Predicting ground water nitrate concentration from land use   总被引：10，自引：0，他引：10  

Gardner KK  Vogel RM 《Ground water》2005,43(3):343-352

Ground water nitrate concentrations on Nantucket Island, Massachusetts, were analyzed to assess the effects of land use on ground water quality. Exploratory data analysis was applied to historic ground water nitrate concentrations to determine spatial and temporal trends. Maximum likelihood Tobit and logistic regression analyses of explanatory variables that characterize land use within a 1000-foot radius of each well were used to develop predictive equations for nitrate concentration at 69 wells. The results demonstrate that historic nitrate concentrations downgradient from agricultural land are significantly higher than nitrate concentrations elsewhere. Tobit regression results demonstrate that the number of septic tanks and the percentages of forest, undeveloped, and high-density residential land within a 1000-foot radius of a well are reliable predictors of nitrate concentration in ground water. Similarly, logistic regression revealed that the percentages of forest, undeveloped, and low-density residential land are good indicators of ground water nitrate concentration > 2 mg/L. The methodology and results outlined here provide a useful tool for land managers in communities with shallow water tables overlain with highly permeable materials to evaluate potential effects of development on ground water quality.  相似文献   

Genetic variation among North American populations of<Emphasis Type="Italic">Phragmites australis</Emphasis>: Implications for management     

Kristin Saltonstall 《Estuaries and Coasts》2003,26(2):444-451

Over the past century, the distribution and abundance ofPhragmites australis (common reed) has dramatically increased in both freshwater and brackish wetlands throughout North America. It has been hypothesized that the increased competitive ability ofPhragmites could be the result of an introduction of a more aggressive genotype. Sequence data from 2 noncoding regions of the chloroplast genome show that, historically, 11 native haplotypes were found across North America and population-structuring distinguishing samples from the Atlantic Coast, Midwest, West, and Gulf Coast regions of the continent was evident. Today a single genetically-distinct haplotype dominates the Atlantic Coast and is also found across the continent in lower frequencies; this type is common in Europe and Asia and has most likely been introduced to North America. Comparisons of modern populations with historic samples show that along the Atlantic Coast, this cosmopolitan type has replaced native haplotypes and it is invading new sites throughout the rest of the country. In the Midwest and West, native populations are still common but introduced populations are found along roadsides throughout the area. Gulf Coast populations are dominated by another population type that is genetically distinct from all other North American population types.  相似文献   

Rock fragment distributions and regolith evolution in the Ouachita Mountains,Arkansas, USA   总被引：2，自引：0，他引：2  

Jonathan D. Phillips  Ken Luckow  Daniel A. Marion  Kristin R. Adams 《地球表面变化过程与地形》2005,30(4):429-442

Rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls, erosion, deposition, bioturbation, and weathering. The distribution of rock fragments in regoliths of the Ouachita Mountains, Arkansas, shows that sandstone fragments are common in all layers, even if sandstone is absent in parent material. Shale and sandstone fragments are produced at the bedrock weathering front, but the shale weathers rapidly and intact fragments are rare in the solum. Sandstone is weathered from ridgetop outcrops and transported downslope. Some of these fragments are moved downward, by faunalturbation and by transport into pits associated with rotting tree stumps. Upward movement by treethrow is common, resulting in a net concentration of rocks near the surface. However, the highest fragment concentrations are in the lower regolith, indicating active production at the weathering front. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities, and that forest soils have likely been extensively mixed within Holocene and historic time. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Formation and evolution of carbonate chimneys at the Lost City Hydrothermal Field     

Kristin A. Ludwig  Deborah S. Kelley  Bruce K. Nelson 《Geochimica et cosmochimica acta》2006,70(14):3625-3645

The Lost City Hydrothermal Field at 30°N, near the Mid-Atlantic Ridge, is an off-axis, moderate temperature, high-pH (9-10.8), serpentinite-hosted vent system. The field is hosted on ∼1.5 Ma crust, near the summit of the Atlantis Massif. Within the field, actively venting carbonate chimneys tower up to 60 m above the seafloor, making them the tallest vent structures known. The chemistry of the chimneys and vent fluids is controlled by serpentinization reactions between seawater and underlying peridotite. Mixing of <40-91 °C calcium-rich vent fluids with seawater results in the precipitation of variable mixtures of aragonite, calcite, and brucite. The resultant deposits range from tall, graceful pinnacles to fragile flanges and delicate precipitates that grow outward from fissures in the bedrock. In this study, mineralogy, petrographic analyses, major and trace element concentrations, and Sr isotopic compositions are used to propose a model for the growth and chemical evolution of carbonate chimneys in a serpentinite-hosted environment. Our results show that nascent chimneys are characterized by a porous, interlacing network of aragonite, and brucite minerals that form extremely fragile structures. The chemistry of these young deposits is characterized by ∼10 wt% Ca and up to 27 wt% Mg, extremely low trace metal concentrations, and ⁸⁷Sr/⁸⁶Sr isotope ratios near 0.70760. During aging of the chimneys, progressive reactions with seawater result in the dissolution of brucite, the conversion of aragonite to calcite, and infilling of pore spaces with calcite. The oldest chimneys are dominated by calcite, with bulk rock values of up to 36 wt% Ca and <1 wt% Mg. These older structures contain higher concentrations of trace metals (e.g., Mn and Ti), and have Sr isotope ratios near seawater values (0.70908). Exposed ultramafic rocks are prevalent along the Mid-Atlantic, Arctic, and Indian Ocean ridge networks and it is likely that other Lost City-type systems exist.  相似文献   

Modelling fundamental waiting time distributions for earthquake sequences     

Kristin Jonsdottir  Mattias Lindman  Roland Roberts  Bjrn Lund  Reynir Bdvarsson 《Tectonophysics》2006,424(3-4):195

The distribution of waiting times between time-neighbouring events for a time series obeying the Omori law is examined theoretically and numerically with the aim of understanding the characteristics of these distributions, how these characteristics change (e.g. scale) with the parameters of the Omori series, and thus how empirical waiting time data may be correctly interpreted. It is found that the waiting time distribution, for a single Omori aftershock sequence, consists in general of two power law segments followed by a rapid decay at larger waiting times. The analyses are illustrated using real data from the SIL network on Iceland. This data often shows characteristics predominantly consistent with the Omori law, but there are significant exceptions. We conclude that waiting time distributions and related statistical analysis has meaningful potential for the analysis of earthquake data sets, as a step towards developing physical models of the earthquake process.  相似文献   

Commercial fishing, conservation and compatibility in the Northwestern Hawaiian Islands     

John N. Kittinger  Kristin N. Duin  Bruce A. Wilcox   《Marine Policy》2010,34(2):208-217

A critical issue in marine ecosystem-based management is addressing the compatibility of extractive use with ecosystem protection. Analysis of the protected area planning process for the Northwestern Hawaiian Islands suggests the key elements of an ecosystem-based approach to protected area management include establishing a common understanding among decision makers of ecosystem boundaries and ecosystem condition, informed by the best available science. A participatory process is proposed that relies on an informed assessment of whether extractive use compromises ecological integrity and is consistent with conservation objectives. Best practices for compatibility determinations are proposed for multi-agency protected area management and planning.  相似文献   

The global potential for whale watching     

A.M. Cisneros-Montemayor  U.R. Sumaila  K. Kaschner  D. Pauly 《Marine Policy》2010

Whaling as a commercial enterprise is now defunct, not least due to the moratorium placed on it by the International Whaling Commission (IWC) almost 20 years ago. However, two distinct groups, one in favor of ‘sustainable’ whaling and one completely opposed to any killing of whales, continue to argue at the IWC and other political arenas. Almost ignored in this debate is the current growth of the whale watching industry, a logical alternative use for whale populations. Based on ecological and socio-economic criteria, the potential for whale watching is estimated for maritime countries that do not currently engage in this industry. Results suggest that whale watching could generate an additional 413 million USD (2009) in yearly revenue, supporting 5,700 jobs. Together with current global estimates, this would bring the total potential for the whale watching industry to over 2.5 billion USD in yearly revenue and about 19,000 jobs around the world. These results are discussed from an economic and conservation policy perspective, with emphasis on potential benefits and limitations.  相似文献   

Insights into Holocene relative sea-level changes in the southern North Sea using an improved microfauna-based transfer function     

Juliane Scheder  Friederike Bungenstock  Kristin Haynert  Anna Pint  Frank Schlütz  Peter Frenzel  Achim Wehrmann  Helmut Brückner  Max Engel 《第四纪科学杂志》2022,37(1):71-85

In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.  相似文献