WHY IS SOLUBLE SILICON IN INTERSTITIAL AND LAKE WATER SAMPLES IMMOBILIZED BY FREEZING

The reasons behind the lowering of the spectrophotometrically measurab le silicon (Si) content in sediment interstitial and unfiltered lake w ater samples after storage in frozen form were explored. The storage c ontainer material had little effect on the immobilization, whereas low ering the pH of interstitial water samples before freezing decreased t he ''loss'' of Si. When interstitial water samples were frozen, both n ative, naturally present Si and added standard solution Si were immobi lized. The same reaction pattern was found for native Si in unfiltered lake water samples. On the contrary, neither the native Si in filtere d lake water nor added standard solution Si was immobilized when lake water samples were frozen, indicating that high concentrations of part iculate material, especially in the interstitial water, was the prime cause of the immobilization phenomenon. The results obtained in a sequ ential filtration (0.2 mu m, 100,000 and 10,000 daltons) experiment wi th interstitial water samples supported the theory that Si is immobili zed through polymerization or complex formation mediated by particulat e material and molecules present in interstitial water. An incubation test revealed that the immobilization process was not entirely reversi ble. The amount, nature and behaviour of Si in interstitial water samp les showed some seasonal variation. Copyright (C) 1996 Published by El sevier Science Ltd