As our climate warms so does water temperatures in rivers. This has the potential to have significant impact on aquatic ecology, especially native fish. Scottish rivers are regularly reaching temperatures that cause stress to trout and salmon and climate change is going to make this worse.
To look in more detail at how rising water temperatures are impacting salmonids, the Scotland River Temperature Monitoring Network (SRTMN) was set up in 2013 as a collaboration between Marine Scotland, the University of Birmingham and Fisheries Trusts. Water temperatures are set to rise due to climate change. A series of water temperature loggers were deployed around Scottish rivers at sites chosen to show how differing factors influence temperatures. The loggers are downloaded twice a year by Fisheries Trusts with the data from the loggers being fed into a model run by Marine Scotland. The data allows the model to predict water temperatures for all Scottish rivers/burns. As part of the national network there are 20 loggers deployed on the River Bladnoch, managed by GFT, which provide data that feeds into the model.
The SRTMN web page states: River temperature is a critical control on the health of freshwater ecosytems, controlling species distribution and abundance. In Scotland many native freshwater species, including iconic fish species such as brown trout and Atlantic salmon, are adapted to live in cool water habitats. Juvenile Atlantic salmon perform best when temperatures are in the mid-teens, and struggle where temperatures extend much beyond 20°C. At 23°C juvenile salmon experience thermal stress and behavioural change, that includes abandoning territories and searching for cool water refuges. Where temperatures reach 32°C juvenile salmon will die in the space of minutes. During the summer of 2018, it is estimated that around 70% of Scotland’s rivers experienced temperatures that exceeded this threshold for thermal stress. UK climate change projections provided by the MET Office (UKCP18) indicate that summers like 2018 could occur every other year by 2050, with increasingly high air temperatures and low summer flows.
The loggers that are used are tinytag temperature loggers which are secured in place in the water. These loggers are approximately 5cm wide. They can accurately store large amounts of temperature data in them until being downloaded in the field.
The temperature logger data from the Bladnoch has provided accurate data on peak temperatures and temperature persistence for the Bladnoch monitoring sites. The map in the gallery shows the maximum temperatures recorded during the summer of 2021 (the warmest year since recording began). Some unshaded burns and the lower River Bladnoch got extremely hot reaching up to 30 degrees which is very close to temperatures that would kill sensitive species including salmon and trout.
In addition to the raw data collected the Marine Scotland model is able to predict maximum water temperatures for the rest of the Bladnoch catchment, and all other Galloway rivers, and prioritise areas where work to reduce temperatures is most needed (see an example in the gallery). Tree planting is the most practical way of reducing water temperatures as the shade provided protects watercourses from direct exposure to sunlight. The predictions from the model allows GFT to prioritise watercourses for tree planting to reduce temperatures, feed the data into priority restoration plans and seek funding to carry out the work.
In addition to the Bladnoch, GFT is also involved in running some temperature loggers on the upper Urr, High Cree and on the lower Dee around Tongland.
If you want to find out more about the SRTMN including the various model outputs then please have a look at this link https://www.gov.scot/publications/scotland-river-temperature-monitoring-network-srtmn/#The%20Scotland%20River%20Temperature%20Monitoring%20Network