Changing headwater suspended sediment yields in the LOIS catchments over the last century: a paleolimnological approach

Abstract

Abstract:This paper describes the methods used to reconstruct suspended sediment yields over the last century, based on 210 Pb and 137 Cs dated bottom sediments in nine lake and/or reservoir catchments. Magnetic susceptibility and dry bulk density are used to correlate between multiple cores taken from each lake/reservoir basin in order to estimate sediment in¯ux through time and reconstruct sediment yield histories. The catchments represent a range of morphological and land use systems, including upland moorland, upland forestry and upland and lowland agricultural systems. The reconstruction provides some background information on pre-20th century sediment yields and permits an evaluation of the eect of 20th century land management systems, especially upland aorestation and agriculture, on changing suspended sediment yields. Reconstructed sediment yields over the last century range from c. 7 to 86 t km À2 yr À1. Average post-1953 yields from pasture, arable, moorland and forested catchments are 13, 31, 29 and 13 t km À2 yr À1 , respectively. The history of human disturbance in individual catchments is clearly recorded in the reconstructed sediment yields. Short-lived disturbance, such as aorestation, produces high yields (over 40 t km À2 yr À1 ) for up to a decade after planting, but yields subsequently decline to pre-planting levels (c. 12 t km À2 yr À1 ). Sustained increases in sediment yield are associated with arable, mixed agricultural and, to a lesser extent, grazing systems. While the strong controls exerted on sediment yield by human disturbance mask the potential eect of regional contrasts in runo and topography between catchments, there is some evidence to suggest that a long-term climate change signal is recorded in the temporal trends in sediment yield from an analysis of Lamb weather types.

Historic and contemporary sediment transfer in an upland Pennine catchment, UK

“…The 1986 Chernobyl peak within the fallout record is not evident within the core sediments, which could be a result of the sporadic fallout of Chernobyl caesium in upland catchments of the UK (Higgitt et al, 1993). These findings are consistent with other studies of the distribution of 137 Cs in reservoir sediments in northern England, although the strength of the various peaks varies between local regions (Foster and Lees, 1999). Lead-210 was also measured in the core samples but the signal was too noisy to yield useful results.…”

Changes in the physical and geochemical properties of suspended sediment delivered to the headwaters of LOIS river basins over the last 100 years: a preliminary analysis of lake and reservoir bottom sediments

“…An increase in the ®ne sediment fraction may lead to increases in the number of exchange sites available for the transport of sediment-associated contaminants, and a change in the Fe, Mn, Ca and organic matter concentration is likely to in¯uence the form and chemical stability of sediment-associated contaminants. Thirdly, with the exception of Elleron Lake, all sites show above-average P concentrations in the time period covered by the most recent sediment yield reconstruction (Foster and Lees, 1999). Above long-term average yields in the most recent time period are recorded in Fillingham and Elleron lakes, Newburgh Priory Pond and Fontburn and Silsden reservoirs, suggesting that the delivery of total P to downstream rivers has increased signi®cantly over the most recent time period.…”

The importance of a small ephemeral tributary for fine sediment dynamics in a main‐stem river

“…For example, Worrall, Burt, and Howden () reported a long‐term average sediment flux of 22.2 t km −2 year −1 for the United Kingdom (5th percentile and 95th percentile of 5.4 and 107.7 t km −2 year −1 , respectively). Foster and Lees () reported long‐term sediment yields of 7 to 86 t km −2 year −1 from their own research in the North of England, set against published values for the region ranging from 0.8 to 488 t km −2 year −1 (see references therein). They argue that the higher values can be attributed to human alterations to catchments, including agriculture and heather burning (Foster & Lees, ).…”

“…Foster and Lees () reported long‐term sediment yields of 7 to 86 t km −2 year −1 from their own research in the North of England, set against published values for the region ranging from 0.8 to 488 t km −2 year −1 (see references therein). They argue that the higher values can be attributed to human alterations to catchments, including agriculture and heather burning (Foster & Lees, ). The estimated specific sediment yield of over 180 t km −2 year −1 for Ben Gill falls close to the range of yields recorded in ephemeral Mediterranean basins (50 to 200 t km −2 year −1 , Walling & Webb, ; Rovira & Batalla, ).…”