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Title: Nitrogen photo-chemistry and the dynamics of CDOM in aquatic environments
Author: Suddick, Emma C.
ISNI:       0000 0001 3489 0708
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2007
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Photochemical ammonium production and photo-bleaching of chromophoric dissolved organic matter (CDOM) kinetics were studied in a variety of aquatic environments including freshwater samples of peatland origin, Caithness, a Tyne Estuary (NE, U.K.) estuary and the Iberian Sea. The main aims of the study were to assess seasonal variability within the peatland catchments, in conjunction with a study of regional and geographical variability of dissolved organic matter (DOM) and ammonium photo-production. Samples collected from a variety of aqueous environments covered the CDaM .absofPtion coefficient at 350 nm (a350) range 0.3 to 69.0 m-I. Selected, filtered samples (n=21) were exposed to natural and artificial light, in order to study ~+ photo-production CDaM photo-bleaching. The photo-chemical degradation of CDaM, as indicated by decreases in a350 over time, also led to increases in the spectral slope of sample absorbance over the wavelength range 290-350 nm, and losses of total fluorescence intensity. In addition we observed hypsochromic shifts of long-wave, humic-like fluorescence (fluorophore A). Photo-chemical ammonium release was observed in 19 of the total 21 irradiation experiments. However the kinetics of ammonium production were complex with 4 of the 21 samples showing a near-linear increase in NH/ concentration while other samples showed an initial lag phase, followed by production and then a decline in NH/ concentrations. In order to assess possible impacts of ~+ release on N balance we estimated NH4+ photoproduction potentials from concentration differences between the initial values and maximum ~+ values divided by irradiation time (i1t). Thus obtained ~+ photo-production potentials between sites ranged from 0 to 3.57 JIM r1 h-I (mean ± stdev 0.7) under solar noon irradiance levels. Using calculated daily sky irradiance and seasonal correction factors, annual depth integrated ~+ photo-production rates were estimated, ranging from 0.06 to 8.05 JIMNm-2 yrI( mean ± stdev 2.73). The photo-chemical production ofNH/ indicates that photo-chemically induced nitrogen release could potentially be an important source of biologically labile nitrogen to aquatic ecosystems, with severe impacts upon the biogeochemistry and nutrient limitation of these environments when compared to N-reservoir size and other N fluxes. However, compared to N deposition photo-ammonification is not a major source ofN. Key words: Dissolved organic matter, chromophoric dissolved organic matter, photoammonification, peatlands, estuaries, marine, and fluorescence.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available