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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.

Distribution of cyanobacteria cannot be evaluated using chlorophyll a (Chl a ) in vivo fluorescence, as most of their Chl a is located in non-fluorescing photosystem I. Phycobilin fluorescence, in turn, is noted as a useful tool in the detection of cyanobacterial blooms. We applied phycocyanin (PC) fluorometer in the monitoring of the filamentous cyanobacterial bloom in the Baltic Sea. For the bloom forming filamentous cyanobacteria Aphanizomenon flos-aquae and Nodularia spumigena , PC fluorescence maximum was identified using the excitation–emission fluorescence matrix. Consequently, the optical setup of our instrument was noted to be appropriate for the detection of PC, and with minor or no interference from Chl a and phycoerythrin fluorescence, respectively. During summer 2005, the instrument was installed on a ferryboat commuting between Helsinki (Finland) and Travemunde (Germany), and data were collected during 32 transects providing altogether 200 000 fluorescence records. PC in vivo fluorescence was compared with Chl a in vivo fluorescence and turbidity measured simultaneously, and with Chl a concentration and biomass of the bloom forming filamentous cyanobacteria determined from discrete water samples. PC fluorescence showed a linear relation to the biomass of the bloom forming filamentous cyanobacteria, and the other sources of PC fluorescence are considered minor in the open Baltic Sea. Estimated by PC fluorescence, cyanobacterial bloom initiated late June at the Northern Baltic Proper, rapidly extended to the central Baltic Proper and the Gulf of Finland, and peaked in the mid-July with values up to 10 mg l −1 (fresh weight). In late July, bloom vanished in most areas. During single transects, or for the whole summer, the variability in Chl a concentrations was explained more by PC fluorescence than by Chl a fluorescence. Thus, filamentous cyanobacteria dominated the overall variability in phytoplankton biomass. Consequently, we show that during the cyanobacterial blooms, the estimation of Chl a concentration using only Chl a in vivo fluorescence is not applicable, but PC in vivo fluorescence is required as a predictor as well.