Modification of fronts by the Alps: Simulations and numerical experimentation

Summary An isentropic limited area model is used to simulate and investigate the frontal passages of 3 May and 8 October 1987. It is demonstrated that a southward outbreak of air with high potential vorticity on 3 May 1987 affected the propagation of the front to the north of the Alps and the related formation of an orographic jet. Moreover, the outbreak plays a crucial role in the genesis of a lee cyclone. On the other hand, no such outbreak occurred on 8 October 1987 and it is shown that the propagation of the front near the ground was hardly affected by the flow at upper levels.With 10 Figures     

The Northeast Kingdom batholith,Vermont: magmatic evolution and geochemical constraints on the origin of Acadian granitic rocks

Five Devonian plutons (West Charleston, Echo Pond, Nulhegan, Derby, and Willoughby) that constitute the Northeast Kingdom batholith in Vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution. The batholith consists of metaluminous quartz gabbro, diorite and quartz monzodiorite, peraluminous granodiorite and granite, and strongly peraluminous leucogranite. Contents of major elements vary systematically with increasingSiO<₂ (48 to 77 wt.%). The batholith has calc-alkaline features, for example a Peacock index of 57, and values for K<₂O/Na₂O (<1), K/Rb (60–350), Zr/Hf (30–50), Nb/Ta (2–22), Hf/Ta (up to 10), and Rb/Zr (<2) in the range of plutonic rocks found in continental magmatic ares. Wide diversity and high values of minor- and trace-element ratios, including Th/Ta (0.5–22), Th/Yb (0–27), Ba/La (0–80), etc., are attributed to intracrustal contributions. Chondrite-normalized REE patterns of metaluminous and relatively mafic intrusives have slightly negative slopes (La/Yb_cn<10) and negative Eu anomalies are small orabsent. The metaluminous to peraluminous inter-mediate plutons are relatively enriched in the light REE (La/Yb_cn>40) and have small negative Eu anomalies. The strongly peraluminous Willoughby leucogranite has unique trace-element abundances and ratios relative to the rest of the batholith, including low contents of Hf, Zr, Sr, and Ba, low values of K/Rb (80–164), Th/Ta (<9), Rb/Cs (7–40), K/Cs (0.1–0.5), Ce/Pb (0.5–4), high values of Rb/Sr (1–18) low to moderate REE contents and light-REE enriched patterns (with small negative Eu anomalies). Flat REE patterns (with large negative Eu anomalies) are found in a small, hydrothermally-altered area characterized by high abundances of Sn (up to 26 ppm), Rb (up to 670 ppm), Li (up to 310 ppm), Ta (up to 13.1 ppm), and U (up to 10 ppm). There is no single mixing trend, fractional crystallization assemblage, or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the Northeast Kingdom batholith. The plutons originated by mixing mantle-derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment. Hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks (<50% by mass), and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals.     

Mapping of benthic enrichment patterns in Narragansett Bay,Rhode Island

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS^® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS^® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS^® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.     

The Role of Bioattenuation in the Management of Aromatic Hydrocarbon Plumes in Aquifers

Ground water scientists have made significant advances in understanding the soil interactions, hydrogeology, fate and transport, and subsurface microbiology of aromatic hydrocarbons (BTEX) in aquifer systems. It is now generally recognized that a major factor responsible for the attenuation and mass reduction of BTEX in plumes is the widespread occurrence of hydrocarbon biodegradation by indigenous soil microorganisms in aquifer material. Most well-studied BTEX plumes that develop from the accidental release of gasoline fuels contain low levels of soluble hydrocarbons (< 1 to 5000 ppb) and have been shown to be spatially confined because of natural biotransformation mechanisms. These in situ processes are controlled by source and aquifer characteristics, permeability, sorption, and geochemical properties of the aquifer. Many laboratory subsoil-ground water microcosms and field studies (10 to 20 C) have demonstrated the rapid biodecay (1 to SO percent/day for microcosms and 0.5 to 1.5 percent/day for plumes) of these aromatic compounds under primarily aerobic conditions (i.e., those with sufficient dissolved oxygen). The ability to implement ground water bioremediation will depend upon our understanding of source control and aquifer recharge effects on the spatial distribution of plumes. In addition, estimating the biodegradation of sorbed BTEX, determining limits and potential for in situ biostimulation of soluble plumes, and establishing data requirements for predictive modeling of natural attenuation will be useful for this remediation technology. The use of these tools to manage ground water quality appears to represent the most practical alternative, particularly for low-risk ground water supplies.     

Miscellaneous information 1989 (Addendum)

Miscellaneous information 1989 (Addendum)