Minor local effects of a River Thames power station on the macroinvertebrate fauna

In July 1996, a survey of the macroinvertebrate fauna of the River Thames w as undertaken in the vicinity of Didcot A Power Station, which is located o n the right (south) bank of the river. The aim was to determine whether sho rt-range biological effects could be detected due to abstraction and discha rge of cooling water. Sampling zones were selected upstream of the abstract ion point (zone A), between the abstraction and discharge point (zone B), a nd below the discharge point (zone C). Five pond-net and five dredge sampli ng units were taken from each bank in each of zones A, B and C and analyses were undertaken at BMWP family level. A total of 46 BMWP families were cap tured during the survey. Marginal pond-net samples from the left bank had a significantly higher mea n number of BMWP taxa than those from the right bank. These differences are thought to be due to the greater diversity of macrophytes and substrata on the left bank. In addition, there were lower numbers of BMWP taxa on the r ight bank of zone C compared with zone B (but not zone A), probably due to poor quality habitat. When the fauna from dredge samples in 'control' zone A was compared with zo ne B, there was no evidence on either bank of a deleterious impact on the f auna in zone B. Comparison of dredge samples from zone C with those from zo nes A and B, revealed no statistically significant differences in the numbe r of BMWP taxa between zones C and A or between C and B on either bank. How ever, the first two dredge sampling units from the right bank of zone C, im mediately downstream of the discharge point, had just five and 12 BMWP taxa , respectively, compared with a range of 17-28 taxa in all other dredge sam ples (on either bank of the three zones). These results correlated with a l ocal change in dominant substratum to sand and associated fine particles, a nd suggest a very localized effect of the discharge on river-bed morphology and hence on the fauna of the right bank in zone C. Copyright (C) 2000 Joh n Wiley & Sons, Ltd.