The canary and the coalmine 

Invertebrate monitoring on the South Esk.  

By Dr Iain Reid 

Introduction 

Those of you living and walking by the South Esk in the Dalkieth area may have noticed that the river looks a bit different of late.   The river has taken on a distinctive orange colour, that you may have noticed at some points in the past, but it has never been as obvious as it is now (Fig 1).  This is due to an increase in minewater draining from the old pit at Bilston.  The minewater flows out into the South Esk via a pit drain known as an Adit (which was used to drain the mine when it was active).  The Adit (called Junkie’s) has always released some minewater but over time the old pit has filled up and the water table has readjusted, so that now a substantial amount of water is draining through the old works and into the river making it more noticeable.  This water is acidic (due to chemical reactions which occur when the water comes in contact with coal and shale seams in the mine) and it contains oxides of iron which settle out in the river giving the distinctive orange rusty colour.   This material also coats the invertebrates that live in the river such as this caseless caddisfly (Fig 2).  There are also some less visible materials dissolved in the minewater such as manganese which can have a toxic effect on plants and animals. 

The Forth Rivers Trust are concerned about what this discharge could be doing to the environment and as a result I’ve been carrying out invertebrate monitoring to see if the effects of the minewater extend to more than just the orange discoloration.   

Methods 

To do this I took standard 3-minute kick samples of invertebrates at 3 different sites for 3 consecutive weeks.  The sites were chosen to best assess the impacts of the minewater pouring into the river.  The first site I chose was directly downstream of the Adit itself, and the second was about 800m downstream.  This would allow me to see how the effects of the minewater changed with distance away from the source of pollution.  Finally, my last site was about 25m above the Adit which was chosen to be a control (a site that was unaffected by minewater which would allow me to compare with the downstream sites).   

To take a kick sample I kicked the rocks in the river-bed with my foot with a net positioned downstream for 3 minutes.  Keeping to the same time for each site was important as it made sure that the samples I took were (roughly) comparable between sites, and that any differences in what I found was due to pollution rather than the amount of time or effort spent kicking.  The kicking released any invertebrates into the net which I then preserved and took home to have a look at under the microscope.  Once back in my lab, or ‘kitchen’ as it was known before lockdown, I identified and counted all the invertebrates in each sample.   

Once I had identified and counted all the different invertebrates, I calculated some biotic index values.  In their simplest form biotic indices are scoring tools used by biologists to assess the health of the environment based on the invertebrates they find.  Each invertebrate family is given a score based on their different sensitivities to pollution, with the most sensitive organisms (like stoneflies, mayflies, and caddis) scoring the highest and the least sensitive (like worms, fly larvae and snails) the lowest.   

The scores for all the different types of invertebrate in the whole sample are then added up and divided by the total number of contributing categories to give an average score across all different groups (or taxon). The higher the average score, the more sensitive the invertebrates that make it up are and therefore the cleaner the environment.  There are different types of index which have been calibrated to look at different types of pollution from general sewage pollution, acidification, or to classify the type of flow regime that shapes the biological community found there.  

For this work I calculated the WHPT scoring index which SEPA use (WHPT is like an average scoring system that also considers abundances and sensitivities together so that the overall score is affected by large numbers of pollution tolerant organisms) and did a bit of statistics to see if any differences I found were significant. The main reason to use statistics is to make sure that our findings are real and not just due to random chance.  In this case ‘significant’ means that I was at least 95% confident that the conclusions I made were accurate or that there was a 1 in 20 chance that I was wrong. 

Results 

So, what did I find?  Unsurprisingly the minewater was shown to have a negative effect on the invertebrate community in river in a number of ways: 

1. The number of different types of invertebrate families was significantly lower in both the Adit and the downstream site when compared with the upstream site (Fig 3).  
2. The total abundance of invertebrates was significantly reduced when the downstream sites were compared with the upstream one (Fig 4).
3. Invertebrates found at the Adit site were also significantly less sensitive (as indicated by WHPT scores) to pollution than the upstream site (because the more sensitive ones had been killed off due to the minewater – Fig 5). 

Conclusions 

So, who cares if there’s less creepy crawlies in the river?  While invertebrates may not be everyone’s cup of tea, they are breakfast, lunch and dinner for other creatures such as birds and fish, who are in turn on the menu for other creatures in the food chain.  A reduced and impoverished invertebrate community will almost certainly affect the number of other organisms that depend on it and like the canary in the coalmine provides a clear indication that action needs to be taken before catastrophe occurs. 

Moving forward 

So, what’s going to happen?  The environmental legacy of mining is one that is here to stay with us in Midlothian and the solutions to it are complex requiring time and money.  Most of all it is difficult to establish who is actually responsible for the issue – while the problem relates to former mineworks, it is difficult to establish that anyone has broken any specific environmental laws. The Forth Rivers Trust have been in contact with both SEPA and the Coal Authority (who have a duty to rectify environmental effects of mining) and plans are in place for a both short and long-term solutions to take place respectively in the order of months and years.  These may involve direct (via chemical treatment) or passive (via reed beds and attenuation ponds) approaches to solve the problem.  

I can appreciate that some folk may find themselves getting very angry about the lack of action on this particularly when it is apparent that as the discharge continues and it is clearly having an effect on the river.  Our principle role at the Trust is to raise awareness of this issue so that we can facilitate the fastest possible solution while minimising the damage done to the river.  In the meantime, I’ll continue to monitor the invertebrate communities to see that things aren’t getting any worse.