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Forschungsbericht 2013
(2014)
Forschungsbericht 2012
(2013)
Forschungsbericht 2015
(2016)
Forschungsbericht 2014
(2015)
In many lakes, the most conspicuous seasonal events are the phytoplankton spring bloom and the subsequent clear-water phase, a period of low-phytoplankton biomass that is frequently caused by mesozooplankton (Daphnia) grazing. In Central European lakes, the timing of the clear-water phase is linked to large-scale climatic forcing, with warmer winters being followed by an earlier onset of the clear-water phase. Mild winters may favour an early build-up of Daphnia populations, both directly through increased surface temperatures and indirectly by reducing light limitation and enhancing algal production, all being a consequence of earlier thermal stratification. We conducted a field experiment to disentangle the separate impacts of stratification depth (affecting light supply) and temperature on the magnitude and timing of successional events in the plankton. We followed the dynamics of the phytoplankton spring bloom, the clear-water phase and the spring peak in Daphnia abundance in response to our experimental manipulations. Deeper mixing delayed the timing of all spring seasonal events and reduced the magnitudes of the phytoplankton bloom and the subsequent Daphnia peak. Colder temperatures retarded the timing of the clear-water phase and the subsequent Daphnia peak, whereas the timing of the phytoplankton peak was unrelated to temperature. Most effects of mixing depth (light) and temperature manipulations were independent, effects of mixing depth being more prevalent than effects of temperature. Because mixing depth governs both the light climate and the temperature regime in the mixed surface layer, we propose that climate-driven changes in the timing and depth of water column stratification may have far-reaching consequences for plankton dynamics and should receive increased attention.
Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO3−), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from three headwaters draining 1–3 km2 catchments to two downstream reaches representing spatially integrated signals from 184–456 km2 catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use × lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO3−, DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contributions from point sources. The seasonal dynamics for NO3− were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO3− contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role. In the two downstream reaches, NO3− was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and in-stream transport, and transformation processes.
Laminated veneer lumber poles for temporary soil nailing ‐ investigation of material properties
(2016)
Within a current research project at Rosenheim University of Applied Sciences and Graz University of Technology the possibilities of using beech wood laminated veneer lumber poles as soil anchors for temporary soil nailing systems are investigated. Therefore tensile and bending properties of laminated veneers with high moisture and permanent cement contact concerning the influence of veneer bending rectangular to the fibre are determined. For investigation of material properties under different climate conditions tensile tests on small and faultless single beech wood veneers as well as tensile tests on 6 layered 3 mm samples and 9 layered 2 mm samples were carried out.
Therefore all samples were stored in extreme climate conditions like high moisture content and permanent cement contact. Six layered samples with 3mm thick veneers show a slightly higher strength and stiffness under dry conditions as well as at a moisture content of the samples above fibre saturation. A strength reduction factor concerning temporary geotechnical applications is suggested which considers the influence of long term loading, veneer bending, water saturation and
cement destruction on tensile properties of laminated veneer lumber poles.