Accuracy assessment of the National Geodetic Survey’s OPUS-RS utility

OPUS-RS is a rapid static form of the National Geodetic Survey’s On-line Positioning User Service (OPUS). Like OPUS, OPUS-RS accepts a user’s GPS tracking data and uses corresponding data from the U.S. Continuously Operating Reference Station (CORS) network to compute the 3-D positional coordinates of the user’s data-collection point called the rover. OPUS-RS uses a new processing engine, called RSGPS, which can generate coordinates with an accuracy of a few centimeters for data sets spanning as little as 15 min of time. OPUS-RS achieves such results by interpolating (or extrapolating) the atmospheric delays, measured at several CORS located within 250 km of the rover, to predict the atmospheric delays experienced at the rover. Consequently, standard errors of computed coordinates depend highly on the local geometry of the CORS network and on the distances between the rover and the local CORS. We introduce a unitless parameter called the interpolative dilution of precision (IDOP) to quantify the local geometry of the CORS network relative to the rover, and we quantify the standard errors of the coordinates, obtained via OPUS-RS, by using functions of the form

Respiration partitioning in contrasting subtidal sediments: seasonality and response to a spring phytoplankton deposition

Biomass and respiration rates of bacteria, nematodes and macrobenthos were estimated in relation to the deposition of the spring phytoplankton bloom at two contrasting sites in the Southern North Sea: one with fine‐grained sediment close to the coastline and another with highly permeable sediments. Sediment community oxygen consumption (SCOC) was also measured. Bacterial biomass was relatively similar at both stations, whereas nematode and macrobenthic biomass were higher in fine‐grained sediment. In fine sediments, bacterial biomass increased quickly after deposition of the phytoplankton bloom, whereas the response of nematodes and macrobenthos was delayed. In coarser sediments, nematodes and macrobenthos also showed a fast response in terms of density and biomass. Respiration in permeable sediments was mainly dominated by bacteria at all periods of the year. Hence, nematode and macrobenthic respiration did not contribute strongly to SCOC. This is in contrast to the patterns observed in finer sediments, where both macrofauna and nematodes were important oxygen consumers as well. Macrobenthos contributed more to total SCOC than did nematodes in winter. However, shortly after the arrival of phytodetritus at the sea floor, nematodes and macrobenthos contributed equally to the total SCOC, indicating that all benthic size classes should be taken into account when investigating marine benthic respiration rates.     

A review of human and natural changes in Maya Lowland wetlands over the Holocene

In the Maya Lowlands of Mexico, Belize, and Guatemala two main types of wetlands have played important roles in human history: bajos or intermittently wet environments of the upland, interior Yucatán and perennial wetlands of the coastal plains. Many of the most important Maya sites encircle the bajos, though our growing evidence for human–wetland interactions is still sparse. The deposits of these wetlands record two main eras of slope instability and wetland aggradation: the Pleistocene–Holocene transition as rainfall increased and forests eclipsed savannas and the Maya Preclassic to Classic as deforestation, land-use intensity, and drying increased. The ancient Maya adapted with terraces around these bajo margins but retracted in the Late Preclassic in some areas. The perennial wetlands of the coastal plains have different histories, and the first conceptual model of human–wetland interaction described intensive wetland agriculture in the Preclassic through Classic based on raised fields and canals. But a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried Archaic and Preclassic fields and there was little Classic era use. We present new data on a third and fourth model in this study. The third is a hybrid of the models one and two, including the Archaic to Preclassic aggradation of the second model, and the first model's Classic period fields and canals as piecemeal attempts by the Maya to adapt to these and other environmental changes. The fourth conceptual model describes a very Late/Terminal Classic, preplanned project on a floodplain. These wetland fields were short-lived, aggraded rapidly but with some reoccupation in the Postclassic. All of these new models display the burgeoning evidence for intricate Maya interactions with wetlands, and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of Maya interaction with tropical wetlands.     

Evidence for non-radial fields in the Sun's photosphere and a possible explanation of the polar magnetic signal

The appearance of the Hα fibrils suggests the presence of magnetic fields inclined at noticeably non-radial angles in the Sun's chromosphere. We present evidence to suggest that these angles continue into the photosphere. The presence even of small non-radial inclinations can significantly affect the appearance of regions observed by a longitudinal magnetograph. In particular, a simple bipolar loop can appear unbalanced when viewed near the limb. We suggest that the observed polar signal may be nothing more than a geometric effect arising when a balanced but systematically aligned array of bipolar pairs is viewed at an angle.     

THE MOST PERFECT EXAMPLE OF AN ALIEN ECOLOGY EVER CONSTRUCTED

Much science-fiction literature is based upon the creation and exploration of alternative environments. Stanley G. Weinbaum's short story, “Parasite Planet,”introduces an unusual environment that may be wrong in the light of recent evidence on Venus but still stimulates the geographical imagination.     

Climate Change Impacts for the Conterminous USA: An Integrated Assessment

As carbon dioxide and other greenhouse gases accumulate in the atmosphere and contribute to rising global temperatures, it is important to examine how derivative changes in climate may affect natural and managed ecosystems. In this series of papers, we study the impacts of climate change on agriculture, water resources and natural ecosystems in the conterminous United States using twelve scenarios derived from General Circulation Model (GCM) projections to drive biophysical impact models. These scenarios are described in this paper. The scenarios are first put into the context of recent work on climate-change by the IPCC for the 21st century and span two levels of global-mean temperature change and three sets of spatial patterns of change derived from GCM results. In addition, the effect of either the presence or absence of a CO₂ fertilization effect on vegetation is examined by using two levels of atmospheric CO₂ concentration as a proxy variable. Results from three GCM experiments were used to produce different regional patterns of climate change. The three regional patterns for the conterminous United States range from: an increase in temperature above the global-mean level along with a significant decline in precipitation; temperature increases in line with the global-mean with an average increase in precipitation; and, with a sulfate aerosol effect added to in the same model, temperature increases that are lower than the global-mean. The resulting set of scenarios span a wide range of potential climate changes and allows examination of the relative importance of global-mean temperature change, regional climate patterns, aerosol cooling, and CO₂ fertilization effects.