Seasonal Variation in Oxygen Isotopic Composition of Two Freshwater Bivalves: Sphaerium striatinum and Anodonta grandis

Oxygen isotopic values have been obtained from microsamples of the aragonitic freshwater bivalves Sphaerium striatinum (Pisidiidae) and Anodonta grandis (Unionidae) collected alive from Wellington Creek, OH. To test whether these organisms secrete their shell in isotopic equilibrium, the SO values of shell aragonite are compared to ambient water temperature and δ¹⁸O values monitored for > 1 yr. These bivalves were chosen for study because they are abundant in surface sediments and cores from Lake Erie where they represent a source of information on the environmental history of the lake. The observed mean values are −5.54‰ for A. grandis and −6.16‰ for S. striatinum. The mean δ¹⁸O value expected for bivalve aragonite if equilibrium precipitation is occurring during May–August in Wellington Creek is −5.69‰. The similarity between measured and predicted isotopic values for both species suggests that they are useful sources of paleoenvironmental data. Overall, the isotopic composition of the shells of the two species reflects less than one half of the calculated range of potential biogenic aragonite values for the stream and omits recording evaporative conditions associated with ponded water. Bivalve δ¹⁸O and δ¹³C data covary. The δ¹³C data are highly negative and values could reflect ¹²C enrichment of dissolved organic carbon from organic matter oxidation and/or ingestion of food carbon.     

Biological Redistribution of Lake Sediments by Tubificid Oligochaetes: Branchiura sowerbyi and Limnodrilus hoffmeisteri/Tubifex tubifex

Mechanisms and rates of sediment mixing by the largest oligochaete in Lake Erie, Branchiura sowerbyi, have been quantitatively investigated using a multiple ¹³⁷Cs tracer layer microcosm technique and compared with a mixture of the dominant tubificids, Limnodrilus hoffmeisteri + Tubifex tubifex. These worms feed head down in the sediment (up to 20 cm for B. sowerbyi and up to 10 cm for L. hoffmeisteri/T. tubifex) on organic-rich particles and deposit fecal pellets at the sediment-water interface (conveyor-belt feeding). Obliteration of tracer layers by these worms was attributed to mixing by both diffusive- and feeding-style (advective) processes. The downward velocities were 2.87 to 3.66 cm/d/100,000 indiv/m² for the cells with B. sowerbyi (∼10 cm body length, 13 mg body mass) and 0.33 to 0.49 cm/d/100,000 indiv/m² for the cells with L. hoffmeisteri / T. tubifex (∼5 cm body length, 1 mg body mass). These downward velocities correspond to sediment fluxes across the sediment-water interface of 66.4 to 86.4 g dry sediment/indiv/m²/yr in cells with B. sowerbyi and 5.91 to 9.09 g dry sediment/indiv/m²/yr in the cells with L. hoffmeisteri / T. tubifex). The differences between species was due to differences in biomass, with recycling rates of 5.11 to 6.65 and 5.91 to 9.09 g dry sediment/mg biomass/m²/yr for B. sowerbyi and L. hoffmeisteri/T. tubifex, respectively. Similarly, biomass normalized downward velocities were 806 to 1,028 cm/yr/kg biomass/m² and 1,205 to 1,789 cm/yr/kg biomass/m² for B. sowerbyi and L. hoffmeisteri/T. tubifex, respectively. Both B. sowerbyi and L. hoffmeisteri / T. tubifex feed selectively on organic-rich fine-grained particles and showed an increase in particle selectivity with an increase in population density. The particle selectivity factor values ranged from 1.0 to 2.5. Food competition at a higher population density might force these organisms to selectively feed on a smaller size range of sediments. The maximum feeding rate for B. sowerbyi (4,000 to 8,000 indiv/m²) ranged from 9.10 to 13.9 per yr at depths between 11.7 and 13.6 cm while the maximum biodiffusion coefficient, D_b, ranged from 0.78 to 1.02 cm²/yr at depths between 1.6 and 2.3 cm. The maximum feeding rate for L. hoffmeisteri / T. tubifex (20,000 to 40,000 indiv/m²) was 8.13 to 13.1 per yr at depths between 5.21 and 5.27 cm and D_b ranged from 0.20 to 0.72 cm²/yr at depths between 0.87 and 2.0 cm.     

Interconnected riverine–lacustrine systems as sedimentary repositories: Case study in southeast Michigan using Pb and Cs-based sediment accumulation and mixing models

Particle-reactive nuclides, such as ²¹⁰Pb and ¹³⁷Cs, serve as powerful chronometric tools in the investigations and reconstruction of historical contamination in coastal marine and lacustrine systems. Towards the first systematic establishment of sediment chronologies of river channel sediments, a set of seven sediment cores from Clinton River and Lake St. Clair riverine–lacustrine system were collected and analyzed for ²¹⁰Pb, ²²⁶Ra, and ¹³⁷Cs activities. Measured inventories of ²¹⁰Pb_xs and ¹³⁷Cs were ~ 2 and ~ 9 times higher than that expected from atmospheric fallout. From the measured ²¹⁰Pb_xs/¹³⁷Cs inventory ratios, erosional input of ¹³⁷Cs was found to be significantly higher than that of ²¹⁰Pb indicating that anthropogenic watershed disturbances have resulted in accelerated sediment erosion. Good agreement between accumulation rates using ²¹⁰Pb_xs and ¹³⁷Cs using four different age models were obtained for four of the seven cores in the riverine–lacustrine environment. Average sediment mass accumulation rates, based on the ²¹⁰Pb_xs CFCS model, in the lower Clinton River (mean: 0.91 g cm⁻² yr⁻¹) were generally higher than those in Lake St. Clair (mean: 0.55 g cm⁻² yr⁻¹) due to a higher sediment flux and the unique riverine system characteristics. Sediment mixing coefficients, based on a ²¹⁰Pb_xs mixing model, were much higher in the river (mean: 64.9 cm² yr⁻¹) compared to the lake (mean: 4.7 cm² yr⁻¹), as was expected due to the frequency of perturbation and resuspension. Net accumulation of datable sediments in the Clinton River indicates that similar river channel deposits may act as repositories for the reconstruction of historical contamination and environmental changes.     

Accumulation rates,focusing factors,and chronologies from depth profiles of 210Pb and 137Cs in sediments of the Laurentian Great Lakes

Sediment cores from 41 sites were collected from the Laurentian Great Lakes during 2010–2014, sectioned into 0.5–2.0?cm intervals, and the activities of ²¹⁰Pb, ¹³⁷Cs, and ²²⁶Ra were measured in the upper 25 to 40?cm of the sediment column by gamma spectrometry. Sediment mass accumulation rates (dry mass) calculated from ²¹⁰Pb profiles range from 0.006?±?0.001 to 0.59?±?0.06?g?cm^?2?yr ^?1 and are similar to those reported in previous Great Lakes sediment studies. Sediment mass accumulation rates decreased with increasing water depth. ²¹⁰Pb-based models in cores exhibiting favorable characteristics (i.e., those having the highest unsupported-²¹⁰Pb activity at the sediment-water interface, exponential decrease of unsupported-²¹⁰Pb with increasing depth in sediment cores, and a clear peak in ¹³⁷Cs activity at some depth below the sediment-water interface) give calendar date profiles that are largely concordant with the maximum ¹³⁷Cs peak activity at 1963. Sediment focusing factors derived from unsupported-²¹⁰Pb inventories range from 0.09 to >5.34, and are well correlated with those derived from ¹³⁷Cs inventories that range from 0.07 to 4.04, demonstrating the ubiquitous occurrence of horizontal sediment transport processes within the lakes. This more recent survey provides a Great Lakes-wide chronological framework for comparing the depositional histories and inventories of a wide variety of persistent, bioaccumulative and toxic pollutants that have been measured in the same sediment cores. This information will be useful for resolving scientific and practical issues pertaining to the environmental quality and management of contaminated sediments in the Laurentian Great Lakes ecosystem.     

Sediment Mixing by Lampsilis Radiata Siliquoidea (Mollusca) from Western Lake Erie

The sediment reworking activities of an abundant Lake Erie unionid bivalve, Lampsilis radiata siliquoidea, have been studied by field observations and laboratory experiments. Unionid burrowing in laboratory microcosms increased sediment water content 10-20%, decreased water content variability, homogenized sedimentary structures, and increased tenfold the volume of oxidized sediment over that in microcosms with no unionids. Incomplete mixing of sediment took place to a depth of 10 cm during burrowing by L. r. siliquoidea. Burrowing by other unionids may extend the depth of maximum reworking to 20 cm. Unionid burrowing, feeding, and respiratory activities may alter the profiles of various elements and radionuclides associated with sediment particles and alter the location and intensity of microbial activity in sediments.     

Estimation of the Uptake of Organochlorines by the Mayfly Hexagenia limbata (Ephemeroptera: Ephemeridae)

Uptake rate coefficients (k_s) and biota-sediment- accumulation-factors (BSAFs) for 17 hydrophobic chemicals with octanol-water partition coefficients (log K_ow) ranging from 5.4 to 7.4 were determined for mayfly nymphs (Hexagenia limbata) exposed to contaminated sediments collected from the Detroit River. Nymphs obtained 95% of steady state conditions within a 32 day exposure period for all chemicals of study. Using two different exposure strategies, estimates of uptake rate coefficients ranged from 0.27 to 11.38 g(sediment)·g(lipid)^−l·h⁻¹ and became independent of K_owfor chemicals of log K_ow > 5.9. Biota Sediment Accumulation Factors ranged from 1.2 to 9.4, and followed similar trends as observed for k_s estimates. The results support the conclusion that bioaccumulation occurred as a result of ingestion of contaminant sorbed to sediment organic carbon, and that sediment was the primary chemical exposure route for hydrophobic organic chemicals with log K_ow > 5.9.     

Organic halogen,heavy metals and biological activities in pristine and pulp mill recipient lake sediments

In order to create a basis for prognosing future intrinsic remediation potential of past pollution by pulping industry, we analyzed biochemical activities and levels of pollution in sediments dated with ²¹⁰Pb and ¹³⁷Cs. A small pristine forest lake and a pulp mill recipient area of a large oligotrophic Lake Saimaa were test sites. Sediment concentration of EOX ranged from 40 to 130 μg Cl (g d.w.)⁻¹ in the pristine lake and from 770 to 4700 μg Cl (g d.w.)⁻¹ in the pulp mill recipient area and the C:Cl (w/w) ratio of sediment organic matter ranged from 2000 to 5100 and 42 to 230, respectively. The organic matter in 10 to 20 years old pulp mill recipient sediment was mainly of waste water origin. The activity gradients of β-glucosidase, butyrate-esterase, methane oxidation potential and endogenous respiration from surface to deeper layers were less steep in polluted than in pristine sediment. Methane oxidation potential was 120 μmol CH₄ d⁻¹ (g C)⁻¹ at the sediment surface of pristine lake sediment and 26 μmol CH₄ d⁻¹ (g C)⁻¹ at the polluted site, endogenous respiration rates of the surface sediment were 670 and 310 μmol CO₂ d⁻¹ (g C)⁻¹, respectively. In the most polluted layer we found a depressed potential for methane oxidation, inhibition of phosphatase and butyratelipase activities and moderately increased induction ratio of β-galactosidase to phosphatase in the SOS-Chromotest strain E. coli PQ 37. The results suggest that at the concentrations observed these effects in the sediment were not due to heavy metals.     

Nitrogen Dynamics in Sandy Freshwater Sediments (Saginaw Bay,Lake Huron)

Sediment-water nitrogen fluxes and transformations were examined at two sites in Saginaw Bay, Lake Huron, as a model for sandy freshwater sediments. Substantial ammonium release rates (74 to 350 μmole NH₄⁺/m²/h¹) were observed in flow-through cores and in situ benthic chamber experiments. Sediment-water ammonium fluxes were similar at the inner and outer bay stations even though inner bay waters are enriched with nutrients from the Saginaw River. The high net flux of remineralized ammonium into the overlying water from these sandy sediments resembles typical data for marine systems (11 to 470 μmole NH₄⁺/m²/h¹) but were higher than those reported for depositional freshwater sediments (0 to 15 μmole NH₄⁺/m²/h¹; Seitzinger 1988). Addition of montmorillonite clay (ca. 1 kg dry weight/m²) to the top of the sandy cores reduced ammonium flux. Mean “steady-state” ammonium flux following clay addition was 46 ± 2 (SE) % of the initial rates as compared to 81 ± 8% of the initial rates without clay addition. Zebra mussel excretion dominanted ammonium regeneration in the inner bay where the bivalve was abundant, but addition of zebra mussel feces/psuedofeces (3.0 g dw/m²) to sediments did not increase ammonium or nitrate flux. Partial nitrification of ammonium at the sediment-water interface was suggested by removal of added ¹⁵NH₄⁺ from lake water passing over dark sediment cores. Sediment-water fluxes of nitrogen obtained from flow-through sediment cores resembled those from in situ benthic chambers. However, extended static incubations in gas-tight denitrification chambers caused more of the regenerated nitrogen to be nitrified and denitrified than occurred with the other two measurement systems.     

Mobility of 2,2’,5,5’-Tetrachlorobiphenyl in Model Systems Containing Bottom Sediments and Water from the Lower Fox River,Wisconsin

Sediment-water partitioning and diffusive transport of 2,2’,5,5’-tetrachlorobiphenyl, PCB congener IUPAC #52 (TCB52) were examined in laboratory experiments with sediments from two sites in the lower Fox River, Wisconsin. Native water was pumped at controlled flow rates through cells containing sediments amended with a known activity of carbon-14-labeled TCB52. Concentrations of TCB52 in water and sediments were determined by liquid scintillation measurements of carbon-14 activity. Sediment-water partitioning was independent of flow rate for rates up to 8 m/d. Distribution coefficients (K_d) and soil-sorption coefficients (K_oc) were found to be at maximum levels 5–10 cm below the surface, despite an absence of significant variation in the fraction of organic carbon (f_oc) through the same profile. Other factors, such as the effects of colloids and microbial activity in the sediments, are likely to be important in controlling the PCB distribution. Log K_d and log K_oc ranges were 4.1–4.9 and 5.3–6.1, respectively, and calculated effective diffusivities at the sediment-water interface ranged from 3 to 8 × 10⁻¹⁰ cm²/s. Gradual increases with time in TCB52 concentrations in the water phase, possibly due to effects of microbial activity, were observed. Diffusion experiments and models showed that the TCB52 migration rate within the sediment column is 8-9 mm/yr.     

Sediment Loading During the 20th Century in Presque Isle Bay,Lake Erie,Pennsylvania

Mud-dominated sediments in Presque Isle Bay are contaminated with metals and hydrocarbons derived from developed watershed and atmospheric sources. Prior to this study, the quantities, rates, and spatial distribution of long-term sedimentation and erosion in the bay were largely unknown. As a result, the fate of contaminated bay-floor sediments and possible rates of natural recovery for this Area of Concern (AOC) could not be determined. To provide baseline data useful to state and federal agencies monitoring recovery of the bay, this paper identifies: (1) the quantities, rates and patterns of 20^th Century sedimentation and erosion, (2) the major sediment inputs and outputs for the bay, and (3) the implications of the sedimentary regime on possible future rates of bay recovery. Bathymetric and sedimentological data show that 20th Century net accumulation totaled approximately 3.94 × 10⁶ m³ which is equivalent to a dry sediment loading of 5.92 × 10⁹ kg (5.92 × 10⁶ t), or 6.29 kg/m²/yr (1.28 lb/ft²/yr) when averaged over the accretional 70% of the bay. This external loading represents approximately 50% of total accretion because externally derived sediments are augmented with resuspended sediments from shallow-water parts of the bay. The principal sediment inputs were littoral drift from ephemeral and permanent inlets (∼42%), artificial infilling along the shoreline (∼28%), streams (∼16%), bank/bluff erosion (∼12%), and biological production (∼2%). Dredging was the principal output. Based on long-term average sedimentation rates and patterns, recovery of the AOC through natural sediment capping will take at least several decades if source contaminants are removed.     

Vertical Distribution of Profundal Benthos in Lake Superior Sediments

Layers of sediment in box cores from 10 Lake Superior open lake sites were sieved at 250 μm to retain benthos. The average density of benthic organisms, 3,055/m², was higher than has previously been reported for profundal regions of the lake, suggesting that biological mixing is important in the sediments. Bottom fauna were distributed from the water-sediment interface to a depth of 1.7 cm in firm glacial till and to a depth of 15 cm in soft clay. There was variability between sampling sites: oligochaetes and nematodes penetrated further into loose sediments than into compacted sand or clay. Ninety-six percent of the profundal benthos was found within the first four centimeters of sediment, with 47% between 0 and 0.5 cm (mostly Pontoporeia hoyi, naidids, sphaeriids, copepods, ostracods, and neorhabdocoels); 49% between 0.5 and 4 cm (mostly nematodes and oligochaetes); and 4% below 4 cm. The location of oligochaete cocoons containing embryos indicated that enchytraeid positions in the cores often represented their in situ vertical distribution, whereas some of the lumbriculids and tubificids migrated downward during the sampling procedures. The density and vertical distribution of Pontoporeia indicated that the potential depth and rate of biological mixing of sediment may exceed the sediment accumulation rate in Lake Superior.     

Assessing the Potential Efficacy of Glutaraldehyde for Biocide Treatment of Un-ballasted Transoceanic Vessels

Treating the ballast water of oceanic vessels with a biocide is one potential management strategy to reduce the number of nonindigenous species released into the Laurentian Great Lakes from NOBOB (no ballast on board) vessels. To evaluate biocide effectiveness, glutaraldehyde, a five-carbon dialdehyde widely used for its antimicrobial properties, was investigated. Biocide effectiveness was assessed for various organisms using 24 h acute toxicity bioassays in water-only and water-sediment environments. Acute studies indicate a 24 h LC₉₀ value of 100 mg glutaraldehyde L^–1 or less for most of the freshwater organisms tested. The main exception was the freshwater amphipod, Hyalella azteca, which was much more resistant to glutaraldehyde (24 h LC₉₀ = 550 mg glutaraldehyde L⁻¹; 95% CI: 476–681). Biocide efficacy was also evaluated in water-sediment exposures. The presence of a test sediment (3% organic carbon) greatly increased lethal concentration estimates for the oligochaete Lumbriculus variegatus, but not for H. azteca: The 24 h LC₉₀ for L. variegatus varied depending on the water-sediment ratio, and ranged from 61 mg glutaraldehyde L⁻¹ (95% CI 52–78) for an 8:1 water-sediment ratio to 356 mg glutaraldehyde L⁻¹ (95% CI 322–423) for a 2:1 water-sediment ratio. This indicates that the amount of sediments present in NOBOB vessels may have a significant impact on biocide efficacy. Experiments using material from actual NOBOB vessels generally corroborated data from the water-sediment experiments and suggest a potential treatment concentration of approximately 500 mg glutaraldehyde L⁻¹ for short exposure periods (e.g., 24 h).     

Lead in Lake Michigan and Green Bay surficial sediments

Sediment samples were collected in 1987–1990 from Green Bay and in 1994–1996 from Lake Michigan. Surficial sediments (0–1 cm) from both locations were analyzed for lead for the purpose of describing the horizontal variation of lead in 1994–1996 Lake Michigan and 1987–1990 Green Bay sediments, estimating lead fluxes to surficial sediments, and comparing results to earlier studies. With Lake Michigan concentrations ranging from below the method detection limit to 180 μg/g, the surficial sediments had mean and median lead concentrations of 70 μg/g and 64 μg/g, respectively. Lead concentrations in Green Bay surficial sediments were similar to those in Lake Michigan and ranged between the method detection limit and 160 μg/g. For the bay, mean and median concentrations were 58 and 59 μg/g, respectively. Surficial lead concentrations were highest in the Southern, Waukegan, and Grand Haven basins of Lake Michigan and in the central region of Green Bay in the vicinity of Chambers Island. For Lake Michigan and Green Bay, dated sediment cores illustrate the decline in lead concentrations during the last 30 and 10 years, respectively. Lead fluxes ranged between < 0.049 and 7.2 μg/cm²/yr for Green Bay and between 0.47 and 20 μg/cm²/yr for Lake Michigan. Lead fluxes to Lake Michigan were lower than those reported for 1972. These are the most comprehensive fluxes of lead to Lake Michigan and Green Bay surficial sediments reported to date.     

Sediment distribution and accumulation in Lake Naivasha,Kenya over the past 50 years

Although surface waterbodies are water sources for socio‐economic activities and ecosystems, their functions are threatened by sedimentation. Sedimentation of lakes and reservoirs can result in a loss of storage capacity and altered water quality. The present study assessed the sedimentation status of Lake Naivasha, Kenya, based on sediment distribution and accumulation over the past 50 years, using a Bathymetric Survey System (BSS). The BSS uses multi‐frequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected with a vibe‐ coring device and dated. Sediment layers corresponding to a period of the past 20 and 50 years were identified. Sediment cores and acoustic images were subsequently used to determine sediment thickness within the lake. The collected depth data from multi‐frequency APS, and dated cores were processed in DepthPic and Surfer software. The sediment depth was extracted in DepthPic, while the sediment volume and distribution were generated from Surfer software. The results from present study indicated that sediment distribution varied from one part of the lake to another for the past 20 and 50 years. High sediment thickness observed in the south‐west and eastern parts of the lake. Between 1996–2016 and 1966–2016 periods, the maximum accumulated sediment thickness was found to be about 0.55 and 1.9 m, with an average sediment thickness of 0.25 and 0.56 m, respectively. The mean sediment load corresponding to the 1966–1996 and 1996–2016 periods was 2.78 × 10⁵ and 4.61 × 10⁵ t/year, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past. Based on the present the study, it was found that combined use of BSS, sediment cores and dating can be adopted in many lakes and reservoirs to determine sediment thicknesses even where no prior bathymetric surveys exist for comparison.     

Precise Radiotracer Measurement of the Rate of Sediment Reworking by Stylodrilus Heringianus and the Effects of Variable Dissolved Oxygen Concentrations

A radiotracer method is used to determine the rate of sediment reworking by the worm, Stylodrilus heringianus, an organism common in profundal sediments of the Great Lakes. A submillimeter layer of sediment labeled with gamma-emitting cesium-137 is added to the surface of worm-inoculated sediments contained in cells of rectangular cross-section placed in an insulated aquarium (10° C). This layer, progressively buried by the conveyor belt feeding action of the worms, is located by scanning the cell with a well-collimated detector mounted on a hydraulically actuated elevator. Precision in locating the marked layer is greatly enhanced by Gaussian profile analysis developed in this study. Relative uncertainties in location of less than 0.01 cm allow reworking rates as low as 10^?3cm/hr to be determined in 1 to 2 days. The effect of variable dissolved oxygen (D.O.) concentrations on sediment reworking rates was determined by adjusting the relative proportions of N₂ and O₂ introduced into the aquarium through a continuous bubbler system. In a cell subject to gradual reductions in D.O. (about 1 mg/L every 50 hours) from saturation concentration (10.6 mg/L), sediment reworking rates remained virtually constant down to 1 mg/L. Below this value, the rate decreased, approaching zero at 0.2 mg/L. On increasing D. O. values above about 4 mg/L, reworking returned to the initial rate. Gradual decreases in D.O. induced a reversible dormant mode in these organisms. In cells subject to coarse D.O. changes (3.7 to 8.8 mg/L per step), reworking stopped at around 4 to 5 mg/L and did not resume following reinstatement of saturation values for up to 18 days. In all cases more than 70% of worms were alive at the end of the experiment. This study illustrates the potential of the gamma scan system for quantitative behavioral bioassay of the interactions of zoobenthos with altered sedimentary environments.     

Estimates of the remineralization and burial of organic carbon in Lake Baikal sediments

Sediment cores collected from several stations throughout Lake Baikal in water depths from 100 m off the Selenga River delta to the deepest basin of the lake (~1640 m), have been analyzed for sedimentary organic carbon, nitrogen, and the remineralized components in pore water. The organic carbon content of surface sediments generally varied from 2.3 to 3.2% by weight, and profiles typically showed an exponential decrease in both organic carbon and nitrogen in the upper 20–30 cm of the sediment column. Steady state models of organic matter diagenesis yield first order decomposition rate constants which range from 0.0009 to 0.022 y⁻¹. The calculated residence times for the metabolizable fraction of the organic matter in these sediments increases roughly with increasing water depth and is on the order of 50–300 years. Pore water concentration profiles were determined for dissolved inorganic carbon, dissolved organic carbon (DOC), methane, and dissolved ammonium. At depth (25–30 cm) methane concentrations ranged from 50 to 800 μmol L_pw⁻¹ and DOC from 400 to 900 μmol L_pw⁻¹. Estimation of carbon recycling rates based upon diffusion along pore water concentration gradients at the sediment-water interface, indicate that combined DOC and methane fluxes generally contribute <15% of the overall turnover of sedimentary organic carbon. Comparisons to Laurentian Great Lakes environments show trends in sediment deposition, organic matter remineralization, and the time scales of carbon recycling across nearly two orders of magnitude with the fraction of organic content buried generally decreasing with decreasing sedimentation rates.     

Heavy metals in sediments and uptake by burrowing mayflies in western Lake Erie basin

During the past two decades, burrowing Hexagenia mayflies have returned to the western basin of Lake Erie. Because of their importance as a prey resource for higher trophic levels and their extensive residence time in potentially contaminated sediment, Hexagenia may be a source of heavy metal transfer. To better understand the distribution and transfer of heavy metals in sediment and mayflies, sediment and mayfly nymphs were collected from 24 locations across the western basin of Lake Erie in May 2007. Following USEPA protocols, samples were analyzed for 16 elements using ICP-OES or ICP-MS. Metal concentrations in the sediments exceeded the Threshold Effect Level for at least one metal at all sample sites. Sediment heavy metal distribution profiles indicate metal concentrations are correlated with organic matter content, and the highest heavy metal concentrations were found in the central deeper region of the western basin where organic content in the sediments was greatest. Hexagenia were distributed throughout the western basin, with greatest density (1350/m²) within the Detroit River plume. The Cd and Zn levels in mayflies were on average approximately 4 and 2 times greater, respectively, than sediment levels, and the Cd concentrations in the sediments exceeded the Threshold Effect Level at 27 of 28 sites and exceeded the Probable Effect Level at 9 of 28 sites. Spatial representation of heavy metal concentrations in mayflies exhibited a similar pattern to the spatial distribution of heavy metals and organic matter in the sediments with higher concentrations of metals found in mayflies residing in the central deeper region of the western basin.     

Prediction of trace metal distribution coefficients (KD) for aerobic sediments

Distribution coefficients for suspended sediments may be estimated from water and sediment quality variables, using detailed conceptual chemical models or semi-empirical models. The predicted K_D values find application in trace metal fate modelling and risk assessment. The detailed chemical model SWAMP (Sediment Water Algorithm for Metal Partitioning) which expresses trace metal distribution coefficients as a function of environmental variables and sediment characteristics was used to describe field K_D values. Besides SWAMP, semi-empirical models were derived from field-K_D values. The field K_D-values for Cd, Cu, Ni, Pb and Zn were measured on samples taken monthly from four surface waters in The Netherlands. In this paper we discuss the differences between the two modeling approaches.     

Record of mercury pollution in sediments of lakes Nakaumi and Shinji in Japan

Two sediment core profiles from lakes Shinji and Nakaumi were studied in order to understand the level of mercury (Hg) pollution in lakes in northwestern Japan. The sedimentation rates were established on the basis of the activity of [²¹⁰Pb] and [¹³¹Cs] in the sediments. In Lake Shinji, the highest level of Hg (130 ng g^–1) in the sediment was found at a depth of 20–22 cm, while 195 ng g^–1 was found at a depth of 10–12 cm in the core profiles from Lake Nakaumi. The relative increase in Hg concentration in lake sediments started after 1960 and significant contamination events occurred in the early 1960s. Mercury profiles in lake sediments from lakes Shinji and Nakaumi are found to reflect the anthropogenic Hg released into the environment in the 1950s and 1960s. A pronounced maximun concentration of Hg is found in both lakes, where sediment accumulation rates differ.     

Recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia) in Western Lake Erie

Burrowing mayflies (Hexagenia spp.) are native to western Lake Erie and were abundant until the 1950s, when they disappeared due to degraded water and sediment quality. Nymphs were absent from the sediments of most of western Lake Erie after the 1950s, although small, widely disjunct populations apparently persisted near shore. Sediment samples collected in 1993 revealed several small populations near the western and southern shores and beyond the mouths of the Detroit and Maumee rivers. A larger population was found in the southern island area, but nymphs were absent in the middle of the basin. By 1995, nymphs had spread throughout the western half and eastern end of the basin but remained absent from the middle of the basin. These data indicate that Hexagenia began recolonizing nearshore areas before offshore areas. Increasingly large swarms of winged Hexagenia on shore and over the lake between 1992 and 1994 further indicate that mayflies are recolonizing the basin. Factors that have permitted Hexagenia recovery in western Lake Erie probably include improved sediment and water quality attributed to pollution abatement programs implemented after the early 1970s, and perhaps environmental changes in the early 1990s attributed to effects of the exotic zebra mussel (Dreissena polymorpha)