Geology topics

John E. Gannon

Publications and source records attributed to John E. Gannon.

6 recordsLinked to original sources

USGS2004

The status of Limnocalanus macrurus (Copepoda: Calanoida: Centropagidae) in Lake Erie

The calanoid copepod Limnocalanus macrurus showed large declines in abundance and a narrowing of spatial distribution with the onset of cultural eutrophication and increases in rainbow smelt (Osmerus mordax) abundances in Lake Erie in the mid 20th century. Since 1995, however, Limnocalanus macrurus appears to have repopulated in western Lake Erie to levels of abundance that have not been observed since the late 1930s. We hypothesize that phosphorus abatement and the subsequent decrease in low dissolved oxygen events have assisted this resurgence. However, Limnocalanus macrurus abundances have not increased in the central and eastern basins, even though water quality has improved there too. High densities of rainbow smelt and associated smelt predation pressure in the central and eastern basins may be responsible for the low numbers in these basins.

Journal of Great Lakes Research↗

USGS2002

Strategic vision for the U. S. Geological Survey in the Great Lakes-St. Lawrence Region, 2001-2010

The U.S. Geological Survey's (USGS) strategic vision for the Great Lakes-St. Lawrence Region is that of a healthy ecosystem, whose ecological integrity and economic health are nurtured and sustained through sound resource-management decisions based on reliable, timely, and objective scientific information and data. The USGS is a leader in providing reliable, relevant, timely, and objective scientific data and information at local, statewide, regional, national, and international scales to assist in the management and restoration of the natural resources in the Great Lakes-St. Lawrence Region. The mission of the USGS in the Great Lakes-St. Lawrence Region is to provide natural science information to the broad community of policymakers, resource managers, regulators, scientists, and private citizens who contribute to informed decisions concerning natural-resource management practices and ecosystem quality and integrity. The strategic vision for the USGS in the Great Lakes-St. Lawrence Region is a plan to address complex issues that require integrated natural-science information. The strategic vision describes how the USGS will coordinate existing programs and draw upon the strengths of the entire organization. It provides the framework for long-term coordination and integration of USGS Programs and activities over the next decade (2001-10). The strategic vision describes the role of the USGS in the Great Lakes-St. Lawrence Region, the coordination of activities within and outside the Bureau and Department of Interior, and interactions between the USGS and its cooperators, partners, and stakeholders in the Region.

Great Lakes-St. Lawrence region↗

USGS1998

Zebra mussels invade Lake Erie muds

Zebra mussels (Dreissena polymorpha) originated in western Russia but have now become widespread in Europe and North America. They are widely known for their conspicuous invasion of rocks and other hard substrates in North American and European watersheds. We have found beds of zebra mussels directly colonizing sand and mud sediments each year across hundreds of square kilometres of North America's Lake Erie. This transformation of sedimentary habitats into mussel beds represents an unforeseen change in the invasive capacity of this species.

Nature↗

USGS1993

Restoration ecology: longterm evaluation as an essential feature of rehabilitation

In its brief existence as a recognized scientific discipline, restoration ecology has focused almost exclusively on terrestrial and wetland habitat. As a consequence, aquatic restoration and rehabilitation, an important component of restoration ecology is a relatively new discipline. This article examines the ecosystem approach to rehabilitation of the Great Lakes Basin and proposes that waterfront redevlopment and terrestrial and wetland habitat restoration should be accompanied by aquatic habitat restoration. Furthermore, aquatic habitat restoration must include rehabilitation of hard-bottom substrates and structures as well as pollution cleanup and management of soft sediments. Lastly, the article suggests that longterm evaluation is indispensable for aquatic habitat restoration and rehabiliation to be truly successful in the Great Lakes region. Only through longterm evaluation can we determine whether habitat restoration goals have been met at specific sites and transfer successful lessons learned at other locations.

Buffalo Environmental Law Journal↗

USGS1991

Effect of environment on reproduction and growth of Mysis relicta

Published and unpublished data were examined to determine whether the time to first reproduction, brood size, and growth rate of Mysis relicta are related to environmental conditions. Time to first reproduction ranged from 1 year in eutrophic lakes to 4 years in a ultraoligotrophic lake. Mysids in nutrient-rich lakes may have 45 eggs per brood, whereas those in less productive lakes had 10-12 eggs per brood. Growth rates ranged from 1.0 to 1.5 mm/month in productive lakes to only 0.2 mm/month in ultraoligotrophic Lake Tahoe. Some differences in reproduction and growth rate consistent with the above observation occurred between areas of Lakes Tahoe and Michigan that differed in trophic conditions.

American Fisheries Society Symposium↗

USGS1973

Thermal characteristics of Lake Michigan, 1954-55

The thermal regime of Lake Michigan is described on the basis of the analysis of 1,671 bathythermograph casts made in 1954 and 1955. The beginning, duration, geographic extent, and ending of thermal stratification were determined from 51 thermal profiles from all areas of the open lake. The lake gained heat for about 5 months (mid-March to mid-August) and lost heat over the rest of the year. It was thermally stratified during much of the warming cycle and vertically isothermal during much of the cooling cycle. The annual warming period began by April and was well underway by mid-May. During the transitional period between the isothermal conditions of winter and the thermal stratification of summer, the rate of warming was relatively fast. Seasonal warming began in the shallow inshore waters, which were usually thermally stratified by mid to late May. Stratification persisted in the deeper offshore water into December. Maximum surface temperatures and highest average metalimnion temperatures were reached in early August. Local variations in water temperatures during stratification, however, were a common feature of the thermal characteristics of Lake Michigan. These sometimes sudden changes were caused by upwellings of cold bottom waters that in some instances affected areas of hundreds of square miles. During the warming period of 1954, the heat content of Lake Michigan increased an average of 425 gm-cal/cm??/day. The annual heat budget of the lake for 1954 was 51,700 calories which is similar to that reported for 1942 (50,000 calories) and 1943 (62,000 calories). Heat was lost from mid-August until March, at a rate of about 250 gm-cal/cm??/day. Seasonal thermal characteristics differed little between 1954 and 1955, and were similar to those observed during studies in 1941 and 1942.

Technical Paper↗