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91.
The Langmuir and Freundlich adsorption isotherm equations were used to model Cs sorption in 6 Welsh soils. The pH (in water), of the soils ranged from 3.5 to 6.5, and the estimated organic matter (determined by loss-on-ignition) ranged from 4.8% to 46%. According to the Langmuir adsorption isotherm, highest sorption maxima,b, were displayed by the loams at 102–204 mg kg−1, compared with organic soils at 37–86 mg kg−1. Subsoil horizons (15–30 cm depth) did not always display higher sorption maxima than their topsoil (0–15 cm depth) counterparts. Where an improved fit to the Freundlich model was found over the Langmuir model, it was assumed that either concurrent desorption of other species, or bond-energy heterogeneity in the substrate, were significant for these soils. 相似文献
92.
The paper reviews and summarises the literature on regulatory enforcement in fisheries. The focus is on the theoretical literature. First, some of the main contributions from the general economic literature of law enforcement are presented, along with extensions that are considered relevant to the study of fisheries law enforcement. Second, a review of the economic literature of law enforcement applied to the study of fisheries is provided. Finally, the paper presents gaps in the fisheries economics literature on regulatory enforcement and offers some possibilities for future work. 相似文献
93.
Linda E. Florer 《Marine Geology》1973,14(1):73-78
Pollen diagrams of postglacial sediments from the continental terrace off the Washington coast reveal trends similar to those observed in continental sections of postglacial age from the Pacific Northwest and appear sufficient for correlation with terrestrial deposits. The absolute pollen frequency (APF) varies from 3000 to 15000 grains/g. Maximum number of pollen grains (500–800/cm2/year) accumulated during the Hypsithermal. 相似文献
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95.
Robert B. Cook Russell G. Kreis Jr. John C. Kingston Keith E. Camburn Stephen A. Norton Myron J. Mitchell Brian Fry Linda C. K. Shane 《Journal of Paleolimnology》1990,3(1):13-34
McNearney Lake is an acidic (pH=4.4) lake in the Upper Peninsula of Michigan with low acid neutralizing capacity (ANC=-38 eq L-1) and high SO
inf4
sup2-
and aluminium concentrations. Oligotrophy is indicated by high Secchi transparency and by low chlorophyll a, total phosphorus, and total nitrogen concentrations. The lake water is currently acidic because base cations are supplied to the lake water at a low rate and because SO
inf4
sup2-
from atmospheric deposition was not appreciably retained by the lake sediments or watershed and was present in the water column.This interdisciplinary paleolimnological study indicates that McNearney Lake is naturally acidic and has been so since at least 4000 years B.P., as determined from inferred-pH techniques based on contemporary diatom-pH relationships. Predicted pH values ranged from 4.7 to 5.0 over the 4000-year stratigraphy. Considerable shifts in species composition and abundance were observed in diatom stratigraphy, but present-day distributions indicate that all abundant taxa most frequently occur under acidic conditions, suggesting that factors other than pH are responsible for the shifts. The diatom-inferred pH technique as applied to McNearney Lake has too large an uncertainly and is not sensitive enough to determine the subtle recent changes in lakewater pH expected from changes in atmospheric deposition because: (1) McNearney Lake has the lowest pH in the contemporary diatom data set in the region and confidence intervals for pH predictions increase at the extremes of regressions; (2) other factors in addition to pH may be responsible for the diatom species distribution in the lake and in the entire northern Great Lakes region; (3) McNearney Lake has a well-buffered pH as a consequence of its low pH and high aluminium concentrations and is not expected to exhibit a large pH change as a result of changes in atmospheric deposition; and (4) atmospheric deposition in the region is modest and would not cause a pH shift large enough to be discernable in McNearney Lake.Elevated atmospheric deposition is indicated in recent sediments by Pb, V, and polycyclic aromatic hydrocarbon accumulation rates and to a lesser extent by those of Cu and Zn; however, these accumulation rates are substantially lower than those observed for acidified lakes in the northeastern United States. Although atmospheric loadings of materials associated with fossil fuel combustion have recently increased to McNearney Lake and apparently are continuing, the present study of the diatom subfossil record does not indicate a distinct, recent acidification (pH decrease).Order of the first two authors is alphabetical 相似文献
96.
97.
Menhaden are one of the most abundant components of fish communities in Gulf and Atlantic estuaries. Juvenile menhaden have been reported to have zooplankton, phytoplankton, andSpartina-derived detritus in their guts. However, there has been disagreement over the importance of the detritus as a food source. We show, using physiological and stable isotope evidence, that detritus can be used by juvenile Gulf menhaden. Their diet is very roughly 30% detritus- and 70% plankton-based. 相似文献
98.
John R. Kelly Suzanne N. Levine Linda A. Buttel Kelly A. Carr David T. Rudnick R. Dana Morton 《Estuaries and Coasts》1990,13(3):301-310
Flow-through seagrass core microcosms were used to examine responses of species and processes to a logarithmic gradient of dosing with14C-labeled tributyltin-chloride (TBT-CI). Experiments involved delivery of TBT-CI to the water column of replicate cores of a treatment (n=16) once per week; one-half of the cores were sacrificed after 3 wk of dosing, the others were dosed for 6 wk. Initial water column concentrations for the three treatments averaged 0.205, 2.23, and 22.21 μg I?1, expressed as the TBT+ cation, but these concentrations dropped rapidly. Retained14C tracer, an estimate of total organotin species, was distributed to sediments, plants, and other biological tissues, all of whose tracer concentrations increased with time. Measures to indicate responses of both autotrophic and heterotrophic organisms were made; in general, treatment effects were demonstrable statistically only at the highest dose level. Accumulation of chlorophyll and biomass on glass slides was highest when suspended for the entire experiment in the water of the highest treatment; this unexpected result was perhaps an indirect effect related to reduced grazing activity in the microcosms. The highest dose of TBT-CI resulted in virtual population mortality of a few macrobenthic species and decreased loss of plant material in litter bags, both demonstrated within the first 3 wk of dosing. Reduced litter loss was coincident with mortality of an amphipod (Cymadusa compta) capable of shredding plant material, and a causal relation between the two effects is plausible. Thus, if concentrated to similar levels in aThalassia bed, TBT+ may have direct species-level effects and process-level effects, potentially causing ecosystem change via disruption of a species-process linkage influential in seagrass detrital food web dynamics. 相似文献
99.
Recognition criteria,characteristics and implications of the fluvial to marine transition zone in ancient deltaic deposits (Lajas Formation,Argentina) 总被引:1,自引:0,他引:1
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Marcello Gugliotta Stephen S. Flint David M. Hodgson Gonzalo D. Veiga 《Sedimentology》2016,63(7):1971-2001
The seaward end of modern rivers is characterized by the interactions of marine and fluvial processes, a tract known as the fluvial to marine transition zone, which varies between systems due to the relative strength of these processes. To understand how fluvial and tidal process interactions and the fluvial to marine transition zone are preserved in the rock record, large‐scale outcrops of deltaic deposits of the Middle Jurassic Lajas Formation (Neuquén Basin, Argentina) have been investigated. Fluvial–tidal indicators consist of cyclically distributed carbonaceous drapes in unidirectional, seaward‐oriented cross‐stratifications, which are interpreted as the result of tidal modulation of the fluvial current in the inner part of the fluvial to marine transition zone. Heterolithic deposits with decimetre‐scale interbedding of coarser‐grained and finer‐grained facies with mixed fluvial and tidal affinities are interpreted to indicate fluvial discharge fluctuations (seasonality) and subordinate tidal influence. Many other potential tidal indicators are argued to be the result of fluvial–tidal interactions with overall fluvial dominance or of purely fluvial processes. No purely tidal or tide‐dominated facies were recognized in the studied deposits. Moreover, fluvial–tidal features are found mainly in deposits interpreted as interflood (forming during low river stage) in distal (delta front) or off‐axis (interdistributary) parts of the system. Along major channel axes, the interpreted fluvial to marine transition zone is mainly represented by the fluvial‐dominated section, whereas little or no tide‐dominated section is identified. The system is interpreted to have been hyposynchronous with a poorly developed turbidity maximum. These conditions and the architectural elements described, including major and minor distributary channels, terminal distributary channels, mouth bars and crevasse mouth bars, are consistent with an interpretation of a fluvial‐dominated, tide‐influenced delta system and with an estimated short backwater length and inferred microtidal conditions. The improved identification of process interactions, and their preservation in ancient fluvial to marine transition zones, is fundamental to refining interpretations of ancient deltaic successions. 相似文献
100.