Svein Rune Erga

Phosphorus and nitrogen limitation of phytoplankton in the inner Oslofjord (Norway)

Abstract Several criteria of potential phosphorus and nitrogen limitation were applied throughout 1986 to the phytoplankton of the inner Oslofjord, a brackish-marine fjord in southeastern Norway. The criteria were hased on information on concentrations and distribution of nutrients, on analyses of the carbon (C), nitrogen (N), and phosphorus (P) content of particulate matter in the water column, and on results of deck experiments on the plankton. Indications of nutrient limitation were obtained from seasonal trends in C:N, C:P and N:P ratios, as well as from further shifts in these ratios in plankton kept in a container on deck for 24 hours. Nitrogen limitation was also deduced from an increase in the uptake capacity for ammonium in plankton during 24 hours of containment, and phosphorus limitation from an increase in alkaline phosphatase activity. During diatom blooms. a lowering of the ratio of light to dark rates of nitrate uptake provided one further test for nitrogen limitation. Two other tests (a st...

Ecological studies on the phytoplankton of Boknafjorden, western Norway. 1. The effect of water exchange processes and environmental factors on temporal and vertical variability of biomass

Abstract Temporal and vertical variability of phytoplankton biomass in terms of in situ fluorescence (ISF), chlorophyll a (chl a), particulate carbon (C), nitrogen (N), and phosphorus (P) were studied throughout 1981 in Boknafjorden, a deep-silled fjord of southwestern Norway. Local blooms of autochthonous populations of the diatom Skeletonema costatum were found in stratified waters of sheltered areas in late February. The first widespread diatom bloom occurred in late March and was probably transported in the brackish ‘upper layer’ from the Norwegian Coastal Current. A second diatom bloom was observed during an upwelling period in early May. After this event, a two-layer system could be recognized. Below the pycnocline shade-adapted cells formed a distinct maximum layer of chl a. Most likely they were introduced to the ‘intermediate layer’ by inflow of coastal water which compensated for the outflow of ‘fjord water’ above. A similar situation appeared in late June, during which autochthonous populations...

Testing Fluorescence Lifetime Standards using Two-Photon Excitation and Time-Domain Instrumentation: Rhodamine B, Coumarin 6 and Lucifer Yellow

Having good information about fluorescence lifetime standards is essential for anyone performing lifetime experiments. Using lifetime standards in fluorescence spectroscopy is often regarded as a straightforward process, however, many earlier reports are limited in terms of lifetime concentration dependency, solvents and other technical aspects. We have investigated the suitability of the fluorescent dyes rhodamine B, coumarin 6, and lucifer yellow as lifetime standards, especially to be used with two-photon excitation measurements in the time-domain. We measured absorption and emission spectra for the fluorophores to determine which wavelengths we should use for the excitation and an appropriate detector range. We also measured lifetimes for different concentrations, ranging from 10−2– 10−6 M, in both water, ethanol and methanol solutions. We observed that rhodamine B lifetimes depend strongly on concentration. Coumarin 6 provided the most stable lifetimes, with a negligible dependency on concentration and solvent. Lucifer yellow lifetimes were also found to depend little with concentration. Finally, we found that a mix of two fluorophores (rhodamine B/coumarin 6, rhodamine B/lucifer yellow, and coumarin 6/lucifer yellow) all yielded very similar lifetimes from a double-exponential decay as the separate lifetimes measured from a single-exponential decay. All lifetime measurements were made using two-photon excitation and obtaining lifetime data in the time-domain using time-correlated single-photon counting.

Seasonal variability in inherent optical properties in a western Norwegian fjord

We present measured seasonal variations in the inherent optical properties (the absorption and scattering coefficients) of water in a deep silled fjord (Samnangerfjorden) in western Norway. These were based on measurements taken at monthly intervals during an annual cycle. The measurements also include concentrations of chlorophyll a and yellow substance, which were assumed to dominate the behaviour of the absorption and scattering coefficients. The stations were at three fixed locations, one being placed in the innermost part of the fjord where there is little mixing of fjord water with water from the coastal current. The other two stations were placed at different distances from the mouth of the fjord, so that the water masses are characterized by different amounts of mixing between fjord water and coastal current water. Our data set shows how the absorption and scattering coefficients vary in a Norwegian fjord during an annual cycle, and how they depend on the concentrations of chlorophyll a and yellow substance. Values of the absorption coefficient at 412 nm varied between 0.1 and 2.0 m , and scattering coefficients were also found to vary within this range. Little variation over the spectral range was found for the scattering coefficients, but the absorption coefficient had larger spectral variations. The chlorophyll a concentrations varied from 0.01 to 6.3 mg m , and the concentration of yellow substance, as expressed by its absorption coefficient at 310 nm, was within the range 0.7–7.8 m .

Scattering properties of microalgae: the effect of cell size and cell wall.

The main objective of this work was to investigate how the cell size and the presence of a cell wall influence the scattering properties of the green microalgae Chlamydomonas reinhardtii. The growth cycle of two strains, one with a cell wall and one without, was synchronized to be in the same growth phase. Measurements were conducted at two different phases of the growth cycle on both strains of the algae. It was found that the shape of the scattering phase function was very similar for both strains at both growth phases, but the regular strain with a cell wall scatters more strongly than the wall-less mutant. It was also found that the mutant strain has a stronger increase in scattering than the regular strain, as the algae grow, and that the scattering from the regular strain is more wavelength dependent than from the mutant strain.

Mueller matrix measurements of algae with different shape and size distributions

The full Mueller matrix was measured to obtain the polarization state of the scattered light for a variety of algae with different shapes, wall compositions, sizes, and refractive indices. The experimental setup was a multiple laser Mueller matrix ellipsometer, by which measurements were performed for scattering angles from 16° to 160° sampled at every second degree for wavelengths of 473 nm and 532 nm. Previously, the polarization of light scattered from microalgae was investigated only for a few species, and the Mueller matrix was found to have little variation between the species. In our work a total of 11 algal species were investigated, representing diatoms, dinoflagellates, coccolithophorids, green algae, and a cryptophyte. The selection of species was made to obtain high variability in shape, size, cell wall, and refractive index. As in previous investigations, very small variations were found between species for most of the Mueller matrix elements, but noticeable variations were found for M(11), (M(12)+M(21))/2 and (M(33)+M(44))/2.

Impact of particulate and dissolved material on light absorption properties in a High-Altitude Lake in Tibet, China

Ground-based measurements of optical properties have rarely been conducted for lakes located on the Tibetan Plateau (TP). In this study, we analyzed the spectral absorption properties of phytoplankton, non-algal particles, and colored dissolved organic matter sampled in Lake Namtso on the TP in order to obtain the variability in the light absorption properties of each of these three components and the relative contribution of each component. The Chlorophyll-a concentration was found to be very low. The mean value of the spectral slope

Bioprospecting North Atlantic microalgae with fast growth and high polyunsaturated fatty acid (PUFA) content for microalgae-based technologies

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