Hydrological connectivity and microbiological fluxes in montane catchments: the role of seasonality and climatic variability

Abstract

There has been an upsurge of interest in the concept of hydrological connectivity to understand various aspects of catchment science (Bracken and Croke, 2007; Ali and Roy, 2008). Much of this work focuses on the dynamic role of connectivity in explaining the nonlinearities in catchment hydrological response; as the transient connection of hillslopes to channel networks is at the heart of important issues such as flood generation (e.g. Lane et al., 2004), diffuse pollutant fluxes (e.g. Jordan et al., 2007) and the trigger of many important ecological events (e.g. Tetzlaff et al., 2007a). These issues come together when considering the risk of microbiological pollution of surface waters by faecal pathogens which may include bacteria, viruses and protozoan parasites from warmblooded animals (Geldreich, 1996). This is an important applied topic with implications for human health, although one, poorly understood and an area where insights from process hydrology have not contributed as much as they might (Kay et al., 2007). Runoff processes in urban, agricultural and more extensively managed ‘wild’ landscapes play a crucial role in connecting pathogen reservoirs in the landscape to the river channel network (Kay et al., 2005). Managing this pollution risk requires different approaches under different land uses; however, there is a particular challenge in relatively undisturbed montane regions where the spatial distribution of pathogenic agents mainly relates to the distributions of wild animal populations which are often unknown. Yet in many such regions, water bodies are used for recreational activities and water supplies for dispersed populations usually have limited treatment. Thus, microbiological pollution may have significant health risks in areas often mistakenly considered ‘pristine’. If policies such as the European Union’s Water Framework Directive (WFD) are to be implemented, integrated catchment management of diffuse pollution requires that these issues receive more attention (Kay et al., 2010). The relationship between microbiological pathogens and hydrological connectivity in montane regions introduces complexities, particularly in terms of the seasonal influence of temperature and moisture availability on microbial survival and reproduction. There is already an identified need to develop appropriate metrics to quantify hydrological connectivity in different environmental settings (Ali and Roy, 2008). Such metrics have generally focused on physical and chemical parameters, which may differ greatly in different catchments. For example, assessing connectivity in overland flow dominated catchments (e.g. Birkel et al., 2010) will require approaches that differ from those applicable to catchments dominated by sub-surface flows (e.g. Lehmann et al., 2007). Here, we highlight the critical importance of seasonality in understanding how hydrological connectivity influences landscape and riverscape interactions to control fluxes of microbiological pollutants in a montane catchment in Scotland.