The Deer in our Waters
Student Spotlight - Eloise Tugwell
Masters research carried out at Lancaster University
Email: eloise.tugwell@yahoo.com LinkedIn: https://www.linkedin.com/in/eloise-tugwell-b16459264
Short Summary
For my master's research at Lancaster University, I investigated the influence of red deer (Cervus elaphus) on hydrological properties within a reedbed, including their effect on nitrogen, phosphorous, turbidity and pH. Deer are often considered in a terrestrial sense for their influence on woodland regeneration; their riparian influence is less well developed. Understanding how mammals and hydrology relate is incredibly interesting and important for conservation of both mammals and the wider environment. Keep on reading to find out more!
The Full Story
Ask someone to picture a red deer, and many people would imagine them against great crags and gloomy Scottish skies, fierce survivors against their harsh northern climes. You may not imagine vibrant green reedbeds in the rich month of June, the warmth and humidity almost tropical in nature, the great grasses towering above as though in a rainforest.
But there they are. Hidden within vegetation more than 10ft tall, a hind tends to her calf, herds graze side by side, and stags deftly weave their way through the wetland, antlers hidden like branches.
The impact of red deer on terrestrial habitats is well documented. Over-browsing can be devastating for landowners as well as for woodland regeneration, and much research has been dedicated to these issues. However, in recent years, research has increasingly focused on the field of “ecohydrology”- the study of the interactions occurring between hydrological systems, and ecological ones (Bond, 2003). Ecohydrology asks the questions- “what is happening to our water?” and “what does ecology have to do with it?”.
These questions don’t have clear cut answers, but research has implied that mammals may act as “ecosystem engineers” and influence the physics of our rivers more than previously thought (Jones, et al., 1994; Beschta & Ripple, 2006). Moose may increase bioturbation and aid bioavailability of nutrients (Bump, et al., 2016), while mass die-offs in the Mara River in Africa have been documented to fundamentally alter its chemistry (Subalusky, et al., 2017). Increasingly, these research questions have been brought to the UK as we aim to conserve our rivers and wetlands.
My masters dissertation aimed to quantify the changes caused by the UK’s largest wild land mammals - the red deer.
But how do you find them amongst the reeds? It’s hard to imagine that you could lose an animal so large, but deer are incredibly shy and generally crepuscular (primarily active at twilight). In amongst stands of 10ft tall Phragmites australis, they’re invisible.
To find them, a colleague suggested taking a bird’s-eye view of the site, as had been done in years prior in order to investigate the influence of deer on biodiversity, so we took to the sky. Drone footage provided the perfect vantage point to record their movements and locate areas of high and low population density. The densities of tracks left by the animals varied from 240km/km2 to essentially non-existent in areas with high human presence, and track patterns told their own story of deer behaviour and community.
Once regions of high and low population density had been identified it was time to take to the field, armed with syringes and an old plastic jug. Water samples were taken inside and outside of the deer tracks, and in high and low population density regions. Unlike footprints left in the soil, the tracks in the reedbed carved deep channels through the water, utilised by deer and rare wading birds alike. These channels connected wet woodlands and ponds to the wider reedbed and were an important feature of the environment. While the focus of the research was primarily on water quality, understanding how these tracks were used by and influenced other flora and fauna provided further insight into the deer’s role as ecosystem engineers. To me, seeing these features in the field is always a highlight of research, and provides context and meaning to the numbers.
As research on ungulate impact on water quality is broad and poorly understood, it was important to look at the data with an appropriate level of detail. As such, a broad spectrum of parameters was chosen to investigate, including water depth, nitrate concentration, phosphate concentration, ammonia concentration, conductivity, turbidity, and pH.
It was hypothesised that bioturbation of sediments may increase bioavailability of nutrients within the water, and thus areas frequented by deer may show higher concentrations of nitrate, phosphate and ammonia, as well as higher conductivity readings. This has been recorded in prior studies on red deer, which noted alterations in water quality parameters resulting from deer use (McDowell, 2008). This is important to understand, as nutrient plumes may influence macrophyte growth and invertebrate communities, which are vital to wetland condition. Too many nutrients, and a site may risk eutrophication.
After the water samples had been collected, analysis in the lab concluded that red deer appear to influence water quality in Phragmites australis-dominant reedbeds. Average values of depth, nitrate, phosphate, turbidity, and conductivity were measured consistently higher in deer tracks compared to samples taken in undisturbed reedbed, showing general agreement with trends observed in previous literature. However, there were few statistically significant results and so the research was inconclusive and may not represent the objective reality. Further research is required to fully understand how deer may influence water quality. It may be that the influence is restricted to small spatial and temporal scales, as observed in previous research on moose (Bump, et al., 2016).
While the research was inconclusive, there is beauty in that. Our understanding of the importance of ecosystem engineers in both terrestrial and riparian environments is continually growing and is an exciting field to research. The reality is that there is so much we don’t know, and so much more to discover.
If you would like to hear more about my research on red deer, or would like to share research, I can be contacted through my email eloise.tugwell@yahoo.com, or on Linkedin https://www.linkedin.com/in/eloise-tugwell-b16459264. I am always interested in hearing about ongoing deer research and would love to hear from you.
Acknowledgements
I would like to thank the reserve rangers for their expertise and guidance during field work, and my dissertation supervisor for his continued support. I’d also like to thank Laura Nunnerley for her guidance when conducting fieldwork.
References
Beschta, R. L. & Ripple, W. J., 2006. River channel dynamics following extirpation of wolves in northwestern Yellowstone National Park, USA. Earth surface processes and landforms, 31(12), pp. 1525-1539.
Bond, B., 2003. Hydrology and ecology meet—and the meeting is good. Hydrological processes, 17(10), pp. 2087-2089.
Bump, J. K. et al., 2016. Nutrient release from moose bioturbation in aquatic ecosystems. Oikos, 126(3), pp. 389-397.
Jones, C. G., H, L. J. & Shachak, M., 1994. Organisms as Ecosystem Engineers. Oikos, 69(3), pp. 373-386.
McDowell, R. W., 2008. Water quality of a stream recently fenced‐off from deer. New Zealand Journal of Agricultural Research, 51(3), pp. 291-298.
Subalusky, A. L., Dutton, C. L., Rosi, E. J. & Post, D. M., 2017. Annual mass drownings of the Serengeti wildebeest migration influence nutrient cycling and storage in the Mara River. Proceedings of the National Academy of Sciences - PNAS, 114(29), pp. 7647-7652.