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  • 1. Alikas, Krista
    et al.
    Kratzer, Susanne
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Brockmann Consult GmbH, Geesthacht, Germany.
    Reinart, Anu
    Kauer, Tuuli
    Paavel, Birgot
    Robust remote sensing algorithms to derive the diffuse attenuation coefficient for lakes and coastal waters2015In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 13, no 8, 402-415 p.Article in journal (Refereed)
    Abstract [en]

    In this study, empirical and semianalytical algorithms are developed and compared for optically complex waters to retrieve the diffuse attenuation coefficient of downwelling irradiance (Kd(lambda)) from satellite data. In the first approach, a band ratio algorithm was used. Various sets of MERIS band ratios were tested to achieve the best estimates for K-d(490) based on the in situ dataset which was measured in Nordic lakes (oligotrophic to eutrophic conditions). In the second approach, K-d(490) was expressed as a function of inherent optical properties which were retrieved from MERIS standard products. The algorithms from both approaches were tested against an independent data set and validated in optically complex coastal waters in the Baltic Sea and in Nordic lakes with high concentrations of coloured dissolved organic matter (0.3 < a(cdom)(442) m(-1) < 4.5), chlorophyll a (Chl a) (0.7< C-Chl a(mg m(-3))< 67.5) and total suspended matter (TSM) (0.5 < C-TSM(g m(-3)) < 26.4). MERIS-derived K-d(490) values showed reliable estimates in case of both methods. The results indicate that for band ratio algorithms, the root mean square error (RMSE) decreases and the coefficient of determination (R-2) increases when using longer wavelengths in the visible spectrum as a reference band. It was found that the best estimates were retrieved from MERIS data when using the ratio of R-rs(490)/R-rs(709) for coastal waters (K-d(490) < 2.5 m(-1)) and the ratio R-rs(560)/R-rs(709) for more turbid inland waters (Kd(490) > 2.5 m(-1)). As a result, a combined band ratio algorithm was developed, which provides a promising approach R-2 = 0.98, RMSE= 17%, N = 34, p < 0.05) for estimating K-d(490) over a wide range of values (0.3-6.1 m(-1)).

  • 2.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    A single-step staining method to evaluate egg viability in zooplankton2010In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 8, 414-423 p.Article in journal (Refereed)
    Abstract [en]

    A simplified method for viability analysis of zooplankton eggs by staining of nonviable eggs with a fluorescent nucleic acid stain TO-PRO-1 iodide is proposed here as a further development of fluorescence-based egg viability assays. This is one-step analysis with no intermediate steps for chorion removal. The method was calibrated using predetermined mixtures of viable and nonviable eggs (rotifers and copepods), and validated using hatching experiments (copepods) and egg development assay (cladocerans) as reference measurements. In these tests, eggs of several zooplankton species, Brachionus plicatilis (Rotatoria), Daphnia magna (Cladocera), Nitocra spinipes (Harpacticoida), Acartia tonsa (Calanoida), were used. Moreover, staining efficiency was not affected by storage of samples for up to 1 month in -80 degrees C, making the assay suitable for egg viability assessment in field and laboratory studies. To illustrate usefulness of the method, it was applied to evaluate how absence of re-mating affects production of viable eggs in females of A. bifilosa (Calanoida). In females separated from males, proportion of sterile eggs increased in 3 d after the separation and no viable eggs were produced after 5 d. The effects of mating frequency on egg viability are important to understand when designing egg production experiments and interpreting field data on egg viability in populations with skewed sex ratios.

  • 3.
    Gustafsson, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gelting, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Per
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Roos, Per
    An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3-year study in the open Baltic Sea comparing sediment traps, 234Th proxy, nutrient, and oxygen budgets2013In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 11, 495-510 p.Article in journal (Refereed)
    Abstract [en]

    Six different approaches for estimating the upper ocean export of carbon and nitrogen has been assessed using 2-3 years of observations in the open Baltic Sea. The long-term average export ratios, relative to primary production, were similar from approaches based on upper ocean N budget (0.29 +/- 0.02), upper ocean O budget (0.25 +/- 0.02), collection-efficiency-corrected sediment traps (0.30 +/- 0.03), and Th-234-derived POC export (0.21 +/- 0.03; POC/Th-234 ratio from traps). Estimates of carbon export efficiency based on direct sediment traps (0.14 +/- 0.02) likely reflected under trapping whereas filter-based Th-234-derived POC export (0.86 +/- 0.03) indicated that POC/Th-234 ratio from filters were larger than the ratio on truly settling matter; these two approaches and estimates are thus not recommended. This study provides improved constraints on the upper ocean C and N export in offshore temperate-boreal continental shelf regimes such as the open Baltic Proper. The long-term export fluxes derived by averaging the four geochemically consistent yet independent approaches were for POC 44.6 +/- 4.0 gC m(-2) y(-1) and for PON 7.0 +/- 0.6 gN m(-2) y(-1). This multi-technique approach improves understanding of carbon and nitrogen cycling in the upper ocean by constraining the export efficiencies through comprehensive time-series measurements.

  • 4.
    Holmborn, Towe
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Dahlgren, Kristin
    Holeton, Claire
    Hogfors, Hedvig
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)2009In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 7, 785-794 p.Article in journal (Refereed)
    Abstract [en]

    Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L–1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

  • 5. Holtappels, Moritz
    et al.
    Kuypers, Marcel M. M.
    Schlueter, Michael
    Brüchert, Volger
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Measurement and interpretation of solute concentration gradients in the benthic boundary layer2011In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 9, 1-13 p.Article in journal (Refereed)
    Abstract [en]

    The coastal ocean is characterized by high exchange rates of organic matter, oxygen, and nutrients between the sediment and the water column. The solutes that are exchanged between the sediment and the overlying water column are transported across the benthic boundary layer (BBL) by means of turbulent diffusion. Thus, solute concentration gradients in the BBL contain valuable information about the respective fluxes. In this study, we present the instrumentation and sampling strategies to measure oxygen and nutrient concentration gradients in the BBL. We provide the theoretical background and the calculation procedure to derive ratios of nutrient and oxygen fluxes from these concentration gradients. The noninvasive approach is illustrated at two sampling sites in the western Baltic Sea where nutrient and oxygen concentration gradients of up to 5 and 30 mu M m(-1), respectively, were measured. Nutrient and oxygen flux ratios were used to establish a nitrogen flux balance between sediment and water column indicating that 20% and 50% of the mineralized nitrogen left the sediment in form of N(2) (station A and B, respectively). The results are supported by sediment incubation experiments of intact sediment cores, measuring denitrification rates, and oxygen uptake. The presented flux ratio approach is applicable without knowledge of turbulent diffusivities in the BBL and is, therefore, unaffected by non-steady-state current velocities and diffusivities.

  • 6.
    Mörth, Carl-Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Backman, Jan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Practical steps for improved estimates of calcium carbonate concentrations in deep sea sediments using coulometry2011In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 9, 565-570 p.Article in journal (Refereed)
    Abstract [en]

    Coulometric titration is a commonly used method for determination of carbonate carbon, and hence calcium carbonate concentrations, in geological materials. Analyzes of 460 samples of pure CaCO3 powder demonstrate that the coulometer output data need to be recalculated using a multi-point regression analysis. These analyses also demonstrate that to generate a precision of +/- 0.8%, at least 7 mg of 100% calcite is needed. A precision of +/- 0.5% requires 12 mg pure calcite. We recommend that 35 mg samples are used for most deep sea sediment samples, which gives a precision of +/- 0.8% down to 20% calcite contents in the sample. Calcite contents <10% in samples require multiple runs to improve precision.

  • 7.
    Mörth, Carl-Magnus
    et al.
    Stockholm University.
    Backman, Jan
    Stockholm University.
    Practical steps for improved estimates of calcium carbonate concentrations in deep sea sediments using coulometryIn: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856Article in journal (Refereed)
  • 8.
    Ploug, Helle
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Terbrueggen, Anja
    Kaufmann, Anna
    Wolf-Gladrow, Dieter
    Passow, Uta
    A novel method to measure particle sinking velocity in vitro, and its comparison to three other in vitro methods2010In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 8, 386-393 p.Article in journal (Refereed)
    Abstract [en]

    We introduce a novel, simple method to measure sinking velocity of particles and aggregates in roller tanks. Using this noninvasive method, it is possible to follow changes in sinking velocities on the same aggregates during time and to make paired measurements of aggregate sinking velocity and composition. Particles and aggregates are video recorded in roller tanks, and their sinking velocity is derived from the orbital trajectories. This new method is compared with three other methods (using roller tanks, a vertical flow system, and a sedimentation column), which have not previously been inter-calibrated. Agar spheres and diatom aggregates were used as model particles in all experimental systems. No method showed significantly different sinking velocities of agar spheres compared with those calculated by theory. Paired measurements showed that sinking velocities from 70 to 700 m d(-1) were linearly correlated between different methods. Highest sinking velocities were measured in a sedimentation column followed by those measured in roller tanks and in the vertical flow system, respectively. The average difference of sinking velocity measured with the different methods ranged from 8% to 11% for agar spheres, and up to 20% for diatom aggregates.

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