Water quality and sediment geochemistry in lakes of Yunnan Province, southern China

 Yungui Plateau lakes in southwestern China are economically important, although few have been studied previously. Water and sediments of 24 lakes throughout Yunnan Province were sampled in October 1994. We describe the chemical and physical characteristics of Yunnan lakes, and address effects of regional geology and human influences on water quality and sediment type. Water quality differs between deep Yunnan lakes of tectonic origin and shallow solution basins. Shallow lakes generally have higher nutrient concentrations and appear to be more susceptible to riparian disturbance than deeper lakes. Shallow lakes with high macrophyte standing crops, nevertheless, exhibit nutrient-poor waters. Principal ions Ca²⁺, Mg²⁺, and HCO₃ ^– reflect regional carbonate geology, except in Cheng Hai, which is a sodium bicarbonate lake. Specific conductance and δ¹⁸O are positively correlated, indicating that evaporation concentrates both solutes and ¹⁸O. Large, shallow lakes in southeastern Yunnan exhibit ¹⁸O-enriched waters because of substantial evaporation, whereas small, deep lakes are ¹⁸O-depleted. Lake waters are ¹⁸O-depleted in small, shallow basins that receive substantial rainwater input relative to their small volumes. ¹⁸O enrichment in Cheng Hai suggests that a recent 5-m water-level decline in this lake was caused by increased evaporation or diversion of freshwater inflow. Yunnan watersheds have undergone substantial deforestation, agricultural cultivation, soil erosion, and industrialization. Limnetic nutrient concentrations indicate that human activities have affected water quality. Organic matter content is low in sediments because of increased non-carbonate, clastic sediment yield from watersheds. Environmental policies are needed to balance ecological contraints with economic activities that impact water quality. Received: 1 July 1996 / Accepted: 2 October 1996     

UNITED STATES RAILWAY TRAFFIC: AN UPDATE

Recent decades have seen changes in the pattern of rail traffic in the United States. This article describes the development of a United States railroad map depicting current levels of traffic on all rail lines handling over five million gross tons per year. This traffic pattern is compared with the 1929 traffic levels appearing on a similiar map developed by Edward Ullman. Revenue ton-miles have nearly doubled since 1929, with most of the increases concentrated on western and southern lines. Traffic on eastern lines has increased only slightly above 1929 levels.     

Centimeter-Level Positioning of a U. S. Coast Guard Buoy Tender

With the availability of high-accuracy, differential global positioning system (GPS) results in real-time, there is a new opportunity to use GPS to accurately measure a marine vessel's dynamic draft (settlement and squat) and 3D attitude (roll, pitch, and heading). The National Geodetic Survey (NGS) and the Coast Survey (CS), offices of the National Ocean Service (NOS), National Oceanic and Atmospheric Administration (NOAA), propose to transfer this technology to the shipping industry. The overall goal of this project is to provide the position of a vessel's keel in real time to within 10 cm (about 4 inches) relative to the bottom of the shipping channel. In support of this phase of the project, there were three meetings hosted by the Port of Oakland, California and NOS to discuss the real-time positioning of vessels project. On December 3 and 4, 1996, CS, NGS, Trimble Navigation Ltd., and the U. S. Coast Guard (USCG) performed GPS tests on a USCG buoy-tender ship. GPS data were used to compute the vessel's dynamic draft and 3D attitude. During the test, five receivers continually collected data; one receiver was located at a base station on the USCG pier on Yerba Buena Island, and four were on the ship: two on the stern and two on the bow. CS installed a TSS-335B vertical reference unit (to measure heave, pitch, and roll) in the engine room of the ship. NOS processed the GPS data and computed the vessel's dynamic draft and 3D attitude. The results indicate that the linear equivalent to the vessel's dynamic draft and 3D attitude were accurate to the 10-cm level using GPS. It was also demonstrated how a ship can be used to measure local water-level changes and actual water-level values everywhere it travels. ? 1999 John Wiley & Sons, Inc.     

Structure of the martian wake

We present the first results from the ion mass analyzer IMA of the ASPERA-3 instrument on-board of Mars Express. More than 200 orbits for May 2004-September 2004 time interval have been selected for the statistical study of the distribution of the atmospheric origin ions in the planetary wake. This study shows that the martian magnetotail consists of two different ion regimes. Planetary origin ions of the first regime form the layer adjacent to the magnetic pile-up boundary. These ions are accelerated to energy greater than 2000 eV and exhibit a gradual decreasing of energy down to the planetary tail. The second plasma regime is observed in the planetary shadow. The heavy ions (considered as planetary ones) are accelerated to the energy of the solar wind protons. Obviously the acceleration mechanism is different for the different plasma regimes. Study of two plasma regimes in the frame referred to the interplanetary magnetic field (IMF) direction (we used MGS magnetometer data to obtain the IMF clock angle) clearly shows their spatial anisotropy. The monoenergetic plasma in the planetary shadow is observed only in the narrow angular sector around the positive direction of the interplanetary electric field.     

Accretion of matter by condensed objects

The equations of motion for steady-state spherical symmetric flow of matter into or out of a condensed object (e.g. neutron stars, black holes, etc.) are displayed and solved for simple polytropic gases. It appears that infalling matter may be heated as hot as 10¹²K and that X-ray luminosities of the order of 10³⁷ erg s^–1 could result. The two fluid (electrons and ions separately) approach is also examined and it is shown that electrostatic fields of the order of 10⁵ V m^–1 are required near the surface of the object. Such fields are not strong enough to significantly modify the space-time metric.     

Environmental and cultural changes in highland Guatemala inferred from Lake Amatitlán sediments

We inferred the late Holocene environmental history of the Guatemala highlands from multiple lines of evidence in a sediment core from Lake Amatitlán. Inferred environmental changes are generally synchronous with archaeologically documented highland Maya cultural shifts. Population increases in the Middle Preclassic, Early Classic, and Late Postclassic are associated with deforestation and soil erosion. Land abandonment in the Late Preclassic, Late Classic, and Early Postclassic is associated with evidence for reforestation and soil stabilization. Diatoms indicate relatively lower lake level and greater trophic status at times of reduced human impact, from ca. 250 B.C. to A.D. 125 and from ca. A.D. 875 to 1375. Decreased water levels were probably due to drier climate, to reforestation, or both. Lake eutrophication was caused by reduced water volume combined with a legacy of long‐term agricultural activity. Our data contribute to the understanding of relations among ancient Maya culture, climate, and environment. © 2011 Wiley Periodicals, Inc.     

The suburbanization of poverty? An alternative perspective

A popular and powerful narrative focuses on a crisis of suburban decline in the United States. However, a consensus regarding the scope and scale of one dimension of suburban decline—poverty—is hindered by the use of contradictory definitions of suburban space. This research presents an alternative approach to measuring suburban poverty that is less computationally intensive yet capable of capturing complex shifts in the spatial distribution of poverty within metropolitan areas. An analysis of the distribution of poverty in the largest 100 metropolitan areas between 1990 and 2007–11 concludes that while poverty is increasing in the low-density suburbs of a handful of large metropolitan areas, the more general trend in most other metropolitan areas is an increase in poverty in moderately dense residential areas. Implicated in these trends are long-term trends in metropolitan area economic growth, a secular decline in inner-ring suburbs, and the impact of gentrification on housing opportunities for at-risk populations in large cities.     

The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables

The temperatures of electrons and ions in the post-shock accretion region of a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass flow rates or for sufficiently weak magnetic fields. At lower mass flow rates or in stronger magnetic fields, efficient cyclotron cooling will cool the electrons faster than the electrons can cool the ions and a two-temperature flow will result. Here we investigate the differences in polarized radiation expected from mCV post-shock accretion columns modeled with one- and two-temperature hydrodynamics. In an mCV model with one accretion region, a magnetic field ?30 MG and a specific mass flow rate of ～0.5 g?cm^?2?s^?1, along with a relatively generic geometric orientation of the system, we find that in the ultraviolet either a single linear polarization pulse per binary orbit or two pulses per binary orbit can be expected, depending on the accretion column hydrodynamic structure (one- or two-temperature) modeled. Under conditions where the physical flow is two-temperature, one pulse per orbit is predicted from a single accretion region where a one-temperature model predicts two pulses. The intensity light curves show similar pulse behavior but there is very little difference between the circular polarization predictions of one- and two-temperature models. Such discrepancies indicate that it is important to model some aspect of two-temperature flow in indirect imaging procedures, like Stokes imaging, especially at the edges of extended accretion regions, were the specific mass flow is low, and especially for ultraviolet data.