Sensitivity of stand dynamics to grazing in mixed Pinus sylvestris and Quercus pubescens forests: A modelling study

Only recently, studies of forest succession have started to include the effects of browsing by wild or domestic ungulates. We aim to contribute to this topic by analysing the influence of goat grazing on the long-term coexistence of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) in the low-elevation forests of an inner-Alpine dry valley. The forest gap model ForClim was first adapted to these site conditions by examining the site-dependent sensitivity of the model with regard to the species-specific parameterisation of the drought tolerance as well as the light demand of establishing and adult trees. In a second step, the behaviour of the model was investigated with respect to different grazing intensities and species-specific browsing susceptibilities. The last step was the application of a grazing scenario based on forest history, with 150 years of heavy browsing (by goats) at the beginning of the simulated forest succession, followed by less intensive grazing pressure.     

Spatial anatomy of species survival: effects of predation and climate-driven environmental variability

The majority of survival analyses focus on temporal scales. Consequently, there is a limited understanding of how species survival varies over space and, ultimately, how spatial variability in the environment affects the temporal dynamics of species abundance. Using data from the Barents Sea, we study the spatiotemporal variability of the juvenile Atlantic cod (Gadus morhua) survival. We develop an index of spatial survival based on changes of juvenile cod distribution through their first winter of life (from age-0 to age-1) and study its variability in relation to biotic and abiotic factors. Over the 25 years analyzed (1980-2004), we found that, once the effect of passive drift due to dominant currents is accounted for, the area where age-0 cod survival was lowest coincided with the area of highest abundance of older cod. Within this critical region, the survival of age-0 cod was negatively affected by its own abundance, by that of older cod, and by bottom depth. Furthermore, during cold years, age-0 cod survival increased in the eastern and coldest portion of the examined area, which was typically avoided by older conspecifics. Based on these results we propose that within the examined area top-down mechanisms and predation-driven density dependence can strongly affect the spatial pattern of age-0 cod survival. Climate-related variables can also influence the spatial survival of age-0 cod by affecting their distribution and that of their predators. Results from these and similar studies, focusing on the spatial variability of survival rates, can be used to characterize species habitat quality of marine renewable resources.     

DOM-Flocculation: A suitable approach for separating free and DOM-bound herbicides?

Dissolved organic matter (DOM) in soil solution is considered to interact with herbicides enhancing their mobility and promoting subsequent leaching. Batch experiments were conducted to test if free and DOM-bound herbicides can be separated by a DOM-flocculation technique with Cu as a coagulant. DOM was extracted from the H and A horizons of two soils (Terric Histosol, Cumuli-Calcaric Cambisol) and from the O horizon of a forest soil (Humic Cambisol). DOM-solutions (100 mL) were fortified with the herbicides terbuthylazine and pendimethalin (100 μg active ingredient each) and equilibrated for 14 hours. After DOM-flocculation with Cu (addition of 0,5 mM CuCl₂) herbicide recovery was determined in the supernatant solutions and in the precipitate of Humic Cambisol-DOM, respectively. Recovery of the herbicides from pure water was 85–99% and was not influenced by the addition of Cu. At low pH (4,8–5,3) DOM-flocculation of different DOM-extracts was insufficient and varied in a range of 18 – 90%. Herbicide recovery from DOM-solutions decreased moderately for terbuthylazine (60–90%) and strongly for pendimethalin (5 – 30%). In general, the addition of Cu caused no further reduction of herbicide recovery from supernatant solutions, except for Humic Cambisol-DOM. The effects of Cu-addition were most evident for pendimethalin (strongly reduced concentration in the supernatant solutions) and were considered to be caused by a flocculation of DOM-bound moieties. Flocculation of Humic Cambisol-DOM increased from 18 – 24% at pH 5 to > 95% at pH 8. However, at this pH the formation of Cu(OH)₂ as a sorbing subcomponent of the flocculated matter lead to an overestimation of DOM-bound pendimethalin. Calculating this side effect 6% of pendimethalin added was DOM-bound. Only traces of terbuthylazine (< 1%) were found in the solid matter of flocculated Humic Cambisol-DOM. To sum up, the new approach to separate freely dissolved herbicides from DOM-bound moieties not fully corresponded to our expectations. DOM-flocculation was found to depend strongly on pH-environment influencing not only DOM-herbicide interactions but also the clear separation of DOM-bound herbicides from herbicides in solutions.     

Membrane introduction/laser photoionization time-of-flight mass spectrometry

Two-photon resonance enhanced multiphoton ionization (REMPI) has been shown to be a unique ionization method for mass spectrometry, exhibiting both high sensitivity and chemical selectivity. Because REMPI is a gas-phase method, its applications have been limited either to direct analysis of vapor phase samples, or in conjunction with an initial laser desorption or other vaporization step. We describe here for the first time a combination of membrane introduction mass spectrometry (MIMS) and REMPI with time-of-flight mass spectrometry (TOF-MS), which allows for the direct analysis of trace amounts of organic compounds in water samples. The objective of our research was the detection of very low levels of aromatic contaminants, particularly benzene, toluene, and xylene (BTX), in aqueous solutions without interference due to the water. We have measured limits of detection (LOD) for selected aromatics in water below 1 part-per-trillion with an averaging time of less than 10 s using a continuous sample flow.     

Contaminant transport in a municipal drinking water supply: a steady-state approach to estimate rate and uncertainty

Contaminant transport is generally considered to be a key factor when assessing and classifying the environmental risk of polluted areas. In the study presented here, a steady-state approach was applied to obtain estimates of the transit time and concentration of the pesticide metabolite BAM (2,6-dichlorobenzoamide) at a site where it is contaminating a municipal drinking water supply. A Monte Carlo simulation technique was used to quantify the uncertainty of the results and to evaluate the sensitivity of the used parameters. The adopted approach yielded an estimated median transit time of 10 y for the BAM transport from the polluted site to the water supply. Soil organic carbon content in the unsaturated zone and the hydraulic conductivity in the saturated zone explained 44% and 23% of the uncertainty in the transit time estimate, respectively. The sensitivity analysis showed that the dilution factor due to regional groundwater flow and the soil organic carbon content at the polluted site explained 53% and 31% of the uncertainty of concentration estimates, respectively. In conclusion, the adopted steady-state approach can be used to obtain reliable first estimates of transit time and concentration, but to improve concentration predictions of degrading contaminants, a dynamic model is probably required.     

Zur Kritik des Hooker-Forbes-Tests (HFT)

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