Wednesday, 10 July 2013

Windrush study-Sampling in the Windrush lasher

Last week I was sampling the lasher (an offshoot of the Windrush just north or Witney) and its associated fish-pass to try and assess water quality, my cousin Alex came along as an extra pair of hands and official photographer.

We attempted to find out the quality of the water by using a method known as the Biological Monitoring Working Party Score (BMWP Score), BMWP looks at the aquatic invertebrates in the habitat and, through much clever work in the past to determine their tolerance to pollution, is given a score (initially 1-10, however I used the recently revised scores which are more accurate and have been tested better in real life situations). You then use these scores to work out the Average Score Per Taxon (ASPT) which tells you about the quality of the site with relatively fewer samples than you would need for assessment using purely BMWP.

The way you sample for BMWP is by using a ‘Three-Minute Kick-Sample’. This entails standing with a net downstream of your feet by an inch or two and stomping and kicking the sediment, hoping to disturb any invertebrates there which will then hopefully drift into the net. The waders are optional but I couldn’t resist the stylistic appeal.

The ASPT scores for the three sites sampled all pointed to excellent water quality but the results do need to be taken with a pinch of salt. The sites were only sampled with a solitary 3 minute kick sample each, this means that the results could be entirely anomalous. But the results that we did achieve were excellent which is always a nice result to get.

Samples of fly larvae from the river

I also went back later in the week to measure the flow rate of the fish pass as our contact at West Oxfordshire District County Council was worried that it was too fast. The environment agency states that anything slower than 3.5m/s is fine for almost all fish and the average reading I took was a leisurely 0.55m/s so based on this brief initial assessment there are no worries on that front either.


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