182 BR. J. ENT. NAT. HIST., 6: 1993 



Biological monitoring is now the main method by which changes in water quality 

 can be detected. Invertebrates have the advantages of being of widespread occurrence, 

 diverse, relatively immobile, cheap to sample, mostly easy to identify to family 

 level, and they show the effects of pollution over time. Different families of 

 insects vary in their tolerance of pollution, especially to organic factors such as 

 the depletion of oxygen. Various monitoring systems using invertebrates have 

 been devised, such as the Saprobien system, Trent biotic index, Chandler score, 

 Continental indices, and the Biological Monitoring Working Party (BMWP) system. 

 It is the last mentioned that is now in use throughout Britain. Families of invertebrates 

 are given a score of 1-10 according to their tolerance of pollution, with the most 

 sensitive scoring 10 and the most tolerant 1. Rivers are sampled by using a net or 

 dredge bucket for a standard time, and the invertebrate families are identified and 

 scored. Adding up the scores gives a total value for the site and the average score 

 per taxon (ASPT) is calculated by dividing the total score by the number of taxa. 

 The ASPT is the more reliable figure, since some high-scoring families will not occur 

 in some rivers however clean they are if other environmental factors are wrong. Total 

 scores can also be increased by more frequent sampling whereas the ASPT figure 

 is more constant. The speaker has been involved in a project called the River 

 Invertebrate Prediction and Classification System (RIVPACS). This involved sampling 

 a wide range of clean rivers and streams throughout Britain at a number of sites along 

 their lengths. Details of the river, such as width, depth, rate of flow, river bed 

 characteristics, altitude, distance from source, and chemical factors such as pH and 

 salinity, were measured, as well as monitoring the invertebrates. Analysis of the results 

 with a system called two way indicator species analysis (TWINSPAN) enables the 

 invertebrate fauna to be related to certain types of river systems. Twenty-five river 

 types have been identified and using the TWINSPAN system it is possible to predict 

 which invertebrate families ought to present in a clean water sample of each of those 

 river types. An environmental quality index (EQI) can be calculated by dividing the 

 observed ASPT value by the predicted value. The closer this is to one, the better is 

 the quality of the water. Statistical means can be used to give confidence limits 

 to the EQI to take into account variations caused by chance in the sampling procedure. 

 Water quality in rivers can be graded into good, fair, poor and bad bands according 

 to the EQI value. 



BOOK REVIEW 



The spiders of Great Britain and Ireland by M. J. Roberts, compact edition, Harley 

 Books, Colchester, 1993. Part 1 "text", 458 pages including 7 colour plates, £49.95, 

 paperback. Part 2 "plates", 256 pages including 236 colour plates, £39.95, paperback. 

 Parts 1 and 2 together £80. — At £80 for the two parts, this edition offers quite a 

 saving on the £135 three-volume hardbound edition (1987). Described as a 'compact' 

 edition, it is a two-volume paperback version of the hardback — Volumes 1 and 2 

 are bound together as Part 1, Volume 3 thus becomes Part 2. In every other way 

 it is identical, word-for-word, page-for-page, to the superbly produced hardback, 

 lavishly illustrated throughout with line figures and diagrams and retaining the 243 

 exquisite colour plates. Also included at the end of Part 1 is a 16-page appendix 

 (available separately, £3.75). It lists corrections, alterations and additions, including 

 numerous changes to the British check list. Six new species are described and illustrated 

 and additional illustrations are shown for various species of Philodromus, a genus 

 recently revised. A snip at £80, this definitive book is now well within the means of 

 many more of us and a must for anyone with even the mildest of interests in spiders. 



R. A. Jones 



