Showing papers on "Water column published in 1984"

Chesapeake bay anoxia: origin, development, and significance.

Abstract: Anoxia occurs annually in deeper waters of the central portion of the Chesapeake Bay and presently extends from Baltimore to the mouth of the Potomac estuary. This condition, which encompasses some 5 billion cubic meters of water and lasts from May to September, is the result of increased stratification of the water column in early spring, with consequent curtailment of reoxygenation of the bottom waters across the halocline, and benthic decay of organic detritus accumulated from plankton blooms of the previous summer and fall. The Chesapeake Bay anoxia appears to have had significant ecological effects on many marine species, including several of economic importance.

A primer on trace metal-sediment chemistry

Abstract: In most aquatic systems, concentrations of trace metals in suspended sediment and the top few centimeters of bottom sediment are far greater than concentrations of trace metals dissolved in the water column. Consequently, the distribution, transport, and availability of these constituents can not be intelligently evaluated, nor can their environmental impact be determined or predicted solely through the sampling and analysis of dissolved phases. This Primer is designed to acquaint the reader with the basic principles that govern the concentration and distribution of trace metals associated with bottom and suspended sediments. The sampling and analysis of suspended and bottom sediments are very important for monitoring studies, not only because trace metal concentrations associated with them are orders of magnitude higher than in the dissolved phase, but also because of several other factors. Riverine transport of trace metals is dominated by sediment. In addition, bottom sediments serve as a source for suspended sediment and can provide a historical record of chemical conditions. This record will help establish area baseline metal levels against which existing conditions can be compared. Many physical and chemical factors affect a sediment's capacity to collect and concentrate trace metals. The physical factors include grain size, surface area, surface charge, cation exchange capacity, composition, and so forth. Increases in metal concentrations are strongly correlated with decreasing grain size and increasing surface area, surface charge, cation exchange capacity, and increasing concentrations of iron and manganese oxides, organic matter, and clay minerals. Chemical factors are equally important, especially for differentiating between samples having similar bulk chemistries and for inferring or predicting environmental availability. Chemical factors entail phase associations (with such sedimentary components as interstitial water, sulfides, carbonates, and organic matter) and ways in which the metals are entrained by the sediments (such as adsorption, complexation, and within mineral lattices). INTRODUCTION The basic goal of most chemically oriented water-quality studies is to describe or evaluate existing environmental conditions and to attempt to identify the source or sources of the constituents under investigation. An equally important goal is to attempt to predict or determine potential impacts. This heading could accommodate such subjects as bioavailability, amount of constituent transport, location of chemical sinks, ultimate fate, and potential toxic effects. Historically, the U.S. Geological Survey has attempted to assess trace metals in aquatic systems by analyzing water samples. This assessment has entailed determining concentrations of total and dissolved elements and compounds through the collection and analysis, respectively, of unfiltered and filtered water. Concentrations associated with suspended sediment (particulates, seston) are determined indirectly by the difference between total and dissolved concentrations. It is recognized that this approach casts doubt on the reliability of reported suspended-sediment chemical analyses. As a result, water quality tends to be evaluated on the kinds and concentration of various constituents found in solution (Feltz, 1980). However, in most aquatic systems, the concentration of trace metals in suspended sediment and the top few centimeters of bottom sediment is far greater than the concentration of trace metals dissolved in the water column. The strong association of numerous trace metals (for example, As, Cd, Hg, Pb, Zn) with seston and bottom sediments means that the distribution, transport, and availability of these constituents can not be intelligently evaluated solely through the sampling and analysis of the dissolved phase. Additionally, because bottom sediments can act as a reservoir for many trace metals, they must, for several reasons, be given serious consideration in the planning and design of any water-quality study. First, an undisturbed sediment sink contains a historical record of chemical conditions. If a sufficiently large and stable sink can be found and studied, it will allow the investigator to study changes over time and, possibly, to establish area baseline levels against which existing conditions can be compared and contrasted. Second, under changing environmental or physicochemical conditions (like pH, Eh, dissolved oxygen, bacterial action), sediment-bound trace metals can dissolve into the water column, possibly enter the food chain, and have a significant environmental impact. Third, several relatively inert or otherwise environmentally harmless inorganic constituents can degrade, or react with others, to form soluble and potentially toxic forms (for example, the conversion of elemental mercury to methyl-mercury). Finally, bottom sediments should be regarded as a major, if not the major, source of suspended sediment. Therefore, they must be investigated to determine transport potential. Under changing hydrologic conditions (such as a heavy storm or spring runoff), a localized pollution problem can suddenly become widespread and result in significant environmental impact. The foregoing discussion indicates that data on suspended and bottom sediments, as well as on the dissolved phase, are a requisite for the development of a comprehensive understanding of the impact of trace metals on water quality. Through the use of such additional data, it may be possible to begin to identify sources and sinks and the fate and potential effects of toxic or environmentally necessary metals. Similarly, sediment-chemical data are a requisite for transport modeling, for estimating geochemical cycles, and for inferring the availability of various trace metals in an ecological system.

Biogeochemistry of particulate organic matter in the oceans: results from sediment trap experiments

Abstract: Particulate organic matter collected in sediment traps from various oceanic regimes— Sargasso Sea, equatorial North Atlantic, central North Pacific, California Current, and Peru coastal upwelling—have been analyzed for their lipid and amino acid composition and flux. Despite rapid settling of the large particles through the water column and a relatively small depth gradient for total organic carbon flux, there are major changes in the composition and flux of lipids and amino acids associated with the particles. The rapid disappearance of the more labile compounds, such as amino acids and polyunsaturated fatty acids, with increasing depth indicates that the major sources of such compounds are in the upper part of the water column and that they are readily degraded as the particles sink. On the other hand, the intermittent appearance of large amounts of wax ester, along with the changing fatty acid composition of the particles, points to deep-water sources for some of these compounds.

Influence of Paleoenvironmental Factors on Preservation of Organic Matter in Middle Cretaceous Greenhorn Formation, Pueblo, Colorado

Abstract: Sedimentological and geochemical studies of the Upper Cretaceous Hartland Shale and overlying Bridge Creek Limestone Members of the Greenhorn Formation reveal close associations between abundance of current-induced sedimentary structures, extent of bioturbation, and type of preserved organic matter. Abundant hydrogen-rich organic matter (4-5 wt. %) and low sulfur to organic carbon ratios are characteristic of the laminated facies, which lack current-induced sedimentary structures. Sparse hydrogen-poor organic matter (0.1-0.5 wt. %) and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies, which contain numerous sedimentary structures indicative of currents. The concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively (by currents) rather than by the rate of oxygen consumption (by decomposition). Thus, paleoclimatic and paleo-oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units. It is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen-depleted bottom water and high preservation of organic matter, thus accounting for the intermittent widespread deposition of organic-rich strata during maximum transgression and depth of the Greenhorn sea. The lateral association of voluminous deltaic deposits with dee -water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the Hartland Shale and Bridge Creek Limestone Members.

Hierarchical control of phytoplankton succession by physical factors

Abstract: The influence of physical factors on phytoplankton succession was assessed during an annual cycle in the St. Lawrence Estuary (Canada), where nutrients remain abundant throughout the whole year. Typically, the phytoplankton production period is short (Jun to Sep) and characterized by the occurrence of 3 distinct peaks. The July bloom was dominated by the 2 diatoms Thalassiosira nordenskioldii and Chaetoceros debilis, while Leptocylindrus minimus and Nitzschia seriata were dominant a t the beginning and at the end of September, respectively. The occurrence of the 3 bloom periods is related to an increase in mean light intensity in the mixed layer, caused by strong density stratification which decreases the depth of the mixed layer. During these bloom periods, the succession of diatom species is mainly controlled by variations in temperature. Flagellates were observed all yearround, although they were more abundant during the diatom bloom periods. Their abundance is related to variations in surface temperature. In the Estuary, where nutrients are usually non-limiting, the observed succession of taxa is restricted to the first stage of the Margalef (1958) succession model (small cells with high growth rates, which are typical species for frequently destabilized environment). Our results demonstrate that the frequency of destabilization of the water column selects the growth rates of the cells, through nutrient conditions. Mean light intensity in the mixed layer determines the occurrence of non-motile forms such as diatoms, and temperature sets the conditions for optimal metabolic activity (flagellate numbers and succession of diatom species). This results in a conceptual model where stability conditions, mean light in the mixed layer and temperature hierarchically control phytoplankton succession.

Dispersal and recruitment of blue crab larvae in Delaware Bay, U.S.A.

Abstract: Results of a three-year survey of the occurrence of Callinectes sapidus larvae in the mouth of Delaware Bay indicated that stage I zoea larvae were most abundant insurface water as compared to mid-depths and near bottom. The major peak in abundance of stage I zoea larvae occurred in early August with a secondary peak in early September. Peaks in abundance of megalopae occurred five weeks after the respective peaks in zoeal abundance. Zoea stages II–VIII were not collected in the bay mouth. Results of sampling every 3 h over consecutive tidal cycles showed that stage I zoea larvae were most common in the water column on ebbing tidal currents. Megalopae were most common in the water column on flooding tidal currents, suggesting a tidally related, vertical migration. It was concluded that stage I zoea larvae are flushed from the estuary and undergo development on the continental shelf. Megalopae are then transported back to inshore waters by a combination of winds and currents and invade the estuary by means of migration into the water column on flooding tidal currents and migration to the bottom on ebbing tidal currents.

Detrital Organic Fluxes Through Pelagic Ecosystems

Abstract: Menzel (1974) wrote ‘particularly lacking is information on the rates of input, utilisation and decomposition of organic matter to and in the deep sea, and the extent to which these processes influence the chemistry of seawater.’ Here we are particularly concerned with the ecological effects and fluxes of detrital organic matter throughout the water column. The steady increase of knowledge of the vertical structure of oceanic midwater communities has gradually increased awareness of the importance of the rain of detrital material in fuelling the bathypelagic and deep benthic communities (e.g. Vinogradov, 1968; Angel and Baker, 1982).

Organic matter degradation and biogenic element cycling in a nearshore sediment (Kiel Bight)

Abstract: Benthic degradation of organic matter and the cycling of its C, N, P components was investigated at a coastal station (20 m) in Kiel Bight (western Baltic). Annual rates of carbon combustion and nutrient release from the sediment were derived from a comparison of input and burial of organic matter in the top sediment layers and from sediment oxygen consumption and nutrient release rates as determined by in situ enclosure experiments (2.9 mol 02*m-2.yr-1, 0.16 mol N*m-2*yr-1, 0.020 mol P.m-2.yr-1, and 0.58 mol Si*m-2*yr-‘). A long term incubation was used to simulate chemical changes during the transition to anoxic conditions. The comparison of diffusive fluxes calculated from porewater profiles with total release rates indicates that the sediment surface is the major site of organic matter degradation, as a consequence of low sedimentation rate. From the organic matter reaching the bottom via sedimentation only 22% of the organic carbon (13% N,, and 15% POJ is accumulated below 10 cm as sedimentary carbon and its reduced sulfur equivalent. While 75% of the carbon and 66% of the organic phosphorus input are returned to the water column, only half of the nitrogen input is released from the bottom; the rest is probably lost due to denitrification. Benthic flux contributes ~20% to the annual P and N requirements for the pelagic primary producers.

Arsenic, antimony, and germanium biogeochemistry in the Baltic Sea

Abstract: Arsenic, antimony, and germanium species concentrations have been determined from fivehydrographic stations along the central axis of the Baltic Sea from the Bornholm Basin to theGulf of Finland. Arsenic and antimony concentrations are lower than in the open oceans and inmost rivers. In the oxic waters, the pentavalent species of As and Sb predominate, while in theanoxic basins, the distribution shifts to the trivalent species and possibly some sulfo-complexes.Methylated arsenic species make up a large fraction of dissolved As in the surface waters, andmethylated species of As, Sb, and Ge are detectable throughout the water column. Germanicacid concentrations are about ten times higher than in the ocean and much higher than can beaccounted for by Ruvial input. The vertical distributions of arsenic, antimony, and germaniumwithin the Baltic Sea are controlled by biogeochemical cycling, involving biogenic uptake,particulate scavenging and partial regeneration. A mass balance including river and atmosphericinputs, exchange with the Atlantic through the Belt Sea, and removal by sediment depositionsuggests that anthropogenic inputs make a significant contribution to the budgets of all threeelements, with atmospheric fluxes dominating the input of Ge to the Baltic. DOI: 10.1111/j.1600-0889.1984.tb00232.x

Thermohaline circulation below the Ross Ice Shelf: A consequence of tidally induced vertical mixing and basal melting

Abstract: The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice shelf cavity, where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at - 1.8 C), formed by winter sea ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at -2.2 C), produced in the well-mixed region, flows out of the sub-ice shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature.

Chemical oceanography of the Indian Ocean, North of the equator

Abstract: Chemical oceanographic studies in the North Indian Ocean have revealed several interesting and unique features. These are caused by the diverse conditions prevailing in the area which include immense river runoff in the northeast (Bay of Bengal) and a large excess of evaporation over precipitation and runoff in the northwest (Arabian Sea, Persian Gulf and Red Sea), resulting in the formation of several low- and high-salinity water masses. The occurrence of coastal upwelling seasonally makes the region highly fertile, and the existence of Asian landmass, forming the northern boundary, prevents quick renewal of subsurface layers. Consequently, dissolved oxygen gets severely depleted below the thermocline and reducing conditions prevail at intermediate depths (ca. 150–1200m) resulting in the reduction of nitrate (denitrification). The North Indian Ocean may contribute up to 10% of the global marine denitrification. The “denitrified” nitrogen, when combined with the rate of photosynthetic production reaching below the euphotic zone, gives the average residence time of water between 75 and 1200m as 43–51 years. The inorganic nutrient concentrations in the subsurface layers are very high in close proximity of the euphotic zone. The two-layered circulation leads to an active recycling of nutrients. The presence of organic fractions of nitrogen and phosphorus in significant concentrations in the deep water suggest that oxidation of organic matter is incomplete even great depths. The relationships between the apparent oxygen utilization (AOU) and nutrients and the stoichiometric composition of organic matter, deduced from the oxidative ratios and by analysis of plankton, are not very different from other oceanic areas. Higher nutrients and lower oxygen concentrations occur in the bottom layer as compared to the overlying water column in deep waters of the Bay of Bengal and Arabian Sea, suggesting that considerable quantities of organic matter reach the deep-sea floor, probably as fecal pellets, and get oxidized in the bottom layer. Very high silicate concentrations occur in the bottom water, especially in the Arabian Sea, decreasing steadily southward, indicating the solution of diatomaceous sediments from the sea floor. The silicate-rich waters appear to move southward over the north-bound, silicate-poor bottom water, resulting in the occurrence of a deep silicate maximum. The calcium: chlorinity ratio in the North Indian Ocean is appreciably higher than the oceanic averages. This is probably due to: (1) a high rate of river runoff in relatively small area; and (2) excessive stripping of calcium at the surface associated with a high biological productivity and its subsequent addition and regeneration in the bottom waters. The upward flux of calcium appears to be higher than in other oceanic areas. Other major constituents investigated (fluoride and magnesium) do not show any anomally. The partial pressure of carbon dioxide in surface waters of the North Indian Ocean is higher than that in the atmosphere which results in a net flux of carbon dioxide from the sea to the atmosphere. Stagnation of intermediate layers, coupled with high organic productivity at the surface, results in high total carbon dioxide content at these levels. An increase in carbonate ion concentration occurs with depth in deep waters (>1000m). Calcite saturation depth varies from 1000 to 3000m, increasing proressively southward. The lysocline lies at about 4000m depth, while the carbonate critical depth is located at 4000–5100m. The lysocline appears to be related to the “critical carbonate ion concentration” of 90±5 μ m kg −1 .

Hypolimnetic phosphorus retrieval by diel vertical migrations of lake phytoplankton

Abstract: SUMMARY. I. Movement of 33P from hypolimnion to epilimnion in a small, dystrophic lake was investigated using small-diameter experimental tubes enclosing thermally stratified water columns. This approach was made possible by the extremely sharp stratification found in such lakes, in which the euphotic zone closely coincides with the epilimnion. 2. The vertical distribution of inorganic phosphorus in the lake showed a sharp increase across the thermocline so that enhanced concentrations were available to phytoplankton just below the thermocline. Inorganic nitrogen concentrations did not show such a marked relation to thermal stratification. 3. One abundant motile alga (Cryptomonas marssonii) showed striking and regular vertical migrations in the lake, moving below the thermocline at night and returning to the surface waters in early morning. These migrations took cells across a 10°C temperature gradient. Non-motile phytoplankton showed constant vertical distributions. 4. In the experimental tubes an upward movement of phosphorus took place from hypolimnion to epilimnion which was only attributable to transport by phytoplankton cells undertaking active vertical migrations. No equivalent movement of phosphorus occurred in control tubes from which algae were absent. 5. The possible significance of such nutrient retrieval is discussed with reference to plankton phosphorus budgets and competition between phytoplankton species.

Water column dissolution of aragonite in the Pacific Ocean

Abstract: Pelagic pteropods are an important component of the oceanic CO2 system. Their shells appear to be a principal source of excess alkalinity in the upper water column of the North Pacific Ocean. Dissolution of aragonite must therefore be taken account of in generating models of the oceanic CO2 system and is also an important cause of sample loss from long-term sediment traps deployed in undersaturated seawater.

The seagrass filter: purification of estuarine and coastal waters

Abstract: Seagrasses can provide a “filtering” mechanism in estuarine waters by trapping suspended sediments and taking up dissolved water column nutrients. These two processes are discussed from the perspective of water filtration by seagrasses in an effort to establish the plants1 benefit to the estuarine system. Previous examinations of such processes have stressed environmental influences on seagrass plants, overlooking the impact that seagrasses may have on the environment. Our approach to the concept of seagrass as a filter has been to examine previous work and combine it with results of measurements of suspended sediment and dissolved nutrient removal in culture tank systems with and without seagrasses. In manipulation experiments, suspended sediment removal was measured by the increase in light penetration, and varied according to added sediment type. Nutrient addition and subsequent depletion in the water column of the culture tanks was measured to determine seagrass community uptake rates. These rates were then extrapolated to a somewhat eutrophic coastal environment for evaluation of potential nutrient removal by seagrasses. A synopsis of these filtering experiments and other studies indicates that seagrass communities remove material of natural or human origin from estuarine waters, but excessive loading of nutrients or suspended material upsets the balance of the seagrass ecosystem, promoting degradation of the seagrass beds and loss of the filtering mechanism.

Investigations on the plankton community of Balsfjorden, Northern Norway. The phytoplankton 1976–1978. Environmental factors, dynamics of growth, and primary production

Abstract: Measurements of incident and sub-surface radiation, plant nutrients, particulate carbon and nitrogen, and ‘in situ’ carbon assimilation were performed from February 1976 to November 1978. The onset, culmination, and magnitude of the spring bloom is described. The dynamics of the phytoplankton spring bloom were highly governed by incident radiation. The spring bloom probably ended because of lowered sub-surface irradiance, due to increased cell densities, and a high degree of mixing of the water column. The spring bloom ended with higher nutrient values than in more southerly areas. The summer situation was comparable with other areas with a ‘chemostat’-growth system. Grazing was probably also an important factor in regulating phytoplankton biomass during summer. Primary production estimates were comparable to other fjords and coastal areas (100 gC/m3 per year) along the Norwegian coast and were probably underestimated due to the methods applied.

Invertebrate drift: Behavioral experiments with intertidal meiobenthos†

Abstract: Water column drift of benthic invertebrates may be the result of either active migration from the bottom or of erosion by water currents. Recent studies have shown that marine meiobenthos occur regularly in the water column; however, whether this is due to active (behavioral) processes or passive (erosional) processes is not known. A series of experiments were performed that showed meiobenthos do not regularly emerge, suggesting that drift of meiobenthos is due to erosion. The behavior of the animals can, however, influence their susceptibility to suspension. Fauna most active on the sediment surface (primarily harpacticoid copepods) were most susceptible to passive suspension. A multi‐factorial experiment tested the effects of time of day (light vs. dark) and tide (high, low, flow) on number of animals active on the sediment surface. Animals frequenting the sediment surface did so only in the absence of currents and regardless of time of day. Animals began to burrow as soon as flow increased. If they wer...

The oceanic carbonate system: a reassessment of biogenic controls.

Abstract: Fluxes of biogenic carbonates moving out of the euphotic zone and into deeper undersaturated waters of the North Pacific were estimated with free-drifting sediment traps. Short-duration (1 to 1.5 day) sampling between 100 and 2200 meters points to a major involvement in the oceanic carbonate system by a class of organisms which had been relegated to a secondary role—aragonitic pteropods. Pteropod fluxes through the base of the euphotic zone are almost large enough to balance the alkalinity budget for the Pacific Ocean. Dissolution experiments with freshly collected materials shed considerable light on a mystery surrounding these labile organisms: although plankton collections from net tows almost always contain large numbers of pteropods, these organisms are never a major component of biogenic materials in long-duration sediment trap collections. Their low abundance in long-duration collections results from dissolution subsequent to collection. Shortduration sampling showed significant increases in the ratio of calcitic foraminifera to aragonitic pteropods in undersaturated waters, indicating the more stable mineralogic form, calcite, was preserved relative to aragonite. Approximately 90 percent of the aragonite flux is remineralized in the upper 2.2 kilometers of the water column.

Particle flux and trace metal residence time in natural waters1,1

Abstract: A simple inverse relationship between trace metal residence time and particle flux through the water column is tested on the trace metals Zn/sup 2 +/ in fresh water and Th(IV) in ocean water systems with available data on the vertical flux and concentration of particulate matter and Zn/sup 2 +/ in lakes or on the disequilibrium of U/Th nuclides in the ocean. Natural or model aquatic ecosystems with different chemical compositions and particle fluxes confirm the concept that the particle flux through the water column is the major factor regulating trace metal concentrations in natural waters.

Vertical transport and sedimentation of hydrocarbons in the central main basin of Puget Sound, Washington [USA].

Abstract: Concentrations and vertical fluxes of total carbon, aliphatic hydrocarbons, and polycyclic aromatic hydrocarbons (PAH) were determined in suspended matter and the underlying sediments in the central main basin of Puget Sound, Washington Suspended matter was collected seasonally at four depths in the water column using sequential sampling traps The flux of PAH through the 50- and 100-m horizons accounted for 84% of the PAH accumulating in the underlying surface sediments The concentration of PAH in the suspended matter from these traps, however, was 3 times greater than the concentration of PAH in the surficial bottom sediments Laterally transported suspended matter in the bottom boundary layer is apparently diluting the PAH during sedimentation The flux of aliphatic hydrocarbons to the sediments was greater than the accumulation rate in the sediments, indicating an alteration of these hydrocarbons within the water column or differential particle transport The vertical distributions of hydrocarbons in the bottom sediments showed concentration increases parelleling the urbanization of the Puget Sound basin 30 references

226Ra and 228Ra in the mixing zones of the Pee Dee River-Winyah Bay, Yangtze River and Delaware Bay Estuaries

Abstract: 226Ra and 228Ra have non-conservative excess concentrations in the mixing zones of the Pee Dee River-Winyah Bay estuary, the Yangtze River estuary, and the Delaware Bay estuary. Laboratory experiments, using Pee Dee River sediment, indicate desorption of 226Ra to increase with increasing salinities up to 20‰. In Winyah Bay desorption from river-borne sediments could contribute almost all of the increases for both isotopes. Desorption adds only a portion of the excess 228Ra measured in the Yangtse River and adjacent Shelf waters and Delaware Bay. In the Yangtze River the mixing zone extends over a considerable portion of the Continental Shelf where 228Ra is added to the water column by diffusion from bottom sediments, while 226Ra concentrations decrease from dilution. Diffusion of 228Ra from bottom sediments in Delaware Bay primarily occurs in the upper part of the bay (< 22‰ water) where fine grained sediments predominate. A diffusive flux for 228Ra of 0·33 dpm cm−2 year was determined for Delaware Bay.