River Mel Restoration Group In last month’s edition of Meldreth Matters, we wrote about our concerns of possible pollution of the River Mel arising from the Melbourn Sewage Treatment Works (STW), which discharges its treated effluent into the River Mel just upstream of the railway bridge in Meldreth. Because of this concern, we were offered the chance to join forces with the Cam Valley Forum (a Cambridge based group) to carry out some sampling of water taken at various sites along the river Mel, as part of a larger study of the various tributaries of the Cam. We received the results just as the publication deadline for this issue approached, so we have not had a great deal of time to study them or their implications in depth, but there is a large increase seen in the number of indicator bacteria found in the samples taken 100 metres downstream of the sewage outlet when compared with “normal” background samples taken from the river 50 metres upstream of the outfall. A similar disparity is found when measuring phosphate levels in the water. Our understanding, and we are certainly not experts, is that the indicator bacteria are not themselves harmful, but that they are present in the human gut where they exist alongside pathogenic (disease causing) bacteria. They are widely used as an indicator of faecal contamination in water. They are also organisms that can be detected in water reliably and at low concentrations. The results are shown in the table below. They are worse than we were expecting…
Sampling Site
River Mel, Meldreth, 50m upstream of Melbourn STW outfall River Mel, Meldreth, c. 100m downstream of Melbourn STW outfall River Mel, North End Meldreth River Mel, Malton, just upstream of confluence with the River Rhee
Count of faecal indicator bacteria (coliforms inc. Escherichia coli – most probable number (MPN) per 100ml; enterococci – colony forming units (CFU) /per 100ml) E. coli Total coliforms Enterococci
Phosphate-P (SRP)
105
436
31
<0.031
8,164
48,840
1300
1.302
548
2,481
150
0.228
411
2,613
170
0.158
16
