A very dilute compost heap …

It is hard to believe that this idyllic view is within a kilometre of the centre of Newcastle.   We are standing in Jesmond Dene, a steep-sided valley that is now, thanks to the largesse of Lord Armstrong in the 19th century, now a public park.  From the point of view of someone teaching freshwater ecology to undergraduates it is a godsend, as it means that we have a fine location for fieldwork within walking distance of the university.  And, because I teach Geography undergraduates, all I need to do is tell them the location and assume that their spatial awareness will lead them to the right place at roughly the right time.  It usually works.

Don’t be misled by the Arcadian scene in this photograph: for most of its length the Ouseburn is an unprepossessing stream with a multitude of problems, which is one of the reasons why I bring the students here in the first place.  We get them to sample the water, which they analyse in the laboratory over the next couple of weeks, and also collect a sample of invertebrates from the stream bed.  But, most importantly, I just want to get them to start thinking about the factors that driver a river ecosystem.

In the lectures beforehand, I make the point that we need to think beyond the stream channel itself if we are to understand its ecology and the visit to the Ouseburn helps to reinforce this.   That sun-dappled scene above is conveying an important truth: that a lot of the sunlight is intercepted by the leaves of the surrounding trees before it can reach the stream itself.   If we thought about ecology solely in terms of the stream channel we might conclude that this means less energy to fuel the stream ecosystem.  However, look at the photograph below of some of my students peering into the tray containing the invertebrates they have just collected.  Around them in the stream are leaves shed by the surrounding trees.   And, in that tray, we find a range of invertebrates but, most commonly, freshwater shrimp (Gammarus pulex), freshwater hoglouse (Asellus aquaticus) both of which are as happy feeding on the rotting remains of leaves from the surrounding trees as they are on food produced within the stream.

Left: Invertebrate sampling at Jesmond Dene, October 2017. Note the dead leaves in the stream, creating a natural food supply for the bugs.  Right: a Petri dish containing the contents from one pond net.  Note the large numbers of freshwater shrimp, Gammarus pulex (see inset).  

This is the time of year when gardeners are raking up piles of leaves and dumping them on their compost heaps.   When I peer into our compost heap I see a writhing mass of invertebrate animals also feeding on dead and decaying vegetation.  There are many segmented worms in both our compost heap and the samples we get from the Ouseburn, although most of the other animals are quite different (slugs, mostly, in our compost heap).   They may not be as exciting as the hyenas and vultures that perform similar functions on African savannahs but they play an essential role in driving nature’s cycles, turning death back into life (or, at least, into the raw materials on which new life will grow).  All flesh is grass…

Two compost bins: useful metaphors for how energy flows through stream ecosystems.

That’s the first lesson that I want to get across to the students: a river, in its natural state, is really a very, very dilute compost heap, full of organisms custom-built to recycle dead and decaying organic matter.   What I don’t tell them is that bringing them to the Ouseburn is a cop-out for me, as a lecturer whose real skills lay with algae rather than invertebrates.  If I took them to a stream further up the Tyne Valley where the hand of man was less obvious, we would have found many more types of invertebrates, and would have been able to demonstrate a much wider range of ways of feeding than we saw in the Ouseburn.  In particular, I would have expected to see stonefly nymphs and caddisfly larvae, some of which have tough jaws capable of ripping apart leaves, as well as mayfly nymphs, some of which will graze directly on algae.

The idea of a “grazer”, however, needs a little qualification.   Freshwater ecologists like to classify bugs into neat categories based on their food preferences as this helps them understand how energy flows through ecosystems.  The bugs-eye view of algae, however is that they are just one of many types of digestible energy found on and around the stream beds they inhabit.  Some ecologists prefer to lump “grazers” into a larger category of “collector-gatherers” that are relatively unfussy about what type of organic matter they eat and will cheerfully hoover up detritus that other organisms have left behind.

That “detritus” is, by the way, a euphemism for, amongst other things, the downloaded remains of the stonefly nymph’s vegetarian dinner.  Freshwater ecologists refer to this as “fine particulate organic matter” but the rest of us have a wealth of scatological language on which to draw.   That’s another lesson that I want to convey to my students: streams contain a lot of small organisms investing a lot of their valuable time searching for and eating other animal’s poo.   And that means that trout and other predators in these aquatic food-webs are eating a mixture of herbivores (the “shredders” plus the bugs that feed directly on algae) plus a lot of invertebrates that are a lot less fussy about food hygiene.   Next time you sit down to eat grilled trout, remember that you are basically eating reprocessed poo.

References

Bloor, M.C., (2011).  Dietary Preference of Gammarus pulex and Asellus aquaticus during a laboratory breeding programme for ecotoxicological studies. International Journal of Zoology 2011: article ID 294394, http://dx.doi.org/10.1155/2011/294394.

Cummins, K.W. (1983).  Trophic relations of aquatic insects.  Annual Review of Entomology 18: 183-206.

Kelly, D.W., Dick, J.T.A. & Montgomery, W.I.  (2002). The functional role of Gammarus (Crustacea, Amphipoda): shredders, predators, or both?   Hydrobiologia 485: 199-203.

Macus, J.H., Sutcliffe, D.W. & Willoughby, L.G. (1978).  Feeding and growth of Asellus aquaticus (Isopoda) on food items from the littoral of Windermere, including green leaves of Elodea Canadensis.  Freshwater Biology 8: 505-519.

Willoughby, L.G. (1983).  Feeding behaviour of Gammarus pulex (L.) (Amphipoda) on Nitella.  Crustaceana 44: 245-250.

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This is not a nitrate standard …

Much of my professional life takes place in the collision zone between ecology and bureaucracy.   These make uneasy partners: ecologists like to think of themselves as Lone Rangers riding out to put the world to rights rather than as small cogs in big administrative machines, but the reality is that environmental regulators need both “carrots” and “sticks”, and wielding the latter makes them part of the criminal justice system, with all the responsibilities – and paperwork – that that implies.

I’ve spent quite a lot of time over the past few years working on developing standards for nutrients in freshwaters.   Roughly speaking, I have been helping to define the freshwater equivalent of the 30 miles per hour speed limit.   Speed limits work partly because everyone understands the dangers of driving too fast in urban areas, and partly because we know that there is a good chance of being caught by a speed camera if we drive too fast.   And so it is (or should be) for pollutants: the lower dashed line on the graph of phosphorus in the Ouseburn in the previous post is the “30 mph” limit based on an understanding of how phosphorus interacts with freshwater ecology.   There is a lot I could write about how these values are derived (a subject for another day) but that, in a nutshell, is what we are trying to achieve.

When my students are analysing the data from the Ouseburn, they find standards for ammonia, BOD and phosphorus relatively easily via the UK TAG website but they come to me each year wondering why they cannot find equivalent values for nitrate.  The UK TAG document says “we consider the general understanding of this [nitrogen] to be insufficient at present for it to be used as a basis for setting standards or conditions.”  This was disingenuous in the extreme because I know that DEFRA has been extremely reluctant to set standards for nitrogen as this would focus attention on agricultural pollution which is both much harder to manage and would incur the ire of the farming lobby.   A few years ago, Nigel Willby and I calculated the nitrogen concentrations that would support good status in UK rivers as a by-product of a project to revise phosphorus standards.  We had the data we needed and it struck us that no-one would turn down our “buy one, get one free” initiative.   Not so.  Our figures for nitrogen were quietly excised from our report using the very good argument that it was going to be a hard enough job to argue the case for tighter phosphorus standards without confusing the issue with nitrogen too.  Since then, little has happened, as far as I know, to push nitrogen up the regulatory agenda.

The table below shows these values simply to indicate the values of oxidised nitrogen (which is mostly as nitrate rather than nitrite) that are associated with different levels of ecological status in UK rivers.  They have no regulatory significance, but should give us a rough idea of how much nitrogen is “too much” when we are trying to understand the ecology of a river.

Predicted Total Oxidised Nitrogen (nitrate-N + nitrite-N)  concentrations associated with EQR values modelled for two altitudes (20 and 200 m asl) and four alkalinities (10, 50, 100 and 200 mg L-1 CaCO3).   Boundaries are normalised at 0.8 (high/good), 0.6 (good/moderate), 0.4 (moderate/poor) and 0.2 (poor/bad)); 0.7 and 0.9, therefore, represent conditions at the middle of their respective status classes.

ton_threshold_table

Applying these values to the Ouseburn, a lowland, hard water river, we see that most of the values lie below this threshold except for those from Woolsington, the headwater stretches which are surrounded by agricultural land where there is likely to be extensive use of artificial fertilisers.   The open circles on the right of the graph are values collected by my students each autumn, which may explain why they are lower than the annual mean values that the closed circles to the left represent.  But note, too, the high values in the Airport tributary in the early 1990s.   These occur at about the same time as the high ammonium concentrations that I discussed in “Part of the problem?”.   The ammonium that the airport released into the stream has a nitrogen atom bound to four hydrogen atoms using strong bonds.   Some microorganisms are able to break these bonds and use the energy that is released to drive their own cells.   This is what we see in Airport tributary where the high nitrate is the result of a two-step process that breaks down the ammonium first to nitrite and then to nitrate.

no3n_in_ouseburn

Trends in concentrations of nitrogen as nitrate in the Ouseburn over time.  Woolsington is upstream of the airport, Airport tributary (Abbotswood Burn) receives runoff from Newcastle Airport and Jesmond Dene is about 10 km downstream from the airport.  Closed symbols are annual means of data collected by the National Rivers Authority and Environment Agency; open symbols are means of data collected and analysed by Newcastle University Geography students in October (once also in February) of each yearThe dashed line is the modelled concentration above which the river is unlikely to support “good ecological status.

The final graph shows concentrations of nitrogen as ammonium and nitrate at the three sites we’ve been examining, along with the (official) standard for nitrogen as ammonium plus my unofficial guide value for healthy nitrate-nitrogen concentrations.  This gives us four quadrants, with bottom left representing situations where both forms of nitrogen are at concentrations that should not significantly impair ecology.   This is the case at the two sites downstream from the airport from the mid-1990s onwards, once ammonia concentrations were under control.

The top right quadrant, by contrast, has just a small number of values from Airport tributary from the early 1990s, when high ammonia was rapidly oxidised to yield high nitrate-nitrogen concentrations too.   A further cluster of sites, mostly from Airport Tributary and Jesmond Dene, also have high ammonium concentrations, although nitrate-nitrogen concentrations are below the threshold.  Finally, at the top left, we have values from Woolsington where concentrations of nitrogen as ammonium are low but nitrate-nitrogen concentrations may be a problem, due to agriculture.

For a river that is less than 20 kilometres from source to mouth, there is a lot happening in the Ouseburn, which makes it ideal for students to become acquainted with the complexities of environmental regulation.   You can read the history of pollution control in the graphs of data too: from intercepting toxic point sources in the 1980s to more general concerns about overflowing storm sewers in the 2000s and, now, more interest in diffuse nutrient pollution from farmland in the headwaters.   That, too, is a good lesson for undergraduates: pollution, itself, is not an unambiguous concept and its definition has evolved as our understanding increases.  One lesson that we can draw from this episode about nitrate standards is that the scientific argument about sensible levels of any pollutant can quickly become obscured by politics and vested interests.  That can never be a good thing.

ouseburn_nitrate_v_ammonium

Relationship between nitrogen as ammonium and as nitrate in the Ouseburn between 1989 and 2016.  The diagonal line has slope = 1 and the horizontal and vertical dashed lines indicate the position of the maximum concentrations that are likely to support good ecological status.   There is no differentiation between Environment Agency data and data collected by Newcastle University students on this graph.

A river is reborn …

I started to tell the story of the Ouseburn in the previous post, but have not yet reached a happy ending.  The Beast that is Newcastle Airport has been transformed, if not by a kiss, then by intelligent regulation, but the river is still far from being beautiful.   The Environment Agency, the Handsome Prince in this particular fairy story (has it ever been described in such terms before?) needs to ride out to find other monsters to slay.

One candidate that my students usually identify in their write-ups is phosphorus, whose concentrations have gradually crept up over the years, as the graph below illustrates.   As in the graphs in my previous posts, I have differentiated between data collected by the Environment Agency and my students.  I have also circled a cluster of points that sit outside the main trend, as a reminder that my students are still learning their craft, and sometimes may make mistakes.   The trend is, nonetheless apparent: the river has had elevated phosphorus concentrations for as long as measurements have been taken, and concentrations are gradually creeping upwards.  The student’s data may exaggerate this slightly, but the trend is definitely there.    Although no sewage works discharge to the stream, there are plenty of storm drains, and there are concerns that domestic “grey water”, and its associated detergent residues, may be entering these rather than the foul sewers.  More recently, a study as part of the Ouseburn River Restoration Project (ORRP) has found that some farmers in the upper part of the catchment are stockpiling farmyard manure on behalf of livery stables and some of the leachate from this may be entering the upper stretches of the river.

phosphorus_in_ouseburn

Trends in concentrations of reactive phosphorus in the Ouseburn over time.  Woolsington is upstream of the airport, Airport tributary (Abbotswood Burn) receives runoff from Newcastle Airport and Jesmond Dene is about 10 km downstream from the airport.  Closed symbols are annual means of data collected by the National Rivers Authority and Environment Agency; open symbols are means of data collected and analysed by Newcastle University Geography students in October (once also in February) of each yearThe lower dashed line is the UK environmental standard for reactive phosphorus to support “good ecological status”; the upper dashed line is the threshold between “moderate” and “poor” status (the threshold between “poor” and “bad” status is at 1.04 mg/L).

In addition to problems such as phosphorus that we can see from our analyses, there are problems that are less obvious because they only happen occasionally, and not necessarily when a sampler is dipping a bottle into the river.  The Pantomime Villain of this story (“He’s behind you …” “oh no he’s not”, “oh yes he is …”) is the overloaded sewerage network and, in particular, the storm sewer overflows which divert foul waste into the river when the sewers are overloaded with surface water from heavy rain.   Even though the graphs in the previous post showed that ammonia and BOD are usually at low levels, there will be short periods when the storm sewers dump raw sewage into the river.  This is a great lesson to my students in why biological monitoring is so necessary: the poor quality of the invertebrate community reflects the state of the river through the whole year, not just the minute or so when the sampler’s bottle is being filled.

A combination of hard impermeable surfaces, the drainage system with its overflows and many artificially-straightened lengths of the river mean that storm water makes its way very quickly to the stream (see “Fieldwork in the rain”).  In extreme cases this can lead to homes and businesses being flooded.   These straightened sections of the river also mean that there is little variation in velocity to create the variation in habitat that would allow a range of organisms to find suitable conditions to thrive.   So another of the objectives of the ORRP is to restore the natural meandering path of the river in the upper stretches as a first step towards creating a more natural river which will, at the same time, slow the flow and reduce the likelihood of flooding downstream.   New property developments such as Newcastle Great Park have been designed with Sustainable Drainage Systems (see “In search of SuDS …”) to create more permeable areas that will soak up rainfall and slow its journey to the river, reducing the size of the flood peaks associated with heavy rainfall.

ouseburn_challenges_oct16

Challenges facing the Ouseburn: left: Newcastle Great Park, one of a number of new or planned housing developments in the upper part of the catchment; right: straightened river channel near Three Mile Bridge beside the Great North Road in Newcastle.

To be honest, there are many grander rivers in the country than the Ouseburn where I would prefer to do my fieldwork.  I feel privileged to be able to visit the River Ehen in the Lake District on a regular basis.   We rightly worry about maintaining fragile ecosystems and rare species in these remote places but the Ouseburn presents equal, if less romantic, challenges.   Most of us are urban, rather than rural dwellers and our most likely interactions with the aquatic world will be with these artificially-straightened extensions to our overloaded sewerage systems.   There is something of Frankenstein’s monster about these rivers: at their worst, in flood, they are our own creations, the result of our own attempts to overrule nature.  So I am very enthusiastic about the work of the ORRP and similar schemes around the country.   These are a small step towards restoring a natural harmony between man and water, and working with, rather than against the powers of nature.  And creating a greener, more pleasant urban milieu in the process.

Part of the problem?

deicer_at_schiphol_dec16

My Newcastle University students are in the final throes of writing up their assignment on the ecological health of the Ouseburn, a small tributary of the Tyne that flows through Newcastle, so I could not resist taking these photographs as my flight from Amsterdam to Bucharest was sprayed with de-icer.  The primary point of the assignment is to make my students better scientists, but I like to also use it to remind them that they can never wholly isolate themselves from the systems that they study.  Most of my students live in the Ouseburn catchment so they are all contributing to the problem that they are simultaneously trying to solve.   And, as I set out this morning on my flight to Amsterdam, I watched de-icer being sprayed and remembered that this, too, may find its way into the Ouseburn.  We are all polluters.  And, these days, the polluter pays …

Newcastle Airport plays a big role in the story of the Ouseburn.  It occupies quite a large site in the upper part of the catchment and has grown over the years from the humble structure which I remember from the 1980s to a major regional airport.  The environmental impact increased as the airport grew in size, particularly in the winter as de-icer drained from the ‘planes, via a small tributary, into the Ouseburn.   The graphs below illustrate this very well.  The original de-icer was a mixture of urea and glycol.  Urea breaks down rapidly to ammonia and, at its peak in 1993, the annual average concentration in this tributary was 35 milligrams – sixty times more than the current target for “good status”.  Over six tonnes of urea could be applied in a single day at this time.

ammonia_in_ouseburn_over_ti

Trends in concentrations of nitrogen as ammonium in the Ouseburn over time.  Woolsington is upstream of the airport, Airport tributary (Abbotswood Burn) receives runoff from Newcastle Airport and Jesmond Dene is about 10 km downstream from the airport.  Closed symbols are annual means of data collected by the National Rivers Authority and Environment Agency; open symbols are means of data collected and analysed by Newcastle University Geography students in October (once also in February) of each yearThe lower dashed line is the UK environmental standard for ammonium-N to support “good ecological status”; the upper dashed line is the threshold between “poor” and “bad” status.

The “yin” of serious pollution in the Ouseburn has, however, been offset by the “yang” of environmental management as the authorities circled around the problems, gradually learning about the river and using regulation and legislation to tackle the issues.   So the graph also shows a rapid decline in ammonia concentrations in the river after 1992 as urea was replaced by a different de-icer, this time based on potassium acetate.  Ammonia concentrations are now generally well within the limits required to support good status, so we should have expected to see organisms characteristic of healthy streams to re-appear.

It has not happened, alas.  As is usually the way, pollution problems are multilayered, like the skins of an onion, and peeling away the first and most obvious problem only reveals further issues lurking below.  In the case of the Ouseburn, the switch from urea to (glycol) created a new problem, as microorganisms in the river were able to use this organic compound as a source of energy, sucking vital oxygen out of the water in the process.  You can see this in the second graph, which shows biological oxygen demand (BOD).  Note how it peaks in the years just after the switch from urea.  Note, too, how values fluctuate (dependent, presumably, on the severity of the winter) and, again, how the peaks exceed the current target for “good status”.   But, on a positive note, more recent values are much lower, as the airport now has better facilities for handling surface water drainage.

bod_in_ouseburn_over_time

Trends in biological oxygen demand (BOD) in the Ouseburn over time.  Details as for the graph showing ammonium-N.

Even after this, however, the river is still in a state that is far from acceptable.  The final graph in this post shows the state of the invertebrates in the Ouseburn (expressed as average score per taxon).  This has gradually crept up over the years but, as can be seen, is still not yet at “good status”.  When we empty the contents of our pond nets into trays and take a look, we see lots of pollution-tolerant water hoglouse (Asellus aquaticus) and freshwater shrimp (Gammarus pulex), bloodworms (Chironomous riparius) and leeches.  There are very few of the caddis flies, stone flies or may flies that we associate with clean water (with the exception of the relatively tolerant Baetis rhodanii).    There are more layers of this onion that still need to be peeled away and I will return to these in a future post.

aspt_in_ouseburn_over_time

I will finish where I began: sitting on an aeroplane that is being sprayed with de-icer.   I’m an ecologist and my particular specialism means that I often need to travel around Europe.  Flying is the only practical way of doing much of this but, in the process, I become part of the problem whilst hoping that I am part of the solution.   I also teach part-time in a Geography department along with colleagues f whose professional calling often makes international travel a necessity.   It makes for some uneasy moral choices.   At worst, we develop a tough veneer that insists that the good we do far outweighs the negative effects of our carbon footprints.   At best … well, perhaps that is not for me to say.   Maybe simply remembering that our travels mean that we are part of the problem should make us approach the systems we study with a little more humility and rather less sanctimoniousness …

References

Turnball, D.A. &Bevan, J.R. (1995).  The impact of airport de-icing on a river: the case of the Ouseburn, Newcastle upon Tyne.  Environmental Pollution 88: 321-332.

A typical Geordie alga …

If the photograph below looks vaguely familiar it may be because you are old enough to remember the 1970s as this scene of the Ouseburn valley in Newcastle is part of the opening sequence of Whatever Happened To The Likely Lads? Were they to revisit now, Terry would be appalled, but proto-bourgeois Bob delighted, to see the first stages of gentrification creeping through the area.

Ouseburn_valley_Newcastle

Lime Street, Ouseburn valley, Newcastle, March 2015, looking upstream towards Jesmond Dene. The entrance to Seven Stories, the National Centre for Children’s Books, is just visible on the right of the picture.

Follow the road off to the right and you pass the Cluny, a pub with a good range of real ale and a strong reputation as a live music venue, then past a warehouse (now converted to artist’s studios) to an old ford across the Ouseburn. I wrote about the Ouseburn back in October, when I made my annual visit with a group of undergraduates but the section I have brought you to today is close to the point where the stream joins the Tyne, and is tidal. I had seen some interesting growths of diatoms here in the past so had come back at low tide to add a brackish dimension to the story I was telling in The Ecology of Cold Days.

I was looking for the chocolaty-brown film on the tops of rocks, similar to those that I described in my earlier post but these were not obvious today. Instead, I found some intriguing diatom growths on the vertical wall of the old warehouse just above the water level. I scraped up some of this film and took it home for a closer look.

These samples were, as I expected, teeming with diatoms, though the assortment of diatoms that I could see was quite different to those I had seen before.   I have written about estuarine diatoms in a couple of posts (see “In the shadow of the Venerable Bede”) but do not pretend to any great expertise. However, most of the genera are familiar to me from freshwaters, even if I cannot name the species.   I could see Navicula and Nitzschia, both common in the river samples that I wrote about in The Ecology of Cold Days; however, the most abundant genera were a species of Surirella (also common in freshwaters) and, in particular, Entomoneis; a genus that is relatively rare in freshwater (see “The Really Rare Diatom Show“).

Ouseburn_diatom_film

The view down the Ouseburn; the former warehouse (now artist studios) is on the right foreground; beyond is the back of Seven Stories.   The right hand image shows the diatom film just above the waterline on the side of the warehouse.

Entomoneis is a diatom whose structure is difficult to capture in a photograph as the cells are twisted around the apical axis (see Chris Carter’s photographs in The Really Rare Diatom Show). The right hand image below is an empty frustule lying in girdle view; the other four images are live cells. The constant motility of the living cells was an additional complication as I was trying to photograph them.

Common features about all these biofilms that I’ve written about over the past year is that they are dominated by diatoms that are capable of movement and they seem to be especially luxuriant in the cooler times of the year.   Being able to adjust their position is, obviously, an advantage in an unstable environment where there is a chance that particles will shift or new ones be deposited, robbing the cell of the light it needs for photosynthesis.   Luxuriance in the winter and early spring may reflect the absence of grazers at these times of the year, but there are also hints in the literature that some algae are particularly well adapted to growing at low temperatures. It is natural selection in action: having a physiology that functions in cold water lessens the chances of the fruits of their photosynthesis being turned into another organism’s roughage.

Entomoneis’ fondness for the cold extends far beyond north-east England: a recent paper recorded it as the most abundant alga growing on the underside of sea ice in the Antarctic. It is, in other words, a typical Geordie alga, swaggering through the Ouseburn’s biofilms dressed in a tee-shirt, regardless of the weather. Terry would have approved.

Entomoneis_Ouseburn

Entomoneis sp. from the tidal section of the Ouseburn, March 2015.   The right hand image is an empty frustule.   Scale bar: 10 micrometres (= 100th of a millimetre).

Reference

Archer, S.D., Leakey, R.J.G., Burkill, P.H., Sleigh, M.A. & Appleby, C.J. (1996). Microbial ecology of sea ice at a coastal Antarctic site: community composition, biomass and temporal change. Marine Ecology Progress Series 135: 179-195.

Fieldwork in the rain

Fortune dealt a bad hand for the annual GEO2042 fieldtrip to the Ouseburn.   For the first time in six years, it rained before and during our visit to collect water and invertebrate samples.   By lunchtime, the water levels had gone up so much that we were worried that the afternoon’s session may have to be abandoned, for safety reasons. Fortunately, the rain eased at about 1300 and the river levels started to drop again.

Ouseburn_fieldwork_GEO2042

Fieldwork on the Ouseburn, Jesmond Dene, October 2014. Left: kick sampling for invertebrates in the river; right: investigating the contents of a pond net.

The progress of the day’s storm are neatly demonstrated on the Environment Agency’s excellent realtime water level monitor, situated about a kilometre upstream from where we were working.   The two groups of students were out between 1100 and 1200 and between 1300 to 1400 – either side of the highest level recorded at about midday.   Look how quickly the water level rose from the baseline.   This particular rainfall followed a long period of warm, dry weather, which has kept water levels down all over the region. The Ouseburn flows through built up areas of Newcastle for most of its short length, which means that a lot of the water will run straight off hard surfaces, into drains and into the river.   Hence the rapid rise of the river levels, followed by the gradual drop as the water that had soaked into the ground gradually found its way to the river. Compare this brief storm event to the hydrograph for the River Coquet that I showed earlier in the year (see “Fieldwork in Northumberland”).    In this instance, the river level went up more gradually, reflecting the much lower proportion of hard surfaces in the upstream catchment, before gradually declining.   To the trained eye, these graphs show the effect of man’s alteration of rivers just as clearly as any measurement of “pollution”.

Ouseburn_levels_141006

River Levels in the Ouseburn, 5th – 7th October 2014, from the Environment Agency’s monitoring station at Crag Hall, about a kilometre upstream from Jesmond Dene (http://apps.environment-agency.gov.uk/river-and-sea-levels/120691.aspx?stationId=8058)

One of the legacies of less-enlightened times that we have inherited is a system of combined sewers that carry both foul waste (don’t ask) and storm runoff.   One effect of prolonged rainfall is to fill these sewers with water from drains and, for this reason, there are overflows built into the system which let the excess flow straight from the sewers to the rivers.   Unfortunately, this overflow includes untreated sewage as well as storm runoff and, by Monday afternoon, the river had a distinctly unsavoury odour. The long-term plan is to replace these combined sewers with separate networks of storm drains and foul sewers. That, however, will take a long time, a lot of money (an awful lot of money) and, as most sewers run under our roads, serious disruption, to implement. So we will probably have to live with these combined sewer overflows for some time to come.

A hint for any GEO2042 students who have read this far: link the words “Ouseburn” and “combined sewer overflows” in your minds now. This might come in useful when you write up your project later this term.   Enough said