Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries

Abstract

Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.

Seasonal Variations in Proton Binding Characteristics of Dissolved Organic Matter Isolated from the Southwest Baltic Sea

“…Terrestrial and marine DOM may also differ in stoichiometry of C, N, and P, with higher C/N ratios found in soil- and river-derived DOM than in autochthonous DOM produced by phytoplankton. 15 Moreover, H/C ratios decrease and O/C ratios increase as DOM ages. 22 The DOM chemical composition is complex, though the general consensus is that carboxylic acids and, to a lower extent, phenolic compounds (ca.…”

“… 14 The physicochemical variations are determined by marine and freshwater inputs, anthropogenic sources, enhanced primary productivity, and soil diversity that influence the DOM residence time, transport, and reactivity. 15 Baltic waters present typically high concentrations of marine and terrestrial DOM (mg·L –1 range) derived from primary production, terrestrial/freshwater inputs, and bio–phototransformation. 16 Furthermore, the enhanced DOM levels in the Baltic Sea may affect the acid–base water chemistry with consequences for modeling of the carbonate system.…”

The Interplay of Macrofauna Functional Groups Shapes Nitrogen Cycling in Oligotrophic Estuarine Sediments

“…1). The estuary is brackish (< 6), and oligotrophic due to limited nutrient inputs from the watershed (Hellemann et al 2017;Voss et al 2020), which mainly consists of coniferous forests and mires. This estuary is strati ed depending on spatiotemporal gradients of salinity, changing upon seasonal river discharge, and summer temperature (Brydsten and Jansson 1989;Bartl et al 2019).…”

Dissolved organic matter concentration, molecular composition, and functional groups in contrasting management practices of peatlands

“…In addition, DOM comprises a mixture of many molecular compositions and functional groups that govern its bioavailability, stability, and reactivity (Voss et al, 2020). Overall, pollution of freshwater by DOM can negatively influence its ecosystem services such as drinking water production, recreational values, biodiversity, and biogeochemical processes (Kritzberg et al, 2020).…”

“…The influence of DOM on ecosystem functions depends on its concentration, molecular composition, and functional groups because DOM is the largest source of energy and nutrients to terrestrial and freshwater ecosystems (Wymore et al., 2016). In addition, DOM comprises a mixture of many molecular compositions and functional groups that govern its bioavailability, stability, and reactivity (Voss et al., 2020). Overall, pollution of freshwater by DOM can negatively influence its ecosystem services such as drinking water production, recreational values, biodiversity, and biogeochemical processes (Kritzberg et al., 2020).…”