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

Sherriff, S. C. and Rowan, J. S. and Melland, A. R. and Jordan, P. and Fenton, O. and O hUallachain, D. O. (2015) Investigating suspended sediment dynamics in contrasting agricultural catchments using ex situ turbidity-based suspended sediment monitoring. Hydrology and Earth System Sciences, 19 (8). pp. 3349-3363. ISSN 1027-5606

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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 L−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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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version made available under open access.
Faculty / Department / School: Current - Institute for Agriculture and the Environment
Date Deposited: 10 Apr 2017 03:02
Last Modified: 18 May 2017 06:20
Uncontrolled Keywords: sediment dynamics; modelling; catchments; soil erosion; in situ turbidity sensors; turbidity
Fields of Research : 05 Environmental Sciences > 0503 Soil Sciences > 050302 Land Capability and Soil Degradation
Socio-Economic Objective: D Environment > 96 Environment > 9609 Land and Water Management > 960905 Farmland, Arable Cropland and Permanent Cropland Water Management
D Environment > 96 Environment > 9614 Soils > 961402 Farmland, Arable Cropland and Permanent Cropland Soils
D Environment > 96 Environment > 9606 Environmental and Natural Resource Evaluation > 960608 Rural Water Evaluation (incl. Water Quality)
Identification Number or DOI: 10.5194/hess-19-3349-2015
URI: http://eprints.usq.edu.au/id/eprint/30873

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