Dissolved organic matter dynamics from rivers to the shelf sea in East Anglia (UK)

Cooper, Chiara (2022) Dissolved organic matter dynamics from rivers to the shelf sea in East Anglia (UK). Doctoral thesis, University of East Anglia.

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Abstract

Dissolved organic matter (DOM) plays an important role in the global carbon and nutrient cycles. DOM is one of the largest carbon pools, taking up and releasing carbon to and from the atmosphere, whilst also containing essential nutrients for the synthesis of organic molecules. In recent years, there has been an increasing number of studies on DOM transport across the land-to-ocean aquatic continuum, recognising the interconnection between terrestrial and marine ecosystems. Despite this, there remain major gaps in our understanding of DOM processing and dynamics as it is transported from rivers to seas, in particular the impact of tidal cycles and instream processing upon DOM composition and the fate of riverine DOM once it reaches the sea.

Through a combination of hourly to monthly-resolution sampling of two East Anglian rivers (River Yare and River Waveney) and the southern North Sea between November 2018 and July 2020, 309 water samples were collected and analysed for a range of variables {fluorescence spectra and indices, coloured DOM absorption, nutrients, chlorophyll-a, suspended solids) to determine DOM composition and dynamics.

Results revealed that the River Waveney (dominated by surface runoff) was characterised by terrestrial and biodegraded DOM, whilst DOM in the River Yare (groundwater dominated) was produced in-situ. In the estuary, DOM was biodegraded, photodegraded, adsorbed to the sediments, or released into the water column by tidal­induced sediment resuspension. Whilst dissolved organic carbon (DOC) was found to behave non-conservatively during some months, overall, DOC was transported conservatively through the rivers, whilst inorganic nitrogen was removed, and organic phosphorus was produced. The estuary exported a total of 3.20 ± 1.81 Gg yr1 of DOC, 1.26± 0.89 Gg yr1 of total dissolved nitrogen and 0.13 ± 0.06 Gg yr1 of total dissolved phosphorus to the shelf sea, with 67.5% of DOM of terrestrial origin (3.09 ± 1.87 Gg yr1 ) and 32.5% produced and remineralised in-situ (1.49 ± 0.90 Gg yr1). After entering the North Sea, riverine DOM mixed with seawater, was photodegraded and biodegraded throughout the year until the terrestrial signature was lost offshore. In spring and summer, DOM was produced in-situ possibly due to riverine nutrient input.

Collectively, these results improve our understanding of DOM dynamics across the land-to-ocean continuum, providing important information to enhance biogeochemical modelling and predictions of climate change impacts upon carbon exported from land to the ocean.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	22 Jun 2023 08:10
Last Modified:	22 Jun 2023 08:10
URI:	https://ueaeprints.uea.ac.uk/id/eprint/92459
DOI:

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