Dissolved organic carbon and nitrogen in coastal waters

Chaichana, Saisiri (2017) Dissolved organic carbon and nitrogen in coastal waters. Doctoral thesis, University of East Anglia.

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Dissolved organic matter (DOM) including carbon and nitrogen (DOC and DON) are important but poorly understood components of the marine biogeochemical cycle. In this study, the distribution and cycling of DOC and DON, and particulate organic carbon and nitrogen (POC and PON) were investigated in North Sea surface and bottom water during the stratified summer season in 2011 and 2012, along with other key biogeochemical parameters such as nutrients. The summer DOC, DON, POC and PON ranged from 32.7-134.5, 2.8-13.7, 1.1-43.8 and 0.3-5.9 μM, respectively. The well-mixed water of the southern North Sea was also surveyed in the winter of 2011; measured concentration of DOC and DON were 56.2-224.8 and 3.7-12.3 μM. In summer, DOM and POM generally exhibited high levels in the southern well-mixed water (SM), whereas inorganic nutrient concentrations were higher in the northern bottom water (NB) due to nutrient regeneration and offshore water inflow. DOM in summer and inorganic nutrients in winter were also clearly influenced by riverine inputs. DON was the dominant nitrogen fraction of northern surface water and SM in summer, while in NB, TOxN (nitrate + nitrite) was the dominant fraction.
Analysis of SmartBuoy samples show phytoplankton provided a net source of DOM over the spring bloom period with net degradation in autumn and winter. Incubation experiments on water collected from two North Sea sites in autumn, winter 2013 and spring 2014 showed no nutrient (N and P) limitation on DOM degradation. The experiments yield mean bacterial decay rate constants (for three seasons) at the two sites of 4 ± 8 and 2 ± 3 %d-1 kDOC and 3 ± 4 and 4 ± 4 %d-1 kDON, under dark conditions. In comparison to the Redfield ratio, the bulk C:N molar ratio is enriched in carbon relative to nitrogen, while the slope C:N ratio is close to the Redfield ratio, but with a background of high C:N material.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Jackie Webb
Date Deposited: 06 Feb 2017 15:14
Last Modified: 06 Feb 2017 15:14
URI: https://ueaeprints.uea.ac.uk/id/eprint/62312

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