The impact of rainfall events, catchment characteristics and estuarine processes on the export of dissolved organic matter from two lowland rivers and their shared estuary
The impact of rainfall events, catchment characteristics and estuarine processes on the export of dissolved organic matter from two lowland rivers and their shared estuary
Terrestrially-derived dissolved organic carbon (DOC) and nitrogen (DON) transported by rivers have been recognised as contributors to aquatic nutrient burdens, and can be of importance in rivers and estuaries already impacted by anthropogenic inorganic nutrient discharges. The concentration of DOC and DON and the flux of both to the estuary and ultimately the coastal zone is dependent upon many factors including rainfall, catchment land use, and biological processes. DOC and DON concentrations together with nitrate plus nitrite and ammonium concentrations were measured in the anthropogenically-impacted estuary Christchurch Harbour (UK) and at sites in the lower reaches of its two source rivers, the Hampshire Avon and the Stour, at weekly intervals for a year during which time several extreme rainfall events occurred. A series of transects along the estuary were also performed after weekly sampling was completed. DOC concentrations were correlated between both rivers and the estuary and were positively related to increases in river flow, but DON concentrations revealed a more complicated picture. Peak instantaneous fluxes of DOC and DON exceeded 60000 kg C d-1 and 7000 kg N d-1 respectively both in the Stour and the estuary during high flow periods. The sources of both and routes by which they enter the aquatic system may account for the differences in dynamics, with flushing of superficial soils being a key source of DOC and point sources such as sewage treatment works being proposed as sources of DON. Removal processes within the estuary were also of importance for DON concentrations while DOC behaved more conservatively with some evidence of local production within the estuary. Estimated annual loads of DON and DOC to the coastal zone from Christchurch Harbour were 118 kg N km-2 y-1 and 2296 kg C km-2 y-1.
DOC, DON, eutrophication, river flow, estuary, Christchurch Harbour
Panton, Anouska
9fff77ed-1abb-4322-abb3-ffb0d17c9601
Couceiro, F.
fefd7ac4-e7d3-46cf-988d-8ecd2e18b7d4
Fones, G.R.
5b71916c-4859-4a6f-b9ad-b6b1f541cbfa
Purdie, Duncan
18820b32-185a-467a-8019-01f245191cd8
15 September 2020
Panton, Anouska
9fff77ed-1abb-4322-abb3-ffb0d17c9601
Couceiro, F.
fefd7ac4-e7d3-46cf-988d-8ecd2e18b7d4
Fones, G.R.
5b71916c-4859-4a6f-b9ad-b6b1f541cbfa
Purdie, Duncan
18820b32-185a-467a-8019-01f245191cd8
Panton, Anouska, Couceiro, F., Fones, G.R. and Purdie, Duncan
(2020)
The impact of rainfall events, catchment characteristics and estuarine processes on the export of dissolved organic matter from two lowland rivers and their shared estuary.
Science of the Total Environment, 735, [139481].
(doi:10.1016/j.scitotenv.2020.139481).
Abstract
Terrestrially-derived dissolved organic carbon (DOC) and nitrogen (DON) transported by rivers have been recognised as contributors to aquatic nutrient burdens, and can be of importance in rivers and estuaries already impacted by anthropogenic inorganic nutrient discharges. The concentration of DOC and DON and the flux of both to the estuary and ultimately the coastal zone is dependent upon many factors including rainfall, catchment land use, and biological processes. DOC and DON concentrations together with nitrate plus nitrite and ammonium concentrations were measured in the anthropogenically-impacted estuary Christchurch Harbour (UK) and at sites in the lower reaches of its two source rivers, the Hampshire Avon and the Stour, at weekly intervals for a year during which time several extreme rainfall events occurred. A series of transects along the estuary were also performed after weekly sampling was completed. DOC concentrations were correlated between both rivers and the estuary and were positively related to increases in river flow, but DON concentrations revealed a more complicated picture. Peak instantaneous fluxes of DOC and DON exceeded 60000 kg C d-1 and 7000 kg N d-1 respectively both in the Stour and the estuary during high flow periods. The sources of both and routes by which they enter the aquatic system may account for the differences in dynamics, with flushing of superficial soils being a key source of DOC and point sources such as sewage treatment works being proposed as sources of DON. Removal processes within the estuary were also of importance for DON concentrations while DOC behaved more conservatively with some evidence of local production within the estuary. Estimated annual loads of DON and DOC to the coastal zone from Christchurch Harbour were 118 kg N km-2 y-1 and 2296 kg C km-2 y-1.
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Accepted/In Press date: 14 May 2020
e-pub ahead of print date: 16 May 2020
Published date: 15 September 2020
Additional Information:
Funding Information:
The authors would like to acknowledge the Environment Agency for provision of river flow data as well as Jack Billinge and Jiraporn Charoenvattanaporn for their valuable assistance with fieldwork. Rebecca Huggett is acknowledged for her assistance with producing Fig. 1 and Supplemental Fig. 1. We also thank two anonymous reviewers for helpful comments on a previous version of the manuscript. This research was funded by the Natural Environment Research Council (NERC) as part of the Christchurch Harbour Macronutrient Project ( NE/J012238/1 and NE/J01205X/1 ) under the Macronutrient Cycles programme.
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© 2020 The Authors
Keywords:
DOC, DON, eutrophication, river flow, estuary, Christchurch Harbour
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Local EPrints ID: 440922
URI: http://eprints.soton.ac.uk/id/eprint/440922
ISSN: 0048-9697
PURE UUID: 8783b34d-a92d-48f5-987e-716ef5a09881
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Date deposited: 22 May 2020 16:38
Last modified: 17 Mar 2024 02:32
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Author:
F. Couceiro
Author:
G.R. Fones
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