Interactive effects of light and salinity stress on the growth,reproduction, and photosynthetic capabilities of<Emphasis Type="Italic">Vallisneria americana</Emphasis> (wild celery)

The effects of light and salinity onVallisneria americana (wild celery) were studied in outdoor mesocosms for an entire growing season. Morphology, production, photosynthesis, and reproductive output were monitored from sprouting of winter buds to plant senescence and subsequent winter bud formation under four salinity (0, 5, 10, and 15 psu) and three light (2%, 8%, and 28% of surface irradiance) regines. Chlorophylla fluorescence was used to examine photochemical efficiency and relative electron transport rate. High salinity and low light each stunted plant growth and reproduction. Production (biomass, rosette production, and leaf area index) was affected more by salinity than by light, apparently because of morphological plasticity (increased leaf length and width), increased photosynthetic efficiency, and increased chlorophyll concentrations under low light. Relative maximum electron transport rate (ETR_max) was highest in the 28% light treatment, indicating increased photosynthetic capacity. ETR_max was not related to salinity, suggesting that the detrimental effects of salinity on production were through decreased photochemical efficiency and not decreased photosynthetic capacity. Light and salinity effects were interactive for measures of production, with negative salinity effects most apparent under high light conditions, and light effects found primarily at low salinity levels. For most production and morphology parameters, high light ameliorated salinity stress to a limited degree, but only between the 0 and 5 psu regimes. Growth was generally minimal in all of the 10 and 15 psu treatments, regardless of light level. Growth was also greatly reduced at 2% and 8% light. Flowering and winter bud production were impaired at 10 and 15 psu and at 2% and 8% light. Light requirements at 5 psu may be approximately 50% higher than at 0 psu. Because of the interaction between salinity and light requirements for growth, effective management of SAV requires that growth requirements incorporate the effects of combined stressors.     

Working borders and shifting identities in the Russian Far North

State-imposed borders inform socio-spatial identities, often encouraging divergent identities for those living of different sides of the border. However, these identities may be discursively appropriated by the groups affected by the borders, in order to manage their relations with the state. We describe how one group of aboriginal people in the Russian Far North forged a common identity based on evasion of state institutions in the 1930–1950s. This group, once articulated with state institutions and divided by the enforcement of a provincial/republican border, developed two socio-spatial identities––and employed these identities as counterhegemonic tactics to state pressures over their lifeways. As types of pressures change, the affordances that the borders provide also change, as evident in the shifting discourses of difference and similitude.     

Biological monitoring of the marine ocean outfall at black rock, Victoria, Australia

The Barwon Region Water Authority in Victoria, Australia, commissioned a new subtidal ocean sewage outfall in February 1989. This outfall replaced an old intertidal outfall, and presently discharges via a diffuser in an average depth of 15m some 1.2km offshore in Bass Strait. Examination of biological communities around the old outfall prior to the change revealed distinct differences in biotic assemblages close to the outfall. An ongoing monitoring programme, implemented in 1986, has assessed not only the recovery in this intertidal area, but also the major changes to macroalgal communities on surrounding reefs, subtidal infauna populations in sandy sediments, and rocky shore communities.     

Seasonal changes in vocalization during behavior of the Atlantic bottlenose dolphin

Four vocalizations (whistles, buzzes, quacks, and pops) were quantified during three behavioral categories (socializing, traveling, and feeding) of the bottlenose dolphin in the Newport River Estuary, North Carolina. This study tested the hypothesis that specific vocalizations of dolphins in this area are associated with specific behavioral categories during the summer and fall. Approximately twice the total number of vocalizations per unit time occurred during the fall as compared to the summer. Each type of vocalization had a distinctive and consistent acoustical structure. The relative frequency of the different vocalization types was significantly dependent on the behavior of the dolphins. Pops were consistently associated with feeding, quacks with socializing, and buzzes with traveling. Whistles, the most common vocalization, were associated with traveling and feeding during the summer and socializing in the fall. Dolphins spent more time involved in undirected activity (socialization) during the summer but spent more time traveling in search of food and feeding during the fall in preparation for migration out of the estuary and movement south.     

Mechanical models for correlation of ring-fracture eruptions at Pantelleria,Strait of Sicily,with glacial sea-level drawdown

Recent K-Ar dating of eruptions at Pantelleria, a peralkaline volcanic island in the Strait of Sicily, shows a correlation between eruption of pantellerite lavas from caldera ring fractures and low stands of sea level as determined from ¹⁸O stratigraphy. Post-caldera pantellerite lavas associated with an 114-ky-old caldera erupted along the ring-fracture zone during a major low stand of sea level at about 67 Ka. The most recent episode of lava-flow emplacement began about 20 ky ago during the last glacial maximum. Magma vented along the ring fault of a 45-ky-old caldera, from fractures radial to the caldera, and along faults formed by intracaldera trapdoor uplift. Two mechanical models based on elasticity theory are presented to explain the correlation of post-caldera ring-fracture eruptions at Pantelleria with lowering of sea level. A simple analysis of a bending circular plate of thickness,T _r, and radius,R, representing the magma-chamber roof block, shows that tensile stress is concentrated by a factor of 0.75R ²/T _r ² at the lower perimeter of the plate when sea level drops. Stress changes may be even greater ifT _r is effectively less than the stratigraphic thickness due to layering of rocks in the roof block. Calculated stress changes due to a 100-m drawdown of sea level are similar in magnitude to stresses associated with dike propagation. More realistic model geometries, including different chamber shapes, a conical volcanic edifice, and sea-level drawdown beyond the surface projection of the magma chamber, were tested using the boundary-element method. Lowering sea level generates a horizontal tensile stress above the chamber, even when sea water is removed outboard of the magma chamber. For some chamber geometries the magnitude of the tensile stress maximum is greater than the 1 MPa pressure of the 100 m of removed water and is of the right order of magnitude for dike propagation. Dikes initiated by the change of the stress field may originate and propagate along fractures inboard of the chamber margin. The magnitudes of tensile maxima along the top of the chamber decrease as original sea level is moved outboard of the chamber margin and as the chamber thickness decreases. When the depth to the top of the magma chamber reaches a critical value, dependent on chamber geometry, the propagation of dikes to the surface is inhibited.     

Sedimentation processes in an impoundment,Union lake,New Jersey

A small (3 75 km²) impoundment. Union Lake, on the Maurice River in southern New Jersey contains fine-grained sediment and organic material being transported through the surface water system Sedimentation is slow and rates calculated from¹³⁷Cs-dated cores indicate a decrease through time from 2 6 mm/yr to 0 57 mm/yr Sediment from shallow areas (<3 m) consists of winnowed preimpoundment fluvial sand, whereas sediment from deeper areas (>3 m) is dy composed of diatoms, organic matter, and silt- and clay-sized mineral grains Sediment distribution is controlled by water moving from the river entrance southward toward the outlet and by wind-generated water motion from shallow areas fringing the shore toward deeper portions of the impoundment     

Surface Estimation for Multiple Misaligned Point Sets

Mathematical Geosciences - Two common tasks when processing point cloud data sets are surface estimation and point cloud registration. In this paper, a statistical approach is developed to solve...     

Beyond 'someone else's agenda': An example of indigenous/academic research collaboration

In recent years, Māori and wider indigenous geographies have flourished. These include works by scholars identifying specific Māori or indigenous issues but less attention has been paid to the way such research is conducted. This paper engages with these developments and presents the practices and lessons learnt from one particular research collaboration. Relationship building, multiple methods, flexibility, communication choices and wider support are all noted as key elements in establishing a supportive and fruitful collaboration.