Loadings of dissolved organic matter and nutrients from the Neva River into the Gulf of Finland - Biogeochemical composition and spatial distribution within the salinity gradient

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Ylöstalo , P , Seppälä , J , Kaitala , S , Maunula , P & Simis , S 2016 , ' Loadings of dissolved organic matter and nutrients from the Neva River into the Gulf of Finland - Biogeochemical composition and spatial distribution within the salinity gradient ' , Marine Chemistry , vol. 186 , pp. 58-71 . https://doi.org/10.1016/j.marchem.2016.07.004

Title: Loadings of dissolved organic matter and nutrients from the Neva River into the Gulf of Finland - Biogeochemical composition and spatial distribution within the salinity gradient
Author: Ylöstalo, Pasi; Seppälä, Jukka; Kaitala, Seppo; Maunula, Petri; Simis, Stefan
Contributor: University of Helsinki, Tvärminne Zoological Station
Date: 2016-11-20
Language: eng
Number of pages: 14
Belongs to series: Marine Chemistry
ISSN: 0304-4203
URI: http://hdl.handle.net/10138/181078
Abstract: We studied the loadings of dissolved organic matter (DOM) and nutrients from the Neva River into the Eastern Gulf of Finland, as well as their distribution within the salinity gradient. Concentrations of dissolved organic carbon (DOC) ranged from 390 to 840 mu M, and were related to absorption of colored DOM (CDOM) at 350 nm, a(CDOM)(350), ranging from 2.70 to 17.8 m(-1). With increasing salinity both DOC and a(CDOM) decreased, whereas the slope of a(CDOM) spectra, S-CDOM(300-700), ranging from 14.3 to 21.2 mu m(-1), increased with salinity. Deviations of these properties from conservative mixing models were occasionally observed within the salinity range of approximately 1-4, corresponding to the region between 27 and 29 degrees E. These patterns are suggested to mostly reflect seasonal changes in properties of river end-member and hydrodynamics of the estuary, rather than non-conservative processes. On the other hand, observed nonlinear relationships observed between a(CDOM)*(350) and S-CDOM(275-295) emphasized the importance of photochemistry among various transformation processes of DOM. Dissolved inorganic nitrogen was effectively transformed in the estuary into particulate organic nitrogen (PON) and dissolved organic nitrogen (DON), of which DON was mostly exported from the estuary, enhancing productivity in nitrogen limited parts of the Gulf of Finland. DON concentrations ranged from 12.4 to 23.5 mu M and its estuarine dynamics were clearly uncoupled from DOC. In contrast to DOC, estuarine DON dynamics suggest that its production exceeds losses in the estuary. Total nitrogen (TN) and phosphorus (TP) loadings from the Neva River and St. Petersburg were estimated as 73.5 Gg N yr(-1) and 4.2 Gg P yr(-1), respectively. Approximately 59% of TN and 53% of TP loads were in organic forms. DOC and DON loadings were estimated as 741.4 Gg C yr(-1) and 19.0 Gg N yr(-1), respectively. Our estimate for DOC loading was evaluated against a previously published carbon budget of the Baltic Sea. According to the updated model, the Baltic Sea could be identified as a weak source of carbon into the atmosphere. (C) 2016 The Authors. Published by Elsevier B.V.
Subject: Baltic Sea
River Neva
Estuaries
Riverine Joading
Absorption
Chromophoric dissolved organic matter
Dissolved organic carbon
Carbon budgets
Dissolved organic nitrogen
SEA TRANSITION ZONE
BALTIC SEA
OPTICAL-PROPERTIES
EASTERN GULF
NORTH-SEA
INORGANIC NUTRIENTS
LAND-USE
IN-SITU
CARBON
NITROGEN
1172 Environmental sciences
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