Temporal trends in soft tissue metal levels in the periwinkle Littorina littorea along the Scheldt estuary, The Netherlands     

De Wolf H  Van den Broeck H  Qadah D  Backeljau T  Blust R 《Marine pollution bulletin》2005,50(4):479-484

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Unstable periodic orbits in a rotationally symmetric potential     

T. A. Agekyan  V. V. Orlov  N. Yu. Kretser 《Astronomy Letters》2001,27(11):754-757

We derive an equation to determine the coordinates of the points at which unstable periodic orbits emerge from a zero-velocity contour in an arbitrary rotationally symmetric potential. Examples of such orbits are given for several model potentials.  相似文献   

Seismic activity related to the 2000 eruption of the Hekla volcano, Iceland     

Heidi Soosalu  Páll Einarsson  Bergþóra S. Þorbjarnardóttir 《Bulletin of Volcanology》2005,68(1):21-36

The 2000 Hekla eruption took place from February 26 to March 8. Its seismic expressions were a swarm of numerous small earthquakes related to its onset, and low-frequency volcanic tremor that continued throughout the eruption. A swarm of small earthquakes was observed some 80 min before the onset of the eruption, and the size of the events increased with time. Low-frequency volcanic tremor, with a characteristic frequency band of 0.5–1.5 Hz and dominant spectral peak(s) at 0.7–0.9 Hz, became visible at 18:19 GMT on February 26, marking the onset of the eruption. The tremor amplitude rose quickly and was very high in the beginning of the eruption. However, it soon began to decrease after about an hour. In general, the seismic activity related to the 2000 Hekla eruption was very similar to what was observed in the previous eruption in 1991. Based on knowledge gained from seismicity and strain observations from 1991, this was the first time that a Hekla eruption was predicted.Editorial responsibility: J Stix  相似文献   

Dissolved organic carbon in pore waters from a hypersaline environment     

W. M. Berry Lyons  Henri E. Gaudette  Heidi C. Gustafson 《Organic Geochemistry》1981,3(4):133-135

Pore waters were collected from a sea-marginal, hypersaline pond in the Sinai and analyzed for dissolved organic carbon (DOC). The pore water DOC values ranged from 121 to 818 mg 1⁻¹ with maxima between 15 and 54 cm deep. These values are some of the highest observed from recent sediments and probably reflect production via abiotic as well as biotic sources.  相似文献   

“Ghana must Progress,but we are Really Suffering”: Bui Dam,Antipolitics Development,and the Livelihood Implications for Rural People     

Heidi Hausermann 《社会与自然资源》2018,31(6):633-648

In late-2013, Bui Dam was commissioned on Ghana’s Black Volta River. The hydroelectric project inundated 444?km², flooding communities, forests, crops, and a national park. State elites promoted the dam through nationalistic discourses while simultaneously framing rural people responsible for accessing its trickle-down economic benefits. Drawing from critical development literature within a political ecology framework, this article examines tensions between discourses underpinning construction of Bui Dam and the lived experiences of rural people. Drawing from data collected in 82 interviews, the dam’s implications for resettlement, food security, mental health, agricultural production, and fishing livelihoods are detailed. I argue interlocking discourses, laws and processes—from eminent domain and compensation metrics to party politics—combined to work as an “antipolitics machine.” Hydroelectric development renders invisible structural processes shaping inequality and creates new injustices. As Bui Power Authority, the corporation managing the dam and surrounding land-uses has a new CEO, the article concludes with several practical suggestions for improving community members’ everyday lives.  相似文献   

Insights from trace element geochemistry as to the roles of subduction zone geometry and subduction input on the chemistry of arc magmas   总被引：2，自引：0，他引：2  

Heidi Wehrmann  Kaj Hoernle  Dieter Garbe-Schönberg  Guillaume Jacques  Julia Mahlke  Kai Schumann 《International Journal of Earth Sciences》2014,103(7):1929-1944

Subduction zones of continental, transitional, and oceanic settings, relative to the nature of the overriding plate, are compared in terms of trace element compositions of mafic to intermediate arc rocks, in order to evaluate the relationship between subduction parameters and the presence of subduction fluids. The continental Chilean Southern Volcanic Zone (SVZ) and the transitional to oceanic Central American Volcanic Arc (CAVA) show increasing degrees of melting with increasing involvement of slab fluids, as is typical for hydrous flux melting beneath arc volcanoes. At the SVZ, the central segment with the thinnest continental crust/lithosphere erupted the highest-degree melts from the most depleted sources, similar to the oceanic-like Nicaraguan segment of the CAVA. The northern part of the SVZ, located on the thickest continental crust/lithosphere, exhibits features more similar to Costa Rica situated on the Caribbean Large Igneous Province, with lower degrees of melting from more enriched source materials. The composition of the slab fluids is characteristic for each arc system, with a particularly pronounced enrichment in Pb at the SVZ and in Ba at the CAVA. A direct compositional relationship between the arc rocks and the corresponding marine sediments that are subducted at the trenches clearly shows that the compositional signature of the lavas erupted in the different arcs carries an inherited signal from the subducted sediments.  相似文献   

Constraining input and output fluxes of the southern-central Chile subduction zone: water,chlorine and sulfur     

David Völker  Heidi Wehrmann  Steffen Kutterolf  Karthik Iyer  Wolfgang Rabbel  Jacob Geersen  Kaj Hoernle 《International Journal of Earth Sciences》2014,103(7):2129-2153

In this paper, we constrain the input and output fluxes of H₂O, Cl and S into the southern-central Chilean subduction zone (31°S–46°S). We determine the input flux by calculating the amounts of water, chlorine and sulfur that are carried into the subduction zone in subducted sediments, igneous crust and hydrated lithospheric mantle. The applied models take into account that latitudinal variations in the subducting Nazca plate impact the crustal porosity and the degree of upper mantle serpentinization and thus water storage in the crust and mantle. In another step, we constrain the output fluxes of the subduction zone both to the subcontinental lithospheric mantle and to the atmosphere–geosphere–ocean by the combined use of gas flux determinations at the volcanic arc, volume calculations of volcanic rocks and the combination of mineralogical and geothermal models of the subduction zone. The calculations indicate that about 68 Tg/m/Ma of water enters the subduction zone, as averaged over its total length of 1,480 km. The volcanic output on the other hand accounts for 2 Tg/m/Ma or 3 % of that input. We presume that a large fraction of the volatiles that are captured within the subducting sediments (which accounts for roughly one-third of the input) are cycled back into the ocean through the forearc. This assumption is however questioned by the present lack of evidence for major venting systems of the submarine forearc. The largest part of the water that is carried into the subduction zone in the crust and hydrated mantle (accounting for two-thirds of the input) appears to be transported beyond the volcanic arc.  相似文献   

Evaluating Light Availability,Seagrass Biomass,and Productivity Using Hyperspectral Airborne Remote Sensing in Saint Joseph’s Bay,Florida   总被引：1，自引：0，他引：1  

Victoria J. Hill  Richard C. Zimmerman  W. Paul Bissett  Heidi Dierssen  David D. R. Kohler 《Estuaries and Coasts》2014,37(6):1467-1489

Seagrasses provide a number of critical ecosystem services, including habitat for numerous species, sediment stabilization, and shoreline protection. Ariel photography is a useful tool to estimate the areal extent of seagrasses, but recent innovations in radiometrically calibrated sensors and algorithm development have allowed identification of benthic types and retrieval of absolute density. This study demonstrates the quantitative ability of a high spatial resolution (1 m) airborne hyperspectral sensor (3.2 nm bandwidth) in the complex coastal waters of Saint Joseph’s Bay (SJB). Several benthic types were distinguished, including submerged and floating aquatic vegetation, benthic red algae, bare sand, and optically deep water. A total of 23.6 km² of benthic vegetation was detected, indicating no dramatic change in vegetation area over the past 30 years. SJB supported high seagrass density at depths shallower than 2 m with an average leaf area index of 2.0?±?0.6 m² m^?2. Annual seagrass production in the bay was 13,570 t C year^?1 and represented 41 % of total marine primary production. The effects of coarser spatial resolution were investigated and found to reduce biomass retrievals, underestimate productivity, and alter patch size statistics. Although data requirements for this approach are considerable, water column optical modeling may reduce the in situ requirements and facilitate the transition of this technique to routine monitoring efforts. The ability to quantify not just areal extent but also productivity of a seagrass meadow in optically complex coastal waters can provide information on the capacity of these environments to support marine food webs.  相似文献