Field calibration and performance of sediment traps in a eutrophic holomictic lake

Abstract

In wind-stressed and unstratified Lough Neagh low aspect ratio sediment traps, which allow for internal resuspension, collected sediment at a rate close to the natural sediment accumulation rate inferred from dated sediment cores. High aspect ratio traps grossly overestimated the natural rate of sediment accumulation as did, but to a lesser extent, burial rate measurements on an artificial stratigraphic marker. The former type of trap deployed over long exposure periods is therefore recommended as providing the best estimate of net downward particle flux in lakes such as Lough Neagh. However, it is emphasized that all sediment trap types, when operated in shallow turbulent lakes, will to a greater or lesser extent be 'contaminated' by secondary or redeposited material and so will not provide a direct measure of primary sedimentation. Use of tube traps in lakes such as Lough Neagh should not, however, be discounted since they can provide a record of the quality of sedimenting material through time.

Empirical evidence of the importance of sediment resuspension in lakes

“…If, as suggested by the data in Table 1, net sedimentation is small relative to gross sedimentation (i.e. Bloesch, 1982Bloesch & Uehlinger, 1986Flower, 1991Rosa, 1985Kansanen et al, 1991Gasith, 1975 # 1. Hakanson measured sedimentation in a centre-of-the-lake trap in 29 lakes (Hakanson et al, 1990;Evans & Hakanson, 1992).…”

“…Of particular interest is the study of resuspension in Lough Neagh by Flower (1991). Sediment traps with different aspects ratios (height:diameter) were used.…”

Mechanisms, measurement and importance of sediment resuspension in lakes

“…Again, an increase in settling flux towards the bottom of the lake indicates resuspension. Flower (1991) used traps with a low aspect ratio and could quantify the 'real' settling flux which he found to be equivalent to the sediment accumulation.…”

A review of methods used to measure sediment resuspension

“…those particles that have settled through the water column but have not become incorporated into the sediments; Walsh et al, 1988;Hicks et al, 1994). A most interesting methodological approach to quantify resuspension using sediment traps has been proposed by Flower (1991). He compared traps having high aspect ratio (recommended height:diameter > 5; Bloesch & Burns, 1980) with traps having lower aspect ratio.…”