RIVER FLY DATA AND ANALYSIS

ANALYSIS

The analysis of river flies (invertebrates) living in a chalkstream is one of the best methods for assessing water quality. Invertebrates that spend all or most of their lifecycle living in a river are constantly exposed to changes in the structural composition of the river bed, to variations in the volume and rate of flow of water in the river and in the chemical composition of the water flowing over them. Different invertebrates are sensitive to different environmental stressors (excessive sediment, low flows, too much phosphate etc.), so by analysing invertebrate species diversity and abundance in samples collected from the river, you can detect the water quality problems and start to design solutions.

River Fly Census: Test and Itchen Conclusions

Salmon and Trout Conservation (STC) conducted a nationwide River Fly Census from 2015-17. The Association helped fund the Census on the Test and Itchen. STC published the results of the Test and Itchen Census in 2018. The results showed that there are fewer river fly species in the Test and Itchen than there should be in a healthy chalkstream. And there are significantly fewer mayfly species in both rivers now than there were 30 years ago. The key problems are sediment, phosphate and a cocktail of complex chemicals. You can read the full text of the Test and Itchen Conclusions here.

Test and Itchen Catchment Invertebrate Fingerprinting Study

Wessex Chalkstreams and Rivers Trust (WCSRT), working with the Environment Agency and with help from the Association, collected and analysed invertebrate samples from more than 50 sites on the Test and Itchen in 2014 and 2015 and compared the results to historical Environment Agency data. The Study showed that sediment and phosphate, in particular, are causing catchment-wide impacts on the ecological condition of the Test and Itchen, with the adverse effects exacerbated when combined with low river flows. You can read the full text of the Test and Itchen Invertebrate Fingerprinting Study here.

River Meon Catchment Invertebrate Fingerprinting Study

Wessex Chalkstreams and Rivers Trust collected invertebrate samples from 12 sites on the River Meon in both the Spring and Autumn of 2017. The Association paid for the analysis of the samples, with the results compared to historical Environment Agency data. The Study showed that the Meon was subject to a range of ecological pressures but evidence of these pressures was less pronounced than on the Test and Itchen. Invertebrates at the sample sites were predominantly Unimpacted or Slightly Impacted by the four key stressors: sediment, phosphate, organic pollution and pesticides. Freshwater shrimp (Gammarus) counts at the sample sites were typically above 1,000, double the recently agreed target of 500 for a healthy chalkstream. You can read the full text of the River Meon Invertebrate Fingerprinting Study here.

DATA

Consolidated river fly data for the Test, Itchen and Meon will be added to this page of the website shortly.