Where’s the Wear’s weir?

There was minor excitement in Durham – and some consternation amongst the rowing fraternity – when river levels dropped rapidly overnight last week.  The river had been very low for some time but was 20 cm lower on Wednesday morning (28 June) due, we learned, to a failure in a sluice gate on the weir just below Prebends Bridge.   It does not look very dramatic in the picture above (a temporary – but not wholly effective – repair had been effected a couple of days earlier) but, as the hydrograph below shows, it was enough to alter the levels to a point where rowing becomes difficult.  The following two days were wet and miserable and the rain caused levels to increase again (note the steep rise on the evening of 29 June as floodwater washed down from Weardale) before gradually tailing off over the next few days.  My photograph was taken in the afternoon of 2 July when levels were back to normal.

“Normal” is, however, a tricky word to apply to any river, so diverse are the alterations to which they are subject.  For me, the ponded section of the Wear upstream of the weir is all I have known and the view of the cathedral looming over the Fulling Mill and its weir is the quintessential impression of Durham, immortalised in J.M.W. Turner’s paintings.  Without that weir there would be no rowing on the river – an important “ecosystem service” within the city (see “Bring on the dambusters …”) – yet that dip in the hydrograph on Tuesday morning offers us a rare glimpse into what the river would have looked like in summers in the far past.  Rowers would be not be very happy were this to pesist but perhaps canoeists would prefer faster-flowing water?  Maximising the ecosystem services that a river provides often involves a trade-off between competing needs.

River levels in the River Wear at New Elvet (NZ 272    ) from 27 June to 2 July.  The orange line indicates the point at which flooding may occur.   From: https://flood-warning-information.service.gov.uk/station/8288425

I saw the opposite situation on the River Tees at Egglestone, just downstream from Barnard Castle.   Turner visited this location as part of the same trip that took him to Durham in 1797 and he sketched the view of Egglestone Abbey which he later worked up into a painting and engraving.   In his pictures you can see an old paper mill, what appears to be a weir across the Tees and open ground on the steep land in front of the abbey itself.   The view today is quite different: the mill is still there, albeit in a dilapidated condition and there is thick woodland on the river banks which completely obscures the view of the abbey.   There is also no sign of the weir but the mill race that diverts river water through the mill can still be seen, though water only flows through when the river is high.

I did wonder if this meant that the weir had been completely washed away since the mill had fallen derelict but another possibility is that the weir is artistic license on Turner’s part.  He made his sketch in 1797 but there is no obvious weir in the drawing that has survived.  The painting on which the engraving is based dates from about twenty years later, and it is possible that the weir was added to the composition, based on memories of other localities that he visited on that trip (including Durham).   The presence of a weir also cannot be confirmed from a painting by Thomas Girtin from about the same time but it is possible that he, too, worked up his watercolours some time after his sketching trips and relied on hazy memories.  And, as we know that Girton and Turner were acquainted, Turner may have fed off Girton’s interpretation of the scene, compounding the intital error.

Egglestone Abbey near Barnard Castle.  Engraved by T. Higham after J.M.W. Turner. 1822.   Image released under Creative Commons CC-BY-NC-ND (3.0 Unported)

The other possibility is that we are not looking at the same river as Turner or Girtin.   The river we look at today is downstream of major reservoirs at Cow Green and on two tributaries, the Greta and Balder, none of which were present when they visited.   Cow Green, in particular, was designed with regulation of the water supply in mind, in order to ensure that there was enough for the industries in Teesside.  One consequence is that there is more water in the Tees during the summer now than when Turner and Girtin visited.   Maybe a weir would have been necessary at that time to keep the water level high enough to feed the mill race during the summer?

So here, as in the Wear, “normal” is a difficult word to apply.   First impressions are that the river is now in a more natural state than two hundred years ago because an impediment to natural flow has been removed.  When we look more closely, however, we see that the river we see today is, in fact, a different type of “abnormal” to that which Turner and Girton sketched.   But we also need to remember that Turner and Girton’s interpretations are not entirely trustworthy guides to the past either.  There is much to be said for walking backwards into the future but occasionally this may mean that we trip ourselves up …

The view across the River Tees towards Abbey Mill and Egglestone Abbey from approximately the same place as Turner’s view.  The mill is just visible amongst the trees in the middle of the picture.

Reference

David Hill (1996).  Turner and the North.   Yale University Press, New Haven and London.

 

A day out in Weardale …

Wear_Frosterley_Apr16

Fine weather towards the end of last week lured me away from my computer screen and out to Weardale on the flimsiest of pretexts, and gave me an opportunity to drag this blog away from musing about pandas and Taoism and back to its core business.   Forty minutes drive from home brings me to Frosterley, in the historic mining and quarrying areas of the valley, though enough time has elapsed for the hard edges of the industrial heritage to have been rubbed away by the gradual incursions of nature.   It is a beautiful spot, with the river meandering down a tree-lined channel with wildlife in profusion.

Understanding a river is partly about recognising patterns at different scales and just as one can look at a landscape such as the one above and infer something about its conditions (fast-flowing water? relatively natural channel?  low population density?) so a naturalist should be able to adjust his or her focus and read the story of the river at smaller and smaller scales.   It takes a few moments to adjust – physically and mentally – to searching at these finer scales, but the story of the river started to open up once I looked more closely.

There were a number of small dark green patches on the river bed, most noticeable towards the margins (maybe because my wellingtons limited my explorations to the shallower parts of the channel).   They were slimy to the touch and I could make a guess at their identity, but needed to get them under a microscope before I could confirm this.   That’s one of the problems with my kind of natural history: there is none of the immediacy that a birdwatcher or field botanist gets from putting a name onto organisms in the field.  Underneath the microscope, however, my alga yielded up its secrets: I could see narrow filaments composed of cells each with a single chloroplast lapped around most of the perimeter, with a number of side branches, each gradually tapering to an acute apex.  This is Stigeoclonium tenue, a common alga of streams and rivers although possibly less common now than was the case a couple of decades ago.  It is hard to be sure because it is easily overlooked and there is no systematic recording of these organisms, but I am not the only person to voice this suspicion.

Stig_tenue_Frosterley_Apr16

Stigeoclonium tenue from the River Wear at Frosterley.  Left: macroscopic view showing tufts of green filaments attached to a submerged stone (scale bar: approximately 1 centimetre); right: microscopic view (scale bar: 10 micrometres = 1/100th of a millimetre).

Looking at these filaments, I can read a little more about the state of the river than I could infer from my landscape-scale perspective at the top of this post.   I can suggest to you that this river is, or has been in the recent past, flush with the nutrients that Stigeoclonium and other plants need to thrive.   Why do I know this?   I shared laboratory space as a PhD student with a colleague, Martin Gibson, who was investigating the physiology of this species and its relatives.  This built on earlier work by Brian Whitton and others which showed that when nutrients were scarce, the branches of Stigeoclonium were much longer, tapering gradually into fine, elongated cells that were devoid of chloroplasts.  These had special enzymes which were able to break down organic compounds that contained the phosphorus that the alga needed.   When nutrients were plentiful, these hairs disappeared.

I strongly suspect that, were I to look at recent phosphorus measurements in this part of the Wear, they would indicate low concentrations, which might suggest that my inference is wrong.  However, the Environment Agency’s standard approach to measuring water chemistry is based on a single visit each month and we know, from finer-scale studies, that phosphorus concentrations can vary greatly over short periods of time (particularly related to changes in the weather and flow regime).  We also know that their standard analytical method does not record phosphorus that is tightly bound into molecules.   The Environment Agency’s approach is good enough to give the basic insights into rivers that they need to regulate the environment, but misses many of the nuances.   That’s why an understanding of the ecology of apparently insignificant organisms can be so useful to river managers.

One of the reasons I wanted some samples of algae from the River Wear was to see if we can simplify the process of identifying algae, in order to make these insights more available.  I’ve written already about RAPPER  (see “The Democratisation of Stream Ecology?”) but so far those of us who have tested this have all had access to high power microscopes.   It is possible to buy field microscopes at a much lower cost but these typically only have a maximum of 100x magnification.  One of my objectives for this year is to see just how can be identified with this limitation.    The image below was taken at 100x using my main microscope, and you can see that the basic form of Stigeoclonium can still be resolved and, indeed, differentiated from related genera such as Draparnaldia (see “The River Ehen in February”), so this is an encouraging first step.  If we can repeat this with the other algae used in RAPPER, then all sorts of possibilities for “citizen science” open up …

Stig_x100_Frosterley_Apr16

Stigeoclonium from the River Wear at Frosterley, photographed at 100x magnification.

References

Gibson, M.T. and Whitton, B.A. (1987).   Hairs, phosphatase activity and environmental chemistry in Stigeoclonium, Chaetophora and Draparnaldia (Chaetophorales). British Phycological Journal 22, 11-22.

Gibson, M.T. and Whitton, B.A. (1987).  Influence of phosphorus on morphology and physiology of freshwater Chaetophora, Draparnaldia and Stigeoclonium (Chaetophorales, Chlorophyta). Phycologia 26: 59-69.

Whitton, B.A. & Harding J.P.C. (1978).  Influence of nutrient deficiency on hair formation in Stigeoclonium.  British Phycological Journal  13: 65-68.

And the waters prevailed on the earth …

Conscious that this blog, which purports to be about natural history, has not actually had any posts reporting my own observations for some time, I had tentative plans to go out and collect some samples this weekend.   Storm Desmond, however, had other plans for me: high winds and heavy rain from Friday evening onwards pushed local river levels up to dangerously high levels, and I was left to contemplate the capricious nature of the British climate from a largely sedentary perspective.

A screenshot of the Environment Agency’s river level gauge shows how the spate developed. We had high winds in Durham, but not excessive amounts of rain, and the steep rise in levels during Saturday reflects the time-lag between rain falling on the Pennines and arriving in the Wear at Durham.   The peak in level occurred early on Sunday morning, and the subsequent pictures show the river in Durham at about 10:30 on Sunday morning. Though high, this is not the highest I can remember: that was in 2009 when the road into Durham was impassable at Shincliffe as the river had broken its banks.

Wear_hydrograph_151206

A screenshot from the Environment Agency’s river level website, showing the passage of Storm Desmond through Sunderland Bridge, a few kilometres upstream of Durham City, from midday on Friday 4 December to midday on Sunday 6 December.

Wear_in_spate_151206_#2

The River Wear in spate on 6 December 2015: the view downstream from Elvet road bridge.

Wear_in_spate_151206

The River Wear in spate on 6 December 2015: the view upstream from close to the Count’s House, showing the same clump of Japanese Knotweed that featured in my post “In praise of Japanese Knotweed” in early November. You can see how the river has risen up and covered the bankside footpath.

As I have some old-fashioned ideas about fieldworkers being part of the benthos not the plankton, I am watching river levels with interest. I have fieldwork planned in Cumbria at the end of the week and am intrigued to see what Storm Desmond has done to the algal communities. The irony being that to study the effect of spates on ecology, one has to first get into the river… or even get close to the river. This may be an issue as my route to the River Ehen passes some of the most affected parts of Cumbria.

However, questions about the effect of a spate on a river can be generalised into a broader question of how occasional catastrophic events alter ecosystems which, in turn, makes us think about problems that may arise from simplistic interpretations of the relationship between explanatory variables and response variables, discussed in the previous post.   The temptation is always to interpret ecology in terms of the variables that are easiest to collect and measure when you are collecting your samples whereas, looking back at “How green is my river?” we see how late summer conditions in the River Atna are at least partly the consequence of high flows in the Spring.

Biologists have suspected this for a long time, and there is anecdotal evidence of changes wrought by individual events. I was pleased, therefore, to see that a whole issue of Freshwater Biology had been devoted to this topic.   With the effects of flooding uppermost in our minds this weekend, the introduction to this issue, by Mark Ledger and Alexander Milner, reminds us that “catastrophic events” can also extend to droughts and heatwaves. One point that emerges, even from a quick scan through the contents of this issue, is the importance of long-term datasets – revisiting, again, topics that wrote about in “How green is my river?” It is more pertinent than ever because of the fiscal squeeze on our environment agencies and, ironically, the flooding that results from Storm Desmond is going to lead to calls for yet more DEFRA money to be diverted to flood defence, which can only mean less money for environmental regulation.   Therein lies the biggest irony of all: a government department that trumpets the virtues of “evidence-based policy” is planning to collect less evidence. Work that one out, if you can.

Reference

Ledger, M.E. & Milner, A.M. (2015). Extreme events in running waters. Freshwater Biology 60: 2455-2460.

Fieldwork tales from the tail of a hurricane …

I had more or less decided to cancel my fieldwork when I heard the weather forecast a couple of weeks ago. The last remnants of Hurricane Gonzalo were blowing themselves out over western and northern Britain and the prediction was for heavy rain over the Pennines. I heard the rain during the night and checked the river levels in the morning. They were not outrageously high, but the trend was upwards and common sense dictated that I wait a day and try again.   You can see from the hydrograph below just how quickly the river rose and then fell again over the course of 24 hours.   Even by 09:00 the following day the river was not at its lowest, but at least it was safe to wade in and collect some samples.

river_levels_stanhope_14102

River Levels in the River Wear at the Environment Agency’s monitoring station at Stanhope, 20th – 22nd October 2014 (http://apps.environment-agency.gov.uk/river-and-sea-levels/120695.aspx?stationId=8196). The arrows indicate the approximate time of the rainfall associated with Hurricane Gonzalo.

A sign that the river was still higher than usual was that some cushions of moss that are usually well clear of the water were at or, in a few cases, still below water level.   There are a few species of moss, including members of the genus Cinclidotus and Racomitrium aciculare, that seem to thrive on the upper parts of boulders.   They spend most of their life out of the water, then just a few days each year submerged. Those few days will bring down suspended material which will become entrapped around the dense network of stems in the cushions and, in the process, provide a nice little “compost heap” that will keep the moss supplied with nutrients. The stems also trap water, through capillary action, so that the cushions stay moist for some time after the water levels have dropped again.   Yet such generalisations do not explain why a few genera thrive in this habitat whereas others are never found here.

Much of the magic of rivers is associated with organisms which are rarely, if ever, seen: the fish, of course, but also otters, kingfishers and other vertebrate organisms. I’m also fascinated by the microscopic world of rivers. Mosses have the opposite problem: we always see them on visits to rivers yet almost never notice them, let alone spend time unravelling the stories that they can tell us.   I am reminded of Mungo Park’s words back in 1795 (see “More about mosses…”). Perhaps I should write a little more about the extraordinary diversity of mosses over the next few months?

Cinclidotus_mucronatus_Wols

Cushions of Cinclidotus mucronatus just above water level in the River Wear at Wolsingham, October 2014.

The politics of pests …

My training for the Great North Run takes me along the banks of the River Wear and, since writing about Himlayan balsam recently (see “An Indian summer on our riverbanks …”) I have had plenty of opportunities to both observe and ponder the biology of this plant.   I remembered, just after posting my piece on Himalayan balsam, that some former colleagues at Durham University had done some research on this species just after I had left.   Another colleague had commented wryly that they had managed to prove that Himalayan balsam lives by river banks though, on reading their work, it is clear that this was a rather unfair judgement.  It is also wrong, as I noticed this morning as I pushed through stands of Himalayan balsam that were encroaching on the path I was running along, some distance from the river.   I have run along this path for several years but this year is the first when I have noticed Himalayan balsam in such abundance.

Himalyan_balsam_seed_pods

Coiled seed pods of Himalayan balsam, photographed on the Durham river banks, July 2014.

If you look closely at the seed pods you can see that they are tightly coiled, like springs. And, when you brush against a mature seed pod, these springs are capable of catapulting the seeds for several metres.   This characteristic, in fact, is the reason why the Latin name of the genus is “Impatiens” (“impatient”).   Each plant can produce many seeds, so all it takes is for a few of these to land in suitable conditions and the stand of Himalayan balsam will, by the next year, have extended itself by a few metres.   The predilection for river banks is partly because these are associated with fertile, moist, often shaded, soils where the seeds are able to thrive, but also because the natural flooding of the river can transport the seeds rapidly between locations.   However, my former colleagues at Durham also noted that Himalayan balsam was also strongly associated with roadsides and, indeed, Frank Smythe, in Valley of Flowers, does not record Himalayan balsam in its natural habitat as being so strongly associated with rivers.

Knowing where Himalayan balsam grows was, however, only the start, as they were able to use their knowledge of the plant’s distribution to build a mathematical model that described how Himalayan balsam spreads and then to manipulate the model to simulate various options for controlling the spread.   They concluded that, once established, Himalayan balsam would be very difficult to eradicate, regardless of strategy.   That’s no big surprise, given what we know about the biology of the plant and also from knowledge of efforts to control other invasive weeds. But that, too, got me thinking …

We are, now, less than 10 months away from a general election.   Expect many fine words about the environment to be spoken between now and then.   But, as is often the way, it will be the economy, health and education which will dominate the campaigns.   Politicians will look for environmental policies that will either give a quick and demonstrable benefit or Grand Gestures with maturation times that extend well beyond the term of the next parliament.   Control of invasive weeds fails on both counts.   The paper on control strategies concludes: “If eradication is a serious goal of control programmes then they must be co-ordinated at a regional or national scale, involve greater investment and extend over a longer duration”. In other words, they will need a bigger slice of the budget that the environment is likely to be allocated.   Moreover, how can regional or national co-ordination be achieved in governments committed to reducing the size of the public sector?   No, I’m afraid that control of Himalayan balsam is very unlikely to feature on any politician’s to-do list in the immediate future.

References

Collingham, Y.C., Wadsworth, R.A., Huntley, B. & Hulme, P.E. (2000).   Predicting the spatial distribution of non-indigenous riparian weeds: issues of spatial scale and extent.   Journal of Applied Ecology 37 (Suppl. 1) 13-27.

Wadsworth, R.A., Collingham, Y.C., Willis, S.G., Huntley, B. & Hulme, P.E. (2000). Simulating the spread and management of alien riparian weeds: are they out of control?   Journal of Applied Ecology 37 (Suppl. 1) 28-38.

 

Bring on the Dambusters …

Mild annoyance lies behind this post.  I’m writing as I travel home from a two day conference, organised by the Chartered Institute of Ecology and Environmental Management with the title ‘Ecosystem Services 3: Rivers – A Framework For Action’.  The meeting had several interesting papers but, at times, lacked a hard critical edge, exemplified by the following example:

Two of the early speakers commented on the problems of physical modification of rivers, noting that in-stream structures such as weirs often present serious obstacles to the migration of salmon and other migratory fish.   In theory, you should be able to construct fish passes around these weirs so that the fish are not obstructed.  In practice, however, many fish passes are not particularly successful.   ‘Why not’ suggested one questioner after the talk (representing Natural England, I think), ‘just remove the weirs altogether and restore natural flow regimes.’   This suggestion was greeted with applause and even a few ironic cheers from parts of the audience.

About six months ago, however, I joined the local rowing club in Durham. ‘Recreation’ is a ‘service’ that society gets from our rivers, just as much as nature and wildlife, the primary focus of interest for this audience of conservationists.   Rowing here depends upon the weirs across the River Wear (you can see one of them in the classic view of Durham Cathedral which I posted on 29 July. (This view, itself, could be classified as an ‘aesthetic’ ecosystem service).  There are about 500 members of the rowing club and, at a guess, between 500 and 1000 students in University and College crews.  That’s a huge constituency whose interests are in conflict with the ambitions of many conservationists.

rowing_on_the_Wear

Rowing on the River Wear, July 2013. 

I had come to the conference to see how this type of conflict of interest would be resolved, and was a little surprised to see how little it featured.  Only three of the 18 speakers addressed the issue of trade-offs between different ecosystem services and only half made any reference to public participation or stakeholder engagement at all.  I heard a good example of constructive engagement with anglers on the River Itchen during a workshop session but this was a situation that could be sold as a ‘win-win’, with both anglers and conservation benefitting.  For the most part it was conservationists talking to conservationists without anyone to challenge their assumptions.   I left feeling with a feeling that life out there in the real world may not always be this cosy.