Diatom paleoecology of Laguna Zoncho,Costa Rica

We analyzed diatoms in a sediment profile from Laguna Zoncho in southern Pacific Costa Rica (lake elevation 1190 m asl, depth 2.6 m, area 0.75 ha) spanning some 3240 cal yr. Diatoms are common in the profile, which we subdivide into three zones. Zone C (3240–1020 cal yr B.P.) is dominated by Staurosira construens var. venter and Aulacoseira spp.; during this time, the lake was dilute and circumneutral. Benthic and acidophilous taxa increase gradually in the upper section of this zone. Zone B (1020–460 cal yr B.P.) almost totally lacks Aulacoseira, and instead is dominated by combinations of Eunotia minor, Encyonema lunatum, Gomphonema gracile, and Pinnularia braunii. Previous pollen and charcoal analysis indicates that this zone falls within the peak of prehistoric agricultural activity at the lake, but diatoms may also reflect climate change. During this period, the lake was likely shallower and more acidic, but not eutrophic. Finally, Zone A (460 cal yr B.P. to AD 1997) begins near a 1.5-cm tephra layer from nearby Volcán Barú; diatom assemblages are dominated by Aulacoseira spp., and suggest deepening of the lake and return to conditions similar to Zone C. This was a time of indigenous population decline and forest recovery in the Zoncho region, probably reflecting the impact of European diseases on the native population, although climate change and impacts of the tephra deposition cannot be wholly discounted.     

Comments on thermal isostasy

The deformation of the lithosphere due to temperature anomalies caused by a heat source located below or within the layer is usually modelled as one of Pratt local isostasy. A more appropriate model is one of rheologically layered lithosphere comprising of a stiff viscoelastic or elastic layer overlying a weaker viscoelastic layer. The surface deformations are a result of not only the perturbations in body forces due to density changes, but thermal bending moments. In geophysically realistic situations the former contribution dominates. Pratt isostasy is attained if the stresses in the entire lithosphere are allowed to relax and this end state is not contingent upon the lithosphere being confined against horizontal deformation. In a rheologically layered lithosphere, even though the non-isostatic thermal stresses persist in the upper layer, the surface deformations are indistinguishable from that of local isostasy if the horizontal dimension of the heat source exceeds about three times the effective elastic thickness of the lithosphere.     

Reliable groundwater management: the continuous improvement method

Over the world, a majority of water resources are managed by small- and medium-sized companies. Despite having limited personnel and financial resources, these companies have to ensure their groundwater management contains adequate quality control. This is an objective that any company can achieve with the means at its disposal, by using the continuous improvement method. In contrast to the technical approaches mainly used, which focus on the aquifer and the groundwater, the method presented in this article is specifically geared towards the individual conditions of the company extracting the water. A method of sustainable groundwater management is steadily built up by starting with the resources a company has available. The advantage of this approach is that any company, with its financial and personal resources, can achieve suitable groundwater by doing as much as it can within the bounds of its possibilities. Instead of calling in expensive external experts for a short period, the continuous improvement method calls at first for the participation of the companys employees and others involved. The aim is, ultimately, for learning organizations to be able to actively develop their own quality assurance strategies. The method introduced also enables a number of different water suppliers to collaborate within a network. Moreover, usage of the same guidelines allows international comparison. The continuous improvement of groundwater quality covers three scopes: groundwater extraction, groundwater protection, and the groundwater management system. In the following, the management system is based on sections from the International Standardization Organization (ISO 9001:2000) international quality management standard. The method is described using the example of mineral water and spa companies, which are often subject to difficult hydrogeological conditions.     

Gravimetria e prospezione della crosta terrestre

Riassunto Richiamandosi al principio secondo il quale fra due superficie equipotenziali la gravità assume un valore determinato, l'A. sviluppa alcune precisazioni sulle ipotesi inerenti alla distribuzione della densità nella crosta terrestre al disotto delle singole stazioni gravimetriche.

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Zusammenfassung Durch Anwendung des Satzes, dass zwischen zwei bestimmten Aequipotentialflächen die Schwere einen bestimmten Wert haben muss, lassen sich die Annahmen über die Dichteverteilung unter dem Beobachtungsort verfeinern.

     

Die Ursachen des Bergsturzes am Reintalanger (Wettersteingebirge)

Ohne ZusammenfassungVon Herrn Dr.Huber begonnene Untersuchungen über »Frostwechsel auf der Zugspitze« lassen, wie ich einer Mitteilung des Verfassers verdanke, erkennen, daß im 15jährigen Durchschnitt die Anzahl der Tage mit Frostwechsel am raschesten ansteigt vom April mit 4,0 Tagen zum Mai mit 12,8 Tagen. Der Mai zeigt die häufigsten Fälle der Erwärmung von einem Tag zum nächsten, aus der Tabelle auf S. 31 einer anderen Untersuchung von A.Huber 2) geht das zahlenmäßig klar hervor.Es ist demnach im Wettersteingebirge ebenso wie in den nördlichen Kalkalpen überhaupt der Mai infolge seiner klimatischen Eigenschaften der eigentliche Frühjahrsmonat, deshalb für Bergstürze besonders günstig. Das zeigt sich auch bei dem vorliegenden Fall, und zugleich tritt die unmittelbare Ursache der Auslösung des Bergsturzes durch die Wetterlage deutlich hervor.     

Der Bau der Südrandstörung des Wettersteingebirges

Zusammenfassung Auf Grund eingehender Untersuchung der Südrandstörung des Wettersteingebirges wird der Nachweis erbracht, daß sie nicht einheitlich, sondern aus hunderten von Einzelverwerfungen in verschiedenen Richtungen zusammengesetzt ist. Diese Verwerfungen mit nahezu horizontalen Rutschstreifen stehen senkrecht, die seltenen Ausnahmen führen zu überschiebungen geringen Ausmaßes. Bezeichnend ist die plötzliche oder allmähliche Richtungsänderung der Verwerfungen und ihre Ablösung am Rande durch neue. Sie beweisen eine Summe von Differentialbewegungen gleichzeitig mit der Gesamtbewegung der Streifenschollen in O-W-Richtung. Das nötigt erneut zur Ablehnung einer, einheitlichen, S-N bewegten Decke.Auf die übereinstimmung mit den Ergebnissen vonCloos im Kristianiagebiete, wo ebenfalls seitliche Verschiebungen von Blöcken gegeneinander die einzige Erklärungsmöglichkeit bieten, wird hingewiesen.     

Über Breccien

Ohne ZusammenfassungDie Untersuchungen wurden ermöglicht durch einen Zuschuß der Notgemeinschaft der Deutschen Wissenschaft, der ich dafür auch hier meinen Dank ausspreche.     

Hatchery programs,stock enhancement,and cost effectiveness: A case study of the Albemarle Sound/Roanoke River stocking program 1981–1996

Fish hatchery programs commonly are used to enhance depleted fish populations. While these programs are highly valued by the public, most likely due to their nonrestrictive approach to restoring a fishery, the effectiveness of these programs has been often questioned. This study investigates economic and ecological effectiveness of the Albemarle Sound/Roanoke River (AR) striped bass stocking program from 1981 to1996 as a case study.     

Population Structure of Blennius incognitos BATH 1968 (Pisces: Teleostei: Blen-niidae) during the Reproductive Period with Comments on Age and Growth of Small Benthic Littoral Fishes

Abstract. Length frequency distribution, condition factor and parasite infection of Blennius incog-nitus from three different areas near Rovinj, Yugoslavia have been investigated. Differences between considered parameters in three populations of B. incognitus have been found and discussed. Fishes were aged by otolith reading. Mean life span, growth rate, sex ratio and a sexual dimorphism in body size were noted in this littoral blenny. Our findings are discussed and compared with data on comparable littoral fishes.     

Spatial scales and evolution of stormwater plumes in Santa Monica Bay

Rainfall during winter storms produces extensive turbid, freshwater plumes in the coastal waters of the Southern California Bight. When the plumes result from urban runoff they contain toxic pollutants along with pathogenic bacteria and viruses, often resulting in closure of public beaches. We examined the spatial structure and evolution of stormwater plumes in Santa Monica Bay in 1996. The plumes resulted from freshwater discharge from the Ballona Creek and Malibu Creek watersheds which supply approximately 60% of the freshwater runoff to Santa Monica Bay. The spatial scales of the plumes were determined using shipboard measurements of water properties obtained from towyo transects and surface underway sampling. Salinity maps showed that the plumes typically extended 4-7 km offshore, consistent with scaling by the internal Rossby radius of deformation. Plumes extended along shore 10 km or more. Generally the plumes occupied the upper 10 m of the water column. The persistence time of a plume offshore of Ballona Creek was about three days based on a sequence of surveys in March 1996 following rainfall of about 21 mm. Limited comparison of plumes from Ballona Creek, which drains a developed watershed, and Malibu Creek, which drains a rural watershed, suggested that Malibu Creek required greater rainfall to produce an offshore plume. A stormwater plume offshore of Malibu Creek was observed on both sides of the creek mouth, possibly due to freshwater discharge from smaller surrounding watersheds or advection of freshwater discharges from the east and south. Plumes offshore of Ballona Creek mainly resulted from the creek itself and usually extended northward from the creek mouth, consistent with the wind forcing and the Coriolis acceleration.