On Saturday the 10th of October 2020 we once more ventured into deepest-darkest Somerset, this time to complete our first full day of fieldwork at our site. Thankfully, the weather was much more conducive for efficient and enjoyable work than it was for our recce; occasional sunny spells as opposed to a near-constant deluge, although we didn’t feel much of the sun’s warmth beneath the dense canopy looming over our heads!

Upon our arrival at approximately 8:45, we decided to explore further downstream beyond the scope of our recce. This involved carefully crossing the stream and navigating steeper, more treacherous terrain well off the beaten track, a prospect that was far less appealing in the previously stormy conditions. This was a fruitful endeavor as we discovered a gigantic, moss-covered tufa barrage just beyond our view from the path, along with an abundance of tufa-covered twiglets and stones within the stream. We also noted that the stream cuts through the local bedrock downstream of the barrage, which may have important ramifications on the water chemistry. This, along with the sighting of a small tributary running off from the adjacent field, convinced us to abandon our predetermined sampling locations and start from that point instead, and then progressively move upstream. You may be wondering why we starting sampling downstream, this is because if we started upstream and disturbed or contaminated the stream, e.g. by inadvertently kicking up a load of sediment, this would potentially affect our measurements downstream.

It was at this point that our supervisor, Professor Fiona Whitaker, arrived. She agreed to join us for a couple of hours (graciously giving up her Saturday morning!) to help us solidify our day-plan and ensure we were following procedure correctly. With her help, we soon developed an effective workflow, we would take two samples from each location, one for measuring dissolved oxygen (DO) content, pH, and conductivity with the Hach Meter, and another for titration in the lab at a later date to determine the carbonate chemistry of the stream. We would also measure the time, water depth, temperature (air and water), and make notes of any particularly interesting features about the site. In order to remember where our sampling locations were on future field days, we took pictures of each, and wrapped a piece of red tape on a nearby branch, unfortunately spoiling the aesthetic of the wood for the locals, at least temporarily!

The time of day is an important control of stream chemistry, especially when the stream contains many photosynthetic organisms such as mosses. This is because at night photosynthesis is limited, while respiration continues, as such, less oxygen is present in the stream relative to carbon dioxide. As mentioned in the previous edition of the blog, this encourages the degassing of carbon dioxide into the air, lowering the pH of the water, and providing more favorable conditions for tufa precipitation. It was because of this that we arrived at the site as early as possible (bus times permitting!), as we wanted to see if the pH and DO readings would vary throughout the day at each site. Because of this, we repeated our cycle of measurements twice throughout the day. We also measured discharge (i.e. volume of water passing a point per second) using the salt dilution method. This involved chucking a bucket of dissolved salt into the stream and seeing how long it took to flow past our Hach Meters (which were measuring conductivity), all good fun!

We were hoping to go back into the field another day that week to gather more data, however one of our group had come into contact with someone who was showing symptoms of COVID-19. As a precaution, we all then went into self-isolation, while thankfully a team of volunteers stepped in to do our titrations in the lab. Unfortunately we will be unable to gather samples at another time due to limited lab availability, however not all hope is lost! We will be going back in the field in the near future to survey the dimensions of the stream, and to obtain some soil samples, tune in next time to see how that went!

The new academic year has coincided with the requirement for an intensive research project to be undertaken by 3^rd year Environmental Geoscience (EGS) students. The group consists of myself, Will Shanks, David Jinks and Alex Taylor. Naturally, we were all curious to discover the topic on which our research would be based and were surprised to discover it was about Tufa-an unfamiliar substance to us.

Tufa is a type of limestone which forms when carbonate minerals precipitate out of ambient temperature water. When alkaline water (pH>7) emerges from underground aquifers, it degases (Loses) CO₂ due to the lower CO₂ content in the atmosphere. The release of CO₂ reduces the acidity of the water (increases the pH) and provides a suitable environment for tufa to precipitate as the solubility of Tufa reduces with less acidity

A quick browse on google and you will find many eye-catching and impressive examples of Tufa deposits, which can sometimes form columns several meters in height. However, the Tufa which we will be investigating is much smaller in scale, with the majority of it being found as crusts on rocks or around vegetation. This leads us to a question: Why is it important?

It could easily be anonymous due to its diminutive appearance, but Tufa is crucial for plant life. Tufa is porous, can store water and acts as a vital habitat in rivers, streams and lakes for a diverse array of plant life (you can even get plant pots made out of tufa-Alan Titchmarsh eat your heart out!). Tufa can also be used as a paleoclimate indicator (a tool to help reconstruct previous climates). In this study, Tufa in Poland was used to reconstruct temperatures from 9500 to 2000 B.P.  https://doi.org/10.1016/0033-5894(88)90022-1.

Armed with a developing knowledge of Tufa, we set out on the morning of the 6^th October 2020 to undertake a field recce in Clutton, which is 14km south of Bristol. This gave us the chance to look at the site, practice using the Hach Meters (Device which measures water pH, dissolved oxygen content and electrical conductivity), determine where our measuring sites would be and narrow down the ideas on which our study will be based (all in the pouring rain-wonderful!).

We have decided to investigate the level of influence of different factors on Tufa formation. What physical conditions are perfect for Tufa precipitation and how important are biological factors? Over the next week or so our group will be conducting more field work and laboratory analysis to provide us with the data to answer this question.