Trace/minor element:calcium ratios in cultured benthic foraminifera. Part I: Inter-species and inter-individual variability

Trace/minor element signatures (D_Cd, D_Ba, D_Mg, and D_Sr) were measured in the tests (shells) of benthic foraminifera cultured in a trace-metal-concentration-controlled system. The culture system was constructed of inert materials and designed to limit microhabitat effects. This system ensured that variation observed in cultured foraminiferal element:calcium (TE/Ca) signatures was due to biologically mediated (vital) effects only. Two species, Bulimina aculeata and Rosalina vilardeboana, reproduced prolifically during two 4-to-8-month culture periods. In every case (i.e., for both species and each element), the inter-individual variability was larger than the analytical precision. Mean (±1 standard deviation) D_E signatures for B. aculeata were: D_Cd: 1.5 ± 0.4, D_Ba × 10: 2.1 ± 0.7, D_Mg × 1000: 0.62 ± 0.15, and D_Sr × 10: 1.5 ± 0.1. Cultured B. aculeata D_Mg, calibrated from culture and core-top (live) field specimens, predicted temperatures within ±2.0 °C. The observed inter-individual variability from culture specimens was as large or larger than comparable results from core-top investigations. R. vilardeboana D_Cd signatures were significantly lower, while D_Ba, D_Mg, and D_Sr signatures were significantly higher than B. aculeata values. Since our culture system minimizes microhabitat variability, the variation in measured TE/Ca ratios suggests that biological processes are a significant factor in inter-individual and inter-species variability. Comparison of cultured and field-collected foraminiferal D_Ba signatures supports previous findings that pore-water chemistry is a major environmental influence on foraminiferal test chemistry.     

Glacial rapid variability in deep-water temperature and δO from the Western Mediterranean Sea

Deep-water temperatures (DWTs) from the Western Mediterranean Sea are reconstructed for the last 50 ka based on the analysis of Mg/Ca ratios in benthic foraminifera from core MD95-2043 collected in the Alboran Sea. The exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the Dansgaard–Oeschger (D–O) rapid climatic variability. The applicability of Mg/Ca thermometry in the Western Mediterranean Deep-Water mass (WMDW) is first tested by the analysis of different benthic species in a collection of Mediterranean core tops. The results indicate the need of a readjustment of the existing Cibicidoides spp. calibrations in order to reconstruct present Western Mediterranean DWT values (12.7 °C). Different physiological effects in the Mg uptake between the C. pachydermus living in different regions could account for this offset in the Mediterranean samples. Consequently, the obtained DWT record still has many uncertainties in absolute terms but trends provide valuable information on past changes in WMDW conditions. The DWT record shows significant oscillations in relation to the D–O cycles, colder values occurred during the time of D–O stadials and warmer ones during D–O interstadials. Surprisingly, the coldest DWTs occurred during the time of Heinrich Event 4 (HE4) and not during the Last Glacial Maximum (LGM) when DWTs were mostly warm. These and other particular features of the DWT reconstruction mimic changes in the vegetation from the Eastern Mediterranean indicating the control of the Mediterranean climate on the DWT record. Paired analyses of Mg/Ca and δ¹⁸Occ (calcite δ¹⁸O) provide the opportunity to reconstruct deep-water δ¹⁸O (δ¹⁸Odw) and past salinities and hence changes in past WMDW density. Due to the large error associated with these calculations, they can only be discussed in terms of relative changes between different intervals. The results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early Holocene in relation to the δ¹⁸Odw conditions present today. Densest WMDW were formed during most of Marine Isotopic Stage (MIS) 2 and during the D–O Stadials not associated with HEs, while lightest WMDW dominated during D–O Interstadials. The δ¹⁸Odw record shows a D–O variability pattern likely controlled by changes in the composition and intensity of the local run-off and also to changes in the δ¹⁸Ow signal of the Atlantic inflow. Changes in the residence time of the Mediterranean waters, governed by the global sea level, are also considered to exert an important role governing Mediterranean δ¹⁸Ow and salinity, particularly during MIS 2. Overall, our results are consistent with the formation of dense WMDW during D–O stadials and even denser during most of MIS 2.     

Application ofBacteroides fragilis phage as an alternative indicator of sewage pollution in Tampa Bay, Florida

Traditional fecal coliform bacterial indicators have been found to be severely limited in determining the significance and sources of fecal contamination in ambient waters of tropical and subtropical regions. The bacteriophages that infectBacteroides fragilis have been suggested as better fecal indicators and at least one type may be human specific. In this study, the phages that infectB. fragilis host RYC2056 (RYC), including phage B56-3, and host ATCC 51477-HSP40 (HSP), including the human specific phage B40-8, were evaluated in the drainage basins of Tampa Bay, 7 samples (n=62), or 11%, tested positive for the presence of phages infecting the host HSP, whereas 28 samples, or 45%, tested positive using the host RYC. A survival study was also done to compare the persistence of phages B56-3 and B40-8 to MS2 coliphage in seawater at various temperatures. The decay rates for MS2 were 0.239 log₁₀ d⁻¹ at 10°C, but increased to 0.896 at 20°C and 2.62 log₁₀ d⁻¹ at 30°C. The twoB. fragilis phages persisted much longer in the seawater compared to the coliphage and showed little variation between the temperatures. All sewage influents sampled from area wastewater treatment plants contained phages that infected the twoB. fragilis hosts at levels from 1.2×10⁴ to 1.11×10⁵ pfu 100 ml⁻¹ for host RYC and 67 to 350 pfu 100 ml⁻¹ for host HSP. Of the 7 chlorinated effluent samples tested, 3 were positive for the presence of the phage using the host RYC and the phage enrichment method, with levels estimated to be <10 pfu 100 ml⁻¹. No phages were detected using the host HSP in the treated sewage effluent. Coliphages were found in 3 of the 7 effluent samples at a range of 30 to 1.2×10³ pfu 100 ml⁻¹.     

The self-organization of step-pools in mountain streams

Spontaneous, autogenic self-organization has been described in numerous geomorphic systems, but it has not been investigated in detail with respect to coarse bedforms in general or step-pools in particular. In this paper, we review the spatial organization of step-pool systems and present example evidence of step-pool development as an autogenic self-organization process. We then outline the mathematical language for defining spatially divergent self-organization and test these ideas using two unique field examples from Oregon (Andrews Experimental Forest) and California (Baxter Creek), where step-pools developed from planar beds in artificially manipulated channels. Results show that step-pool development is consistent with a spatially divergent self-organization phenomenon. Entropy increases as initially undifferentiated planar channels diverge into steps and pools, then declines when a series of steps and pools of consistent size and spacing is established, signifying stability in the system. The self-organization process is accompanied by increasing flow resistance and decreasing slope (through increasing the “vertical sinuosity” of the step-pool profile and creation of low- or negative gradient pool areas), suggesting a minimization of stream power. The self-adjustment of the step-pool bed profile over time represents another manifestation of a general process that results in rhythmic patterns on the surface of Earth.     

The perfect landscape

The “perfect storm” metaphor describes the improbable coincidence of several different forces or factors to produce an unusual outcome. The perfect landscape is conceptualized as a result of the combined, interacting effects of multiple environmental controls and forcings to produce an outcome that is highly improbable, in the sense of the likelihood of duplication at any other place or time. Geomorphic systems have multiple environmental controls and forcings, and degrees of freedom in responding to them. This allows for many possible landscapes and system states. Further, some controls and forcings are causally contingent. These contingencies are specific to time and place. Dynamical instability in many geomorphic systems creates and enhances some of this contingency by causing the effects of minor initial variations and small disturbances to persist, and grow disproportionately large, over time. The joint probability of any particular set of global controls is low, as the individual probabilities are < 1, and the probability of any set of local, contingent controls is even lower. Thus, the probability of existence of any landscape or earth surface system state at a particular place and time is negligibly small: all landscapes are perfect. Recognition of the perfection of landscapes leads away from a worldview holding that landforms and landscapes are the inevitable outcomes of deterministic laws, such that only one outcome is possible for a given set of laws and initial conditions. A perfect landscape perspective leads toward a worldview that landforms and landscapes are circumstantial, contingent results of deterministic laws operating in a specific environmental context, such that multiple outcomes are possible.     

Differential productions of rural gentrification: illustrations from North and South Norfolk

This paper focuses attention on the making of space for rural gentrification, both discursively and materially. The paper emphasises the differential constructions of gentrification within urban and rural studies. Connections are drawn between production-side theories of gentrification, notions of the ‘post-productivist countryside’ and studies that have related rural demographic change and gentrification with planning and property relations. Drawing on these three sets of ideas, the paper explores gentrification in rural Norfolk. It is argued that the contemporary geography of rural gentrification may in part reflect historic structures of landownership as well as settlement classifications associated with the land-use planning system. Country and District level analysis is followed up by detailed study of gentrification of two villages in Norfolk, which highlights how gentrified rural spaces may be produced in rather different way and through different agencies, and as a result takes different forms.     

Quantitative assessment of the residual risk in a rockfall protected area

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d’Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d’Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10⁻⁴ to 9.1×10⁻⁷ and the societal risk from 1.5×10⁻² of annual probability of loss of life to 1.2×10⁻⁵.     

The effects of seasonal variability and weather on microbial fecal pollution and enteric pathogens in a subtropical estuary

The Charlotte Harbor estuary in southwest Florida was sampled monthly for one year at twelve stations, in the lower reaches of the Myakka and Peace Rivers. The objectives of the study were to address the distribution and seasonal changes in microbial indicators and human pathogen levels in Charlotte Harbor shellfish and recreational waters, and to determine those factors that may be important in the transport and survival of pathogens. Monthly water samples and quarterly sediment samples were analyzed for fecal coliform bacteria, enterococci,Clostridium perfringens, and coliphage. Quarterly samples also were analyzed for the enteric human pathogens,Cryptosporidium spp.,Giardia spp., and enteroviruses. Fecal indicator organisms were generally concentrated in areas of low salinity and high densities of septic systems; however, pollution became widespread during wet weather in, the late fall and winter of 1997–1998, coincident with a strong El Nino event. Between, December 1997 and February 1998, enteroviruses were detected at 75% of the sampling stations; none were detected in other months. Enteric protozoa were detected infrequently and were not related to seasonal influences. Fecal indicators and enteroviruses were each significantly associated with rainfall, streamflow, and temperature. Regression models suggest that temperature and rainfall can predict the occurrence of enteroviruses in 93.7% of the cases. Based on findings in this watershed, factors such as variability in precipitation, streamflow, and temperature show promise in modeling and forecasting periods of poor coastal water quality.     

Geomorphological characteristics and slope processes associated with different basins: Mallorca (Western Mediterranean)

We compare the different geomorphological processes which occurred in Pliocene–Quaternary times on two very similar slopes in Mallorca, one located at the Tramuntana Range and the other in the Llevant Ranges. Both slopes have the same geological structure, the same stratigraphic and lithological levels, and the same altitude and orientation. The different slope processes are due to the relationship between the accommodation space and the sedimentation rate in the adjacent basins: In the Valencia Trough (located N of the Tramuntana Range), the sedimentation rate has not been sufficient to fill the accommodation space, whereas in the Alcudia Basin (adjacent to the Llevant Ranges), the sedimentation rate has been sufficient to fill the accommodation space. This difference has resulted in major landslides on the Tramuntana slope, whereas the Llevant slope is characterized mainly by alluvial fans and debris screes.