Biogenic Silica Content Research Articles

Change in the elemental composition and cell geometry of the marine diatom Attheya longicornis under nitrogen- and iron-depleted conditions

The morphology of the siliceous cell wall (frustule) is fundamental to the identification of diatom species. One of the fundamental questions is the ecophysiological role of the diatom frustule, which often shows morphological plasticity under different growth conditions. In this study, the morphology and elemental composition of the diatom Attheya longicornis were investigated under nutrient-replete (control), iron-depleted and nitrogen-depleted conditions. This cylindrical, unicellular species has four siliceous horns per cell. The horns are each formed from a hoop-like structure with a supporting rod, which greatly increases the surface area (SA) of the cell. Under the iron-depleted conditions, relative to the controls, the SA to cell volume ratio, silicon cell quota and siliceous horn length increased 2.3-, 2.3- and 1.4-fold, respectively. Under the nitrogen-depleted conditions, the cell size decreased without an increase in horn length, and the cellular biogenic silica (BSi) content was the highest between the three growth media. The change in cell geometry and elemental composition modified the sinking behaviour of A. longicornis. Estimated sinking rate was fastest in the nitrogen-depleted cells, followed by the controls and iron-depleted cells. The data suggest that the biogeochemical processes of BSi could show vertically opposite direction depending on the growth-limiting factors through a change in the elemental composition and cell morphology of diatoms. Such plastic responses to nitrogen and iron depletion may contribute to the relatively wide distribution of this species from the coastal to open ocean in the subarctic region.

Influences of tide on silicon and nitrogen contents in soil and porewater in the Minjiang Ri-ver estuary, Southeast China

Taking Shanyuntan wetland in the Minjiang River estuary as test object, the dissolved silicates (DSi) and inorganic nitrogen contents in porewater and the biogenic silica (BSi) and total nitrogen contents in surface soil of the Phragmites australis wetland, Cyperus malaccensis wetland and Spartina alterniflora wetland were measured in October 2014 (spring tide month) and April 2015 (neap tide month), respectively, to illuminate the influence of tide on silicon and nitrogen contents in soil and porewater of estuarine wetland. Results showed that the DSi content in porewater and the BSi content in surface soil in spring tide month were slightly higher than those in neap tide month, with the highest being observed on neap tide day and the lowest occurring on spring tide day. In contrast, the BSi content in surface soil on spring tide day showed an opposite trend with that on neap tide day. The contents of NH4+-N and NO3--N in porewater of different wetland soils in spring tide month were higher than those in neap tide month, while the content of NH4+-N on spring tide day was significantly higher than that on neap tide day (P<0.05). The study found that hydrological conditions such as flooding duration and drying-wetting alternation caused by tide had great influences on silicon and nitrogen contents in porewater and surface soil, and vegetation types also showed great influences on their distributions in intertidal wetland of the Minjiang River estuary.

Distribution of Biogenic Silica in Sediments of the Yellow River (Upper and Middle Reaches)

An experiment is held to extract the biogenic silica from Yellow River sediments to explore how such four influencing factors as extraction time, the type and concentration of extracting agent, and solid-liquid ratio affect the content of biogenic silicon in the samples. Besides, the distribution characteristics of biogenic silica in sediments of the Yellow River (upper and middle reaches) are discussed based on the measured results. The experiment results demonstrate the optimal conditions for the extraction of biogenic silica in sediments of the Yellow River: weight 0.050g of sediment sample at 90°C and extract biogenic silica for 7 hours with 40mL 1.0mol/L Na2CO3 solution as the extracting agent. The biogenic silica content of the surface sediments in the upper and middle reaches of the Yellow River varies greatly from 0.07-3.06mg/g. In descending order, the samples are arranged as: MD1>XH2>BT9>WLT8>SSG7>SZS5>XG4>GD3>WH6. The highest content appears in Maduo segment at the source of the Yellow River, and the lowest content appears in Wuhai segment.

Biogenic silica composition and δ13C abundance in the Changjiang (Yangtze) and Huanghe (Yellow) Rivers with implications for the silicon cycle.

The study was carried out to address a method for separation of terrestrial and marine biogenic silica (BSi) in estuaries based on BSi compositions and δ13C values in BSi associated organic matter (δ13CBSi). We used two world-class major rivers - the Changjiang (Yangtze) and Huanghe (Yellow) Rivers as examples to illustrate our approach. Our results for these rivers indicate that riverine BSi is comprised mainly of phytoliths and diatoms. River BSi concentrations vary with terrestrial inputs and in-stream primary production. Although the fluvial BSi sources are complex, the terrestrial δ13CBSi signals are quite unique (-24.7±0.8), significantly lower than the marine δ13CBSi values (-21.3±0.07, central Yellow Sea) (p<0.01). Thus, the variation of δ13C within BSi organic matter can provide terrestrial source information on the biogeochemistry of silicon in estuaries and the adjacent shelf. The δ13CBSi combination could potentially act as an efficient tool to study environmental change in coastal areas on decadal time-scales since this index may respond to variable terrestrial fluxes from land, as well as to changed phytoplankton assemblages in the coastal ocean.

Effects of hydrogen peroxide treatment on measurements of lake sediment grain-size distribution

Grain-size analysis is routinely performed on soft sediments, and has been applied in numerous paleoenvironmental studies using lake sediment archives. Despite the frequent use of this method, no common protocol exists for the treatment of lake sediment samples prior to analysis. In this study, differences in grain-size distribution before and after treatment with hydrogen peroxide (H2O2) were evaluated for sediment sequences from four lakes in Norway characterized by different geological and environmental settings. We found that removal of organic matter had a profound effect on the grain-size distribution of the sediment samples, which might have important bearing on how such data are interpreted. One of the analysed sediment sequences showed a systematic shift toward more fines after treatment, whereas no clear systematic effects were observed for the remaining three. The observed differences might derive from (1) variable concentrations of biogenic silica, which could cause shifts in the Sedigraph readings as a consequence of the porosity and fragility of diatom frustules, (2) clogging of organic matter during initial mechanical sieving, and (3) disturbance of the internal flow regime in the Sedigraph as a result of the dispersive agent having a viscosity that is too low. These possible explanations require further testing. Nevertheless, we propose that the paleolimnological community should develop a common protocol for pre-treatment of sediments from lacustrine settings that both enables reproducibility of results and reduces the risk of misinterpretation. Our observations suggest that sediments from boreal lakes should be treated with hydrogen peroxide prior to grain-size analysis, although treatment should be relatively mild to avoid possible mineral degradation.

Holocene climate variability from the lake sediment core in Schirmacher Oasis region, East Antarctica: Multiproxy approach

Abstract A 1.62 m sediment core was retrieved from one of the landlocked freshwater lakes (L-6) in the Schirmacher Oasis (SO), East Antarctica during the 24th Indian Antarctic Expedition (2004–2006). The sediment core samples were analyzed for Total Organic Carbon (TOC), Biogenic Silica (BSi), grain size and elemental concentration ratios (Mg/Ca and Mn/Fe). The sediment core represents the time period of last ∼11.6 cal ka BP as ascertained by AMS 14 C radiocarbon dates. The sedimentation accumulation rate variation of ∼13.6 cm/ka from ∼11.6 to ∼10 cal ka BP reveals a warm phase followed by a low sedimentation accumulation rate of ∼2.9 cm/ka from ∼10 ka BP to ∼3.1 ka BP, indicating a cold period in the region. The sedimentation accumulation rate again increased from ∼3.1 cal ka BP to recent with a maximum of ∼88 cm/ka which reveals the initiation of glacier retreat or ice-free conditions in the study area. The Total Organic Carbon (TOC) is

Distribution and budget of dissolved and biogenic silica in the Bohai Sea and Yellow Sea

Silicon (Si) is essential for growth of diatoms and other siliceous organisms, and plays a key role in marine ecosystems. We established a Si budget for the Bohai Sea and Yellow Sea (BSYS) on the basis of dissolved silicate (DSi) and biogenic silica (BSi) concentration measurements in two major rivers and in the water column and sediment of BSYS, and additional data from literature. The results show that BSi accounts for about 25 % of total reactive Si (DSi + BSi) in the BSYS. The budget shows that the major Si source that supports primary production in the water column of BSYS is the benthic flux, accounting for 54 % of total Si input, followed by water exchange from the East China Sea, accounting for 26 %, direct riverine input (9 %), submarine groundwater discharge (7 %), surface runoff (3 %) and atmospheric deposition (<1 %). The dominant processes that remove dissolved Si (DSi) from the water column of BSYS are primary production and subsequent BSi sedimentation, and export to East China Sea, accounting for 80 and 20 % of the Si output, respectively. About 89 % of gross BSi production is recycled in the water column over the shelf of BSYS, and 11 % settles on the sea floor. The benthic flux to the water column of the BSYS is an important DSi source, but the budget indicates that overall there is a net burial of BSi amounting to 3.6 % of total BSi production.

Diatom communities in the High Arctic aquatic habitats of northern Spitsbergen (Svalbard)

As High Arctic environments are particularly sensitive to global and regional climate changes, a growing number of studies have focused on that region. It has been shown that living and fossil diatoms can be successfully used to track environmental changes in polar habitats. Nevertheless, the diatom flora of many Arctic areas remains unknown. The present study set out to examine the diatom flora in the rarely visited and near-pristine zone of northern Spitsbergen. Examination by light and scanning electron microscopy of 25 sediment samples, collected in fjords, tidal plains and lakes, indicated significant differences between the diatom assemblages identified in lakes located within different fjord watersheds. Altogether, 96 diatom taxa (46 genera) were found. The most abundant species (Achnanthidium minutissimum, Staurosirella pinnata and Nitzschia alpina) occurred in at least eight of the 11 investigated lakes. Assemblages from the Woodfjorden region were characterized by the presence of Cavinula pseudoscutiformis and Encyonema reichardtii, along with Navicula spp., which coincided with relatively low conductivity (34–58.7 µS cm−1) and near-neutral pH (7.2–7.5). Diatom assemblages found in the Wijdefjorden area were typically characterized by Denticula kuetzingii and Nitzschia inconspicua, with these lakes generally having higher water conductivity (>184 µS cm−1) and pH (7.5–8.1) conditions. Conductivity, biogenic silica concentration and water temperature were indicated as significant predictors of diatom community species composition and structure. No diatom frustules were found in fjord and tidal plain sediments. The effects of selected environmental factors on diatom assemblage formation are discussed.

Paleo-ecological analyses to assess long-term environmental effects of pearl farming in Western Australia

Small environmental disturbances accumulating over a long period of time may cause a regime shift in marine ecosystems, particularly in sensitive oligotrophic waters. Pearl oyster aquaculture, which has a 50 yr history in Australia, has been regarded as an anthropogenic activity with low environmental risk. To assess the long-term environmental effects of pearl oyster farming, sediment cores taken in Cygnet Bay, Western Australia, were used to reconstruct environmental processes covering an approximately 90 yr period. Biogeochemical parameters in sediment cores from inside and outside a pearl farming area displayed contrasting characteristics over time. Total organic carbon, total nitrogen, biogenic silica (BSi), and fine-grained sediment at the farming site displayed significant increases with the expansion of oyster stocking. In contrast, only small variations in response to climatic signals (rainfall and temperature) occurred over time in the cores outside the farm. The variation in the C:N ratio, delta C-13 and delta N-15 ranges over time suggested that increased organic matter was mainly contributed by autochthonous sources rather than terrestrial input. The sequential t-test for a regime shift detected approximately 2-to 3-fold increases in organic matter, 1-to 5-fold increases in silt proportion and 2-to 5-fold increases in BSi concentrations after pearl oyster farming, in contrast to the control site. The rapid development of modern long-line culture since the late 1980s is presumed to have been the dominant driver of environmental changes in sediments. The results provide insight into the magnitude of environmental change which can occur over decades as a result of even minimal anthropogenic activity.

Environmental changes in Jiaozhou Bay of northern China during the past 90 years using metals and biogenic elements in sediments

Metals and biogenic elements were analyzed from surface sediments and a 100cm core collected from Jiaozhou Bay in July 2009, to determine how the environment has changed over the past 90years due to increasing anthropogenic influences in this region. High concentrations of biogenic silica (BSi) represented the dominance of diatoms in the bay. Most metals were lower than the marine sediment quality guidelines; however, Hg, Zn, and Mn were at polluted levels. The vertical profiles of biogenic elements and metals in the sediment core suggest that the most significant environmental changes occurred since the 1990s, and three stages could be defined: (1) before 1950, characterized by low concentrations of biogenic elements and metals; (2) between 1950 and 1990, displaying an obvious increase of Hg and a slow increase of biogenic elements; (3) after 1990, reflected by a significant increase of total organic carbon (TOC), total nitrogen (TN), total phosphate (TP), and most metals, but a decrease of BSi. Correlation and principal component analyses indicated that most metals originated from lithogenic sources, industrial and domestic discharges as well as maricultural activities.

Seasonality, phytoplankton succession and the biogeochemical impacts of an autumn storm in the northeast Atlantic Ocean

Phytoplankton chemotaxonomic distributions are examined in conjunction with taxon specific particulate biomass concentrations and phytoplankton abundances to investigate the biogeochemical consequences of the passage of an autumn storm in the northeast Atlantic Ocean. Chemotaxonomy indicated that the phytoplankton community was dominated by nanoplankton (2–20μm), which on average represented 75±8% of the community. Microplankton (20–200μm) and picoplankton (<2μm) represented 21±7% and 4±3% respectively with the microplankton group composed of almost equal proportions of diatoms (53±17%) and dinoflagellates (47±17%). Total chlorophyll-a (TCHLa=CHLa+Divinyl CHLa) concentrations ranged from 22 to 677ngL−1, with DvCHLa making minor contributions of between <1% and 13% to TCHLa. Higher DvCHLa contributions were seen during the storm, which deepened the surface mixed layer, increased mixed layer nutrient concentrations and vertically mixed the phytoplankton community leading to a post-storm increase in surface chlorophyll concentrations. Picoplankton were rapid initial respondents to the changing conditions with pigment markers showing an abrupt 4-fold increase in proportion but this increase was not sustained post-storm. 19′-HEX, a chemotaxonomic marker for prymnesiophytes, was the dominant accessory pigment pre- and post-storm with concentrations of 48–435ngL−1, and represented 44% of total carotenoid concentrations. Accompanying scanning electron microscopy results support the pigment-based analysis but also provide detailed insight into the nano- and microplankton communities, which proved to be highly variable between pre-storm and post-storm sampling periods. Nanoplankton remained the dominant size class pre- and post-storm but the microplankton proportion peaked during the period of maximum nutrient and chlorophyll concentrations. Classic descriptions of autumn blooms resulting from storm driven eutrophication events promoting phytoplankton growth in surface waters should be tempered with greater understanding of the role of storm driven vertical reorganization of the water column and of resident phytoplankton communities. Crucially, in this case we observed no change in integrated chlorophyll, particulate organic carbon or biogenic silica concentrations despite also observing a ∼50% increase in surface chlorophyll concentrations which indicated that the surface enhancement in chlorophyll concentrations was most likely fed from below rather than resulting from in situ growth. Though not measured directly there was no evidence of enhanced export fluxes associated with this storm. These observations have implications for the growing practice of using chlorophyll fluorescence from remote platforms to determine ocean productivity late in the annual productivity period and in response to storm mixing.

A Holocene Sediment Record of Phosphorus Accumulation in Shallow Lake Harris, Florida (USA) Offers New Perspectives on Recent Cultural Eutrophication.

We studied a complete Holocene sediment record from shallow (zmax = 9.7 m) Lake Harris, Florida (USA) to infer the historical development of the lake and its current eutrophic status. We used 210Pb and 14C to date the 5.9-m sediment sequence (core LH-6-13) and determined accumulation rates for bulk sediment, organic matter, calcium carbonate, phosphorus fractions and biogenic silica fractions. The chronology of changes in sediment characteristics for LH-6-13 is consistent with the general paleoenvironmental framework established by core studies from other Florida lakes. Lake Harris began to fill with water in the early Holocene, ca. 10,680 cal a BP. A shift from carbonate-dominated to organic-rich sediments ca. 5,540 cal a BP corresponds to a transition to wetter climate in the middle Holocene. A rapid increase in diatom biogenic silica concentrations and accumulation rates ca. 2,600 cal a BP signals that the lake had deepened to its modern limnetic state. In LH-6-13, an up-core decrease in rates of accumulation for several sediment variables indicates time-course oligotrophication of the lake through the Holocene. In near-surface sediments, abrupt increases in the accumulation rates of these same variables indicate progressive cultural eutrophication after ca. AD 1900. Comparison of the modern state of Lake Harris to its condition 50–100 years ago provides a measure of the impact of recent cultural eutrophication. Because the pre-disturbance trajectory of this lake was one of oligotrophication, the true impact of cultural eutrophication is even greater than what is inferred from the changes over the past century.

闽江口潮滩湿地不同植被带土壤及间隙水中硅的分布特征

PDF HTML阅读 XML下载 导出引用 引用提醒 闽江口潮滩湿地不同植被带土壤及间隙水中硅的分布特征 DOI: 10.5846/stxb201501140109 作者: 作者单位: 福建师范大学地理研究所,浙江大学环境与资源学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41401114）；福建省教育厅项目（JA14082） Changes in the distribution of silica in the porewaters and sediments of the intertidal zone with different plant communities in the Min River Estuary Author: Affiliation: Key Laboratory of Humid Sub-tropical Eco-geographical Process of Ministry of Education,Research Centre of Wetlands in Subtropical Region,Fujian Normal University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以闽江口潮滩湿地为研究对象，由岸及海方向对芦苇、短叶茳芏、互花米草（潮沟内）和互花米草（潮沟外）4种湿地土壤生物硅和土壤间隙水氮硅营养盐含量及其随深度变化的特征进行为期1a的季度观测。结果显示：互花米草（外）、短叶茳芏、芦苇和互花米草（内）带湿地土壤生物硅的年均含量依次降低，分别为14.33、10.40、9.98、7.50 mg/g；互花米草（外）、互花米草（内）、短叶茳芏和芦苇带湿地土壤间隙水活性硅酸盐年均含量依次降低，分别为407、359、344、323 μmol/L；湿地各植被带土壤及间隙水含硅量均呈现夏秋季节高于冬春季节的趋势。统计分析表明：间隙水活性硅酸盐与土壤生物硅含量、距潮沟的距离之间的正相关性均比较显著（P<0.05），温度对土壤中硅含量的影响也有一定的正相关性，说明湿地植被、温度和潮汐作用是影响闽江口湿地硅分布的重要因素。与土著种对比，互花米草入侵在一定程度上改变了闽江口潮滩湿地土壤硅分布的格局。 Abstract:Silicon (Si) is an essential nutrient for many plants as well as an important element that controls the functions of terrestrial and aquatic ecosystems. Wetland ecosystems are considered to be very important for Si transport and transformation in nutrient biogeochemical cycles. However, information on Si cycling in wetland ecosystems is scarce. The Shanyutan wetland is the largest tidal wetland in the estuary of the Min River, southeast China. In this study, the Si distribution pattern and its influencing factors were determined by seasonally measuring the levels of dissolved silicates (DSis) in the porewater and biogenic silica (BSi) in the sediments of Phragmites australis wetland (PAW), Cyperus malaccensis wetland (CMW), and Spartina alterniflora wetland (SAW) from October 2012 to September 2013. For better comparison, three sampling sites were added in SAW since January 2013; these sites were isolated by a 30m wide tidal creek. The sampling sites near the land were marked as S. alterniflora wetland (inside; SAWI), whereas those near the sea were marked as S. alterniflora wetland (outside; SAWO). The results indicated that the average contents of BSi were 14.33 mg/g in SAWO, 10.40 mg/g in CMW, 9.98 mg/g in PAW, and 7.50 mg/g in SAWI. The average concentrations of DSis in the sediment porewater were 407 μmol/L in SAWO, 359 μmol/L in SAWI, 344 μmol/L in CMW, and 323 μmol/L in PAW. Generally, the contents of BSi in the sediments and DSis in the porewater were higher in summer and autumn, whereas they were lower in spring and winter. Statistical analysis revealed significantly positive correlations between DSi concentration in the porewater and BSi content in the sediments or the distance from the shoreside to the tidal creek (P<0.05). BSi content in the sediments was slightly positively correlated with temperature. Taken together, our findings suggest that the distribution of Si in the wetlands of the Min River estuary was correlated with vegetation, temperature, and tidal action. Unlike that of native species, the invasion of S. alterniflora, to some extent, altered the distribution patterns of Si in the wetlands. 参考文献 相似文献 引证文献

Age and evolution of the Littorina Sea in the light of geochemical analysis and radiocarbon dating sediment of cores from the Arkona Basin and Mecklenburg Bay (SW Baltic Sea)

Two sediment cores from the Mecklenburg Bay and Arkona Basin were analysed in terms of their geochemical composition and stratigraphy. The main stages of the Baltic Sea evolution – Baltic Ice Lake, Ancylus Lake, and Littorina Sea – were identified in both analysed cores. The most pronounced period was the transition between the Ancylus Lake and the Littorina Sea. The character of the initial stage of the Littorina Sea was clearly defined in the Mecklenburg Bay sediments and is marked by a stepwise increase in loss on ignition and contents of biogenic silica, calcium, magnesium, iron, and strontium. The record of the onset of the Littorina Sea in the Arkona Basin sediments is marked by an abrupt change of the geochemical parameters. The age of the initial Littorina Sea in the Mecklenburg Bay was estimated at about 8200 cal years BP and was probably older than the transgression within the Arkona Basin.

Testing commonly used X‐ray fluorescence core scanning‐based proxies for organic‐rich lake sediments and peat

X‐ray fluorescence (XRF) core scanning has become widely available for geological studies during the last decade. The data obtained from XRF core scanning, however, may be strongly influenced by the amount of organic matter, water content, density and porosity of the sediment matrix. In this study we discuss the usefulness of XRF core scanning to distinguish different kinds of organic‐rich sediments and peat based on examples from tropical Lakes Kumphawapi and Nong Leng Sai in Thailand. We examined how sedimentary factors influence XRF core scanning analyses by comparing elemental and scattering ratios to lithological changes and quantitative LOI, TOC, biogenic silica (BSi) and grain‐size values. Our comparison suggests that the (inc/coh) scattering ratio is of limited use as an indicator for variations in LOI and TOC in peaty gyttja or peat. In Lake Kumphawapi's sediments, Si/Ti ratios reflect clastic input associated with grain‐size variations rather than BSi contents. The Ti‐normalized ratios of Si, Zr, Sr, K and Rb are linked to mineral input and associated grain‐size variations. We conclude that XRF core scanning of organic‐rich tropical lake sediments and peat is useful to infer palaeoenvironmental conditions. However, XRF core scanning data does not stand‐alone and needs to be underpinned by additional proxies.

Specific features of Bazhenov suite sediments in south-eastern Nurolsk sedimentary basin (Tomsk Oblast)

The specific sediment features in Georgiev (J3kmgr), Bazhenov (J3vbg) and Kulomzin (K1bkl) suites, exposed by drilling in the S-E Nurolsk depression (Tomsk Oblast), were defined and described via petrographic, X-ray diffraction and fluorescence-microscopy analysis methods. The classification of agrillites was identified, the structure-texture features, composition, voids and bitumen types and their distribution were determined. It was defined that Bazhenov suite argillites are characteristic of fine-dispersion, high biogenic silica content and scattered organic matter, enriched multi-composite syngenetic bitumen (from light to resin- asphaltine), as well as fractured surface where the migration of light bitumen occurs.

Distribution and sources of organic matter in surface sediments of Bohai Sea near the Yellow River Estuary, China

Total organic carbon (TOC) and total nitrogen (TN) concentrations and C and N stable isotope compositions in 64 surface sediment samples from the mouth of the Yellow River (YR) and from the Bohai Sea (BS) outline the distribution and sources (terrestrial and marine) of sediment organic matter. Comparatively high TOC (0.5–0.9%) and TN (0.07–0.11%) concentrations in the Central BS correlate with fine-grained sediments that contain high concentrations of algal-derived organic carbon (AOC) and biogenic silica (BSi). Together, they indicate a dominant contribution of autochthonous organic matter from marine primary production. Low TOC (<0.2%) and TN (<0.03%) contents characterize surface sediments in the Bohai Strait and are typically associated with coarse-grained sediments of low AOC and BSi contents. δ13C values (−21 to −22‰) are characteristic of marine-derived organic carbon in the Central BS and the Bohai Strait, whereas a significant terrigenous contribution of 40–50% is indicated by lower values (<−23‰) near the YR mouth. The spatial pattern of rising δ13C from the YR mouth to offshore areas indicates rapid sedimentation of fluvial suspensions within the vicinity of the river mouth and in Laizhou Bay, so that only approximately 10–20% of YR-derived sediments are transported to and deposited in the Central BS and/or the Bohai Strait. At most sites, δ15N values are in the typical range of marine organic matter produced from assimilation of marine nitrate by phytoplankton (5–5.5‰), but some relatively high values (6–7.28‰) mark the southern area of the Laizhou Bay as a significant sink of anthropogenic nitrogen.

Distribution and contamination of metals and biogenic elements in sediments from Zhifu Bay of the Yellow Sea, China

Metals and biogenic elements were analyzed from surface sediments of sixteen stations and a 32cm core collected from Zhifu Bay in July 2009. High concentrations of biogenic silica (BSi) reflected the high diatom productivity in the Bay. Meanwhile, total organic carbon (TOC) in Zhifu Bay was mainly from terrestrial sources. All metals were lower than the marine sediment quality guidelines. Based on the vertical profiles of biogenic elements, there was a clear increase of TOC, total nitrogen (TN), and total phosphate (TP) between 1985 and 2000. TN concentrations decreased after the start of the operation of the sewage treatment plant in 1998; however TOC and BSi remained at high levels. Metal concentrations showed a general increase from the bottom to the top of the core. Most anthropogenic metals reached a maximum during 1996 and 2000, and decreased after the startup of the sewage plant; however, they have increased again recently. The results from correlation analysis and principal component analysis show that industrial pollution is the main source of Cd, Cr, Cu, Ni, Pb and Zn contamination in Zhifu Bay, and Yantai Port and ship transportation also contribute a lot to Cd, Cu, Hg, and Pb pollution.

The evolution of the Mecklenburg Bay environment in the Holocene in the light of multidisciplinary investigations of the sediment cores

Multi-proxy studies of the sediment cores and acoustic profiles from Mecklenburg Bay display a more detailed picture of the evolution of the environment in the Holocene. Studies of diatoms, geochemistry, grain size and radiocarbon dating clearly reveal the age and character of freshwater and marine transgressions and regressions. After the final regression of the Baltic Ice Lake, a local lake and swamp environment was recorded by peat gyttja sediments. This environment existed until the Ancylus Lake transgression dated ca 10,500 cal BP. During the Ancylus Lake period, the area remained a shallow-water lake, transitional isolated from the main Baltic Basin. The first slightly brackish marine inflows confirmed by the appearance of planktonic, mesohalobous and halophilous diatoms were identified at the beginning of the Initial Littorina Sea stage and dated ca 8800 cal BP. The boundary between the Ancylus Lake and the Initial Littorina Sea is marked by increasing contents of biogenic silica and iron. The Initial Littorina Sea stage was characterized by increasing mesohalobous and polyhalobous diatom forms and decreasing oligohalobous species. The Initial Littorina Sea environment was recorded as a slightly brackish reservoir sporadically affected by weak marine inflows. The Littorina transgression appeared in the Mecklenburg Bay at ca 7500–7700 cal BP and is reflected by the domination of polyhalobous diatoms, increasing mean grain size, biogenic silica, and calcium and magnesium contents. The Initial Littorina Sea was a 1500-year-long period in Mecklenburg Bay, existing until the Littorina transgression. The main Littorina transgression first appeared in Mecklenburg Bay around 7700 cal BP and after a few hundred years at around 7200 cal BP in the Arkona Basin.

Biogenic Si analysis in volcanically imprinted lacustrine systems: the case of Lake Rutundu (Mt. Kenya)

Diatoms are important primary producers in lake ecosystems and, as a sink for dissolved (DSi) and biogenic silica (BSi) originating from land, can significantly impact the global Si cycle. After burial in lake sediments, resistant diatom frustules can also be used for reconstructions of past ecosystem change. The BSi content of lake sediments is thus often used as a proxy for past diatom productivity, and measured using a time-step analysis of Si extracted in 0.1 M Na2CO3. However, studies in soils and ocean sediments have shown that also certain non-biogenic Si fractions are prone to dissolve in alkaline solutions, contributing to a potential overestimate of sedimentary BSi concentration. In lakes, volcanic and terrestrial Si compounds reactive at high pH are likely to interfere with the analysis. In this study we used a continuous analysis of Si and Al extracted in 0.5 M NaOH and a new mathematical model improved from Koning et al. (Aquat Geochem 8:37–67, 2002) to distinguish between biogenic and non-biogenic Si fractions in lake-sediment extracts. We tested this approach in 43 samples of a 19,000-year sediment sequence recovered from Lake Rutundu, a volcanic crater lake on Mt. Kenya. Our results show that a significant fraction of the extractable Si is of non-biogenic origin, especially in the part of the sequence deposited during the glacial period. We conclude that this technique is essential for the characterization of different Si phases, and in particular the diatom-derived BSi, in the sediment of lakes situated in volcanic catchments. It allows calculating a correction, based on the distinct Si:Al ratio of each of those Si phases, that eliminates the contribution from non-BSi fractions.