excess nutrients (see “A brief excursion to Norway”).   In nature, such natural abundance would not last for long: it would be scoured away by a flood or eaten by hungry invertebrates on the river or lake bed. Based on my experience of northern English rivers, I would only get concerned if the high biomass persisted beyond a few weeks.

The flask with added nutrients that was kept in the refrigerator offers another perspective. Even if we could argue that it is not strictly “eutrophic”, we should acknowledge that there is a risk of a high biomass developing.   In our thought experiment, the cool dark environment of the refrigerator minimised the risk of a high biomass developing.   However, for as long as there are elevated nutrient concentrations, we have to acknowledge that both “plus phosphorus” treatments represent a hazard to healthy ecosystem functioning.

A final, and slightly pedantic, interpretation was that none of these treatments fulfilled the final criterion in the definition of causing “… an undesirable disturbance to the balance of organisms …”. In this case, of course, there was only a single organism present, so it was impossible to demonstrate this particular criterion. However, a quick scan of the literature on eutrophication does show a strong bias towards establishing a link between nutrients and aquatic plants and algae, and the secondary effects are often neglected.   These, however, provide the essential “so what?” to our arguments.   I live in a world of algae-obsessed nerds and we sometimes need a sharp poke in the ribs to be reminded that most people need a better return on the expensive investment in better water treatment than just to be told that the algae have changed (see “So what?”).

The state of things, part 2

If the last post presented a fairly optimistic picture of the quality of Britain’s rivers over the past 30 years, this one is more of a reality check, highlighting some areas where our rivers are still suffering from pollution which means that they are unlikely to meet EU targets.

The first pollutant I will consider in this post is phosphorus.   The data for this and other inorganic nutrients is not summarised by regions but by the predominant type of agriculture in the catchment, reflecting the importance of run-off from land as a source of these pollutants.   However, much phosphorus enters our rivers via sewage works and, as we saw for BOD and other pollutants associated with organic pollution, the trend over the past twenty years or so is generally downwards. Note that the start of the downward trend does not start until the mid 1990s.   This is because reducing phosphorus in effluents only became a legal requirement when the EU’s Urban Wastewater Treatment Directive came into force. The horizontal lines, once again, represent the UK standards for dissolved phosphorus in rivers.   There is a story behind these standards, in which I played a minor role.


Trends in average inorganic phosphorus (PO4-P) concentrations in rivers draining three different land types in Great Britain. Note that the vertical axis is on a logarithmic scale.   The horizontal lines show recent UK standards required to support different classes of ecological status (see text for more details).

You’ll see that the trend lines for the two lowland land types are approaching but have not decisively crossed the line which indicates “good status”.   Presence of a certain phosphorus concentration does not, itself, determine status but these indicate guide values that ecologists believe should be attained if the river is to support a healthy ecosystem. I was involved in setting the original standards and our team originally set values that were much lower than those that were eventually adopted.   We had worked out concentrations that were associated with locations where we had found healthy ecosystems.   However, when these figures made their way through the bureaucracies of our regulatory organisations, they encountered strong resistance from those charged with actually achieving the reductions.   You’ll see that average concentrations have more than halved during the first decade of the 21st century – a considerable achievement. To be told that these concentrations were not low enough was a bitter pill to swallow. To cut a long story short, statistical black arts were performed behind the scenes (not by us, I hasten to add) to justify a higher standard, eventually set at 0.12 milligrams per Litre.

The cavalier fashion in which this original phosphorus standard was set meant that, before long had passed, weaknesses started to become apparent.   Not least of which was that rivers that should, on paper, have had conditions suited to good ecological status continued to have plant and algal communities that were not characteristic of good status.   Eventually, the phosphorus standards were revisited and, in most cases, made more stringent, though not without opposition from the water companies who would bear much of the burden of meeting these.   These new standards would pull each of the horizontal lines on my graph lower, and so make the overall position look yet more pessimistic.

The trend for one other important plant nutrient in GB rivers is equally pessimistic. Concentrations of nitrogen as nitrate have shown virtually no reductions at all over the period that the HMS has been operating.   There are, I think, two reasons for this. The first is that ecologists generally stress the importance of phosphorus over nitrogen as the key nutrient in freshwaters, which means that nitrogen concentrations have received less attention than, perhaps, they deserve. The second reason is more political: the biggest source of nitrates in our rivers is agriculture and DEFRA has to balance the interests of the environment with that of the vocal and politically-powerful farming lobby.   That there is no ecologically-based standard for nitrates in UK rivers tells its own story.   We could easily have produced a standard for nitrates at the same time as we revised the phosphorus standards (the information we needed was in the same spreadsheet) but were warned off. There is, in theory, a standard for nitrates in freshwaters, produced to meet the requirements of the EU’s Nitrates Directive but this was designed to protect human health, not ecology, and is set at a very high concentration. Rather than use this, I have plotted the standards used in the Republic of Ireland on my charts and, assuming that an equivalent UK standard would be of a similar magnitude, these show that the nitrate concentration of lowland rivers is generally much higher than these values.   This is, of course, a very broad-brush picture but it gives us a rough idea of what is going on.


Trends in average inorganic nitrogen (as nitrate) concentrations in rivers draining three different land types in Great Britain. There are no current UK standards for nitrate-N concentrations required to support different classes of ecological status; those plotted here are for the Republic of Ireland.

Looking back at the two posts, the picture that emerges is of reasonably good regulation of those types of pollutants that have been the traditional focus of regulation.   Both the water companies and the regulators understand the processes need to reduce organic pollution levels in sewage effluents, and the necessity for doing this.   The last twenty years or so have seen a change in focus towards inorganic nutrients and here we run into problems. First of all, the benefits for the public are often not immediately clear which, in turn, makes increasing water bills to pay for the expensive process of phosphorus removal more difficult. I have heard staff from water companies raise this argument several times when arguing against tighter regulation of phosphorus.   But the second problem is that regulation of nutrients needs to embrace diffuse inputs from agriculture as well as point sources.   This presents a huge problem as there are many more farms than sewage works to be visited, many of which are struggling to survive in a tough economic climate.   Consequently, there is little political will to drive the process from the top.   These are, indeed, challenging times for freshwater ecologists.