Recovery of added ¹⁵N-labelled ammonium-N from Louisiana Gulf Coast estuarine sediment     

C.J. Smith  R.D. DeLaune 《Estuarine, Coastal and Shelf Science》1985,21(2):225-233

The loss of added ¹⁵N-labelled NH₄⁺ from bottom sediment was studied in situ in a shallow saline Louisiana Gulf Coast lake. ¹⁵N-labelled NH₄⁺ was uniformly mixed with sediment at the level of 35 μg N g^?1 dry sediment for 24 h before being weighed into polyethylene containers. The ¹⁵N-enriched sediment was incubated on the lake bottom for periods up to 337 days. At intervals, triplicate samples were taken and analyzed for inorganic NH₄⁺, organic N, and denitrification rates. Concentrations of NH₄⁺ in the ¹⁵NH₄⁺ enriched sediment samples were at levels similar to those measured in vertical intact cores removed from the lake at each sampling date. The initial and final isotopic compositions of NH₄⁺ in the incubated sediments were 44.26 and 0.521 atom % ¹⁵N excess, respectively. ¹⁵N enrichment in the organic N fraction increased rapidly during the first 15 days of incubation and then increased slowly from 15 to 123 days. Denitrification, estimated by the acetylene blockage technique, ranged from 0.994 to 0.079 ng N g^?1 dry sediment per hour. The mean denitrification rate for the 337-day period was 0.28 ng N g^?1 h^?1. There was no statistical difference in the recovery of ¹⁵N between 15 and 337 days of incubation. When the added ¹⁵N became incorporated into the organic N pool, little or no further ¹⁵N was lost.  相似文献   

Numerical Simulation of phytoplankton productivity in partially mixed estuaries     

David H. Peterson  John F. Festa 《Estuarine, Coastal and Shelf Science》1984,19(5):563-589

A two-dimensional steady-state model of light-driven phytoplankton productivity and biomass in partially mixed estuaries has been developed. Effects of variations in river flow, suspended sediment concentration, phytoplankton sinking, self-shading and growth rates on distributions of phytoplankton biomass and productivity are investigated.Numerical simulation experiments show that biomass and productivity are particularly sensitive to variations in suspended sediment concentrations typical of natural river sources and to variations in loss rates assumed to be realistic but poorly known for real systems. Changes in the loss rate term within the range of empirical error (such as from dark bottle incubation experiments) cause phytoplankton biomass to change by a factor of two. In estuaries with adequate light penetration in the water column, it could be an advantage for phytoplankton to sink. Species that sink increase their concentration and form a phytoplankton maximum in a way similar to the formation of the estuarine turbidity maximum. When attenuation is severe, however, sinking species have more difficulty in maintaining their population.  相似文献   

The tidal exchange of Callianassa californiensis (Crustacea,Decapoda) larvae between the ocean and the Salmon River estuary,Oregon     

Gary E. Johnson  J.J. Gonor 《Estuarine, Coastal and Shelf Science》1982,14(5):501-516

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The composition of phytoplankton within the Chesapeake Bay plume and adjacent waters off the Virginia coast,U.S.A.     

Harold G. Marshall 《Estuarine, Coastal and Shelf Science》1982,15(1):29-43

Phytoplankton composition differences were used to identify and plot the extent of the Chesapeake Bay plume over the continental shelf. Distinct but different phytoplankton assemblages were noted within the plume for March, June and October 1980. The major constituents in the plume were Skeletonema costatum, a variety of other diatoms and an unidentified ultraplankton component assumed to consist of several cyanophycean and chlorophycean species. The shelf plankton outside of the plume was mainly characterized by the coccolithophores and other phytoplankters that formed different seasonal assemblages than what was within the plume. Patchiness and fluctuations in the shape, size and extent of the plume were noted. A total of 235 species is given, with their presence within the plume and at shelf stations indicated.  相似文献   

Some features of the dynamic structure of a deep estuary     

Michael Devine 《Estuarine, Coastal and Shelf Science》1983,16(3):271-289

A boundary layer formulation for the dynamic structure of a deep estuary is developed. Cross-stream averages are used, but the boundary layer structure is shown to depend on the cross-stream geostrophic constraint. A similarity transformation and a weighted residual method are used to derive an approximate solution for the velocity and salinity structure of the upper layer. This solution indicates that, in the central regime of the estuary, outflow extends through the entire halocline. Inflow takes place in a much less stratified lower layer, and mass exchange between the layers is by upwelling. This structure is modified in the outer regime of the estuary, where mixing between the layers develops, and in the inner regime, where a sharp halocline develops and where the dynamics are dominated by river runoff. The implications of the dynamics for the flushing process and for pollutant movement and dispersion are discussed.  相似文献   

Weathered IXTOC I oil effects on estuarine benthos     

Richard D. Kalke  Thomas A. Duke  R. Warren Flint 《Estuarine, Coastal and Shelf Science》1982,15(1):75-84

The impact of weathered IXTOC I oil on experimental benthic communities colonized in the laboratory and in situ was observed. Test systems containing clean sand and receiving seawater from Aransas Pass Inlet were placed in the laboratory while similar systems were placed on the seafloor. All of these test systems were allowed to colonize for 8 weeks by settlement of planktonic larvae. Weathered IXTOC I oil was added to randomly selected laboratory and in situ replicate compartments within the test systems and these were then exposed to flowing seawater in the laboratory for an additional 4 weeks. Observations of the structure and biomass of the communities at the end of the 12-week period indicated no significant effects on the laboratory colonized communities. However, total density was significantly affected in the in situ colonized systems as was species composition. Although not significant, total biomass was substantially reduced by oiling. Eh measurements of sediments showed that the oil reduced the depth of the oxygenated layer approximately half. This reduction may reduce subsurface benthic production and alter processes such as nutrient regeneration.  相似文献   

A sediment budget for the Choptank River estuary in Maryland,U.S.A.     

L.A. Yarbro  P.R. Carlson  T.R. Fisher  J.P. Chanton  W.M. Kemp 《Estuarine, Coastal and Shelf Science》1983,17(5):555-570

A sediment budget for the Choptank River, one of the three largest estuaries on the eastern shore of Chesapeake Bay, was developed from measurements of sediment carried in upland runoff, shore erosion, sedimentation, and levels of suspended sediments in estuarine waters. Shore erosion was the major source of sediment (340 × 10⁶ kg y^?1), contributing seven times more sediment than upland runoff. Low relief, the rural character of the Coastal Plain drainage basin, and the susceptibility of poorly consolidated shoreline materials to erosion contributed to the dominance of shore erosion over runoff as a sediment source. Box modelling indicated a net annual flux (14–44 × 10⁶ kg y^?1) of sediment from the Choptank River to Chesapeake Bay. A mass balance estimate of sedimentation, calculated as the difference between total inputs and loss at the mouth of the estuary, (350 × 10⁶ kg y^?1) agreed well with an estimate based on ²¹⁰Pb profiles (340 × 10⁶ kg y^?1) measured along the longitudinal axis of the estuary. Lead-210 sedimentation rates correspond to accumulation rates of 1·5–7·9 mm y^?1.  相似文献   

The Use of Pigment Signatures to Assess Phytoplankton Assemblage Structure in Estuarine Waters     

A. Ansotegui  J. M. Trigueros  E. Orive 《Estuarine, Coastal and Shelf Science》2001,52(6):689

The seasonal dynamics of chlorophyll a and the main accessory pigments accompanied by microscopic observations on live and fixed material were investigated in the Urdaibai estuary, Spain. Fucoxanthin was the dominant pigment during the peak in chlorophyll a, with which it was strongly correlated. Concentrations of fucoxanthin (81·30 μg l⁻¹) in the upper estuary were amongst the highest found in the literature, and were mainly associated with diatoms and symbiotic dinoflagellates. In the lower estuary, fucoxanthin showed values typical of coastal waters (<5 μg l⁻¹) and was mainly due to diatoms and prymnesiophytes. Chlorophyllb concentration was high along the estuary, followed the same seasonal pattern as chlorophyll a, and was associated with the presence of euglenophytes, chlorophytes and prasinophytes. High values of 19′-butanoyloxyfucoxanthin were often measured, but no organisms containing this pigment were observed in live or fixed samples. Alloxanthin and peridinin were found in low concentrations which was in agreement with cell counts of cryptophytes and peridinin-containing dinoflagellates. Two main patterns of phytoplankton assemblages were observed along the estuary. In the upper segments, during the chlorophylla maximum fucoxanthin containing algae masked the other algal groups, which were relatively more abundant during or after enhanced river flows. In the lower estuary, although dominated by fucoxanthin-containing algae, the other algal groups were important all year around. In this study, the use of diagnostic pigments has provided considerable insight into the temporal and spatial dynamics of phytoplankton assemblages by detecting phytoplankton taxa generally underestimated or overlooked by microscopy.  相似文献   

Cesium-137, metals and organic carbon in the sediments of the James River estuary,Virginia     

George T.F. Wong  Colin S. Moy 《Estuarine, Coastal and Shelf Science》1984,18(1):37-49

A wide variety of sedimentary subenvironments are found within a 10-km stretch of James River including a flood dominated channel (Rocklanding Channel) and its bank (Rocklanding Shoal), a shoal with a water depth of 1 m separating two channels (Point of Shoals), an ebb-dominated channel (Burwell Bay Channel) and its bank (Burwell Bay Bank) and a tributary (Warwick River). The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in the fine-grained sediments (i.e. < 63 μm) and the amount of fine-grained sediments in eight cores covering these subenvironments were determined. The sedimentation rates, estimated by Cs-137 geochronology, range from 0·4 to > 3 cm year^?1. The sedimentation rates in the Burwell Bay region are two or more, times those in the Point of Shoals and in the Rocklanding Channel and Shoal, reflecting the weaker currents in the Burwell Bay region. These sedimentation rates agree well with those obtained independently by measuring changes in the bathymetry of this area between 1873 and 1943. The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in surface sediments vary by a factor of two to three. The concentrations are higher in the Burwell Bay region, probably as a result of the higher rates of accumulation of recently formed sediments in these subenvironments. The inventories of fine-grained sediments and of Cs-137, Cu, Pb, Zn and organic carbon accumulated since 1954 are also up to an order of magnitude higher in the Burwell Bay region. Although the concentrations of fine-grained sediments in three cores obtained in this region are similar, the inventories still vary by a factor of two to three. The inventories of Cs-137, Cu, Pb, Zn, organic carbon and fine-grained sediments correlate well with each other indicating that Cs-137 can be a useful tracer for studying the fate of these metals and organic carbon in estuarine environments. The inhomogeneity of the concentrations and inventories of the different elements along a 10-km segment of a river suggests that a closely-spaced sampling programme is essential for characterizing the sedimentary provinces within an estuary. The concentrations of Cs-137, metals and organic carbon in the coarse-grained sediments (i.e. > 63 μm) are considerably lower than those in fine-grained sediments. Thus, the contribution of coarse-grained sediments to the total inventory of these elements is small.  相似文献   

The effects of prolonged aquatic macrophyte senescence on the biology of the dominant fish species in a southern African coastal lake     

A.K. Whitfield 《Estuarine, Coastal and Shelf Science》1984,18(3):315-329

The littoral zone of Swartvlei, an estuarine lake on the southern Cape coast, was characterized by extensive beds of submerged aquatic macrophytes. May 1979 marked the beginning of a regression phase which lasted more than three years. The senescence of the Potamogeton pectinatus and charophyte beds resulted in a 60% decline in primary production, a 74% slump in littoral invertebrate biomass and a 54% decline in the abundance of the fishes Monodactylus falciformis (Lacepede) and Rhabdosargus holubi (Steindachner) associated with the macrophytes. Gravimetric and calorific analyses of their food revealed that invertebrates and filamentous algae from the littoral zone were of major importance. The two fish species consumed approximately 2% of the primary production during the Potamogeton canopy phase and 3% during the Potamogeton senescent phase. Invertebrate consumption declined from 33 mg m^?2 day^?1 during the canopy phase to 8 mg m^?2 day^?1 during the senescent phase. The disappearance of the Potamogeton and charophyte beds also resulted in a decrease in the condition of both species but the effect was indirect and related mainly to the collapse of invertebrate stocks associated with the plants.  相似文献