Changes in Streams between Swallets and Inlets in the Cave at St. Cuthbert's Swallet, Priddy, Somerset. (UBSS Proceedings v.22(2))

Abstract: At every site where water flows from a surface stream sink to an inlet in the cave, there are changes in calcium, magnesium and bicarbonate concentrations, in spite of the fact that in many cases, these distances are short. The changes are caused by limestone dissolving in the stream in the space between swallet and the open cave, and not by admixture with water percolating from a different source. When the size of a surface stream rises, concentrations of many solutes in the stream, including calcium and bicarbonate, fall. However, results show that at every near-surface inlet for which sufficient data is available, the rate of limestone solution increases when stream sizes rises. Once the stream is within the open cave, stream characteristics are remarkably stable and, in sampling trips in normal conditions, they only change when mixed with water from a different source. The present results demonstrate that the quantity of limestone passing into solution increases very considerably as a result of an increase of stream size. Although the total volume of the streams entering the cave is the same as it was in the past, after the largest stream entering the cave changed its route the hydrochemical characteristics of the Main Stream downstream of Plantation Junction have changed. The change is not limited to an increase in the hardness of the stream. Although the number of data points is small, it is clear that the response of the total hardness to stream size has undergone a major change. Regression equations describing temperature changes between the sinks and the inlets were statistically significant in the earlier period of study when more sensitive thermometers were used.