Analysis of the Results of sampling the Dingly Dell stream, L.316,734
The Dingly Dell stream was sampled on Wednesday 16 February 1998 following complaints of a bad smell coming from it. A baseline survey of the stream has been carried out previously by the County Council and the results obtained today will be compared with these. Any significant differences in the two sets of results might indicate a pollution incident.
In order to assess the biological quality of the stream a scheme needs to be employed whereby the macroinvertebrate community present in the stream will indicate biological water quality. There a a number of schemes in use today which attempt to to this. In order to discuss these results I will use two schemes, the AFF Q rating scheme and the Chandler Biotic Score.
It is known that the stream runs through dairying farmland and previously there was a piggery with 3,000 sow capacity. It would be expected then that if effluent from these practices found its way into the stream that there would be a pollution incident. It can be seen from the baseline survey that there was a lot of pollution tolerant species present in the stream, however there numbers are reduced in the sampling survey of 16.02.98. The AFF Q Rating Scheme attempts to determine water quality by using the relative abundance and the diversity of key groups of organisms of known sensitivities. It is divided into classes fom Q1 which is bad quality to Q5 which is good quality. All classes inbetween are intermediate and can be used where appropriate. By using the AFF Q Scheme that the biological water quality of the Dingly Dell stream on the 16.02.98 was of Q5 Rating. It can be considered to of Q5 Rating because of the number of sensitive species which were recorded. There was also a lack of very tolerant species. The dissolved oxygen (% sat.) level was also quite high at 101%. Using the Chandler Biotic Score which was developed in 1970 it can also be said that the stream is of good quality. The Chandler Biotic Score is based on the abundance of fauna present. If the groups of organisms are present in high numbers a high score is given to them. The higher the score the better the quality of the water.
By use of these two schemes we now know that the stream is of good quality. By examination of the table provided it can also be shown that the biological quality of the stream has improved since the baseline survey. It can be seen that the pollution tolerant species such as Tubifex, Asselus and Chironomus have almost disappeared in the samples from the 16.02.98. Pollution sensitive species such as Caenis and Ephemerella are now present instead. Between the two sampling dates the piggery has closed down. This piggery was most likely polluting the stream and its closure has allowed the recovery of the stream. Grey wagtail and Kingfisher were also noted at trhe site and these would only be present around unpolluted waters. The following chart shows the variability between the baseline survey and the latest sampling. From an examination of this chart it is easy to see the changes that have taken place in species since the closure of the piggery
From the results of the sampling on the 16.02.98 it is likely that the reported bad smell did not originate from the stream.