The main pathways for phosphorus flux from land to sea are particle-associated (erosion) and dissolved runoff (rivers, groundwater, and agricultural drainage systems). These pathways can act as diffused sources for aquatic systems and support primary production, therefore, counteracting the efforts aimed at reducing phosphorus input from point sources such as sewage treatment plants. Phosphorus supports primary production in the water column and can elevate phytoplankton and macrophyte growth. Coastal wetlands with emerged (Phragmites australis) and submerged (Stuckenia pectinata and Chara sp.) macrophytes can affect phosphorus fluxes in the land-water transitional zone. The macrophytes have the potential to act as a buffer for phosphorus run-off. The aim of this study was to determine the phosphorus stocks in the transitional land-sea zone of a cold temperate lagoon at the southern Baltic Sea. Phosphorus in macrophytes, water samples, and phytoplankton growth were analyzed along a gradient moving away from the wetland. The phosphorus stocks in the above ground biomass of the Phragmites plants were the highest at the end of August and with more than 8000mgPm in the interior zone of the wetland, threefold the amount of P in Phragmites plant tissue at the wetland fringe. The submerged macrophytes stored only 300mgPm, close to the wetland. Concentrations of soluble reactive phosphorus in the water column were higher in the zones of emerged macrophytes than in the zones of submerged macrophytes and decreased along the land-sea transect. Phytoplankton could grow proximal to the wetland during all seasons, but not further away. This study indicates that macrophytes can act as phosphorus sinks. However, short-term releases of phosphate within the Phragmites wetland have the potential to lead to phytoplankton growth. Phytoplankton can use these nutrient pulses either immediately or later, and support high biomass and turbidity within the system.

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A characteristic feature of lagoons and estuaries along the Baltic Sea is the dominance of reed (Phragmites australis) along their coasts. Reed wetlands are ecologically valuable ecosystems and play an important role for nutrient and matter cycling as well as for biodiversity. They provide a broad spectrum of ecosystem services and have been utilized by humans already for centuries. We assess the ecosystem service provision of reed wetlands and analyze how this is affected by different management scenarios and how the results of an expert-based ecosystem service assessment can be used in practice. Because of strong internal gradients and interactions with the surrounding, coastal reed belts show a higher ecosystem service provision compared to homogeneous inland reed. The three different coastal management scenarios are (1) winter harvest of reed, (2) summer harvest of reed, and (3) grazing by livestock. According to the views of 18 involved experts from Lithuania, Poland, and Germany, winter harvest is regarded as the scenario with the lowest conflict potential between nature protection and reed utilization. Experts expect no changes or even slight increases for regulating and cultural services. However, experts see the need to establish a sustainable and regionally anchored winter harvest concept. Summer harvest and grazing entail the risk to change the ecosystem structure and could lead to a shift in vegetation pattern toward short salt marsh grassland. Experts expect a slight decrease in regulating services. In particular, erosion control, biodiversity, and nutrient sequestration are rated controversially. To our experience, these expert-based ecosystem service assessments can support policy implementation (e.g., NATURA 2000, European Water Framework Directive or Marine Strategy Framework Directive). It can serve as a tool that allows stakeholders to visualize trade-offs, analyze patterns and processes at regional scales, and hence facilitate decision-making.

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A high resolution analysis of benthic foraminifera as well as of aeolian terrigenous proxies extracted from a 37 m-long marine core located off the Mauritanian margin spanning the last ~ 1.2 Ma, documents the possible link between major continental environmental changes with a shift in the isotopic signature of deep waters around 1.0–0.9 Ma, within the so-called Mid-Pleistocene Transition (MPT) time period. The increase in the oxygen isotopic composition of deep waters, as seen through the benthic foraminifera δ18O values, is consistent with the growth of larger ice sheets known to have occurred during this transition. Deep-water mass δ13C changes, also estimated from benthic foraminifera, show a strong depletion for the same time interval. This drastic change in δ13C values is concomitant with a worldwide 0.3‰ decrease observed in the major deep oceanic waters for the MPT time period. The phase relationship between aeolian terrigeneous signal increase and this δ13C decrease in our record, as well as in other paleorecords, supports the hypothesis of a global aridification amongst others processes to explain the deep-water masses isotopic signature changes during the MPT. In any case, the isotopic shifts imply major changes in the end-member δ18O and δ13C values of deep waters.

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Coastal wetlands are important for carbon (C) storage and sequestration. Still, there are large knowledge gaps concerning the amount of “blue carbon” in coastal wetlands dominated by common reed (Phragmites australis). We quantified carbon stocks at the southern Baltic Sea coast at six representative Phragmites wetland sites at the Darss-Zingst-Bodden Chain (DZBC) and the Strelasund, which include different categories of adjacent land use (arable land, woodland, pasture, urban), topography (totally flat to undulating), and geographical restrictions (dyking). Sediment samples were taken to a depth of 1 m, in line with the IPCC guidelines, and total carbon concentrations and bulk densities were measured in 10 cm intervals. The sites stored, on average, 17.4 kg C m−2 with large variability between sites, ranging from 1.76 to 88.6 kg C m−2. The estimated average is generally in good agreement with carbon stocks reported for tidal salt marshes, mangroves, and seagrass meadows. According to our estimation, based on widths of the reed belts and carbon stocks at the sampled sites, approximately 264,600 t of blue carbon could be stored in the coastal reed belts along the DZBC, a typical lagoon system of the southern Baltic Sea. Our study underlines the importance of these unique ecotones between land and sea for storage and sequestration of blue carbon. Since Phragmites is also a common (sometimes invasive) species along other large brackish water basins, such as the Black Sea or Chesapeake Bay, these estimates can be used for improved precision of modeling blue carbon budgets.