According to the 2015 Riverfly Census, undertaken by Salmon & Trout Conservation UK (S&TC UK), virtually all of England’s 200 chalk streams are in a “dismal state of decline†due to poorly treated sewage, agricultural and road run-off, septic tanks and discharges from watercress and fish farms.
According to the study, carried out by ecological consultants Aquascience Consultancy Ltd, only 14 out of the 120 sites sampled remain in pristine condition.
Dr Nick Everall from Aquascience Consultancy said, “The national river survey showed a mixture of improving, stable and all too many sadly declining reaches in terms of overall ecological condition, environmental stresses and riverfly life in particular. Several rivers showed loss of condition with measures like mayfly species richness and freshwater shrimp population status over time.
“Breaking some of these river findings down with controlled laboratory tests has recently shown that raised levels of phosphate and sediment, akin to many of our stressed river conditions, has a detrimental impact upon the survival of early life stages of the base of the aquatic food chain for species such as the blue-winged olive.â€
According to Paul Knight, Chief Executive of S&TC UK, most of the rivers surveyed and analysed were impacted to some extent or the other, but the chalk rivers were the worst with virtually all of them being in a dismal state of decline. England’s chalk streams form approximately 85% of the total global stock of this richly diverse and complex habitat.
During the survey, ground-breaking research and chemical analysis was used for the first time to accurately identify the problem, as riverflies and other invertebrates are the best indicators of the underlying ecological condition in the rivers because the various species of invertebrates in these rivers exhibit different tolerances to various forms of stress from pollution.
Three of England’s most highly protected SAC chalk streams; the Lambourn, the Wensum and the Itchen, rank badly in the Census. Populations of the blue-winged olive have collapsed in the Itchen, despite having been comparatively abundant in the early 1990s.
Environment Agency figures have proven that 83% of the rivers in England fail to meet the standard of ‘Good Ecological Condition’ classification, as per the European Water Framework Directive.
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