Estuarine assemblages are exposed to multiple disturbances that overlap in time and space. Along the Atlantic Intracoastal
Waterway (east coast, United States), two disturbances that frequently co-occur are the production of wake by boats and the
disposal of sediment dredged from boat channels. Boat wake generally coarsens sediments by eroding finer particles while deposition
of dredge spoil decreases mean grain size. If previously demonstrated effects of boat wake on infauna are due to coarsening
of grain size, deposition of dredge spoil on wake affected sites may, through compensatory effects, prevent an effect of wake
from being detected. Epifaunal assemblages associated with seagrass blades that are more likely to be structured by hydrodynamic
forces than granulometry may instead be affected by boat wake irrespective of the previous deposition of fine materials. To
test these hypotheses, in fauna and epifauna were sampled in patchy seagrass habitat at sites with and without boat wake that
were affected by historic deposition of dredge spoil and at sites without wake that had not received dredge spoil. Sediment
granulometry and infaunal assemblages differed between sites with and without dredge spoit but not between spoil affected
sites differing in exposure to wake. Epifaunal assemblages differed between sites with and without wake irrespective of sediment
granulometry. The effect of wake on epifauna was primarily due to lesser abundances of the gastropodBittiolum varium and the slipper limpet,Crepidula fornicata, at wake exposed sites. These results suggest that because of their opposing effects on sediment granulometry, boat-wake
and sediment disposal may have compensatory effects on infaunal assemblages. The detection of an effect of wake on epifauna
despite the absence of a sedimentological effect of the disturbance shows that ecological impacts do not necessarily mirror
physical effects and should be considered separately when adopting strategies of management. 相似文献
Scanning electron microscopy and instrumental neutron activation analyses of filtered suspended matter from the Atlantic Ocean show that particulate aluminium (Alp) is a sensitive measure of bottom derived or resuspended material. The proportion of Alp in suspended particulate matter (SPM) increases slightly between surface and intermediate depths but shows large and steady increases in deep waters with approach to the bottom.
Fep/Alp andMnp/Alp ratios are always higher than the crustal ratios throughout the water column. We show that the processes which can explain such enrichments are different for particulate matter in surface waters (scavenging, incorporation in biogenic particles) than for resuspended material (precipitation from interstitial waters on surficial sediments).
Close to the Mid-Atlantic Ridge, the bottom suspended matter exhibits higher Fep/Alp andMnp/Alp ratios than in abyssal plains. A ridge crest source must be invoked to explain the striking enrichment of Mnp. This source could also explain the enrichment of Fep, although primarily because the resuspended flux is small in that region, one cannot exclude the contribution of particles from the mid-water column. 相似文献
Molluscs were collected monthly for a year from two low salinity (0–9‰) intertidal marshes dominated by the macrophytesJuncus roemerianus orSpartina cynosuroides in St. Louis Bay, Mississippi. TheJuncus marsh had lower soil organic matter, higher pH and was more frequently inundated than theSpartina marsh. Eight species of gastropods were abundant and dominated in the higherSpartina marsh, while three bivalve species were dominant in theJuncus marsh. Of the common species,Succinea ovalis, Vertigo ovata andDeroceras laeve are gastropods of terrestrial origins;Geukensia demissa granosissima (bivalve) andMelampus bidentatus (gastropod) are euryhaline estuarine species and the remaining gastropods (Detracia floridana, Littoridinops palustris, Onobops jacksoni) and bivalves (Polymesoda caroliniana, Cyrenoida floridana) are brackish species. Most species were capable of continuous recruitment (based on size class analysis), but exhibited peak activity in particular seasons. Bivalve abundance correlated to temperature, and gastropod abundance was negatively correlated to soil pH. These correlations reflect the influence of flooding regime at the two sites. Biomass was greater in theJuncus marsh because of the increased presence of the large-bodiedPolymesoda. Polymesoda represented >90% and >50% of the total biomass in theJuncus andSpartina (except summer) marshes respectively but always <-5% of the individuals collected. Gastropod biomass was the same in both marshes. Species diversity (H′) was greater inSpartina except for summer months. TheJuncus marsh always exhibited greater species richness. Evenness (J′) determined seasonal changes in diversity (H′). Similarity values (Cz) were always quite low, with highest values in spring In contrast to faunal studies from Gulf and East Coast salt marshes, we found 1) fewer species, 2) communities comprised of unique species combinations, 3) greatest mean densities in summer, and 4) potentially less productivity by the molluscs of our sites. These mollusc communities exhibit structural characteristics that emphasize the unique ecotonal nature of the oligohaline marshes within which they are found. 相似文献
The distribution of Ca and Mg among coexisting olivine, clinopyroxene and orthopyroxene has been studied in a piston-cylinder apparatus in the temperature range 1100–1300°C and pressure range 9–41 kbar. Ca in olivine decreases with increasing pressure and decreasing temperature. The pressure effect is the result of Ca going into the higher-coordination M2 site in clinopyroxene as pressure is increased. For the CaMg exchange reaction between olivine and clinopyroxene, ΔV°=0.249J bar?1 mole?1; this is sufficient for pressure estimates accurate to ±3kbar if temperatures of equilibration are independently known. CaMg exchange between olivine and orthopyroxene is not sufficiently pressure dependent to be used as a geobarometer.Application of the olivine-clinopyroxene geobarometer to coarse garnet lherzolites from southern Africa gives P-T results consistent with a continental geotherm. For spinel lherzolites from southwestern United States, the geotherm appears to be displaced to higher temperatures indicating oceanic affinities. Application of the geobarometer to natural systems requires assumptions about activity relationships in clinopyroxene which should be checked by experiment. 相似文献
Multi-model ensembles are commonly used in climate prediction to create a set of independent estimates, and so better gauge the likelihood of particular outcomes and better quantify prediction uncertainty. Yet researchers share literature, datasets and model code—to what extent do different simulations constitute independent estimates? What is the relationship between model performance and independence? We show that error correlation provides a natural empirical basis for defining model dependence and derive a weighting strategy that accounts for dependence in experiments where the multi-model mean would otherwise be used. We introduce the “replicate Earth” ensemble interpretation framework, based on theoretically derived statistical relationships between ensembles of perfect models (replicate Earths) and observations. We transform an ensemble of (imperfect) climate projections into an ensemble whose mean and variance have the same statistical relationship to observations as an ensemble of replicate Earths. The approach can be used with multi-model ensembles that have varying numbers of simulations from different models, accounting for model dependence. We use HadCRUT3 data and the CMIP3 models to show that in out of sample tests, the transformed ensemble has an ensemble mean with significantly lower error and much flatter rank frequency histograms than the original ensemble. 相似文献
This study examined how the inactivation of bacteriophage MS2 in water was affected by ionic strength (IS) and dissolved organic carbon (DOC) using static batch inactivation experiments at 4 °C conducted over a period of 2 months. Experimental conditions were characteristic of an operational managed aquifer recharge (MAR) scheme in Uppsala, Sweden. Experimental data were fit with constant and time-dependent inactivation models using two methods: (1) traditional linear and nonlinear least-squares techniques; and (2) a Monte-Carlo based parameter estimation technique called generalized likelihood uncertainty estimation (GLUE). The least-squares and GLUE methodologies gave very similar estimates of the model parameters and their uncertainty. This demonstrates that GLUE can be used as a viable alternative to traditional least-squares parameter estimation techniques for fitting of virus inactivation models. Results showed a slight increase in constant inactivation rates following an increase in the DOC concentrations, suggesting that the presence of organic carbon enhanced the inactivation of MS2. The experiment with a high IS and a low DOC was the only experiment which showed that MS2 inactivation may have been time-dependent. However, results from the GLUE methodology indicated that models of constant inactivation were able to describe all of the experiments. This suggested that inactivation time-series longer than 2 months were needed in order to provide concrete conclusions regarding the time-dependency of MS2 inactivation at 4 °C under these experimental conditions. 相似文献
Since transport of planktonic larvae is essential to the maintenance and expansion of many marine species, we examined the spatial and temporal distribution of green porcelain crab Petrolisthes armatus (Gibbes, 1850) larvae and the possible underlying physical and behavioral mechanisms using a combination of field observations and numerical modeling. The field study consisted of observations of larval abundance and distribution as well as hydrographic surveys of the Satilla River estuary on the east coast of the USA in August 2006. Larvae were found throughout the water column within the tributaries but primarily at depth in the main river. A numerical model was used to examine the effect of flow and possible larval behavior responsible for the observed distribution and the consequences for larval retention in the estuary. Model results that included downward larval movement are consistent with the field observations, supporting the hypothesis that P. armatus larvae vertically migrate within the water column, which aids in their retention within the estuary. 相似文献