Source, biogeochemical cycling, and fluorescence characteristics of dissolved organic matter in an agro‐urban estuary

Abstract

Seasonal measurements of dissolved organic matter (DOM) fluorescence characteristics were combined with weekly to bi-weekly measurements of carbon (C), nitrogen (N), and phosphorus (P) (including particulate, dissolved organic and inorganic forms) and chlorophyll to determine how riverine inputs and autochthonous production influence DOM and nutrient dynamics in the Swan-Canning estuary, Western Australia. Estuarine concentrations of C, N, and P were influenced by multiple factors, including the seasonal riverine flux of DOM, N, and P, the regeneration of mainly inorganic N and P from benthic anoxia, and the delivery of DOM and nutrients from urban drains. Parallel factor analysis of excitation-emission matrices identified eight fluorescence components that were used to fingerprint three distinct sources of estuarine DOM: (1) riverine DOM derived mainly from vascular plant material, (2) autochthonous DOM recently produced within the estuary (indicated by tryptophan-like fluorescence), and (3) autochthonous DOM originating from within the lower estuary or coastal marine environment enriched in marine humic-like and tyrosine-like fluorescence. Overall, fluorescence DOM characteristics shifted from humic-like in the upper and mid-estuary to protein-like in the lower estuary, which likely reflects the increased contribution of autochthonous relative to terrigenous DOM closer to the estuary mouth. Our findings show that DOM composition varies with season and estuary position as riverine DOM inputs, mainly from terrestrial plant material, are supplemented by autochthonous DOM contributions associated with discrete inputs of inorganic nutrients.

Spatiotemporal characterization of dissolved carbon for inland waters in semi-humid/semi-arid region, China

“…These methods primarily dependent on the ultraviolet-visible (UV-Vis) and fluorescence measurements have been widely applied and reported (Chin et al, 1994;Vodacek et al, 1997;Helms et al, 2008;Zhang et al, 2007Zhang et al, , 2010Fellman et al, 2011;Stedmon et al, 2011). Using the ratio of the absorptions at 250 to 365 nm (E 250 : 365 ), De Han and De Boer (1987) successfully tracked changes in DOM molecule size, which was confirmed by other researchers (Peuravouri and Pihlaja, 1997;Zhang et al, 2007).…”

“…High values of both E 250 : 365 and Sr are observed in brackish waters, which may be regulated by the DOC flux for inland waters both in time and space (Jaffé et al, 2008;Spencer et al, 2009Spencer et al, , 2012Zhang et al, 2010;Fellman et al, 2011). Nevertheless, the E 250 : 365 and Sr values are found to be useful for indicating seasonal DOC compositional variations (Fichot and Benner, 2011).…”

“…DOC mass balances are subject to the influences of temperature and precipitation, which can have important effects on DOC source, transport and fate (Larson et al, 2007;Jaffé et al, 2008;Fellman et al, 2011). Studies have indicated that concentrations of DOC in inland waters tend to decrease with increasing water residence times due to increased photobleaching and microbial activities (Curtis and Adams, 1995;Helms et al, 2008;Julian et al, 2008Julian et al, , 2011Stedmon et al, 2011).…”

Interacting effects of climate and agriculture on fluvial DOM in temperate and subtropical catchments

“…Fellman et al, 2010;Helms et al, 2008), especially when combined to parallel factor analysis (PARAFAC, Murphy et al, 2013;Stubbins et al, 2014). Spectroscopic measurements of DOM composition revealed that DOM from catchments with intensive agriculture is usually dominated by complex, humic fluorophores, is characterized by high humification and low contribution of protein-like fluorophores, and is likely to be released from microbial sources (Wilson and Xenopoulos, 2009;Williams et al, 2010;Graeber et al, 2012b;Fellman et al, 2011;Heinz et al, 2015). Moreover, existing time series indicate a stable composition of DOM exported from agricultural catchments across seasons, most likely linked to stable catchment DOM sources (Graeber et al, 2012b;Heinz et al, 2015).…”

Characterizing the Molecular Structure and Reactivity of Natural Organic Matter in The Everglades

“…characterized dissolved organic matter as 'humic-like' and 'protein-like' fluorophores. While the former are mainly derived from soil OM and plants, the latter may be plankton-derived and positive correlation between the 'protein-like' fluorescence and DOM bioavailability have been reported (Hood et al, 2009;Fellman et al, 2011). Therefore, 'protein-like' fluorescence has been applied as a proxy for bioavailable DOM (Fellman et al, 2009) and an indicator for biological reactivity of DOM (Parlanti, et al, 2000).…”