Reproductive conditions of the Atlantic sturgeon (Acipenser oxyrinchus) in the Hudson River

Ninety-four prespawning adult Atlantic sturgeon (Acipenser oxyrinchus) were sampled in the Hudson River for age, sex, body size, gonad weight, fecundity, mature oocyte size, and plasma concentrations of gonadotropins, sex steroids, and vitellogenin during the spring spawning migrations in 1992 and 1993. In males, the age and total length ranged from 12 yr to 19 yr and from 133 cm to 204 cm and in females from 14 yr to 36 yr and from 197 cm to 254 cm. The majority of males were 13–16 yr old, and females were 16–20 yr old. Some females had residual atretic ovarian bodies, presumably remaining from a previous spawning and indicating iteroparity. Pre-ovulatory condition was recognized by migration of the germinal vesicle or by germinal vesicle breakdown and by significantly elevated plasma gonadotropins, progesterone, and vitellogenin. All pre-ovulatory females were captured upriver from Hudson River kilometer 136. Individual fecundity ranged from 0.4 million to 2.0 million eggs and oocyte diameter from 2.4 mm to 2.9 mm, and both characters exhibited a significant (p<0.05) positive relationship with female body size. Iteroparous females, tentatively identified by the presence of atretic bodies remaining in the ovary from a previous spawning, had significantly (p<0.05) higher fecundity and produced larger eggs, compared with females spawning presumably for the first time.     

Methane and carbon dioxide flux from a macrotidal salt marsh,Bay of Fundy,New Brunswick

Fluxes of methane (CH₄) and carbon dioxide (CO₂) to the atmosphere at 52 sites within a salt marsh were measured by a dark static chamber technique from mid July to mid September. Mean CH₄ fluxes ranged from 0.2 mg m^?2 d^?1 to 11.0 mg m^?2 d^?1, with an overall average of 1.6 mg m^?2 d^?1. Flux of CH₄ was inversely correlated (r²=0.23, p = 0.001) with salinity of the upper porewater at the site, suggesting the dominant role of SO₄ ^2? in inhibiting methanogenesis in salt-marsh sediments. The combination of salinity and water table position was able to explain only 29% of the variance in CH₄ emission. Mean soil flux of CO₂ ranged from 0.3 g m^?2 d^?1 to 3.7 g m^?2 d^?1, with an overall average of 2.5 g m^?2 d^?1; it was correlated with aboveground biomass (positive, r²=0.38, p = 0.001) and position of the water table (negative, r² = 0.55, p = 0.001). The combination of biomass and water table position accounted for 63% of the variance in CO₂ flux. There were high variations in gas flux within the six plant communities. The sequences were CH₄: upland edge > panne > pool > middle marsh > low marsh > high marsh, and CO₂: middle marsh > low marsh > upland edge > high marsh > panne > pool. Compared to other salt-marsh systems, this Bay of Fundy marsh emits small amounts of CH₄ and CO₂.     

The effect of dissolved water on the oxidation state of iron in natural silicate liquids

Ferric-ferrous ratios have been measured in 22 experiments on three natural compositions equilibrated at known temperature (950°–1100° C) and oxygen fugacity, and at water-saturated conditions over a pressure range from 0.05 to 0.2 GPa. There does not appear to be any reaction between the melt and the capsule material that affects the redox state of the iron in the melt. An empirical expression for the anhydrous behavior of the redox state of iron in each of these compositions has also been determined at 1 bar as a function of temperature and oxygen fugacity. A direct comparison of the hydrous ferric-ferrous values with the calculated anhydrous values shows that the dissolution of water in a per-alkaline rhyolite, andesite, and an augite minette has no effect on the redox state of the iron in these melts. This result parallels the effect of water on sulfide speciation in basaltic melts, and confirms published results on experimental hydrous basalts.     

On the inability of magnetically constricted transition regions to account for the 105 to 106 K plasma in the quiet solar atmosphere

Although back conduction from the corona has been shown to be inadequate for powering EUV emission below T 2 × 10⁵ K, it is thought to be adequate in the temperature range 2 × 10⁵ K < T < 10⁶ K. No models to date, however, have included the large magnetic constriction which should occur in the legs of coronal loops where conductive transition regions, hitherto thought to contain the bulk of the plasma in this higher temperature range, are located. On the basis of fine scale magnetograms, Dowdy et al. (1986) have estimated that these magnetic flux tubes are constricted from end to end by an areal factor of approximately 100. Furthermore, on the basis of simple steady-state conductive models, Dowdy et al. (1985) have shown that the large constriction can inhibit the conductive flow of heat by an order of magnitude. We are thus led to re-examine static models of this region of the atmosphere which incorporate not only conduction and radiation but also the effects of large magnetic constrictions. We find that the structure of this plasma depends not only on the magnitude of the constriction but also on the tube's shape.Our results show that no model with a constriction of order 100 can simultaneously (a) produce the variation of differential emission measure with temperature derived from measured line intensities and (b) satisfy the observed constraint (Reeves, 1976) that EUV emission from below T 7 × 10⁵ K be confined to the supergranular network, covering no more than 0.45 of the solar surface. The failure of the models suggests that the bulk of the 10⁵–10⁶ K plasma in the quiet solar atmosphere is not in transition region structures, but is instead magnetically isolated from the corona and heated internally. Even though the transition region component of 10⁵–10⁶ K plasma in the legs of coronal loops should exist, it comprises only a small fraction of the total 10⁵–10⁶ K plasma and, hence, produces only a small fraction of the observed EUV emission from this temperature range.We also find that for any permitted tube shape, constriction factors of order 100 reduce the coronal conductive energy losses to the transition region to a value which is less than a third of the value for an unconstricted field, i.e., to less than 2 × 10⁵ erg cm ^–2 s ^–1. In particular, if the magnetic geometry of the upper transition region is extremely concave (i.e., horn-shaped geometry with most of the areal divergence near the hot end), then a constriction of order 100 results in a conductive loss of less than 1 × 10⁴ erg cm^–2 s^–1 and, hence, much less than the coronal radiative energy loss. For such geometries, the constriction in the magnetic field hence provides an effective thermal insulation of the corona from the cooler parts of the solar atmosphere.Presidential Young Investigator.     

Artisanal and Small-Scale Gold Mining in Senegal: Livelihoods,Customary Authority,and Formalization

In Sub-Saharan Africa, efforts to formalize the artisanal and small-scale gold mining (ASGM) sector under legal frameworks and to improve its environmental and health practices have largely failed as a result of top-down policy measures that make change complicated and burdensome for low-resource miners. Using evidence from a case study of the ASGM sector within areas of Senegal, this article demonstrates that ASGM has become an important source of income for many traditionally agricultural rural populations. The findings point toward the embedded nature of ASGM within customary management structures in Senegal, and demonstrate that customary authority is an important component of ASGM operations and development, and should be recognized and integrated into innovative formalization policies and better practices initiatives.     

Stable isotope (δ<Superscript>13</Superscript>C, δ<Superscript>15</Superscript>N, δ<Superscript>34</Superscript>S) analysis of sediment cores suggests sockeye salmon (<Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>) did not historically spawn in Lake Roberta,Washington (USA)

Historically, the Sanpoil River, Washington (USA) produced spawning runs of chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (O. mykiss). Lake Roberta is connected to the Sanpoil River and local oral history suggests it may have supported anadromous sockeye salmon (O. nerka) until the completion of Grand Coulee Dam in the 1940s. Post-spawning mortality of anadromous salmon provides large pulses of marine-derived nutrients to aquatic and terrestrial ecosystems in the vicinity of spawning sites. Unique isotopic ratios of these marine-derived nutrients are often transferred to freshwater algae and archived in lake sediments. However, marine-derived isotope signatures may be overpowered by large inputs of other nutrient sources such as agricultural fertilizers, reactive nitrogen deposition, nitrogen fixation, or poor trophic transfer to freshwater algae. We compared nitrogen and sulfur isotope compositions for pre-1940 and post-1940 sediments to those collected from a control lake with no history of anadromy to investigate the possible historic presence of anadromous salmon in Lake Roberta. We also analyzed carbon isotopes, carbon:nitrogen ratios, and sediment accumulation rates to determine if changes in the lake sediments resulted from eutrophication rather than salmon exclusion. If sockeye did spawn in Lake Roberta historically, and if excessive nitrogen inputs did not overpower the marine-derived signal, we would expect pre-1940 sediment organic matter isotope compositions indicative of the large pulses of marine nutrients from decomposing salmon carcasses. Isotope results and land use in the Lake Roberta watershed present no conclusive evidence to support anecdotal accounts of anadromy. There is some evidence to suggest that marine-derived nutrients transferred to riparian communities within the lake’s watershed may have moved downstream to the lake. However, most of the evidence suggests eutrophication and a switch to increased autochthonous productivity are the main causes of changes in the lake sediment isotope composition.     

An intelligent geospatial processing unit for image classification based on geographic vector agents (GVAs)

Spatial modeling methods usually use pixels and image objects as fundamental processing units to address real‐world objects, geo‐objects, in image space. To do this, both pixel‐based and object‐based approaches typically employ a linear two‐staged workflow of segmentation and classification. Pixel‐based methods segment a classified image to address geo‐objects in image space. In contrast, object‐based approaches classify a segmented image to identify geo‐objects from raster datasets. These methods lack the ability to simultaneously integrate the geometry and theme of geo‐objects in image space. This article explores Geographical Vector Agents (GVAs) as an automated and intelligent processing unit to directly address real‐world objects in the process of remote sensing image classification. The GVA is a distinct type of geographic automata characterized by elastic geometry, dynamic internal structure, neighborhoods and their respective rules. We test this concept by modeling a set of objects on a subset IKONOS image and LiDAR DSM datasets without the setting parameters (e.g. scale, shape information), usually applied in conventional Geographic Object‐Based Image Analysis (GEOBIA) approaches. The results show that the GVA approach achieves more than 3.5% improvement for correctness, 2% improvement for quality, although no significant improvement for completeness to GEOBIA, thus demonstrating the competitive performance of GVAs classification.     

Regional variation in modern radiocarbon ages and the hard-water effects in Lakes Michigan and Huron

Eight new radiocarbon ages, all determined by accelerator mass spectrometry, on modern (pre-bomb) mollusks have been added to similar data provided from three samples in the Lake Michigan and Huron basins. These data confirm the existence of a substantial hard water effect correction ranging from about 250 years to 500 years in these lakes. They also show that the magnitude of these corrections form a spatially coherent pattern that can be related to the pattern of outcrop of Paleozoic (radioactively inert) carbonates that surround the basins and the pattern of circulation within the basins.