Accumulation Of Fine-grained Sediments Research Articles

Litho- and biostratigraphy of the Holocene sediments in the southern part of Lake Ladoga

We present the results of study sediment core, taken in the southern part of Lake Ladoga at the depth of 44 m. The sediments are gray silt with total thickness of 0.8 m. Diatom and loss-on-ignition and grain-size analyzes and radiocarbon dating were carried out. The retrieved sediments formed during the Holocene starting from the regression of the Ancylus Lake at the Baltic ca. 10,200 cal. BP. Changes in the composition of diatom assemblages and the dynamics of organic accumulation correspond to the typical scenarios that we recorded in the Holocene sediments in the central part of Lake Ladoga. No sedimentary hiatuses were recorded. Thus, it has been established that aquatic, relatively deep-water conditions existed in this part of the Ladoga basin starting from the Early Holocene with the accumulation of fine-grained sediments.

How did the climate and human activities modulate the sedimentary evolution of the central Yellow Sea Mud, China

• The sedimentary evolution and provenance variation of Central Yellow Sea Mud was the result of sea level rising at the begin of Holocene and the established shelf circulation after 7.0 ka. • Drastic environmental changes in the Yellow River basin after 4.0 ka induced by weakening of East Asian Summer Monsoon and enhanced human activities increased the sediment accumulation in the Central Yellow Sea Mud. • The sedimentation of Central Yellow Sea Mud was controlled by the sediment supply under the regulation of monsoon climate and human activities after 4.0 ka. The Central Yellow Sea Mud (CYSM) archived important signals of regional environment and climate changes during the Holocene. We performed high-resolution analysis of two sediment cores taken from the CYSM, including measurements of radiocarbon chronology and grain size, as well as the mineralogical and geochemical measurements on the sediment samples. The results indicate that the Yellow River were likely a dominant source of the CYSM before 6.8 ka BP, with minimal contributions from the local small rivers in the Shandong Peninsula and Korean Peninsula, as confirmed by the mineralogical and geochemical evidences. After 6.8 ka BP, the fine-grained sediments accumulated in the CYSM presented a mixture of those from both the Yangtze and Yellow River with an individual contribution of 55 ± 8% and 45 ± 6%, respectively, as the sea level reached its highstand and initiated the establishment of modern shelf circulation. The drastic environmental changes in the Yellow River basin after 4.0 ka BP driven by the weakened East Asian Summer Monsoon and enhanced human activities that significantly increased the sediment yield from the Chinese Loess Plateau should be responsible for the abrupt increase in the fine-grained sediment (<2 μm) accumulation in the CYSM. After 1.4 ka BP the decrease in precipitation in the Yellow River basin resulted in the imbalance between sediment yield and river runoff, which perhaps induced lower channel aggradation and frequent avulsions, and consequently decreased the accumulation rate of the Yellow River-derived sediment in the CYSM. During the Holocene, the rising sea level played a primary role in shaping the sedimentation of the CYSM including the retreated coastline and establishment of shelf circulation system, whereas the monsoonal climate and human activities dominated the terrestrial sediment supply and accumulation in the CYSM after 4.0 ka BP.

Unraveling Anthropocene Paleoenvironmental Conditions Combining Sediment and Foraminiferal Data: Proof-of-Concept in the Sepetiba Bay (SE, Brazil)

The Sepetiba Bay (SB), located in the state of Rio de Janeiro (SE Brazil), is a transitional ecosystem highly anthropized. Because of its great environmental, economic, and social importance, the SB has been the target of several studies to investigate the sources of pollution and their environmental impact. However, studies on the response of foraminifera to pollution are rare. This study applies for the first time in the SB the Ecological Quality Ratio (EQR) based on the biotic index exp(H’bc), related to foraminiferal diversity, coupled with granulometric, mineralogical, and geochemical data and a robust age model (based on 210Pb and 137Cs activity). This study aims to evaluate the paleo-ecological quality status (PaleoEcoQS) along core SP5, collected in the inner central region of the SB. In the sedimentary record of the first half of the 20th century, no foraminifera were found, and the moderate enrichment in lithogenic elements was probably related not only to weathering and erosion of rocks but also to mining activities in the region. From the second half of the 20th century, the study area was under higher marine influence. Progressive siltation took place because of anthropogenic interventions in river courses, eutrophication, and metal pollution. Weak hydrodynamic conditions favored the accumulation of fine-grained sediments and organic matters. In the same period, low diversified benthic foraminiferal assemblages, including mainly opportunist species, were developed. Paleo-ecological conditions inferred by the biotic index exp(H’bc) were poor around 1970 and worsened after the metal spill released by Companhia Ingá Mercantil (a zinc ore processing plant). After that, progressively recovery has led to good ecological conditions in 2015. This study shows how benthic foraminiferal methods could represent a very useful tool to track changes in the evaluation of PaleoEcoQS.

Подводные извержения вулканов в начале образования озер Байкал и Хубсугул

Terrestrial volcanism was widely distributed in the Tunka Valley of the Baikal Rift Zone. Underwater eruptions were characteristic only of the areas of connection of the eastern and western ends of the valley, respectively, with basins of lakes Baikal and Khubsugul. The Kultuk volcano erupted in underwater conditions in the early Miocene, about 18 Ma and the Hulugaisha and Gorkhonka ones – in the middle of the Miocene, about 15–14 Ma. Underwater volcanic eruptions, along with the accumulation of fine-grained sediments show existence in the early and middle Miocene of water reserviors that could belong to lakes Baikal and Khubsugul that were formed at that time.

Using Fine-Grained Sediment and Wave Attenuation as a New Measure for Evaluating the Efficacy of Offshore Breakwaters in Stabilizing an Eroded Muddy Coast: Insights from Ca Mau, the Mekong Delta of Vietnam

Offshore breakwaters can be effective in reducing the energy of incident waves through dissipation, refraction or reflection. Breakwaters are increasingly constructed to stabilize eroded muddy coasts, particularly in developing countries. Accumulation of fine-grained sediment and wave attenuation are two attributes of a stable muddy coast. Effective interventions in stabilizing eroded muddy coasts include two important elements: accumulation of fine-grained sediment and wave reduction. The efficacy of offshore breakwaters in stabilizing eroded muddy coasts is, however, not yet adequately understood. A crucial question needing attention is whether accumulation of fine-grained sediment and wave attenuation should be used in evaluating the efficacy of these offshore breakwaters in stabilizing eroded muddy coasts. To address this issue, a pile-rock offshore breakwater in Huong Mai, Tieu Dua of Ca Mau, Vietnam was selected as an appropriate example in this regard. Accumulation of fine-grained sediment and wave attenuation were tested as means to investigate the efficacy of the Huong Mai structure in stabilizing the eroded muddy coast. The study was undertaken using field-based measurements and semi-structured interviews in three stages between October 2016 and December 2020. We found that this structure has had limited efficacy in stabilizing the eroded muddy coast. The structure was effective in dissipating the energy of incident waves, but we found no evidence of fine-grained sediment accumulation due to an inappropriate structural design. There was also no monitoring system in place, leading to difficulties in evaluating its efficacy in terms of wave attenuation and accumulation of fine-grained sediment. The gaps between the shoreline and the structure have not been adequately explained, resulting in substantial challenges in replicating the structure elsewhere. The Huong Mai structure should be strengthened using supplementary measures and granulometric tests in order to improve the efficacy in stabilizing eroded muddy coasts. The methods in this study provide new insights in this regard.

Estimated Minimum Life Span of the Jezero Fluvial Delta (Mars).

The paleo-lake floor at the edge of the Jezero delta has been selected as the NASA 2020 rover landing site. In this article, we demonstrate the sequences of lake filling and delta formation and constrain the minimum life span of the Jezero paleo-lake from sedimentological and hydrological analyses. Two main phases of delta evolution can be recognized by utilizing imagery provided by the High Resolution Imaging Science Experiment (NASA Mars Reconnaissance Orbiter) and High Resolution Stereo Camera (ESA Mars Express): (1) basin infilling before the breaching of the Jezero rim and (2) the delta formation itself. Our results suggest that delta formation occurred over a minimum period of 90-550 years of hydrological activity. Breaching of the Jezero rim occurred in at least three distinct episodes, which spanned a far longer time-period than overall delta formation. This evolutionary history implies that the Jezero-lake floor would have been a haven for fine-grained sediment accumulation and hosted an active environment of significant astrobiological importance.

The distribution and accumulation of mercury and methylmercury in surface sediments beneath the East China Sea.

China is a massive mercury emitter, responsible for a quarter of the world's mercury emissions, which transit the atmosphere and accumulate throughout its watercourses. The Changjiang (Yangtze) River is the third largest river in the world, integrating mercury emissions over its 1.8 × 106km2 catchment and channelling them to the East China Sea where they can be buried. Despite its potential global significance, the importance of the East China Sea as a terminal mercury sink remains poorly known. To address this knowledge gap, total mercury and methylmercury concentrations were determined from 51 surface sediment samples revealing their spatial distribution, whilst demonstrating the overall pollution status of the East China Sea. Sedimentary mercury distributions beneath the East China Sea are spatially heterogeneous, with high mercury concentrations (> 25ngg-1) corresponding to areas of fine-grained sediment accumulation. In contrast, some sites of fine-grained sediment deposition have significantly lower values of methylmercury (< 15ngg-1), such as the Changjiang estuary and some isolated offshore areas. Fine-grained particles and organic matter availability appear to exert the dominant control over sedimentary mercury distribution in the East China Sea, whereas in situ methylation serves as an additional control governing methylmercury accumulation. Estimated annual sedimentary fluxes of mercury in the East China Sea are 51 × 106g, which accounts for 9% of China's annual mercury emissions.

Morphodynamics of a field of crescent-shaped rippled scour depressions: Northern Monterey Bay, CA

Despite the prevalence of rippled scour depression (RSD) on the world's continental shelves and their importance as nursery habitats for many commercially-important species, the processes responsible for their formation and geomorphic evolution are still not well understood. Most studies that focused on RSD evolution have been based on data acquired over multiple years to decades, and often during calmer summer months. Here, multiple geophysical seafloor mapping surveys of a field of RSD's off Santa Cruz, California, USA, were conducted over the course of two winters with distinctly different oceanographic forcing; these results were compared to time series oceanographic measurements made within the survey area, and put into the context of long-term trends from survey data collected during previous decades. Although the migration of these features across the seafloor occurs on decadal time scales, significant change was detected within a given year, depending on the wave climate and fluvial sediment input. RSDs shrank up to 16% or grew up to 28% in a span of a few months. Such change was predominantly the result of redistribution of fine-grained sediment input to the system by local rivers. Migration of the seafloor features appears to be the result of accumulation of fine-grained sediment at the boundary between the RSD and the surrounding fine-grained cap.

Diatom-inferred hydrological changes and Holocene geomorphic transitioning of Africa's largest estuarine system, Lake St Lucia

The diverse lagoons and coastal lakes along the east coast of South Africa occupy incised valleys that were flooded during the rise and subsequent stabilisation of relative sea-level during the Holocene. Sedimentary deposits contained within these waterbodies provide an opportunity to investigate complex hydrological and sedimentological processes, and examine sea-level controls governing system geomorphic evolution. In this paper, we combine diatom and sulfur isotope analyses from two sediment cores extracted from the northern sub-basins of Lake St Lucia, a large shallow estuarine lake that is today largely isolated from direct ocean influence behind a Holocene-Pleistocene barrier complex. Analyses allow the reconstruction of hydrological changes associated with the geomorphic development of the system over the mid-to late Holocene. The sedimentary sequences indicate that St Lucia was a shallow, partially enclosed estuary/embayment dominated by strong tidal flows prior to ∼6200 cal. BP. Infilling was initiated when sea-level rise slowed and stabilised around present day levels, resulting in the accumulation of fine-grained sediment behind an emergent proto-barrier. Diatom assemblages, dominated by marine benthic and epiphytic species, reveal a system structured by marine water influx and characterised by marsh and tidal flat habitats until ∼4550 cal. BP. A shift in the biological community at ∼4550 cal. BP is linked to the development of a back-barrier water body that supported a brackish community. Marine planktonics and enrichments in δ34S suggest recurrent, large-scale barrier inundation events during this time, coincident with a mid-Holocene sea-level highstand. Periodic marine incursions associated with episodes of enhanced storminess and overwash remained prevalent until ∼1200 cal. BP, when further barrier construction ultimately isolated the northern basins from the ocean. This study provides the first reconstruction of the palaeohydrological environment at Lake St Lucia and highlights the long-term geomorphic controls that have shaped the recent evolution and natural dynamics of the system. Unlike most coastal lake systems, this system is particularly effective as an archive of geomorphological change. Systems driven by back-barrier modifications, such as Lake St Lucia, highlight how geomorphological changes driven by sediment-supply, climate and sea level can be distributed unevenly over several isolated back-barrier basins.

Life cycle of estuarine islands — From the formation to the landlocking of former islands in the environs of Miletos and Ephesos in western Asia Minor (Turkey)

The focus of this article is to link historical accounts about former islands of the Anatolian gulfs of the Aegean Sea to geoarchaeological evidence. During the Holocene, prominent environmental and coastline changes have taken place in many tectonic grabens of western Asia Minor, today's Turkey. The Büyük and the Küçük Menderes fault systems are excellent examples for deciphering these changes. Since mid-Holocene times, the eponymous rivers have advanced their deltas, silting up marine embayments which had once reached inland for tens of kilometres. To describe this terrestrial–marine–terrestrial evolution of estuarine islands we coin the term “life cycle of estuarine islands”. Besides other factors, such as natural erosion, sea-level changes, and tectonic activities, the delta progradation was mainly governed by riverine sediment load, which, in turn, was to a great extent dependent on human impact on the vegetation cover of the drainage basins. Based on historical accounts as well as modern geoarchaeological research it is possible to reconstruct the spatio-temporal evolution of the landscape.For Miletos and the Büyük Menderes (Maiandros, Maeander) graben, remarkable transformations have been revealed: the metamorphosis of the marine gulf into residual lakes (Lake Azap, Lake Bafa), the landlocking of islands (Hybanda, Lade, Asteria, Nergiz Tepe), the transition of the Milesian archipelago to a peninsula and finally to a part of the floodplain. A dramatic effect of the ongoing accumulation of fine-grained sediments was the siltation of harbours – a major reason for the decline of the once flourishing coastal cities of Myous, Priene, Herakleia, and finally Miletos, today some 8km inland.For Ephesos and the Küçük Menderes (Kaystros) graben, the research focused on the former island of Syrie. Pliny the Elder (Naturalis Historia, c. CE 77) attributed the landlocking of Syrie to the Kaystros River – a scenario which has been verified by our geoarchaeological research and 14C–dated to the 5th century BC. The local foundation myth according to which an island, presumably Syrie, was the location of the first settlement of immigrants from the Greek mainland in the 11th century BCE can neither be proven nor disproven for lack of archaeological evidence. The delta advance was the main reason why the settlement sites and the harbours of Ephesos were relocated several times from the Early Iron Age to the Middle Ages.

Quantifying organic carbon storage and sources in sediments of Dong Rui mangrove forests, Tien Yen district, Quang Ninh province using carbon stable isotope

Quantifying organic carbon storage and sources in sediments of Dong Rui mangrove forests, Tien Yen district, Quang Ninh province using carbon stable isotope

Seismic stratigraphy of the Heuksan mud belt in the southeastern Yellow Sea, Korea

To establish the seismic stratigraphy of the Heuksan mud belt (HMB) and reconstruct its depositional history, approximately 1,600 km of high-resolution seismic data were newly obtained using chirp acoustic sub-bottom profiler, sparker, and air-gun seismic systems. Based on seismic stratigraphic analysis, the HMB can be divided into three major seismic units (I, II, and III, from top to bottom) and four subunits (II-a, II-b, III-a, and III-b) overlying transgressive sands, pre-last glacial maximum (LGM) deposits, and the acoustic basement. Each unit and subunit show different seismic facies and geometry, being clearly separated from each other by bounding surfaces formed since the LGM. The spatial distribution, thicknesses and volumes of the seismic units were determined and plotted to document the sequential formation of the HMB. The correlation between deep drill core data (HMB-101, HMB-102, HMB-103, YSDP-101, and YSDP-102) and the seismic data suggests that subunits III-b and III-a were formed by the continuous accumulation of fine-grained sediment with partial sandy sediment in an estuarine/deltaic environment during the early to middle transgressive stage, accompanied by landward migration of the shoreline. Subunits II-b and II-a were probably formed by re-deposition of large volumes of sediment eroded from unit III during the middle transgressive to early highstand stage. Unit I is interpreted as the most recent mud deposit representing the highstand systems tract when sea-level rise terminated. The careful definition of seismic units and their interpretation proposed in this study, on the basis of the large and partly new seismic dataset covering the entire HMB together with deep drill core data, have been instrumental in reconstructing the depositional environment and formation mechanisms of the HMB.

Evaluation of a Fine Sediment Removal Tool in Spring-fed and Snowmelt Driven Streams

The accumulation of fine-grained sediments impairs the structure and function of streams, so removing fine sediments may be required to achieve restoration objectives. There has been little work on methods of removing excess sediment or on the efficacy of the methods. We used a 4-year before-after-control-impact design in southeastern Idaho streams to test a fine sediment removal system (FSRS) manufactured by Streamside Environmental LLC. The FSRS agitates fine sediment in the substrate with clean pump water and then vacuums the sediment out of the stream with a second pump. Our objectives were: 1) to test if the FSRS can selectively remove fine sediment; 2) to monitor the bio-physical responses in FSRS treated and downstream waters; and 3) to compare the bio-physical responses to the FSRS in spring-fed and snowmelt driven stream reaches. The FSRS removed ~ 14 metric tons of sediment from the two treated reaches. More than 90% of this sediment was

Tidally- and wind-driven residual circulation at the multiple-inlet system East Frisian Wadden Sea

The residual circulation in lagoon-type multiple-inlet systems is primarily driven by the non-linear interaction of the offshore tides, wind-induced currents and the morphology of communicating sub-basins. Residual discharges at tidal inlets and across tidal divides of a chain of back-barrier basins are calculated with a process-based hydrodynamic model in the East Frisian Wadden Sea, southern North Sea. Non-linear mechanisms of dominant water fluxes between the sub-basins and the coastal sea are deciphered with respect to tidal and meteorological drivers. The orientation of residual pathways of annually-integrated water fluxes is consistent and similar for variable model scenarios, i.e. meteorological forcing, an imposed sea level rise or different bed friction coefficients, which permits the identification of dominant residual circulation cells in the system. It is further shown that the multi-basin system imports a substantial surplus of water from the western and eastern boundaries of the East Frisian Wadden Sea having an impact on the mass budget of the interconnected basins that has been underestimated so far in hydrological, sedimentological and ecosystem studies. The implications for the accumulation of fine-grained sediments, flushing capacities (residence times) and nutrient cycles in the Wadden Sea area are discussed.

Evidence of modern fine-grained sediment accumulation in the Monterey Fan from measurements of the pesticide DDT and its metabolites

The documented presence of the pesticide DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its metabolites DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), collectively referred to as ΣDDT, in sediments from the Monterey Submarine Canyon, Monterey Fan Channel and Monterey Fan indicates that during the present sea-level highstand the Monterey Fan has been an active depositional system. The presence of ΣDDT in marine sediment is an indication of the recent arrival of terrigenous fine-grained sediment because DDT was only applied on land in California between 1944 and 1972, and is being transported to the ocean in the fine-grained sediment fraction of rivers. ΣDDT was found in 81 out of 82 cores collected in water depths deeper than 3000 m in the Monterey Fan Channel and in the Monterey Fan, within a geographical extent of 250 km to the south and 210 km to the west of the Monterey Canyon head, with surface concentrations averaging 6 and 3 ng g− 1, in the upper and lower Monterey Fan, respectively. This is the first documentation of ΣDDT presence in ocean sediments below 3000 m water depth worldwide. The estimated total amount of ΣDDT in the fan is consistent with the amount of ΣDDT discharged by the Salinas and Pajaro Rivers since DDT started being used in California, suggesting that current fine-grained sediment discharge from these rivers has been accumulating in the fan. The ratio DDE/ΣDDT, an indication of the extent of DDT degradation, provides a first-order proxy for the relative age of the sediments. DDT is found along the thalweg of the Monterey Fan channel as far as 215 km from the canyon head, indicating recent fine-grained sediment transport along the channel. In contrast, only DDE was detected in sediments on the fan, which suggests that the fan does not accumulate fine-grained sediments at a constant rate.

Response of mollusc assemblages to climate variability and anthropogenic activities: a 4000‐year record from a shallow bar‐built lagoon system

With their position at the interface between land and ocean and their fragile nature, lagoons are sensitive to environmental change, and it is reasonable to expect these changes would be recorded in well-preserved taxa such as molluscs. To test this, the 4000-year history of molluscs in Great South Bay, a bar-built lagoon, was reconstructed from 24 vibracores. Using x-radiography to identify shell layers, faunal counts, shell condition, organic content, and sediment type were measured in 325 samples. Sample age was estimated by interpolating 40 radiocarbon dates. K-means cluster analysis identified three molluscan assemblages, corresponding to sand-associated and mud-associated groups, and the third associated with inlet areas. Redundancy and regression tree analyses indicated that significant transitions from the sand-associated to mud-associated assemblage occurred over large portions of the bay about 650 and 294 years bp. The first date corresponds to the transition from the Medieval Warm Period to the Little Ice Age; this change in climate reduced the frequency of strong storms, likely leading to reduced barrier island breaching, greater bay enclosure, and fine-grained sediment accumulation. The second date marks the initiation of clear cutting by European settlers, an activity that would have increased runoff of fine-grained material. The occurrence of the inlet assemblage in the western and eastern ends of the bay is consistent with a history of inlets in these areas, even though prior to Hurricane Sandy in 2012, no inlet was present in the eastern bay in almost 200 years. The mud dominant, Mulinia lateralis, is a bivalve often associated with environmental disturbances. Its increased frequency over the past 300 years suggests that disturbances are more common in the bay than in the past. Management activities maintaining the current barrier island state may be contributing to the sand-mud transition and to the bay's susceptibility to disturbances.

Holocene coastal change in the ancient harbor of Yenikapı–İstanbul and its impact on cultural history

An extensive rescue excavation has been conducted in the ancient harbor of İstanbul (Yenikapı) by the Sea of Marmara, revealing a depositional sequence displaying clear evidence of transgression and coastal progradation during the Holocene. The basal layer of this sequence lies at 6 m below the present sea level and contains remains of a Neolithic settlement known to have been present in the area, indicating that the sea level at ~ 8–9 cal ka BP was lower than 6 m below present. Sea level advanced to its maximum at ~ 6.8–7 cal ka BP, drowning Lykos Stream and forming an inlet at its mouth. After ~ 3 cal ka BP, coastal progradation became evident. Subsequent construction of the Byzantine Harbor (Theodosius; 4th century AD) created a restricted small basin and accumulation of fine-grained sediments. The sedimentation rate was increased due to coastal progradation and anthropogenic factors during the deposition of coarse-grained sediments at the upper parts of the sequence (7th–9th centuries AD). The harbor was probably abandoned after the 11th century AD by filling up with Lykos Stream detritus and continued seaward migration of the coastline.

Distribution, behavior, and transport of inorganic and methylmercury in a high gradient stream

Concentrations of Hg remain elevated in physical and biological media of the South River (Virginia, USA), despite the cessation of the industrial use of Hg in its watershed nearly six decades ago, and physical characteristics that would not seem to favor Hg(II)-methylation. A 3-a study of inorganic Hg (IHg) and methylmercury (MeHg) was conducted in physical media (soil, sediment, surface water, porewater and soil/sediment extracts) to identify non-point sources, transport mechanisms, and potential controls on Hg(II)-methylation. Data collected from surface water and sediment indicate that the majority of the non-point sources of IHg to the South River are within the first 14 km downstream from the historic point source. Partitioning data indicate that particle bound IHg is introduced in this reach, releasing dissolved and colloidal bound IHg, which is transported downstream. Extraction experiments revealed that floodplain soils released a higher fraction of their IHg content in aqueous extractions than fine-grained sediment (FGS). Based on ultrafiltration [<5000 nominal molecular weight cutoff (NMWC)] the majority of soil IHg released was colloidal in nature, providing evidence for the continued evolution of IHg for Hg(II)-methylation from soil. Strong seasonal patterns in MeHg concentrations were observed in surface water and sediment. The highest concentrations of MeHg in surface water were observed at moderate temperatures, suggesting that other factors limit net Hg(II)-methylation. Seasonal changes in sediment organic content and the fraction of 1 N KOH-extractable THg were also observed and may be important factors in controlling net Hg(II)-methylation rates. Sulfate concentrations in surface water are low and the evidence suggests that Fe reduction may be an important Hg(II)-methylation process. The highest sediment MeHg concentrations were observed in habitats with large amounts of FGS, which are more prevalent in the upper half of the study area due to the lower hydrologic gradient and agricultural impacts. Past and present land use practices and other geomorphologic controls contribute to the erosion of banks and accumulation of fine-grained sediment in this section of the river, acting as sources of IHg.

Foraminiferal response to environmental changes in Kiel Fjord, SW Baltic Sea

The living benthic foraminiferal assemblages in Kiel Fjord (SW Baltic Sea) were investigated in the years 2005 and 2006. The faunal studies were accomplished by geochemical analyses of surface sediments. In general, sediment pollution by copper, zinc, tin and lead is assessed as moderate in comparison with levels reported from other areas of the Baltic Sea. However, the inner Kiel Fjord is still exposed to a high load of metals and organic matter due to enhanced accumulation of fine-grained sediments in conjunction with potential pollution sources as shipyards, harbours and intensive traffic. The results of our survey show that the dominant environmental forcing of benthic foraminifera is nutrients availability coupled with human impact. A comparison with faunal data from the 1960s reveals apparent changes in species composition and population densities. The stress-tolerant species Ammonia beccarii invaded Kiel Fjord. Ammotium cassis had disappeared that reflects apparently the changes in salinity over the last 10 years. These changes in foraminiferal community and a significant increase of test abnormalities indicate an intensified environmental stress since the 1960s.

Paleogene terrigenous (flysch) sequences in Etoloakarnania region (W. Greece). Plankton stratigraphy and paleoenvironmental implications

Based on calcareous nannofossils and planktonic foraminifera1 biostratigraphic data from flysch sequences, we give evidence for the paleoenvironmental evolution of Gavrovo and Ionian foreland basins (External Hellenides, Etoloakarnania region). Our data suggest that the onset of clastic sedimentation in both foreland basins in the study area is chronostratigraphically placed at Late Eocene (from 36.2–34.4 Ma; nannofossil biozones NP19–20, planktonic foraminifera biozones P16–17). During the earliest Oligocene (NP21–22 nannofossil biozones/34.4–32.45 Ma), both basins represent restricted accumulation of sediments, mainly composed of clays and silts. The presence of thick flysch deposits, accumulated during Early Oligocene (33.4–30 Ma, nannofossil zone NP23), indicates an increasing rate of sediment supply. The flysch sequences in the Ionian basin are associated with a distal depositional environment, while in the same time the sedimentation in the external part of Gavrovo basin is related to a more proximal environment that is gradually deepening. On the contrary, the internal part of Gavrovo basin is characterised by deep-water facies, deposited in the Early Oligocene. At the end of Early Oligocene and the onset of Late Oligocene (nannofossil zone NP24/30–27.2 Ma, planktonic foraminifera zone P21), the deposition of coarse grained sediments in both basins indicates a shift to shallower depositional environment. The accumulation of fine-grained sediments during Late Oligocene (27.2–23.2 Ma, NP25 nannofossil biozone) in the Ionian basin marks the youngest flysch sediments in the Etoloakarnania region and specifies the time of the Gavrovo nappe emplacement on the Ionian zone. Moreover the emplacement of Pindos nappe on the Gavrovo zone is estimated between 30–27.2 Ma (NP24 biozone) as supported by the nannofossil analysis of samples in front of Pindos thrust.