Concentrations In Overlying Water Research Articles

Chronic effects and thresholds for estuarine and marine benthic organism exposure to perfluorooctane sulfonic acid (PFOS)-contaminated sediments: Influence of organic carbon and exposure routes

Guideline values for perfluorooctane sulfonic acid (PFOS) in estuarine/marine sediments have been derived based on determinations of water quality guideline values, using data for toxicity to benthic biota, and a consideration of partitioning between sediments and overlying waters. Measured and literature chronic toxicity data for PFOS to 11 benthic estuarine/marine species were used in a species sensitivity distribution yielding 99% and 95% species protection concentrations of 6 and 25 μg PFOS/L respectively. The lowest dissolved PFOS concentrations causing toxicity were 0.28 mg/L (LOEC) to 28-day bivalve growth, 0.49 mg/L to survival and growth of juvenile amphipods, and 1.2 and 0.9 (0.7–1.6) mg/L as a LOEC and EC10 values for 10-day amphipod reproduction, respectively. A strong relationship (Kd) existed for PFOS-partitioning between sediment and overlying water concentrations and organic carbon (0.1 to 5.6% OC), with a Kd range of 16 to 150 L/kg. A conservative Kd value of 10 was used to derive a benthic sediment PC99 screening value of 60 μg/kg PFOS (for 1% OC) representing a low risk to benthic organisms in estuarine/marine environments from direct toxicity and secondary poisoning. No toxicity from PFOS occurred to benthic algae, copepod, or crab species in exposures with 170–180 mg/kg in spiked-sediments and 0.8–2 mg/L in the overlying waters. Toxicity of PFOS to amphipod survival and reproduction occurred and was attributed to dissolved rather than dietary exposure. The derived sediment quality screening value was used to assess a range field-collected sediments. These sediments were dominated by PFOS, with 4–15 μg/kg (1% OC) at estuarine/marine sites, being below the screening value. None of the sediments caused chronic toxicity to benthic algae, amphipod, and copepod tests, where the most highly PFAS-contaminated field-collected sediment had 0.18 mg/kg PFOS and resulted in 0.0014 mg/L PFOS in the overlying waters during tests. • Strong relationship between sediment-water partitioning of PFOS and organic carbon. • Species protection concentrations, PC99 and PC95 of 6 and 25 μg/L PFOS from SSD. • Benthic PC99 screening value of 60 μg/kg PFOS for 1% organic carbon (Kd = 10). • PFAS-contaminated field sediments were dominated by PFOS and below the PC99.

Effects of benthivorous fish disturbance and snail herbivory on water quality and two submersed macrophytes

Benthivorous fish disturbance and snail herbivory are two important factors that determine the community structure of submersed macrophytes. We conducted an outdoor mesocosm experiment to examine the separate and combined effects of these two factors on water quality and the growth of two mixed-cultivation submersed macrophytes, Vallisneria natans and Hydrilla verticillata, with different growth forms. The experiment involved two levels of fish (Misgurnus anguillicaudatus) disturbance crossed with two levels of snail (Radix swinhoei) intensity. The results revealed that fish activity rather than snail activity significantly increased the overlying water concentrations of total suspended solids (TSS), total nitrogen (TN), ammonia nitrogen (N-NH4), total phosphorus (TP) and phosphate phosphorus (P-PO4). However, no differences among treatments were observed for chlorophyll a (chl a) concentrations. Fish disturbance or snail herbivory alone did not affect the relative growth rate (RGR) of H. verticillata, but their combined effects significantly decreased the RGR of H. verticillata. Although snail herbivory alone did not affect the RGR of V. natans, fish disturbance alone and the combined effects of these factors drastically reduced its RGR. Both species exhibited increased free amino acid (FAA) contents and decreased ramet numbers, soluble carbohydrate (SC) contents and starch contents in the presence of the fish. Moreover, compared to H. verticillata, V. natans showed exceedingly low ramet numbers and starch contents in the presence of the fish. H. verticillata had a higher RGR and summed dominance ratio (SDR2) than V. natans in all treatments; H. verticillata also displayed a larger competitive advantage in the presence of fish disturbance. The present study suggests that (1) fish disturbance rather than snail activity increases water nutrient concentrations, (2) low snail density may be harmful to submersed macrophyte growth when the plants are under other abiotic stress conditions and (3) the competitive advantage of H. verticillata over V. natans is more preponderant in a turbid environment.

Polyoxymethylene passive samplers to monitor changes in bioavailability and flux of PCBs after activated carbon amendment to sediment in the field

Field and laboratory exposures of polyoxymethylene passive samplers to sediments and the water column were applied to monitor changes in bioavailability and flux of polychlorinated biphenyls (PCBs) following a pilot-scale amendment of activated carbon in Grasse River. Following amendment, reductions in passive sampler uptake tracked reductions in bioaccumulation in a freshwater invertebrate, which supports a biological basis for utilizing passive samplers for in situ site investigations following a remediation. Freely dissolved concentrations of PCBs were reduced in sediment pore waters compared to untreated sediments indicating reduced bioavailability of PCBs after activated carbon amendment. Freely dissolved PCB concentrations in sediment pore water in treated sites were also lower than overlying water concentrations indicating a reversal of the sediment from being a source to a sink of PCBs from the water column. These observations indicate that activated carbon amendment to sediment limits contaminant exposure to both the benthic and pelagic food webs through reductions in bioavailability and flux of PCBs into the water column.

Effects of linuron on a rooted aquatic macrophyte in sediment-dosed test systems

Effects of linuron on the sediment-rooted aquatic macrophyte Myriophyllum spicatum L. were studied in sediment-dosed test systems following a proposed guideline with extended test duration. Sediment, pore water, overlying water and macrophyte shoots were sampled weekly for chemical analyses. Linuron was stable in the sediments. Sediment and pore water concentrations were in equilibrium after 48 h. Overlying water concentrations increased over time, but did not reach equilibrium with pore water concentrations and were 100 times lower. Mass balances showed a rapid uptake of linuron by macrophyte roots. Known pathways and the compound's properties support the conclusion that Myriophyllum takes up linuron from pore water directly through the roots. Hence, effects on macrophytes in this type of sediment toxicity test should be expressed in terms of pore water concentrations. Pore water concentration is the most relevant parameter for describing effects on macrophytes.

Nonequilibrium of Organic Compounds in Sediment–Water Systems. Consequences for Risk Assessment and Remediation Measures

In many cases, sediment risk assessment, and remediation rely on the assumption of equilibrium between chemical concentrations in sediment pore water and overlying surface water and thus rely on pore water concentrations only and do not additionally include assessment of the overlying water concentration. Traditionally, the validity of this assumption was insufficiently documented due to a lack of data. Recent studies using passive samplers, however, provided sufficient data for the first systematic evaluation of the extent of disequilibrium between sediment pore water and overlying surface water. Recent bioaccumulation studies reveal uncertainty as to which of these concentrations govern bioaccumulation by benthic organisms. Here, we provide the first review of studies measuring disequilibrium identifying general patterns and implications for the aforementioned areas of application. In most studies on water/sediment (dis)equilibrium, sediment pore water and overlying surface water are close to equilibrium. For lower molecular weight PAHs, overlying water concentrations tended to be relative low, which is tentatively ascribed to biodegradation in the water column. Substantial nonequilibrium was observed at some hot-spot locations such as in semistagnant harbors. In such cases, efficacy of sediment remediation measures to improve overlying water quality can be questioned because differences between overlying water concentrations at the hot-spots and those at reference locations typically are small. For nonequilibrium situations and some benthic taxa, exposure may be determined best by pore water concentrations. Improving our understanding in this area may further improve risk assessment of contaminated sediments.

Occurrence of PAHs and PCBs in the Alna River, Oslo (Norway)

Thirty two polychlorinated biphenyl congeners (PCBs), hexachlorobenzene (HCB) and pentachlorobenzene (PeCB) were analysed in passive sampler extracts from surface water-exposed semipermeable membrane devices (SPMDs) and in bed sediment samples from a small urban watercourse, the River Alna (Oslo, Norway). Performance reference compound-corrected data from the passive samplers deployed at three sites along the river were used to track PCB contamination in the overlying water. SPMDs were able to detect an increase in dissolved PCB concentrations at the site furthest downstream that was corroborated by bed sediment concentrations. In comparison, no major increase in concentration of HCB, PeCB or PAHs could be observed. Comparison of passive sampling-based overlying water concentrations with total concentrations measured in bed sediments supports the possibility of further PCB sources upstream of the study area. Diagnostic PAH ratios (from SPMDs) and PCB congener pattern (from sediments) were used in an attempt to identify possible contaminant sources to the Alna River. Selected PAH diagnostic ratios support a multiple emission source scenario and demonstrate the complexity of identifying specific sources of these compounds to surface waters. PCB congener patterns in sediments from all three sites tend to indicate a source of highly chlorinated PCBs (of the Archlor 1260 type) and either a source of lower chlorinated PCBs or the less-likely occurrence of dechlorination in sediment. Information collected during the present screening study also confirms the Alna River as a continuous source of PCBs to the Oslofjord.

Fate and effects of Composition B in multispecies marine exposures

The vast majority of investigations into the bioavailability and toxicity of explosives to receptors in aquatic environments has focused on deriving toxicity metrics for discrete chemical exposures to single species using pure compounds at relatively high concentrations. This study assessed the environmental fate and potential for biological effects of a common military formulation, Composition B, under more realistic exposure scenarios (e.g., those that more closely simulate a breached artillery round or residual exposure following a low-order detonation). We used a novel approach incorporating multiple species and toxicity endpoints in sediment exposures over a 34-d exposure period. Composition B fragments exposed at the sediment surface rapidly released 2,4,6-trinitrotolune (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to the overlying water column. In comparison, burial of fragments resulted in dramatically reduced exposure, bioconcentration, and toxicity. The addition of a conservative flow rate to the aquaria also reduced water and tissue concentrations by factors of two to three. Although the exposure system likely represented a worst-case scenario relative to most conditions found in coastal and estuarine environments, overlying water concentrations generally did not approach known toxicity thresholds, while porewater concentrations were sufficiently elevated above toxicity thresholds immediately adjacent to the fragments, limiting hazardous exposure only to very localized scales. Bioconcentration correlated closely with observed toxicity and was either not detectable (buried), or low (exposed), as is expected based on the low hydrophobicities of TNT and RDX.

Evaluation of the effects of coal fly ash amendments on the toxicity of a contaminated marine sediment

Approaches for cleaning up contaminated sediments range from dredging to in situ treatment. In this study, we discuss the effects of amending reference and contaminated sediments with coal fly ash to reduce the bioavailability and toxicity of a field sediment contaminated with polycyclic aromatic hydrocarbons (PAHs). Six fly ashes and a coconut charcoal were evaluated in 7-d whole sediment toxicity tests with a marine amphipod (Ampelisca abdita) and mysid (Americamysis bahia). Fly ashes with high carbon content and the coconut charcoal showed proficiency at reducing toxicity. Some of the fly ashes demonstrated toxicity in the reference treatments. It is suspected that some of this toxicity is related to the presence of ammonia associated with fly ashes as a result of postoxidation treatment to reduce nitrous oxide emissions. Relatively simple methods exist to remove ammonia from fly ash before use, and fly ashes with low ammonia content are available. Fly ashes were also shown to effectively reduce overlying water concentrations of several PAHs. No evidence was seen of the release of the metals cadmium, copper, nickel, or lead from the fly ashes. A preliminary 28-d polychaete bioaccumulation study with one of the high-carbon fly ashes and a reference sediment was also performed. Although preliminary, no evidence was seen of adverse effects to worm growth or lipid content or of accumulation of PAHs or mercury from exposure to the fly ash. These data show fly ashes with high carbon content could represent viable remedial materials for reducing the bioavailability of organic contaminants in sediments.

Benthic fluxes of mercury species in a lagoon environment (Grado Lagoon, Northern Adriatic Sea, Italy)

Abstract The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive fluxes from porewater and overlying water concentrations, (2) measurements of benthic fluxes using a deployed light benthic chamber in situ and (3) measurements of benthic fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g −1 , showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g −1 ) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L −1 , 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive fluxes (up to 17 ng m −2 day −1 ) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and benthic flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive fluxes in the lagoon (up to 110 ng m −2 day −1 ) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg benthic fluxes were highest in summer at both sites (41,000 and 33,000 ng m −2 day −1 at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O 2 and inversely with DIC, suggesting an important influence of benthic photosynthetic activities on lagoon benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the benthic flux of MeHg was up to 15-fold higher in sediments overlain by O 2 depleted waters. In the anoxic phase, the MeHg fluxes proceeded in parallel with Fe fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column.

Marine sediment toxicity identification evaluation methods for the anionic metals arsenic and chromium

Marine sediments accumulate a variety of contaminants and, in some cases, demonstrate toxicity because of this contamination. Toxicity identification evaluation (TIE) methods provide tools for identifying the toxic chemicals causing sediment toxicity. Currently, whole-sediment TIE methods are not available for anionic metals like arsenic and chromium. In the present paper, we describe two new anion-exchange resins used in the development of whole-sediment TIE methods for arsenic and chromium. Resins were shown to reduce whole-sediment toxicity and overlying water concentrations of the anionic metals. Sediment toxicity, expressed as the median lethal concentration, was reduced by a factor of two to a factor of nearly six between amended sediment treatments containing resin and those without resin. Aqueous concentrations of arsenic and chromium in the toxicity exposures decreased to less than the detection limits or to concentrations much lower than those measured in treatments without resin. Interference studies indicated that the anion-exchange resins had no significant effect on concentrations of the representative pesticide endosulfan and minimal effects on concentrations of ammonia. However, the anion-exchange resins did significantly reduce the concentrations of a selection of cationic metals (Cd, Cu, Ni, Pb, and Zn). These data demonstrate the utility of anion-exchange resins for determining the contribution of arsenic and chromium to whole-sediment toxicity. The present results also indicate the importance of using TIE methods in a formal TIE structure to ensure that results are not misinterpreted. These methods should be useful in the performance of marine whole-sediment TIEs.

Sensitivities of Australian and New Zealand amphipods to copper and zinc in waters and metal-spiked sediments

The sensitivities of eight benthic amphipods, Chaetocorophium cf. lucasi, Corophium colo, Grandidierella japonica, Hyale crassicornis, Hyale longicornis, Melita awa, Melita matilda and Melita plumulosa, to copper and zinc in water-only and whole-sediment toxicity tests were compared. Whole-sediment tests used copper- (1300 mg/kg) and zinc- (4000 mg/kg) spiked sediments after equilibration for sufficient time to produce pore water and overlying water concentrations below the lowest observable effect concentrations of water-only exposures. Survival of adults (after 10 d) and juveniles (after 96 h), and the metal concentrations in the body tissues of adults, were determined at the end of the tests. Two epibenthic amphipods from the genus Melita were the most sensitive species to aqueous copper and zinc, with a 96-h LC50 value of 120 μg Cu/l for both M. awa and M. plumulosa juveniles, and a 96-h LC50 value of 640 μg Zn/l for juveniles of M. plumulosa. Juvenile amphipods (7-d old) were more sensitive than adult amphipods (>30-d old) in both water-only and whole-sediment tests, with adult-LC50/juvenile-LC50 ratios in water-only tests ranging from 1.2 to l.5 for copper and 1 to 1.4 for zinc. All species except C. colo, C. cf. lucasi and M. matilda were sensitive to the copper-spiked sediment, with survival between 14% and 74% of controls. Similarly, all species except C. colo and G. japonica, showed a response to the zinc-spiked sediment (26–81% of control survival). The epibenthic amphipods were more sensitive than the infaunal tube-dwelling amphipods and are recommended as test species.

Toxicity and bioaccumulation of tributyltin in Hyalella azteca from freshwater harbour sediments in the Great Lakes Basin, Canada

This study was designed to evaluate the risk that tributyltin (TBT) levels in harbour sediments pose to the freshwater invertebrate Hyalella azteca and to rank TBT as an environmental concern compared with inorganic metal species. Four-week toxicity tests and 2-week bioaccumulation tests were conducted with sediments collected from five harbours historically contaminated with TBT: Montreal, Kingston, Toronto, Hamilton, and Port Weller. While there was no observable effect of TBT on survival or growth of H. azteca, bioaccumulation of TBT exceeded levels expected to cause chronic toxicity in some sediments from Kingston, Montreal, and Port Weller. There was a positive relationship between TBT in H. azteca and TBT in sediments (r2 = 0.72), although TBT in field sediments was less bioavailable than in laboratory-spiked sediments. Body concentrations of arsenic, cadmium, chromium, cobalt, lead, manganese, nickel, and thallium were well below levels expected to cause toxicity in H. azteca. However, overlying water concentrations of copper and zinc approached or exceeded levels of concern in Toronto, Hamilton, and Port Weller sediments. This research suggests that levels of TBT in harbour sediments may cause chronic toxicity to H. azteca and freshwater invertebrate species of similar sensitivity and that copper and zinc also pose a risk at these sites.

Assessing the cause of impacts on benthic organisms near Rouyn-Noranda, Quebec

Sediments from lakes near Rouyn-Noranda, Quebec, contain elevated concentrations of several metals, including Cd, Cu, Pb and Zn. Amphipods, fingernail clams, mayflies and tanytarsid midges were absent, and sediment toxicity was observed in chronic tests with Hyalella in sediments from Lac Dufault, the lake closest to Rouyn-Noranda. Bioaccumulation by Hyalella demonstrated elevated bioavailability of Cd, Co, Cr, Pb and Tl, but only Cd was accumulated to levels close to the toxic threshold. Copper, which is regulated by Hyalella, was not elevated in these amphipods, but it was elevated in overlying water in the toxicity tests. Toxic effects in Lac Dufault sediments are probably caused primarily by Cd, at least in amphipods, with a possible minor contribution from Cu. An integrated assessment, including sediment chemistry, benthic community composition, sediment toxicity, metal bioaccumulation in benthos, and comparison of bioaccumulation and/or overlying water concentrations with threshold effect concentrations, provides the best indication of effects and their cause.

A tropical sediment toxicity test using the dipteranChironomus crassiforcepsto test metal bio availability with sediment pH change in tropical acid-sulfate sediments

The wetlands of the Magela floodplain of northern Australia, which is the major sink for dissolved metals transported in the Magela Creek system, contain acid-sulfate sediments. The rewetting of oxidized acid-sulfate soil each wet season produces acidic pulses that have the potential to alter the bioavailability of sediment-associated metal contaminants. Acute toxicity tests (72-h mean lethal concentration [LC50]) using the tropical chironomid Chironomus crassiforceps Kieffer showed that copper toxicity decreased from 0.64 mg/L at pH 6 to 2.30 mg/L at pH 4. Uranium toxicity showed a similar trend (36 mg/L at pH 6 and 58 mg/L at pH 4). Sediment toxicity tests developed using C. crassiforceps also showed that both metals were less toxic at the lower sediment pH with pore-water copper toxicity having a lowest-observed-effect concentration of 4.73 mg/L at pH 4 compared to 1.72 mg/L at pH 6. However, a lower pH increased pore-water metal concentrations and overlying water concentrations in bioassays. Hydrogen ion competition on metal receptor sites in C. crassiforceps was proposed to explain the decrease in toxicity in response to increased H+ activity. This study highlights the need to consider site-specific physicochemical conditions before applying generic risk assessment methods.

A tropical sediment toxicity test using the dipteran Chironomus crassiforceps to test metal bioavailability with sediment pH change in tropical acid-sulfate sediments.

The wetlands of the Magela floodplain of northern Australia, which is the major sink for dissolved metals transported in the Magela Creek system, contain acid-sulfate sediments. The rewetting of oxidized acid-sulfate soil each wet season produces acidic pulses that have the potential to alter the bioavailability of sediment-associated metal contaminants. Acute toxicity tests (72-h mean lethal concentration [LC50]) using the tropical chironomid Chironomus crassiforceps Kieffer showed that copper toxicity decreased from 0.64 mg/L at pH 6 to 2.30 mg/L at pH 4. Uranium toxicity showed a similar trend (36 mg/L at pH 6 and 58 mg/L at pH 4). Sediment toxicity tests developed using C. crassiforceps also showed that both metals were less toxic at the lower sediment pH with pore-water copper toxicity having a lowest-observed-effect concentration of 4.73 mg/L at pH 4 compared to 1.72 mg/L at pH 6. However, a lower pH increased pore-water metal concentrations and overlying water concentrations in bioassays. Hydrogen ion competition on metal receptor sites in C. crassiforceps was proposed to explain the decrease in toxicity in response to increased H+ activity. This study highlights the need to consider site-specific physicochemical conditions before applying generic risk assessment methods.

Partitioning and bioaccumulation of cadmium in artificial sediment systems: application of a stable isotope tracer technique

The utility of stable isotope tracers for investigating the relationship between cadmium (Cd) partitioning in artificial sediment–water systems and Cd accumulation in a benthic detritivore ( Asellus racovitzai, Isopoda) was explored. In the laboratory, Cd isotopes were applied to synthetic sediment and isotope concentrations were measured in sediment, overlying water and exposed asellids over a 10-day period. Isotope ratios measured in sediment and water were compared to ratios measured in asellids to determine whether Cd partitioning could predict metal bioaccumulation. Two different parameters which might affect Cd partitioning between the sediment and overlying water compartments were investigated: the chemical form in which Cd was added to systems, and the organic matter content of the sediment. To test the effect of chemical form on Cd partitioning, three isotopes of cadmium were individually applied to formulated sediment in varying combinations of 113 Cd( NO 3) 2 , 112Cd-humic acid (HA) 114 CdSO 4 . The results demonstrated that chemical form did not influence partitioning, as the Cd isotope that was applied to sediment in the nitrate form exhibited similar partitioning between sediment and overlying water as the isotope that was applied in the sulfate or HA form. However, Cd isotope concentrations in overlying water were strongly related to the pattern of isotope accumulation in asellids suggesting that overlying water concentrations determined Cd bioaccumulation. In contrast, when the organic matter content of sediment was increased through the addition of Sphagnum peat moss, total Cd concentrations in overlying water and tissue were low, and there was no relationship between Cd-isotope concentrations in tissue and water. These results indicate that Cd accumulation occurred primarily from water, and factors that increase metal partitioning to sediment, such as increased sediment organic matter content, decrease Cd accumulation in asellids. The stable isotope tracer method described herein appears to be a useful technique for investigating the relationship between metal partitioning and bioaccumulation in simple sediment systems, but could also be extended to more complex systems, and used with different metals that have multiple stable isotopes.

Patterns of gross deposition in reservoirs enriched in inorganic tripton

Magnitudes and patterns in the deposition of chlorophyll (Chl), organic carbon, particulate phosphorus (PP), and suspended solids are documented for seven New York reservoirs based on analyses of metalimnetic and near-bottom sediment trap collections. Inorganic material dominated the trap collections and caused a decoupling of the downward fluxes of Chl and PP because of major contributions of inorganic components to P deposition. These contributions were manifested in the stoichiometry of trap collections, the much higher estimates of settling velocity (SV) for PP compared with Chl, and differences in patterns of Chl and PP deposition within individual reservoirs and among these systems. Most of the deposited phosphorus in these reservoirs (71–98%) was associated with nonphytoplankton particles. In contrast to the other constituents, the estimates of SV for Chl were lower and more uniform; nearly 50% of the individual estimates (n = 188) were between 0.15 and 0.25 m·day–1. Longitudinal gradients in sediment deposition occurred as a result of gradients in both overlying water concentrations and settling characteristics of the particles. Seasonal and vertical patterns in trap collections and budget calculations indicate that resuspension contributed to deposition, to varying extents, in all of the reservoir basins.

Assessing the toxicity of lead in sediments to Hyalella azteca: the significance of bioaccumulation and dissolved metal

The relationship between bioaccumulation and toxicity of Pb to Hyalella was the same for animals exposed to Pb in water alone and for those exposed to Pb-spiked sediments, provided that the animals were gut cleared before Pb analysis. The same critical body concentration (about 126 nmol·g dry mass-1) can be used to predict Pb toxicity in both water-only and sediment exposures. Furthermore, Pb bioavailability in Pb-spiked sediments was due primarily to dissolved metal: animals caged above the sediments accumulated the same amount of Pb and had the same mortality as animals exposed directly to sediment. Increasing the water to sediment ratio from 4:1 to 67:1 resulted in a lower dissolved organic C and lower total dissolved Pb concentration in the water but no change in bioavailable Pb (i.e., bioavailable Pb was not proportional to total dissolved Pb). The overlying water concentration may be a useful indicator of bioavailable Pb in sediment tests, provided a large water to sediment ratio is used to reduce the effect of sediment on overlying water quality (i.e., Pb-complexing capacity). Although less reliable than body concentration measurements, this could provide a useful screening tool for possible Pb-induced toxicity because it can be measured without test animals present.

Use of Ulva Lactuca to distinguish pH‐dependent toxicants in marine waters and sediments

AbstractUlva lactuca (sea lettuce) is a cosmopolitan marine attached green seaweed capable of sequestering high environmental levels of ammonia. Ammonia can be acutely toxic to marine organisms and is often found in dredged sediments from highly industrial areas or from areas with high carbon inputs. For the purposes of dredged sediment disposal as well as in determining causes of toxicity in complex mixtures, it is important to distinguish ammonia toxicity from the toxicity of other compounds. The use of U. lactuca to selectively remove ammonia from waters and sediments as part of a toxicity identification and evaluation (TIE) procedure was evaluated. Ulva lactuca lowered concentrations of total ammonia from 75 to 17 mg/L in <8 h in water‐only exposures. This treatment also reduced 48‐h amphipod mortality from 75 to 20%. In whole sediments, U. lactuca lowered interstitial water concentrations of ammonia from 60 to 20 mg/L, while keeping overlying water concentrations below detectable limits (<1 mg/L). To determine the limitations of the U. lactuca method to selectively remove ammonia from solution, metal and organic accumulation experiments were performed. Ulva lactuca generally took up <15% of metals present, with most of the exposures resulting in less than a 10% uptake. In contrast, U. lactuca removed 77% of lindane and 95% of fluoranthene. Results of a TIE conducted on sediments from an industrial marine harbor indicated U. lactuca was useful, in conjunction with other procedures, in categorizing ammonia as a sediment toxicant.

Relaxation of phosphorus limitation due to typhoon‐induced mixing in two morphologically distinct basins of Lake Biwa, Japan

We measured changes in hydrodynamics and phosphorus cycling due to a typhoon in two morphologically distinct basins of Lake Biwa, Japan. The typhoon, with wind speeds up to 20 m s−1, led to physical, chemical, and physiological responses that differed dramatically in the shallow (mean depth of 3.5 m), eutrophic south basin compared to the deep (mean depth of 45.5 m), oligo‐mesotrophic north basin. Prior to the typhoon, PO4‐P concentrations were <l µg liter−1 in both basins. A suite of physiological tests (protein:carbohydrate ratio, sestonic C:N:P ratios, nutrient‐enrichment bioassays, alkaline phosphatase activity, 32P uptake) all indicated that the plankton was P‐deficient. Bacteria dominated (avg of 65%) the uptake of 32PO43−. As a result of the typhoon, P concentrations increased to −2.5 pg liter−1 and suspended solids increased from 4.5 to ~17 mg liter−1 in the south basin. The day after the typhoon, all physiological tests indicated that the south basin plankton was P‐sufficient and that phytoplankton dominated (65%) 32P‐uptake. A week after the typhoon, P concentrations had dropped to near pre‐typhoon levels and the physiological tests indicated that the plankton was again P‐deficient. Only on the day of the typhoon were wavg‐induced shear stresses great enough to cause considerable entrainment of sediment and associated pore waters in the South Basin. Because interstitial porewater P concentrations were ≥2 orders of magnitude greater than the overlying water concentration, we concluded that the increase in P was caused by entrainment of nutrient‐rich pore water. In the north basin the typhoon‐induced upwelling and mixing in the thermocline did not penetrate to depths where P concentrations were elevated. Consequently, plankton were as P deficient immediately after the typhoon as they were prior to it.