When I wrote about the importance of the Chalk and its place in Yorkshire's natural landscape and ecosystems in a "Telling our Story" blog last year, I was conscious of having missed out one particular habitat type - the Chalk Stream.

What is a "Chalk Stream"? Quite simply it's a river fed by springs issuing from the Chalk - this is the rock that forms the low, rolling hills of the East Yorkshire Wolds. At their magnificent best, chalk streams are endowed with gin-clear, mineral-rich waters that support a rich community of plant and animal life. They owe their existence to a particular combination of geology and climate that is quintessentially English - our country is home to around 85% of the World's chalk streams. Such is their uniqueness and importance that they have been referred to as "England's Rain Forests".

Unfortunately, human activity has adversely impacted water quality and water quantity throughout much of this globally unique ecosystem, and biodiversity has suffered as a consequence. Drought, which can be associated with climate change, is an additional emerging risk. Addressing these issues requires the combined efforts of multiple government agencies, water companies, land owners and conservation groups. This, then, is where Yorkshire Wildlife Trust comes in...

On a wonderfully sunny day in August, I was fortunate to visit Jon, Clare, Calum and their team of volunteers at Skerne Wetlands Nature Reserve. Skerne is centred on the chalk-fed upper reaches of the River Hull, and the drains and old fish ponds that link into it. I joined them for a training and catch-up session devoted to the stream survey work that the team does.

We began with introductions, and I was pleased when Clare invited me to tell everyone a bit about myself and the "Telling our Story" concept.

Jon followed, detailing the background to the habitat restoration and improvement work that is being advanced at Skerne. A particularly important point that he made was that because of its small size - 45 hectares - it is essential to look beyond the reserve boundaries to develop strategies which enhance Skerne's resilience to the threat of environmental degradation. This includes linking in with wider conservation projects such as the National Chalk Stream Strategy.

The National Chalk Stream Strategy aims to improve water flow, reduce pollution, and restore the physical state of our chalk streams and their surroundings - the three major factors contributing to chalk stream health.  Under this strategy, Skerne forms a part of a flagship programme that covers the Hull Headwater Chalk Stream, with YWT as its main delivery agent.  Reliable data is at the heart of this strategy, which is why the team's survey work is so important.

We held our discussion sat outside the shed the team uses as a base. It really was the most perfect setting, surrounded as we were by a soundscape consisting of the susurration of willow trees, the softly gurgling river and pinging kingfishers.

"A river of green is sliding unseen beneath the trees

Laughing as it passes through the endless summer, making for the sea..."

Roger Waters - Granchester Meadows, 1969

Speckled Wood Butterflies dropped by as we talked and listened...

...and we were buzzed by ever inquisitive hawker dragonflies...

Clare then conducted an open discussion session with the team, checking on how everyone is getting on, and that they had the equipment and literature needed. I learned that the team of volunteers support each other by working in pairs, with survey work conducted where the footpaths and banks give easy, safe access to the river, and that for consistency they all follow the same ways of working. There was a lot of positive feedback during this discussion and the whole team seemed to me to be really engaged with each other and with what they are doing.

While all this was going on, Jon went to collect water samples so that the team could practice their species identification skills. When he returned, he had mixed water and sediment from the main stream with some from the feeder ditches, where the water is naturally slower and more silty.

The faunal diversity and abundance was - to my eyes at least - simply amazing. There were scores of freshwater shrimps, mayfly and damselfly larvae, water diving beetles, sticklebacks and - oh wow, a brook lamprey, one of the species that features on the information board at the reserve entrance. Lampreys are primitive, jawless fish with a very long geological record. At university, I spent three years studying the fossils of an animal very similar to the lamprey but this was the first time I’d seen one in the flesh. It was quite a moment for me, I can tell you.

As the discussion session came to a conclusion, biscuits were passed around, and batteries for the water flowmeters the team uses were handed out. Suitably energised, we headed up river to a location where the group could practice their surveying skills.

Jon had gone ahead and found an ideal spot with easy bank side access to a stretch of river with a good mix of water depths.

We began with Kick Sampling, a simple qualitative method for assessing stream biodiversity. Kick Sampling does exactly what it says on the tin. Everything starts by donning a pair of very large rubber over-trousers (très chic, très élégant!).

The next step is to get into the stream - an art in itself - and having found a suitable spot, you face downstream.  Then the thing to do is to kick and shuffle your feet in river bed for about 30 seconds, catching the disturbed sediment in a long-handled net...

... you bring your catch ashore...

... you empty your catch into a sample tray, and ...

... examine for beasties! There is a keen sense of anticipation - much as on any fishing expedition - while you wait for the sediment to settle so you can see what you've caught. At this particular location, we found mainly freshwater Gammerus shrimps and cased caddis flies which was as the team expected given the water depths and gravelly river bed. Jon explained that other species - uncased caddis flies and those lovely lampreys, for example - prefer the slower, deeper and siltier parts of the river where the banks are undercut.

Some members of the team took the opportunity to practice using the water flow meters the team pairs have been provided with - a good water flow is one of the key factors affecting river health. The bit of kit they use is essentially a small propeller on a stick, which links to a meter that counts the spins of the propeller. Wade out into the middle of the river, hold the propeller into the flow at mid-depth in the water, let it spin for one minute and you have your reading. A standard graph converts the data into velocity, which is what is needed for final analysis.

We didn't get a chance to practice the third component of the survey work the teams does. This is a check on water quality, specifically the phosphate and nitrate content, the by-products of agricultural chemicals and sewage. Left unchecked, increased concentrations can lead to "eutrophication", marked by algal blooms and thus reduced oxygen content in the river.

The biodiversity and water quality data that the team collects and collates are essential components of the work carried out at the reserve, and will also feed into the national strategy for chalk streams. YWT's recent "State of Yorkshire's Nature" Report emphasises the importance of reliable data for planning and prioritising our conservation efforts. The Skerne team are working together very well to put this into action.

The practice session came to an end, and I made my way back to my car.  Stopping to take a last look at the river before leaving, I shared the view with one of my fellow volunteers. We watched the river for a while and agreed that Skerne is a really special place. We agreed too that volunteer work is both a fantastic learning experience and a wonderful escape from all the trials and tribulations occurring elsewhere.

"Rivers and the inhabitants of the watery element are made for wise men to contemplate, and for fools to pass by without consideration.”

Izaak Walton - The Compleat Angler ,1653

You can find out more about practical conservation days YWT website here.