Food Web Structure in a Chesapeake Bay Eelgrass Bed as Determined through Gut Contents and <Superscript>13</Superscript>C and <Superscript>15</Superscript>N Isotope Analysis

Changes in seagrass food-web structure can shift the competitive balance between seagrass and algae, and may alter the flow of energy from lower trophic levels to commercially important fish and crustaceans. Yet, trophic relationships in many seagrass systems remain poorly resolved. We estimated the food web linkages among small predators, invertebrate mesograzers, and primary producers in a Chesapeake Bay eelgrass (Zostera marina) bed by analyzing gut contents and stable C and N isotope ratios. Though trophic levels were relatively distinct, predators varied in the proportion of mesograzers consumed relative to alternative prey, and some mesograzers consumed macrophytes or exhibited intra-guild predation in addition to feeding on periphyton and detritus. These findings corroborate conclusions from lab and mesocosm studies that the ecological impacts of mesograzers vary widely among species, and they emphasize the need for taxonomic resolution and ecological information within seagrass epifaunal communities.     

Identifying ephemeral and perennial stream reaches using apparent thermal inertia of an ungauged basin in Central New Mexico

The night and day temperature images from advanced spaceborne thermal emission and reflection radiometer (ASTER) remote sensing images are used to identify ephemeral and perennial stream reaches for use in the calibration of an integrated hydrologic model of an ungauged basin. The concept is based on apparent thermal inertia [ATI = (1-albedo)/(day temperature ? night temperature)]. These calculations help both the conceptual model and the calibration for the hydrologic model by indicating where there are thin alluvium and/or shallow groundwater. The study is on the Sevilleta National Wildlife Refuge, a long-term ecological research project that ASTER has included in its regular duty cycle. There are over 360 ASTER scenes in 8 years; however, only 10 night/day pairs suitable for ATI were found. The results correlate to the soil moisture recorded at two locations near the channel (R ² of 0.88). The relationship between soil moisture and surrounding materials allows for differentiation of the perennial and ephemeral stream reaches.     

Hydrological Modeling and Prehistoric Settlement on Santa Rosa Island,California, USA

Fresh water availability was an important variable that influenced prehistoric human settlement on California's northern Channel Islands. Previous attempts to understand settlement on the islands use watershed size as a proxy for water at canyon mouths. In semi‐arid regions, this approach has limitations because streams may lose much or all of their flow to groundwater. We developed a distributed hydrological model for Santa Rosa Island that incorporates geospatial and temporal data for climate (precipitation, solar radiation, wind speed, relative humidity, temperature), soils, vegetation, and topography to simulate the complex land‐surface‐groundwater behavior of island hydrology for hypothetical wet, dry, and median centuries. Our simulations show that water flow is greatest in drainages on the northwest and east coasts of the island. This correlates with some of the earliest and most persistent settlement on the island. During the most extreme droughts of the last 2000 years during the Medieval Climatic Anomaly (1150–600 cal BP), island populations contracted to a small number of large coastal villages. We argue that this was related in part to the greater availability of surface water at these locations. This study expands the theoretical and methodological scope of past studies that have applied hydrological simulation to archaeological investigations.     

Writing difference differently

This paper investigates the writing of situated knowledge and explores the possibilities of enacting difference by writing differently. We present a selection of research stories in which carrier bags, sounds, baskets, gardens and potatoes are interpreted less as objects of research or metaphors to aid in analysing phenomena, than as mediators of the stories. Our stories emphasise the ontological politics of engaging with and representing the relational, the messy, the spontaneous, the unpredictable, the non‐human and bodily experiences. These stories demonstrate how writing is performative and how it is integral to the production of knowledge.     

The equation of state of CaSiO3 perovskite to 108 GPa at 300 K

Pressure–volume measurements have been performed for CaSiO₃ perovskite to 108 GPa at 300 K using NaCl and argon pressure-transmitting media, and energy dispersive X-ray diffraction (EDXD) in a diamond-anvil cell (DAC). By determining a parameter that is the product of the elastic anisotropy, S, and the uniaxial stress component, t, for each data point, we define the stress condition of the sample. For different points at the same pressure in a temperature-quenched sample, the St value can differ by as much as a factor of 5, indicating heterogeneity in the stress condition. This may be responsible for the large scatter of earlier P–V measurements in the DAC which in general used a large diameter X-ray beam. Also, the St value provides insight into the elastic anisotropy, S, of CaSiO₃ perovskite and platinum. The sign of S (positive) for CaSiO₃ perovskite agrees with first principles calculations but the magnitude may be inconsistent. A new compression curve at 300 K was obtained for CaSiO₃ perovskite by using those data points which represent the most nearly hydrostatic conditions. It is observed that the data points with high St values yield larger volumes than the points with small St values at a given pressure. By selecting the data points having low St values (St≤0.005), combining with lower pressure large volume press (LVP) measurements and fitting to third order Birch–Murnaghan equation of state (EOS), we find that CaSiO₃ perovskite is more compressible (V₀=45.58±0.05 ų, K_T0=236±4 GPa, and K_T0′=3.9±0.2 GPa) than suggested by previous studies. The density and bulk modulus of CaSiO₃ perovskite at lower mantle pressures and 300 K are 1–3% greater and 5–15% smaller, respectively, than found in previous studies. This study demonstrates that defining the stress state of the sample is crucial to obtain an accurate 300 K compression curve for unquenchable high-pressure phases.     

Single-crystal elastic constants of fluorite (CaF2) to 9.3 GPa

 The second-order elastic constants of CaF₂ (fluorite) have been determined by Brillouin scattering to 9.3 GPa at 300 K. Acoustic velocities have been measured in the (111) plane and inverted to simultaneously obtain the elastic constants and the orientation of the crystal. A notable feature of the present inversion is that only the density at ambient condition was used in the inversion. We obtain high-pressure densities directly from Brillouin data by conversion to isothermal conditions and iterative integration of the compression curve. The pressure derivative of the isentropic bulk modulus and of the shear modulus determined in this study are 4.78 ± 0.13 and 1.08 ± 0.07, which differ from previous low-pressure ultrasonic elasticity measurements. The pressure derivative of the isothermal bulk modulus is 4.83 ± 0.13, 8% lower than the value from static compression, and its uncertainty is lower by a factor of 3. The elastic constants of fluorite increase almost linearly with pressure over the whole investigated pressure range. However, at P ≥ 9 GPa, C ₁₁ and C ₁₂ show a subtle structure in their pressure dependence while C ₄₄ does not. The behavior of the elastic constants of fluorite in the 9–9.3 GPa pressure range is probably affected by the onset of a high-pressure structural transition to a lower symmetry phase (α-PbCl₂ type). A single-crystal Raman scattering experiment performed in parallel to the Brillouin measurements shows the appearance of new features at 8.7 GPa. The new features are continuously observed to 49.2 GPa, confirming that the orthorhombic high-pressure phase is stable along the whole investigated pressure range, in agreement with a previous X-ray diffraction study of CaF₂ to 45 GPa. The high-pressure elasticity data in combination with room-pressure values from previous studies allowed us to determine an independent room-temperature compression curve of fluorite. The new compression curve yields a maximum discrepancy of 0.05 GPa at 9.5 GPa with respect to that derived from static compression by Angel (1993). This comparison suggests that the accuracy of the fluorite pressure scale is better than 1% over the 0–9 GPa pressure range. Received: 10 July 2001 / Accepted: 7 March 2002     

Contemporary process controls on the evolution of sedimentary coasts under low to high energy regimes: western Ireland

Sedimentary environments, representative of the Irish west coast, have been studied to examine their responses at the microscale (10^-1–10⁰ yr). This was achieved using a variety of techniques, including grain-size analysis, measurement of accretionary responses and radiometric dating. Monthly elevation monitoring of silt-dominated marshes shows an annual pattern in sediment accumulation. This reflects two processes: a) winter accretion attributable to storm events, and b) summer consolidation and contraction of the marsh sediments. Together, the results suggest that intertidal sedimentation is likely to be dominated by episodic processes, primarily storms. Examination of the tidal regime shows a weaker than expected influence of hydroperiodicity on intertidal accretion, although this influence remains distinctive, as expressed by a landward textural fining. Storms were also identified as of major importance in the functioning of higher-energy sandy coastal systems, again having a largely accretional influence, primarily through aeolian transport. Erosion at such study sites is probably controlled by the attainment of a critical threshold surface elevation, or by exceptional storm action, or a combination of both. The linking of microscale sedimentation rates with those at the meso- to macroscale, and assessment of their importance for coastal functioning, is difficult due to the geological averaging effect of the sedimentary record. Human impacts on this coast in historical times are large but difficult to quantify.     

Initial observations of water quality indicators in the unconfined shallow aquifer in Dili City,Timor-Leste: suggestions for its management

The management of groundwater quality is a critical issue in developing nations where sanitation and drinking water targets are commonly addressed by facilitating access to groundwater, which is then managed as a common-pool resource. We investigate the quality of the shallow unconfined groundwater in Dili’s alluvial fan system, which 50% of Dili’s rapidly growing population use for all their water requirements. Using the basic chemical and microbiological analyses that are locally available (sulfate, total hardness, fluoride, manganese, iron, ammonia, nitrite, nitrate, total coliform and E. coli) we show that the shallow wells commonly contain enhanced concentrations of dissolved solids and microbiological contaminants (total coliform and E. coli), relative to deeper wells. Cool, shallow wells are worse than warm equivalents. Elevated nitrate and nitrite pollution in the embassy district are tentatively attributed to affluence factors, such as lawn cultivation and water filtration equipment. Microbiological contamination, and associated manganese contamination of groundwater, mimic population patterns, but are concentrated in the finer grained sediments of the small fans and low-slope interdistributary areas. We suggest that rapid development and successful implementation of appropriate sanitation policy in Dili (and elsewhere) is required to address the problematic features of the shallow groundwater system. Success will be predicated on (1) the establishment of baseline data, and (2) development of a systems-thinking approach to holistic water resource management.     

The strength of ruby from X-ray diffraction under non-hydrostatic compression to 68 GPa

Polycrystalline ruby (α-Al₂O₃:Cr³⁺), a widely used pressure calibrant in high-pressure experiments, was compressed to 68.1 GPa at room temperature under non-hydrostatic conditions in a diamond anvil cell. Angle-dispersive X-ray diffraction experiments in a radial geometry were conducted at beamline X17C of the National Synchrotron Light Source. The stress state of ruby at high pressure and room temperature was analyzed based on the measured lattice strain. The differential stress of ruby increases with pressure from ~3.4 % of the shear modulus at 18.5 GPa to ~6.5 % at 68.1 GPa. The polycrystalline ruby sample can support a maximum differential stress of ~16 GPa at 68.1 GPa under non-hydrostatic compression. The results of this study provide a better understanding of the mechanical properties of this important material for high-pressure science. From a synthesis of existing data for strong ceramic materials, we find that the high-pressure yield strength correlates well with the ambient pressure Vickers hardness.