The carbon dioxide devil is the small scale detail



 Science is good at generalising, sometimes even when it shouldn't. One of the twentieth century's great ecological insights, the ecosystem as a formal idea, is essentially a means of generalising habitats into a series of flows and reservoirs of gases, energy or nutrients. You can scale this up to a whole planet. Scaling down might be trickier. Pete is experimenting with scaling down, measuring carbon dioxide and methane exchange rates in different ponds. Here he is at Hauxley using the gas analyser (the yellow box) linked to a plastic chamber floating on one of the experimental ponds and allowing small scale measures as the gases exchange between the water under the box and air trapped inside. In this case carbon dioxide was bring dissolved down into the water. At the same time the pH in the pond was high, ~9.0 which is markedly more than you'd expect for a natural, clean pond in north east England. Except that this pond was being blasted by mid afternoon sunshine and, being full of plants, it is likely that photosynthesis was elevating the pH as the plants strip out HCO₃ ions toget at the CO₂ but in the process release  OH^- ions into the water raising the pH. Here is the gas chamber with the pH probe just to the top left

Pete also tried the measures in the pond next door. This time the pond appeared to be a net releaser of  CO₂ gas. Generalising for these two, adjacent ponds would be tricky. The variability of animals and plants between near by ponds is well established, one of the reasons they are such biodiveristy hot spots at the landscpae scale. It is beginning to look like they are just as variable in the way their gas fluxes work. the fine scale detail matters, whether it is counting up numbers of ponds, the variation of animal and plant communities between sites or the geochemistry.

From a small pond to the heavens

Whilst Pete and Scott have been trying out the elemental analyser in the lab the spring sunshine lures me back out into the field. Here is a perfect example of how field work stretches the imagination and challenges what is possible. The little ponds at Hauxley were dug out in 1994 to start off experiments tracking the changes to their wildlife over the years. I had not planned that the monitoring would last twenty years but it has. Better still the documented history of the ponds has been a boon for the new work exploring carbon capture: we are able to check the past hydrology and plant data from each pond to explore how those changes might influence carbon levels in the sediments. Neat. Meanwhile, overhead the last of the winter geese gather, stacking up in squadrons, circle to let stragglers catch up with the security and economy of the flying Vs. They will be off soon, a little piece of the Druridge Bay ecosystem unplugging itself and migrating to new lands. They will be carrying energy, microbes, maybe even the occasional plant seed or insect egg with them. Part of the Hauxley experiment will have gone away, not that the geese use the pond field much; it is the haunt of crows and teenage heron. If all the geese did choose to land in the pond field and bathe, graze and poo in the ponds the habitats would be much impacted. The experiment would have been changed, but perhaps in more intersting ways. The pond experiment is therefore not so neat. I cannot radio-control skeins of geese to migrate where I want them to, land them in a field of my choosing or slough off old feathers, seeds and eggs under my control. Field work has that unpredictable thread running through it, part of the appeal for me. Along with the wheeling geese and strengthening sun.

Lab coat? check. Goggles? Check. Elemental Analyser? Check

The public image of science often plays to the idea of men in white coats. It can be women, but the cliché is generally male.  Labs are intimidating places. For our first year undergraduates one of my aims is to get them to enjoy being in labs, relax a little, not be intimidated by the hardware most of which I do not know how to use either. It is a tricky balance in the day to day struggle to detach 18-21 year olds from their mobile phones, which should be safely put away in lockers. Perhaps there is a specific psychology around labs versus field work. Put me in a swamp with mosquitoes, dragonflies and toads and I’m happy. The unpredictability of fieldwork (nudists, motorbike gangs, stoats trying to help....) is the charm. Field experiments and surveys are inherently prone to interesting (mis)fortune. The interplay between the predictable, systematic processes and the unexpected strikes me as an irresistible core to the natural world. Conversely I know scientists who find the uncertainty of nature troublesome but they are superb sleuths for the precision and detail that a lab allows. It is easy to paint this as a difference between whacky explorers versus OCD geeks but that is a daft conceit. Both outlooks represent a fascination with deep and troublesome problems, often working best when brought together.

Pete and Scott spend a great deal of time out in the field at Druridge Bay, slogging through the mud, digging out sediment  cold and battered by the wind, but are equally good in the lab. Here they are getting to grips with the new elemental analyser. This will allow them to measures organic carbon in their cores and wetlands much more exactly.  “Elemental analyser” is also hard to say. Try it out loud. Perhaps this is my lab-angst showing itself. I watched for a little while but was generally superfluous to the training. Scott and Pete have been working with undergraduate project students Paul White and Chris Maguire who are measuring sediment carbon from new sites along the Bay but also some restored peri-urban landscapes in Gateshead where wetlands have been engineered into old industrial sites. Two years ago those same undergrads might have been just as uncertain in the labs as our current first years, but, given the opportunity to get involved, flourish.

The pond gas detective: tupperware and hi-tech

The new field season is underway at Druridge Bay. Pete has been experimenting with measurements of carbon dioxide and methane fluxing in and out of the wetlands. This needs a delicate mix of high-tech gas analysing kit cunningly attached to an upside down plastic sandwich box wrapped round with an old bicycle tyre inner-tube as a flotation device. Here is Pete gently positioning the floating box over the grassy shallows of a pond in a grazing meadow. The red and blue tubes allow gasses to be pumped through the analyser sitting snuggly in its black case perched on a plastic box (it does not like water), which records the changing concentrations. Pete's design uses a small floating chamber so that we can position the box over the distinct plant communities such as amphibious grasses or submerged pondweed in the ponds. There is something very immediate about watching the measures tick up on the digital displays. Suddenly the invisible chemistry is brought to life, the molecules in the air made apparent, complementing the seeping cold and the calls of the last winter geese, who did not approve of all this fiddling about in their field. The technology is, as usual, temperamental and easy to de-calibrate with one push of the wrong button but also very impressive when it switches from prima donna to primary data collection. Pete's first try outs showed steady carbon dioxide release with methane too, although at much lower concentrations. As Spring builds and the plant growth surges he will be aiming to capture gas fluxes from different pond types and plant communities. Early results show some pond types pumping out carbon dioxide whilst others are much less active. As with their plant and animal communities it seems that ponds represent a fine-grained diversity of geochemical drivers. If we can combine the flux measures for different pond types with data on the organic carbon trapped in the sediments we should be able to identify the wetlands that make the most powerful carbon sinks, perhaps even the role of different plant communities in these processes. Just so long as the wrong button does not get pressed.....

The classic Christmas crisis: "i think these batteries are flat"

Science sometiems depends on the right bit of kit to measure, map or probe. Personally I'm a great fan of lo-fi and mostly use a pond net and a white plastic tray. Not much that can go wrong there, although the wind that whips across Druridge Bay can pick up a tray and hurl  it across a swamp with nonchalent ease. However detailed chemistry requires proper measures and we have just got a new probe which will allow Scott to measure the chlorophyll, oxygen and conductivity in his experimental ponds simultaneosuly and live in the field. It came in a tough, field protable case which was opened with glee to reveal the shiny, exciting bits and pieces. Even came with its own screw driver. Here are Dave and Scott having a first go at starting it up in the office. In perfect synchrony with the seasons the batteries that came with it were flat. How many Christmas Day mornings throughout the UK have been blighted by that howl of anguish? You see why I like a net and a plastic tray.... They'll get it working I'm sure.

This Druridge Bay pond blog has been going for just a bit over a year now. We are taken aback by the global coverage: Russia, Argentina, South Africa, Latvia, Canada... Even if you have stumbled across Ponds, Time and Place accidently I hope something of this magical landscape has lightened your day and the mysterious lives of the pond plants and animals have captured your imaginations. Merry Christmas to all our readers.

The ostracods eat their spinach

The three ostracods featured in the last blog are typical of their kind; widespread in small ponds and pools, especially those prone to drying, relying on tough eggs to resist drought. During the good times when ponds flood again they use asexual reproduction to churn out young through parthenogenesis, the process in which unfertilised eggs develop and mature. Despite the adults tough bivalve carapaces many predators catch these small prey. Dragonfly larvae and water boatmen have been shown to reduce populations significantly. The Ostracods respond by changing behaviour migrating to safer parts of the pond. Heterocyrpis incongruens reacts to chemical cues in the water, shifting to more open water and being less active. Moving about less is potentially tricky for male ostracods in search of a mate, although experiments to compare predation on sexual versus asexual individuals of Eucypris virens showed no marked difference in vulnerability. Male ostracods are unknown for some species, but it seems unlikely that being eaten is the cause of this absence. Asexual reproduction could have advantages faced with intense predation, because one female can potentially found a population.  Ostracods themselves seem to be rather generalist feeders but with some preferences. Eucypris virens has a liking for spinach when offered a variety of foods and also Tolypothrix tenuis a type of cyanobacterium, a combination humans are unlikely to encounter outside of an extreme sushi bar. Animal prey can be on the menu too, especially sickly or injured larger creatures, who can be overwhelmed by the sheer number of ostracods ganging up on them. ... perhaps, like Popeye,  it’s is the beneficial effects of all that spinach.

Schmit, O. et al (2012) Vulnerability of sexual and asexual Eucypris virens (Crustacea: Ostracoda) to predation: an experimental approach with dragonfly naiads. Fundamental and Applied Limnology, Vol 181, 207-214.

Schmit, O. et al (2007) Food selection in Eucypris virens (Crustacea: Ostracoda) under experimental conditions. Hydrobiologia, Vol 585, 135-140.

Pea shrimps: the charm of the Ostracoda

Amongst the scurrying, skipping and gliding specks at the bottom of a tray of pond life there are certain animals notorious for being tricky to identify and generally misunderstood. The jelly-bean like threesome above are all members of just such a group, the Ostracods, sometimes called pea shrimps. Most of what you can see are two valves, largely enclosing a scrunched up body with a handful of antennae, legs and other sticky out bits. They are little crustaceans, their jointed limbs at least giving away their kinship with more familiar water fleas and shrimps. Identification is tricky, largely needing a good view of the legs and antennae, “extremely difficult and can only be undertaken by a specialist ” as it says in Wolgang Engelhardt’s classic The Young Specialist looks at Pond-Life. Whilst ecologists may be wary of this awkward group geologists have a wealth of knowledge of their historic distributions, using fossils of the tough valves and the various shapes, spines and surface sculpture. Size, colour and shape are handy for the living adults and these three are fairly distinct: Herpetocypris reptans, Heterocypris incongruens and Eucypris virens. The “cypris” bit of the names is essentially saying “shrimp”. All three are a millimetre or two long, stuttering uncertainly across the sediment in search of food which can be any old detritus but they can gang up on enfeebled prey too. Although individually small their populations are robust, sustained through the ups and downs of drought and flood by desiccation resistant eggs, so they often appear in puddles and flashy pools. Heterocypris incongruens in particular seems to prefer these conditions and is lost from ponds as permanent, dense emergent plants such grasses and spike rush colonise. Under a microscope they are objects of great beauty, their valves sculpted or fringed with bristles and serrations. I am fond of these enigmatic beauties.