Plasticity,Not Adaptation to Salt Level,Explains Variation Along a Salinity Gradient in a Salt Marsh Perennial

Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high- and low-salt microhabitats, assigned seedlings to high- and low-salt treatments in a greenhouse, and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity in many traits may be fixed for this species.     

Multi‐decadal variability of drought risk,eastern Australia

A number of previous studies have identified changes in the climate occurring on decadal to multi‐decadal time‐scales. Recent studies also have revealed multi‐decadal variability in the modulation of the magnitude of El Niño–Southern Oscillation (ENSO) impacts on rainfall and stream flow in Australia and other areas. This study investigates multi‐decadal variability of drought risk by analysing the performance of a water storage reservoir in New South Wales, Australia, during different climate epochs defined using the Inter‐decadal Pacific Oscillation (IPO) index. The performance of the reservoir is also analysed under three adaptive management techniques and these are compared with the reservoir performance using the current ‘reactive’ management practices. The results indicate that IPO modulation of both the magnitude and frequency of ENSO events has the effect of reducing and elevating drought risk on multi‐decadal time‐scales. The results also confirm that adaptive reservoir management techniques, based on ENSO forecasts, can improve drought security and become significantly more important during dry climate epochs. These results have marked implications for improving drought security for water storage reservoirs. Copyright © 2004 John Wiley & Sons, Ltd.     

Mechanisms and models of iridium anomaly shape across the Cretaceous–Paleogene boundary

The interpretation of the Cretaceous–Paleogene (K–Pg) iridium anomaly – and other impact ejecta – as the result of a single, large asteroid impact has been the subject of much debate, in part due to the distribution of impact markers beyond the narrow confines of the K–Pg boundary sedimentary layer. Here, we revisit the hypothesized processes leading to the shape of K–Pg iridium profiles including geochemical remobilization and/or diffusion, prolonged deposition, volcanism, multiple impacts, and sediment mixing. Using evidence from the literature and modeling of one North Pacific site, we find that sediment mixing of a single impact event provides the most parsimonious mechanism for iridium profile shape in open ocean oxic sediments, while the increase in background iridium bracketing the boundary likely has a volcanic origin. In some past studies, a sediment mixing mechanism for iridium profile shape was ruled out based on an overly simplified set of expectations for the effect of sediment mixing on markers of geologically instantaneous events. Thus, we introduce and use a Lagrangian sediment mixing model to illustrate the theoretical effects of mixing on records of rapid events. The sediment mixing origin for iridium anomaly shape, the correspondence in mixing extent between iridium and microfossils, and the fit of sediment mixing models to an empirical iridium profile indicate that iridium may provide a better tracer of mixing than previously proposed K–Pg mixing tracers such as Ni-spinels.     

Factors controlling variability in nearshore fecal pollution: The effects of mortality

A suite of physical–biological models was used to explore the importance of mortality and fluid dynamics in controlling concentrations of fecal indicator bacteria (FIB) at Huntington Beach, CA. An advection–diffusion (AD) model provided a baseline to assess improvements in model skill with the inclusion of mortality. Six forms of mortality were modeled. All mortality models performed better than the AD model, especially at offshore sampling stations, where model skill increased from <0.18 to >0.50 (Escherichia coli) or <?0.14 to >0.30 (Enterococcus). Models including cross-shore variable mortality rates reproduced FIB decay accurately (p < 0.05) at more stations than models without. This finding is consistent with analyses that revealed cross-shore variability in Enterococcus species composition and solar dose response. No best model was identified for Enterococcus, as all models including cross-shore variable mortality performed similarly. The best model for E. coli included solar-dependent and cross-shore variable mortality.     

Southern California inner basin sediment trap calibration

The deployment of particle interceptor traps (PITs) in the three inner basins of the Southern California Bight (Santa Barbara, Santa Monica, and San Pedro) where preserved, laminated, bottom sediments occur, provides a natural calibration between the parameters determined with the PITs and those derived from the historical sedimentary deposits. The accumulation rates and chemical composition of the PIT materials compare favorably with these recently deposited bottom sediments. The ratio of the measured particle collection rate to the sediment accumulation rate for these three basins averaged0.93±0.20. Radionuclide (²¹⁰Pb,²²⁸Th/²³²Th) and trace element (Fe, Cu, Zn, Cd, Pb) compositions of the PIT materials and surface sediments agree within, generally, 30% in each basin.An application of PITs as a sampling system in an outer basin (San Nicolas) where the sedimentary record has been obscured by bioturbation is also presented to further demonstrate the utility of PITs for spatial and temporal studies of various aspects of particle transport and sediment deposition. Based on the calibration of the PITs in the three inner basins we conclude from the comparison of the radionuclide and trace element compositions between the PIT materials and surface sediments from the San Nicolas Basin that recently deposited sedimentary material has been mixed by bioturbation with older material from the last several hundred years. Excess²¹⁰Pb and the²²⁸Th/²³²Th activity ratio in the PIT material are 6 and 15 times higher than in the surface sediment. Total Pb and1N HNO₃-leachable Pb are 4- and 8-fold higher in the PIT material.     

Subsidence on steep slopes due to longwall mining

Summary A two dimensional finite element model is used to simulate the extraction of coal by the longwall method underneath idealized surface slopes. The resulting subsidence, tilt and horizontal displacement values are compared with similar extractions using the same method beneath initially horizontal surfaces. The conclusions of a parametric study using this model, supported by field evidence, indicate that in areas of rugged topography, simple application of the procedures outlined in the National Coal BoardSubsidence Engineer's Handbook (1975) does not give acceptable predictions of the induced ground movements.     

Eddy properties in the Southern California Current System

The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for ~?190 days at ~?2 km day^?1. We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of ~?67% California Current waters and ~?33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy’s core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.     

Use of On-Site High Performance Liquid Chromatography to Evaluate the Magnitude and Extent of Organic Contaminants in Aquifers

Scientists engaged in the appraisal of ground water contaminated by organic substances are faced with the problems of difficult sample collection and timely chemical analysis. High-performance liquid chromatography was evaluated for on-site determination of specific organic contaminants in ground water samples and was used at three study sites. Organic solutes were determined directly in water samples, with little or no preparation, and usually in less than an hour after collection. This information improved sampling efficiency and was useful in screening for subsequent laboratory analysis. On two occasions, on-site analysis revealed that samples were undergoing rapid change, with major solutes being upgraded and alteration products being formed. In addition to sample stability, this technique proved valuable for monitoring other sampling factors such as compositional changes with respect to pumping, filtration, and cross contamination.     

Lead pollution in subtropical ecosystems on the SE Gulf of California Coast: a study of concentrations and isotopic composition

Lead pollution was investigated in environmental matrices and biological indicators collected from two typical subtropical coastal ecosystems in the southeast Gulf of California, Mexico. Lead concentrations and isotopic compositions ((206)Pb/(207)Pb and (208)Pb/(207)Pb) were measured using high resolution inductively-coupled plasma-mass spectrometry (HR-ICP-MS) and thermal ionization mass spectrometry (TIMS), respectively. Lead in surface estuary sediments (10.0-34.2microgg(-1)) and particulate Pb (25.0-128.7microgg(-1), >98% of total Pb) in the water column were significantly higher than levels in natural bedrock soils (15.1+/-8.3microgg(-1)) and river runoff (1.9+/-1.4microgg(-1)). Aquatic plants had Pb concentrations between 2.5 and 7.2microgg(-1), while those in macroalgae ranged from 3 to 5microgg(-1). The ranges of mean Pb concentrations in the aquatic animals studied (ranges in microgg(-1)) were as follows: zooplankton 32+/-3, mussels 2.3-3.9, oysters 1.9-7.9, snail 2.0-7.7, barnacles 0.1-18.5, fish 1.4-8.9, crab 6.3-40.2 and polychaetae 8.5-16.7. Pb values in 20-40% of oyster and fish samples and in all samples of crab exceeded acceptable levels for a food source for human consumption. Pb isotope ratios (206)Pb/(207)Pb, (208)Pb/(207)Pb in biota ranged from 1.188 to 1.206 and 2.448 to 2.470, respectively. A plot of (206)Pb/(207)Pb versus (208)Pb/(207)Pb for the environmental and biological samples collected from two study areas indicates that they contain lead from ores mined in Mexico and used in the past to produce leaded gasoline in use until 1997, natural Pb weathered from the Sierra Madre Occidental mother rock, and the later influence of inputs from a more radiogenic source related to industrial activity in the United States. Statistical software IsoSource results revealed that the Pb contained in environmental matrices and biomonitors is mostly derived from gasoline (20-90%) and US emissions (10-40%).