The development of a digital terrain model for the geomorphological engineering of the ‘rolling’ foredune of Terschelling,the Netherlands

The foredunes form an important element of the line of defence which protects the low-lying parts of the Netherlands from the sea. The foredune of the eastern part of the Wadden island of Terschelling has been managed as a ‘rolling’ foredune to maximize the amount of sand available in times of emergency. Following a decision of the Dutch Government to maintain the coastline of 1990, this foredune will now be stabilized. A plan is made to reshape the morphology of the foredune according to a geomorphological design. A simulation model was developed to produce a Digital Terrain Model with the required geometrical information. The transformation which is on the macro-level scale can be achieved within the envisaged medium-scale planning period of five years only by applying earth-moving machinery, placing fences or planting sand-trapping vegetation.     

Effects of Changes in Biodiversity on Ecosystem Function in Tropical Forests

Changing land use in the tropics has resulted in vast areas of damaged and degraded lands where biodiversity has been reduced. The majority of research on biodiversity has been focused on population and community dynamics and has rarely considered the ecosystem processes that are intimately related. We present a framework for examining the effects of changes in biodiversity on ecosystem function in natural, managed, and damaged tropical forests. Using a whole-ecosystem approach, the framework identifies key nutrient and energy cycling processes and critical junctures or pathways, termed interfaces, where resources are concentrated and transferred between the biotic and abiotic components of the ecosystem. Processes occurring at these interfaces, and the organisms or attributes participating in these processes, exert a strong influence on ecosystem structure. We use examples from Puerto Rico, Southern China, Dominica, and Nicaragua to illustrate how the functional diversity framework can be applied to critically examine the effects of changes in biodiversity on ecosystem function, and the relative success or failure of rehabilitation strategies. The few available data suggest that functional diversity, and not just species richness, is important in maintaining the integrity of nutrient and energy fluxes. High species richness, however, may increase ecosystem resiliency following disturbance by increasing the number of alternative pathways for the flow of resources. We suggest ways in which the framework of functional diversity can be used to design research to examine the effects of changes in biodiversity on ecosystem processes and in the design and evaluation of ecosystem management and land rehabilitation projects in the tropics.     

Schwermetalle in Regenwürmern Baden-Württembergs Teil 2: ?kotoxikologische Bewertung des Bodens

Methoden  

Zur Bewertung der gemessenen Schwermetallbelastungen des Bodens wurden sog. Risiko-Kennlinien für die Metalle Blei, Cadmium, Kupfer, Nickel und Zink entwickelt, die eine einheitliche Charakterisierung von Bodengehalten im Hinblick auf ihre Wirkung auf den Regenwurm sowie auf naturr?umliche Gegebenheiten erm?glichen. Die Mobilit?t der Metalle, die für die biologische Wirkung entscheidender ist als der Gesamtgehalt im Boden, wurde bei der Bewertung berücksichtigt.     

Diving behavior of immature hawksbills (Eretmochelys imbricata) in a Caribbean cliff-wall habitat

Time-depth recorders were attached to immature hawksbills (Eretmochelys imbricata Linnaeus, 1766) residing at the northwestern cliffs of Mona Island, Puerto Rico. Data on diving profiles obtained from four turtles of 32.0 to 53.4 cm straight carapace length revealed strong similarities in behavioral patterns. During daylight hours, turtles were active an average 8.4 h per day, surfacing 3.6% of the time. Length of foraging dives correlated with turtle size, with mean durations ranging from 8.6 to 14.0 min. Foraging dives, with a mean depth of 4.7 m, were associated with feeding on encrusting sponges. At night, turtles were mostly inactive, surfacing 1.8% of the time and with individual mean submergence intervals of between 30.4 and 37.1 min. From the surfacing behavior of turtles making deep and long dives, it is inferred that dives were aerobic, with the turtles making use of oxygen stores in addition to that of the lung.     

Substance flows through the economy and environment of a region

In the tradition of the study of materials flows through society, the Substance Flow Analysis (SFA) method and its software tool SFINX are presented. SFA aims at providing the relevant information for a country’s overall management strategy regarding single substances or coherent groups of substances. Three modelling techniques and their possibilities and limitations are discussed: Bookkeeping, static modelling, and dynamic modelling. The computer program SFINX can be used for varoius purposes: (1) to obtain an overview of stocks and flows of a substance in, out and through a nation’s economy and environment for a specific year, (2) to trace the origins of specific pollution problems, and (3) to estimate the effectiveness of certain abatement measures. Each application has its own requirements with regard to data and modelling.     

75 Jahre Theorie des expandierenden Kosmos: Friedmann Modelle und der “Einstein–Limit”

  Die geschichtliche Entwicklung der kosmologischen Modelle für den homogen–isotropen Kosmos, beginnend mit Alexander Friedmanns epochalen Arbeiten (1922 und 1924) bis zur heutigen Diskussion aktueller Modelle wird dargestellt. Eine kardinale Rolle spielt die offene Frage: Besteht die Materie des Kosmos zum weit überwiegenden Teil aus nicht–baryonischer (sog. exotischer) Dunkel–Materie oder reicht die gesamte baryonische Materie aus, die aus den bekannten Atomen und Molekülen besteht, um die Entwicklung des Kosmos zu verstehen. Auch von der normalen (baryonischen) Materie im Kosmos ist nur ein geringer Anteil (etwa 20 5 Prozent) in leuchtenden Objekten (Sterne, Gas, Staub) direkt beobachtbar. Im Abschnitt 3 wird der “Einstein–Limit” für die kosmologische Konstante erl?utert und eine leicht einsichtige Herleitung des Zahlenwertes gegeben.     

Seasonal occurrence of the ctenophore Pleurobrachia pileus in the western Dutch Wadden Sea

Due to the short residence time of the water in the western Dutch Wadden Sea the ctenophore Pleurobrachia pileus has to be considered as an allochthonous species, which enters the estuary passively from the North Sea. The seasonal occurrence of this species in the Dutch Wadden Sea is a reflection of its abundance in the coatal zone of the North Sea and is characterized by a pronounced spring peak of up to 17000 individuals per 1000 m³ and a lower autumn peak with numbers up to 400 individuals per 1000 m³. Similar to other areas, predation by Beroë gracilis, another ctenophore species, may be a factor in controlling the P. pileus population in this region, although B. gracilis abundance is low. P. pileus is only important as a predator for a short time, i.e. the month of May, when it reaches maximum biomass values of up to 12 00 mgC per 1000 m³. Both the estimated potential consumption rates in comparison with the available food as well as the observed suboptimal growth rate of the population suggest that in the coastal zone of the North Sea area food conditions may not be optimal for P. pileus.