Biography:

In the past N. Wasmund has collaborated on articles with A. Hansen. One of their most recent publications is Regular ArticlesTrophic Status of the South-Eastern Baltic Sea: A Comparison of Coastal and Open Areas. Which was published in journal Estuarine, Coastal and Shelf Science.

More information about N. Wasmund research including statistics on their citations can be found on their Copernicus Academic profile page.

N. Wasmund's Articles: (3)

Regular ArticlesTrophic Status of the South-Eastern Baltic Sea: A Comparison of Coastal and Open Areas

AbstractPrimary production, nutrient concentrations, phytoplankton biomass (incl. chlorophyll a) and water transparency (Secchi depth), are important indicators of eutrophication. Earlier basin-wide primary production estimates for the Baltic Sea, a shallow shelf sea, were based mainly on open-sea data, neglecting the fundamentally different conditions in the large river plumes, which might have substantially higher production. Mean values of the period 1993–1997 of nutrient concentrations (phosphate, nitrate, ammonium and silicate), phytoplankton biomass, chlorophyll a (chl a) concentration, turbidity and primary production were calculated in the plumes of the rivers Oder, Vistula and Daugava and Klaipeda Strait as well as the open waters of the Arkona Sea, Bornholm Sea, eastern Gotland Sea and the Gulf of Riga. In the plumes, these values, except for primary production, were significantly higher than in the open waters. N:P ratios in the plumes were >16 (with some exceptions in summer and autumn), indicating potential P-limitation of phytoplankton growth, whereas they were <16 in the open Baltic Proper, indicating potential N-limitation. On the basis of in situ phytoplankton primary production, phytoplankton biomass and nutrient concentrations, the large river plumes and the Gulf of Riga could be characterized as eutrophic and the outer parts of the coastal waters and the open sea as mesotrophic. Using salinity to define the border of the plumes, their mean extension was calculated by means of a circulation model. Taking into account the contribution of coastal waters, the primary production in the Baltic Proper and the Gulf of Riga was 42·6 and 4·3×106 t C yr−1, respectively. Hence, an annual phytoplankton primary production in the whole Baltic Sea was estimated at 62×106 t C yr−1. The separate consideration of the plumes had only a minor effect on the estimation of total primary production in comparison with an estimate based on open sea data only. There is evidence for a doubling of primary production in the last two decades. Moreover, a replacement of diatoms by dinoflagellates during the spring bloom was noticed in the open sea but not in the coastal waters. A scheme for trophic classification of the Baltic Sea, based on phytoplankton primary production and biomass, chl a and nutrient concentrations, is proposed.

Succession of micro- and nanoplankton groups in ageing upwelled waters off Namibia

Highlights•Phytoplankton countings and chla measurements accord to RGB pictures.•Micro- and nanoplankton species have been assigned to functional groups.•The data have been rearranged by using a pseudo age approach.•A clear succession was found with nutrient depletion.•The diatoms to dinoflagellate ratio is suggested as a quantitative descriptor.

Primary production rates calculated by different concepts—an opportunity to study the complex production system in the Baltic Proper

AbstractPrimary production in the eastern Gotland Sea was calculated by three different approaches: (1) the nutrient concept based on the consumption of inorganic nutrients, (2) the biomass concept based on the increase of POC + DOC, and (3) the CO2 concept based on the consumption of total CO2 in the water. The comparison of these three integrating methods concentrated on a 108-d period of new production (28 March–13 July 2001), when all concepts were applicable. New production on the basis of winter nitrogen was approximately 1352 mmol C m− 2 (108 d)− 1. The excess PO4, still available after the spring bloom, allowed an additional new production of 1245 mmol C m− 2 (108 d)− 1 if additional nitrogen was supplied, e.g. by nitrogen fixation. The sum of 2597 mmol C m− 2 (108 d)− 1, based on the Redfield ratio, increased to 3098 mmol C m− 2 (108 d)− 1 if the measured POC/PON ratios were applied. The net community production, derived from the biomass concept, was 3294 mmol C m− 2 (108 d)− 1. Literature data from the CO2 concept were extrapolated to the euphotic zone, resulting in a net community production of 3327 mmol C m− 2 (108 d)− 1. In the period considered, new production and net community production were close to each other. The three concepts agree well and reveal a close range of 3098–3327 mmol C m− 2 (108 d)− 1 of net community production in the eastern Gotland Sea. The difference between net primary production rates and net community production is attributed to the respiration by the heterotrophs within the euphotic zone (3144 mmol C m− 2 (108 d)− 1). The share of new production in net primary production (f-ratio) was 48%. Differences of the CO2 concept and the biomass concept in the upper mixed layer owing to sedimentation across the thermocline were estimated at 1717 mmol C m− 2 (108 d)− 1. If calculated from the nutrient concept, nitrogen fixation accounts for 19–23% of net primary production.

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