Saturday, October 21, 2006

Various buckets and tanks

October 7 2006. Photograph the various buckets and tanks used for floatation in seawater experiments and also the now dry coconuts and pinecones. Various items and topics are reviewed here. In experiments involving fruit and wood a white bacterial film grows on the surface of the water and these objects even with frequent aerations or exchanges with new seawater. Probably sugar solutions exit the fruit and feed the bacteria, which then deoxygenate the water if they die and sink to the bottom. In addition materials such as wood and pinecones eventually stain the water brown and also make it form a foam when shaken-up, which then inhibits oxygenation. One pair of photographs, in different lighting conditions, shows a relatively new seawater on the left with apples in it and an older seawater with only less active materials present since this right-hand water was previously used to float apples and has been stained slightly brown by the pinecones.

two buckets with apples and wood showing white bacteria
two pails Posted by Picasa


In it there is a greater quantity of white bacteria present. What is odd is that only the nearly emergent tops of these and other pinecones are stained white while it is the submerged upper parts of the wood and apples, which develop this white film. To some extent it just defines a waterline on inert materials, such as the plastic bucket and floating coconuts; but on the cones it also extends higher than this level film. Consequently when coconuts are removed and dried one can see a waterline of white or grey bacterial and algal staining present where they spent most of their time floating, and this also provides clues in Nature about drifting orientations on shells since I have recently cut some wood in the garden, due to the drought/subsidence problem outlined previously. It was interesting to compare the densities of instantaneously cut and floated wood in their summer state of moisture. Hawthorne logs sank straight away in seawater, but samples left ash cut ends on the tree before further cutting sometimes floated for a few minutes. Elder wood generally sank instantaneous but a few samples did float without drying, but only for a few days. When that is the case then longer sections of wood, termed logs, float longer than slices cut from between them, due to rates of water and air inside the structure being involved. Also as one moves from the stem to the thin twigs, even of Hawthorne, the floatation times increase, presumably because the new wood is less dense. Thus when one considers a less dense wood such as Ash, the twigs can float longer than the logs because they are initially less dense and more liable to dry if left on the ground. On the other hand the logs float longer than smaller slices of the same density and some twigs, due to rates of waterlogging and decay being increased when the surface to volume ratio is larger in a smaller structure. In a further complication seasonal variations in moisture change both the initial density and the rates of waterlogging. The photograph shows two logs of an Ash Fraxinus still floating after 7 days, compared to one and two days for the wood slices of 10 to 20mm length which were cut off them before floatation.

two pails with logs in them
2 pails Posted by Picasa

The logs have a length around 195 mm and diameters around 65 mm, representing the base of a major twenty-year old branch. Judging from previous tests done at this time of year on an adjacent branch these logs may only float in these buckets until November, while the record for Ash twigs is held by one cut in November 30 2000 that sank after 276 days (diameter 19mm, cut to 74 mm length and kept in plastic bag until floated December 16 2000).

The associated floating objects in the left hand bucket are four apples of Malus domestica Borkhausen which fell from the tree and were floated in the morning of September 8 2006 (out of a sample of 10, 4 have sunk, 2 others float in another container), a wine cork made from Quercus suber L. which has nearly sunk after being floated on March 12 2001 (it can hardly be seen in the photograph, being tilted up and almost submerged) and the last of a batch of 8 Pinus nigra Arnold cones collected and floated on September 11 2006. The other bucket shows some driftwood, stranded corks and more recently collected cones from below the same tree. The record from Pinus nigra cones from that tree is currently held by two that fell in winter and floated for 65 days after January 7 2002. This is somewhat mysterious since drier; more open summer cones might be expected to float longer. Colder experimental conditions in winter and the larger size of the cones available that day probably explain that anomaly.

Friday, October 06, 2006

London Clay and climate change

September 29 2006. My diary lists the following dates when rain wetted my garden this year in the rain shadow of the Rayleigh Hills, Essex.

February 12 and particularly 15th.
March 7, 10 and 24 (minor events).
April 1-2 heavy, but short showers.
April 10 extensive rain.
May 14, 16, 20, 22 and 25 (20th and 25th extensive).
May 26, 27, 29, 30 (minor events).
June 13, 14, 15, 21 (minor events).
June 26 extensive rain.
July 5 heavy but short shower.
July 7,9,11, and 22, August 1 and 7 (minor events).
August 13 finally have significant rain.
August 17 extensive rain (minor on 21st).
August 23-24 extensive rain (minor on 26th).
August 28 extensive (minor on Sept 1st).
September 13 extensive rain.
September 22 short heavy shower.

Essex Radio had a program earlier in the week on the subsidence caused by tree roots dehydrating the London Clay terrain in southern Essex this summer. More sandy substrates do not subside in this way but during wetter years, particularly winters when the deciduous trees are not extracting water in this way; they produce springs and slumps at the junction with the London Clay. Presumably having minor sand or silt layers within the London Clay itself has the dual effect of producing a slightly steeper, stronger slope below the dwellings, and a route for tree roots to extract water from the interbedded clays in a dry summer. The tendency to cover Essex with buildings and parking lots, rather than gardens, is encouraged by insurance companies faced with subsidence claims. This in turn reduces the ability of water to wet the subsoil rather than run off down the road, drains rivers and into the sea in a few hours. During wetter weather this rapid exit of the water itself causes problems for property owners living near rivers which cannot hold the increased water supply, often supplied in short thunder storms and a flash flood. Given a larger slope with London Clay below sands or natural streams one can observe major slumps such as the Southend Bandstand visited on May 10.

Southend Bandstand - major slump of London Clay


London Clay drainage problems
London Clay drainage problems, Southend-on-Sea. London Clay slope opposite a river liable to flash flooding along its new concrete channel (below railings on left). Also shows a continuous spring-line above the opposite sidewalk (red warning signs behind cars) apparently from a sandy layer with the London Clay. The finer laminated clays and septaria of the Beaver Tower bed occur below it and reach the sidewalk beside the white car (5th from right). After rain the water exits about one metre up the traditional garden paths in the middle of the photograph. Posted by Picasa


Map showing Southend England
Map showing Southend England. Posted by Picasa

Cuttlebone flotation times

September 26 2006. Between 6.10 and 6.20 hrs. G.M.T. the last of the 25 cuttlebones found and refloated without drying in March 24 to April 3 sank in the seawater tanks. A few 10 mm long fragments of reed collected with them have remained floating, although many hundreds sank within a few days. Data for the Whelk egg cases also stranded around that time showed no correlation with their size and a wide variation on a shorter time-scale (e.g. 12 ranged from 1.6 to 54.65 days, with an average of 38.0 days). Intact cuttlebones of the same species and morphology would be expected to show a linear correlation between floatation time and length, due to the volume of gas being extracted and replaced by seawater via the porous surface area of the striated ventral chamber openings. Judging from results in my article in The Drifting Seed (2006) a large cuttlebone from the North Sea floats for four years in the test conditions reviewed here and the small shells stranded in March might float for one year or more. However, these predictions are modified by breakage and puncturing of the shells by fulmars presumably while the shell is still associated with the floating corpse of this squid-like animal. Moreover, some water is present inside the shell in life and more soon enters when they are punctured before stranding on an uncertain time-scale. Finally on arrival on the beach the shells tend to break in half and undergo further damage which makes them non-buoyant within a few days. Nonetheless the experimental floatation time is instructive as a guide to the possible transatlantic dispersal of these shells after death and presents some statistical problems due to the wide variation in observed times. In the latest test the original size of the shells is evident from their width, inclusive of their chitinous margin when intact and only ranged from 22 to 39 mm (Av. 30.4). The preserved length of these shells with a probable original length of up to 100 mm averaged 62.7 mm and the ratio of it divided by the with was more proportional to the floatation time than the absolute preserved length ranging from 35 mm (sank 14.4 days) to 96 mm (sank 122.4 days). However, the correlation was still poor, probably because the birds produced many deep punctures in some shells without breaking them. Since the sample was 25 one can remove the median result of 107.3 days, corresponding to the average of 91.0 days, and consider the averages and range in four subsets of six shells. The rapidly sunk set ranged from about 4.6 to 24.0 days (i.e. when they sank in the night, the time was recorded half-way through it) with a mean of 11.7 days and a length/width ratio averaging 1.89 to one. The next six averaged 44.5 days and 1.92 to one. The next six with times greater than the median sample averaged 128.8 days and 2.32 to one, mainly because they were more intact. Finally the six with the longest times, ranging from about 158.1 to 185.4 days average 176.5 days and a length ratio of 2.44 to one. Overall the average floatation time of 91.0 days occupied a rather rare period in a polymodal distribution with the four sunk between 182.2 and 185.4 days perhaps close to the limit for these damaged small cuttlebones?

a cuttlefish
a cuttlefish Posted by Picasa

Northern Fulmar landing on a cliff top at Hunstanton, Norfork, England
Northern Fulmar (Fulmarus glacialis) landing on a cliff top at Hunstanton, Norfork, England. Photograph copyrighted Andrew Dunn, 18 February 2006 (http://www.andrewdunnphoto.com). This file is licensed under Creative Commons Attribution ShareAlike 2.0 License

Posted by Picasa