Researchers from Froglife and the University of Hull are investigating how endangered and protected amphibians use man-made tunnels to cross roads and also, if such tunnels suffer from chemical pollution from the road traffic above them. A new study, published today in the Water and Environment journal indicates that such road tunnels, while extensively used by amphibians, including the protected great crested newt (Triturus cristatus), can indeed accumulate multiple potentially harmful substances including metals, salt and petroleum hydrocarbons. This is the first published research linking road pollution to amphibian tunnels for the great crested newt.
Amphibians need water to breed and in a heavily urbanised country such as the UK, the long distances they have to cross between their terrestrial grounds and breeding ponds are often crossed by roads. Roads are not just deadly obstacle courses for amphibians, killing millions each year but also have more insidious effects such as creating barriers for movement, effectively preventing animals from breeding and isolating them in smaller and smaller fragments of habitats. This means that in many parts of the world, amphibian populations have become increasingly fragmented, rare and isolated. Installing amphibian tunnels under roads can be a really positive and important step in order to reduce mortality and encourage connectivity. However, roads are known to be important sources of chemical pollution and amphibians are more susceptible than most animals due to their permeable skin which means dangerous substances can enter the body through direct contact.
The team of scientists investigated a site with four amphibian tunnels and collected numerous soil and water samples over multiple seasons and compared them to a nearby reference site, away from roads. To their surprise, the amphibian tunnels showed substantial pollution, ranging from high concentrations of metals such as copper and zinc and extreme pH values, much higher than those found in natural habitats. While the presence of chemical pollutants was not unexpected the high levels found came as a shock, especially as the road was very recently built and was less than 3 years old. Metals can accumulate on road surfaces due to car braking and other wear and tear on vehicles, while the high pH may be related to leaching from materials used in road and tunnel construction. Equally, salt concentrations were strongly seasonal, meaning winter applications of road grit were likely responsible. However, other pollutants were more difficult to pinpoint to the source, especially the hydrocarbons. Their impact on amphibians and other species is largely unknown currently, but several pollutants were at concentrations that suggested they could be harmful for the aquatic environment.
Dr Will Mayes from the University of Hull and who led the study said: “This is an interesting initial finding to demonstrate that there is a potential pathway which means amphibians could be exposed to road pollutants in tunnels. Understanding the risks associated with these pollutants can hopefully inform management guidance to minimise any potentially negative side-effects of amphibian tunnels, which play a key role in mitigating against the impacts of urban developments on amphibian communities.”
Dr Silviu Petrovan, a trustee from wildlife charity Froglife and who participated in the study said: “This is the first study that shows that small amphibian tunnels can accumulate potentially significant pollutants from the road surface. We currently do not know how these interact with amphibians and other species that use the same areas, such as voles, reptiles, hedgehogs and even otters. We need a better understanding of the spread of such road pollutants but also, there are simple measures that can be put in place in amphibian tunnels, especially washing them with a high-pressure water hose at the end of winter, in late February. This is carried out regularly in countries on the continent such as Germany, principally to remove leaf litter that could block amphibian movement but also to remove salt. It is extremely cheap and simple to do.”
White K, Mayes W, Petrovan S (2017) Identifying pathways of exposure to highway pollutants in great crested newt (Triturus cristatus) road mitigation tunnels. Water and Environment Journal DOI:10.1111/wej.12244