Carbon cycling in benthic diatom mats: Novel applications of LC/IRMS

Life on our planet is based on carbon and this life-sustaining element is essential in order to live, grow and reproduce. The cycling of carbon from the atmosphere, land and ocean into organisms, and back again needs to be in balance. If not, serious consequences, such as global climate disruption, may result. Benthic diatoms are main-contributors to the carbon cycle in coastal zones, and provide the basis of the marine food web and fix large amounts of the greenhouse gas CO₂. Understanding the function of benthic diatoms and their involvement in the carbon cycle will enhance our knowledge of ecosystems, and it will be important to predict effects of future environmental conditions (e.g. predicted sea level rise). Hence, the development of analytical methods to enable the study of carbon cycling in marine ecosystems in a detailed way is crucial. Is there a methodology to track the production and fate of carbon fixed by benthic diatoms in specific biochemical pools (e.g. carbohydrates, amino acids, lipids, and nucleic acids)? Are there seasonal changes that affect the physiology of diatoms by a different partitioning of fixed carbon between major biochemical pools? Do associated heterotrophic bacteria benefit from the organic matter released by the diatoms? Does the seasonal variation of diatom exudates play a role in shaping the composition of the community of the associated heterotrophic bacteria? These questions and others are addressed in this PhD thesis

Field research on the effects of UV-B filters on terrestrial Antarctic vegetation

Patches of vegetation of six common species growing on Leonie Island (67 degrees 35' S, 68 degrees 20' W), Antarctic Peninsula region were covered with either UV-B transparent perspex screens or UV-B absorbing screens. Uncovered plots served as a control. Temperature and relative humidity were monitored during the austral summer under and outside the screens. The mean effective PSII quantum efficiency showed significant differences among the species, but not between the UV-B treatments. It was concluded that the temperature and the moisture status of the vegetation obscured any possible influence of UV-B treatment on the tteffective PSII quantum efficiency. he usefulness of various UV-B exclusion and supplementation methods used to study the influence of UV-B in the field is discussed. [KEYWORDS: alga; Antarctica; grass; lichen; moss; ozone depletion; photosynthetic efficiency; UV-B filters; UV-B radiation; UV-B supplementation Ultraviolet-b; chlorophyll fluorescence; active radiation; bean-plants; growth; photosynthesis; irradiances; ozone]

Vertical gradients for particulate Cu fractions in estuarine water over tidal flats

The speciation of particulate copper was determined at several depths (0, 5 and 15 cm above the sediment surface) in the water column above intertidal flat systems in the polluted estuary Westerschelde (WS) and the relatively un-polluted Oosterschelde sea-arm (OS), in order to assess differences in water quality between the main body of water routinely determined in monitoring programmes and that at the sediment-water interface which is factually interacting with the benthic organisms. The bioavailable fraction was estimated by two sequential extraction's: a pH=5 acetic acid (Ac) and a pH=8 Na- dodecylsulphate (Dod) extraction. Irrespective the different character of the systems, when the differences in salinity were taken into account, dissolved fractions (DOC, pH) differed hardly between seasons and stations. Although occasionally a quantitative differentiation between sampling depths could occur, with higher particulate concentrations (Cu, Ac-Cu, Dod- Cu, C, sediment, POC, chlorophyll a) near the sediment-water interface, the qualitative properties (Cu/POC, Ac-Cu/POC, Dod- Cu/POC, Chl-a/POC, C/N) of the water remained constant all over the tidal cycle and between depths. The measurements carried out during monitoring programmes in main water streams thus result in a strong under-estimation of the quantities of particulate substances (seston, POC, chlorophyll a, Cu) available to the benthos at intertidal flats, whereas the qualitative (relative) properties are correctly estimated. With regard to the interaction with benthic organisms, it is concluded that the unexpected levels of Cu in the clam Macoma balthica (equal or higher in the OS than in the polluted Westerschelde) are partly caused by differences in sediment Cu concentrations (Hummel et al., 1997). Additionally the low concentration of suitable, chlorophyll a related, food in OS force the clam to filtrate at higher rates, whereby a higher volume of water and thus ultimately an equal or higher amount of Cu, will be taken in. [KEYWORDS: copper; speciation; estuary; bioavailability particulate organic carbon; bivalve Macoma-balthica mollusca; dutch wadden sea; scheldt estuary; trace-metals; organic-carbon; food-intake; netherlands; sediment; copper; matter]

Relations between free copper and salinity, dissolved and particulate organic carbon in the Oosterschelde and Westerschelde, Netherlands

In a previous investigation, relatively simple relations were found to estimate free Cu, and hence a good approximation of bio-available Cu, at two sites in estuarine waters of the Dutch Oosterschelde and Westerschelde. In the present study, these relations are validated for the remainder of the two sea arms. In the Westerschelde the relation between the concentration of a dissolved organic ligand (K = 10(13)), DOC (dissolved organic carbon) and salinity is valid in a range of salinities at least from 10 up to 25 to 30. This ligand group is primarily riverine and partly estuarine. It is, as far as we know, the strongest Ligand for Cu, and its concentration dominantly affects the free Cu ion concentrations, which are around 50 fM. At high salinities, dilution and mineralisation diminish the riverine member of the ligand group too much and the relation with salinity and DOC is no longer valid. In the Oosterschelde the relations between POC (particulate organic carbon) and particulate Cu and between POC and the ratio of particulate and dissolved Cu are valid for the western, central and eastern compartments. Since equilibrium was assumed to exist between dissolved and particulate Cu, foe Cu can be calculated from POC and particulate Cu concentrations. Due to the large adsorption capacity of POC, the Oosterschelde is with respect to Cu a very well-buffered system with [Cu2+] of 20 fM. [KEYWORDS: estuaries; copper; speciation; bio-availability Cathodic stripping voltammetry; scheldt estuary; eastern scheldt; trace-metals; sea-water; complexation; speciation; zinc; bay; cu]

LC/IRMS analysis: A powerful technique to trace carbon flow in microphytobenthic communities in intertidal sediments

Microphytobenthic communities are important for primary production in intertidal marine sediments. Extracellular polymeric substances (EPS), comprising polysaccharides and proteins, play a key role in the structure and functioning of microphytobenthic biofilms and allow interactions between the benthic microalgae and the associated heterotrophic bacteria. The use of stable isotopes has provided major insights into the functioning of these microbial ecosystems. Until recently, gas chromatography–isotope ratio mass spectrometry (GC/IRMS) was the principal method for compound specific stable isotope analysis in these studies. Liquid chromatography linked to IRMS (LC/IRMS) is a more recently developed technique that broadens the range of compounds that can be targeted, in particular enabling the analysis of 13C in non-volatile, aqueous soluble organic compounds, such as carbohydrates and amino acids. In this paper we present an overview of the possibilities and limitations of the LC/IRMS technique to study metabolic processes in microphytobenthic biofilms consisting of mainly diatoms. With a preliminary in-situ labeling experiment, we show that the biosynthesis of carbohydrates and amino acids in EPS and total carbohydrate and amino acid pools can be determined by LC/IRMS. Water extractable EPS were composed predominantly of carbohydrates, whereas amino acids played a minor role, both in terms of content and production. By using LC/IRMS, we will be able to quantify the biosynthesis of metabolites and, hence, to unravel in detail the metabolic pathways of the transfer of carbon from the diatoms via EPS to the bacteria

The effects of altered levels of UV-B radiation on an Antarctic grass and lichen

We report a long-term experiment on the photosynthetic response of natural vegetation of Deschampsia antarctica (Poaceae) and Turgidosculum complicatulum (Lichenes) to altered UV-B levels on Leonie Island, Antarctica. UV-B above the vegetation was reduced by filter screens during two seasons. Half of the screens were transparent to UV-A and UV-B (ambient treatment) or absorbing UV-B and part of the UV-A (below-ambient treatment). Half of the wedge- shaped filters had side walls leading to an enhancement of the daily mean temperature in summer by 2-4 degreesC, simulating rising mean air temperature on the Antarctic Peninsula. The other half of the filters were without side walls resulting in close-to-ambient temperature underneath. Plots without filters served as controls. UV-B supplementation of an extra 1.3 kJ UV-B-BE was achieved using UV-mini-lamp systems during 15 days in the second season. We found no evidence that altered incident UV-B levels and temperature had an effect on maximum photosystem II efficiency (F-v/F-m) and effective photosystem II efficiency (DeltaF/F-m') in both species. UV-B reduction did not influence contents of chlorophyll, carotenoids and methanol-soluble UV absorbing compounds in D. antarctica. Flowering shoot length of D. antarctica was not affected by UV-B reduction. Temperature enhancement tended to result in longer inflorescence axes. Results of two austral summer seasons of UV- reduction in natural stands of D. antarctica and T. complicatulum suggest that current ambient levels of UV-B do not have a direct effect on the photosynthetic performance and pigment contents of these species. Cumulative effects on growth have not been recorded after two years but can not be excluded on a longer term. [KEYWORDS: Antarctica; carotenoids; Deschampsia antarctica; photosynthesis; Turgidosculum complicatulum; UV-B radiation; UV-B supplementation Ultraviolet-radiation; vascular plants; umbilicaria-americana; argentine islands; photosystem-ii; growth; peninsula; photosynthesis; reproduction; physiology]