Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Factors Governing Site and Charge Density of Dissolved Natural Organic Matter

Rolf David Vogt
* ORCID logo ,
Øyvind A. Garmo
,
Kari Austnes
,
Øyvind Kaste
,
Ståle Leif Haaland
,
James Sample
,
Jan-Erik Thrane
,
Liv Bente Skancke
,
Cathrine Brecke Gundersen
,
Heleen A. De Wit
Version 1 : Received: 7 April 2024 / Approved: 8 April 2024 / Online: 8 April 2024 (11:39:03 CEST)

How to cite: Vogt, R.D.; Garmo, Ø.A.; Austnes, K.; Kaste, Ø.; Haaland, S.L.; Sample, J.; Thrane, J.; Skancke, L.B.; Gundersen, C.B.; De Wit, H.A. Factors Governing Site and Charge Density of Dissolved Natural Organic Matter. Preprints 2024, 2024040533. https://doi.org/10.20944/preprints202404.0533.v1 Vogt, R.D.; Garmo, Ø.A.; Austnes, K.; Kaste, Ø.; Haaland, S.L.; Sample, J.; Thrane, J.; Skancke, L.B.; Gundersen, C.B.; De Wit, H.A. Factors Governing Site and Charge Density of Dissolved Natural Organic Matter. Preprints 2024, 2024040533. https://doi.org/10.20944/preprints202404.0533.v1

Abstract

Rising organic charge in northern freshwaters is attributed to increasing levels of Dissolved Natural Organic Matter (DNOM) and shifts in water chemistry. Organic charge concentration may be determined by charge balance calculations (Org.-) or modelled (OAN-) using the conceptual Oliver and Hruška models based on the density of weak acid functional sites (SD) present in DNOM. The charge density (CD) is governed by the SD and protonation and complexation reactions on the functional groups. The models use this SD as a key parameter in empirically fitting the model to Org.-. Utilizing extensive datasets of water chemistry, this study shows that spatial and temporal differences in SD and CD are influenced by variations in the humic-to-fulvic ratio of DNOM and the organic aluminum (Al) complexation, as well as the mole fraction of CD to SD governed by the acidity. Site median SD obtained for 44 long-term monitored acid-sensitive lakes was 11.1 and 13.9 µEq/mg C for the Oliver and the Hruška model, respectively. During the 34 years of monitoring the CD increased by 70%, likely due to rising pH and declining Al complexation with DNOM. Present-day median SD values for the Oliver and Hruška models in 16 low-order streams are 13.8 and 15.8 µEq/mg C, respectively, and 10.8 and 12.5 µEq/mg C, respectively, in 10 high order rivers.

Keywords

Dissolved Natural Organic Matter; Organic charge; Site density; Charge density; Oliver model; Hruška model

Subject

Environmental and Earth Sciences, Environmental Science

Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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