Sediment accumulation rates in subarctic lakes: Insights into age-depth modeling from 22 dated lake records from the Northwest Territories, Canada

Age-depth modeling using Bayesian statistics requires well-informed prior information about the behavior of sediment accumulation. Here we present average sediment accumulation rates (represented as deposition times, DT, in yr/cm) for lakes in an Arctic setting, and we examine the variability across space (intra- and inter-lake) and time (late Holocene). The dataset includes over 100 radiocarbon dates, primarily on bulk sediment, from 22 sediment cores obtained from 18 lakes spanning the boreal to tundra ecotone gradients in subarctic Canada. There are four to twenty-five radiocarbon dates per core, depending on the length and character of the sediment records. Deposition times were calculated at 100-year intervals from age-depth models constructed using the 'classical' age-depth modeling software Clam. Lakes in boreal settings have the most rapid accumulation (mean DT 20±10 yr/cm), whereas lakes in tundra settings accumulate at moderate (mean DT 70±10 yr/cm) to very slow rates, (>100yr/cm). Many of the age-depth models demonstrate fluctuations in accumulation that coincide with lake evolution and post-glacial climate change. Ten of our sediment cores yielded sediments as old as c. 9000cal BP (BP=years before AD 1950). From between c. 9000cal BP and c. 6000cal BP, sediment accumulation was relatively rapid (DT of 20-60yr/cm). Accumulation slowed between c. 5500 and c. 4000cal BP as vegetation expanded northward in response to warming. A short period of rapid accumulation occurred near 1200cal BP at three lakes. Our research will help inform priors in Bayesian age modeling

Assessing the ecological status of candidate reference lakes in Ireland using palaeolimnology

This is the peer reviewed version of the following article: Leira, M., Jordan, P., Taylor, D., Dalton, C., Bennion, H., Rose, N., & Irvine, K. (2006). Assessing the ecological status of candidate reference lakes in Ireland using palaeolimnology. Journal of applied Ecology, 43(4), 816-827., which has been published in final form at https://doi.org/10.1111/j.1365-2664.2006.01174.x.This study provides the first systematic examination of changes to water quality in (perceived) pristine lakes over the last c. 150 years for Ireland, and demonstrates the potential of palaeolimnology to support the implementation of the WFD. The results indicate that diatom communities in low alkalinity lakes have been particularly altered, and acidification and nutrient enrichment appear to have been important drivers for some lakes. Furthermore, higher resolution results call into question the validity of applying c. 1850 as the date for reference conditions across Ireland.The research presented here was supported by the EPA (project number 2002-W-LS/7). Thanks are due to Jim Bowman of the EPA, Eddie McGee for the 210Pb data from Lough Nambrackkeagh, Sheila McMorrow for assistance with the figures, and to several staff and postgraduate research students from UU Coleraine, Trinity College, University of Dublin and University of Limerick, most notably Richard McFaul and Guangjie Chen, for assistance with fieldwork. Finally, thanks are owed to the numerous landowners who facilitated access to CRL and to the referees of an earlier version of this paper for their very helpful and constructive comments.S

Microalgae community of the Huaytire wetland, an Andean high-altitude wetland in Peru

AIM: The diversity and distribution of microalgae communities in a high-altitude (3,000 to 4,500 m a.s.l) Andean wetland, regionally known as bofedal, were examined to assess seasonal and spatial patterns. METHODS: Samples were taken monthly from June to December, 2008 at 13 stations in the Huaytire wetland (16° 54’ S and 70° 20’ W), covering three areas (impacted by urban land use, impacted by camelid pasture, and non-impacted) and three climatologically induced periods (ice-covered, ice-melt and ice-free). RESULTS: A total of 52 genera of algae were recorded. Diatoms were the predominant group in abundance and richness. We found a significantly higher abundance during the ice-melting period, when light exposure and runoff were intermediate, in comparison to the ice-covered (low light and flushing) and ice-free (high light and low runoff) periods. Microalgae abundance was significantly lower in the non-impacted area compared to the sites close to the urban area and to the camelid pastures. Alpha diversity ranged from 8 to 29 genera per sample. High genera exchange was observed throughout the wetland, showing a similar floristic composition (beta diversity = 4%). CONCLUSIONS: We found that diatoms were dominant and adapted to the extreme conditions of the Andean wetland, showing higher abundance during the ice-melt period and in the livestock area. Also, taxa richness was higher in the ice-melt period and in the most-impacted areas