Algae from the Alto Duoro …

From the highlands of Serra da Estrela w headed north-west towards the vineyards of the Duoro Valley from which the grapes that make port are picked.  I’m supposed to be on holiday but, as the narrow road twists and turns down a steep hillside, with vineyards on both sides, I see a case study in how humans alter rivers and their catchments to suit their needs.  I wonder if the passengers on the cruise ships that move sedately through this beautiful landscape have any idea of just how difficult this same journey would have been just fifty years ago.   Now there are 51 large dams within the watershed, regulating the flow and, at the same time, generating much-needed hydroelectricity.   Before these were in place, the only way to get the port from the quintas in the Alto Duoro to Porto was to load the barrels onto a “barco rabelo”, and then to plot a perilous path through the rapids before using a combination of sail, oars and oxen to make the slow journey back upstream (you can see videos of these journeys on YouTube).

A replica of a barco rabelo moored in the Rio Duoro at Porto, September 2018.

The Rio Douro is a type of river that is rare in the UK but very common throughout the rest of Europe in that it crosses (and, for part of its course, forms) national boundaries.  There are a few rivers in Ireland which straddle borders (the Foyle is one, and some of the headwaters of the Shannon can be found in County Fermanagh) but, mostly, this is a complication that our river managers do not have to face.  By contrast, eighty per cent of the Rio Douro’s catchment lies in Spain (where it is called the Duero) and it is actually the largest watershed on the Iberian Peninsula.   The whole European project, and its environmental policy in particular, makes so much more sense when you are looking at a well-travelled river.

Our immediate objective was the Quinta do Bomfin at Pinhão, which produces grapes for Cockburns’, Dow’s and Taylor’s ports.  However, after a morning walking through the vineyards and following a tour of the winery (the robot that has replaced human grape treaders has, we learned, been carefully calibrated to match the pressure that a human foot exerts, lest the grape seeds are crushed, imparting bitterness to the resulting wine) plus some port tasting, the lure of the river was too strong.

A view across the Douro Valley from Quinta do Bomfin at Pinhão.   This, and the previous two photographs, were taken by Heather Kelly.

The river bank at Pinhão is lined with rip rap (loose stones) enclosed in mesh cages to protect it from erosion from the waves created by the many cruise ships that make their way up the river with tourists.   This, along with the floating jetties at which they embark and disembark, meant that it was not easy to get access to the river; however, I eventually found a small slipway close to the point where a small tributary joins.  There were a few loose stones with a green film in shallow water that I could just reach, plus some algal mats coating the concrete of the slipway at water level.   I managed to get small samples of each to bring back for closer examination, attracting the usual curious stares from passers-by in the process.

The mats on the slipway were composed of an alga (technically, a cyanobacterium) that has featured in this blog on several occasions in the past: Phormidium autumnale (see “In which the spirit of Jeremy Clarkson is evoked”).   This is the time of year when the Douro is at its lowest so living at this point on the slipway means that it spends a small part of the year exposed to the air, but most of it submerged.

Phormidium cf autumnale on a slipway beside the Rio Douro at Pinhão, September 2018.  The left hand image shows the mats on the lower part of the slipway; the right hand image shows individual filaments.  Scale bar: 20 micrometres (= 1/50th of a millimetre).

The stones beside the slipway had a thick greenish film which, when I looked at it under a microscope, turned out to consist largely of bundles of thin cyanobacterial filaments belonging to a relative of Phormidium: Homoeothrix janthina (kindly identified for me by Brian Whitton).   Homoeothrix differs from Phormidium in that the filament are often slightly tapered, rather than straight-sided and usually aggregated into colonies, often growing vertically towards the light rather than intertwined to form mats.   It is a genus that I see in the UK (including, sometimes, in the River Wear) but which I have not previously written about on this blog.   The photos below show tufts of filaments but it would be quite easy to imagine several of these clumps joined together to form a hemispherical colony, before I disrupted them with my vigorous sampling technique.

Left: the rip rap at the edge of the Douro at Pinhão from which I sampled algae in September 2018; right: the stone after vigorous brushing with a toothbrush.

Bundles of filaments of Homoethrix janthina from the River Douro at Pinhão. Scale bar: 20 micrometres (= 1/50th of a millimetre).

Many of my posts try to make the link between the algae that I find in lakes and rivers and physical and human factors in those water bodies and their surroundings.  That is not an easy task in a large river basin such as that of the Douro as there is so much more of a hinterland including large towns in Spain such as Valladolid.   The river, to some extent, integrates all of these influences and, whereas the vines around Pinhão have their roots in nutrient-poor granite and schist soils, the river’s journey to this point has covered a range of different rock types, including chalky clay soils in the Spanish part of the catchment and the water reflect this.   This cocktail of physical alteration and pollution, shaken up with a dash of international relations, recurs in the largest rivers throughout Europe and is either a fascinating challenge for an ecologist or a complete pain in the backside, depending on your point of view.

I’ll come back to the Douro in a few weeks, once I’ve had a chance to have a closer look at the diatoms.  Meanwhile, I have one more stop on my travels along the Rio Douro, at the port lodges of Vila Nova de Gaia to try some vintage port …

Reference

Bordalo, A.A., Teixeira, R. & Wiebe, W.J. (2006).  A water quality index applied to an international shared river basin: the case of the Douro River.  Environmental Management 38: 910-920.

The end of the journey: port maturing in barrels at Cockburn’s lodge in Vila Nova de Gaia.

 

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The stresses of summertime …

One reaches a stage in an ecological career when your “niche” becomes the office not the field and you are expected to focus your hard-earned experience on data that others have collected.  That means that I spend more time than I wish – even in the summer – staring at computer screens and writing reports – and far too little time engaging directly with nature.   Today’s post is the result of a Saturday’s excursion around some of the more enigmatic parts of the Yorkshire Dales National Park (the enigma being, basically, that we spent most of our time in Cumbria, not Yorkshire).

The photograph above shows a steam locomotive hauling a train along the Settle to Carlisle railway as it makes its way through Mallerstang, the upper part of the Eden Valley.   It is a beautiful little valley, hidden away from the main tourist drags and the sight of a steam train imparted a sense that we were somehow detached, albeit briefly, from the modern world.   The river channel itself lies amidst the ribbon of woodland in the valley bottom.

The River Eden in Mallerstang (SD 778 985) with (right) a large pebble with a Cyanobacterial film.

Curious to see what kind of life thrives in such a heavily shaded stream, I hopped over a fence, pushed through some bankside vegetation, crouched down and lent out as far as possible to grab a few of the stones from the streambed.   As I would have expected in a stream in such a location, the slippery film on the stone surface was thin (this is the time of year when the algae and other microbes can barely grow fast enough to keep up with the voracious appetites of the invertebrates that inhabit the crevices among the rocks) but, when I held it up to the light, there was a distinct greenish tinge that piqued my curiosity.

Under the microscope, this green tinge revealed itself to be due to numerous filaments of a thin, non-heterocystous cyanobacterium (blue-green alga), similar to that which I see in the River Ehen (see “’Signal’ or ‘noise’?”).  There, Phormidium autumnale forms tough leathery mats whereas here there was no obvious arrangement of the filaments.   In fact, the filaments seemed to be randomly organised within a mass of organic matter that made photography difficult and the photograph below is of one that had glided into a clear space on the coverslip.   I was surprised that there were relatively few diatoms present but, amidst the clumps of cyanobacteria and organic matter, I could see cells of Gomphonema pumilum, though it was very definitely sub-dominant to the Phormidium.  That was not very easy to photograph either, and my images have been built-up using Helicon Focus stacking software.

Some of the algae living on stones in the upper River Eden, August 2017: a. Phormidium cf autumnale; b. and c.: Gomphonema cf pumilum.  Scale bar: 10 micrometres (= 100th of a centimetre). 

I have seen other streams where non-heterocystous cyanobacteria thrive during the summer months and suspect that their unpalatability relative to other algae may play a part in this.  This is partially induced by the proximity of grazers – a recent study suggested that filaments of Phormidium did not need to come into contact with the grazer itself, only to detect chemicals associated with the grazer in the ambient water.  This, in turn, can promote production of a tougher sheath, making the filaments less palatable.   I’m always a little surprised that aquatic invertebrates find diatoms, with their silica cell walls, palatable, but I see enough midge larvae greedily hoovering-up diatoms to recognise that they know something that I do not.

My brief visit to the upper River Eden reminds me that summer can be a tough time for stream algae.   Not only is this the time that the invertebrate larvae are scouring rock surfaces for algae to serve as the fuel that will catapult them into their brief adult phases, but also the trees are in full leaf, limiting the amount of energy that the algae can capture in order to power their own growth.   Not surprising, then, that so many algae – diatoms and other groups alike – are more prolific in the winter, when the invertebrates are not so active and there is less shade from marginal trees (see “Not so bleak midwinter?” and “A winter wonderland in the River Ehen”).   I’ll probably be sitting indoors staring at spreadsheets and writing reports this winter too, but I’ll still be looking for excuses to get out and explore nature’s hidden diversity.

Pendragon Castle, guarding the entrance to Mallerstang in the upper Eden Valley. 

Reference

Fiałkowska, E.  & Pajdak-Stós, A. (2014).  Chemical and mechanical signals inducing Phormidium (Cyanobacteria) defence against their grazers.   FEMS Microbiology Ecology 89: 659-669.