Wednesday, 31 October 2012

Coring for carbon

Here is the target of Scott’s coring, pictured in last Saturday’s blog; a core of sediment drilled out from the bottom of a pond at Hauxley Nature Reserve. The ponds were dug in a field that was back-filled after the Hauxley coal mine closed. The soil that was used for this was very clayey. To the right you can see the sheer, glistening clay from deeper in the core. To the left side of the core the clay is conspicuously gnarly and flecked with bits of plant; this is the sediment from the bed of the pond and immediately below. The ponds started as bare, square holes but since their creation in 1994 have colonised with amphibious mosses and grasses, or, occasionally, submerged plants such as water buttercup, Ranunculus aquatilitis, and Stoneworts, Chara. As the plants die their debris is mired in the sediment at the bottom of the pond. Where thick swards of moss have covered the bed of the pond the mud underneath has become black and foetid because of a lack of oxygen and these conditions slow natural decay. Hence the top of the core has the accumulated plant fragments, creating the darker, rougher texture. Coring is surprisingly hard work in the clinging clay but the greater challenge is to measure how much organic carbon the plant fragments have locked into the mud. The little ponds are very verdant and productive so the plant growth has the potential to take significant amounts of carbon dioxide out of the air and down into the mud when the plants die. One little pond may not seem very important, but there are a lot of little ponds out there.....

Saturday, 27 October 2012

The carbon economy

October has experimented with the possibilities of every season. Blue skies and the last of the Red Admirals showing off in the sunshine, boy racers at heart, barely alighting long enough to flaunt their colours before away again, impatient. Then fog leaving the Blakemoor wind farm as stumps propping up the gloom or else we’d all be squashed down into the mud and browning grasses. Now snow, the flakes freezing together in an overnight crust . The blues skies in the photo above are Hauxley Nature Reserve scarcely a week ago. Scott is using a corer to drill out a plug of sediment from the little pond. This pond and twenty nine others were dug out in the Autumn of 1994 to monitor the initial colonisation by invertebrates and plants, then how the various species would respond to changes such as dry years or prolonged flooding. This also means we know how old the ponds are to the day, along with their history. Age and history are not the same thing. The ponds are all eighteen years old but some have had a fraught life of drought and flood. Others are more sedate, a steady progress of clogging by mosses and grass. The ponds are the closest we have to a time machine. We can ask questions of their contemporary nature and know enough to check back how their history may be responsible for this. Scott, Pete and Dave are extracting the plugs of sediment to measure the amount of carbon trapped in the mud since the ponds were dug. Some of the carbon is bound up in the obvious fragments of plant which have drawn carbon dioxide out of the air as they photosynthesise but there are also microscopic algae plus bits of plant fallen in from the land around too. The ponds may be small but the verdant plant growth, much of it trapped in the sediment, may be a powerful trap pulling carbon out of the air and down into the mud.

Sunday, 21 October 2012

"An elephant walks over it...." antelope round it and an ant through it” is an evocative summary of how different animals see the world, the “it” being a scrub thicket and the obvious trait being size. Humans are relatively large animals so we see the world through a mix of elephant and antelope scales. Up at the Bay this means we see fields and woodland, dunes and lagoons. Most of the Bay’s creatures are much smaller, so the world becomes much bigger for them and much of our familiar landscape invisible, just as the whole of Northumberland is to any one of us as we walk through it . The photo shows a pond at Hauxley from a water beetles’ perspective. Not that we know how beetles interpret the world but their subtle reactions suggest more than just dull ‘turn left, turn right’ mechanics. One species takes flight more often from ponds harbouring higher numbers of its own kind. This would make sense if the populations were so high that lean times beckoned as beetles overwhelmed their prey. Another species leaves ponds as the density of pond weeds increases beyond a tolerable threshold of tangles and stems, which suggests some sense of space and structure. For some predatory beetles a thicket of pond weed is both a baffle to their hunting and perhaps camouflage for their own predators to use. For invertebrates the underwater wetlands must feel much like the wall of a forest does to our senses. The world becomes a much more complicated shape at beetle size. There are many more ways to crawl and swim, hide and seek. Much smaller than 1mm though and the pattern changes, the world becomes simpler in many ways. The architecture of plants becomes insensible, although surfaces matter very much. Plants are revealed as corrugated or sheer, encrusted or furred.  I know nothing about the microscopic ciliates or algae of the Bay, although they sometimes twitch into view when I’m puzzling over larger creatures. Their world beckons to be explored.

Monday, 15 October 2012

Daphnia HQ

The swarm of water fleas (Daphnia obtusa) featured in the 10th October blog were photographed in a dune slack just across the road from Cresswell Lagoon in 2008. Their pond has changed rapidly and conspicuously. The left hand photograph shows the slack in 2007, largely bare mud, with a tuft of bulrush (Schoenoplectus lacustrus) in the middle and grasses around the edge. To the right is the same field edge in winter 2011, now thickly carpeted with grasses, spike rush (Eleocharis palustris) and silver weed (Potentilla anserina). The Daphnia are more abundant when the substrate is bare mud. Perhaps they are wiped out as the plants create a climbing frame for the many predators which favour the Daphnia as food, or the planktonic algae that the Daphnia themsleves need do less well amongst the thicker stems. If you spend some time watching the twitching shoals of Daphnia you will notice they steer clear of plants or other underwater architetcure. The slack is routinely inundated when Cresswell lagoon overflows across the dune road. The water is saline, which does not cause too much of a problem for the plants and animals in the slack, but cars surfing through the backwash may end up rather rustier rather more quickly than expected. The slack is at its best when largely bare of vegetation. There is a string of thse little slacks along the fence line adjacent to the road, easily overlooked but strikingly beautiful when ochre black mud combines with the flash of shallow water, lurid green of early colonisers such as celery leaved buttercup (Ranunculus scelatatus) and fluted blue-green arches of bulrush.

Wednesday, 10 October 2012

The meek inheriting the Earth

Water fleas are not the biggest or fiercest of pond-life. They are food for most predators: you can even buy them in bags of bloated, farmed fleas for feeding to tropical aquarium fish. The wild water fleas of Druridge Bay tell a more successful story. The water flea, top left, is a species called Daphnia obtusa, a 3-4mm long crustacean and common in shallow, muddy pools along the Bay. You can spot them as jerky specks swimming indecisively hither and thither, although “swimming” is too elegant a description as they row themselves with their antennae (the long arms in the photo).  Their legs are enclosed within the carapace which gives them their rounded shape, each limb equipped with a fine-meshed net of bristles for raking algae out of the water for food. Each Daphnia may not be large, but the photograph to the right shows a swarm of thousands, each speck a Daphnia, in a dune pool near Cresswell. In the good times they reproduce by cloning. Most of the population are female and they develop embryos asexually. In the left hand photo you can see several baby Daphnia, the greenish blobs to the right of the adult’s sinuous gut. This cloning allows rapid population growth. As water levels drop and ponds begin to dry out the Daphnia produce tougher, drought resistant eggs which linger in the mud long after the adult hordes have been wiped out. When the rains come and ponds refill these eggs hatch and the Daphnia numbers boom, benefitting from the absence of fish.  It is a successful strategy; Daphnia obtusa is found throughout Europe and North America as well as just north of Cresswell.

Monday, 8 October 2012

Autumn nerves

Today Druridge Bay glowed in a luminous autumn sun, picking out every gradient of green turning into brown or orange. The low rays saturated the reds; a robin singing on a Blakemoor farm rooftop, Hawthorn berries being revealed as the leaves fall away, the faces of goldfinches working the hedge lines. Enough warmth to bounce back off walls and wood. Deceptive too. One step into the shade and the frost lingered, picking out the edges of lost leaves, waiting for the shadows to move back across, unhurried. The birds seemed overly casual, putting on a brave face but busy. Autumn nervous ticks, still pretending this was summer. The lapwings on Cresswell lagoon could not settle. Every few minutes they would rise, a drifting chequer board, out over the water, white bellies flashing against the sun, then settling back, fidgeting. The Bay makes a fine theatre for the seasons and the wildlife is rehearsing for winter, reluctantly and nervously. Many pools have refilled and the amphibious grasses make a late flush of green. Flote grass, Glyceria fluitans, is particularly vivid, the parallel sided leaves criss-crossing over the surface in a style reminisecnt of the artist Goldsworthy. Look closely and the leaves show occasional runs of pink or purple green in the bright sun. Flote grass and its companions Creeping Bent (Agrostis stolonifera) and Marsh Foxtail (Alopecurus geniculatus) are common enough, often overlooked but it is these pond margins where grass and water refuse to define an edge that are especially rich in invertebrates. If you want a good wildife pond you will do better with straggling grasses than you ever will with water lilies.

Wednesday, 3 October 2012

Six scientists and a bit of plastic tube

Science and scientists are condemmed to suffer from easy cliches: studious, introspective, objective sleuths in pursuit of some incomprensible data. Perhaps scientists are good at hiding a deeper truth in case it is seen as undermining what we do. Science is fun. For example here are Dave Thomas, Scott, Pete Gilbert, Dave Cooke (you met Scott and Dave C in the 20th September entry) and, to the right, Mike Deary, plus me taking the photos, struggling with a complex problem. How do you remove a plug of mud taken from the bottom of a pond using a plastic tube core without demolishing the mud in the process? The core might reveal subtle layering from year after year as the pond silted up, each layer perhaps trapping nutrients from the water and revealing the changing enviroments at Druridge Pools, which is where these cores came from. We have technology worth tens of thousands of pounds able to detect delicate variations in the patterns of elements and molecules. If only we can get the mud out the tube. Watching half a dozen people in white lab coats fretting how to do this without the mud rocketing across the lab as if shot out of a bazooka makes for an entertaining half hour. The expertise in these pictures could explain to you how to separate out different sources of carbon buried in the mud or the process of X-ray diffraction or emergency response to a major air pollution incident. Much more challenging is to take cores whilst teetering in clinging, foetid mud, hammering the tube down without falling over and all the while fending off overly inquistive wild ponies. That needs at least three hands.