Follow the data, stupid …

A perennial problem with ecology is that it is a discipline that is far better at describing problems than it is at solving them. The Water Framework Directive (WFD) encapsulates this: after nineteen years, we have a pretty good idea of the condition of Europe’s waters but have made very little progress in restoring the half that do not yet achieve good ecological status.

The reason for this is, I suspect, because describing the problem is a task that lies squarely within the remit of a scientist whilst finding solutions requires interactions that go beyond the boundaries of science, encountering vested interests along the way.   The agricultural sector’s enthusiasm for the environment is tempered by their desire to maximise yield and earn a living from the land, politicians are wary of regulations that may deter business or raise prices for the consumer and all of us are too wedded to the luxuries that the modern world offers.

The WFD can be seen as an embodiment of the social contract, articulated by philosophers such as Thomas Hobbes whereby individuals forego some rights in order to transcend the state of nature (“… nasty, brutish and short.”) and give us access to the benefits of an ordered society.  In this case, we all consent to forego some freedoms in return for a share in the benefits that a healthy aquatic environment will bring to all of us.   “Freedom” might seem like a weighty word in this context but anyone who has watched their sewerage charges creep steadily upwards over the past twenty years should recognise this as the price we pay for the freedom to flush away life’s less desirable by-products.

The problem is defining the point at which we hand over our natural rights to a higher authority.   We understand this when driving: an urban speed limit of 30 miles per hour reflects the point at which the risk we pose to other road users are deemed societally unacceptable and our right to drive as fast as we wish has to be curtailed.  If we can translate that principle into environmental governance then we can set “speed limits” for the major pressures that impact on the aquatic environment.   How do we get from an ecologist’s understanding of a “healthy” river (“good ecological status”, in WFD parlance) to the “speed limit” for nutrients, widely recognised as one of the major pressures affecting both freshwater and marine systems?

That’s been the focus of some work I’ve been doing under the auspices of the European Commission’s Joint Research Centre, one strand of which has just been published in Science of the Total Environment.  This paper looked at the threshold concentrations for nutrients (phosphorus and nitrogen) used by EU countries, noting the very wide range of values chosen as the national “speed limit”.   The situation is complicated because, just as is the case for roads, different types of rivers require different limits and we had to look for variation between countries amidst an array of variation within countries.   What emerged, however, was a clear relationship between the threshold values and the method used to set the standard.  Those that had applied statistical or modelling techniques to national data generally had tighter thresholds than those that relied upon “expert judgement”.  I’ve included the two figures from this paper that make this point.

Poikane_et_al_2019_Fig7

Range of good/moderate lake phosphorus (a) and nitrogen (b) threshold values grouped by method used to determine the value. Different letters indicate groups that are statistically different (p ≤ 0.05).   Fig. 7 from Poikane et al. (2019).

“Expert judgement” is one of those slippery terms that often creeps into official reports.   There needs to be space within a decision-making process for an experienced professional to see through the limitations of available evidence and present a reasoned alternative.  However, “expert judgement” too often becomes a shorthand for cutting corners and, in this case, grabbing numbers from the published literature that seem vaguely plausible.  There is also a darker side because, having unhitched decision-making from the evidence, “expert judgement” can become a euphemism for the “art of the possible”.  I have seen this occur during discussions around setting and revising river phosphorus standards in the UK: the regulators themselves are under pressure to balance environmental protection with economic development and tight standards can potentially limit what can be done in a catchment.

Another of our recent papers (this one’s not open-access, I’m afraid) shows that setting standards using empirical models is far from straightforward and we also recognise that standard setting is just one part of a longer process of nutrient management.   However, setting inappropriate standards simply as an expedience seems completely barmy, as you are never going to attain your desired ecological benefits.   The cynical view might be that, as the process of environmental change is invariably greater than the electoral cycle, there is limited accountability associated with such decisions, compared with more immediate political capital kudos from bringing investment and jobs to a region.

Poikane_et_al_2019_Fig8

Range of good/moderate river phosphorus (a) and nitrogen (b) threshold values grouped method used to determine the value. Different letters indicate groups that are statistically different (p ≤ 0.05).   Fig. 8 from Poikane et al. (2019).

All of our work has shown that, in most cases, the relationship between biology and nutrients is weak and, for this reason, large datasets are needed if robust inferences are to be drawn.  This leads to one further consequence of our work: setting environmental standards may only be possible if countries pool their data in order to produce big enough datasets with which to work.  This is particularly the case for smaller countries within the EU, but also applies to water body types that may be relatively infrequent in one country but are more widespread elsewhere.   I had recent experience of this when working on the Romanian stretches of the Danube: they simply did not have a wide enough gradient of conditions in their own territory, and we had to incorporate their data into a larger dataset in order to see the big picture (see “Beyond the Tower of Babel …”).    Writing about the benefits of international collaboration as the Brexit deadline looms obviously has a certain irony, but it needs to be said.  Far from being the distant and unaccountable law maker of Brexiteer mythology, in this field the European Commission has been quietly encouraging Member States to share experience and promote best practice.  One can only speculate about the future of the UK environment once free of Brussels oversight.

References

Philips, G., Teixeira, H., Poikane, S., Salas, F. & Kelly, M.G. (2019).   Establishing nutrient thresholds in the face of uncertainty and multiple stressors: a comparison of approaches using simulated data sets.   Science of the Total Environment684: 425-433.

Poikane, S., Kelly, M.G., Salas Herrero, F., Pitt, J.-A., Jarvie, H.P., Claussen, U., Leujak, W., Solheim, A.L., Teixera, H. & Phillips, G. (2019).  Nutrient criteria for surface waters under the European Water Framework Directive: Current state-of-the-art, challenges and future outlook.  Science of the Total Environment 695.  

Note on figures:

The methods used by Member States to derive nutrient thresholds are described in more detail in Poikane et al. (2019).   In brief, the approaches are:

1 – regression between nutrient and biological response;

2 – modelling;

3 – distribution of nutrient concentrations in water bodies classified (using ecological criteria) as high, good or moderate status;

4 – distribution of nutrient concentrations in all water bodies using an arbitrary percentile;

5 – expert judgement.  This includes values taken from the literature or from older European Directives. For example, for nitrate, the common use of the value 5.65 mg-N L−1 in freshwaters is likely to be derived from the guideline value of 25 mg L−1 of nitrate in the Nitrates Directive (91/676/EEC) or now repealed Drinking Water Directive (80/778/EC).

6 – The so-called OSPAR Comprehensive Procedure is used widely in coastal and transitional waters. In this, a water body is considered to be an ‘Eutrophication Problem Area’ if actual status deviates 50% or more from reference conditions.

7 – insufficient information.

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Is algal gloop on the increase?

This post summarises a series of emails that piqued my interest last week.   The first was from Paul Brazier of Natural Resources Wales, asking for information about terrestrial algae. Behind the query lay a concern amongst some bryologists that the quantities of gelatinous algae in some habitats in the west of Britain was increasing and threatening rare mosses and liverworts found in these places.   He quoted bryophyte expert Nick Hodgetts who has recorded less of the rare moss Sematophyllum (Hageniella) micens who had also noted that the sites where he once found it now have a great deal of algal slime.   Other experts had confirmed this trend, and expressed concerns that it was out-competing small oceanic mosses and liverworts. Des Callaghan, another bryophyte specialist noted that a “gelatinous gloop” (which turned out to be the green alga Gloeocystis polydermatica) had overwhelmed the rare liverwort Lejeunea patens at Glen Trool in Galloway, south-west Scotland.

Des also gave me the photograph below, showing the gelatinous algae Coccomyxa confluens on Betula pubescens, competing for space with the neighbouring oceanic liverwort Scapania gracilis. He commented that at this site (Gallwyd, near Dolgellau, in North Wales), the algae is most abundant in the most humid locations, notably in the mist zone of the main waterfall. It appears that, at least here, it is a normal part of the flora and isn’t so abundant that it is something to worry about. At other sites, though, these terrestrial gelatinous species can be much more abundant.

Coccomyxa_&_Scapania_on_Bet

Coccomyxa confluens growing on Betula pubescens at Gallwyd, near Dolgellau, Wales (photo: Des Callaghan)

The other photograph Des sent shows another green alga, Klebsormidium growing on heather (Calluna vulgaris) at Wybunbury Moss in Cheshire. I described Klebsormidium in one of my posts about the River Ehen (see “The River Ehen in November”) noting how it was often found in habitats that were not fully submerged although I had not previously seen it competing for epiphytes on terrestrial plants, as Des’ image shows.   Des directed me to some circumstantial evidence that Klebsormidium may benefit from high N-deposition.

Interestingly, Glen Trool, mentioned above, is close to Round Loch of Glenhead, the subject of intensive studies on the causes and consequences of acid deposition by Rick Battarbee and colleagues at University College London.   These studies have shown a gradual recovery from the worst effects of acid deposition since the 1980s but the decline in sulphur-containing compounds has been more significant than the decline in nitrogen-containing compounds. They suggested that one result is that Galloway lochs such as Round Loch of Glenhead may, as a result, be slightly more nitrate-rich now than in the far past. Until very recently, the effects of this extra nitrogen was masked by the generally negative consequences of the acidity but now the sulphur deposition has reduced, it is possible that the algae are able to benefit from this nitrogen and thrive at the expense of other plants.   Whether the same may hold true for the terrestrial and semi-terrestrial vegetation in the surrounding woods must remain speculation for a little longer but it may help to explain why bryologists are seeing more algae at locations where they hoped to find rare bryophytes.

Klebsormidium_on_Calluna_Wy

The green alga Klebsormidium growing on Calluna vulgaris (heather) at Wybunbury Moss, Cheshire, March 2015 (photo: Des Callaghan).

References

Battarbee, R.W., Simpson, G., Shilland, E., Flower, R.W., Kreiser, A., Hong, Y. & Clarke, Gina (2012). Recovery of UK lakes from acidification: an assessment using combined palaeoecological and contemporary diatom assemblage data. Ecological Indicators 37: 1-16.

I also discuss the ecology of Round Loch of Glenhead in:

Kelly, M. (2012). The semiotics of slime: visual representation of phytobenthos as an aid to understanding ecological status.   Freshwater Reviews 5: 105-119.

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.

HMS_PO4P_trends

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.

HMS_NO3N_trends

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.