Trends in fog frequencies in the Los Angeles Basin

Data from throughout the Los Angeles area were examined to determine the horizontal distribution of dense fog (visibility < 400 m) in the region and trends over time. The relationship between the occurrence of dense fog to the phase of two atmosphere–ocean cycles: the Pacific Decadal Oscillation (PDO) measured by the PDO Index and the Southern Oscillation measured by the Southern Oscillation Index (SOI) was investigated. In addition, the influence of the urban heat island and the amount of suspended particulate matter were assessed. For the three stations that had 22 or more years of data, we examined trends and the relation to atmosphere–ocean cycles. Results show a decrease in the occurrence of very low visibilities (< 400 m) at the stations in close proximity to the Pacific Ocean, Los Angeles International Airport (LAX) and Long Beach International Airport (LGB). Occurrence of the frequency of low visibilities at these two locations was also highly correlated with the phase of the PDO. Only a weak, non-statistically significant relationship was seen with the SOI. At Burbank, a reporting station about 30 km from the ocean, no trends were noted, and there was no evidence of a correlation with either the PDO Index or the SOI. In the Los Angeles Central Business District (CBD) when comparing dense fog occurrence in the early 1960s to a similar period in the early 2000s we saw a decrease in dense fog from a mean of 10 h per year to a mean of 3 h per year. Also contributing to the decrease was decreasing particulate pollution and increased urban warming. A downward trend in particulate concentrations coupled with an upward trend in urban temperatures were associated with a decrease in dense fog occurrence at both LAX and LGB. These trends were evident for the period 1966–1997, but appear to have ended by the late 1990s.     

A model to predict stream water temperature across the conterminous USA

Stream water temperature (t_s) is a critical water quality parameter for aquatic ecosystems. However, t_s records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict t_s at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (t_a) and t_s. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the t_a–t_s linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict t_s resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict t_s at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the t_a–t_s relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean t_s in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean t_s in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on t_s across the USA. Copyright © 2014 John Wiley & Sons, Ltd.     

Polybrominated diphenyl ethers and their hydroxylated/methoxylated analogs: environmental sources, metabolic relationships, and relative toxicities

Brominated compounds are ubiquitous in the aquatic environment. The polybrominated diphenyl ether (PBDE) flame retardants are anthropogenic compounds of concern. Studies suggest that PBDEs can be biotransformed to hydroxylated brominated diphenyl ethers (OH-BDE). However, the rate of OH-BDE formation observed has been extremely small. OH-BDEs have also been identified as natural compounds produced by some marine invertebrates. Another class of compounds, the methoxylated BDEs (MeO-BDEs), has also been identified as natural compounds in the marine environment. Both the OH-BDEs and MeO-BDEs bioaccumulate in higher marine organisms. Recent studies have demonstrated that MeO-BDEs can be biotransformed to OH-BDEs and this generates greater amounts of OH-BDEs than could be generated from PBDEs. Consequently, MeO-BDEs likely represent the primary source of metabolically derived OH-BDEs. Given that for some endpoints OH-BDEs often exhibit greater toxicity compared to PBDEs, it is prudent to consider OH-BDEs as chemicals of concern, despite their seemingly "natural" origins.     

Context-Dependent Eelgrass–Macroalgae Interactions Along an Estuarine Gradient in the Pacific Northwest,USA

Land-based eutrophication is often associated with blooms of green macroalgae, resulting in negative impacts on seagrasses. The generality of this interaction has not been studied in upwelling-influenced estuaries where oceanic nutrients dominate seasonally. We conducted an observational and experimental study with Zostera marina L. and ulvoid macroalgae across an estuarine gradient in Coos Bay, Oregon. We found a gradient in mean summer macroalgal biomass from 56.1 g dw 0.25 m⁻² at the marine site to 0.3 g dw 0.25 m⁻² at the riverine site. Despite large macroalgal blooms at the marine site, eelgrass biomass exhibited no seasonal or interannual declines. Through experimental manipulations, we found that pulsed additions of macroalgae biomass (+4,000 mL) did not affect eelgrass in marine areas, but it had negative effects in riverine areas. In upwelling-influenced estuaries, the negative effects of macroalgal blooms are context dependent, affecting the management of seagrass habitats subject to nutrient inputs from both land and sea.     

Temporal and vertical distribution of crab larvae in a tidal pass

We investigated the vertical and temporal distributions of portunid zoea andCallinectes megalopae in a tidal pass of the Texas coast. Zoea were equally abundant on ebb and flood tide but were more abundant during the day than at night. Megalopae were more abundant during flood tide and at night than during ebb tide or during the day. We examined the evidence for selective tidal stream transport in both life-history stages. Depth of the centers of mass of the larval distributions and the dispersions around those centers were unrelated to temperature, salinity, current velocity, and time of day. Scaling arguments suggest that the absence of pattern in the vertical distributions was not due to turbulent mixing. There was little evidence that either larval stage used these environmental characteristics as cues for changes in behaviour. However, the presence of megalopae in the water column primarily during flood tide does support the tidal transport hypothesis. Megalopae may have difficulty sensing and reacting to environmental cues in wellmixed estuaries with semidiurnal tides.     

Variations in geometric measures of topographic surfaces underlain by fractured granitic plutons

Silicate melts impose systematic fracture patterns on their hosts and their own subsolidus portions as they crystallize and cool to ambient conditions. Weathering of these plutonic bodies accentuates the fractures and produces fragmented topographic surfaces whose geometric measures exceed those of a Euclidean surface. Because geometric measures of these surfaces are potentially indicative of the percolation properties of the fracture network, contours and vertical sections were digitized from 1250000 and 1240000 scale maps, and their statistical fractal dimensions,D, were computed. Regions underlain by granitic plutons with similar fragmentation patterns were found to haveD values ranging from 1.15 to 1.28 within a single pluton. This range of values is caused by noise and several geologic factors. The values contain noise introduced by the map-making and digitizing procedures that amounts toD1.05. However all values lie well above this threshold, and they correlate closely with local differences in weathering. SmallerD values derive from contours where accumulation of screen or glacial erosion has smoothed the surface, whereas largerD values derive from contours along aretes and in unglaciated terrains. In each of these regions, largerD values occur locally where fractures are most frequent and/or continuous. LargeD values were also derived from regions underlain by host rocks that lie in the near-field region of the stress field caused by the pluton. The fractral values derived are apparently related to the magma-hydrothermal event, they can potentially be used to derive properties of the percolation networks that were active during the hydrothermal events.     

Re and Os concentrations in arc basalts: The roles of volatility and source region fO2 variations

Olivine and spinel compositions, major elements (including ferric and ferrous iron), S, Re and Os contents have been measured for a suite of primitive (most >6 wt% MgO) basalts from the Trans Mexican Volcanic Belt (TMVB), including the western Mexican volcanic belt, the Michoacan-Guanajuato Volcanic Field, Sierra Chichinautzin, Pico de Orizaba region, Palma Sola, San Martin Tuxtlas, and the eastern alkaline province (EAP). Sulfur contents at sulfide saturation were calculated to determine whether the measured S contents are representative of sulfide saturated liquids. Most of the samples have S contents much lower than expected for sulfide saturation. A few have higher contents than calculated perhaps due to the presence of sulfate in the measured total sulfur (i.e., more oxidized samples). Comparison of the TMVB samples along with previously analyzed MORB, OIB, BABB and arc samples reveals a continuum of Re and Os contents that is best explained by variation in oxygen fugacity—and thus sulfide stability—in the source region. High Re and Os magmatic suites are best explained by derivation by melting of oxidized mantle, where sulfide is no longer stable and Re and Os behave incompatibly, whereas low Re and Os magmatic suites are derived from melting of relatively reduced mantle where sulfide is stable, and Re and Os behave compatibly. Intermediate examples abound, and arc magmas span a wide range of Re and Os concentrations due to variation of fO₂ in the source during genesis of arc magmas. Low Re magmatic suites are furthermore potentially affected by volatility which can lower Re by a factor of 3-5.     

Distribution and significance of long-chain alkenones as salinity and temperature indicators in Spanish saline lake sediments

We investigated relationships between sedimentary solvent-extractable long-chain alkenone (LCA) concentration and composition and environmental factors in a suite of endorheic lakes from inland Spain. LCAs were found in 14 of the 54 lakes examined, with concentrations comparable with those from previously published lacustrine settings. The composition of LCAs in our sites, however, contrast from the majority of those previously reported from lake environments; in our study the tri-unsaturated component is the most abundant component at most sites where LCAs are detected, and C_38:3 is the most abundant LCA in the majority of sites. LCA occurrence appears to be restricted to brackish-hypersaline sites and C₃₇ LCAs are absent above a salinity of ∼40 g L⁻¹ suggesting a salinity control on LCA-producing organisms in these sites. Low concentrations of C₃₇ LCA components means and temperature indices are generally not applicable. Instead we find good relationships between C₃₈ components and (in particular mean autumn) temperature and the strongest LCA-temperature relationships are found when using a combination of all C₃₇ and C₃₈ compounds. We propose a new alkenone temperature index for lakes with elevated salinity and where the C₃₈ components dominate the LCA distributions. This is expressed as (r² = 0.80, n = 13). In this paper, we provide the first account of sedimentary LCA distributions from lakes in inland Spain, extending the range of environments within which these compounds have been found and highlighting their significance as indicators of both salinity and temperature in saline, endorheic lake environments. This has important implications for extending the potential role of LCAs as palaeoclimatic indicators in lacustrine environments.     

Reconstituting nature conservation: Towards a careful political ecology

This paper is about the relationship between nature conservation in theory and nature conservation in practice. I argue that in theory nature conservation is concerned with revealing presence and rendering the present eternal. In practice, the spaces and times of conservation are less clear. Conservationists work with matters of concern that are neither self-evident nor unproblematically co-present. Presence has to be made and re-made. These matters of concern, like rare species, do not always announce themselves to political ecology and they do not always perform to type. Such difficulties are analysed through discussion of practical work conducted in a UK city with field ecologists and nonhuman inhabitants. It is argued that a careful political ecology is one that is intent on making spaces for others that are not simply about presence, inclusion or accumulation. It also involves uncertainties, precautionary measures and looser forms of assemblage.     

Using landscape characteristics to define an adjusted distance metric for improving kriging interpolations

Interpolation of point measurements using geostatistical techniques such as kriging can be used to estimate values at non-sampled locations in space. Traditional geostatistics are based on the spatial autocorrelation concept that nearby things are more related than distant things. In this study, additional information was used to modify the traditional Euclidean concept of distance into an adjusted distance metric that incorporates similarity in terms of quantifiable landscape characteristics such as topography or land use. This new approach was tested by interpolating soil moisture content, pH and carbon-to-nitrogen (C:N) ratio measured in both the mineral and the organic soil layers at a field site in central Sweden. Semivariograms were created using both the traditional distance metrics and the proposed adjusted distance metrics to carry out ordinary kriging (OK) interpolations between sampling points. In addition, kriging with external drift (KED) was used to interpolate soil properties to evaluate the ability of the adjusted distance metric to incorporate secondary data into interpolations. The new adjusted distance metric typically lowered the nugget associated with the semivariogram, thereby better representing small-scale variability in the measured data compared to semivariograms based on the traditional distance metric. The pattern of the resulting kriging interpolations using KED and OK based on the adjusted distance metric were similar because they represented secondary data and, thus, enhanced small-scale variability compared to traditional distance OK. This created interpolations that agreed better with what is expected for the real-world spatial variation of the measured properties. Based on cross-validation error, OK interpolations using the adjusted distance metric better fit observed data than either OK interpolations using traditional distance or KED.