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At least 379 records · Page 21Linked to original sources
USGS2003

Automated calibration of a stream solute transport model: Implications for interpretation of biogeochemical parameters

The hydrologic processes of advection, dispersion, and transient storage are the primary physical mechanisms affecting solute transport in streams. The estimation of parameters for a conservative solute transport model is an essential step to characterize transient storage and other physical features that cannot be directly measured, and often is a preliminary step in the study of reactive solutes. Our study used inverse modeling to estimate parameters of the transient storage model OTIS (One dimensional Transport with Inflow and Storage). Observations from a tracer injection experiment performed on Uvas Creek, California, USA, are used to illustrate the application of automated solute transport model calibration to conservative and nonconservative stream solute transport. A computer code for universal inverse modeling (UCODE) is used for the calibrations. Results of this procedure are compared with a previous study that used a trial-and-error parameter estimation approach. The results demonstrated 1) importance of the proper estimation of discharge and lateral inflow within the stream system; 2) that although the fit of the observations is not much better when transient storage is invoked, a more randomly distributed set of residuals resulted (suggesting non-systematic error), indicating that transient storage is occurring; 3) that inclusion of transient storage for a reactive solute (Sr2+) provided a better fit to the observations, highlighting the importance of robust model parameterization; and 4) that applying an automated calibration inverse modeling estimation approach resulted in a comprehensive understanding of the model results and the limitation of input data.

Journal of the North American Benthological Societ↗
USGS1978

Interpreting the results of nesting studies

Nesting studies are used to assess the production of birds and to evaluate nesting habitats. Most such studies involve finding nests in a given area and subsequently determining the proportion that hatched. Unfortunately, the results are often biased by unrecognized differences in the probabilities of finding successful and unsuccessful nests. The observed hatch rates of 1,900 nests of blue-winged teal ( Anas discors ) are presented to illustrate the relationship of hatch rates to time remaining until the nests should hatch. The Mayfield method of correcting for these biases is illustrated. Other examples demonstrate the possible effects of sampling procedures on observed hatch rates and nest density.

Journal of Wildlife Management↗
USGS1998

Interpreting carnivore scent-station surveys

The scent-station survey method has been widely used to estimate trends in carnivore abundance. However, statistical properties of scent-station data are poorly understood, and the relation between scent-station indices and carnivore abundance has not been adequately evaluated. We assessed properties of scent-station indices by analyzing data collected in Minnesota during 1986-03. Visits to stations separated by <2 km were correlated for all species because individual carnivores sometimes visited several stations in succession. Thus, visits to stations had an intractable statistical distribution. Dichotomizing results for lines of 10 stations (0 or ≥ 1 visits) produced binomially distributed data that were robust to multiple visits by individuals. We abandoned 2-way comparisons among years in favor of tests for population trend, which are less susceptible to bias, and analyzed results separately for biogeographic sections of Minnesota because trends differed among sections. Before drawing inferences about carnivore population trends, we reevaluated published validation experiments. Results implicated low statistical power and confounding as possible explanations for equivocal or conflicting results of validation efforts. Long-term trends in visitation rates probably reflect real changes in populations, but poor spatial and temporal resolution, susceptibility to confounding, and low statistical power limit the usefulness of this survey method.

Minnesota↗
USGS1998

Interpretation of ages of arc magmatism, metamorphism, and collisional tectonics in the Taconian orogen of western New England

Available geochronologic ages of volcanic and intrusive rocks of the Taconian arc complex of western New England suggest that the Shelburne Falls and Bronson Hill arcs are not temporally or spatially discrete. Arc activity ranges from earliest Ordovician to Silurian. Activity in the Early and Middle Ordovician coincided with outboard accretionary tectonics and metamorphism that was contemporaneous with the older igneous activity in the Shelburne Falls arc and Bronson Hill arcs. Activity at about 455 to 445 Ma coincides with the collisional stage of the Taconian orogeny that affected Caradocian and older rocks of the Laurentian margin. The 455 to 445 Ma range for the collisional stage of Taconian orogeny in western New England is bracketed by biostratigraphic ages of sedimentary rocks formed on the Laurentian margin and 40Ar/39Ar ages of prograde hornblende formed during Taconian metamorphism. The previous 40Ar/39Ar age estimate of 465 Ma for this collisional and metamorphic event is now known to be too old because this age violates the age of metasedimentary rocks involved in the collisional tectonics. Acceptance of the newer 40Ar/39Ar age estimates of 445 to 450 Ma for Taconian metamorphism during collision establishes the contemporaneity with arc activity in the Bronson Hill arc. Taken together these data support the concept of a long-lived volcanic arc terrane(s) that prograded oceanward. Collision with this time-composite arc terrane(s) in the Caradocian produced the Taconian orogeny rather than the collision of a separate and smaller arc called the "Shelburne Falls arc" by Karabinos and others (1998).

American Journal of Science↗
USGS1953

Interpreting geologic maps for engineering purposes: Hollidaysburg quadrangle, Pennsylvania

This set of maps has been prepared to show the kinds of information, useful to engineers, that can be derived from ordinary geologic maps. A few additional bits of information, drawn from other sources, are mentioned below. Some of the uses of such maps are well known; they are indispensable tools in the modern search for oil or ore deposits; they are the first essential step in unraveling the story of the earth we live on. Less well known, perhaps, is the fact that topographic and geologic maps contain many of the basic data needed for planning any engineering construction job, big or little. Any structure built by man must fit into the topographic and geologic environment shown on such maps. Moreover, most if not all construction jobs must be based on knowledge of the soils and waters, which also are intimately related to this same environment. The topographic map shows the shape of the land the hills and valleys, the streams and swamps, the man-made features such as roads, railroads, and towns. The geologic map shows the kinds and shapes of the rock bodies that form the land surface and that lie beneath it. These are the facts around which the engineer must build.

Pennsylvania↗
USGS1953

Regional interpretation of the geology of the Kongakut - Firth Rivers area, Alaska

In 1952 the National Park Service became interested in setting aside a large wilderness area in northeastern Alaska. The area is approximately 7,000 square miles in size, with boundaries as follows: beginning at Camden Bay south along the Katakturuk River to lat. 68° N.; then east to long. 144° 33' W.; south to lat. 68° N.; then east to the Canadian Boundary. The two river areas which the Park Service is most interested in examining for ecology, botany, archaeology, and geology are the upper Firth and Kongakut Rivers.

Alaska↗
USGS1970

Geologic interpretation of reconnaissance aeromagnetic survey of northeastern Alaska

Aeromagnetic reconnaissance of northeastern Alaska in 1965 covered approximately 100,000 square miles, from lat 64° N. to the Arctic Ocean and from the Alaska-Yukon boundary to long 148°30' W. A magnetic contour map was compiled from data from the 1965 survey and earlier surveys. On the basis of these data, northeastern Alaska may be divided into five areas, each having a distinct magnetic character. A study of specific anomalies within these areas led to the tracing of such features as the Tintina fault zone, Ruby uplift, and Kobuk trench for more than 100 miles. Other features, such as inferred north-trending faults and serpentine belts, had not been identified previously by surface geologic methods. The probable extension of volcanic rocks beneath the Yukon Flats limits the size of a possible Tertiary petroleum basin. Discovery of large magnetic anomalies in the Yukon-Tanana Upland provides new possibilities for exploration for mineral deposits associated with ultramafic rocks.

Alaska↗