Oxyanion Concentrations in Eastern Sierra Nevada Rivers – 2. Arsenic and Phosphate

Water samples were collected from the Truckee River-Pyramid Lake system, the Walker River-Walker Lake system, and the Carson River, all located in eastern California and western Nevada, U.S.A., at three different times (i.e., summer 1991, spring 1992, and autumn 1992) over a two year period. The concentrations of As, Na, Cl, PO4, and pH were measured in these river samples and the associated terminal lakes. Arsenic values ranged from below 13 nmol/kg near Truckee, California to 160 nmol/kg at Nixon, Nevada in the Truckee River, from 40 nmol/kg in the headwaters of both West and East Walker Rivers to 270 nmol/kg below Weber Reservoir on the main branch of the Walker River, and from <27 nmol/kg to 234 nmol/kg for the lower Carson River system. Arsenic concentrations in Steamboat Creek (0.91 mol/kg–1.80 mol/kg) in the Truckee River catchment are above the U.S. EPA drinking water maximum contaminant level of 0.67 mol/kg, as are the As concentrations in both Pyramid Lake (1.33 mol/kg–1.57 mol/kg ) and Walker Lake (13.7 mol/kg–18.7 mol/kg). Sources of As for all three rivers include weathering of As-rich rocks and/or regolith and input of high-As geothermal spring waters, both processes primarily, although not exclusively, adding As to the headwater regions of these rivers. Steamboat Hot Springs (29 mol/kg As 54.5 mol/kg), for example, is identified as a source of As to the Truckee River via Steamboat Creek. The high As concentrations in Pyramid and Walker Lakes are likely due to (1) desorption of arsenate from aquatic particulate matter in these high pH waters (9.0 pH 9.5), (2) limited biologic uptake of arsenate, and (3) evaporative concentration of the lake waters. Evaluation of molar PO4}/As ratios of river waters and geothermal spring waters (e.g., Steamboat Hot Springs), indicates that phosphate is substantially enriched in Steamboat Creek as well as the mid to lower reaches of the Walker and Carson Rivers. These regions of each river are dominated by agricultural interests and, additionally, in the case of Steamboat Creek, residential areas and golf courses. Our data strongly imply that phosphate-rich agricultural return flow has likely added P to these streams and, consequently, increased their respective P:As ratios.     

Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair⁻¹ vs. 1.40 young fledged pair⁻¹) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation.     

The effect of a layer of varying density on high-frequencyreflection, forward loss, and backscatter [seafloor acoustics]

This paper examines the impact that a thin layer of varying density would have on high-frequency reflection, forward loss, and backscattering of acoustic plane waves from the seafloor. A functional form for density stratification was found by examination of several high-resolution density profiles obtained from X-ray computed tomography (CT) scans of seafloor cores. A solution based on these general profiles was used to estimate the reflection coefficient. The influence of the density profile on reflection loss and backscatter was then calculated using the estimated reflection coefficient. Parameter values used in simulations were obtained from the literature or from the CT scans of cores. It was found that inclusion of a density profile adds a strong frequency dependence to estimates of the reflection coefficient and forward loss. The largest effect on total scattering strength is near normal incidence where returns are dominated by interface scattering. The effect of the density profile on the strength of acoustic returns suggests that care should be taken when using high-frequency systems for measuring sediment properties, especially near normal incidence     

The Hg geochemistry of a geothermal stream, Steamboat Creek, Nevada: natural vs. anthropogenic influences

 A series of water samples from Steamboat Creek, Nevada, was analyzed for total mercury concentrations. Concentrations from these waters were 40 to 60 times higher than the pristine mountain streams entering the creek. The major source of the mercury entering Steamboat Creek is probably from gold/silver processing that took place in the 1860s. Received: 10 March 1997 · Accepted: 2 September 1997     

Patterns of hydrologic connectivity in the McMurdo Dry Valleys,Antarctica: a synthesis of 20 years of hydrologic data

Streams in the McMurdo Dry Valleys (MDVs) of Antarctica moderate an important hydrologic and biogeochemical connection between upland alpine glaciers, valley‐bottom soils, and lowland closed‐basin lakes. Moreover, MDV streams are simple but dynamic systems ideal for studying interacting hydrologic and ecological dynamics. This work synthesizes 20 years of hydrologic data, collected as part of the MDVs Long‐Term Ecological Research project, to assess spatial and temporal dynamics of hydrologic connectivity between glaciers, streams, and lakes. Long‐term records of stream discharge (Q), specific electrical conductance (EC), and water temperature (T) from 18 streams were analysed in order to quantify the magnitude, duration, and frequency of hydrologic connections over daily, annual, and inter‐annual timescales. At a daily timescale, we observe predictable diurnal variations in Q, EC, and T. At an annual timescale, we observe longer streams to be more intermittent, warmer, and have higher median EC values, compared to shorter streams. Longer streams also behave chemostatically with respect to EC, whereas shorter streams are more strongly characterized by dilution. Inter‐annually, we observe significant variability in annual runoff volumes, likely because of climatic variability over the 20 record years considered. Hydrologic connections at all timescales are vital to stream ecosystem structure and function. This synthesis of hydrologic connectivity in the MDVs provides a useful end‐member template for assessing hydrologic connectivity in more structurally complex temperate watersheds. Copyright © 2016 John Wiley & Sons, Ltd.     

C NMR, micro-FTIR and fluorescence spectra, and pyrolysis-gas chromatograms of coalified foliage of late Carboniferous medullosan seed ferns, Nova Scotia, Canada: Implications for coalification and chemotaxonomy

The cuticles and cuticle-free compressions of three Carboniferous medullosan seed-fern leaf species (Macroneuropteris scheuchzeri, Neuropteris ovata var. simonii and Alethopteris lesquereuxii) were analyzed by elemental, ¹³C nuclear magnetic resonance (NMR), micro-FTIR (Fourier transform infrared) and coal petrographic techniques. The 13C NMR spectra of the cuticle-free compressions and the associated whole coal (high volatile A/B bituminous coal rank) are generally similar and consist of a large aromatic carbon peak, a smaller aliphatic carbon peak and a shoulder on the aromatic peak, representing phenolic carbons. In contrast, the ¹³C NMR spectra of the cuticles from the same leaves have a predominant peak for aliphatic carbons and a much smaller aromatic carbon peak. This difference in aromaticity between the cuticles and the cuticle-free compressions is also reflected in the higher atomic H/C ratios of the cuticles. Micro-FTIR spectra of the cuticles show oxygenated functional groups (carboxyl and ketone) similar to those in modern cuticles but their most characteristic feature is very strong bands in the aliphatic stretching region. The cuticle-free compressions (mainly vitrinite), in turn, show the absence or significant reduction in oxygenated functional groups, reduction in aliphatic stretching bands and, usually, increased absorbance of aromatic out-of-plane deformation in the 700–900 cm⁻¹ region. Fluorescence spectra for the cuticles from all three species show a great similarity with a λ_max at 580–590 nm, probably reflecting a similardegree of coalification, which is consistent with the similar vitrinite reflectance (R_r) and H/C and O/C ratios of the cuticlefree compressions.These results indicate that leaf cuticle-free compressions, which were initially cellulose rich ( 90% cellulose and hemicellulose, < 10% lignin), can alter, during peatification and coalification, to a macromolecular structure similar to that of coalified wood (initially 50% cellulose and hemicellulose, 30%–50% lignin). Thus, a lignin-enriched structure is not a prerequisite for the formation of the macromolecular structure of vitrinite. In addition, the micro-FTIR spectra reveal the complexity of the molecular structure in coalified seed-fern leaves. The micro-FFIR data reveal some significant differences among the cuticles that may be of chemotaxonomic value. Clearly, a combination of macro- and micro-techniques offers a better basis for the interpretation of the molecular structure of pre-macerals and their alteration during peatification and coalification. Also, the data presented in this paper provide important new information that extends the data from morphological and cuticular taxonomic studies of some seed ferns. The data are encouraging preliminary advances in the chemotaxonomy of medullosan seed fern species.Pyrolysis-gas chromatography (PY-GC) data for the cuticles of three seed-fern leaves indicate distinct chemical signatures for the two neuropterid leaves as compared to the Alethopteris leaf. This perhaps indicates a chemotaxomic factor, or it could be related to the greater thickness of the cuticle of Alethopteris. Mass spectrometric data are needed to identify individual components in the PY-GC chromatograms.     

Porewater geochemistry and solute flux from bottom sediments,Devils Lake,North Dakota

Sediment cores were collected for pore-water analysis from the eastern end of Devils Lake, located in northeastern North Dakota, to determine diagenetic reactions occurring in surficial bottom sediments and to evaluate the impact of these reactions on chemical concentrations in the overlying lake water. Sediment pore waters are enriched in major ions and nutrients relative to lake water. The principal sources of major ions to pore water are saline sediments located in the upper 1 m of bottom sediment. The principal source of titration alkalinity and nutrients to pore water is microbial decomposition of sedimentary organic matter by sulfate reduction. Sediment pore waters in the eastern part of Devils Lake have higher major-ion concentrations and solute-flux rates than the sediment pore waters in the central part of the lake. In contrast, sediment pore waters in the central part of Devils Lake have significantly higher nutrient concentrations and solute-flux rates. Major-ion concentrations and solute-flux rates in sediment pore water increase from west to east. These trends indicate that bottom-sediment diagenetic processes are, in part, responsible for the observed concentration gradient in the lake. The higher nutrient concentrations and the higher nutrient diffusional-flux rates in Main Bay are the result of more labile sedimentary organic matter and the occurrence of sulfate reduction. Environmentally-reactive trace-metal concentrations (Cu, Pb, Zn, and Fe) in bottom sediments decrease from west to east with distance from the surface-water sources and with increasing surface-water salinity.     

Stagnation and nocturnal temperature jumps in a desert region of low relief

Observations of mesoscale variations in temperature and wind fields in a desert environment are presented and discussed. In particular the influence of low relief under conditions of strong stability is highlighted and stagnant flow is shown to occur below a critical Froude number of 1.5. Sudden nocturnal temperature increases are also analysed and possible mechanisms for their formation discussed.     

Trace metal fluxes to nearshore Long Island Sound sediments

Sediments are very important as trace metal ‘sinks’ in coastal areas. In this paper we present data on the concentrations and calculated fluxes of the trace metals, Fe, Mn, Cu, Pb, Zn, Cd and Ag at nearshore sites in Long Island Sound. In both areas a percentage of the metal accumulation can be ascribed to local human activities with the highest anthropogenic metal fluxes occurring closest to their source.