Sediments In Aquatic Systems Research Articles

ASSESSMENT OF PHYSICOCHEMICAL PARAMETERS AND METAL CONTAMINATION IN SEDIMENTS OF THE PERI-URBAN AMAGBA-OKOROMA RIVER, BENIN CITY, NIGERIA.

The key role of sediments in aquatic systems is widely known, sediments are frequently neglected as a factor in the evaluation of water quality assessment. This study assessed the sediment quality of the Peri-urban Amagba-Okoroma River, Benin City, Nigeria, emphasizing physicochemical parameters and heavy metal contamination. Three sites (Upstream site 1, Midstream site 2 and Downstream site 3) were studied and river sediments were collected from each of these sites using Van veen grab. The sediments were collected three times each in the month of March and July, 2023. The results revealed temperature (25.67°C-26°C), slightly alkaline pH (7.55-7.68), and low electrical conductivity (49.33µS/cm-54.67µS/cm). Heavy metals evaluated were all within threshold/probable effect level guideline: Cd (0.09-0.10 mg/kg), Cr (5.61-6.10mg/kg), Cu (18.62-19.90mg/kg), Pb (0.33t-0.37mg/kg), and Zn (32.47-35.01mg/kg). However, Cu slightly exceeded thresholds-effect level limits at midstream site 2 and downstream site 3, indicating localized pollution sources. Principal component analysis and cluster analysis identified significant correlations between Cd-Cr and Cu-Zn, suggesting shared pollution sources likely from industrial or agricultural runoff. Cluster analysis reveal that sites 2 and 3 are more similar compare to site 1 (upstream). The heavy metal pollution indices collectively indicated no sediment contamination across the sites. Geo-accumulation index values for Cd, Cr, Cu, Pb, and Zn suggested unpolluted conditions across all sampling sites. Contamination factor values corroborated these findings, indicating low contamination levels for all metals. Contamination degree values further confirmed the sediment's low degree of contamination, aligning with Pollution load index values, indicating non-pollution. This study underscores the significance of regular monitoring and targeted mitigation efforts to sustain the ecological health of the river ecosystem amidst potential anthropogenic pressures.

Spatiotemporal Changes in Trace Metal Bioavailability in the Sediment Pore water of a Constructed Wetland Using Passive Pore water Samplers.

Sediments in aquatic systems often act as a major sink for contaminants. Diffusive gradient in thin films (DGTs) and in situ equilibrium dialysis samplers (peepers) are two major in situ pore water sampling devices that overcome the problems associated with conventional pore water sampling methods. In the present study, DGTs and peepers were used to study the spatial and seasonal effects (cool months, October-February; warm months, May-September) on metal bioavailability in the H-02 constructed wetland and the sink versus source role of the sediments by calculating the metal resupply capacity. Data showed similar seasonal trends in metal concentrations using passive samplers, peepers, and DGTs. Pooled Cu and Zn concentrations measured using DGTs were lower in warm months (1.67 ± 1.50 and 2.62 ± 0.68 μg L-1 , respectively, p < 0.001) versus in cool months (2.12 ± 0.65 and 5.58 ± 1.33 μg L-1 , respectively, p < 0.001; mean ± 95% confidence interval). Sulfate (SO4 2- ) concentrations were significantly (p = 0.0139) lower in warm months (averaged at 0.22 ± 0.05 mg L-1 ) compared to in cool months (0.16 ± 0.05 mg L-1 ). The increase in SO4 2- concentration is an indicator of the lower activity of sulfate-reducing bacteria, which need SO4 2- during anaerobic respiration, in which SO4 2- is reduced to sulfide (S2- ) that forms insoluble salts with Cu and Zn, which could partially explain the higher bioavailability of these metals in the cool season. Metal resupply capacity of the sediments was mostly <0.2 for Cu and Zn. Taken together, the H0-2 wetland sediments mostly acted as a sink to both Cu and Zn over the course of the present study. Environ Toxicol Chem 2023;42:2726-2736. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Evaluation of preventative algaecide treatments for cyanobacterial resting cells in sediments of a central US lake

Kinley-Baird CM, Smith EF, Calomeni AJ, McQueen AD, Gusler GO, Boyer M, Decker KN, Clyde GA. 2023. Evaluation of preventative algaecide treatments for cyanobacterial resting cells in sediments of a central US lake. Lake Reserv Manage. 39:340–355.Cyanobacteria can overwinter in sediments of aquatic systems as resting cells and contribute to harmful algal bloom (HAB) resurgences. We evaluated field-scale preventative algaecide treatments in April 2022 in terms of effectiveness for decreasing viability of cyanobacterial resting cells, with the goal of minimizing planktonic growth in season. Two consecutive treatments of a granular peroxide-based algaecide (GreenClean PRO) were applied (48 h apart) in a Kansas, United States, lake. Treatments were applied to a 31.5 ha treatment zone, separated from a 12.9 ha control zone using a silt curtain. Treatment design was informed by laboratory algaecide efficacy experiments using site-collected samples. In-lake treatment performance was evaluated based on comparisons of planktonic cyanobacterial densities in the treatment and control zones measured every 2 weeks for 4 months, then monthly for 2 additional months. Other lines of evidence included resting cell densities and recruitment viability in sediments 3 d after treatments were performed. For 9 of 11 sampling events from May to October, average planktonic cyanobacterial densities trended lower in the treatment zone than in the control zone (ranging from 6 to 97% lower). Declines in sediment cell density and recruitment of resting cells in laboratory assessments were not measurable 3 d after treatments were performed. Additional studies will be necessary to strengthen the database supporting use of this management strategy. However, there may be an opportunity to expand the model for how algaecides are used to manage HABs more effectively and efficiently in freshwater resources.

Source apportionment of polychlorinated dibenzo-p-dioxins and dibenzofurans in the sediments of an urban estuary.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in the sediments of aquatic systems are a persistent global problem that poses serious health risks. Identifying the sources of dioxins in natural water systems and the extent of their contributions to observed sediment concentrations is important from a health advisory and mitigation perspective. This paper proposes novel distribution-based qualitative and quantitative methods as source apportionment techniques and alternatives to conventional source attribution methods. Using sampled data, air, runoff, industrial effluent, and industrial paper and pulp wastes were identified as four distinct dioxin contributors to concentrations found in the sediments of the test bed region: the Houston Ship Channel-San Jacinto River-Galveston Bay (HSC-SJR-GB) estuarine system that also includes 2 Superfund sites with dioxin contamination. Two qualitative methods, the Kullback-Leibler divergence (K-L divergence) and the Bhattacharya measure (BM), and a quantitative method, the L2 norm, were used to investigate the spatial and temporal sourcing patterns of dioxins in the system sediments. The results indicated a global contribution from air and runoff sources across the estuarine system and over time with more localized impacts of the Superfund sites and the industrial sources. The results using the developed methodologies were compared with the output from the more conventional positive matrix factorization (PMF) method. Statistically significant correlations were observed among source contributions from the proposed methods and the PMF method, with Spearman's ρ ranging between - 0.596 to - 0.963 and 0.652 to 0.719, demonstrating the utility of the sourcing approaches used in the study. Additionally, the proposed methods were found to be rigorous in terms of elucidating spatial and temporal changes in the sourcing of dioxin to the estuary, indicating their suitability for use for other contaminants and other estuarine systems.

Mercury methylation in oxic aquatic macro-environments: a review

Mercury methylation in aquatic environments is a key process that incorporates this neurotoxin into the food chain and ultimately the human diet. Mercury methylation is considered to be essentially biotic and mainly driven by sulfate-reducing bacteria present in the bottom sediments in aquatic systems. However, in recent decades, many researchers have shown that this methylation also occurs in oxic layers in conjunction with a high content of particulate organic matter and localized depletion of dissolved oxygen. The goals of this review are to summarize our current understanding of Hg methylation in water columns of both marine and freshwater environments, as well as to highlight knowledge gaps and future research needs. Most of the literature showed that suspended particles (known as marine and lake snow) could be the microenvironment in which Hg methylation could occur across oxic water columns, because they have been recognized as a site of organic matter mineralization and as presenting oxygen gradients around and inside them. To date, the majority of these studies concern marine environments, highlighting the need for more studies in freshwater environments, particularly lacustrine systems. Investigating this new methylmercury production environment is essential for a better understanding of methylmercury incorporation into the trophic chain. In this review, we also propose a model which attempts to highlight the relative importance of a MeHg epilimnetic path over a MeHg benthic-hypolimnetic path, especially in deep lakes. We believe that this model could help to better focus future scientific efforts in limnic environments regarding the MeHg cycle.

Synthesis and evaluation of zirconia/magnetite/zeolite composite for controlling phosphorus release from sediment: A laboratory study

Although the conventional zirconium-based solid-phase phosphorus (P)-inactivating agents (ZrPIAs) have high potential for controlling P release from sediments in aquatic systems, they are difficultly retrieved from sediments after their application. Therefore, it is very necessary to develop new ZrPIAs that can be readily retrieved from sediments after their application. In this study, a novel magnetic ZrPIA, i.e., zirconia/magnetite/zeolite composite (ZMZ) was prepared, characterized and used as a sediment amendment to control the release of P from sediments. The adsorption performance and mechanism of phosphate on ZMZ were studied using batch experiments and XPS analysis. The impact of ZMZ addition on the releasing flux of P from sediments to the overlying water as well as on the fractionation and bioavailability of P in sediments was studied using microcosm incubation experiments. In addition, the stability of P captured by ZMZ was also investigated. Results showed that ZMZ exhibited high adsorption ability towards phosphate, with a maximum phosphate adsorption capacity of at least 4.1 mg P/g, and phosphate adsorption onto ZMZ was mainly controlled by inner-sphere complex formation mechanism. The ZMZ addition greatly decreased the releasing flux of P from sediments into the overlying water in anoxic environment, with a DTP (dissolved total P) reduction efficiency of 61.8–97.8%. Moreover, the added ZMZ could immobilize mobile P in sediments by changing P species from Na2S2O4/NaHCO3-extractable P (BD-P) to NaOH-extractable P (NaOH-rP) and residual P (ResP). Furthermore, the bioavailability of P in sediments could be reduced by the addition of ZMZ. The stability evaluation of P captured by ZMZ after its application showed that a majority of P adsorbed by ZMZ existed in the form of NaOH-rP and ResP, which were difficult to be re-released into the water column under common pH (5–9) and reducing condition. In summary, the above results demonstrate the high potential for the application of ZMZ as an amendment in the control of P release from sediments.

Speciation, Distribution and Risk Assessment of Metals in Sediments from a Water Body Replenished by Effluent from a Wastewater Treatment Plant.

To assess the status and risk of metal pollution in landscape water body replenished by wastewater treatment plant effluent, the distribution of metals in sediments from three regions [regulation pond (RP), wetland lake (WL), and main lake (ML)] of Harbor Lake, Tianjin, China, was characterized. Higher levels of all metals (except Cr and Pb) were observed in RP sediments. As, Cr, Cu, Ni, Pb, and Zn were mainly bound to organic matter and sulfide (F3) and residual fractions (F4), while the exchangeable and carbonate fraction (F1) and Fe/Mn oxide fraction (F2) were the dominant forms for Cd. Additionally, finding showed that the overall risk of sediments in aquatic systems was affected by both metal toxicity and metal fractionation. Thus, according to a modified risk assessment code (RAC), the potential adverse effect of metals in sediments was medium (although As, Cd, Ni, and Zn had high mobility risks based on the RAC), decreasing in the order RP > WL > ML.

The importance of sediments in ecological quality assessment of stream headwaters: embryotoxicity along the Nidda River and its tributaries in Central Hesse, Germany

BackgroundAlthough the crucial importance of sediments in aquatic systems is well-known, sediments are often neglected as a factor in the evaluation of water quality assessment. To support and extend previous work in that field, this study was conducted to assess the impact of surface water and sediment on fish embryos in the case of a highly anthropogenically influenced river catchment in Central Hesse, Germany.ResultsThe results of 96 h post fertilisation fish embryo toxicity test with Danio rerio (according to OECD Guideline 236) revealed that river samples comprising both water and sediment exert pivotal effects in embryos, whereas surface water alone did not. The most prominent reactions were developmental delays and, to some extent, malformations of embryos. Developmental delays occurred at rates up to 100% in single runs. Malformation rates ranged mainly below 10% and never exceeded 25%.ConclusionA clear relationship between anthropogenic point sources and detected effects could not be established. However, the study illustrates the critical condition of the entire river system with respect to embryotoxic potentials present even at the most upstream test sites. In addition, the study stresses the necessity to take into account sediments for the evaluation of ecosystem health in industrialised areas.

Determining the Sediment Quality of Yağlıdere Stream (Giresun)

Sediments in aquatic systems are often contaminated by various pollutants originating from the sources such as industrial and agricultural discharges, municipal wastewater treatment plants, and storm water. These effects lead to the need to develop sediment quality objectives regarding the protection of aquatic ecosystems and human health. In this study, the sediment samples were collected from five sampling sites and then analyzed in order to identify the concentrations of certain metals (As, Se, Ag, Cd, Na, and K), the levels of pH, conductivity, water content (%) and organic matter (%) in the Yağlıdere Stream. Finally, Geo-accumulation index values calculated based on the estimations regarding the background trace element concentrations suggested the anthropogenic influences in most of the samples. In conclusion, it was observed that K, Na, As, and Se dominantly accumulated in the study area. These metals may have a negative impact on the research area and create an environmental risk.

Distribution of high Zn concentrations in unvegetated and Typha domingensis Pers. vegetated sediments

Fil: Di Luca, Gisela Alfonsina. Universidad Nacional del Litoral. Facultad de Ingenieria Quimica. Laboratorio de Quimica Analitica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

&lt;b&gt;Diffuse sources of pollution and their influence on the nature of the sediments in Água Preta Lake

Sediments in aquatic systems are indicators of contamination levels. Therefore, they play an important role in the assessment of the nature and intensity of human impact on aquatic environments. The objective of this work was to assess the levels of pollution by determining the concentrations of various metals and phosphorus forms in the sediments of Água Preta Lake, which supplies water to the Metropolitan Region of Belém, in north-eastern Brazil. Our data indicate non-uniform sedimentation with a large granulometric fraction of silt. The predominant form of phosphorus was inorganic phosphorus, to the detriment of the organic form. Observed mean concentrations of nickel, copper, lead, and zinc were lower than the PEL (Probable Effect Level). However, the highest observed concentrations of nickel and lead exceeded the prescribed TEL (Threshold Effect Level), which suggests pollution from an anthropogenic source.

Combined effects of cadmium and zinc on growth, tolerance, and metal accumulation in Chara australis and enhanced phytoextraction using EDTA

Chara australis (R. Br.) is a macrophytic alga that can grow in and accumulate Cd from artificially contaminated sediments. We investigated the effects of Zn independently and in combination with Cd on C. australis growth, metal tolerance, and uptake. Plant growth was reduced at concentrations ≥75mg Zn (kg soil)−1. Zn also increased the concentration of glutathione in the plant, suggesting alleviation of stress. Phytotoxic effects were observed at ≥250mg added Zn (kg soil)−1. At 1.5mg Zn (kg soil)−1, the rhizoid bioconcentration factor (BCF) was >1.0 for both Cd and Zn. This is a criterion for hyperaccumulator status, a commonly used benchmark for utility in remediation of contaminated soils by phytoextraction. There was no significant interaction between Cd and Zn on accumulation, indicating that Chara should be effective at phytoextraction of mixed heavy metal contamination in sediments. The effects of the chelator, ethylenediaminetetraacetic acid (EDTA), were also tested. Moderate levels of EDTA increased Cd and Zn accumulation in rhizoids and Cd BCF of shoots, enhancing Chara′s potential in phytoremediation. This study demonstrates for the first time the potential of macroalgae to remove metals from sediments in aquatic systems that are contaminated with a mixture of metals.

An interlaboratory comparison of sediment elutriate preparation and toxicity test methods

Elutriate bioassays are among numerous methods that exist for assessing the potential toxicity of sediments in aquatic systems. In this study, interlaboratory results were compared from 96-h Ceriodaphnia dubia and Pimephales promelas static-renewal acute toxicity tests conducted independently by two laboratories using elutriate samples prepared from the same sediment. The goal of the study was to determine if the results from the elutriate tests were comparable between two U.S. Environmental Protection Agency (USEPA) laboratories when different elutriate preparation procedures were employed by each lab. Complete agreement in site characterization was attained in 22 of the 25 samples for both bioassays amongst each lab. Of the 25 samples analyzed, 10 were found to be toxic to at least one of the species tested by either laboratory. The C. dubia elutriate tests conducted by the National Exposure Research Laboratory (NERL) indicated that 7 of the 25 sediment samples were toxic, while 8 sediment samples were characterized as such in testing conducted by USEPA Region 6 (Region 6). The P. promelas elutriate tests conducted by NERL determined 8 samples as toxic, while Region 6 tests displayed toxicity in 5 of the samples. McNemar's test of symmetry for C. dubia (S = 0.33, p = 0.5637) and P. promelas (S = 3.0, p = 0.0833) tests indicated no significant differences in designating a site toxic between NERL and Region 6 laboratories. Likewise, Cohen's kappa test revealed significant agreement between NERL and Region 6 C. dubia (K = 0.7148, p < 0.01) and P. promelas (K = 0.6939, p < 0.01) elutriate tests. The authors conclude that differences in interlaboratory elutriate preparation procedures have no bearing on the ability of either the C. dubia or P. promelas bioassay testing methods to detect toxicity while yielding similar results.

Cd Tolerance and Accumulation in the Aquatic Macrophyte,Chara australis: Potential Use for Charophytes in Phytoremediation

We investigated the potential use of the alga Chara australis (R. Br.) forphytore mediation of Cd-contaminated sediments in aquatic systems. Chara tolerated up to 20 mg added Cd (kg soil)⁻¹ in laboratory culture. Chlorophyll a and b levels were not affected even at Cd concentrations that suppressed growth. Levels of glutathione were suppressed at 2-35 mg added Cd (kg soil)⁻¹ to 200-350 nmol GSH (g DW)⁻¹, while control levels were 660 nmol GSH (g DW)⁻¹). Histochemical studies showed Cd occurred throughout cell walls and cytoplasm in plants grown in 5-20 mg Cd (kg soil)⁻¹. Quantification using ICP-MS showed the maximum concentration in shoots was 72 mg Cd (kg DW)⁻¹ at 35 mg added Cd (kg soil)⁻¹, while the maximum in rhizoids was 116 mg Cd (kg DW)⁻¹ at 25 mg added Cd (kg soil)⁻¹. The bioconcentration factor (BCF, concentration in plant/concentration in soil) exceeded 1.0, the critical value for hyperaccumulators, for shoots exposed to 35 mg Cd (kg soil)⁻¹ and rhizoids exposed to ≥25 mg Cd (kg soil)⁻¹. Translocation factors (TF, shoot concentration/rhizoid concentration) did not exceed 1.0 for any treatment. While Chara cannot be considered a hyperaccumulator, it shows promise for use in phytoremediation efforts.

Sediments and the “System”: from site-specific to regional-scale research

Sediments are part of the erosion–sedimentation cycle; material from the terrestrial environment is turned into rock, boulders and sand-, siltand clay-sized particles through weathering, which are subsequently transported by wind and water erosion through rivers, and ultimately end up in the ocean. During transport, temporary deposition takes place in the river beds, flood plains, wetlands, deltas and estuaries (Fig. 1). In these depositional areas, sediment is an integral part of the ecosystem. Geology deals with research in both ancient and recent deposits of sediments. More than 14,000 books listed by Amazon under the search term “sediments” reflect the current education and research effort on this topic, which started more than 200 years ago (Hutton 1788). The more recent aspects of sediments and sedimentology are covered by our journal; the impact of humans on the quality and quantity of sediments in aquatic systems. Here, the survey of Amazon, using “sediment pollution”, shows about 1,200 books which are still for sale. On the other hand, searching in Google Scholar really shows how active our field is: for “sediment”, there are 1,460,000 hits and for “sediment pollution”, the number is 583,000. These simple crude statistics suggest that one third of all sediment research deals with pollution aspects. Looking back, research on sediment pollution reflects the typical sequence of academic research through research for legislation to implementation (Fig. 2). In the first part of the twentieth century, sediment pollution research was in the realms of classic geochemistry (Goldschmidt 1954). Important applied areas included research for ore prospecting and micronutrients in soil science. In fact, in The Netherlands, elevated levels of heavy metals in wetlands from the Rhine–Meuse delta were detected during soil surveys in order to determine their potential for agricultural use after embankment. Human fatalities in Japan, linked to sediments and soils (Hagino and Yoshioka 1961; Fujiki 1972), caused worldwide concern. These and other incidents really put contaminated sediments on the political agenda as a societal issue. Hence, since the 1970s sediment research became policy driven with ample funding to determine its extent and potential impact (i.e. “Coming to Grips” in Fig. 2). Subsequently, several techniques were developed to determine and predict such impacts. These included geochemical modelling of aquatic systems (e.g. Garrels and Christ 1965; Stumm and Morgan 1971) and the biogeochemical processes in the deposited sediments (e.g. Berner 1971) and the introduction of bio-assays (e.g. Sunda and Guillard 1976). In addition, comparisons were made with contaminant levels to those found in unpolluted sediments, and the mode of occurrence of contaminants in sediments was studied to infer their reactivity (e.g. Forstner and Salomons 1980). For both of us, it has been a struggle on how to write a kind of official “Farewell address” to our colleagues. After all, we do it only once in our lifetime. The result is twofold; we will have one editorial with a broad and short (admittedly very biased) history and outlook of our experience, and a second, more scientific editorial, which covers the first 10 years of our Journal of Soils and Sediments.

Increasing Precision of Turbidity‐Based Suspended Sediment Concentration and Load Estimates

Turbidity is an effective tool for estimating and monitoring suspended sediments in aquatic systems. Turbidity can be measured in situ remotely and at fine temporal scales as a surrogate for suspended sediment concentration (SSC), providing opportunity for a more complete record of SSC than is possible with physical sampling approaches. However, there is variability in turbidity-based SSC estimates and in sediment loadings calculated from those estimates. This study investigated the potential to improve turbidity-based SSC, and by extension the resulting sediment loading estimates, by incorporating hydrologic variables that can be monitored remotely and continuously (typically 15-min intervals) into the SSC estimation procedure. On the Roanoke River in southwestern Virginia, hydrologic stage, turbidity, and other water-quality parameters were monitored with in situ instrumentation; suspended sediments were sampled manually during elevated turbidity events; samples were analyzed for SSC and physical properties including particle-size distribution and organic C content; and rainfall was quantified by geologic source area. The study identified physical properties of the suspended-sediment samples that contribute to SSC estimation variance and hydrologic variables that explained variability of those physical properties. Results indicated that the inclusion of any of the measured physical properties in turbidity-based SSC estimation models reduces unexplained variance. Further, the use of hydrologic variables to represent these physical properties, along with turbidity, resulted in a model, relying solely on data collected remotely and continuously, that estimated SSC with less variance than a conventional turbidity-based univariate model, allowing a more precise estimate of sediment loading, Modeling results are consistent with known mechanisms governing sediment transport in hydrologic systems.

Comparison of Bulk Sediment and Sediment Elutriate Toxicity Testing Methods

Numerous methods exist for assessing the potential toxicity of sediments in aquatic systems. In this study, the results from 10-day bulk sediment toxicity test methods using Hyalella azteca and Chironomus tentans were compared to results from 96-h Pimephales promelas and Ceriodaphnia dubia renewed acute toxicity tests conducted using elutriate samples prepared from the same sediments. The goal of the study was to determine if the results from the elutriate tests were comparable to those obtained from the bulk sediment tests. Of the 25 samples analyzed, 16 were found to be toxic to at least one of the species tested, in either elutriate or bulk sediment tests. The C. tentans 10-day bulk sediment test was the most sensitive, with 12 sediment samples exhibiting toxicity to this species, whereas the H. azteca bulk sediment test and C. dubia 96-h elutriate test were the least sensitive, exhibiting toxicity in only 7 of the 25 sediments tested. The P. promelas elutriate test found 8 of the 25 sediments to be toxic. Based on the total number of sites found to show toxicity, results from testing indicate 96-h elutriate tests show a level of sensitivity comparable to 10-day bulk sediment tests in assessing toxicity quantitatively. However, the methods did not always find toxicity at the same sites, suggesting that the ability of elutriate tests to predict toxicity (quantitatively) is not statistically correlated with bulk sediment methods. This would indicate that a suite of toxicity test methods would provide the most complete measure of site condition; however, in circumstances where bulk sediment testing is not feasible, elutriate tests can provide a practical and credible alternative for toxicity assessment.

Rhizon sampling of porewaters near the sediment‐water interface of aquatic systems

Rhizon samplers were originally designed as micro‐tensiometers for soil science to sample seepage water in the unsaturated zone. This study shows applications of Rhizons for porewater sampling from sediments in aquatic systems and presents a newly developed Rhizon in situ sampler (RISS). With the inexpensive Rhizon sampling technique, porewater profiles can be sampled with minimum disturbance of both the sediment structure and possible flow fields. Field experiments, tracer studies, and numerical modeling were combined to assess the suitability of Rhizons for porewater sampling. It is shown that the low effort and simple application makes Rhizons a powerful tool for porewater sampling and an alternative to classical methods. Our investigations show that Rhizons are well suited for sampling porewater on board a ship, in a laboratory, and also for in situ sampling. The results revealed that horizontally aligned Rhizons can sample porewater with a vertical resolution of 1 cm. Combined with an in situ benthic chamber system, the RISS allows studies of benthic fluxes and porewater profiles at the same location on the seafloor with negligible effect on the incubated sediment water interface. Results derived by porewater sampling of sediment cores from the Southern Ocean (Atlantic sector) and by in situ sampling of tidal flat sediments of the Wadden Sea (Sahlenburg/Cuxhaven, Germany) are presented.

Bioavailability and effects of malathion in artificial sediments on Simocephalus vetulus (Cladocera: Daphniidae).

The pollution of aquatic sediments is critical to the health of aquatic ecosystems. Sediment dwelling organisms are key links in food webs that can lead toxic materials to higher level consumers, such as fish and humans. Sediments in aquatic systems can be both sink and source for inorganic and organic contaminants. The assessment of sediment contamination by laboratory bioassays is essential since it measures the toxicity and the biological response associated with specific concentrations of chemical pollutants. Furthermore, these can indicate if degradation or binding could reduce the bioavailability of chemicals, and can also set the basis for the establishment of safe concentrations.

The use of Fick's First Law for predicting porewater nutrient fluxes under diffusive conditions

AbstractPorewater fluxes into or out of the sediments in aquatic systems are frequently estimated using Fick's First Law. This assumes that diffusive processes control the transport of nutrients. As a corollary, advection, bioturbation and chemical processes are assumed not to be significant. Through a series of sediment core incubations, this paper seeks to quantify the uncertainties involved in such assumptions. Duplicate sediment cores were collected from 28 sites along the Swan–Canning Estuary, returned to the laboratory and incubated under oxic or anoxic conditions. Porewater nutrient concentrations, sediment porosity and initial nutrient concentrations in the overlying water were measured. These parameters were used to estimate the expected nutrient fluxes via Fick's First Law. The estimated fluxes were then compared with measured fluxes of nutrients out of the sediments over the incubation period. Severe bioturbation occurred in several of the anoxic treatments, resulting in large releases of nutrients into the overlying water. Aside from these bioturbated cores, phosphate and ammonium fluxes under anoxic conditions are well predicted by Fick's First Law. Nitrate fluxes are predicted well under oxic conditions. For coarse sediments (D10 averaging 0·3 mm) and under redox conditions favourable for nutrient release, Fick's First Law predicted close to 100% of the observed fluxes. For finer grain sediments (D10 &lt; 0·01 mm), Fick's First Law overestimated the observed flux by up to 40%. Under unfavourable oxygen conditions, chemical retardation processes are likely to dominate fluxes, and the error associated with using Fick's First Law is increased. These results confirm the usefulness of using Fick's First Law for a baseline estimate of nutrient fluxes under favourable redox conditions. Much greater care must be taken when using Fick's First Law to estimate nutrient fluxes under unfavourable redox conditions, or under conditions when bioturbation is likely to be severe. Copyright © 2001 John Wiley &amp; Sons, Ltd.