Deer, climate and pathogen risk

Posted on September 21, 2011

An understanding of landscape-scale flows can be crucial when attempting to assess how the risks of water pollution vary with environmental conditions.  In mountainous regions, drinking water supplies for dispersed human populations usually receive only limited pre-treatment.  However, such areas often support large populations of warm-blooded  animals which have the capacity to contaminate water bodies with faecal parasites.  For example, in the highlands of Scotland, sizable numbers of red deer gather around wetlands in the bottoms of valleys to drink, graze and cool themselves in summer, and other mammals such as otters, water voles and rabbits live close to local streams.  Over a 14 month period researchers collected water samples from the Girnock catchment in the Scottish Cairngorms and made counts of faecal coliform bacteria.  Coliform counts were highest in summer (May – September), reflecting an increase in biological activity in warmer weather.  Although coliform levels  were low compared with those in urban and agricultural streams, they were still high enough to cause health risks.  Over 70% of the summer variation in coliform counts could be explained by four factors: water flow, alkalinity, the degree of catchment saturation and air temperature.  Flow rates gave an instantaneous measure of connectivity, while alkalinity and catchment saturation reflected the background conditions at the times when rainfall events occurred.   Using concentrations of >100 faecal coliforms / 100 ml as a measure of potential risk, it was estimated that acceptable safety levels were exceeded on around 13 days in dry years (2002-3), but much more often in wetter years (83 days in 2006-7).

 Reference:  Tetzlaff, D., Soulsby, C. & Birkel1, C.  (2010).   Hydrological connectivity and microbiological fluxes in montane catchments: the role of seasonality and climatic variability.  Hydrological Processes  24, 1231–1235.