Neogene through Pleistocene paleoclimate of the Great Salt Lake region, northeastern Great Basin, USA

In a cooperative agreement between Amoco Production Company and the University of Arizona Geosciences Department, extensive data and resources associated with 15 deep wells drilled in the Great Salt Lake are currently on loan at the University of Arizona. Seismic data, electric and lithologic logs, cuttings and previously-prepared pollen slides will eventually permit a thorough study of both the tectonic and climatic history of the Great Salt Lake region. The preliminary study presented here concentrates on the Late Tertiary and Pleistocene climatic reconstruction of the eastern Great Basin through examination of fossil pollen.

Fire, climate, and vegetation: the sedimentary record of fire in montane meadows, Sierra Nevada, California, USA [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Though knowledge of fire occurrence and weather pattern relationships has been used for many years by land managers in, for instance, prescribed fire planning, understanding of the relationship between Holocene climates and fire is just beginning to be investigated. We are investigating this relationship in a major mountain range in California, examining charcoal and pollen content in sediments of montane meadows to compare paleo-fire and paleo-vegetation (thus, climate) sequences for the Holocene.

A detailed 2,000-year late-Holocene pollen record from Lower Pahranagat Lake, southern Nevada, USA [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Preliminary analysis of 128 pollen samples and 7 radiocarbon dates from a 5-meter-long, 10-centimeter-diameter sediment core retrieved from Lower Pahranagat Lake (elevation 975 meters), Lincoln County, Nevada, gives us a rare, continuous record of vegetation change at 14-year intervals over the past 2,000 years.

A late-Holocene pollen record from Lower Pahrangat Lake, southern Nevada, USA: high resolution paleoclimatic records and analysis of environmental responses to climate change

EXTRACT (SEE PDF FOR FULL ABSTRACT): High resolution paleobotanical records provide sufficient detail to correlate events regionally. Once correlated events can be examined in tandem to determine the underlying inputs that fashioned them. Several localities in the Great Basin have paleobotanical records of sufficient detail to generate regional reconstructions of vegetation changes for the last 2 ka and provide conclusions as to the climates that caused them.

Manipulation of host density affects infestation of a peritrich ciliate (Epistylis lacustris) on a calanoid copepod (Leptodiaptomus minutus) in Crystal Lake, Wisconsin, USA

Specimens of the calanoid copepod, Leptodiaptomus minutus, collected in June 1994 in oligotrophic: north temperate Crystal Lake, were infested with the stalked ciliate Epistylis lacustris. E. lacustris was highly specific to L. minutus and no other coexisting zooplankters were infested. Excluding nauplii, nearly 70% of copepods carried 1-20 ciliates, although the maximum load was as high as 250 ciliates. A lower percentage of nauplii were infested by the ciliate; those that were infested had a lower ciliate load than other copepod stages. Infestation by ciliates had no significant influence on the average egg number of female copepods. In a field experiment, higher copepod densities in enclosures resulted in a significantly higher infestation rate, but the ciliate load per individual copepod did not differ significantly among treatments.

Nutrient dynamics and the eutrophication of shallow lakes Kasumigaura (Japan), Donghu (PR China), and Okeechobee (USA)

We compared the nutrient dynamics of three lakes that have been heavily influenced by point and non-point source pollution and other human activities. The lakes, located in Japan (Lake Kasumigaura), People's Republic of China (Lake Donghu), and the USA (Lake Okeechobee), all are relatively large(>30 km(2)), very shallow (<4 m mean depth), and eutrophic. In all three lakes we found strong interactions among the sediments, water column, and human activities. Important processes affecting nutrient dynamics included nitrogen fixation, light limitation due to resuspended sediments, and intense grazing on algae by cultured fish. As a result of these complex interactions, simple empirical models developed to predict in-lake responses of total phosphorus and algal biomass to external nutrient loads must be used with caution. While published models may provide 'good' results, in terms of model output matching actual data, this may not be due to accurate representation of lake processes in the models. The variable nutrient dynamics that we observed among the three study lakes appears to be typical for shallow lake systems. This indicates that a greater reliance on lake-specific research may be required for effective management, and a lesser role of inter-lake generalization than is possible for deeper, dimictic lake systems. Furthermore, accurate predictions of management impacts in shallow eutrophic lakes may require the use of relatively complex deterministic modeling tools. (C) 2000 Elsevier Science Ltd. All rights reserved.

Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain n-alkanes and stable carbon isotope compositions

Elemental (TOC, TN, C/N) and stable carbon isotopic (delta(13)C) compositions and n-alkane (nC(16-38)) concentrations were measured for Spartina alterniflora, a C-4 marsh grass, Typha latifolia, a C-3 marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. delta(13)C values of organic matter preserved in the upper fresh water site sediment were more negative (-23.0+/-0.3) as affected by the C-3 plants than the values of organic matter preserved in the sediments of middle (-18.9+/-0.8) and mud flat sites (-19.4+/-0.1) as influenced mainly by the C4 marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC(21) to nC(33) long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC(29) was the most abundant homologue in all samples measured. Both delta(13)C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters. (C) 2003 Elsevier Ltd. All rights reserved.