Historic nutrient loading and recent species invasions caused shifts in water quality and zooplankton demography in two Finger Lakes (New York, USA)

We investigated the paleolimnology of Owasco and Seneca Lakes (New York, USA) and compiled water-quality monitoring data to describe environmental change during the past two centuries. Trophic shifts were detected in the oligotrophic to mesotrophic range and were likely driven by nutrient loading and species invasion. Based on box core reconstructions, primary production increased in both lakes during the last century, which is evidenced by the amount, type and isotopic composition of material preserved in the sediment. Organic matter accumulation and its stable carbon isotopic composition, as well as carbonate abundance, began to increase during the 1960s in Owasco Lake and the 1850s in Seneca Lake. Further, the abundance of phytoplanktivorous cladocera subfossils increased beginning in the 1910s in Seneca Lake and in the 1960s in Owasco Lake. The different timing and magnitude of the trophic shifts likely resulted from contrasts in lake residence time and species assemblages between the two lakes. The increases in primary and secondary production paralleled, and are interpreted to reflect, increased allochthonous nutrient loading. However, nutrient loading was not detected in the water-quality data, perhaps because of strong uptake of phosphates by phytoplankton or due to limited data collection. Rapid changes in cladoceran subfossils and water quality were also detected during the last decade. Concurrent with the establishment of non-native Cercopagis pengoi (fishhook waterflea), phytoplanktivorous cladocera remains declined, and the mucrone length of Bosmina increased, consistent with predictions of increased invertebrate predation. Additionally, the post-1990 decline in sediment carbonate, increased Secchi depth and decreased chlorophyll a concentrations followed the establishment of filter-feeding Dreissena spp. (zebra and quagga mussels). Collectively, paleolimnological data and water-quality monitoring provided a more complete and consistent record of shifts in the productivity of Owasco and Seneca Lakes, which were useful to understand environmental changes over different time scales. Physical, geochemical and biological changes were temporally consistent among three cores collected from different locations in each lake, but differed in magnitude for several variables (e.g., grain size and cladoceran subfossils), which could reflect near-shore to offshore gradients.     

The Australian Air Quality Forecasting System: Exploring First Steps Towards Determining The Limits of Predictability For Short-Term Ozone Forecasting

Physical parameterisations of turbulent transfer processes in the atmospheric boundary layer, such as the stability parameterisations developed by Joost Businger, and recent advances in computing capabilities, have been important factors leading to the emergence of operational, numerical air quality forecasting systems. The present paper investigates the performance of the Australian Air Quality Forecasting System (AAQFS) in forecasting the peak 1 h ozone for the current or next day. These 24/36 h forecasts are generated for the Sydney and Melbourne regions and issued twice daily. Quantitative evidence is presented of the potential for the AAQFS to provide accurate numerical air quality forecasts. A second goal is to provide an initial benchmark for investigating the limits of predictability for air quality in the Sydney and Melbourne regions by looking at the dependence of the forecasts on the domain spatial scale (while maintaining the same model grid resolution), the starting time and length of the forecast (0000 UTC starts are 36-h forecasts and 1200 UTC starts are 24-h forecasts), and the sophistication of the photochemical mechanism (simple chemistry, Generic Reaction Set (GRS) and complex chemistry, Carbon Bond IV (CBIV)). The probability of detection by the forecast model is much better than persistence, showing considerable skill. The normalised bias, in general, decreases going from regional scale to sub-regional scale and becomes negative at the station scale. In Melbourne the gross error increases as the domain spatial scale decreases, but in Sydney there is a dip in the error at the sub-regional scale due to a sampling artifact. Better results are obtained at the smaller domain scales for 1200 UTC forecasts in Sydney. These are attributed to the shorter forecast period and secondarily to greater model spin-up effects at 0000 UTC. In Melbourne the results are ambiguous. Similar conclusions are derived from scatter plots of forecasts versus observations. Dividing the scatter plots into four sections by plotting vertical and horizontal lines (at 60 ppb) forms contingency tables for categorical forecasting. These plots show the increase in missed forecasts due to underprediction and the decrease in the number of extreme events detected as the spatial scale decreases. A comparison of the highly condensed GRS photochemical mechanism with the comprehensive CBIV mechanism indicates that, in general, GRS performs well for predicting ozone in urban situations provided that the background concentrations are appropriately specified. The potential to improve the forecasts at the smaller spatial scales, particularly for extreme events at high ozone concentrations, may require moving to a more complex mechanism as computer resources become available. This paper is dedicated to Joost Businger, who had strong ties with the atmospheric boundary-layer community in Australia over the past 40 years. It was while visiting CSIRO in Aspendale, Victoria, in 1965–1966 that Joost determined the stability dependence of the Monin-Obukhov surface-layer profiles. He immediately walked over to Arch Dyer’s office to show Arch his results. Arch carefully examined them, and then opened his desk drawer and pulled out his own plots of the stability dependence that he and Bruce Hicks had obtained. They showed the same curves, and thus the Businger-Dyer-Hicks stability functions were born. Arch and Bruce at the time were struggling with how to handle the internal politics; they needed Bill Swinbank’s approval, as Assistant Divisional Chief, before they could submit their results for publication. Bill had his own very strong ideas that conflicted with observations. Joost’s independent confirmation of their results provided a way forward (Bruce Hicks, personal communication, 2003). Joost has contributed significantly, either directly or indirectly, to experimental field programs both within Australia and overseas and to the development of parameterisations of turbulent transfer processes in the boundary layer.     

Infrared constraints on the dark mass concentration observed in the cluster Abell 1942

We present a deep H -band image of the region in the vicinity of the cluster Abell 1942 containing the puzzling dark matter concentration detected in an optical weak lensing study by Erben et al. We demonstrate that our limiting magnitude, H =22 , would be sufficient to detect clusters of appropriate mass out to redshifts comparable with the mean redshift of the background sources. Despite this, our infrared image reveals no obvious overdensity of sources at the location of the lensing mass peak, nor an excess of sources in the I − H versus H colour–magnitude diagram. We use this to constrain further the luminosity and mass-to-light ratio of the putative dark clump as a function of its redshift. We find that for spatially flat cosmologies, background lensing clusters with reasonable mass-to-light ratios lying in the redshift range 0< z <1 are strongly excluded, leaving open the possibility that the mass concentration is a new type of truly dark object.     

The biology,ecology and history of toheroa (Paphies ventricosa): a review of scientific,local and customary knowledge

Toheroa (Paphies ventricosa) were formerly abundant on west and south-facing New Zealand surf beaches. Harvesting of this surf clam was intense during the early to mid-1900s, and populations declined to levels where harvesting was no longer viable. Despite having now been protected for 35–45 years, toheroa have failed to recover. This paper reviews the history of human interactions with toheroa and our understanding of their ecology, with a view to identifying knowledge requirements for management and restoration. Historical and legal documents pertaining to the use of marine resources are reviewed and scientific understanding compared with customary and local knowledge. We consider the factors that may be preventing toheroa recovery and make recommendations for research into life history, habitat requirements and the ecological consequences of changing land use. Management options are suggested to address the effects of vehicle use on beaches, poaching and the failings of the customary harvest system.     

Zoning of phosphorus in igneous olivine

We describe P zoning in olivines from terrestrial basalts, andesites, dacites, and komatiites and from a martian meteorite. P₂O₅ contents of olivines vary from below the detection limit (≤0.01 wt%) to 0.2–0.4 wt% over a few microns, with no correlated variations in Fo content. Zoning patterns include P-rich crystal cores with skeletal, hopper, or euhedral shapes; oscillatory zoning; structures suggesting replacement of P-rich zones by P-poor olivine; and sector zoning. Melt inclusions in olivines are usually located near P-rich regions but in direct contact with low-P olivine. Crystallization experiments on basaltic compositions at constant cooling rates (15–30°C/h) reproduce many of these features. We infer that P-rich zones in experimental and natural olivines reflect incorporation of P in excess of equilibrium partitioning during rapid growth, and zoning patterns primarily record crystal-growth-rate variations. Occurrences of high-P phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling. Most cases of oscillatory zoning in P likely reflect internal factors whereby oscillating growth rates occur without external forcings, but some P zoning in natural olivines may reflect external forcings (e.g., magma mixing events, eruption) that result in variable crystal growth rates and/or P contents in the magma. In experimental and some natural olivines, Al, Cr, and P concentrations are roughly linearly and positively correlated, suggesting coupled substitutions, but in natural phenocrysts, Cr zoning is usually less intense than P zoning, and Al zoning weak to absent. We propose that olivines grow from basic and ultrabasic magmas with correlated zoning in P, Cr, and Al superimposed on normal zoning in Fe/Mg; rapidly diffusing divalent cations homogenize during residence in hot magma; Al and Cr only partially homogenize; and delicate P zoning is preserved because P diffuses very slowly. This interpretation is consistent with the fact that zoning is largely preserved not only in P but also in Al, Cr, and divalent cations in olivines with short residence times at high temperature (e.g., experimentally grown olivines, komatiitic olivines, groundmass olivines, and the rims of olivine phenocrysts grown during eruption). P zoning is widespread in magmatic olivine, revealing details of crystal growth and intra-crystal stratigraphy in what otherwise appear to be relatively featureless crystals. Since it is preserved in early-formed olivines with prolonged residence times in magmas at high temperatures, P zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma’s history. Study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks, especially because these features can be observed with standard electron microprobe techniques.     

Home-Work Links,Labor Markets,and the Construction of Place in Lawrence,Massachusetts, 1929–1939

This paper addresses the issue of how to combine, on one hand, the everyday links that are established and maintained between home and work, and on the other, the demand-driven social regulation of labor markets. It is argued that by taking an approach acknowledging the complexity of networks and the “constellations of relations” involved in forming local labor markets, we can better understand the meshing of divisions of labor at home and at work, in concert with the demands of local employers. In this respect, the roles of households, ethnic communities, and employers are taken to be critical and interdependent in forming local labor markets and, ultimately, constructing places. Census and archival data are used from Lawrence, Massachusetts to examine these issues through the situation of woolen mill workers of the 1920s and 1930s.     

Diagenesis in porosity evolution of opening-mode fractures, Middle Triassic to Lower Jurassic La Boca Formation, NE Mexico

Opening-mode fractures (joints) in Middle Triassic to Lower Jurassic La Boca Formation sandstones, northeastern Mexico, have patterns of fracture porosity, mineral-fill structures, and size distributions not previously described from outcrop. Patterns match those found in cores from many basins. We used aperture measurements along lines of observation (scanlines), fracture-trace maps, petrography, high-resolution scanning-electron-microscope-(SEM)-based cathodoluminescence, and fluid inclusions to characterize fracture populations. Open fractures are lined by quartz that precipitated while fractures were opening, whereas sealed fractures additionally contain calcite deposited after fractures ceased opening. Large fractures and arrays of contemporaneous microfractures have consistent power-law aperture-size scaling over approximately three orders of magnitude. Our results imply that open fractures and fracture sizes depend on diagenetic state. The interplay of fracture mechanics and diagenetic history is a determinant on effective porosity within fractures and, thus, open fracture persistence, connectivity, and fluid flow.