Previous site-specific studies designed to assess the impacts of unsewered subdivisions on ground water quality have relied on upgradient monitoring wells or very limited background data to characterize conditions prior to development. In this study, an extensive monitoring program was designed to document ground water conditions prior to construction of a rural subdivision in south-central Wisconsin. Previous agricultural land use has impacted ground water quality; concentrations of chloride, nitrate-nitrogen, and atrazine ranged from below the level of detection to 296 mg/L, 36 mg/L, and 0.8 microg/L, respectively, and were highly variable from well to well and through time. Seasonal variations in recharge, surface topography, aquifer heterogeneities, surficial loading patterns, and well casing depth explain observed variations in ground water chemistry. This variability would not have been detected if background conditions were determined from only a few monitoring wells or inferred from wells located upgradient of the subdivision site. This project demonstrates the importance of characterizing both ground water quality and chemical variability prior to land-use change to detect any changes once homes are constructed. 相似文献
In the rural Guatemalan Central Highlands, drinking water wells are a rare commodity due to lack of data regarding depth and sustainability of groundwater. At a study well in Lemoa, aquifer sustainability and other characteristics were estimated using hydrograph data and Theiss recovery method for pumping tests. These tests showed that while specific capacity remained fairly constant, transmissivity increased, indicating development of the well subsequent to installation of the study well. The time domain electromagnetic (TDEM) method was evaluated at the site as a prospective groundwater prospecting technique. Characterization of subsurface conditions using TDEM is feasible with local subsurface data for correlation; however, it is limited to delineating low electrical resistive zones without geologic data for correlation. Data showed that groundwater produced from volcanic alluvium at approximately 79 m in depth is sustainable at the study area at current use rates. 相似文献
Dynamical friction is incorporated in the numerical modeling of colliding ring galaxies. We show that dynamical friction may lead to the capture of an initially unbound companion into a damped oscillatory orbit before ultimately merging with the target disk. In the late stages of its motion the companion may be virtually merged with the main galaxy while rings are still propagating in the disk. This raises the possibility that there exist (at least) two classes of ring galaxies: a class of ring galaxies with separate detached companions in which dynamical friction is too weak to have captured the collider, and a second class with no apparent companion in which the latter has either merged with the target galaxy or has disrupted. These two classes could possibly be identified with O-type and P-type ring galaxies of Few and Madore (1986). 相似文献
We describe a balloon payload designed to study the processes of energy release, particle acceleration, and heating of the active corona, in hard X-ray microflares and normal flares. An array of liquid nitrogen-cooled germanium detectors together with large area phoswich scintillation detectors provide the highest sensitivity (∼500 cm2) and energy resolution (≤0.7 keV) ever achieved for solar hard X-ray (∼15–600 keV) measurements. These detectors were flown in February 1987 from Australia on a long duration RAdiation COntrolled balloON (RACOON) flight (LDBF) which provided 12 days of observations before cutdown in Brazil. The payload includes solar cells for power, pointing and navigation sensors, a microprocessor controlled data system with VCR tape storage, and transmitters for GOES and ARGOS spacecraft. This successful flight illustrates the potential of LDBF's for solar flare studies.
We evaluate the effects of land-use change since c.1890 on Little Lake Jackson in south-central Florida, USA. The lake currently is alkaline despite the prevalence of acidic lakes in the region. Watershed soils are acidic and poorly drained, but are underlain by limestone bedrock. Limnetic pH inferences, based on weighted-averaging tolerance regression of sedimented diatoms, indicate that Little Lake Jackson became significantly alkalized during the 1900s. Two driving forces that appear to be responsible for water-quality change are increased ionic loading and increased nutrient loading. Golf courses and residential lawns in the watershed receive substantial applications of lime, fertilizer, and irrigation with alkaline waters from deep wells, some of which reaches the lake in channelized runoff. Stormwater runoff and septic leachate also contribute to nutrient and solute loading. Sedimentary total P accumulation increased 5-fold and total N accumulation increased 3-fold since c. 1890. δ15N values suggest agricultural and septic sources for N loading. Sedimented pigments, inferred limnetic chlorophyll a values, and δ13C values of organic matter indicate that increased primary productivity occurred. Surface and subsurface inflow is nutrient-rich but low in hardness. Increased cation deposition in sediments indicates that ionic input might have reduced the lake’s natural resistance to alkalization. Lake waters remain low in ionic content, which suggests that the addition of base from carbonate sources is not responsible for all of the observed alkalization. Acid neutralization might have been facilitated by phosphate loading that led to increased base generation through greater nitrate assimilation. Inadvertent alkalization might occur commonly in regions where poorly buffered lakes are subject to significant ionic and nutrient loading from agriculture, turfgrass, and septic sources in their watersheds. 相似文献
Lake Lochloosa, Florida (USA) recently underwent a shift from macrophyte to phytoplankton dominance, offering us the opportunity to use a whole-basin, mass-balance approach to investigate the influence of phosphorus loading on ecosystem change in a shallow, sub-tropical lake. We analyzed total phosphorus (TP) sedimentation in the basin to improve our understanding of the forcing factor responsible for the recent shift to phytoplankton dominance. We measured 210Pb activity, organic matter (OM), organic carbon (OC) and TP in short sediment cores from 20 locations to develop a comprehensive, whole-basin estimate of recent mass sedimentation rates (MSR) for bulk sediment, OM, OC and TP. The whole-basin sedimentation models provided insights into historic lake processes that were not evident from the limited, historic water quality data. We used Akaike’s Information Criteria to differentiate statistically between constant MSR and exponentially increasing MSR. An eightfold, exponential increase in TP accumulation over the past century provided evidence for the critical role of increased P loading as a forcing factor in the recent shift to phytoplankton dominance. Model results show increased TP retention and decreased TP residence time were in-lake responses to increased TP loading and the shift from macrophyte to phytoplankton dominance in Lake Lochloosa. Comparison of TP loading with TP retention and historic, diatom-inferred limnetic TP concentrations identified the TP loading threshold that was exceeded to trigger the shift to phytoplankton dominance. 相似文献