Plutonium,radiocesium and radiocobalt in sediments of the Hudson River estuary

Anthropogenic radionuclides have reached the Hudson estuary as global fallout from nuclear weapons testing and through local releases from commercial nuclear reactors. Significant activities of²³⁸Pu and^239,240Pu (fallout-derived),¹³⁴Cs and⁶⁰Co (reactor-released), and¹³⁷Cs (derived from both sources), have accumulated in the sediments throughout the estuary, with the primary zone of accumulation near the downstream end of the system in New York harbor. The estuary appears to have trapped nearly all of the^239,240Pu delivered as fallout, and consequently, ocean dumping of dredged harbor sediment is currently the primary means for the net transport of these nuclides to coastal waters. In contrast, only 10–30% of the¹³⁷Cs,¹³⁴Cs and⁶⁰Co delivered to the estuary have been retained on the fine particles which accumulate at a rapid rate in the harbor.The primary factors which have governed the distribution of anthropogenic radionuclides in Hudson sediments are: (1) spread of fine particles labeled with both fallout and reactor nuclides throughout the axis of the estuary, (2) differences in timing of the peak fallout years (1962–1964) and years of maximum reactor releases (1971–1972), (3) large variations in sediment accumulation rates, ranging from a few millimeters per year or less to many tens of centimeters per year, (4) appreciable desorption of¹³⁷Cs and¹³⁴Cs from particles at higher salinities, and (5) possible enhanced desorption of⁶⁰Co at higher salinities (relative to¹³⁴Cs and¹³⁷Cs) which may be associated with the release of reduced manganese from the harbor sediments.     

Pu, Cs and excess Pb in Russian Arctic sediments

The activity ratios of Pu and radiocesium isotopes have been used to delineate the major sources (such as global and close-in (debris) fallout, nuclear fuel reprocessing and fabrication plant effluents) in the environment. We have measured ²³⁸Pu, ^239,240Pu, ¹³⁷Cs, and excess ²¹⁰Pb concentrations in 107 surficial sediments as well as in 5 sediment cores collected in the summer months of 1993 and 1994 from the Ob and Yenisey Rivers (Russia) and the Kara sea. A comparison of the sediment core inventories of ^239,240Pu and ¹³⁷Cs, along with the ²³⁸Pu/^239,240Pu activity ratios, with those expected from global fallout allows us to estimate the relative amounts, if any, of reactor-derived ²³⁸Pu and ^239,240Pu from the dumped reactor sites in the study area.

In surficial sediment samples collected in 1993 and 1994, the ^239,240Pu concentrations varied between 4.2 and 856 mBq kg⁻¹, with a mean of 239 mBq kg⁻¹. In samples with a measurable ²³⁸Pu, the ²³⁸Pu/^239,240Pu activity ratios varied between 0.010 and 0.069, with an average value of 0.035 ± 0.014. This range can be compared to the average ²³⁸Pu/^239,240Pu activity ratio of 0.030 for the year 1993 from nuclear weapons testing and SNAP fallout obtained from soil studies, indicating very little (≤ 5%) additional sources of ²³⁸Pu to the sediments in the study area. The inventories of Pu in the 5 sediment cores from the study area varied between 2.67 ± 0.67 and 24.5 ± 2.2 Bq m⁻² with a mean value of 8.83 Bq m⁻². The ¹³⁷Cs concentrations in the upper 3 cm of the sediments varied between below detection limit to 71.4 Bq kg⁻¹, with a mean of 14.9 Bq kg⁻¹. The ¹³⁷Cs inventories in the 5 sediment cores varied between 156.7 ± 28.3 and 1600 ± 153.3 Bq m⁻², with a mean value of 583.3 Bq m⁻². The mean ratio of inventories of Pu to that of ¹³⁷Cs, 0.015, is comparable to the values in other places in the Arctic region. There is a significant correlation between total organic carbon and concentrations of ¹³⁷Cs, ^239,240Pu and ²¹⁰Pb, suggesting that organic matter-enriched fine particles are a likely carrier phase for these nuclides. The ratio of ¹³⁷Cs/^239,240Pu also suggests that most of these nuclides are derived from global fallout.     

Fallout radionuclides in the Pacific Ocean: Vertical and horizontal distributions,largely from GEOSECS stations

From GEOSECS stations, largely, the 1974 distributions of Pu and of¹³⁷Cs are described in the Pacific Ocean north of about 20°S latitude. Changes in some of these distributions are described from 1978 cruises by the authors.The Pacific exhibited, everywhere, a shallow subsurface layer of Pu-rich water with its concentration maximum at about 465 m in 1974; over a large portion of the central North Pacific a second layer of Pu-labelled water, less concentrated than the shallow layer, lay just above the bottom. Similar features were not observed in the case of¹³⁷Cs.The inventories of both Pu and¹³⁷Cs in the water column at most 1974 stations are substantially greater than those to be expected from world-wide fallout alone; these inventory excesses appear to be attributable to close-in fallout, but only if the ratio Pu/¹³⁷Cs in this source was much higher than in world-wide fallout. The North Pacific mean ratio of the inventories is 2.2 times that observed in world-wide fallout.Resolubilization of Pu both from sinking particles and from sediments explains peculiarities of its depth distributions.There is little evidence for tracer movement by sliding downward along density surfaces;¹³⁷Cs appears to have moved to depth by downmixing at the edge of the Kuroshio, and then moved horizontally and upward alongσ_t contours. The shallow Pu-rich layer shows no coordination with density, salinity or O₂ isopleths. The deep Pu-rich layer is restricted to a narrow range of O₂ concentrations that confirm its origin in the Aleutian Trench and rapid spread southward and laterally. Near-bottom circulation processes have been much more active than here-to-fore described.     

Plutonium and210Pb distributions in northeast Atlantic sediments: subsurface anomalies caused by non-local mixing

The depth distributions of²¹⁰Pb and^239,240Pu measured in a suite of box cores collected from water depths of 4000–5000 m in the northeast Atlantic Ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna. Small-scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters.²¹⁰Pb and^239,240Pu activity distributions from each subcore exhibit a high degree of correlation, and most tracer profiles exhibit one or more subsurface maxima.One-dimensional, “biodiffusion” analogue models do not adequately simulate the principal features of this data set. However, an inverse “conveyer belt” mixing model which simulates subsurface egestion (or a functionally equivalent process) of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima. Single-event and continuous subsurface egestion models have been formulated and solved for different “feeding rates” and background biodiffusive fields. The single-event model provides a better fit to the data and, in particular, ensures the observed, high degree of correlation between the²¹⁰Pb and^239,240Pu activity profiles, regardless of the different tracer input functions. The most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum Sipunculida which dominates the biomass below a depth of 3 cm.     

Variability of natural and bomb-produced radionuclide distributions in abyssal red clay sediments

The nature of sedimentation and mixing are examined in abyssal red clay sediments from the North Central Pacific using three types of indicators: ²³⁰Th/²³²Th, organic¹⁴C, and¹³⁷Cs and ^239.240Pu.²³⁰Th/²³²Th analysed revealed that the clay sedimentation rate in three box cores collected within a 50 km radius was less than 1.0 mm/10³ yr. However, analyses of the organic carbon in thin layers of sediment revealed that radiocarbon was present much deeper in the cores (down to 20 cm) than was expected from the ²³⁰Th/²³²Th distribution. In addition, both the stratigraphy and inventory of radiocarbon was significantly different between box cores. The distributions and inventories of¹³⁷Cs and^239.240Pu were similar to that found for radiocarbon, further illustrating the spatial variability of radionuclides in oligotrophic North Pacific red clays. These data suggest that bioturbational processes are important for transporting organic carbon down into the sediment column.     

Atmospherically-derived radionuclides as tracers of sediment mixing and accumulation in near-shore marine and lake sediments: Evidence from7Be,210Pb,and239,240Pu

Cosmogenic⁷Be(t_1/2 = 53.3days) has been used to estimate particle-mixing rates in the upper layers of lacustrine and near-shore marine sediments. Excess²¹⁰Pb and/or^239,240Pu have provided limits on rates of sediment accumulation in these environments and indices of the efficiency of the sediments as collectors of reactive nuclides over longer time scale.In sediment cores from Long Island Sound (marine) and Lake Whitney (fresh-water)⁷Be was measurable in the top 2–3 cm. Diffusion-analog particle-mixing coefficients calculated from these data are in the range of 10^?7 cm²/s. For Long Island Sound the coefficients are lower by factors of 3–6 than those estimated from the depth distributions of excess²³⁴Th at the same stations [14]. For Lake Whitney the calculated mixing coefficient is an upper limit because of the possibility of a sampling artifact.Measurements of total (wet + dry) atmospheric deposition of⁷Be in New Haven give an average flux of 0.07 dpm/cm² day during March-November, 1977; this is equivalent to a steady-state inventory of 5.4 dpm/cm² in a perfect collector. Sediment cores from Long Island Sound contain about half this⁷Be inventory, consistent with either a mean residence time for⁷Be in the water column of about one half-life or with post-depositional loss of⁷Be from Long Island Sound sediments. The Lake Whitney cores contain about 5 dpm/cm², much nearer the atmospheric delivery. A higher inventory of⁷Be in fresh-water, as compared to marine, sediments could be due either to a shorter mean residence time for⁷Be in fresh water or to lateral transport processes in the lake or its catchment. High inventories of excess²¹⁰Pb and^239,240Pu in Lake Whitney sediments demonstrate the importance of lateral transport on longer time scales at least.     

241Pu and241Am in sediments from coastal basins off California and Mexico

In sediments deposited in the coastal basins off the western North American continent since the early 1960's, there is more²⁴¹Am activity than one would predict if its presence was solely due to the decay of²⁴¹Pu that was produced during the testing of weapons in 1961–1962 (taken as July 1, 1962 for calculations). This excess can be accounted for by the decay of²⁴¹Pu, if pre-1962 fallout (fallout from the pre-moratorium testing) has been continuously introduced into the recent sediments along with fallout from post-moratorium testing. This hypothesis is supported by the plutonium depth profiles which do not reflect direct fallout from the atmosphere, as characterized by two peaks corresponding to the two major weapons testing periods, but continuously increasing plutonium and americium concentrations from 1954 to 1974. Thus, the nuclides may be coming from a large reservoir that has accumulated and mixed fallout since 1952. Such a concentration gradient for all of the nuclides requires their immobilization in the sediment after deposition.     

Sedimentary processes in the inner New York Bight: Evidence from excess210Pb and239,240Pu

Particle-reactive radionuclides were determined in sediments from the inner New York Bight to trace transport and storage of fine-grained sediments and associated reactive materials. Seven sediment ? cores 20–50 cm in length were analyzed for water content, loss on ignition (LOI) and excess²¹⁰Pb; three of these were also analyzed for^239,240Pu. Excepting some depth horizons in a core from a dredge-spoil dumpsite, every sample analyzed contained excess²¹⁰Pb. Variations in the concentration of excess²¹⁰Pb with depth in the sediment at all stations correlated strongly with LOI, which apparently traces that fraction of the sediment which is active in removing reactive elements from the water column. In the cores analyzed for^239,240Pu, every sample contained finite Pu, and Pu concentrations correlated strongly with excess²¹⁰Pb.The radionuclide distributions may be simply viewed as products of steady-state sediment accumulation or of mixing. Geochemically reasonable accumulation rates are very high (0.5–2.6 g/cm² y) and could probably only be sustained by offshore transport of dumped materials. At the other extreme the relationships between excess²¹⁰Pb and LOI are compatible with rapid mixing of a²¹⁰Pb carrier phase (traced by LOI) into the pre-existing substrate with little or no actual accumulation. Other non-steady-state processes, such as sediment gravity flow, could also explain the observed distributions.Measured sediment inventories (dpm/cm²) of excess²¹⁰Pb and Pu at these stations are greatly in excess of those supportable by direct atmospheric deposition: lateral supply is required. Incorporation of sedimentary fines into the sand substrate could make the inner New York Bight an important repository of reactive materials.     

Radionuclide ratios in wet and dry deposition samples from June 1976 through December 1977

²³⁸Pu,²³⁹Pu and¹³⁷Cs in rain and dry fallout and⁹⁰Sr in rain samples were measured at Woods Hole, Massachusetts, from June 1976 through December 1977. The dry fallout was estimated to be about 7.8% of the total deposition of²³⁹Pu and¹³⁷Cs.²³⁹Pu/¹³⁷Cs ratios, almost constant at about 0.011 in rain or dry fallout, February through December 1977, suggested that fractionation between the refractory and volatile radionuclides is insignificant in stratospheric fallout. This supports the idea of regional homogeneity of radionuclide ratios in fallout.     

Can channel banks be the dominant source of fine sediment in a UK river?: an example using 137Cs to interpret sediment yield and sediment source

Cultivated fields have been shown to be the dominant sources of sediment in almost all investigated UK catchments, typically contributing 85 to 95% of sediment inputs. As a result, most catchment management strategies are directed towards mitigating these sediment inputs. However, in many regions of the UK such as the Nene basin there is a paucity of sediment provenance data. This study used the caesium‐137 (¹³⁷Cs) inventories of lake and floodplain cores as well as the ¹³⁷Cs activities of present day sediment to determine sediment provenance. Sediment yields were also reconstructed in a small lake catchment. Low ¹³⁷Cs inventories were present in the lake and floodplain cores in comparison to the reference inventory and inventories in cores from other UK catchments. Caesium‐137 activities in the present day sediments were low; falling close to those found in the channel bank catchment samples. It was estimated that 60 to 100% of the sediment in the Nene originated from channel banks. Pre‐1963 sediment yields were approximately 11.2 t km^?2 yr^?1 and post‐1963 was approximately 11.9 t km^?2 yr^?1. The lack of increased sediment yield post‐1963 and low sediment yield is unusual for a UK catchment (where a yield of 28 to 51 t km^?2 yr^?1 is typical for a lowland agricultural catchment), but is explained by the low predicted contribution of sediment from agricultural topsoils. The high channel bank contribution is likely caused by the river being starved of sediment from topsoils, increasing its capacity to entrain bank material. The good agreement between the results derived using cores and recently transported sediments, highlight the reliability of ¹³⁷Cs when tracing sediment sources. However, care should be taken to assess the potential impacts of sediment particle size, sediment focusing in lakes and the possible remobilization of ¹³⁷Cs from sedimentary deposits. Copyright © 2016 John Wiley & Sons, Ltd.     

Pu in coastal marine environments

Analysis of water samples from the New York Bight area and Narragansett Bay reveals that a small fraction of the total Pu (probably Pu (III + IV) species) is continuously removed to the sediments at a rate similar to that of the particle-reactive isotope²²⁸Th. A more “soluble” Pu species appears to be released at times from the sediments to the water column in these nearshore regions. Sediments in shallow areas of the New York Bight south of Rhode Island and Narragansett Bay have high Pu inventories and relatively deep penetration of this element, although the net sediment accumulation rate is generally low (<0.03 g/cm² yr). The high Pu inventories can be explained if both sediment resuspension and sediment mixing are assumed to be the major controlling factors for the effective transfer of Pu from the water column to the sediments. By simultaneous modelling of the depth distribution of three tracers which operate on vastly different time scales:²³⁴Th (half-life 24 days),²¹⁰Pb (half-life 22 years) and^239,240Pu (introduced into the environment during the past 30 years), bioturbation rates ranging from 4 to 32 cm²/yr in the surface mixed layer (5–10 cm thick) and from 0.3 to 2.5 cm²/yr in the layer below (up to 40 cm thick) and net sediment accumulation rates of approximately zero to 0.14 g/cm² yr were calculated for these areas.     

The state of Lake Ladoga pollution by global 90Sr, 137Cs, and 239,240Pu

The state of radioactive pollution of Lake Ladoga has been studied. The purification half-life of lake water from ⁹⁰Sr was found to be 21.7 year. The ratio of ⁹⁰Sr storage in lake water volume to its storage in silts (0?C10 cm layer) was 2: 1. Lake water purification from global ¹³⁷Cs was slower than that from ¹³⁷Cs originating from Chernobyl emergency emission because of the chronic supplement of global ¹³⁷Cs reserve by atmospheric fallouts. The behavior of ⁹⁰Sr, ¹³⁷Cs, and ^239,240Pu in bed soils was in agreement with the geochemical nature of the elements. By the distribution of ^{239, 240}Pu in bed soils, the sedimentation of substances of non-radiation nature was estimated at 0.3 and 0.5 mm/year at denting and flat relief, respectively.     

Natural and anthropogenic radionuclide distributions in the northwest Atlantic Ocean

We have used in-situ pumps which filter large volumes of sea water through a 1 μm cartridge prefilter and two MnO₂-coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans. Two sites in the northwest Atlantic show subsurface maxima of the fallout radionuclides¹³⁷Cs,^239,240Pu and²⁴¹Am. Although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions, comparison of predicted and measured water column inventories suggests that at least 35–50% of the Pu and²⁴¹Am are supplied to the deep water by advection.The depth distributions of the naturally occurring radionuclides²³²Th,²²⁸Th and²³⁰Th reflect their sources to the oceans.²³²Th shows high dissolved concentrations in surface waters, presumably as a result of atmospheric or riverine supply. Activities of²³²Th decrease with depth to values 0.01 dpm/1000 l.²²⁸Th shows high activities in near surface and near bottom water, due to the distribution of its parent,²²⁸Ra. Dissolved²³⁰Th, produced throughout the water column from²³⁴U decay, increases with depth to 3000 m. Values in the deep water (> 3000 m) are nearly constant ( 0.6–0.7 dpm/1000 l), and the distribution of this tracer (and perhaps other long-lived particle-reactive tracers as well) may be affected by the advection inferred from Pu and²⁴¹Am data.The ratio of particulate to dissolved activity for both²³⁰Th and²²⁸Th is 0.15–0.20. This similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium. Moreover, in mid-depths²²⁸Th tends to have a higher particulate/dissolved ratio than²³⁰Th, suggesting uptake and release of²³⁰Th and²²⁸Th by different processes. This could occur if²²⁸Th, produced in surface water, were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking.²³⁰Th, produced throughout the water column, may more closely approach a sorption equilibrium at all depths.²³⁰Th,²⁴¹Am and^239,240Pu are partitioned onto particles in the sequence Th > Am > Pu with 15% of the²³⁰Th on particles compared with 7% for Am and 1% for Pu. Distribution coefficients (K_d) are 1.3–1.6 × 10⁷ for Th, 5–6 × 10⁶ for Am and 7–10 × 10⁵ for Pu. The lower reactivity for Pu is consistent with analyses of Pu oxidation states which show 85% oxidized (V + VI) Pu. However, theK_d value for Pu may be an upper limit because Pu, like²²⁸Th, may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase.     

The application of caesium‐137 measurements to investigate floodplain deposition in a large semi‐arid catchment in Queensland,Australia: a low‐fallout environment

Floodplains comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of large dryland floodplains is not well understood. Processes occurring on such floodplains are often difficult to observe, and techniques used to investigate smaller perennial floodplains are often not practical in these environments. This study assesses the utility of ¹³⁷Cs inventory and depth‐profile techniques for determining relative amounts of floodplain sedimentation in the Fitzroy River, northeastern Australia; a 143 000 km² semi‐arid river system. Caesium‐137 inventories were calculated for floodplain and reference location bulk soil cores collected from four sites. Depth profiles of ¹³⁷Cs concentration from each floodplain site and a reference location were recorded. The areal density of ¹³⁷Cs at reference locations ranged from 13 to 978 Bq m^–2 (0–1367 Bq m^–2 at the 95% confidence interval), and the mean value ± 2 (standard error of the mean) was 436 ± 264 Bq m^–2, similar to published data from other Southern Hemisphere locations. Floodplain inventories ranged from 68 to 1142 Bq m^–2 (0–1692 Bq m^–2 at the 95% confidence interval), essentially falling within the range of reference inventory values, thus preventing calculation of erosion or deposition. Depth‐profiles of ¹³⁷Cs concentration indicate erosion at one site and over 66 cm of deposition at another since 1954. Analysis of ^239+240Pu concentrations in a depositional core substantiated the interpretation made from ¹³⁷Cs data, and depict a more tightly constrained peak in concentration. Average annual deposition rates range from 0 to 15 mm. The similarity between floodplain and reference bulk inventories does not necessarily indicate a lack of erosion or deposition, due to low ¹³⁷Cs fallout in the region and associated high measurement uncertainties, and a likely influence of gully and bank eroded sediments with no or limited adsorbed ¹³⁷Cs. In this low‐fallout environment, detailed depth‐profile data are necessary for investigating sedimentation using ¹³⁷Cs. Copyright © 2009 John Wiley & Sons, Ltd.     

Anthropogenic Radionuclides in the Caspian Sea

Analysis and interpretation of the distribution of anthropogenic radionuclides ⁹⁰Sr, ¹³⁷Cs, and ^239,240Pu in the Caspian Sea water are presented. These radionuclides are shown to be of environmental importance and to be useful for studying water mass dynamics.     

Organic carbon flow in the Ob, Yenisey Rivers and Kara Sea of the Arctic region

Stable carbon isotope and elemental C/N ratios of the organic fraction of a set of samples along a transect in the Ob and Yenisey Rivers into the Kara Sea in the Arctic were measured. Previously, the concentrations of 239,240Pu and 137Cs in these same samples had been determined. The coupled measurements were carried out to assess possible connectivity between organic carbon flow into the Kara Sea and transport of radioactive nuclides in this marine environment. Organic carbon flow into the Kara Sea is influenced significantly by terrigenous sources carried by the Ob and Yenisey Rivers. The carbon isotope-organic carbon relationship provides evidence that a rich source of terrigenous carbon exists in the riverine system. A weak, but significant relationship between stable carbon isotope ratio and 137Cs suggests that most of the 137Cs is derived from riverine particles, as compared to Pu which is also derived from in situ scavenging within the water column.     

Sedimentation rates in the central lake constance determined with210Pb and137Cs

Sediment cores from central Lake Constance were dated with²¹⁰Pb and¹³⁷Cs. A sedimentation rate of (0.11±0.02) g·cm⁻²·y⁻¹ was determined with the²¹⁰Pb method.¹³⁷Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm⁻²·y⁻¹ and (0.08±0.01) g·cm⁻²·y⁻¹ respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the¹³⁷Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30–125 days residence times for suspended particulate matter were calculated from⁷Be measurements.     

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

Vertical profiles of the activities of ¹³⁷Cs and ²¹⁰Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm^?2 yr^?1 and were in good agreement with sedimentation rates calculated from the inventories of ¹³⁷Cs and ²¹⁰Pb. Sedimentation rates calculated from the position of the ¹³⁷Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of ¹³⁷Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the ¹³⁷Cs and ²¹⁰Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.     

Rating Water Quality in Sevastopol Bay by the Fluxes of Pollutant Deposition in Bottom Sediments

Sevastopol Bay is used as an example for the development of criteria for rating anthropogenic impact by elimination fluxes from the water area of post-Chernobyl (⁹⁰Sr, ¹³⁷Cs, ^239,240Pu) and natural (²¹⁰Pо) radionuclides, as well as mercury and organochlorine compounds. The differentiation of the bay water area into zones with different biogeochemical conditions and the balance approach to interpreting field observation data were used to assess the conditioning capacity of Sevastopol Bay ecosystem for conservative radioactive and chemical substances by elimination fluxes of pollutants into aqueous depot, which is the open part of the Black Sea and into the geological depot, i.e., its bottom sediment stratum.     

Elevated sedimentation in lake records linked to agricultural activities in the Ishikari River floodplain,northern Japan

The purpose of this study was to examine the historical change in sedimentation rates in lakes that have been impacted by river regulation and agricultural activities in the Ishikari River floodplain. We dated sediment cores using caesium‐137 (¹³⁷Cs) dating and tephrochronology, and we estimated sediment sources from ¹³⁷Cs concentrations in the topsoil of representative land covers. We found that, between 1739 and 1963, the distance between the lake and the main river channel and whether or not the lake was connected to the river affected the sedimentation rates. After 1963, agricultural drainage systems were established in the Ishikari River floodplain. The average sedimentation rate before and after the construction of drainage ditches varied between 1–66 and 87–301 mg cm^–2 a^–1, respectively. The increase in the sedimentation rate after 1963 was caused by the construction of a number of drainage networks, as well as extensive cultivation activity and/or fragmentation of the swamp buffers surrounding the lakes. The ¹³⁷Cs activities at the surfaces of the lake as well as the catchment‐derived ¹³⁷Cs contributions and ¹³⁷Cs inventory in the lake profiles were used to examine the sediment influx from the various drainage areas after the establishment of the drainage system. Our results indicate that the majority of the lake sediments were derived from cultivated areas, and therefore the catchment‐derived ¹³⁷Cs contribution in the lakes was strongly correlated with the sedimentation rate. The ¹³⁷Cs inventory across all of the lake profiles was also significantly greater than the atmospheric fallout. We identified a negative correlation between the ¹³⁷Cs lake profile inventory and the sedimentation rate. This is because the sediment originating from the drainage areas contained low ¹³⁷Cs concentrations, which diluted the overall concentration of ¹³⁷Cs in the lake sediment. Copyright © 2009 John Wiley & Sons, Ltd.