30,000 words on water quality

Rosie Nelson – Masters Student

Rosie, geared up for outdoor working - copyright NYMNPAI have finally finished my research masters. All that stands between me and the real world is corrections and actually printing a 30,000 (ish) word document. So did I actually achieve anything. Well I’d like to think so, but first up I’ll tell you a bit about what I did, and how I did it.

I spent six blissful months walking three beautiful watercourse catchments in the North York Moors – Toad Beck, Danby Beck and Great Fryup Beck which are all tributaries into the River Esk. Aside from sun kissed skin and being chased by sheep, dogs and cows, I somehow managed to collect what I was after – a lot of useful data. To establish the water quality of a river a variety of sampling techniques is required. My favourite was using a probe which measures dissolved oxygen, conductivity, pH, salinity, temperature and much much more. Imagine, dangling a very expensive cable off the side of a bridge and waiting in anticipation for the numbers on the screen to settle. I loved it. Although once or twice the probe did ricochet off rocks to produce an alarming sound.

As my data collection evolved, I also started to gather water samples to take back to the laboratory for COD, BOD, DOC, anion and cation analysis. You might think I’ve just put some letters together to appear clever, but they do actually stand for things:
– COD is chemical oxygen demand (amount of oxygen required to oxidise the organic matter in the solution);
– BOD is biochemical oxygen demand (amount of dissolved oxygen being used by aerobic microorganisms when decomposing the organic matter in the solution);
– DOC is dissolved organic carbon (amount of organic matter in the solution);
– An anion is a negatively charged ion, a cation is a positively charged ion, and an ion is an electrically charged atom.

So what did I actually find out in these three catchments? Well I analysed the spatial and temporal variations of a variety of water parameters. The significance of focusing on both spatial and temporal variations within a catchment is it can easily identify areas of point source pollution at a small scale, something which isn’t done often enough.

For this post I’m focusing on dissolved oxygen and conductivity. The very important key species Freshwater Pearl Mussels require dissolved oxygen levels between 90 – 110% (Oliver, 2000). Other aquatic life like fish can survive on much lower saturations of dissolved oxygen, as low as <30%. The graph below shows how dissolved oxygen (a vital parameter for ascertaining the health of a river) changes through the year. Changes in water levels and plant growth can have serious effects on the amount of dissolved oxygen available for organic and aquatic life. During the summer months, plants will become abundant in a river, thus using up more oxygen and depleting the overall amount of dissolved oxygen available in a river. Once rainfall increases in the autumn dissolved oxygen levels should be replenished. As you can see September 2016 was a particularly poor month for dissolved oxygen, with average levels as low as 80%. Similarly, August on Toad Beck was low as well with an average of 75% saturation. But aside from in September for all three watercourses, and in August for Toad Beck, the dissolved oxygen levels remained within or above the proposed dissolved oxygen threshold.

2016 Dissolved Organic Carbon data graph - copyright Rosie Nelson

Next up – conductivity. Conductivity is a measure of a watercourse’s ability to conduct electrical flow and is therefore related to the concentration of ions in a river. Particular aquatic species need higher or lower conductivity – the Freshwater Pearl Mussel likes a lower conductivity. There are variations between suggested thresholds for conductivity: Moorkens (2000) suggests it should be 65µs/cm, whilst Bauer (1988) suggests <70µs/cm and Oliver (2000) suggests <100µs/cm. So I chose the only logical way forward and used all three thresholds. Focusing again on the month of September 2016, I produced the map below.

2016 Conductivity levels map - copyright Rosie Nelson

This is where analysing data spatially comes into its element. First up, the circles represent sampling locations (every now and again samples were missed out say if there were a herd of cows approaching as I climbed the style into their field, needless to say my flight or fight response would always be flight as advised in the National Park Authority’s Risk Assessments). Using a traffic light system, green circles represent good conductivity levels. As you can see, September was a poor month for both dissolved oxygen and conductivity. What I found particularly interesting was the variations that could occur in a small watercourse like Danby Beck, where as tributary field drains entered the beck conductivity levels could spike or decrease dramatically; how fantastic!

So to round off I thought I’d quickly summarise my thesis’ findings. Water quality is good in the three catchments, but it’s not good enough for Freshwater Pearl Mussels, and that’s the gist of it. The work of the River Esk catchment officers at the National Park to address the issues is great, the water bodies are reaching and maintaining ‘good’ ecological status, unfortunately the Freshwater Pearl Mussels require pristine water conditions and ‘high’ ecological status. However the future direction is positive for the health and conservation of Freshwater Pearl Mussels. And I too am looking forward to the future; I shall be taking a few weeks off from being chased by animals and I can’t wait*.

 

 

 

 

* Editor’s note: Rosie didn’t get much time off – she’s gone off to pastures new and is now a Community (Water Quality) Modelling Project Officer at Thames21. We wish her all the best.

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