A COMPARISON OF HYDROLOGY AND VEGETATION BETWEEN A CHANNELIZED STREAM AND A NONCHANNELIZED STREAM IN WESTERN TENNESSEE

The purpose of this study was to provide baseline data on floodplain forest structure, composition, and function that would be needed to predict and monitor the consequences of a proposed stream restoration project. This project would involve the “dechannelization” of Stokes Creek, a stream in western Tennessee that was channelized and leveed in the first half of the 1900s. To this end, we collected data on surface hydrology, soil redox potential (Eh), and the structure and composition of the floodplain vegetation of Stokes Creek. To place our findings into a regional context, we also collected comparable vegetation data from plots located along a nonchannelized stream reach of the Wolf River near Moscow, Tennessee. While hydrologic fluctuations of floodplain sites were synchronous with river dynamics for the Wolf River, the hydrology of floodplain sites at Stokes Creek was constrained by the influence of beaver dams, backflooding, and ponding of overland flow behind levees. Consequently, composition of the forest overstory, understory, and herbaceous strata was significantly different between the two sites. For example, Stokes Creek had a noticeable lack of cypress and tupelo sites, and a greater abundance of red maple. Analyses of size-class structure and woody debris quantity reinforced the existing differences between the more natural and human-impacted systems. While the current hydrology apparently has a negative affect on bottomland hardwoods, scattered regeneration stems and soil redox measurements indicate that a dechannelization effort that yielded lower water tables in the Stokes Creek floodplain potentially could increase bottomland hardwood establishment. [Key words: channelization, western Tennessee, bottomland hardwoods, hydrology.]     

Rockfall Hazard Analysis From Discrete Fracture Network Modelling with Finite Persistence Discontinuities

Developing an accurate representation of the rock mass fabric is a key element in rock fall hazard analysis. The orientation, persistence and density of fractures control the volume and shape of unstable blocks or compartments. In this study, the discrete fracture modelling technique and digital photogrammetry were used to accurately depict the fabric. A volume distribution of unstable blocks was derived combining polyhedral modelling and kinematic analyses. For each block size, probabilities of failure and probabilities of propagation were calculated. A complete energy distribution was obtained by considering, for each block size, its occurrence in the rock mass, its probability of falling, its probability to reach a given location, and the resulting distribution of energies at each location. This distribution was then used with an energy–frequency diagram to assess the hazard.     

Tracing groundwater discharge in a High Arctic lake using radon-222

In the High Arctic, groundwater fluxes are limited by the presence of continuous permafrost, although it has been hypothesized that there may be localized groundwater flow and hydraulic connectivity beneath large lakes, due to the presence of taliks, or large regions of unfrozen ground. However, due to the logistical difficulty of employing seepage meters and piezometers in deep, ice-covered lakes, relatively little is known about groundwater discharge to polar lakes. One method of assessing groundwater discharge is through the use of geochemical tracers. We conducted a pilot study to quantify groundwater discharge into a High Arctic lake using dissolved radon gas as a geochemical tracer. Lake water was collected in 15 L polyvinyl chloride (PVC) bags with minimal atmospheric interaction from a 25-m deep lake near Shellabear Point, Melville Island, Northwest Territories, Canada. Sample bags were aerated through a closed water loop for 60 min to allow sufficient radon to equilibrate in a coupled air circuit. Radon in air concentrations were measured on a Durridge RAD7 portable alpha spectrometer. The field trial in a remote setting and separate tests with groundwater samples collected from a temperate site demonstrate the utility of the methodology. The limited results suggest that radon levels in the lower water column are elevated above background levels following nival melt in the surrounding watershed. Although these results are insufficient to quantify groundwater discharge, the results suggest subsurface flow may exist, and further study is warranted.     

Photographic assessment of retroreflective film properties

Retroreflective film is used widely for target manufacture in close-range photogrammetry, especially where high precision is required for applications in industrial or engineering metrology. 3M Scotchlite 7610 high gain reflective sheeting is the gold standard for retroreflective targets because of the high level of response for incidence angles up to 60°. Retroreflective film is now widely used in the transport industry for signage and many other types of film have become available. This study reports on the performance of six types of retroreflective sheeting, including 7610, based on published metrics for reflectance. Measurements were made using a camera and flash, so as to be directly applicable to photogrammetry. Analysis of the results from this project and the assessment of previous research indicates that the use of standards is essential to enable a valid comparison of retroreflective performance.     

Ecological status of seagrass ecosystems: An uncertainty analysis of the meadow classification based on the Posidonia oceanica multivariate index (POMI)

Quantifying the uncertainty associated with monitoring protocols is essential to prevent the misclassification of ecological status and to improve sampling design. We assessed the Posidonia oceanica multivariate index (POMI) bio-monitoring program for its robustness in classifying the ecological status of coastal waters within the Water Framework Directive. We used a 7-year data set covering 30 sites along 500 km of the Catalonian coastline to examine which version of POMI (14 or 9 metrics) maximises precision in classifying the ecological status of meadows. Five factors (zones within a site, sites within a water body, depth, years and surveyors) that potentially generate classification uncertainty were examined in detail. Of these, depth was a major source of uncertainty, while all the remaining spatial and temporal factors displayed low variability. POMI 9 matched POMI 14 in all factors, and could effectively replace it in future monitoring programs.     

Sulfur biogeochemical cycling and novel Fe-S mineralization pathways in a tidally re-flooded wetland

Sulfur biogeochemical cycling and associated Fe-S mineralization processes exert a major influence over acidity dynamics, electron flow and contaminant mobility in wetlands, benthic sediments and groundwater systems. While S biogeochemical cycling has been studied intensively in many environmental settings, relatively little direct information exists on S cycling in formerly drained wetlands that have been remediated via tidal re-flooding. This study focuses on a tidal wetland that was drained in the 1970s (causing severe soil and water acidification), and subsequently remediated by controlled re-flooding in 2002. We examine reduction rates and Fe-S mineralization at the tidal fringe, 7 years after the commencement of re-flooding. The initial drainage of the wetland examined here caused in-situ pyrite (FeS₂) oxidation, resulting in the drained soil layers being highly acidic and rich in -bearing Fe(III) minerals, including jarosite (KFe₃(SO₄)₂(OH)₆). Tidal re-flooding has neutralized much of the previous acidity, with the pore-water pH now mostly spanning pH 5-7. The fastest rates of in-situ reduction (up to ∼300 nmol cm⁻³ day⁻¹) occur within the inter-tidal zone in the near-surface soil layers (to ∼60 cm below ground surface). The reduction rates correlate with pore-water dissolved organic C concentrations, thereby suggesting that electron donor supply was the predominant rate determining factor. Elemental S was a major short-term product of reduction, comprising up to 69% of reduced inorganic S in the near-surface soil layers. This enrichment in elemental S can be partly attributed to interactions between biogenic H₂S and jarosite - a process that also contributed to enrichment in pore-water Fe²⁺ (up to 55 mM) and (up to 50 mM). The iron sulfide thiospinel, greigite (Fe₃S₄), was abundant in near-surface soil layers within the inter- to sub-tidal zone where tidal water level fluctuations created oscillatory redox conditions. There was evidence for relatively rapid pyrite re-formation within the re-flooded soil layers. However, the results indicate that pyrite re-formation has occurred mainly in the lower formerly drained soil layers, whereas the accumulation of elemental S and greigite has been confined towards the soil surface. The discovery that pyrite formation was spatially decoupled from that of elemental S and greigite challenges the concept that greigite is an essential precursor required for sedimentary pyrite formation. In fact, the results suggest that greigite and pyrite may represent distinct end-points of divergent Fe-S mineralization pathways. Overall, this study highlights novel aspects of Fe-S mineralization within tidal wetlands that have been drained and re-flooded, in contrast to normal, undisturbed tidal wetlands. As such, the long-term biogeochemical trajectory of drained and acidified wetlands that are remediated by tidal re-flooding cannot be predicted from the well-studied behaviour of normal tidal wetlands.     

On the origins of GEMS grains

From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation.We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.     

Chronostratigraphy and lake-level changes of Laguna Cari-Laufquén, Río Negro, Argentina

Evidence from shoreline and deep-lake sediments show Laguna Cari-Laufquén, located at 41°S in central Argentina, rose and fell repeatedly during the late Quaternary. Our results show that a deep (> 38 m above modern lake level) lake persisted from no later than 28 ka to 19 ka, with the deepest lake phase from 27 to 22 ka. No evidence of highstands is found after 19 ka until the lake rose briefly in the last millennia to 12 m above the modern lake, before regressing to present levels. Laguna Cari-Laufquén broadly matches other regional records in showing last glacial maximum (LGM) highstands, but contrasts with sub-tropical lake records in South America where the hydrologic maximum occurred during deglaciation (17–10 ka). Our lake record from Cari-Laufquén mimics that of high-latitude records from the Northern Hemisphere. This points to a common cause for lake expansions, likely involving some combination of temperature depression and intensification of storminess in the westerlies belt of both hemispheres during the LGM.     

What kind of countryside do the public want: community visions from Wales UK?

This paper assesses how far community led rural visions accord with the current thrust of rural planning policy delivery in the UK. Adapting conventional visioning methods, qualitative techniques were used on eight different communities across urban, exurban and rural Wales to elicit views relating to the kind of local countryside(s) that were desired. The results show that the communities’ visions reflect an emerging consensus around local countryside priorities: multifunctionality, integration, wider countryside protection, development based on need, and local distinctiveness according with the thrust of current planning policy at national and local levels. However, there is a clear dichotomy between this and the reality of what communities actually experienced in developments affecting their countryside. Here, universal criticism was encountered over the type, pace and scale of development, the lack of rural specificity and the failure to take account of local community needs and priorities. It is hypothesized that tensions between national and local politics and stakeholder power relations are playing a crucial role in distorting the delivery of town and country planning. It is recommended that rural policy delivery must become more “joined up” and rural proofed at national and local levels concomitant with a change in the operational culture of agencies at the forefront of rural delivery. Essentially, effective engagement of top down approaches synergising with bottom up community led ideas is long overdue.     

A spatially explicit degree-day model of Rift Valley fever transmission risk in the continental United States

A spatially explicit degree-day model was used to evaluate the risk of Rift Valley fever virus (RVFV) transmission by mosquitoes to humans and livestock within five target states in the continental United States: California, Minnesota, Nebraska, New York, and Texas. A geographic information system was used to model potential virus transmission based on a 12-day moving window assessment of the extrinsic incubation period theorized for RVFV in the United States. Risk of potential virus transmission in each state was spatially evaluated on a 10-km grid using average historical daily temperature data from 1994 to 2003. The highest levels of transmission risk occur in California and Texas, with parts of these states at risk of RVFV transmission for up to 8 months per year. Northern Minnesota, central New York, and most of coastal and high-elevation California are at low to null risk. Risk of impact to the livestock industry is greatest in California, Texas, and Nebraska. A standard global climate model was used to evaluate future risk in the year 2030 in Nebraska, and showed an increase of transmission risk days from approximately 3 to 4 months per year.