Palaeoenvironmental Reconstructions Based on Geochemical Parameters from Annually Laminated Sediments of Sacrower See (northeastern Germany) Since the 17th Century

The history of hardwater lake Sacrower See (Brandenburg, northeastern Germany) was reconstructed back to the 17th century based on a multi-proxy study of five short sediment cores dated by varve chronology, ²¹⁰Pb and ¹³⁷Cs isotopes. We were able to distinguish three main phases: The lake was mesotrophic prior to the 1830s with an oxic hypolimnion. From the early 19th century on, δ¹³C of organic matter indicates that primary productivity starts to increase slowly. Between the 1830s and 1872, the lake went through a transition towards eutrophy. Low calcite contents in the homogeneous sediment are caused by dissolution connected to increasing primary productivity and growing importance of decomposition processes. After 1873, and accelerated since 1963, Sacrower See is characterised by growing nutrient input, and thus further increasing primary productivity. The lake is eutrophic, and decomposition of organic matter causes high oxygen consumption in the hypolimnion, which becomes regularly anoxic during thermal summer stratification. Biogenic varves are preserved in the sediment, characterised by layers of autochthonous, biochemically precipitated calcite crystals. In this study, we were able to demonstrate that Sacrower See is an example of exceptional slow increase of anthropogenically enhanced nutrient input, and of the imprint which these processes have on sediments of a hardwater lake.     

Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter

The role of microbial sulfate reduction on organic matter oxidation was studied quantitatively in temperate intertidal surface sediments of the German Wadden Sea (southern North Sea) on a seasonal base in the years 1998–2007. The sampling sites represent the range of sediments found in the back-barrier tidal area of Spiekeroog Island: sands, mixed and muddy flats. The correspondingly different contents in organic matter, metals, and porosities lead to significant differences in the activity of sulfate-reducing bacteria with volumetric sulfate reduction rates (SRR) in the top 15 cm of up to 1.4 μmol cm^?3 day^?1. Depth-integrated areal SRR ranged between 0.9 and 106 mmol m^?2 day^?1, with the highest values found in the mudflat sediments and lower rates measured in sands at the same time, demonstrating the impact of both temperature and organic matter load. According to a modeling approach for a 154-km² large tidal area, about 39, 122, and 285 tons of sulfate are reduced per day, during winter, spring/autumn, and summer, respectively. Hence, the importance of areal benthic organic matter mineralization by microbial sulfate reduction increases during spring/autumn and summer by factors of about 2 and 7, respectively, when compared to winter time. The combined results correspond to an estimated benthic organic carbon mineralization rate via sulfate reduction of 78 g C m^?2 year^?1.     

Feeding behaviour of adult Centropages hamatus (Copepoda, Calanoida): Functional response and selective feeding experiments

The feeding behaviour of adults of the marine calanoid copepod Centropages hamatus was studied in laboratory experiments with ciliates and phytoplankton as food sources. The ingestion rate of algal (flagellates, diatoms) and ciliate prey (oligotrichs) as a function of prey concentration could be described by a Holling type III functional response, with close to zero ingestion rates at concentrations below 5 µg C l^− 1. In general, ingestion of ciliates was higher than ingestion of algae, and maximum feeding rates by adult males reached were half the feeding rates of adult females at prey concentrations exceeding 50 µg C l^− 1. When diatoms and ciliates were offered together C. hamatus (both sexes) fed exclusively on ciliates as long as they contributed with more than 5% to the mixture. This indicates the capability of active prey selection and switching between suspension feeding and ambush predation. Therefore, the feeding behaviour of adult C. hamatus can be characterised as omnivorous with a preference for larger motile prey. This implies a trophic level above two, if there is a sufficient abundance of protozoan food available.     

The influence of pull-out load on the efficiency of jetting during spudcan extraction

Mobile jack-up drilling rigs are deployed at many locations during their service life. This necessitates retrieval of the platform’s legs and spudcan footings before the rig move. In soft soils, where the spudcans embed deeply, the extraction process can be difficult, time consuming and therefore costly. Water jetting systems, devised to ease spudcan extraction, are a common feature on modern jack-up units. However, their effectiveness in reducing the pull-out load required is questioned by the offshore industry. To investigate their efficiency, centrifuge experiments of a reduced scale spudcan model with jets have been performed at the University of Western Australia. The footing was extracted from penetrations of up to 1.5 diameters in normally consolidated clay. Similar to spudcan extraction in the field, these were carried out under load control, applying a constant extraction force. Both influences of pull-out load magnitude and jetting flow rate were investigated. The study demonstrates that jetting is efficient in facilitating spudcan extraction, as it reduces the required uplift load. Practical guidance is provided in applying the results to field conditions.     

The Factors that Drive Forestry Export Ties: A Network Perspective

Abstract

Forestry exports are considered one of the major drivers of forest loss worldwide, especially for developing nations. Building on these insights, this article considers the factors that explain forestry flows using a network perspective. Using network data from measuring forestry export flows between all nations from 1997 to 2012, this article offers an explanation for what factors contribute to the network ties of exporting nations in the global forestry network. Fixed effects negative binomial regression analysis for a panel of 94 low- and middle-income nations shows that economic and neo-institutional factors are the strongest predictors of forestry export network ties. The findings have important theoretical and methodological implications. Future research may aim to incorporate more explicit ideas of social connectedness to their cross-national analyses by integrating a network perspective.     

Geological and environmental factors involved in natural gas accidents

Variability in soil mineralogy, texture, and pavement cover are involved in events leading to undetected gas leaks and subsequent explosions in Bowie, Md. and Washington, D.C. These geologic parameters are involved in selectively removing the gas odorant additive t-butyl merceptan as the gas came into contact with the soil near the pipeline breaks. This removal resulted in an accumulation of combustable natural gas without detectable odor. Soil samples from drill holes and near surface sites were utilized to map soil type, texture, and mineralogy. Residual methane content of the samples was also measured. The data from two dissimilar sites indicates that finegrained soil enriched in montmorillonite preferentially removes the odorant.     

Atmospheric input of nitrogen into the North Sea: ANICE project overview

The aim of the atmospheric nitrogen inputs into the coastal ecosystem (ANICE) project is to improve transport–chemistry models that estimate nitrogen deposition to the sea. To achieve this, experimental and modelling work is being conducted which aims to improve understanding of the processes involved in the chemical transformation, transport and deposition of atmospheric nitrogen compounds. Of particular emphasis within ANICE is the influence of coastal zone processes. Both short episodes with high deposition and chronic nitrogen inputs are considered in the project. The improved transport–chemistry models will be used to assess the atmospheric inputs of nitrogen compounds into the European regional seas (the North Sea is studied as a prototype) and evaluate the impact of various emission reduction strategies on the atmospheric nitrogen loads. Assessment of the impact of atmospheric nitrogen on coastal ecosystems will be based on comparisons of phytoplankton nitrogen requirements, other external nitrogen inputs to the ANICE area of interest and the direct nitrogen fluxes provided by ANICE. Selected results from both the experimental and modelling components are presented here. The experimental results show the large spatial and temporal variability in the concentrations of gaseous nitrogen compounds, and their influences on fluxes. Model calculations show the strong variation of both concentrations and gradients of nitric acid at fetches of up to 25 km. Aerosol concentrations also show high temporal variability and experimental evidence for the reaction between nitric acid and sea salt aerosol is provided by size-segregated aerosol composition measured at both sides of the North Sea. In several occasions throughout the experimental period, air mass back trajectory analysis showed connected flow between the two sampling sites (the Weybourne Atmospheric Observatory on the North Norfolk coast of the UK and Meetpost Noordwijk, a research tower at 9 km off the Dutch coast). Results from the METRAS/SEMA mesoscale chemistry transport model system for one of these cases are presented. Measurements of aerosol and rain chemical composition, using equipment mounted on a commercial ferry, show variations in composition across the North Sea. These measurements have been compared to results obtained with the transport–chemistry model ACDEP which calculates the atmospheric inputs into the whole North Sea area. Finally, the results will be made available for the assessment of the impact of atmospheric nitrogen on coastal ecosystems.     

Toxic effects of decomposing red algae on littoral organisms

Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l⁻¹ dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe.