1990 Watershed Management Symposium Durango, Colorado, USA

Reports

1990 Watershed Management Symposium Durango, Colorado, USA     

The relationship between trends in a condition index of the American oyster,Crassostrea virginica,and environmental parameters in three Virginia estuaries

Oyster Condition Index (CI) was partitioned, using a moving average filter, into seasonal cycles and long-term trends in the James, York, and Rappahannock rivers for the period 1970–1983. Seasonal cyclic fluctuations in CI could be explained partially by changes in salinity and number of days within various temperature regimes. Long-term trends in the James River show a steady increase in CI over the study period, while a concurrent decline was noted in the Rappahannock River. Superimposed on these trends is a 4 to 5 yr cycle that is in synchrony with river discharge (salinity). In the York River, CI peaked in 1975–1976 at all stations. Measured environmental parameters do not sufficiently explain the trends. We speculate that the differences in the Rappahannock and James rivers may be due to a decline in bottom oxygen as a result of gravitational circulation differences.     

Interpretation of metal concentrations in estuarine sediments of Florida using aluminum as a reference element

Metal contamination of estuarine sediments is an increasing problem in Florida and elsewhere as urbanization extends into previously undeveloped areas. Effective estuarine management practices require scientifically valid tools to assess the extent of estuarine contamination. Interpretation of anthropogenic metal contributions has been hampered by the fact that natural metal concentrations in sediments vary by orders of magnitude in different sediments. Normalization of metal concentrations to a reference element, aluminum, appears to be a promising method for comparing estuarine sediment metal concentrations on a regional basis. In this paper we describe an interpretive method based on the relationship between sediment metals and aluminum derived from statewide data on natural estuarine sediments in Florida. We show how the method can be used to interpret metal concentrations with an example using data from the Miami River and Biscayne Bay.     

Age of intrusion and rapid cooling of the Frankenstein gabbro (Odenwald,SW-Germany) evidenced by40Ar/39Ar and single-zircon207Pb/206Pb measurements

The Frankenstein gabbro complex in the northern Odenwald/FR Germany is one of the Hercynian plutonic bodies of the Saxothuringian zone in the Variscan belt.⁸⁷Sr/⁸⁶Sr isotopic investigations on pyroxene,⁴⁰Ar/³⁹Ar age determinations on hornblendes, plagioclases, biotites and pyroxenes and²⁰⁷Pb/²⁰⁶Pb dating on single zircon crystals have been carried out. The⁸⁷Sr/⁸⁶Sr initial ratio of the gabbro (0.70380) indicates uncontaminated derivation of the magma from the mantle. The results on hornblendes, plagioclases and zircons establish the isotopic age of intrusion and the mode of cooling. Pyroxene and biotite data indicate disturbed K-Ar systems of these minerals. The average ages of the hornblendes (363±7 Ma), of the plagioclases (359±3 Ma) and of the zircons (362 ±9 Ma) agree within the 1-sigma levels and constrain the early history of the plutonic intrusion at the turn from Devonian to Carboniferous times. These minerals must have been cooled below their closure temperatures within a time-interval shorter than the error margins of 10 Ma. The ages therefore are, unlike those of the neighbouring Bergsträßer Odenwald, not long-time cooling ages due to largescale and slow geological uplift of the crustal segment. Instead, they will closely estimate the time of intrusion of the Frankenstein pluton into a shallow crustal level. The hiatus of about 20 Ma compared to the average ages of the crystalline rocks of the Bergsträßer Odenwald in the south characterizes the mafic Frankenstein pluton as a separated unit of the Odenwald crystalline, and underlines the importance of the Carboniferous tectonic fault zone in-between. The present data set clearly demonstrates the importance of the applied combination of methods and techniques to constrain the history of intrusion and cooling of mafic plutonic rocks.     

I. Erdöl Ergebnisse der erdölgeologischen Erforschung Nordwestdeutschlands 1932–1947, ein Überblick

Ohne Zusammenfassung     

Die Spuren eiszeitlicher Vergletscherung in Anatolien

Ohne Zusammenfassung