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K. G. Johnson

Publications and source records attributed to K. G. Johnson.

7 recordsLinked to original sources
USGS2006

Dietary exposure of largemouth bass to OCPs changes expression of genes important for reproduction

Dieldrin and p,p???-DDE are ubiquitous contaminants known to act as endocrine disruptors, causing impaired development and reproduction in fish and wildlife. In order to elucidate the mechanisms by which dieldrin and p,p???-DDE cause endocrine disruption in largemouth bass (Micropterus salmoides), fish were exposed subchronically through the diet to both contaminants. Following 120 days of exposure, p,p???-DDE decreased estradiol in females, but increased 11-ketotestosterone in both sexes. Dieldrin on the other hand, decreased estradiol and 11-ketotestosterone in both sexes. Both pesticides also altered steady state mRNA expression levels of a set of genes chosen to represent three possible mechanisms of endocrine disruption: (1) direct interaction with soluble sex steroid receptors, (2) biosynthesis of endogenous sex hormones, and (3) metabolism of endogenous hormones. p,p???-DDE acted as a weak estrogen, increasing the expression of vitellogenin and estrogen receptor ?? in the liver. p,p???-DDE also altered the expression of genes involved in the synthesis of endogenous hormones as well as their metabolism. Dieldrin, on the other hand, only altered expression of vitellogenin and not estrogen receptor ??. Dieldrin also altered the expression of genes involved in hormone synthesis and metabolism, and it dramatically lowered plasma hormone levels. Both pesticides targeted expression of genes involved in all three modes of action, suggesting that they each have multiple modes of action. ?? 2006 Elsevier B.V. All rights reserved.

Aquatic Toxicology↗
USGS1987

The floods of May 17-18, 1985 and October 6-7, 1985 in Puerto Rico

Severe floods occurred in Puerto Rico twice in 1985. During May 15-19, 1985, as much as 25 in. of rainfall produced significant floods along north and north-central basins in the island. A nearly stationary tropical depression affected Puerto Rico during October 5-8, 1985, resulting in 24-hr precipitation totals of as much as 23 in. and severe floods along the south-central coastal areas. During the May 17-18, 1985 event, the areas most seriously affected by flooding were along the north coast. These included the lower reaches of the Rio Grande de Manati and the Rio Grande de Arecibo. Significant flooding also occurred at Utuado and Jayuya. The recurrence interval of most of the flood peaks was generally < 25 yr. The floods of October 6-7, 1985, affected mostly rural areas in southern Puerto Rico, but caused significant loss of life and widespread property damages. Landslides near Ponce, the collapse of a bridge at Rio Coamo, and the destruction of homes near Ponce resulted in about 170 fatalities and > 125 million dollars in damages. Flooding was also severe at Barceloneta on the north coast. Recurrence intervals = or > 100 yr were estimated for peak discharges at several index stations. (Author 's abstract)

Open-File Report↗
USGS1987

Hydraulic analyses of water-surface profiles in the vicinity of the Coamo Dam and Highway 52 bridge, southern Puerto Rico: Flood analyses as related to the flood of October 7, 1985

The magnitude, frequency and extent of the flood of October 7, 1985 at the Rio Coamo in the vicinity of the Coamo Dam and Highway 52 bridge in southern Puerto Rico, were investigated. The observed flood profiles were used to calibrate a step-backwater model. The calibrated model was then used to investigate several alternative flow conditions in the vicinity of the bridge. The peak discharge of the flood at the Highway 52 bridge was 72,000 cu ft/sec. This peak discharge was determined from the peak computed at a reach in the vicinity of the Banos de Coamo, about 1.2 mi upstream from the bridge. The computed discharge at the Banos de Coamo of 66,000 cu ft/sec was adjusted to the dam and bridge location by multiplying it by the ratio of the drainage areas raised to the 0.83 power. The flood had a recurrence interval of about 100 yr, exceeding all previously known floods at the site. The flood overtopped the spillway and levee of the Coamo Dam just upstream of Highway 52. The flow over the spillway was 54,000 cu ft/sec. Flow over the levee was about 18,000 cu ft/sec. About 10,000 cu ft/sec of the flow over the levee returned to the main channel at the base of the embankment at the northeast approach to the bridge. The remaining 8,000 cu ft/sec flowed south through the underpass on Highway 153. The embankment and shoulder on the northern span of the bridge were eroded with the eventual collapse of the approach slab.

Puerto Rico↗
USGS1977

Floods of November 12, 1974 in the Charlotte Amalie area, St Thomas, US Virgin Islands

The flood on St. Thomas, U.S. Virgin Islands, of November 12, 1974, was the largest recorded flood in the area from Fort Christian through Charlotte Amalie and Frenchtown to the end of Crown Bay. This flood has a recurrence interval of about 60 years. With the exception of a few narrow beaches, very little flooding occurred outside of the Charlotte Amalie area. The flood boundaries are controlled to a large extent by the prevailing channel and flood-plain conditions. Inundation from future floods may be affected by changes in channel conditions, alteration of waterway openings at roads, changes in runoff characteristics of the stream caused by increased urbanization, and other cultural developments. The areas inundated by the 1974 flood are shown on 2 maps. (Woodard-USGS)

U.S. Virgin Islands↗