Spatial and temporal patterns in the macroinvertebrate communities in streams
My research looked for evidence of community persistence in two suites of sites. Twenty-nine stream sites were in the Ashdown Forest of southern England and twelve streams which form part of the United Kingdom Acid Waters Monitoring Network. Benthic macroinvertebrates were collected using different methods and the species and physico-chemical data analysed. The Ashdown sites were sampled in 1989 and 1990, and the data collected was compared with previous studies and an analysis made of community persistence over a period of thirteen years. Persistence was assessed using measures of similarity and rank correlation coefficients. The data showed that several physico-chemical factors, in particular stream pH, were related to the structure of the benthic communities. Summer temperatures and stream discharge were also significantly associated with the patterns obtained. Using multivariate methods, TWINSPAN, DECORANA and CANOCO, spatial patterns were discerned. Comparisons of the two previous surveys and my own data showed that sites with low pH, low summer temperatures and low discharge had consistent spatial patterns. The United Kingdom Acid Waters Network stream sites were originally chosen for their susceptibility to acidification and are located in different geological and geographical parts of the UK. The same persistence measures were used as for the Ashdown data and, although there was greater variability, similar underlying patterns were found. Using the same methods the Ashdown and UKAWMN sites were then analysed together.