Natural Bottom Sediments Research Articles

Microplastics distribution in bottom sediments of the Baltic Sea Proper

An abundance of microplastics particles (0.2–5 mm, MPs) in bottom sediments is analyzed based on 53 samples (3 to 215 m deep) obtained in 8 cruises of research vessels across the Baltic Sea Proper in March–October 2015–2016. MPs content varied between stations from 103 up to 10,179 items kg−1 d.w., with the bulk mean of 863 ± 1371 items kg−1 d.w., showing a statistically significant increase with water depth. As many as 74.5% of MPs are of fibrous shape, followed by films (19.8%) and fragments (5.7%). The distributions of fibres, fragments, films, and different types of natural bottom sediments are significantly different, highlighting the specific behaviour of each of these kinds of bottom deposits. A statistically significant correlation between water depth and fibres content is found. Based on the analysis of oceanographic factors and sedimentological principles, an erosion/transition/accumulation pattern for fibres in the Baltic Sea Proper is outlined. Fibres can be considered as a specific type of “synthetic sediment”, while principles of distribution of other MPs are not yet certain.

Accumulation of polychlorinated biphenyls (PCB) associated with bottom sediments in larvae of Chironomus riparius Meigen

Patterns of bioaccumulation of polychlorinated biphenyls (PCBs) by chironomid larvae (Chironomus riparius Meigen) were studied under laboratory conditions. Larvae were maintained for 20 days, separately in two batches of natural bottom sediments sampled from Rybinsk Reservoir (Russia), each differing in PCB content (425.6 μg / kg or 24.8 μg / kg dry weight, respectively). The study revealed that chironomid larvae accumulated PCBs at levels comparable to the PCB content measured in sediments from each exposure. The bioaccumulation coefficient (1.11 and 1.59, respectively, as per dry weight for compared sediment batches) depended directly on the sum PCB content in sediments. At high sediment PCB content, the ratios of homologous groups of PCBs in larvae and sediment were identical and corresponded to the Aroclor 1254 congeners profile; at lower PCB content, pronounced differences were revealed. In larvae, the ratios of 3, 4, 5, and 6CB homologues were evenly distributed at levels of 20–34 %, while the 4CB homologues prevailed (47 %) in sediments. The content of the latter compounds in larvae was lower than in sediments, and higher for the other homologous groups. The study indicates selective bioaccumulation of various homologous groups of PCBs under conditions of low sediment PCB content.

Reservoir bottom sediments as heterogeneous catalysts for effective degradation of a selected endocrine-disrupting chemical via a Fenton-like process

The work detailed here investigated the efficiency of Fenton-like processes in degrading endocrine-disrupting chemicals, as exemplified by di-n-butyl phthalate (DBP). Specifically, a heterogeneous Fenton process was applied, as catalyzed by natural or modified bottom sediments collected from Rzeszów and Solina Reservoirs (Poland). A number of sediments with different physicochemical properties and different contents of Fe, Mn and Cu were in fact obtained and used, with “modification” entailing ion-exchange reaction and impregnation. It thus proved possible to demonstrate the possibility and legitimacy of Fenton's reagent being modified by natural bottom sediments that may therefore be regarded as heterogeneous catalysts, given a status as endogenous sources of iron, manganese and copper ions. While the effectiveness of DBP degradation was indeed influenced by sediment type and composition (and modification thereof), it was also affected by the factors of time, pH, DBP concentration, sediment dose and H2O2. The use of natural bottom sediments in the role of solid catalysts in heterogeneous Fenton processes represents a promising alternative to environmental remediation technology, given their abundance, low cost and environment-friendly nature.

Germination fluctuation of toxic Alexandrium fundyense and A. pacificum cysts and the relationship with bloom occurrences in Kesennuma Bay, Japan

While cyst germination may be an important factor for the initiation of harmful/toxic blooms, assessments of the fluctuation in phytoplankton cyst germination, from bottom sediments to water columns, are rare in situ due to lack of technology that can detect germinated cells in natural bottom sediments. This study introduces a simple mesocosm method, modeled after previous in situ methods, to measure the germination of plankton resting stage cells. Using this method, seasonal changes in germination fluxes of toxic dinoflagellates resting cysts, specifically Alexandrium fundyense (A. tamarense species complex Group I) and A. pacificum (A. tamarense species complex Group IV), were investigated at a fixed station in Kesennuma Bay, northeast Japan, from April 2014 to April 2015. This investigation was conducted in addition to the typical samplings of seawater and bottom sediments to detect the dinoflagellates vegetative cells and resting cysts. Bloom occurrences of A. fundyense were observed June 2014 and February 2015 with maximum cell densities reaching 3.6×106 cells m−2 and 1.4×107 cells m−2, respectively. The maximum germination fluxes of A. fundyense cysts occurred in April 2014 and December 2014 and were 9.3×103 cells m−2day−1 and 1.4×104 cells m−2day−1, respectively. For A. pacificum, the highest cell density was 7.3×107 cells m−2 during the month of August, and the maximum germination fluxes occurred in July and August, reaching 5.8×102 cells m−2day−1. Thus, this study revealed the seasonal dynamics of A. fundyense and A. pacificum cyst germination and their bloom occurrences in the water column. Blooms occurred one to two months after peak germination, which strongly suggests that both the formation of the initial population by cyst germination and its continuous growth in the water column most likely contributed to toxic bloom occurrences of A. fundyense and A. pacificum in the bay.

Chromosomal abnormalities in roots of aquatic plant Elodea canadensis as a tool for testing genotoxicity of bottom sediments

Submersed freshwater macrophytes are considered as relevant indicators for use in bulk bottom sediment contact tests. The purpose of this study was to estimate the validity of endpoints of aquatic plant Elodea canadensis for laboratory genotoxicity testing of natural bottom sediments. The inherent level of chromosome abnormalities (on artificial sediments) in roots of E. canadensis under laboratory conditions was lower than the percentage of abnormal cells in bulk sediments from the Yenisei River. The percentage of abnormal cells in roots of E. canadensis was more sensitive to the presence of genotoxic agents in laboratory contact tests than in the natural population of the plant. The spectra of chromosomal abnormalities that occur in roots of E. canadensis under natural conditions in the Yenisei River and in laboratory contact tests on the bulk bottom sediments from the Yenisei River were similar. Hence, chromosome abnormalities in roots of E. canadensis can be used as a relevant and sensitive genotoxicity endpoint in bottom sediment-contact tests.

Metabolic responses of the deep-water sponge Geodia barretti to suspended bottom sediment, simulated mine tailings and drill cuttings

Northeast Atlantic sponge beds are recognized as local hotspots for biodiversity and nutrient cycling. Despite their important functional role little is known about their sensitivity to effluents from the expanding hydrocarbon-, mining- and bottom trawling industry. Here, data on physiological and biological responses of the common demosponge Geodia barretti to short (4h) and long-term (50day) cyclic exposure of suspended particles are presented. The laboratory study showed that 4hour pulse exposures with crushed rock particles at 500mgl−1 caused a 50% drop in oxygen consumption but with a quick recovery to pre-exposure oxygen consumption once suspended sediment loads returned to background levels. Long-term cyclic exposure (12h each 24h) for 29days caused a permanent drop in oxygen consumption with 60% in sponges exposed to 50mgl−1 of crushed rock but with no apparent effect on the energy content of the sponge. Oxygen consumption and energy content of sponges exposed to natural bottom sediments at the same concentration remained unchanged. In conclusion, G. barretti appears to have well developed mechanisms to resist sediment stress, however, the study demonstrated that operations releasing large amounts of suspended crushed rock such as exploration drilling and submarine tailings disposal near sponge beds should be carefully planned to avoid long-term losses of benthic ecosystem functions, such as organic matter re-mineralization.

Method of Complex Assessment of the Bottom Sediments Toxicity using Benthic and Planktonic Organisms

The method has been developed of the bottom sediments toxicity assessment using two species of the aquatic invertebrates − benthic Chironomus riparius and planktonic Daphnia magna. The method can be used also for analysis of the toxicants' bioavailability in the model experiments at the toxicants' adding either to the bottom sediments or to water. Reliability of the method has been shown in analysis of the natural bottom sediments with different toxicity rate.

Behavior of metals (Cu, Zn and Cd) in the initial stage of water system contamination: Effect of pH and suspended particles

The fate of potentially harmful metals (PHM) after their entry into an unpolluted fresh water body depends on the physicochemical and biological parameters of the aquatic ecosystem. This paper considers the effect of pH and suspended particles (SP) on the behavior of Cu, Zn and Cd when they enter a fresh water reservoir. In a field experiment, four mesocosms were constructed in the Novosibirskoye Reservoir to allow systematic variation of SP concentration (15 or 250 mg/L) and pH (8.5 or 6.5). The initial concentrations of Cu, Zn and Cd in the mesocosms were 1000, 1000 and 200 μg/L, respectively. Natural bottom sediments were used to provide additional mineral SP, and water hyacinth was used as a floating plant species. Over 11 days, measurements were made of several indicators: residual metal concentration in solution ([PHM] w ); metal concentration in SP ([PHM] s ); primary productivity of the phytoplankton community; mass of settled SP; PHM concentration in settled SP; and PHM bioaccumulation by water hyacinth. The ratio [PHM] w /[PHM] s in the water varied in the order Cu < Zn < Cd and was higher at pH 6.5 than at pH 8.5. This observation reflects different PHM sorption (Cu > Zn > Cd) onto mineral SP and PHM biosorption by planktonic organisms. Phytoplankton acts as a renewable source of organic SP and plays an important role in metal removal from the water in the mesocosms. After 11 days the residual concentrations of Cu, Zn and Cd in the mesocosm without SP addition (initial SP concentration was 15 mg/L) were 272, 355 and 84 μg/L, respectively. The residual concentrations of Cu, Zn and Cd in mesocosms with SP addition were 57, 100 and 14 μg/L at pH 8.5 and 80, 172 and 20 μg/L at pH 6.5, respectively. Therefore, addition of SP resulted in faster and more complete removal of metals into the bottom sediments. Floating plants (water hyacinth) accumulated PHM (Cu > Zn > Cd) more effectively at pH 8.5 than at pH 6.5, and PHM concentrations in the roots were higher than in settling SP. The general trends of PHM removal from contaminated water via sedimentation and bioaccumulation are compared with changes of metal speciation in solution.

Colonization process in soft-bottom macrofauna communities using azoic sediments: comparison of two wetland systems with different organic loads

The main goal of the study was to follow the colonization process of soft-bottom macrofauna commu- nities in two wetland systems with different organic inputs: a lagoon reservoir and a fish-farm system in the Ria Formosa, Portugal. After a previous treatment in the natural sediments, the resulting experimental azoic sediments were placed in suspended boxes. Two sets of boxes were used to study seven cumulative colonization periods of increasing duration, and seven colonization periods of one month each. Community structure was studied and percentage of organic matter in surface sediments was measured. Descriptors of the macrozoobenthic community included abundance, density, number of species, and diversity, dominance and evenness indices for polychaete taxa. Significant differences were observed in the community structure between colonization periods and between systems. Cumulative experiments revealed that organic enrichment is associated with sediment colonization which is marked by a macroinvertebrate community of increasing total abundance of settlers and diversity in the reser- voir, and several peaks for abundance of a few opportunistic polychaete species in the fish-farm which is typical of a highly disturbed system. Comparison of experimental and natural bottom sediments revealed that predation and organic inputs are important factors determining the community structure, for density in the case of predation and diversity in the case of organic loads. We observed that the duration of the colonization period is a key factor in the community structure of the less disturbed system, as shown by the higher diversity in bottom sediments of reservoir.

Life cycle of the ichthyotoxic dinoflagellate Cochlodinium polykrikoides in Korean coastal waters

Since 1995, blooms of the harmful dinoflagellate, Cochlodinium polykrikoides, have caused considerable mortality of aquatic organisms and economic loss in Korea. However, little is known about the life cycle of the species, except for the planktonic vegetative stage; therefore, the aim of this paper was to elucidate the life cycle of C. polykrikoides. Its life cycle has two morphologically different stages: an armored and an unarmored vegetative stage. Armored vegetative cells were found in seawater samples collected in late-November and developed into four-cell chained, unarmored vegetative cells under laboratory culture. In samples collected in late-May, both the armored and unarmored types (vegetative swimming stage) occurred; the former easily developed into an unarmored vegetative cell type, suggesting that the armoured–unarmored transition occurs as early as May. A presumptive resting cyst, round but folded at one side, was produced from armored type cells in laboratory conditions. It was also collected from natural bottom sediments, which suggests it is the dormant resting cyst of C. polykrikoides.

Mechanical resuspension of autochthonous calcite (Seekreide) failed to control internal phosphorus cycle in a eutrophic lake

The attempt to restore the highly eutrophic Lake Arendsee (Germany) by means of artificial resuspension of calcareous mud (Seekreide) and capping of the natural bottom sediments in 1995 did not show the expected effects of decreasing the phosphorus (P) content in the water body. To understand this, the sorption characteristics and the mechanisms of P uptake of Seekreide were studied with laboratory experiments. These experimental results were combined with model simulations at field conditions to evaluate the efficiency of Seekreide for controlling the P cycle in the lake. The littoral deposits of Seekreide in Lake Arendsee mainly consist of calcite (70–87% dw) and are characterised by low contents of organic matter (5–8% dw), total P (0.13–0.47 mg g −1 dw) and iron (3.2–3.8 mg g −1 dw). Phosphorus uptake under laboratory conditions could be described with Langmuir sorption isotherms. A substantial portion of this uptake was not due to sorption to the CaCO 3 surfaces but to iron oxihydroxides, since most P was found in the reductant-soluble fraction (BD-P). Although the theoretical maximum of sorbed P ranged between 0.19 and 0.22 mg g −1 dw, no substantial P uptake occurred under field conditions. The model predicted that resuspension of about 25,000 tons of littoral sediment would transiently remove not more than 0.3 tons of P from the water column (1.3% of TP lake) during sedimentation. After deposition of resuspended Seekreide, anaerobic conditions prevented any additional P retention. The close agreement of laboratory based simulations with field observations indicates: (1) capping of the lake sediments did not significantly prevent P-release, and, therefore (2) the -negligible- total effect of the large scale treatment and the failure to decrease P concentration in Lake Arendsee may be explained by and predictable from P uptake experiments, only.

Flocculation of fine‐grained sediments due to differential settling

The flocculation of fine‐grained particles depends on collisions due to Brownian motion, fluid shear, and differential settling. Previous experimental work on the flocculation of fine‐grained sediments has emphasized the effects of fluid shear. These effects are significant in high‐turbulence regions. However, as the turbulence and fluid shear decrease, as, for example, in open waters away from shore, differential settling becomes the dominant mechanism for flocculation. In the present article, previous work on the effects of fluid shear is reviewed. However, the emphasis is on recent experimental work on the effects of differential settling on the flocculation of fine‐grained, primarily inorganic particles. The transition in effects between situations where fluid shear is dominant and the other extreme, where differential settling is dominant, was also investigated and is discussed. The sediments used in these studies were natural bottom sediments from the Detroit River inlet to Lake Erie. The tests were initiated with disaggregated sediments and were continued as the particles aggregated and formed flocs. These flocs then grew until a steady state size distribution was reached. In order to reach a steady state the differential settling tests sometimes continued for as long as 30 days; they were done in both freshwater and seawater at sediment concentrations from 1 mg/L to 200 mg/L and with and without treatment to remove organic matter. Floe size distributions as a function of time were determined. From the experiments it is shown that the times to steady state and the steady state median diameters are much larger when differential settling is the dominant mechanism for flocculation than when fluid shear is the dominant mechanism for flocculation. It is also shown that the effects of sediment concentration and salinity are qualitatively similar; i.e., as these quantities increase, both the time to steady state and the steady state floe size decrease. Settling speeds of the flocculated particles were also measured; the settling speeds of flocs are much larger and increase more rapidly with floc diameter when produced by differential settling than when fluid shear is dominant.

Effects of various environmental factors on egg development of several species of Acartia in Southern California

The hatching of the eggs of 3 Acartia species (A. tonsa, A. clausi, and Acartia sp. I) spawned in the laboratory and the eggs of Acartia (species undetermined) isolated from natural bottom sediments was examined under various environmental conditions (temperature, salinity and temperature combinations, oxygen concentration, illumination, and the presence of bottom mud). The range of temperature and salinity in which eggs hatched differed from one species to another. Egg hatching was inhibited under certain environmental conditions for all species, although egg viability under such conditions varied from one species to another. In relation to these findings, habitat separation of planktonic Acartia populations and the role of dormant eggs during their seasonal absence in the plankton of Southern California coastal waters are discussed.