Silt Content Of Sediment Research Articles

Historic and contemporary anthropogenic effects on granulometry and species composition detected from sediment cores and death assemblages, Nelson Bays, Aotearoa-New Zealand

To effectively manage anthropogenic stressors causing widespread and pervasive habitat change, resource managers and policy makers require advice on priority stressors to optimally target conservation and restoration outcomes. This is difficult in soft sediment ecosystems affected by multiple stressors operating across centuries with possible legacy interactions. Using tools from the emerging discipline of conservation paleobiology, we attempted to disentangle the effects of two stressors: i) changes to sediments (sedimentation rate, composition) and ii) fishing disturbance across pre-human to contemporary timescales by analysing death assemblages (DA) at a rare location protected from power fishing methods for ca. 30 yr in Nelson Bays, Aotearoa-New Zealand. Replicate sediment cores and surface grab samples were collected at paired stations, spread across three depth profiles (25, 30, 35 m), split inside and outside the fishing exclusion zone. Sediment core geochronologies were established using radioisotope dating and analysis of terrestrial plant palynomorphs (spores, pollen, starch) associated with Māori and European introduction to Aotearoa-New Zealand. Results unearthed a complex of brachiopods, molluscs, crustacea, bryozoan, and Māori-introduced pollen and starch remains – the latter a marine first. Following human arrival in the region (ca.1500AD) statistical models revealed separation of DAs between time periods were correlated with a 10–15% increase in sediment silt content following a ca.11-fold increase in Sediment Accumulation Rates (SAR). In contrast, separation of recent surface DAs (ca. 60yr) are now more strongly correlated with sediment mixing, detected by discordance in radioisotope profiles, consistent with exposure to homogenising effects of fishing disturbance outside the exclusion zone. We conclude that historic legacy effects, ongoing sedimentation and fishing disturbance have synergistically modified the sediment characteristics from “natural” baseline conditions. Those changes have likely contributed to the collapse and lack of recovery of Nelson Bays shellfish fisheries.

Biological and physical drivers of bio-mediated sediment resuspension: A flume study on Cerastoderma edule

Predictive models accounting for the effect of bioturbation on sediment resuspension must be based on ecological theory as well as on empirical parametrizations. The scaling trend of individual metabolic and activity rates with body mass may be a key to the mechanistic understanding of the observed patterns. With this study we tested if general size scaling rules in bio-mediated sediment resuspension may apply to a broad range of physical contexts for the endobenthic bivalve Cerastoderma edule. The effect on sediment resuspension of populations of C. edule differing by individual size was measured across physical gradients of current velocity and sediment composition in terms of fraction of fine particles. C. edule were able to enhance the resuspension of sediment containing silt, while they had scarce effect on the resuspension of coarse sediment. The effect of bioturbation was maximal at intermediate current velocity, when the hydrodynamic forcing is not strong enough to overcome the abiotic sediment resistance but it is able to suspend the bioturbated sediment. Although differences in sediment silt content and intensities of hydrodynamic stress have a relevant influence in determining the bioturbators individual contribution to sediment resuspension, the observed mass scaling trend is consistent across all treatments and close to theoretical expectation for size scaling of individual metabolic rates. This observation supports the hypothesis that the contribution of individual bioturbators to sediment resuspension is directly related to their energy use. Therefore, the proposed approach allows the formulation of expectations of biotic contribution to sediment resuspension based on the general size scaling laws of individual energy use.

섬진강 하구역에 서식하는 대형저서동물군집의 분포양상

This study was carried out to investigate the spatial distributions of the macrobenthic communities in the Seomjin River estuary from May, 2015 to May, 2016. The number of species was 163, the mean density was <TEX>$1,865ind.m^{-2}$</TEX>, biomass was <TEX>$204g{\cdot}wet\;m^{-2}$</TEX> during this study period. The highest number of species and density appeared among polychaetes whereas the most biomass was contributed by mollusks due to the presence of Corbicula japonica in every season. The study area was divided into 3 regions with similar benthic fauna responding to the gradient of the salinity. Praxillella praetermissa was the dominant species in regions of over 30 psu during all seasons. C. japonica and Hediste diadroma were dominant in the upper regions of the Seomjin River where the salinity was less than 10 psu. Heteromastus filiformis showed the broadest distributional range and dominated in all seasons except for the most upper stream at st. 7. From the result of the Bio-Env analysis, salinity was the most important environmental factor affecting the formation of macrobenthic communities in the study area, and salinity and TOC were the highest contributors to the macrobenthic communities. From the correlation analysis between major dominant species and environmental factors, C. japonica, Prionospio japonica and H. diadroma showed a negative correlation with salinity, while P. praetermissa and Scolectoma longifolia showed a positive correlation. H. filiformis was little affected by salinity but showed a positive correlation with TOC or silt content of sediment.

A Comparative Analysis of Runoff and Soil Loss Characteristics between “Extreme Precipitation Year” and “Normal Precipitation Year” at the Plot Scale: A Case Study in the Loess Plateau in China

The highest annual precipitation in Ansai during the past 60 years was observed in 2013. Studying the effects of such extreme annual precipitation on soil erosion can deepen similar research and help predict environmental damage under future extreme rainfall. We selected the runoff plots (area: 4 m × 10 m) of three land-use types: cultivated land (C), wild grassland (W) and switchgrass (S). We monitored corresponding indices in the “extreme year” (2013) and “normal year” (2010–2012). The results were as follows: (1) The rainfall parameters (rainfall amount, EI30, EI60) in the “extreme year” were all higher than those in the “normal year”, especially in July; (2) In July and August, the runoff and soil loss of cultivated land in the “extreme year” increased by 1492.5% and 538.2%, respectively, compared to those in the “normal year”. The silt content of sediment was the highest generally, but the sand content increased relatively in the “extreme year”; (3) The effect of rainfall on soil erosion was the smallest in W; (4) In the “extreme year”, the same EI30 generated more runoff and soil loss than those in the “normal year”. The high antecedent precipitation which would cause high antecedent soil moisture was one of the reasons. The threshold value (100 MJ·mm·ha−1·h−1) of EI30 related to extreme erosion risk was proposed.

Deep-sea methane seep sediments in the Okhotsk Sea sustain diverse and abundant anammox bacteria

Marginal sea methane seep sediments sustain highly productive chemosynthetic ecosystems and are hotspots of intense biogeochemical cycling. Rich methane supply stimulates rapid microbial consumption of oxygen; these systems are thus usually hypoxic to anoxic. This and reported evidence for resident nitrogen fixation suggest the presence of an anaerobic ammonium-oxidizing (anammox) bacterial community in methane seep sediments. To test this hypothesis, we employed detection of genes encoding 16S rRNA gene and hydrazine dehydrogenase (hzo) to investigate the structure, abundance and distribution of the anammox bacterial community in the methane seep sediments of the Okhotsk Sea. Diverse complements of Candidatus Scalindua-related 16S rRNA and hzo gene sequences were obtained. Most of the deep-sea sites harbored abundant hzo genes with copy numbers as high as 10(7) g(-1) sediment. In general, anammox bacterial signatures were significantly more abundant in the deep-water sediments. Sediment porewater NO3-, NOx- (i.e. NO3-+NO2-), NOx-/NH4+ and sediment silt content correlated with in situ distribution patterns of anammox bacterial marker genes, likely because they determine anammox substrate availability and sediment geochemistry, respectively. The abundance and distribution of anammox bacterial gene markers indicate a potentially significant contribution of anammox bacteria to the marine N cycle in the deep-sea methane seep sediments.

Contamination profile of DDT and HCH in surface sediments and their spatial distribution from North-East India

Contamination status and spatial distribution of DDTs and HCHs were investigated in sediments collected from ponds and riverine system from districts Nagaon and Dibrugarh, North East India. A total of 113 surface sediment samples were collected from both the districts including 43 from ponds/wetlands and 70 from rivers/streams. Based on dry weight (dw), the mean concentration of ∑HCH and ∑DDT in sediments were found to be 287ng/g (71.2–834ng/g) and 321ng/g (30.1–918ng/g) for district Dibrugarh while 330ng/g (39.2–743ng/g) and 378ng/g (72.5–932ng/g) for district Nagaon, respectively. DDTs and HCHs in sediments were well influenced by total organic carbon, clay and silt content of sediments. Source identification revealed that sediment residue levels have originated from long and recent mixed source of technical HCH and Lindane for HCHs and mainly technical DDT for DDTs. Majority of samples exceeded the sediment quality guidelines (SQG) for γ-HCH, p,p′-DDT and ∑DDT indicating potential environmental risk. This baseline data can be used as reference for regular ecological and future POPs monitoring program.

Cymodocea nodosa vs. Caulerpa prolifera: Causes and consequences of a long term history of interaction in macrophyte meadows in the Mar Menor coastal lagoon (Spain, southwestern Mediterranean)

Seagrass communities are under direct threat as a result of anthropogenic impact and competition with macroalgae. Present day macrophyte meadows in the Mar Menor are the result of successive colonization events, associated with changes in the hydrographical conditions. In the last of these events, Caulerpa prolifera (Forsskål) J.V. Lamouroux colonized the lagoon in the early 1970's following the widening and deepening of the El Estacio inlet into a navigation channel, which caused a substantial decrease in the salinity level and a lower annual water temperature range. The seaweed C. prolifera expanded rapidly and replaced the previous seagrass meadows with monospecific algae meadows or with meadows mixed with the seagrass Cymodocea nodosa (Ucria) Ascherson. This work analyzes the factors that explain the distribution of macrophyte meadows and their evolution, as well as subsequent sediment alterations. The mean biomass of C. prolifera (Ca) in the deeper areas of the Mar Menor increased from 1982 to 1987 and remained constant thereafter until 2008, while the mean biomass of C. nodosa (Cy) showed a continuous decrease during the same period. The evolution of the Ca/Cy ratio showed a progressive expansion of C. prolifera monospecific meadows from north to south. The decline in the C. nodosa meadows was more pronounced in the deeper areas and was especially verified in the inner or more confined areas. At present, monospecific C. nodosa meadows are restricted to the southern and western, shallowest areas of the lagoon.The negative relationship between Caulerpa prolifera and Cymodocea nodosa shown by multiple regressions suggests that there is a competition between the two species. A complex interaction of factors could be responsible for the equilibrium and evolution of the relationships between both species in the Mar Menor. In shallow waters, coarse sediments, high light levels and physiological adaptations could favour C. nodosa. In deeper areas, light scarcity might limit C. nodosa biomass, but a negative effect of C. prolifera through increasing the sediment silt content, sulphide production, organic matter and anoxia, cannot be ruled out.

Impact of sediment type, light and nutrient availability on benthic diatom communities of a large estuarine bay: Moreton Bay, Australia

Shifts in diatom species composition may be used to infer past changes in environmental conditions in fresh, estuarine and marine systems. Establishing the primary drivers of present day diatom community composition is a vital step in their use as a proxy for past conditions. Moreton Bay, Australia, has experienced extensive modification of its catchments and western and southern shorelines. Regional weather patterns and terrestrial runoff have created a gradient in water quality from relatively degraded western and southern areas to relatively pristine northern and eastern areas. The aim of this study was to examine the relative impact of short term changes to light and/or nutrient availability and long term changes in sediment type, light and nutrient availability to subtidal benthic community composition. Short term changes were imposed using a manipulative field experiment whilst long term changes were obtained from a field survey of sites across the gradient of water quality. Diatoms were found to be the dominant microalgal group at all studied sites. The diatom communities were comprised primarily of small benthic epipsammic species and community composition was primarily driven by changes in sediment silt content. Short term changes in light and/or nutrient availability had little impact on community composition. In this open estuarine system the use of diatom indices to infer past water quality must take into account the sediment silt content in their interpretations.

Diversity and Distribution of Sediment NirS-Encoding Bacterial Assemblages in Response to Environmental Gradients in the Eutrophied Jiaozhou Bay, China

A gene-clone-library-based molecular approach was used to study the nirS-encoding bacteria-environment relationship in the sediments of the eutrophic Jiaozhou Bay. Diverse nirS sequences were recovered and most of them were related to the marine cluster I group, ubiquitous in estuarine, coastal, and marine environments. Some NirS sequences were unique to the Jiaozhou Bay, such as the marine subcluster VIIg sequences. Most of the Jiaozhou Bay NirS sequences had their closest matches originally detected in estuarine and marine sediments, especially from the Chesapeake Bay, indicating similarity of the denitrifying bacterial communities in similar coastal environments in spite of geographical distance. Multivariate statistical analyses indicated that the spatial distribution of the nirS-encoding bacterial assemblages is highly correlated with environmental factors, such as sediment silt content, NH4+ concentration, and OrgC/OrgN. The nirS-encoding bacterial assemblages in the most hypernutrified stations could be easily distinguished from that of the least eutrophic station. For the first time, the sedimentological condition was found to influence the structure and distribution of the sediment denitrifying bacterial community.

DO ALTERNATE STABLE STATES OCCUR IN NATURAL ECOSYSTEMS? EVIDENCE FROM A TIDAL FLAT

Studies from a wide variety of ecosystems indicate that primary producers may protect their environment against degrading processes such as erosion by water current or wind. Theoretical analyses showed that the dynamics of these systems are governed by positive feedback. We investigated the implications of a positive feedback between growth of benthic diatoms and erosion of silt in tidal flat systems. A simple mathematical model shows that alternate stable states may occur in systems with positive feedback between diatom growth and silt accumulation, particularly in sediments with intermediate bottom shear stress. High diatom cover, high silt content, and low levels of erosion characterize one state. The other state is dominated by erosion, and hence both diatom cover and silt content are low. In an experimental study, we tested the critical model assumption that the growth rate of diatoms increases with the silt content of the sediment. Net growth of diatoms was significantly higher on silt than on sandy sediment after nine days of incubation, supporting the premise that diatom-silt interactions are governed by positive feedback. Furthermore, we compared model predictions to data on the physical and biological prop- erties of sediments of a tidal flat. In accordance with our model, the silt content of sediments with intermediate to high bottom shear stress showed a clear and significant bimodal dis- tribution, which may reflect the existence of alternate stable states. At low bottom shear stress, silt content was better explained by a unimodal distribution, as was predicted by our model. Patterns in chlorophyll a content were less clear. Nevertheless, chlorophyll a content was best explained by a bimodal distribution at high bottom shear stress, and in two of the three periods at low bottom shear stress. Our study indicates that the positive feedback between enhanced production of diatoms and decreased erosion of sediment sig- nificantly affects the dynamics of intertidal flat systems.

Evidence for Holocene environmental change from C/N ratios, and delta-13C and delta-15N values in Swan Lake sediments, western Sand Hills, Nebraska

Profiles of percent carbon and nitrogen, carbon/nitrogen (C/N) ratios and stable carbon (δ13C), and nitrogen (δ15N) isotopic ratios in organic matter from an 11.6 m core were used to reconstruct environments of deposition in the Swan Lake basin during the past 5300 YBP. The upper 6.5 m consisted of gyttja containing variable amounts of reddish brown-colored fine organic matter and calcium carbonate. It was followed by a 0.5 m sandy silt, which was followed by a 3.6 m reduced layer characterized by large quantities of black organic plant remains, sapropel, and then by another sapropel layer consisting mainly of well-sorted sapropelic sand with relatively low organic matter content. The C- and N-contents in the organic matter in the sediment profile ranged from 0.5 to 23% and from 0.02 to 2%, respectively. Carbon content were positively correlated to both N and clay content while carbon content was negatively correlated to sand content. Two major environmental phases in Swan Lake were apparent from large differences in the C and N data of the sediment organic matter. These include the sapropel (marsh) stage that stretched from approximately 5330 to 3930 YBP, and the following gyttja (open water stage). During the sapropel marsh plants identified in a previous pollen study as cattails and sedges proliferated and produced copious amounts of well-preserved organic matter. C/N ratios, δ13C values, and δ15N values in the sapropel were significantly different from those that characterized organic matter in the gyttja. During the gyttja δ13C values indicated that deep primary producers have dominated lake biomass. By utilizing bicarbonate as their C-source, the accumulating biomass became relatively enriched δ13C values. The presence of high sediment CaCO3 contents indicated more alkaline and deeper water conditions prevailed during the gyttja. Further refinement of the data suggested that each major phase initially contained an identifiable transition stage. During the sapropelic (initial marsh stage) which occurred before 5330 YBP, sand content gradually decreased as organic matter increased. As reflected by high C/N ratios and slightly enriched δ13C values, these sands appear to have contained sufficient permeability to promote partial mineralization of accumulated organic-N containing compounds. A short initial gyttja transition period from about 3930–3830 YBP occurred in which the sediment silt content was anomalously high relative that measured in the surrounding layers. The silt content suggests that this turbid transition layer can not be completely explained by sediment mixing via bioturbation. The silts appeared to have been associated with the sharp climate change that resulted in higher water-table conditions during the gyttja stage.