Assessment of the distribution of sponge chips in the sediment of East Pacific Ocean reefs          下载免费PDF全文

Jose Luis Carballo  Humberto Ovalle‐Beltrán  Benjamin Yáñez  Eric Bautista‐Guerrero  Héctor Nava‐Bravo 《Marine Ecology》2017,38(1)

Sponges are one of the principal agents of bioerosion and sediment production in coral reefs. They generate small carbonate chips that can be found in the sediments, and we investigated whether these could provide a means for assessment of bioerosion applicable to reef monitoring. We tested this hypothesis on samples from 12 Mexican coral reefs distributed along the Pacific coast, where boring sponges were particularly abundant, and quantified the amount of chips in samples of superficial sediment in three grain‐size fractions: fine (<44 μm), medium (44–210 μm) and coarse (>210 μm). The grain‐size distribution varied among reefs, with the majority of the sediment of most reefs being composed of coarse sands, and the medium and fine fractions dominating only at La Entrega and Playa Blanca. All the reefs presented clear evidence of bioerosion by sponges, with the characteristic chips present in the sediment, although at most sites the percentage of chips was very low (from 1% to 3% of the total sediment). Only at La Entrega and Playa Blanca did they constitute a significant fraction of the total sediment (18% and 16%, respectively). While not statistically significant, there was an interesting trend between sponge chips versus sponge abundance that suggests that quantification of the chips in the sediment could be used as a proxy for sponge erosion of the entire community, which cannot be estimated in by laboratory experiments. However, while this methodology could provide an integrated approach to monitor sponge bioerosion, more studies are necessary due to the influence of environmental factors on the transport and deposition of these chips.  相似文献   

Quantitative aspects of inorganic nutrient fluxes in the Gazi Bay (Kenya): implications for coastal ecosystems     

Mwashote BM  Jumba IO 《Marine pollution bulletin》2002,44(11):1194-1205

Fluxes of dissolved inorganic nutrients: NH4+, NO2-, NO3-, PO4(3-) and Si(OH)4 from nearshore sediments of Gazi Bay were measured in situ within mangrove, seagrass and coral reef biotopes using benthic flux bell-jar chambers of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, fluvial discharge and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay. The directly measured fluxes ranged from -270 to +148 micromol NH4+-N/m2/h; -60 to +63 micromol NO2(-)-N/m2/h; -79 to +41 micromol NO3(-)-N/m2/h; -79 to +75 micromol PO4(3-)-P/m2/h and +30 to +350 micromol Si(OH)4-Si/m2/h for and respectively. It was established that benthic fluxes are the major sources of dissolved inorganic NH4+, NO2- and Si(OH)4 while fluvial sources are important for NO3- and PO4(3-) into Gazi Bay waters. Seasonal variations had an appreciable effect on the PO4(3-) fluxes, N:Si ratio, river nutrient discharge, plankton productivity and important environmental factors such as salinity and temperature. Tidal and spatial variations had no significant effect on nutrient concentrations and net fluxes within the water column. The results imply that benthic fluxes are largely responsible for the nutrient dynamics of the nearshore coastal ecosystems especially where direct terrestrial inputs do not contribute significantly to the nutrient budget.  相似文献   

Algorithms for GPS operation indoors and downtown   总被引：6，自引：0，他引：6  

Nainesh Agarwal  Julien Basch  Paul Beckmann  Piyush Bharti  Scott Bloebaum  Stefano Casadei  Andrew Chou  Per Enge  Wungkum Fong  Neesha Hathi  Wallace Mann  Anant Sahai  Jesse Stone  John Tsitsiklis  Benjamin Van Roy 《GPS Solutions》2002,6(3):149-160

The proliferation of mobile devices and the emergence of wireless location-based services has generated consumer demand for availability of GPS in urban and indoor environments. This demand calls for enhanced GPS algorithms that accommodate high degrees of signal attenuation and multipath effects unique to the "urban channel." This paper overviews the market for location-based services and discusses algorithmic innovations that address challenges posed by urban environments. Electronic Publication  相似文献   

Water quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem   总被引：1，自引：0，他引：1  

Benjamin?L.?PeierlsEmail author  Robert?R.?Christian  Hans?W.?Paerl 《Estuaries and Coasts》2003,26(5):1329-1343

Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.  相似文献   

Origin of regional climate differences: role of boundary conditions and model formulation in two GCMs     

Benjamin A. Cash  Edwin K. Schneider  Lennart Bengtsson 《Climate Dynamics》2005,25(7-8):709-723

Model differences in projections of extratropical regional climate change due to increasing greenhouse gases are investigated using two atmospheric general circulation models (AGCMs): ECHAM4 (Max Planck Institute, version 4) and CCM3 (National Center for Atmospheric Research Community Climate Model version 3). Sea-surface temperature (SST) fields calculated from observations and coupled versions of the two models are used to force each AGCM in experiments based on time-slice methodology. Results from the forced AGCMs are then compared to coupled model results from the Coupled Model Intercomparison Project 2 (CMIP2) database. The time-slice methodology is verified by showing that the response of each model to doubled CO₂ and SST forcing from the CMIP2 experiments is consistent with the results of the coupled GCMs. The differences in the responses of the models are attributed to (1) the different tropical SST warmings in the coupled simulations and (2) the different atmospheric model responses to the same tropical SST warmings. Both are found to have important contributions to differences in implied Northern Hemisphere (NH) winter extratropical regional 500 mb height and tropical precipitation climate changes. Forced teleconnection patterns from tropical SST differences are primarily responsible for sensitivity differences in the extratropical North Pacific, but have relatively little impact on the North Atlantic. There are also significant differences in the extratropical response of the models to the same tropical SST anomalies due to differences in numerical and physical parameterizations. Differences due to parameterizations dominate in the North Atlantic. Differences in the control climates of the two coupled models from the current climate, in particular for the coupled model containing CCM3, are also demonstrated to be important in leading to differences in extratropical regional sensitivity.  相似文献   

Ecological response to hurricane events in the Pamlico Sound system, North Carolina, and implications for assessment and management in a regime of increased frequency   总被引：1，自引：0，他引：1  

Hans W. Paerl  Lexia M. Valdes  Alan R. Joyner  Benjamin L. Peierls  Michael F. Piehler  Stanley R. Riggs  Robert R. Christian  Lisa A. Eby  Larry B. Crowder  Joseph S. Ramus  Erika J. Clesceri  Christopher P. Buzzelli  Richard A. Luettich 《Estuaries and Coasts》2006,29(6):1033-1045

Since the mid 1990s, the Atlantic and Gulf Coast regions have experienced a dramatic increase in the number of hurricane landfalls. In eastern North Carolina alone, eight hurricances have affected the coast in the past 9 years. These storms have exhibited individualistic hydrologic, nutrient, and sediment loading effects and represent a formidable challenge to nutrient management aimed at reducing eutrophication in the Pamlico Sound and its estuarine tributaries. Different rainfall amounts among hurricanes lead to variable freshwater and nutrient discharge and variable nutrient, organic matter, and sediment enrichment. These enrichments differentially affected physical and chemical properties (salinity, water residence time, transparency, stratification, dissolved oxygen), phytoplankton primary production, and phytoplankton community composition. Contrasting ecological responses were accompanied, by changes in nutrient and oxygen cycling, habitat, and higher trophic levels, including different direct effects on fish populations. Floodwaters from the two largest hurricances, Fran (1996) and Floyd (1999), exerted, multi-month to multi-annual effects on hydrology, nutrient loads, productivity, and biotic composition. Relatively low rainfall coastal hurricanes like Isabel (2003) and Ophelia (2005) caused strong vertical mixing and storm surges, but relatively minor hydrologic and nutrient effects. Both hydrologic loading and wind forcing are important drivers and must be integrated with nutrient loading in assessing short-term and long-term ecological effects of these storms. These climatic forcings cannot be managed but should be considered in the development of water quality management strategies for these and other large estuarine ecosystems faced with increasing frequencies and intensities of hurricane activity.  相似文献   

Uncertainties in plate reconstructions relative to the hotspots; Pacific-hotspot rotations and uncertainties for the past 68 million years     

David L. Andrews  Richard G. Gordon  Benjamin C. Horner-Johnson 《Geophysical Journal International》2006,166(2):939-951

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Integrating the maximum capture problem into a GIS framework     

Benjamin D. Spaulding  Robert G. Cromley 《Journal of Geographical Systems》2007,9(3):267-288

This paper presents a methodology for reformulating the maximal capture problem by using the data representation and manipulation capabilities of GIS to define: (1) the coverage region captured by each potential facility, and (2) each unique demand region covered by a specific combination of potential facilities. The formulation is modeled on the maximum covering problem although the integer restriction on the demand capture variables is relaxed. Because demand regions are not exogenously given, areal interpolation is used to estimate the demand associated with each of these regions The model is used to determine the location on a network for a set of home improvement stores that are hypothetically in competition with existing Home Depot stores in Southeastern New Hampshire.   相似文献   

Coupling chemical weathering with soil production across soil‐mantled landscapes     

Benjamin C. Burke  Arjun M. Heimsath  Arthur F. White 《地球表面变化过程与地形》2007,32(6):853-873

Soil‐covered upland landscapes constitute a critical part of the habitable world. Our understanding of how they evolve as a function of different climatic, tectonic and geological regimes is important across a wide range of disciplines and depends, in part, on understanding the links between chemical and physical weathering processes. Extensive previous work has shown that soil production rates decrease with increasing soil column thickness, but chemical weathering rates were not measured. Here we examine a granitic, soil‐mantled hillslope at Point Reyes, California, where soil production rates were determined using in situ produced cosmogenic nuclides (¹⁰Be and ²⁶Al), and we quantify the extent as well as the rates of chemical weathering of the saprolite from beneath soil from across the landscape. We collected saprolite samples from the base of soil pits and analysed them for abrasion pH as well as for major and trace elements by X‐ray fluorescence spectroscopy, and for clay mineralogy by X‐ray diffraction spectroscopy. Our results show for the first time that chemical weathering rates decrease with increasing soil thickness and account for 13 to 51 per cent of total denudation. We also show that spatial variation in chemical weathering appears to be topographically controlled: weathering rate decreases with slope across the divergent ridge and increases with upslope contributing area in the convergent swale. Furthermore, to determine the best measure for the extent of saprolite weathering, we compared four different chemical weathering indices – the Vogt ratio, the chemical index of alteration (CIA), Parker's index, and the silicon–aluminium ratio – with saprolite pH. Measurements of the CIA were the most closely correlated with saprolite pH, showing that weathering intensity decreases linearly with an increase in saprolite pH from 4·7 to almost 7. Data presented here are among the first to couple directly rates of soil production and chemical weathering with how topography is likely to control weathering at a hillslope scale. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Spatial and seasonal variability of polygonal tundra water balance: Lena River Delta, northern Siberia (Russia)     

Manuel Helbig  Julia Boike  Moritz Langer  Peter Schreiber  Benjamin R. K. Runkle  Lars Kutzbach 《Hydrogeology Journal》2013,21(1):133-147

The summer water balance of a typical Siberian polygonal tundra catchment is investigated in order to identify the spatial and temporal dynamics of its main hydrological processes. The results show that, besides precipitation and evapotranspiration, lateral flow considerably influences the site-specific hydrological conditions. The prominent microtopography of the polygonal tundra strongly controls lateral flow and storage behaviour of the investigated catchment. Intact rims of low-centred polygons build hydrological barriers, which release storage water later in summer than polygons with degraded rims and troughs above degraded ice wedges. The barrier function of rims is strongly controlled by soil thaw, which opens new subsurface flow paths and increases subsurface hydrological connectivity. Therefore, soil thaw dynamics determine the magnitude and timing of subsurface outflow and the redistribution of storage within the catchment. Hydraulic conductivities in the elevated polygonal rims sharply decrease with the transition from organic to mineral layers. This interface causes a rapid shallow subsurface drainage of rainwater towards the depressed polygon centres and troughs. The re-release of storage water from the centres through deeper and less conductive layers helps maintain a high water table in the surface drainage network of troughs throughout the summer.  相似文献