Effects of Docks on Salt Marsh Vegetation: an Evaluation of Ecological Impacts and the Efficacy of Current Design Standards     

John M. Logan  Amanda Davis  Charles Markos  Kathryn H. Ford 《Estuaries and Coasts》2018,41(3):661-675

Private docks are common in estuaries worldwide. Docks in Massachusetts (northeast USA) cumulatively overlie ~ 6 ha of salt marsh. Although regulations are designed to minimize dock impacts to salt marsh vegetation, few data exist to support the efficacy of these policies. To quantify impacts associated with different dock designs, we compared vegetation characteristics and light levels under docks with different heights, widths, orientations, decking types and spacing, pile spacing, and ages relative to adjacent control areas across the Massachusetts coastline (n = 212). We then evaluated proportional changes in stem density and biomass of the dominant vegetation (Spartina alterniflora and Spartina patens) in relation to dock and environmental (marsh zone and nitrogen loading) characteristics. Relative to adjacent, undeveloped habitat, Spartina spp. under docks had ~ 40% stem density, 60% stem biomass, greater stem height and nitrogen content, and a higher proportion of S. alterniflora. Light availability was greater under taller docks and docks set at a north-south orientation but did not differ between decking types. Dock height best predicted vegetation loss, but orientation, pile spacing, decking type, age, and marsh zone also affected marsh production. We combined our proportional biomass and stem elemental composition estimates to calculate a statewide annual loss of ~ 2200 kg dry weight of Spartina biomass (367 kg per ha of dock coverage). Managers can reduce impacts through design modifications that maximize dock height (> 150 cm) and pile spacing while maintaining a north-south orientation, but dock proliferation must also be addressed to limit cumulative impacts.  相似文献   

Stakeholder engagement in adaptation interventions: an evaluation of projects in developing nations     

Mya H. Sherman  James Ford 《Climate Policy》2013,13(3):417-441

Institution-oriented, top-down and community-oriented, bottom-up stakeholder approaches are evaluated for their ability to enable or constrain the implementation of adaptation in developing nations. A systematic review approach is used evaluate the project performance of 18 adaptation projects by three of the Global Environment Facility's (GEF) adaptation programmes (the Strategic Priority for Adaptation (SPA), the Special Climate Change Fund (SCCF), and the National Adaptation Programs of Action (NAPA)) according to effectiveness, efficiency, equity, legitimacy, flexibility, sustainability, and replicability. The ten SPA projects reviewed performed highest overall, especially with regards to efficiency, legitimacy, and replicability. The five SCCF projects performed the highest in equity, flexibility, and sustainability, and the three NAPA-related projects were the highest-performing projects with regards to effectiveness. A comparison of top-down and bottom-up approaches revealed that community stakeholder engagement in project design and implementation led to higher effectiveness, efficiency, equity, flexibility, legitimacy, sustainability, and replicability. Although low institutional capacity constrained both project success and effective community participation, projects that hired international staff to assist in implementation experienced higher overall performance. These case studies also illustrate how participatory methods can fail to genuinely empower or involve communities in adaptation interventions in both top-down and bottom-up approaches. It is thus crucial to carefully consider stakeholder engagement strategies in adaptation interventions.Policy relevanceWhile adaptation is now firmly on the policy and research agenda, actual interventions to reduce vulnerability and enhance resilience remain in their infancy, and there is limited information on the factors that influence the successful implementation of adaptation in developing areas. Engaging stakeholders in assessing vulnerability and implementing adaptation interventions is widely regarded to be an important factor for adaptation implementation and success. However, no study has evaluated the effects of stakeholder engagement in the actual implementation of adaptation initiatives. Effective stakeholder engagement is challenging, especially in a developing nation setting, due to high levels of poverty, inadequate knowledge on adaptation options, weak institutions, and competing interests to address more immediate problems related to poverty and underdevelopment. In this context, this article documents and characterizes stakeholder engagement in adaptation interventions supported through the GEF, examining how top-down or bottom-up stakeholder approaches enable or constrain project performance.  相似文献   

Upscaling microbial chemotaxis in porous media     

Francisco J. Valds-Parada  Mark L. Porter  Karthik Narayanaswamy  Roseanne M. Ford  Brian D. Wood 《Advances in water resources》2009,32(9):1413-1428

Biodegradation is an important mechanism for contaminant reduction in groundwater environments; in fact, in situ bioremediation and bioaugmentation methods represent alternatives to traditional methods such as pump-and-treat. Microbial chemotaxis has been shown to significantly increase contaminant degradation in subsurface environments. In this work, the method of volume averaging is used to upscale the microscale chemotactic microbial transport equations in order to obtain the corresponding effective medium models for the mass balance of bacteria and the chemical attractant to which they respond. As a first approach, cellular growth/death and consumption of the attractant by chemical reaction are assumed to be negligible with respect to convective and diffusive transport mechanisms. For microorganisms, two effective coefficients are introduced, namely a total motility tensor and a total velocity vector. Our results show that, under certain conditions, these coefficients can differ considerably from the values corresponding to non-chemotactic transport. These transport coefficients show strong dependence of the microstructure of the porous medium, the fluid flow fields and the distribution of the attractant.  相似文献   

Self‐Organized Permeability in Carbonate Aquifers     

S.R.H. Worthington  D.C. Ford 《Ground water》2009,47(3):326-336

Advances over the past 40 years have resulted in a clear understanding of how dissolution processes in carbonate rocks enhance aquifer permeability. Laboratory experiments on dissolution rates of calcite and dolomite have established that there is a precipitous drop in dissolution rates as chemical equilibrium is approached. These results have been incorporated into numerical models, simulating the effects of dissolution over time and showing that it occurs along the entire length of pathways through carbonate aquifers. The pathways become enlarged and integrated over time, forming self‐organized networks of channels that typically have apertures in the millimeter to centimeter range. The networks discharge at point‐located springs. Recharge type is an important factor in determining channel size and distribution, resulting in a range of aquifer types, and this is well demonstrated by examples from England. Most carbonate aquifers have a large number of small channels, but in some cases large channels (i.e., enterable caves) can also develop. Rapid velocities found in ground water tracer tests, the high incidence of large‐magnitude springs, and frequent microbial contamination of wells all support the model of self‐organized channel development. A large majority of carbonate aquifers have such channel networks, where ground water velocities often exceed 100 m/d.  相似文献   

Model of particulate organic carbon transport in an agriculturally impacted stream   总被引：1，自引：0，他引：1       下载免费PDF全文

William I. Ford  James F. Fox 《水文研究》2014,28(3):662-675

The present contribution focuses on modeling the total particulate organic carbon (POC) and benthic POC transport from a lowland stream impacted by agricultural land‐use. A mass balance, reach scale model is verified that accounts for water, sediment and POC transport, sediment and POC temporary storage and exchange with the streambed, and production and degradation of carbon pools in the benthos. We found that the POC load is highly variable during individual hydrologic events and is influenced by transport of mixed carbon sources including upland, streambank and benthic POC sources. Benthic POC stocks and transport were found to vary seasonally and annually but are in a state of long‐term equilibrium. Equilibrium is governed by negative feedback mechanisms whereby high POC export due to extreme hydrologic events and high‐frequency hydrologic events reduces benthic POC stocks and inhibits benthic POC growth. Benthic POC accounted for 4 tC y^?1 or 22% of the total annual POC loading in the stream's main stem and 8.9 tC y^?1 or 48% of the POC yield for the entire watershed. These results suggest that further attention should be given to benthic‐derived POC when budgeting stream ecosystem carbon for low‐order stream systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Spatially-averaged flow statistics within a canopy of large bluff bodies: Results from direct numerical simulations     

Omduth Coceal  T. Glyn Thomas  Stephen E. Belcher 《Acta Geophysica》2008,56(3):862-875

The flow within a canopy of large bluff bodies is highly turbulent and spatially heterogeneous. Results from direct numerical simulations over groups of cubical obstacles are analysed using the double-averaging methodology. The obstacles occupy a significant fraction of the canopy space; this gives rise to substantial dispersive stresses within the canopy. The underlying bluff-body turbulent dynamics is different from typical canopy turbulence, and this is reflected in the double-averaged statistics. The spatially-averaged velocities, stresses and drag force depend significantly upon the layout of the obstacles. An ongoing challenge is to parameterise these spatially-averaged quantities in terms of the obstacle geometry and layout.  相似文献   

Seasonal variability in organic substances in surface and cave waters at Marengo Cave,Indiana     

Philip van Beynen  Derek Ford  Henry Schwarcz 《水文研究》2000,14(7):1177-1197

Water samples from forest soils and a shallow cave underlying them were collected for the hydrological year 1996–1997. The soil waters did not display much seasonal variability in concentrations of organic substances in them but the cave waters yielded distinct highest levels in the spring and autumn seasons. The important controls on the amount of organic substances reaching the cave are the seasonal fluctuation in volume of the percolation waters and the soil's ability to provide organic material for these waters. Fluorescence studies of the organic compounds isolated from these waters revealed shorter peak excitation and emission wavelengths for the cave waters than for the soil waters, a result of both differences in concentration and probably also of significant change in the proportional organic assemblages in the waters. Precipitation appears to affect the fluorescence in both waters, with the dry autumn producing the highest yields. Molecular size fractionation revealed how the larger hydrophobic compounds are preferentially removed from the water before it reaches the cave, with the consequence that the smaller hydrophilic compounds become the dominant fluorophore there. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

The evaluation of BATSE line candidates     

D. L. Band  S. Ryder  L. A. Ford  J. L. Matteson  D. M. Palmer  B. J. Teegarden  M. S. Briggs  W. S. Paciesas  G. N. Pendleton  R. D. Preece 《Astrophysics and Space Science》1995,231(1-2):203-206

We evaluated the significance of the line candidates identified by the visual search of burst spectra from BATSE's spectroscopy detectors. None of the candidates satisfy the detection criteria: anF-test probability less than 10^–4 for a feature in one detector and consistency among the detectors which viewed the burst. Most of the candidates are not very significant, and are likely to be fluctuations. Because of the expectation of finding absorption lines, the search was biased towards absorption features. We do not have a quantitative measure of the completeness of the search which would form the basis of a comparison with previous missions. Therefore a more objective computerized search has begun.  相似文献   

1980s' oceans policy — resources and technology: ‘The decade of the oceans’, 16th annual conference of the Marine Technology Society,Washington, DC,USA, 6–8 October 1980     

Hugh Cameron  Glyn Ford 《Marine Policy》1981,5(2):159-161

  相似文献   

Globular clusters as probes of galaxy evolution: NGC 5128     

S. K. Yi  E. Peng  H. Ford  S. Kaviraj  S.-J. Yoon 《Monthly notices of the Royal Astronomical Society》2004,349(4):1493-1499

  相似文献