Clean Water for Wildlife . . . the Science

The test kits we are using for Clean Water for Wildlife are great, because they give everyone the opportunity to ‘see’ nutrient pollution: quickly, easily and inexpensively for the first time. But, all test equipment works to different levels of precision and accuracy. To ensure the results from the Clean Water for Wildlife survey are credible, we have provided a scientific summary of the strengths and limitations of the Packtest kits.

katy water smapleClean Water testing Blackwater 12mar2016 Michael Sleigh 01

We have produced a technical report, “Clean Water for Wildlife: Using Packtest nitrate and phosphate test kits to find clean water and assess the extent of pollution”. The report defines the meaning of the term ‘clean’ water, provides a summary of the strengths and limitations of the Packtest kits and suggests how to get the best results from them. Importantly, the report summarises the results of extensive comparisons of the Packtest kits with laboratory analysed water samples to assess the reliability of the kits.

The report is currently in the consultation stage, as we are sharing it with – and incorporating comments from – our partner organisations. Please see below for the latest version. If you would like to be involved in the consultation process please contact the PPW Project Administrator on peoplepondswater@freshwaterhabitats.org.uk

In summary . . .

The Packtest kits are good for quickly identifying areas of clean water which are likely to have little or no nutrient pollution. They also good for quickly providing a broad assessment of the extent of pollution in ponds, lakes, streams, rivers, ditches, springs, flushes across a landscape.

Overall, the kits provide a reliable method for quickly screening large numbers of sites to determine whether nutrient concentrations are at, or near, natural background levels, and identifying sites experiencing nutrient pollution.

However, because the kits categorise nutrient concentrations into quite broad bands, they are less accurate than laboratory data (i.e. they cannot get as close to the true value of a nutrient concentration as a laboratory measurement). For nitrate, although results from the kits are broadly correlated with laboratory data, they seem to consistently underestimate concentrations, compared to the values measured in the laboratory. The difference is less pronounced for phosphate but the kits do still consistently under-estimate true values. It is also worth remembering that the kits will place a water sample in the correct water quality class, as shown by laboratory analysis, about 80% of the time. Conversely this means that roughly 1 in 5 samples will suggest that the water is less polluted than it really is.

In practice, this is not too big a problem when the main distinction drawn from using the kits is between water which is ‘clean’ (i.e. has little or no pollution) and that which is polluted. At individual sites, where getting the ‘right’ result is important, it is probably a good idea to take several samples over a period of time to get a feel for variation in nutrient concentrations over the year.

Further use and testing will help us to understand the extent to which the kits can be used to monitor change in pollution levels: given that changes in nutrient concentration resulting from management interventions are often small, it is likely that laboratory levels of accuracy will continue to be needed to measure short-term variations.