Investigating suspended sediment dynamics in contrasting agricultural catchments using ex situ turbidity-based suspended sediment monitoring

S. C. Sherriff (Lead / Corresponding author), J. S. Rowan, A. R. Melland, P. Jordan, O. Fenton, D. Ó. Huallacháin

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Soil erosion and suspended sediment (SS) pose risks to chemical and ecological water quality. Agricultural activities may accelerate erosional fluxes from bare, poached or compacted soils, and enhance connectivity through modified channels and artificial drainage networks. Storm-event fluxes dominate SS transport in agricultural catchments; therefore, high temporal-resolution monitoring approaches are required, but can be expensive and technically challenging. Here, the performance of in situ turbidity sensors, conventionally installed submerged at the river bankside, is compared with installations where river water is delivered to sensors ex situ, i.e. within instrument kiosks on the riverbank, at two experimental catchments (Grassland B and Arable B). The in situ and ex situ installations gave comparable results when calibrated against storm-period, depth-integrated SS data, with total loads at Grassland B estimated at 12 800 and 15 400 t, and 22 600 and 24 900 t at Arable B, respectively. The absence of spurious turbidity readings relating to bankside debris around the in situ sensor and its greater security make the ex situ sensor more robust. The ex situ approach was then used to characterise SS dynamics and fluxes in five intensively managed agricultural catchments in Ireland which feature a range of landscape characteristics and land use pressures. Average annual suspended sediment concentration (SSC) was below the Freshwater Fish Directive (78/659/EEC) guideline of 25 mg Lg'1, and the continuous hourly record demonstrated that exceedance occurred less than 12 % of the observation year. Soil drainage class and proportion of arable land were key controls determining flux rates, but all catchments reported a high degree of inter-annual variability associated with variable precipitation patterns compared to the long-term average. Poorly drained soils had greater sensitivity to runoff and soil erosion, particularly in catchments with periods of bare soils. Well drained soils were less sensitive to erosion even on arable land; however, under extreme rainfall conditions, all bare soils remain a high sediment loss risk. Analysis of storm-period and seasonal dynamics (over the long term) using high-resolution monitoring would be beneficial to further explore the impact of landscape, climate and land use characteristics on SS export.

Original languageEnglish
Pages (from-to)3349-3363
Number of pages15
JournalHydrology and Earth System Sciences
Volume19
Issue number8
DOIs
Publication statusPublished - 3 Aug 2015

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agricultural catchment
suspended sediment
turbidity
monitoring
sensor
arable land
catchment
bare soil
soil erosion
grassland
land use
soil drainage
soil
drainage network
sediment transport
river water
connectivity
runoff
erosion
water quality

Cite this

Sherriff, S. C. ; Rowan, J. S. ; Melland, A. R. ; Jordan, P. ; Fenton, O. ; Huallacháin, D. Ó. / Investigating suspended sediment dynamics in contrasting agricultural catchments using ex situ turbidity-based suspended sediment monitoring. In: Hydrology and Earth System Sciences. 2015 ; Vol. 19, No. 8. pp. 3349-3363.
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abstract = "Soil erosion and suspended sediment (SS) pose risks to chemical and ecological water quality. Agricultural activities may accelerate erosional fluxes from bare, poached or compacted soils, and enhance connectivity through modified channels and artificial drainage networks. Storm-event fluxes dominate SS transport in agricultural catchments; therefore, high temporal-resolution monitoring approaches are required, but can be expensive and technically challenging. Here, the performance of in situ turbidity sensors, conventionally installed submerged at the river bankside, is compared with installations where river water is delivered to sensors ex situ, i.e. within instrument kiosks on the riverbank, at two experimental catchments (Grassland B and Arable B). The in situ and ex situ installations gave comparable results when calibrated against storm-period, depth-integrated SS data, with total loads at Grassland B estimated at 12 800 and 15 400 t, and 22 600 and 24 900 t at Arable B, respectively. The absence of spurious turbidity readings relating to bankside debris around the in situ sensor and its greater security make the ex situ sensor more robust. The ex situ approach was then used to characterise SS dynamics and fluxes in five intensively managed agricultural catchments in Ireland which feature a range of landscape characteristics and land use pressures. Average annual suspended sediment concentration (SSC) was below the Freshwater Fish Directive (78/659/EEC) guideline of 25 mg Lg'1, and the continuous hourly record demonstrated that exceedance occurred less than 12 {\%} of the observation year. Soil drainage class and proportion of arable land were key controls determining flux rates, but all catchments reported a high degree of inter-annual variability associated with variable precipitation patterns compared to the long-term average. Poorly drained soils had greater sensitivity to runoff and soil erosion, particularly in catchments with periods of bare soils. Well drained soils were less sensitive to erosion even on arable land; however, under extreme rainfall conditions, all bare soils remain a high sediment loss risk. Analysis of storm-period and seasonal dynamics (over the long term) using high-resolution monitoring would be beneficial to further explore the impact of landscape, climate and land use characteristics on SS export.",
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Investigating suspended sediment dynamics in contrasting agricultural catchments using ex situ turbidity-based suspended sediment monitoring. / Sherriff, S. C. (Lead / Corresponding author); Rowan, J. S.; Melland, A. R.; Jordan, P.; Fenton, O.; Huallacháin, D. Ó.

In: Hydrology and Earth System Sciences, Vol. 19, No. 8, 03.08.2015, p. 3349-3363.

Research output: Contribution to journalArticle

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