The R4ever Kent project have been out and about confirming the final location sites for our upcoming DGT Passive phosphorous study across the River Kent and tributaries catchment.

The study is needed in order to determine suitable locations to reintroduce populations of critically endangered freshwater pearl mussels, which are currently being bred in captivity at our Species Recovery Centre.

The R4ever Kent team assessing river locations for DGT Passive phosphorous study.

DGT sampling gets underway

A DGT passive sampler is a plastic device deployed directly in water. It contains a binding agent that, in this case, accumulates phosphorous in the water, providing a time-averaged sample of p levels.

This kind of monitoring helps to eliminate issues from results where there have been isolated spikes or troughs in chemical levels and gives us an idea of how quickly our freshwater pearl mussels would take up the p from the water. This will give us solid data on the suitability of water quality across the catchment and at potential reintroduction sites.

Project Manager, Morgan, and Catchment Management Advisers, Richard and Joe, compared potential sampling sites with expert advice on device siting from Lancaster University, ensuring no disruption of spawning sites with fisheries advice from project partner staff at the Environment Agency.

Things to consider

There is a lot to consider between looking at a point that makes sense on a map and what will work on the ground. We picked sites upstream from confluences where watercourses join so we can map where p levels are coming from and identify areas needing to be targeted in more detail in future.

Firstly, however, these sites need to be accessible.  After securing access permission from landowners, physical access comes next – can you actually climb down that bank or will it be too icy in winter or brambly in summer? The substrate and flow rates also need to be suitable – no stagnant backwaters; no ripping away of the devices in torrents.

Our DGT devices will be placed in metal cages weighted down on the riverbed using rocks from the area to reduce external inputs. That means we need cobbles big enough to hold our devices in place when the water gets frisky, so areas of bedrock are not suitable, nor are, as one landowner we were chatting to put it, ‘sandy bottoms’! Our study will be year-round, so assessing a site where the water will not be likely to get too low in summer, or too high to enter in winter is also a very tricky balance.

Finally, after all these criteria have been met, we have to ask: is this an area with salmon or trout spawning?

What a redd looks like!

These sites can be shown up on some occasions by redds – these are fan shaped areas of cleared gravel made by the fish ready for laying eggs. However, these are only visible at some times of year and, even then, only to a trained eye – even in pictures where they have been circled in a big red pen, it’s still hard to honestly say you can see the difference!

That’s where nothing is a substitute for local knowledge and years of experience providing information on favoured spots to avoid, or ones that are safe and are not used by the fish.

Knowledge exchange

It was a great day out where we got to be more spatially aware of the proposed sampling sites throughout the catchment, discuss the study in more detail with Ben Surridge from the University of Lancaster and gain a wealth of knowledge from Graeme McKee from the Environment Agency.

It was also an opportunity to get some outstanding permissions in place from landowners and, at the same time, have a good natter with owners and occupiers, explaining more about the project as a whole, the phosphorous sampling itself and even get some more interest in restoration work while we were at it!

We came away with a finalised decision on our sampling strategy, which should lead to a really robust and informative study over the next year.

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