Convergent human and climate forcing of late-Holocene flooding in northwest England

Abstract

Concern is growing that climate change may amplify global flood risk but short hydrological data series hamper hazard assessment. Lake sediment reconstructions are capturing a fuller picture of rare, high-magnitude events but the UK has produced few lake palaeoflood records. We report the longest lake-derived flood reconstruction for the UK to date, a 1500-year record from Brotherswater, northwest England. Its catchment is well-suited physiographically to palaeoflood research, but its homogeneous, dark brown sediment matrix precludes visual identification of flood layers. Instead, an outlier detection routine applied to high-resolution particle size measurements showed a >90% match, in stratigraphic sequence, to measured high river flows. Our late-Holocene palaeoflood reconstruction reveals nine multi-decadal periods of more frequent flooding (CE 510-630, 890-960, 990-1080, 1470-1560, 1590-1620, 1650-1710, 1740-1770, 1830-1890 and 1920-2012), and these show a significant association with negative winter North Atlantic Oscillation (wNAO) phasing and some synchrony with solar minima. These flood-rich episodes also overlap with local and regional land-use intensification, which we propose has amplified the flood signal by creating a more efficient catchment sediment conveyor and more rapid hillslope-channel hydrological connectivity. Disentangling anthropogenic and climatic drivers is a challenge but anthropogenic landscape transformation should evidently not be underestimated in palaeoflood reconstructions. Our paper also demonstrates that flood histories can be extracted from the numerous lakes worldwide containing organic-rich, visually homogeneous sediments. This transformative evidence base should lead to more reliable assessments of flood frequency and risks to ecosystems and infrastructure.

Paleolimnological characterization of metal(loid) sources and transport processes in Canadian subarctic lakes

“…Abandoned mine sites such as at Yellowknife provide useful data to predict recovery from pointsource metal pollution. Our estimation of recovery time for Pb contamination of Yellowknife Bay was 1-97 years after mine closure, depending on the distance from the source, which is slightly lower than the 54-128 years estimated for the recovery from Pb pollution of a lake near a gold mine in Brotherswater, northeast England (Schillereff et al, 2016). Mining activity went on for 250 years in…”

“…Such long time series are necessary to evaluate recent dynamics in the context of natural variations and obtain an assessment of background conditions to which current conditions and trends can be compared. Environmental archives have been successfully used to reconstruction point source pollution (e.g., mining, smelters) (Schillereff et al, 2016;Wiklund et al, 2017), in addition to long-range transport (Catalan et al, 2013;Korosi et al, 2018;Muir et al, 2009).…”

“…Paleolimnological assessments of point-source metal pollution from mines have most commonly reported on recovery processes of elements such as As, Cd, Pb, Hg, Sb and Zn pollution (Child et al, 2018;Laperriere et al, 2008;Schillereff et al, 2016;Thienpont et al, 2016;Van Den Berghe et al, 2018). Post-mining trajectories can also be described and predicted spatially using spatial regressions from multiple cores.…”

“…Post-mining trajectories can also be described and predicted spatially using spatial regressions from multiple cores. Using the temporal least squares linear model of metal concentration or metal fluxes over time, Schillereff et al (2016) estimated that the post-mining trajectories for Pb and Zn project a return to pre-mining levels within 54-128 years for Pb and 75-187 years for Zn. However, they highlighted the uncertainties related to changing remobilization regime of legacy contaminants in the watershed.…”