Freshwater Umbrella Presentations

Are upland lakes in the UK succumbing to the nitrogen cascade?

Gavin L. Simpson and Chris J. Curtis


Recent evidence has emerged, mostly from North America, suggesting that base poor upland/mountain aquatic ecosystems are demonstrating a response to atmospheric nitrogen deposition even at very low inputs (e.g. Baron et al., 2000; Wolfe et al., 2001; Fenn et al., 2003; Sickman et al., 2003). Whether this is independent from or an interaction with climate change has not yet been ascertained. Furthermore, the interactions between acidification and eutrophication or oligotrophication are complex; for example, the aluminium released by acidification may inactivate P through complexation (Kopácek et al., 2001), leading to P limitation. Other work in the UK uplands has used phytoplankton bioassays to show that around three quarters of 30 study lakes are either N limited or co-limited by N and P (Maberly et al., 2002).

Hence for the first time there is direct evidence from the UK that there may be a widespread eutrophication effect of N deposition on upland waters, while the relative contribution of N deposition to eutrophication in the lowlands has never been properly quantified. A key question is therefore how N (as an eutrophier) is affecting the productivity and biodiversity of upland lakes. We have found evidence of long term shifts in diatom species composition in clean areas of the far north-west of the UK which mimic changes seen in other, more remote parts of the northern hemisphere. Can these be related to changing N deposition? May there be varying sensitivity to N deposition between lake types?

In this presentation we will attempt to answer these and other questions through detailed, high-resolution palaeolimnological analyses of sediment cores from a number of upland sites in the UK combining biological proxies, stable isotope measurements of carbon and nitrogen and other sediment proxies.


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  • Fenn M.E., Baron J.S., Allen E.B., Rueth H.M., Nydick K.R., Geiser L., Bowman W.D., Sickman J.O., Meixner T., Johnson D.W. and Neitlich P. 2003 Ecological effects of nitrogen deposition in the western United States. BioScience 53, 404–420. [ article ]
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