Bed Area Research Articles

수중음향과 Kompsat-2 위성영상을 이용한 해초지 분포 추정

Despite the ecological importance of seagrass beds, their distributional information in Korean coastal waters is insufficient. Therefore, we used hydroacoustic system to collect accurate bathymetry and classification of seagrass, and Kompsat-2 (4 m spatial resolution) image for detection of seagrass beds at Deukryang Bay, Korea. The accuracy of Kompsat-2 image classification was evaluated using hydracoustic survey result using error matrix and Kappa value. The total area of seagrass beds from satellite image classification was underestimated compared to the hydroacoustic survey, estimated 3.9 and from satellite image and hydroacoustic data, respectively. Nonetheless, the accuracy of Kompsat-2 image classification over hydroacoustic-based method showing 90% (Kappa

Abundance and culture trials ofRuditapes philippinarum(Adam and Reeve, 1850), and abundance ofTellina (Quidnipagus) palatum(Iredale, 1929) at two sites in Kāne'ohe Bay, O'ahu, Hawai'i

Abundance, length-frequencies and distribution of Ruditapes philippinarum (Manila Clams) and Tellina (Quidnipagus) palatum were measured at two beaches in Kāne'ohe Bay, O'ahu, Hawai'i in June, 2010. Abundances had decreased from 866.2 m−2 to 3.4 m−2 for Ruditapes and from 75.5 m−2 to 1.5 m−2 for T. palatum since 1977. Distribution of both species was patchy, but both were most commonly found >40 m from shore. Size frequencies of live clams compared with empty shells suggest that few Ruditapes survive to sexual maturity. A similar trend was not detected for T. palatum. Aquaculture trials of R. philippinarum were conducted at the He'eia and Moli'i traditional Hawaiian fishponds in the same bay. The clams failed to thrive, although triploid and diploid Crassostrea gigas performed well in concurrent trials in the same fishponds. Current lower abundances for wild R. philippinarum could be due to factors related to predation or nutrient limitations. Previously, two large sewage outfalls existed at the surveyed clam bed areas which may have temporarily increased nutrient availability for both wild and cultured clams. Current nutrient levels may inhibit Manila clam growth and recruitment in Kāne'ohe Bay.

Abnormal Fetal–Maternal Interactions

There is clinical and ultrasonographic evidence that "abnormal fetal-maternal interactions" or "fetal-maternal conflicts" may be central to the mechanisms of injury in pregnancy complications such as fetal growth restriction, preeclampsia, fetal death, gestational diabetes, and a subset of patients with preterm parturition. This conceptual framework integrates abnormalities in the placental bed, placental vasculature, and other areas of fetal-maternal interactions with pregnancy complications in light of their possible evolutionary value.

Two-Dimensional Mathematical Modeling of Heat and Mass Transfer in Fluidized-Bed Drying of Porous Material

A two-dimensional mathematical model of simultaneous heat and mass transfer for porous media drying was derived based on the Whitaker’s theory in the present study. The cylindrical coordinate system, which is more practical than the spherical one, was adopted. The model was solved numerically under the circumstance of fluidized-bed drying. The control-volume method with the fully implicit scheme was applied for discretization of governing equations. Physical properties of apple were selected in the simulation. Under typical operating conditions, heat and mass transfer mechanisms were analyzed based on the profiles of temperature and saturation inside the particles. Effects of the temperature, humidity and inlet velocity of hot gas were examined under different operating conditions. Simulation results show that the drying process can be significantly affected by coupled heat and mass transfer between gas and solid phases. The drying time increases with the increase in temperature and velocity of inlet hot gas, and decreases with the increase in humidity and bed area factor.

P-0161 Evaluation of Doses to Organs at Risk in Conformal Radiotherapy of Periampullary Cancers: Implications for Dose Escalation by IMRT

ABSTRACT Introduction Periampullary carcinomas are defined as those arising from a 1cm area around the ampulla of Vater. They are treated with surgery followed by adjuvant radio chemotherapy. Conventionally doses of 40 -45 Gray have been used in treating periampullary cancers. Higher doses required for adequate local control were not possible with conventional radiotherapy due to surrounding normal structures. Since majority of patients fail locally or locoregionally dose escalation should be done using intensity modulated radiotherapy, keeping surrounding normal tissue constraints in mind. Methods Ten patients of periampullary cancer who underwent Whipple's surgery and post-operative radiotherapy and chemotherapy for stage II and III periampullary carcinomas were evaluated in this analysis. Post operatively contrast enhanced planning CT scan were done using 2.5mm slice thickness and images transferred to Eclipse treatment planning system version 8.6.0(Varian, Palo Alto, CA, USA). CTV (Clinical target volume) included the tumor bed and nodal areas. A 1 cm margin was taken around CTV to create the PTV (Planning treatment volume). Conformal radiotherapy plans using three fields (One anterior and two laterals) were generated and evaluated. The patients were planned by 3-DCRT to aPTV dose of 45Gyin 25 fractions (PTV45 Gray). Doses to surrounding organs at risk were computed. Doses received by Kidneys, spinal cord, stomach, liver and small bowel were documented. For statistical analysis the SPSS v.18.0 was used. Results The mean dose received by Right kidney, left kidney, liver, spinal cord and stomach were (Mean±S.D) 14.6±3.2Gray, 12.1±1.5Gray, 27.7±2.4 Gray, 16.83±1.2 Gy, and 31.4±1.6 Gray respectively. The median volume of small bowel receiving greater than 45 Gy was 35%. Conclusion With a prescription of 45Gy in 25 fractions the doses received by surrounding critical structures are well within acceptable limits. Dose escalation should thus be tried using IMRT with an aim to increase local control.

Biodiversity and fish farming intensification in French fishpond systems

Fishponds are artificial ecosystems in which biodiversity may be strongly affected by fish farming management. We studied biodiversity variation along a gradient of fish farming intensification within a 180-pond sample of a French region to establish whether biodiversity primarily depended on extensive management with the alternative hypothesis that some habitat characteristics could compensate for the effect of intensification. We compared the relationships of three biodiversity indicators (breeding birds, protected plants, macrophytes) to an index of intensification and to habitat characteristics likely to influence each indicator. In all selected indicators, species richness did not vary according to the composite intensification gradient. Protected plant richness was best explained by periodic drainage, which could thus benefit biodiversity in intensified fishponds provided that shallow littoral areas are still present. Bird richness was linked to macrophyte cover and probably to reed bed areas. Macrophyte richness and coverage were negatively influenced by low water transparency and high fish biomass which seemed likely to affect bird habitat above 350–400 kg/ha. Aquatic vegetation, which may reflect interactive effects of environmental factors and fish farming management, may then contribute to assessment of the ecological status of fishponds under the E.U. Water Framework Directive.

91 LONG TERM OUTCOMES AND RECURRENCE PATTERN FOLLOWING ACCELERATED PARTIAL BREAST IRRADIATION USING MAMMOSITE

Purpose/Objective: To evaluate: 1. The incidence of locoregional recurrence in early breast cancer treated by APBI using the MammoSite device in patients grouped according to ASTRO consensus panel 'suitable 'and 'cautionary' category. 2. The recurrence pattern in patients with 'triple negative tumor' (TN) (negative Estrogen, Progesterone receptor and Human Epidermal Growth factor (HER-2)) and the association and outcomes of African American, Hispanic ethnicity and ER negative tumor. Materials and Methods: Between June 2003 and December 2009, 83 post-menopausal patients:76 invasive ductal carcinoma (IDC), 7 ductal carcinoma in situ (DCIS), with diagnosis of early stage breast cancer and node negative status met our inclusion criteria for APBI using the single lumen MammoSite balloon catheter. Following a CT scan based 3D plan a dose of 3400cGy was prescribed in 10 fractions at distance of 1 cm from surface of balloon delivered twice daily, 6 hours apart using the high dose rate system. Patients were categorized as 4 groups: ASTRO consensus 'suitable', 'cautionary', TN and TN plus Her-2 positive ('High Risk'). Data on treatment outcome with for ipsilateral breast tumor recurrence (IBTR), tumor bed area failure (TBF), elsewhere failure in the same breast (EF), ipsilateral axilla failure (IAF) was analyzed. Results: There were 42/83 (51%) patients in the 'suitable' and 41/83 (49%) in the 'cautionary' group. TN was 11% (8/76) and 'High risk' was 24% (18/76) of invasive cancer patients. Mean age of invasive cancer patients was 72 years. Median follow-up for all 83 patients was 61 months; 'cautionary' group= 61 months; triple negative= 59; 'suitable' group=61 and 'High risk'= 59. Adjuvant chemotherapy was given in 18% (14/76) and hormones in 85% ER+ IDC patients. The locoregional control was 98.6%. IBTR that was EF occurred in 2/83 (2.4%) patients; one from the 'cautionary' group (ER-, HER2+) and another from the 'suitable' group (ER+, HER2-). IAF was seen in the first patient. There was a significant association between tumor grade and ethnicity with grade 3 tumors seen more in Hispanic and black women as compared to others (31% vs. 8%; p=0.03) in the invasive group. There was a higher proportion of ER-negative tumors seen among African American and Hispanics compared to other ethnicities (56.25% vs. 8.33%; p<.0001)

Superposition of Four Generations of Folds and Development of Horse Creek Dome, Black Hills, South Dakota

The study area is a part of the Precambrian basement of the Black Hills that was uplifted during Laramide Orogeny. Early Proterozoic meta-conglomerate and greywacke units occupy the study area and form a crescent fold which is unusual structural pattern, mapped in the Precambrian core of the Black Hills. This study aims to determine how the crescent shape was formed via fieldwork investigation and structural data analysis. Four Precambrian (F1, F2, F3 and F4) folding events affected the study area prior to the uplift. Minor folds indicated that F1 and F4 exhibited isoclinal folding, F2 reflected similar folding and F3 displayed kink band and chevron folding. F2 is associated with axial plane cleavage (S2), trends towards the west, and is associated with regional metamorphism. F3 trends NNW and is associated with spaced cleavage (S3). F4 trends WSW and is associated with spaced crenulation cleavage (S4). The area was structurally divided into five domains. Poles to bedding (S0) and axial plane cleavage (S2) equal area stereographic projections show steeply plunging maxima that have monoclinic symmetry, resulting from superposition of two oblique F2 and F3 folding events. Domain I contains the Horse Creek dome that resulted from superposition of F3 on F2. The meta-conglomerate unit formed a crescent fold, due to superposition of the first two generations of folds. The crescent fold follows the Horse Creek dome, trends and opens westerly, and it is parallel to F4 folds.

Long-Term Remission After Gefitinib Therapy in an Elderly Patient With Advanced Non-Small-Cell Lung Carcinoma

The prognosis for non-small-cell lung carcinoma (NSCLC) pat ients in advanced stages is poor. Gefitinib inhibits the tyrosine kinase activity of epidermal growth factor receptor (EGFR) and have been studied extensively. Oral epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have been as the 2nd-line treatment for NSCLC. It is widely accepted that some clinicopathologic characteristics (female, nonsmoking status, Asian, and EGFR mutations) are the main clinical positive predictive factors when using EGFR-TKIs. The el der patients often suffer from deterioration of performance status (PS). The side reaction caused by chemotherapy is serious and unavoidable. For the elder patients with positive predictive factors and poor PS, there is no report about anti-NSCLC using gefitinib as the 1st-line treatment. We report the case of an 84-year-old woman with diffuse bone metastases from lung cancer. She received oral gefitinib 150 mg / day, combined with three dimensional conformal radiation therapies (3DCRT). A total tumor dose of 36Gy / 12fractions was delivered to the tumor bed and localized metastatic bone pain areas, respectively. After concurrent gefitinib-3DCRT, gefitinib was continued as maintenance therapy. She experienced total regression of the metastases under gefitinib treatment for 30 months. Gefitinib therapy provided effective anti-tumor results. Therefore, for NSCLC patients of multiple metastases with favorable predictive factors such as EGFR mutations, adenocarcinoma, Asian, female gender and nonsmoking status, we suggest that gefitinib may become the 1st-line treatment even with poor PS. doi:10.4021/jmc513w

Myocardial improvement with human embryonic stem cell-derived cardiomyocytes enriched by p38MAPK inhibition

We have shown previously that inhibition of the p38 mitogen-activated protein kinase (p38MAPK) directs the differentiation of human embryonic stem cell (hESC)-derived cardiomyocytes (hCM). We investigated the therapeutic benefits of intramyocardial injection of hCM differentiated from hESC by p38MAPK inhibition using closed-chest ultrasound-guided injection at a clinically relevant time post-myocardial infarction (MI) in a mouse model. MI was induced in mice and the animals treated at day 3 with: (a) hCM, (b) human fetal fibroblasts (hFF) as cell control, or (c) medium control (n = 10 animals/group). Left ventricular ejection fraction (LVEF) was evaluated post-MI prior to therapy, and at days 28 and 60 post-cell therapy. Hearts were analyzed at day 60 for infarct size, angiogenesis, cell fate and teratoma formation. LVEF was improved in the hCM-treated animals compared with both hFF and medium control-treated animals at day 28 (39.03 ± 1.79% versus 27.89 ± 1.27%, P < 0.05, versus 32.90 ± 1.46%, P < 0.05, respectively), with sustained benefit until day 60. hCM therapy resulted in significantly smaller scar size, increased capillary bed area, increased number of arterioles, less native cardiomyocyte (CM) apoptosis, and increased CM proliferation compared with the other two groups. These benefits were achieved despite a very low retention rate of the injected cells at day 60, as assessed by immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR). Therapy with hCM did not result in intramyocardial teratoma formation at day 60. This study demonstrates that hCM derived from p38MAPK-treated hESC have encouraging therapeutic potential.

Measuring sediment transport and bed disturbance with tracers on a mixed beach

A new tracer deployment method is applied to the problem of resolving rates and patterns of littoral sediment transport on mixed beaches. We applied the method at the morphologically complex, meso-tidal beach fringing the Elwha River delta, Washington. Clasts were transformed into tracers using Radio Frequency Identifier (RFID) tags. These tracers were deployed in and on the bed along a cross-shore oriented beach transect. Along- and cross-shore variations in tracer velocity were used to estimate sediment transport patterns, including the depth and cross-sectional area of the disturbed bed and bulk alongshore transport rates. We found that the peak bed disturbance averaged 22% of the tidal maximum significant wave height and that tracer velocity declined approximately logarithmically with depth in the bed. Across all deployments the maximum alongshore tracer velocity occurred between 1.0 and 2.0m above Mean Lower Low Water (MLLW), corresponding to elevations 0.3m below and 0.7m above Mean Sea Level (MSL) at this location. Alongshore bulk sediment transport rates estimated from the advection of tracers ranged from 1.1 to 173.1m3/d under significant wave heights of 0.1 to 2.1m and these transport rates related linearly to measured wave energy transport. Both the volumetric sediment transport rates and a CERC-type k coefficient derived from the results agreed well with results from other published studies.

The effect of discrete recharge by moulins and heterogeneity in flow-path efficiency at glacier beds on subglacial hydrology

AbstractSubglacial conduit systems are thought to consist of dendritic networks that exist at lower pressure than distributed systems and have locations that are determined by theoretical hydraulic potential. On glaciers with moulins, however, meltwater is delivered to glacier beds at discrete points, violating assumptions of uniform recharge needed to calculate potential. To understand how moulins affect subglacial conduit hydrology, we used speleological techniques to map 0.4 km of subglacial conduit at the base of a moulin in Hansbreen, Svalbard, and compared our observations with theoretical predictions. The conduit began in an area predicted to lack drainage, crossed equipotential contours at oblique rather than right angles and was locally anastomotic rather than dendritic. We propose moulin locations, which are determined by the locations of supraglacial streams and crevasses, control locations of subglacial recharge. Because conduits have no direct causal relationship with gradients in effective pressure, this recharge can form conduits in areas of glacier beds that may not be predicted by hydraulic potential theory to have conduits. Recharge by moulins allows hydraulic head to increase in conduits faster and to higher values than in adjacent distributed systems, resulting in an increase rather than a decrease in glacier sliding speeds above subglacial conduits.

Influence of Electric Field Application by Reducing Area of Electrode Compared with Cross-Sectional Area of Sludge Bed on Electro-Osmotic Dewatering Process

In the process of electro-osmotic dewatering of a semi-solid sludge put between two plate-type electrodes placed above and below a sludge bed, the water content in part of the bed near the upper electrode opposite to a lower drainage surface is considerably reduced, resulting in electrically poor contact between the upper electrode and the bed being dewatered, and then an excessive increase in electrical contact resistance between them. This obviously obstructs the efficiency of electro-osmotic dewatering throughout the entire bed, and consequently, the continuation of the dewatering process becomes increasingly difficult. From the viewpoint of lowering the influence of increasing electrical contact resistance, the usage of an upper plate-type electrode, in which the area of such electrode is smaller than the cross-sectional area of the sludge bed, is regarded to be practical in improving electro-osmotically the performance of sludge dewatering. In this study, electro-osmotic dewatering is experimentally investigated by reducing the area of not only the upper electrode, but both the upper electrode and the lower one on the drainage surface, and compared with the same-area electrode as the cross-section of the bed. Thus, the influence of such electrode arrangements in reducing the area of the electrode(s) on the dewatering process in terms of water removal and electrical energy consumption is examined using calcium carbonate as solid particles for sludge conditioning. As a result, it has been found that the amount of removed water and electrical energy efficiency for water removal can be increased compared with the same-area electrode as the bed, except for the case of an excessively small electrode area.

Long-Term Remission After Gefitinib Therapy in an Elderly Patient With Advanced Non-Small-Cell Lung Carcinoma

The prognosis for non-small-cell lung carcinoma (NSCLC) patients in advanced stages is poor. Gefitinib inhibits the tyrosine kinase activity of epidermal growth factor receptor (EGFR) and have been studied extensively. Oral epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have been as the 2nd-line treatment for NSCLC. It is widely accepted that some clinicopathologic characteristics (female, nonsmoking status, Asian, and EGFR mutations) are the main clinical positive predictive factors when using EGFR-TKIs. The elder patients often suffer from deterioration of performance status (PS). The side reaction caused by chemotherapy is serious and unavoidable. For the elder patients with positive predictive factors and poor PS, there is no report about anti-NSCLC using gefitinib as the 1st-line treatment. We report the case of an 84-year-old woman with diffuse bone metastases from lung cancer. She received oral gefitinib 150 mg/day, combined with three dimensional conformal radiation therapies (3DCRT). A total tumor dose of 36Gy/12fractions was delivered to the tumor bed and localized metastatic bone pain areas, respectively. After concurrent gefitinib-3DCRT, gefitinib was continued as maintenance therapy. She experienced total regression of the metastases under gefitinib treatment for 30 months. Gefitinib therapy provided effective anti-tumor results. Therefore, for NSCLC patients of multiple metastases with favorable predictive factors such as EGFR mutations, adenocarcinoma, Asian, female gender and nonsmoking status, we suggest that gefitinib may become the 1st-line treatment even with poor PS. J Med Cases. 2012;3(2):140-143 doi: https://doi.org/10.4021/jmc513w

Experimental study of a novel hybrid constructed wetland for water reuse and its application in Southern China

A new type of hybrid constructed wetland (CW), consisting of both vertical-baffled flow wetland (VBFW) and horizontal subsurface flow wetland (HSFW), has been deployed in Southern China to naturally accelerate the removal of organic matter and nitrogen. The hybrid CW system is characterised by a combination of continuous baffled flow vertical wetland and 'S' pattern horizontal subsurface flow wetland with natural aeration ditches to increase the concentration of dissolved oxygen in the HSFW bed. An internal circulatory system from the HSFW effluent back to the VBFW may optionally be operated to enhance the biological denitrification effect. Cyperus alternifolius is the main macrophyte in the wetland bed. The performance of the hybrid CW was studied with a pilot-scale system and three full-scale systems for municipal sewage treatment in Southern China. The results suggest that this new hybrid CW can achieve removal efficiencies of chemical oxygen demand, suspended solids, ammonia nitrogen, total nitrogen, and total phosphorus of better than 83.6, 95.0, 71.7, 64.5 and 68.1% respectively, with a specific wetland bed area of 0.70-0.93 m(2) PE(-1). The mean effluent concentrations of these parameters would meet the regulatory discharge limits for wastewater treatment systems (GB18918, 2002) and reuse in the context of agricultural irrigation solutions in China.

Hydraulic factors controlling the benthic invertebrate distribution within and among dunes of the Middle Paraná River (Argentina) and sampling techniques

Dunes are ubiquitous bed forms in river channels which deeply interact with the mean and turbulent flow dynamic. These interactions involve the intricate mechanisms governing the entrainment, transport, and deposition of bed sediment which are being studied since long time ago. However, the links between dunes and stream ecology, such as the benthic fauna distribution, was not yet investigated to the authors’ knowledge. This study aims to optimize the benthic sampling techniques on bed forms, and links the different hydraulic characteristics prevailing on crests and troughs of dunes and the invertebrate distribution on the Middle Paraná River (Argentina). It was also possible to have an insight of the invertebrate distribution living in these bed areas (i.e. crests and troughs) as well as the influence of dunes location on the channel bed. A significant distinction of benthic distribution (densities) on dunes, as a consequence of their location on the bed and hydraulic conditions, was found. The overall results showed a clear preference by invertebrates for the dune with lower bed shear stresses. The study concluded that dunes could be considered as biotopes hydraulically differentiated and, consequently, with a stratified benthic distribution. Consequently, to discriminate bottom areas, by an appropriate selection of the hydraulic variables over the associated geometry of dunes, is an effective way to reduce the variance and to increase the accuracy of benthic samplings in large rivers.

Management and production of the brown algae Ascophyllum nodosum in the Canadian maritimes

Commercial exploitation of Ascophyllum nodosum (rockweed) along the coast of Nova Scotia began in the late 1950s when it was used as a raw material for manufacturing alginate and “kelp” meal. Today, this resource is used as a biostimulant extract for crops and animal feed supplements and is the main economic resource of the seaweed industry in the Maritime Provinces and Canada. The management of rockweed, by dividing the resource into many sectors, permitted the assessment of yield per unit area of bed. In Nova Scotia, mechanical harvesting of A. nodosum operated on a pulse of 2- to 3-year schedule providing yields of 21.9 to 47.7 wet t ha−1 averaging 35.3 ± 7.6 wet t ha−1. Acadian Seaplants Limited (ASL) has become the dominant player in the region since 1995 with more than 75% of the total biomass under its leases and more than 90% of the total landing of rockweed in the last 13 years. Sustained harvests at ASL leases and under an annual harvest schedule using hand cutting methods have averaged 17.4 ± 2.6 t ha−1. Exploitation rates above 35% of the harvestable crop lead to a pulse harvest strategy and the need to move infrastructure year after year. In New Brunswick, a new approach to management began in 1995 with a regulated 17% exploitation rate. Thus, the yield in that province is 14.3 wet t ha−1. The current summer standing crop for this region has been calculated at 352,723 wet t, covering an area of 4,960 ha, with an average biomass of 71.3 t ha−1. The harvest in the region reached peak landings in 2010 with just over 40,100 t. The consistent yield per hectare of A. nodosum beds is proof of good management practices and an ecologically sustainable harvest in the Canadian Maritimes.

Sheep Bedding in the Centennial Mountains of Montana and Idaho: Effects on Vegetation

ABSTRACT. In summer, bands of sheep are grazed in western North American mountains. At night the sheep are concentrated into bedding areas. In the study area, each bedding area is only utilized by sheep for one night a year for 2 out of 3 years. Vegetation in the bedding areas was compared to vegetation outside these areas. Both perennial forb cover and total perennial cover were greater outside (48% and 61%, respectively) than inside (29% and 36%, respectively) the bedding areas. Annual forb cover one year after sheep grazing was greater inside (17%) bedding areas than outside (5%). Immediately after sheep bedding, total forb cover was greater outside the bedding areas. Forb and grass biomass were greater outside the bedding areas compared to inside. Total vegetation biomass outside (240 g · m-2) the bedding areas was more than double the amount inside (86 g · m-2) immediately after bedding. In the year after bedding, vegetation biomass inside the bedding areas increased, but was still less than outside....

Quantifying gravel overlap and dislodgement forces on natural river bars: implications for particle entrainment

ABSTRACTEquations for predicting particle entrainment typically assume that clast weight is the only factor resisting motion in the force balance on individual grains. In this work, increases in the force required to dislodge surface particles due to overlapping by surrounding clasts is quantified. Field data were collected at two subaerially‐exposed bars along the Colorado River in central Texas, USA, with median gravel diameters (D50) of 37 and 64 mm. Clast size, shape, weight, the force required for vertical removal, and the fraction of clast area covered by surrounding grains were measured. Small hooks were glued to individual clasts without disrupting their positions and quasi‐static peak forces required to vertically dislodge each clast were measured using a force gauge. Clasts were also colored with dye before being dislodged, and image analysis was used to calculate the fraction of clast surface area covered by surrounding grains. The effect of overlap on the particle force balance is quantified by defining the ‘excess force ratio’ as the dislodgement force divided by the weight of the clast. Excess force ratio varies weakly but systematically with clast size: lifting larger clasts can require forces up to two times the clast's weight, while smaller clasts can require forces up to seven times their weight. The fraction of clast surface area covered by surrounding particles is also weakly correlated with excess force ratio. By assuming that critical shear stresses are proportional to the excess force ratio, the effect that overlap alone may have on particle entrainment is calculated. For a given size class, the most mobile grains should have critical shear stresses controlled only by their weight. However, clast overlap also causes broad distributions of critical stresses for partially‐exposed surface grains. The data quantify the significant fraction of bed area that should be less mobile than grain size alone would predict. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Particle Retention Efficiency of a Coastal Ecosystem in the Northeastern Atlantic Ocean

Based on filtration rates obtained in situ at several habitats (mud flats, sand flats, and seagrass beds of Cymodocea nodosa), particle retention efficiency of benthic communities was estimated at Ria Formosa, a coastal lagoon in southern Portugal. The distinct physical characteristics of the water flow (water depth, current speed) at different tidal regimes (spring tide and neap tide) were also considered. Median filtration rates ranged 5.0−45.0 l m−2 h−1, despite the lack of dense bivalve beds or reefs. Based on median filtration rates of benthic communities on the studied substrate types, a model we developed showed that seagrass bed areas retained 15% of suspended particles during spring tide and 47% during neap tide. These retention efficiencies were much higher than those observed on mud flats (2.8% during spring tide, and 8% during neap tide), sand flats of finer grain size (8.8% during spring tide, and 50% during neap tide), and sand flats of coarser grain size (7% during spring tide, and 31% during neap tide). Removal of particles from water column was higher during the ebb tide than during flow tide, with particles of <5 μm diameter (especially diatoms, flagellates, and small-sized particulate matter) being the most commonly removed.