For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. AcknowledgmentsThe work described in this report would not have been possible without the extraordinary efforts of the field biologists, data managers, and analysts who have studied Florida manatees over the last three decades. We are particularly grateful to Cathy Beck, Howard Kochman, Gaia Meigs-Friend, Claudia Peñaloza, and Amy Teague of the U.S. Geological Survey; Martine AbstractTrichechus manatus (West Indian manatee), especially T. m. latirostris, the Florida subspecies, has been the focus of conservation efforts and extensive research since its listing under the Endangered Species Act of 1973. To determine the status of, and severity of threats to, the Florida manatee, a comprehensive revision and update of the manatee Core Biological Model was completed and used to perform a population viability analysis for the Florida manatee. The probability of the Florida manatee population falling below 500 adults on either the Gulf or East coast within the next 100 years was estimated to be 0.42 percent. This risk of quasi-extinction is low because the estimated adult survival rates are high, the current population size is greater than 2,500 on each coast, and the estimated carrying capacity for manatees is much larger than the current abundance estimates in all four regions of Florida. Three threats contribute in roughly equal measures to the risk of quasi-extinction: watercraft-related mortality, red-tide mortality, and loss of warm-water habitat. Only an increase in watercraft-related mortality has the potential to substantially increase the risk of quasi-extinction at the statewide or coastal level. Expected losses of warm-water habitat are likely to cause a major change in the distribution of the population from the regions where manatees rely heavily on power plant effluents for warmth in winter (Southwest and Atlantic regions) to the regions where manatees primarily use natural springs in winter (Northwest and Upper St. Johns regions). The chances are nearly 50 percent that manatee populations in the Southwest and Atlantic regions will decrease from their 2011 levels by at least 30 percent over the next century.A large number of scenarios were examined to explore the possible effects of potential emerging threats, and in most of them, the risk of quasi-extinction at the coastal scale within 100 years did not rise above 1 percent. The four...

No abstract

Development of digital groundwater flow models of the Mississippi River Valley alluvial aquifer in eastern Arkansas was prompted by the growing concern about large water-level declines in the alluvial aquifer and by the need to better understand the flow system. Several flow models have been developed previously, but at scales that are too large for analyzing the effect of future pumping at a farm or local scale. Models developed and described in this report are at a one-square-mile cell scale that can be used to define local conditions. Because of the size of the study area, two models (a north model and a south model) were developed; the Arkansas River divides the study area and functions as a hydrologic boundary to the models. Both models simulate groundwater flow in one layer with recharge entering the aquifer from surface infiltration through the overlying confining unit and from seepage through riverbeds.

No abstract

The U.S. Geological Survey's participation in a study of the water resources in eastern Arkansas involved the development and calibration of a digital ground-water flow model of the Mississippi River Valley alluvial aquifer and the use of that model to evaluate the effects of future pumping on the saturated thickness of the aquifer. The study was prompted by the growing concern about significant water-level declines in the alluvial aquifer north of the Arkansas River.Thickness of alluvial sediments in the study area ranges from 125 to 200 feet and averages about 150 feet. The most permeable material lies in the lower part of the sediments and averages about 100 feet in thickness. Hydraulic conductivity of the aquifer ranges from about 120 to about 390 feet/day.Recharge to the aquifer occurs mainly by percolation through the overlying confining layer in interstream areas and by seepage through riverbeds. A small amount of recharge also comes from the sediments underlying the alluvium.Recharge rates in interstream areas range from less than 1 to as much as 10 inches in areas where recharge from underlying sediments is substantial.Digital model simulations were made to represent flow in the aquifer and to quantify flow into and out of the system. The dynamic ground-water system was simulated by using seven stress periods between 1917 and 1987. Pumpage used in the simulation ranged from 86,950,000 to 420,970,000 cubic feet per day. Pumpage was distributed uniformly over each county after eliminating areas where the predominant land use precluded ground-water withdrawals.-4 Storage coefficient values of 0.3 and 1x10 for unconfined and confined aquifer conditions, respectively, were used in the simulations. measures were not in place and 258 (1,486,080 acres) of the active cells with conservation measures in place.