Food source determines stable isotope discrimination factors ΔN and ΔC in tadpoles

Analyses of stable isotope ratios are widely applied in studies on a large variety of aspects in trophic ecology. Most studies rely on a precise estimation of the relevant discrimination factor Δ (also called the fractionation factor), that reflects the fractionation or differences in isotope ratios of a certain element (mainly nitrogen N and carbon C) between an animal’s diet and its tissue and is used to identify one step in the food web. We experimentally determined ΔN and ΔC of two species of widespread amphibians in Europe, Rana temporaria and Bufo bufo, and tested for the effect of food source (cyanobacteria Spirulina vs. zooplanktonic Daphnia) on Δ and for interspecific differences. Our study shows high variation in Δ in relation to the food source, but low interspecific differences. Tadpoles that were fed with Spirulina did have considerably lower ΔN than tadpoles fed with Daphnia in both species, and lower ΔC only in R. temporaria. The range of Δ obtained here can be a useful baseline for future trophic studies on tadpoles of Rana and Bufo. The strong diet-dependency of Δ, however, argues strongly against the use of a fixed discrimination factor in future isotope studies.

LIDAR BATHYMETRIC EVALUATION BASED ON SCATTERING CLASSIFICATION ALGORITHM

The evaluation of the bathymetric capability of traditional airborne lidar system is mostly based on the formula of bathymetric capability by evaluating the diffuse attenuation coefficient (Kd). This method is derived form the assumption that the reflectance of sediment is fixed. In this study ,however,the reflectance of sediment is not fixed. Therefore, this study improves the ability of bathymetric formula, and proposes a particle scattering classification algorithm to obtain the transmissivity value. The algorithm filters the scattering modes of particles by scattering discrimination factor (q), and obtains the transmissivity values by using the scattering intensity formulas. Experiments show that, when the transmissivity is in the range of 0–1 and the average values of Kd(532 nm) are 0.1150 m−1, 0.0894 m−1 and 0.0903 m−1 in January, June and October respectively, accordingly, the bathymetric capabilities are 0–44 m, 0–61.5 m and 0–52.5 m, respectively. Compared with the original bathymetric method, these results show that the maximum bathymetric value has measured by the improved bathymetric capability formula and scattering classification algorithm has decreased under the influence of the change of sediment reflectance, and the result is more consistent with the actual situation and more accurate.

Effects of potassium fertilization on Radiocaesium transfer from sandy soil to barley (Hordeum vulgare L.)

Uptake and translocation of radiocesium artificially added to sand soil cultivated with barley as affected by different rates of potassium were traced in outdoor pot experiment. Experimental soil was contaminated with 0.01 and 0.1 mM 137Cs equal to (200 and 400 Bq/kg) in the form of CsCl and incubated for 14 days prior to 150 days plant growth period. The transfer factor (TF) average values from soil-to-total biomass were found to range from 0.40 up to 0.53 as affected by interaction between tested treatments. Increasing K rates from 125 to 250 kg/ha markedly reduced the mean averages of TFs of 137Cs from soil-to-roots by about 24 to 68%, respectively and from soil-to-total biomass by about 36 and 74%, respectively lower than corresponding control. In all cases, the discrimination factor was below unity, indicating that Cs is less efficiently absorbed from soil than its nutrient analogue K.