Norbert Wasmund

Internal ecosystem feedbacks enhance nitrogen-fixing cyanobacteria blooms and complicate management in the Baltic Sea

Abstract Eutrophication of the Baltic Sea has potentially increased the frequency and magnitude of cyanobacteria blooms. Eutrophication leads to increased sedimentation of organic material, increasing the extent of anoxic bottoms and subsequently increasing the internal phosphorus loading. In addition, the hypoxic water volume displays a negative relationship with the total dissolved inorganic nitrogen pool, suggesting greater overall nitrogen removal with increased hypoxia. Enhanced internal loading of phosphorus and the removal of dissolved inorganic nitrogen leads to lower nitrogen to phosphorus ratios, which are one of the main factors promoting nitrogen-fixing cyanobacteria blooms. Because cyanobacteria blooms in the open waters of the Baltic Sea seem to be strongly regulated by internal processes, the effects of external nutrient reductions are scale-dependent. During longer time scales, reductions in external phosphorus load may reduce cyanobacteria blooms; however, on shorter time scales the internal phosphorus loading can counteract external phosphorus reductions. The coupled processes inducing internal loading, nitrogen removal, and the prevalence of nitrogen-fixing cyanobacteria can qualitatively be described as a potentially self-sustaining “vicious circle.” To effectively reduce cyanobacteria blooms and overall signs of eutrophication, reductions in both nitrogen and phosphorus external loads appear essential.

State and Evolution of the Baltic Sea, 1952–2005

Based on a fifty-year study conducted by the Leibniz Institute for Baltic Sea Research, this book brings together a comprehensive summary of their observations and findings. Written by well-known experts, this revealing book concentrates on long-term changes in the Baltic Sea?which can be extrapolated to shed light on the environmental problems of other shelf seas, brackish seas, and large estuaries?thereby contributing to our understanding of water exchange processes, eutrophication, and climatic impacts at the forefront of international concern.

The surface water CO2 budget for the Baltic Proper: a new way to determine nitrogen fixation

Abstract Six cruises were performed in the eastern Gotland Sea in about monthly intervals between March and September 2001 in order to establish a surface water carbon/nitrogen budget and to derive N2 fixation rates. Balancing the concentration changes of total CO2 and dissolved organic carbon, the CO2 air/sea exchange and the effect of mixed layer deepening yielded the net production of particulate organic carbon (POC) for each time interval. A total net production of 3.5 mol m−2 was obtained, which is consistent with earlier estimates of the POC export into the deep water. Measured C/N ratios in the particulate organic matter (POM) were applied to calculate the net formation of particulate organic nitrogen (PON), which was used to balance the nitrogen pools and fluxes. Taking into account the changes in dissolved organic nitrogen, the atmospheric input of NO3−/NH4+, and mixed layer deepening, the N2 fixation was calculated for each period. A total N2 fixation of 318±53 mmol m−2 was obtained, which substantially exceeded any previous estimate for the Baltic Proper (14–260 mmol m−2) and which corresponded to almost twice the spring bloom nitrogen consumption. The temporal distribution was characterized by an unexpected peak (108 mmol m−2) in late spring that was attributed to the activity of Aphanizomenon. A second maximum (106 mmol m−2) was found for the June–July period when Nodularia dominated the planktonic community.

Assessing impacts of invasive phytoplankton: the Baltic Sea case.

There is an increasing understanding and requirement to take into account the effects of invasive alien species (IAS) in environmental quality assessments. While IAS are listed amongst the most important factors threatening marine biodiversity, information on their impacts remains unquantified, especially for phytoplankton species. This study attempts to assess the impacts of invasive alien phytoplankton in the Baltic Sea during 1980-2008. A bioinvasion impact assessment method (BPL - biopollution level index) was applied to phytoplankton monitoring data collected from eleven sub-regions of the Baltic Sea. BPL takes into account abundance and distribution range of an alien species and the magnitude of the impact on native communities, habitats and ecosystem functioning. Of the 12 alien/cryptogenic phytoplankton species recorded in the Baltic Sea only one (the dinoflagellate Prorocentrum minimum) was categorized as an IAS, causing a recognizable environmental effect.

Regime shifts in the marine environment: The scientific basis and political context

Regime shifts in the marine environment have recently received much attention. To date, however, few large-scale meta-analyses have been carried out due to insufficient data coverage and integration between sustained observational datasets because of diverse methodologies used in data collection, recording and archival. Here we review the available data on regime shifts globally, followed by a review of current and planned policies with relevance to regime shifts. We then focus on the North and Baltic Seas, providing examples of existing efforts for data integration in the MarBEF Network of Excellence. Existing gaps in data coverage are identified, and the added value from meta-analyses of multiple datasets demonstrated using examples from the MarBEF integrated data project LargeNet. We discuss whether these efforts are addressing current policy needs and close with recommendations for future integrated data networks to increase our ability to understand, identify and predict recent and future regime shifts.

Data integration for European marine biodiversity research: creating a database on benthos and plankton to study large-scale patterns and long-term changes.

The general aim of setting up a central database on benthos and plankton was to integrate long-, medium- and short-term datasets on marine biodiversity. Such a database makes it possible to analyse species assemblages and their changes on spatial and temporal scales across Europe. Data collation lasted from early 2007 until August 2008, during which 67 datasets were collected covering three divergent habitats (rocky shores, soft bottoms and the pelagic environment). The database contains a total of 4,525 distinct taxa, 17,117 unique sampling locations and over 45,500 collected samples, representing almost 542,000 distribution records. The database geographically covers the North Sea (221,452 distribution records), the North-East Atlantic (98,796 distribution records) and furthermore the Baltic Sea, the Arctic and the Mediterranean. Data from 1858 to 2008 are presented in the database, with the longest time-series from the Baltic Sea soft bottom benthos. Each delivered dataset was subjected to certain quality control procedures, especially on the level of taxonomy. The standardisation procedure enables pan-European analyses without the hazard of taxonomic artefacts resulting from different determination skills. A case study on rocky shore and pelagic data in different geographical regions shows a general overestimation of biodiversity when making use of data before quality control compared to the same estimations after quality control. These results prove that the contribution of a misspelled name or the use of an obsolete synonym is comparable to the introduction of a rare species, having adverse effects on further diversity calculations. The quality checked data source is now ready to test geographical and temporal hypotheses on a large scale.

Climate-related Marine Ecosystem Change

This chapter deals with climate-related changes in the marine ecosystem of the Baltic Sea. The Baltic Sea is often described as one of the world’s largest brackish water bodies. It has a unique combination of oceanographic, climatic, and geographic features. Most important in this context is: the sea is a nearly enclosed area having a water residence time of 30 years, due to restricted water exchange through the Danish Straits. It is situated in northern Europe and has, therefore, some arctic characteristics and a pronounced seasonality. It is affected alternately by continental and marine climatic effects. It has a catchment area approximately four times larger than the sea itself, while it is as the same time very shallow, with an average depth of only 56 m, having thus a relatively small water body. Seasonal vertical mixing of the water reaches a depth of 30–50 m and contributes to resuspension of nutrients and pollutants. In deeper parts, a permanent halocline appears, below which anoxia is common and interrupted only by major inflows of North Sea water.

The exceptional Oder Flood in summer 1997 — the fate of nutrients and particulate organic matter in the Baltic Sea

The distribution of dissolved inorganic nutrients, particulate organic matter and phytoplankton pigments in the Oder plume was investigated at peak discharge of the Oder River during the exceptional flood event in summer 1997. Mixing diagrams of dissolved inorganic nutrients (NO3-, PO43-, SiO44-) reveal a nearly complete removal of nitrate during the first steps of estuarine mixing, whereas phosphate and silicate were still available over the entire salinity range. In contrast to silicate and phosphate, the nitrate riverine end-member concentration was about 3–4 times lower than during peak discharge in spring. It appears that during the summer flooding event inorganic nitrogen was not as available as in spring due to a stronger dilution effect and the advanced retention of nitrogen by land vegetation within the drainage area in summer. Therefore, algal biomass production in the Pomeranian Bight was most certainly nitrogen limited and significant removal of other dissolved inorganic nutrients by phytoplankton blooming did not occur.

Micro-autoradiographic determination of the viability of algae inhabiting deep sediment layers

Abstract Examination of sediment cores taken from shallow coastal regions of the Baltic showed that some algae were still alive at depths beyond the depth of light penetration. Their cells contained chlorophyll and photosynthesis resumed when they were exposed to light. Photosynthesis was detected by simultaneous measurement of oxygen production and 14 C uptake. Autoradiography was used to detect incorporated 14 C. The autoradiographic method was improved by a few modifications.

The Diatom/Dinoflagellate Index as an Indicator of Ecosystem Changes in the Baltic Sea 1. Principle and Handling Instruction

An ecosystem shift in the Baltic Proper at the end of the 1980s could be identified by a decreasing springtime diatom/dinoflagellate ratio. Therefore the suggested diatom/dinoflagellate index (Dia/Dino index) was developed as a descriptive indicator of ecosystem changes for applications pertaining to the Marine Strategy Framework Directive (MSFD). Changes in the dominance of these two phytoplankton classes impact the food web because both their quality as a food source for grazers and their periods of occurrence differ, which may lead to a mismatch in zooplankton growth. The rapid sinking of diatoms results in a high Dia/Dino index, indicative of low-level food availability for zooplankton but high-level food delivery to the zoobenthos. Consequently, the Dia/Dino index can be used to follow the food pathway (Descriptor 4 of MSFD: “food web”). Moreover, a low Dia/Dino index may indicate silicate limitation caused by eutrophication, whereas a high Dia/Dino index supports mitigated eutrophication, as the strong sedimentation of nutrients removes them from the water and deposits them in the sediment (Descriptor 5 of MSFD: “eutrophication”). Diatom dominance, and thus a high Dia/Dino index, is typical in historical data and is therefore assumed to reflect good environmental status (GES). The principles of the Dia/Dino index are explained herein using examples from two very different regimes, the Eastern Gotland Basin and Kiel Bay. In the assessment of the environmental status of these water bodies, GES boundaries of 0.5 and 0.75, respectively, are suggested. The conditions for calculating the Dia/Dino index are described and the limitations and advantages of this indicator are discussed.