Saturday, 1 December 2012

Pond anti-freeze

A clear night has allowed the frost to grip the Bay. You can see to Cheviot through the rain washed air, the hill tops now with snow, though more a light dusting than the full royal icing effect. Thousands of winter geese are milling over the fields at Cresswell, taking their time to land. Against the blue sky last Thursday the distant flocks milled and switched, suddenly lining up then falling apart like the iron filings in one of those magnetic beard sketching toys. The calls of the geese have a counter point in the squeek of new ice which has clamped across most of the ponds. Most but not all. One or two have not frozen over, especially where springs emerge in the fields around Blakemoor Farm. The water in the springs has a peculiarly high conductivity, which is a means of measuring the amount of material dissolved in the water; very pure distilled water has almost zero conductivity because the current needs disolved ions, such as salts and metals, to be conducted. The conductivity in unpolluted ponds in lowland Northumberland varies but is typically 200-300 microSiemens per centimetre. The water in the springs is ~1000 microSiemens. Trouble is that conductivity does not tell you exactly what is dissolved in the water, although our occasional attempts to pin this down have revealed high sodium levels. It could be that sea water is getting in under the Bay, perhaps via the now abandoned deep coal mine galleries which run beneath the site. The low sun has thawed the frost from the turfs in the field above, but not in the shadows beyond. However the little pool of spring water remains clear and ice free, the very slightly higher salt levels providing a natural anti-freeze.

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