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D R Engstrom

Publications and source records attributed to D R Engstrom.

6 recordsLinked to original sources
PubMed2006

Mercury in soils, lakes, and fish in Voyageurs National Park (Minnesota): importance of atmospheric deposition and ecosystem factors.

Concentrations of methylmercury in game fish from many interior lakes in Voyageurs National Park (MN, U.S.A.) substantially exceed criteria for the protection of human health. We assessed the importance of atmospheric and geologic sources of mercuryto interior lakes and watersheds within the Park and identified ecosystem factors associated with variation in methylmercury contamination of lacustrine food webs. Geologic sources of mercury were small, based on analyses of underlying bedrock and C-horizon soils, and nearly all mercury in the 0- and A-horizon soils was derived from atmospheric deposition. Analyses of dated sediment cores from five lakes showed that most (63% +/- 13%) of the mercury accumulated in lake sediments during the 1900s was from anthropogenic sources. Contamination of food webs was assessed by analysis of whole, 1-year-old yellow perch (Perca flavescens), a regionally important prey fish. The concentrations of total mercury in yellow perch and of methylmercury in lake water varied substantially among lakes, reflecting the influence of ecosystem processes and variables that affect the microbial production and abundance of methylmercury. Models developed with the information-theoretic approach (Akaike Information Criteria) identified lake water pH, dissolved sulfate, and total organic carbon (an indicator of wetland influence) as factors influencing methylmercury concentrations in lake water and fish. We conclude that nearly all of the mercury in fish in this seemingly pristine

Air Pollutants↗
PubMed2001

Pronounced climatic variations in Alaska during the last two millennia.

Paired oxygen-isotopic analyses of abiotic carbonate and benthic-ostracode shells from lake sediments provide a continuous quantitative record of growing-season temperature for the past 2000 years in the northwestern foothills of the Alaska Range. This record reveals three time intervals of comparable warmth: anno Domini (A.D.) 0-300, 850-1200, and post-1800, the latter two of which correspond to the Medieval Climatic Anomaly and climatic amelioration after the end of the Little Ice Age. The Little Ice Age culminated at A.D. 1700, when the climate was approximately 1.7 degrees C colder than at present. A marked climatic cooling also occurred around A.D. 600, coinciding with extensive glacial advances in Alaska. Comparisons of this temperature record with ostracode trace-element ratios (Mg/Ca, Sr/Ca) further suggest that colder periods were wetter and vice versa during the past 2000 years.

Journal Article↗
PubMed2000

Chemical and biological trends during lake evolution in recently deglaciated terrain.

As newly formed landscapes evolve, physical and biological changes occur that are collectively known as primary succession. Although succession is a fundamental concept in ecology, it is poorly understood in the context of aquatic environments. The prevailing view is that lakes become more enriched in nutrients as they age, leading to increased biological production. Here we report the opposite pattern of lake development, observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay, Alaska. The lakes have grown more dilute and acidic with time, accumulated dissolved organic carbon and undergone a transient rise in nitrogen concentration, all as a result of successional changes in surrounding vegetation and soils. Similar trends are evident from fossil diatom stratigraphy of lake sediment cores. These results demonstrate a tight hydrologic coupling between terrestrial and aquatic environments during the colonization of newly deglaciated landscapes, and provide a conceptual basis for mechanisms of primary succession in boreal lake ecosystems.

Alaska↗
PubMed1979

Muscle tension and experienced control: effects of alcohol intake vs biofeedback on alcoholics and non-alcoholics.

Tension reduction has often been implicated as a central cause of excessive alcohol consumption among alcoholics, based on the premise that drinking reduces tension and reinforces subsequent overconsumption. Also, cognitive and personality variables clearly mediate the effects of alcohol. Drinking may be a means of increasing the degree of control experienced over internal and external sources of tension. Integrated frontalis EMG levels for a group of 74 alcoholic patients were significantly greater than for 74 non-alcoholics. During a period of alcohol consumption, significant change scores were found between alcoholic (N = 18) and non-alcoholic (N = 18) groups for both EMG and experienced control (EC). Significant changes were found within both groups on EMG but only for the alcoholic group on EC. During a biofeedback period, there were significant differences between alcoholic (N = 12) and non-alcoholic (N = 12) groups on both baseline measures, EMG and EC. Increases in EC were significantly related to decreases in EMG in both groups.

Alcoholism↗