A microsensor for carbonate ions suitable for microprofiling in freshwater and saline environments

A novel carbonate microsensor, based on the ion‐selective ionophore N,N,‐dioctyl‐3a,12 a‐bis(4‐trifluoroacetylbenzoxy)‐5β‐cholan‐24‐amide, is presented. The sensor chemistry and filling electrolyte, used previously for macrosensors, was improved for use in microsensors, and a simple calibration procedure was designed. The sensor is highly selective for carbonate, having a similar selectivity as the macrosensor, and is so insensitive to Cl− interference that it can be used in seawater. The ability to measure accurate profiles with the carbonate sensor was verified in agar gels with artificial carbonate gradients. Several environmental applications are presented, including photosynthesis and calcification measurements in freshwater stromatolites (tufas) and foraminifera. Carbonate profiles in illuminated and darkened hypersaline microbial mats were qualitatively as expected and aligned with the oxygen and pH profiles. The dissolved inorganic carbon profiles calculated from local pH and carbonate values, however, did not follow the expected trends, both in the foraminifera and the hypersaline mat. Temporal and spatial heterogeneities make perfect alignment of pH and carbonate profiles, needed for DIC calculations, unrealistic. The calculation of dissolved inorganic carbon microprofiles from pH and carbonate microprofiles is not recommended. The microsensor is highly useful in studies on calcification and decalcification, where direct concentrations of carbonate and calcium ions are needed

A H<inf>2</inf>S microsensor for profiling biofilms and sediments: Application in an acidic lake sediment

We developed a microsensor for the amperometric detection of dissolved hydrogen sulfide, H2S, in sediments and biofilms. The microsensor exhibits a fast (t90 1000 μmol H2S l-1, and has a low stirring dependency of the microsensor signal (<1 to 2%). We used the new microsensor to obtain the first microprofiles of H2S in an acidic lake sediment with a several cm thick flocculant surface layer. Despite the low pH of 4.6, a relative low SO42- level in the lake water, and a broad O2 respiration zone of ca 6 mm, we were able to measure H2S depth profiles in the sediment at a good resolution, that allowed for calculation of specific sulfate reduction and H2S oxidation activities. Such calculations showed highest sulfate reduction activity in the anoxic sediment down to ca 20 mm depth. A comparison of calculated areal rates of O2 consumption and sulfate reduction indicated that sulfate reduction accounted for up to 13% of total organic carbon mineralization in the acidic sediment. All produced H2S was reoxidizecl aerobically with O2 at the oxic-anoxic interface. In addition to its good performance in acidic environments, the new H2S microsensor has proven useful for sulfide measurements in neutral and moderate alkaline (pH < 9) biofilms and sediments, and thus is a true alternative to the traditionally used potentiometric Ag/Ag2S microelectrode for most applications in aquatic ecology and biogeochemistry

Microsensor for radioactivity

Microsensors for a variety of chemical compounds have been developed 1 . Their application has enormously enhanced the insight in the functioning of dense microbial communities, as occuring in biofilms, sedi- ments and microbial mats, in which metabolic pro- cesses are typically confined to narrow zones of 0.1–10 mm wide. With microsensors high spatial resolution studies are possible towards transport and conversion 2 , however, the range of compounds that can be measured with chemical microsensors is limited. The here described microsensor for radioactivity allows studies towards transport and binding of all com- pounds that can be radioactively labelled

In situ applications of a new diver-operated motorized microsensor profiler

Microsensors are powerful tools for microenvironment studies, however their use has often been restricted to laboratory applications due to the lack of adequate equipment for in situ deployments. Here we report on new features, construction details, and examples of applications of an improved diver-operated motorized microsensor profiler for underwater field operation to a water depth of 25 m. The new motorized profiler has a final precision of 5 μm, and can accommodate amperometric Clark-type microsensors for oxygen and hydrogen sulfide, potentiometric micro- sensors (e.g., for pH, Ca2+), and fiber-optic irradiance microsensors. The profiler is interfaced by a logger with a signal display, and has pushbuttons for underwater operation. The system can be pre-programmed to autonomous operation or interactively operated by divers. Internal batteries supply power for up to 24 h of measurements and 36 h of data storage (max. 64 million data points). Two flexible stands were developed for deployment on uneven or fragile surfaces, such as coral reefs. Three experimental pilot studies are presented, where (1) the oxygen distribution in a sand ripple was 3-D-mapped, (2) the microenvironment of sediment accumulated on a stony coral was studied, and (3) oxygen dynamics during an experimental sedimentation were investigated. This system allows SCUBA divers to perform a wide array of in situ measurements, with deployment precision and duration similar to those possible in the laboratory