Terrestrial-marine continuum of sedimentary natural organic matter in a mid-latitude estuarine system
- 14 Downloads
Humic acids (HA) have several environmental roles, but are particularly important in aquatic environments, being recognized as redox active natural organic matter (NOM) components. We examined NOM in recent sediments of a low-energy coastal environment which is free from inputs of dissolved terrestrial HA as their solubility is suppressed by bonding with Ca2+ ions. Our aim is to investigate the contribution of autochthonous versus terrestrial C sources to HA and their fractions along a river-coastal lagoon transect.
Materials and methods
Surface sediments were collected along the Aussa River (R), in the central basin of the Marano and Grado Lagoon (L) and within a secluded lagoon fish farm (FF). Extractable NOM components were obtained by extracting sediments first with 0.5 M NaOH (free NOM) and then with 0.1 M NaOH plus 0.1 M Na4P2O7 (bound NOM). Extracts were separated into non-humic and humic fractions by solid phase chromatography. Organic carbon (Corg), total nitrogen (Ntot), δ13C, and δ15N were determined with an Isotope Ratio Mass Spectrometer (Thermo Scientific Delta V Advantage) coupled with an Elemental Analyzer (Costech Instruments Elemental Combustion System). Fourier-transform infrared (FTIR) spectra were recorded with a FT-IR100 PerkinElmer Spectrometer. UV-vis spectra were recorded at pH 7 by a Varian Cary Spectrophotometer.
Results and discussion
Both NOM and HA display typical traits of terrestrial origin in river sediments and of a more marine (algal) origin in lagoon and fish farm sediments. This trend is evident in free HA, whereas bound HA seem more influenced by terrestrial inputs. A larger proportion (60–70%) of non-humic C was extracted by NaOH in all samples. Bound HA differ from free HA for their C/N ratios, which are higher and vary within a much narrower range. The changes in HA’s 13C isotopic composition, FTIR spectra, and spectroscopic parameters (SUVA254, SR, and aromaticity) highlight a progressive mixing of terrestrial and marine substrates that either undergo in situ humification or are transported as materials sorbed onto suspended mineral particles.
Our results highlight the existence of a complex, but continuous pattern of terrestrial and marine contributions to C sequestration and humification even in transitional environments where allochthonous humic C inputs are restricted due to insolubilization of humic substances by Ca2+. Along the examined transect, the NOM and free and bound HA appear well differentiated. Terrestrial inputs contribute to the bound HA fraction via transported mineral particles in all the samples, no matter the environment encountered.
KeywordsHumic acids Lagoon Natural organic matter Sediments Stable isotopes
Elisa Petranich, Stefano Cirilli, and Stefano Sponza from the University of Trieste are warmly acknowledged for their technical assistance during sampling operations. We are grateful to Claudio Furlanut for his valuable support and kind hospitality at the fish farm during field work.
This study was partially supported by the University of Trieste (Finanziamento di Ateneo per progetti di ricerca scientifica - FRA 2014, ref. Stefano Covelli).
- Acquavita A, Aleffi IF, Benci C, Bettoso N, Crevatin E, Milani L, Tamberlich F, Toniatti L, Barbieri P, Licen S, Mattassi G (2015) Annual characterization of the nutrients and trophic state in a Mediterranean coastal lagoon: the Marano and Grado Lagoon (northern Adriatic Sea). Reg Stud Mar Sci 2:132–144CrossRefGoogle Scholar
- Aliaume C, Do Chi T, Viaroli P, Zaldívar JM (2007) Coastal lagoons of Southern Europe: recent changes and future scenarios. Trans Wat Monogr 1:1–12Google Scholar
- Andersson A, Brugel S, Paczkowska J, Rowe OF, Figueroa D, Kratzer S, Legrand C (2018) Influence of allochthonous dissolved organic matter on pelagic basal production in a northerly estuary. Estuar Coast Shelf Sci 204:225–235Google Scholar
- Brambati A (1996) Metalli pesanti nelle lagune di Marano e Grado: piano di studio finalizzato all’accertamento della presenza di eventuali sostanze tossiche persistenti nel bacino lagunare di Marano e Grado e al suo risanamento. Regione Autonoma Friuli-Venezia Giulia, Servizio Idraulica, TriesteGoogle Scholar
- Croué JP, Korshin GV, Leenheer J, Benjamin MM (2000) Isolation, fractionation and characterization of natural organic matter in drinking water. AWWARF, Denver, COGoogle Scholar
- R Development Core Team (2018) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, AustriaGoogle Scholar
- Faganeli J, Fanuko N, Malej A, Stegnar P, Vokovic A (1981) Primary production in the Gulf of Trieste (North Adriatic). Rapp Comm Int Merc Medit 27:69–71Google Scholar
- Ferrarin C, Umgiesser G, Scroccaro I, Mattassi G (2009) Hydrodynamic modelling of the lagoons of Marano and Grado, Italy. Geo Eco Mar 15:13–19Google Scholar
- Gatto F, Marocco R (1993) Morfometria e geometria idraulica dei canali della laguna di Grado (Friuli-Venezia Giulia). Geogr Fis Din Quaternaria 16:107–120Google Scholar
- Marocco R (1995) Sediment distribution and dispersal in the northern Adriatic lagoons (Marano and Grado paralic system). J Geol 57:77–89Google Scholar
- Miller JC, Miller JN (2010) Statistics and chemometrics for analytical chemistry, 6th edn. Pearson, HarlowGoogle Scholar
- Souza SO, Silva MD, Santos JCC, de Oliveira LC, do Carmo JB, Botero WG (2016) Evaluation of different fractions of the organic matter of peat on tetracycline retention in environmental conditions: in vitro studies. J Soils Sediments 16:1764–1775Google Scholar
- Stevenson FJ (1982) Humus chemistry: genesis, composition, reactions. John Wiley, New YorkGoogle Scholar
- Wada E, Goldber ED, Horibe Y, Saruhashi K (1980) Nitrogen isotope fractionation and its significance in biogeochemical processes occurring in marine environments. In: Goldberg ED, Horibe Y, Saruhashi K (eds) Isotope marine chemistry. Uchida Rokakuho, Tokyo, pp 375–398Google Scholar