Human impacts on headwater fluvial systems in the northern and central Andes   总被引：4，自引：1，他引：4  

Carol P. Harden   《Geomorphology》2006,79(3-4):249

South America delivers more freshwater runoff to the ocean per km² land area than any other continent, and much of that water enters the fluvial system from headwaters in the Andes Mountains. This paper reviews ways in which human occupation of high mountain landscapes in the Andes have affected the delivery of water and sediment to headwater river channels at local to regional scales for millennia, and provides special focus on the vulnerability of páramo soils to human impact. People have intentionally altered the fluvial system by damming rivers at a few strategic locations, and more widely by withdrawing surface water, primarily for irrigation. Unintended changes brought about by human activities are even more widespread and include forest clearance, agriculture, grazing, road construction, and urbanization, which increase rates of rainfall runoff and accelerate processes of water erosion. Some excavations deliver more sediment to river channels by destabilizing slopes and triggering processes of mass-movement.The northern and central Andes are more affected by human activity than most high mountain regions. The wetter northern Andes are also unusual for the very high water retention characteristics of páramo (high elevation grass and shrub) soils, which cover most of the land above 3000 m. Páramo soils are important regulators of headwater hydrology, but human activities that promote vegetation loss and drying cause them to lose water storage capacity. New data from a case study in southern Ecuador show very low bulk densities (median 0.26 g cm^− 3), high organic matter contents (median 43%), and high water-holding capacities (12% to 86% volumetrically). These data document wetter soils under grass than under tree cover. Effects of human activity on the fluvial system are evident at local scales, but difficult to discern at broader scales in the regional context of geomorphic adjustment to tectonic and volcanic processes.  相似文献   

Linking spatial data from different sources: the effects of change of support     

Linda J. Young  Carol A. Gotway 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):589-600

A nationwide Environmental Public Health Tracking program is being created to monitor environmental impacts on human health. This, and many other efforts to relate environmental and health outcomes, depend largely on the synthesis of existing data sets; little new data are being generated for this purpose. More often than not, the data available for such synthesis have been collected for different geographic or spatial units, and any set of these units may be different from the one of interest. In this paper, we compare and contrast two approaches that can be used within a Geographic Information System to link spatial data from different sources. The first approach works with centroids of areal units and is commonly used in environmental health analyses. The second approach honors the spatial support (size, shape and orientation) of the data. Using traditional regression models and a spatially-varying coefficient regression model, we show that different linkage methods can lead to different inference. We describe key ideas pertaining to the support of spatial data that are often ignored in many analyses of environmental health data and present a general analytical approach to change-of-support problems.  相似文献   

Spectral analyses of solar photospheric fluctuations     

Frank N. Edmonds Jr.  Carol J. Webb 《Solar physics》1972,23(1):47-57

Residual intensity fluctuation measurements within the wings of the 5183.6 Mgi b₁ line, obtained from two, high-resolution, high-dispersion, Sacramento Peak Observatory spectrograms, have been subtracted from intensity fluctuations in the adjacent continuum in order to isolate fluctuations associated exclusively with line formation. The useable spectral range for studying these lineformation fluctuations is restricted to wavelengths between 1040 and 7170 km because the subtraction increases the relative importance of noise and large-scale photographic variations across the spectrograms could not be completely removed. Power and cross-power (coherence and phase) spectra proved to be valuable diagnostic tools in isolating line-formation fluctuations.Over this spectral range, the line-formation fluctuations are characterized by flat power spectra as compared to those for continuum fluctuations, appreciable fluctuation rms relative to that for continuum fluctuations, and the necessity to multiply the wing fluctuations by a factor 0.95 _min 1.00 to most effectively isolate these fluctuations (Figures 3 and 4). That continuum fluctuations are modified in shape but otherwise not drastically changed in the line wings explains the flat spectrum. The relative rms's vary from 0.34 in the inner wing to 0.22 in the outer. The range of possible values for _min results from uncertainties in the photographic density-residual intensity calibration.  相似文献   

Impacts of future climate and land cover changes on landslide susceptibility: regional scale modelling in the Val d’Aran region (Pyrenees,Spain)     

Hürlimann  Marcel  Guo  Zizheng  Puig-Polo  Carol  Medina  Vicente 《Landslides》2022,19(1):99-118

It is widely accepted that future environmental changes will affect rainfall-induced shallow slides in high-mountain areas. In this study, the Val d’Aran region located in the Central Pyrenees was selected to analyze and quantify the impacts of land use and land cover (LULC) and climate changes on regional landslides susceptibility. We analyzed 26 climate models of the EURO-CORDEX database focussing on the future rainfall conditions. The IDRISI TerrSet software suite was used to create the future LULC maps. These two inputs were analyzed individually and in a combined way defining 20 different scenarios. All these scenarios were incorporated in a physically based stability model to compute landslides susceptibility maps. The results showed that both environmental conditions will considerably change in the future. The daily rainfall will increase between 14 and 26% assuming a return period of 100 years. This intensification of precipitation will produce an overall decrease of the stability condition in the study area. Regarding the LULC prediction, the forest area will significantly increase, while in particular grassland, but also shrubs decrease. As a consequence, the overall stability condition improves, because the root strength is higher in forest than in grassland and shrubs. When we analyzed the combined impacts, the results showed that the positive effect of LULC changes is larger than the negative influence of rainfall changes. Hence, when combining the two aspects in the future scenarios, the stability condition in the study area will improve.

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Assessment of the genotoxicity of produced water discharges associated with oil and gas production using a fish embryo and larval test     

Carol B. Daniels  Jay C.Means 《Marine environmental research》1989,28(1-4)

Widespread discharge of produced waters (PW) into brackish and marine waters of the northwest Gulf of Mexico, which serve as spawning grounds for many commercially important species of fish, has raised concern over the potential impact that these complex mixtures may have on aquatic life. In the present study, the results of investigations which assess the clastogenic effects of production water discharged as the result of oil and gas production activity at two coastal sites are reported. In order to assess the impact of the PW discharges on spawning populations of aquatic organisms, chromosome aberration analysis was performed on Cyprinodon variegatus embryos 4–7 days old, which were exposed directly to varying dilutions of PW collected at Pass Fourchon and Timbalier Island for a period of 5 days. Metaphase chromosomes were scored (percentage aberration per 100 metaphases) for aberrations at a magnification of 1000 ×. When compared to the control treatment, higher levels of chromosomal aberrations were observed for treatments (2 and 4% PW) in which embryos were exposed to PW from Pass Fourchon or Timbalier Island. A maximum frequency of 13% was found to occur at the highest test concentration (4% PW), with most of these expressed as breaks (chromatid and chromosome). In contrast, exposure to water from the enclosed canal at Fourchon resulted in the formation of chromosome breaks and changes in ploidy.  相似文献   

Oxygen isotopes of phosphatic compounds—Application for marine particulate matter, sediments and soils     

Karen McLaughlin  Adina Paytan  Carol Kendall  Steven Silva   《Marine Chemistry》2006,98(2-4):148-155

The phosphate oxygen isotopic composition in naturally occurring particulate phosphatic compounds (δ¹⁸O_p) can be used as a tracer for phosphate sources and to evaluate the cycling of phosphorus (P) in the environment. However, phosphatic compounds must be converted to silver phosphate prior to isotopic analysis, a process that involves digestion of particulate matter in acid. This digestion will hydrolyze some of the phosphatic compounds such that oxygen from the acid solution will be incorporated into the sample as these phosphatic compounds are converted to orthophosphate (PO₄³⁻). To determine the extent of incorporation of reagent oxygen into the sample, we digested various phosphatic compounds in both acid amended with H₂¹⁸O (spiked) and unspiked acid and then converted the samples to silver phosphate for δ¹⁸O_p analysis. Our results indicate that there is no isotopic fractionation associated with acid digestion at 50 °C. Furthermore, we found that reagent oxygen incorporation is a function of the oxygen to phosphorus ratio (O:P) of the digested compound whereby the percentage of reagent oxygen incorporated into the sample is the same as that which is required to convert all of the P-compounds into orthophosphate. Based on these results, we developed a correction for reagent oxygen incorporation using simple mass balance, a procedure that allows for the determination of the δ¹⁸O_p of samples containing a mixture of phosphatic compounds. We analyzed a variety of environmental samples for δ¹⁸O_p to demonstrate the utility of this approach for understanding sources and cycling of P.  相似文献   

Resisting a ‘Doomed’ Fate: an analysis of the Pacific Climate Warriors     

Karen E. McNamara  Carol Farbotko 《The Australian geographer》2017,48(1):17-26

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High-Al gabbros in the Laramie Anorthosite Complex,Wyoming: implications for the composition of melts parental to Proterozoic anorthosite   总被引：3，自引：0，他引：3  

Jeremy N. Mitchell  James S. Scoates  Carol D. Frost 《Contributions to Mineralogy and Petrology》1995,119(2-3):166-180

High-Al gabbro represents one of the latest phases of magmatism in the 1.43 Ga Laramie anorthosite complex (LAC) in southeastern Wyoming. This lithology, which is mineralogically and geochemically the most primitive in the LAC, forms dikes and small intrusions that cross cut monzonitic and anorthositic rocks. High-Al gabbro is characterized by high Al₂O₃ (15–19 wt%), REE patterns with positive europium anomalies (Eu/Eu^*=1.2–3.8), and the lowest initial ⁸⁷Sr/⁸⁶Sr (as low as 0.7033) and highest initial _Nd (up to +2) in the LAC. Their Sr and Nd isotopic characteristics indicate a mantle origin followed by crustal assimilation during ascent. Intermediate plagioclase (An_50–60) and mafic silicate (Fo_54–63) compositions suggest that they are not primary mantle melts and that they differentiated prior to final emplacement. High-Al gabbros of the LAC are similar compositionally to gabbros from several other Proterozoic anorthosite complexes, including rocks from the Harp Lake complex and the Hettasch intrusion in Labrador and the Adirondack Mountains of New York. These gabbros are considered to be parental to their associated anorthositic rocks, a theory that is supported by recent experimental work. We interpret LAC high-Al gabbros to represent mantle-derived melts produced by the differentiation of a basaltic magma in an upper mantle chamber. Continued evolution of this magma eventually resulted in the formation of plagioclase-rich diapirs which ascended to mid-crustal levels and formed the anorthositic rocks of the LAC. Because these gabbros intrude the anorthositic rocks, they do not represent directly the magma from which anorthosite crystallized and instead are younger samples of magma formed by identical processes.  相似文献   

Special focus on new studies of gully erosion     

Carol Harden 《自然地理学》2016,37(6):385-386

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Bidding farewell and greeting a new year     

Carol P. Harden 《自然地理学》2016,37(1)

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