Decaying in different clays: implications for soft‐tissue preservation

Lagerstätten, places where soft‐bodied organisms became mineralized, provide a substantial bulk of palaeobiological information, but the detailed mechanisms of how soft‐tissue preservation takes place remain debatable. An experimental taphonomy approach, which allows for direct study of decay and mineralization, offers a means to study the preservational potential of different soft‐bodied organisms under controlled conditions. Here we compare the preservational capacity of two types of clay (kaolinite and montmorillonite) through a long‐term (24 month) experiment involving the burial and decay of small crustaceans. Our experimental design is innovative in that it models catastrophic sedimentation in fine‐grained colloidal suspension, which is believed to form Lagerstätten deposits. We demonstrated better preservation of buried organisms in clays compared to water, and in kaolinite compared to montmorillonite. As aluminium cations were present in high concentrations in kaolinite sediment but not in montmorillonite, the better preservation in kaolinite is attributed to the tanning properties of aluminium, which catalyses cross‐linking in proteins, protecting them from bacterial degradation. Anaerobic environments and acidification also slow down decay, but they are less effective than tanning. Kaolinite and montmorillonite replaced the crustacean integuments differently: in the remains buried in kaolinite, Al and Si were detected in equal proportions, while in those buried in montmorillonite, the Si content appeared to be much higher even in comparison with the initial sample of the clay. These variations probably arose from the different dynamics of acidic hydrolysis in the two clays associated with anaerobic decomposition of organic matter. Our results show that the preservation mechanism includes multi‐component interactions between the solution, mineral, sediment and organic remains; taken separately, any single component explains little. The specific conditions that occur within the colloidal clay sediments can facilitate conservation and start fast mineralization according to chemical properties and elemental content.     

Glass transition and time-dependent crystallization behavior of dehydration bioprotectant sugars

It has been suggested that the crystallization of a sugar hydrate can provide additional desiccation by removing water from the amorphous phase, thereby increasing the glass transition temperature (T_g). However, present experiments demonstrated that in single sugar systems, if relative humidity is enough for sugar crystallization, the amorphous phase will have a short life. In the conditions of the present experiments, more than 75% of amorphous phase crystallized in less than one month. The good performance of sugars that form hydrated crystals (trehalose and raffinose) as bioprotectants in dehydrated systems is related to the high amount of water needed to form crystals, but not to the decreased water content or increased T_g of the amorphous phase. The latter effect is only temporary, and presumably shorter than the expected shelf life of pharmaceuticals or food ingredients, and is related to thermodynamic reasons: if there is enough water for the crystal to form, it will readily form.     

Effects of sediment eluates and extracts from differently polluted small rivers on zebrafish embryos and larvae

The effects on newly fertilized eggs, embryos and larvae of zebrafish Danio rerio following exposure to sediment samples from the more heavily contaminated River Körsch, southern Germany, occurred earlier and were more prominent than in samples from the less contaminated Krähenbach. Dose- and time-related effects following exposure to Körsch sediment eluates and extracts included: (1) hatching failure and subsequent death of larvae exposed to undiluted aqueous sediment eluates and reduced hatching rates at sediment extract concentrations 0·0125%; (2) increased mortality after exposure to 25 and 50% dilutions of aqueous sediment eluates, and dilutions of 0·00625% sediment extracts; (3) reduction of heart beat frequency for 50% dilutions of sediment eluates and concentrations of 0·025% extracts; (4) increased frequency of heart and yolk sac oedema after exposure to 0·0125% sediment extracts. Since adverse effects of sediment extracts observed in zebrafish laboratory tests correlated with reproductive failure in natural populations of brown trout Salmo trutta f. fario in the severely polluted River Körsch, early life stages tests with zebrafish appear to be a suitable tool to assess the contamination rate of natural sediments.     

Heterotrophic Activity Throughout a Vertical Profile of Seawater and Sediment in Halifax Harbor, Canada

The relative heterotrophic activity of marine microorganisms was determined at two sites by the heterotrophic uptake technique throughout the water column, the sediment-water interface, and the surface layer of sediment. In the water column, uptake was greatest at the surface and steadily decreased with depth. The percentage of the substrate that was respired also decreased with depth from 69 to 56%. The activity of the sediment-water interface was several orders of magnitude greater than that of the overlying water and twice that of the sediment immediately below. Hand-collected water samples carefully taken as close as 1 cm from the sediment-water interface had the same characteristically low activity as the bottom few meters of water. Microautoradiography with ³H-labeled glucose, glutamic acid, or thymidine revealed a general decrease in the percentage of active cells with depth from 35 to <1%. The number of active cells in the interface and sediment averaged <10% of the total population. The data indicate that the sediment-water interface is the most active region in this system due to an increased number of active cells rather than an increased percentage of active cells or increased per-cell activity.     

放射性锆在模拟海水、底质及海洋生物系统中的动态

研究了放射性锆(^95Zr)在模拟海水、底质及海洋生物间的迁移、消长的动态．结果表明,海水中^95Zr的比活度在最初4h内下降了90％以上,此后呈缓慢递减趋势;底质中^95Zr的比活度至48h达到最大值,随后逐渐降低;半褶织纹螺螺壳和螺肉的放射性百分比分别为68．7％和31．30％;大弹涂鱼的鳃、鳍、内脏、头骨、皮、脊柱和肌肉等组织的放射性百分比分别为22．80％、12、64％、34．82％、10．31％、4．48％、11．55％和3．71％．半褶织纹螺对^95Zr的积累比大弹涂鱼更强、^95Zr在海水、底质、半褶织纹螺和大弹涂鱼中浓度的大小顺序是：底质>半褶织纹螺>海水>大弹涂鱼、各分室中^95Zr浓度(即比活度)随时间变化的动态可用指数函数表达．     

Impacts of nutrient enrichment and sediment on phytoplankton community structure in the northern Baltic Sea

A three-week mesocosm experiment was conducted in order to study the effects of bottom sediment and nutrient enrichment on phytoplankton and zooplankton community structure in the Archipelago Sea, northern Baltic Sea. The transparent polyethylene enclosures included the whole water column and varied in volume from 30 to 40 m³. There were two types of enclosures: some with natural sediment as a bottom and others with a plastic bottom. The experiment was a 2 × 2 factorial design with presence of sediment and nutrient enrichment as treatment factors. Both the sediment presence and nutrient enrichment significantly increased water nutrient concentrations and the rate of primary production. However, external nutrient enrichment and the presence of sediment stimulated the growth of different phytoplankton groups, indicating that the effect of sediment was not related to nutrient fluxes alone, but involved more complex interactions. External nutrient enrichment was primarily channelled to picoplanktonic cyanobacteria, the biomass of which increased four- to fivefold due to enrichment. The presence of sediment increased the biomass of cryptophytes, chrysophytes and prasinophytes, but decreased the biomass of N₂-fixing cyanobacteria. Zooplankton biomass increased during the experiment, but was not affected by the treatments. The study shows that sediment plays a significant role in phytoplankton dynamics, underlining the importance of including sediment in shallow-water mesocosm experiments. Handling editor: J. Padisak     

Experimentally observed soft‐tissue preservation near a marine brine seep

A sea urchin placed on the sea floor near an active brine seep was recovered after 13 years with detailed soft‐tissue preservation. Growth of an amorphous calcium carbonate solid with small amounts of the mineral bassanite occurred on the spines and test. The solid also exhibits striations at both the macro‐ and microscopic scales that preserve the muscle texture of the sea urchin. Such soft‐tissue replacement and mineralization could lead to exquisite fossilization. Soft‐tissue mineralization has been previously replicated in controlled laboratory conditions; however, this is the first report of the lithologic replication of soft tissues in an open marine experiment. Examples of extraordinary fossil preservation, or Lagersätten, give a distinct snapshot of the past and have led to a greater understanding of the history of life. Soft‐tissue lithification occurs in special circumstances in which local chemical conditions (often mediated by decay or bacterial factors) promote early diagenetic mineralization, the first steps of which are observed in this instance. The preservation of articulated skeletons, especially within echinoderms, is normally attributed to rapid burial, but that may not be necessary given that this urchin was at or very near the sediment–water interface for 13 years.     

Factors influencing the extent and development of the oxic zone in sediments

Dissolved oxygen concentrations in river-sediment porewaters are reported and modelled using a zero-order reaction rate and the Monod equation. After mixing the sediments and allowing settling, the dissolved oxygen profile in the bed-sediment was expected to reach a steady-state rapidly (< 1 h). However changes in the vertical profile of oxygen over a period of 38 days revealed that the penetration of oxygen increased and the dissolved oxygen flux at the interface decreased with time, probably as the oxidation kinetics of organic matter and redox reactions in the sediment changed. Experiments with three contrasting silt and sand dominated sediments (organic matter content between 0.9 and 18%) at two water velocities (ca 10 and 20 cm s^–1) showed that the dissolved oxygen profiles were independent of velocity for each of the sediments. The most important controls on the reaction rate were the organic matter content and specific surface area of the sediment. A viscous diffuse-boundary-layer above the sediment was only detected in the experiments with the silt sediment where the sediment oxygen demand was relatively high. In the coarser sediments, the absence of a diffuse layer indicated that slow oxidation processes in the sediment controlled the dissolved oxygen flux at the interface. The problem of determining a surface reference in coarse sediment is highlighted. The results are discussed with reference to other studies including those concerned with estuarine and marine sediments.     

Characterization of biogenic organic matter by stepwise thermogravimetry (STG)

The STG method presented here is a simple approach facilitating the characterization of biogenic organic materials. Pre-dried (130°C and grounded (< 0.5 mm) samples were heated in a muffle furnace at 280 °C for 6 h and subsequently at 520 °C for 6 h. The weight loss in the temperature range, 130–280°C (PI) and 280–520 °C (PII), provided an index (Rp) defined as, Rp = PII/(PI + PII). Plant materials rich in structural carbohydrates generally showed a Rp index around 0.3, whereas Rp for animal tissues rich in proteins usually were around 0.6. A general relationship between Rp and C:N for living biogenic organic matter, ranging from leaves of terrestrial origin to marine invertebrate tissue, was described by the equation: Rp = 0.791 x (C:N)^-0.246 (n = 13, r² = 0.946). During biological decomposition of composting barley straw, Rp increased from 0.17 to 0.37 and C:N decreased from 87 to 16. A similar Rp-C:N pattern was observed with depth in the upper 2 cm of an organic poor marine lagoon sediment (Rp increased from 0.43 to 0.47; C:N decreased from 8.4 to 7.7); indicating that microbial protein synthesis may have occurred with depth in this layer. The observed increase in both Rp and C:N with depth from 2 to 8 cm (Rp increased from 0.47 to 0.52; C:N increased from 7.7 to 10.3) suggested that humification may predominate in this zone. Accordingly, humic acids are found to have a Rp as high as 0.64. The Rp-C:N relationship appears to be a powerful two-dimensional tool applicable to characterize the bulk composition of various biogenic organic materials at different stages of decomposition.     

Factors influencing respiration data in freshwater sediment

Sediment respiration (oxygen consumption and CO₂ evolution) was measured in freshwater sediment samples using both flask- and core-microcosms, and the estimates were compared. Oxygen consumption data were also compared in flask-microcosms constructed with sediment samples of different masses, sediment: water ratios, and storage times. Furthermore, sediment respiration was examined under different incubation conditions of temperature and agitation. O₂ consumption was markedly higher in flask-microcosms than in sediment core-microcosms, when compared on a per g dry weight basis. However, when the results were expressed as O₂ consumed per unit surface area, the values were more similar. CO₂ evolution was less dependent on surface area as evidenced by similar CO₂ values per g sediment in both microcosms. In addition, the effect of sediment mass on O₂ consumption and CO₂ evolution was examined. Both O₂ consumption and CO₂ evolution (expressed as µmole g^–1 dry weight sediment) decreased significantly with increasing sediment mass between 3 and 12 g dry weight. Maximum O₂ consumption per unit headspace was measured when a wet sediment mass between 10.0 and 20.0 g was used in the flask-microcosms. It was also shown that the sediment: water ratio, agitation, incubation temperature, and previous storage time of sediment all affected the respiration estimates. Initial O₂ consumption and CO₂ evolution in flasks were significantly higher in flasks with a decreased sediment: water ratio (1:1 versus 1:2), increased flask agitation, and increased incubation temperature (15 °C versus 5 °C). Also, respiration decreased significantly over the first 100 days of storage at 4 °C.     

Effects of acute fresh water exposure on water flux rates and osmotic responses in Kemp's ridley sea turtles (Lepidochelys kempi)

Water flux rates and osmotic responses of Kemp's Ridley sea turtles (Lepidochelys kempi) acutely exposed to fresh water were quantified. Salt-water adapted turtles were exposed to fresh water for 4 d before being returned to salt water. During the initial salt water phase, absolute and relative water flux rates were 1.2+/-0.1 l d(-1) and 123.0+/-6.8 ml kg(-1) d(-1), respectively. When turtles were exposed to fresh water, rates increased by approximately 30%. Upon return to salt water, rates decreased to original levels. Plasma osmolality, Na(+), K(+), and Cl(-) decreased during exposure to fresh water, and subsequently increased during the return to salt water. The Na(+):K(+) ratio was elevated during the fresh water phase and subsequently decreased upon return to salt water. Aldosterone and corticosterone were not altered during exposure to fresh water. Elevated water flux rates during fresh water exposure reflected an increase in water consumption, resulting in a decrease in ionic and osmotic concentrations. The lack of a change in adrenocorticoids to acute fresh water exposure suggests that adrenal responsiveness to an hypo-osmotic environment may be delayed in marine turtles when compared to marine mammals.     

典型冷暖季沉水植物凋落物分解特性及沉积物微生物群落变化

为研究湿地沉水植物腐败分解对水体的污染状况,选择典型沉水植物金鱼藻（暖季植物）和菹草（冷季植物）进行了为期60 d的凋落物分解实验。结果表明金鱼藻和菹草凋落物分解规律相似,0—15 d快速分解,15—60 d缓慢分解,60 d凋落物失重率分别达到60.43%和66.72%。菹草的有机物释放量明显高于金鱼藻,N和P释放量相反,分解释放的N主要是NH4+-N和有机氮。三维荧光光谱（Excitation-Emission Matrix Spectroscopy, EEMs）结合平行因子分析法解析出一种类色氨酸物质C2和3种类腐殖质物质C1、C3、C4,易降解的类色氨酸有机物先增加后减少,难降解的类富里酸和类腐殖酸有机物逐渐增加。EEMs和四种组分的最大荧光强度百分比表明,溶解性有机物（Dissolved organic matter, DOM）在0—15 d以易降解有机物为主,15—60 d以难降解有机物为主。两种植物凋落物分解释放的DOM含量及特性不同,整体上呈低腐殖化特征,可能是水中难降解DOM的一个重要来源。植物凋落物的分解促进了沉积物中微生物的丰富度,降低了微生物的多样性;参与分解的主要微生物包括4 d时的Pseudomonas属（26%—35%）、15 d和30 d时的Malikia属（>8%）和Bacillus属（2.6%—9%）,分解难降解有机物的微生物逐渐增加,如Flavobacterium属;沉积物中微生物群落结构的变化受营养物质可利用性变化的影响。分析发现植物凋落物分解对水质的影响具有阶段性,0—15 d,N和P释放量增加暂时导致了水质恶化;15—60 d,N和P释放量降低,难降解有机物含量逐渐增加,可能会加剧水体甚至是沉积物的腐殖化程度。因此,在植物衰亡期应及时打捞或者做好植物平衡收割管理,避免因植物大量腐败导致水质恶化。     

Adsorption/Desorption of toluene on clay minerals

Adsorption/desorption of toluene on montmorillonite, illite, and kaolinite was studied using the batch equilibrium method. The isotherms measured fit the Freundlich equation (r² >0.95). Montmorillonite adsorbed more toluene than illite or kaolinite; the adsorption of toluene on illite and kaolinite was not significantly different. Adsorption of toluene by montmorillonite showed an exponential increase as the ratio of toluene to clay was increased from 5 to 100. The rate studies showed that 62% of the adsorption was completed within 6 h. A rapid desorption was observed initially, followed by slow desorption after 1 h. The desorption rate decreased as the time of adsorption was increased. Almost all of the adsorbed toluene was extracted with water from the clay when the adsorption time was 0.1 h, but only 61% of the toluene could be desorbed when the adsorption time was 24 h.     

The interaction between water movement,sediment dynamics and submersed macrophytes

Water movement in freshwater and marine environments affects submersed macrophytes, which also mediate water movement. The result of this complex interaction also affects sediment dynamics in and around submersed macrophyte beds. This review defines known relationships and identifies areas that need additional research on the complex interactions among submersed macrophytes, water movement, and sediment dynamics. Four areas are addressed: (1) the effects of water movement on macrophytes, (2) the effects of macrophyte stands on water movement, (3) the effects of macrophyte beds on sedimentation within vegetated areas, and (4) the relationship between sediment resuspension and macrophytes. Water movement has a significant effect on macrophyte growth, typically stimulating both abundance and diversity of macrophytes at low to moderate velocities, but reducing growth at higher velocities. In turn, macrophyte beds reduce current velocities both within and adjacent to the beds, resulting in increased sedimentation and reduced turbidity. Reduced turbidity increases light availability to macrophytes, increasing their growth. Additionally, macrophytes affect the distribution, composition and particle size of sediments in both freshwater and marine environments. Therefore, establishment and persistence of macrophytes in both marine and freshwater environments provide important ecosystem services, including: (1) improving water quality; and (2) stabilizing sediments, reducing sediment resuspension, erosion and turbidity.     

Litter Decomposition of Scirpus maritimus L. in a Mediterranean Coastal Marsh: Importance of the Meiofauna during the Initial Phases of Detached Leaves Decomposition

Growth, senescence and decomposition rates of Scirpus maritimus were studied in a Mediterranean brackish wetland. Plant tussocks were tagged in March, 2002 and were totally dead by September, 2002. Decomposition rates were determined over 360 days using litter bag technique and mass loss, nutrient dynamics, fungal biomass, meiofauna and macroorganisms were determined. Decomposition rate of detached S. maritimus litter was 0.00196 (k, day^–1) with a 54% of mass lost observed in 1 year. The pattern of mass loss was characterized by an initial phase of fast loss of organic matter with high density of meiofauna and a decrease of oxygen content, followed by two slower phases, with no significant losses from 50 to 180 days and with 21% of mass lost from 180 to 360 days. Nitrogen (N) and phosphorus (P) content of plant litter increased during decomposition process whereas atomic C:N and C:P ratios decreased, suggesting a nutrient immobilization on plant detritus. Fungal biomass measured as ergosterol content decreased after submersion of leaves, indicating that their importance in litter decomoposition decreases in submerged leaves during the first days of decomposition. An inverse relationship (r = –0.79, P < 0.005) was observed between ergosterol content and nematodes density on S. maritimus litter. Our results suggest that in Mediterranean brackish marshes, where large amounts of dead organic matter is accumulated over the sediment surface, decomposition process is greatly affected by extremely high temperatures in summer that, if water is available, accelerates microbial activity decreasing oxygen content thus slowing decomposition. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of estuarine sediment on virus survival under field conditions

The survival of poliovirus 1 (LSc) and echovirus 1 (Farouk) in estuarine water and sediment was studied in Galveston Bay, Texas. Viruses were suspended in estuarine water and sediment both in dialysis tubing and in chambers constructed with polycarbonate membrane walls. Virus inactivation rates in seawater were similar in both types of chambers. Virus adsorption to sediment greatly increased survival time. The time required to inactivate 99% (T-99) of poliovirus increased from 1.4 days in seawater alone to 6.0 days for virus adsorbed to sediment at a relatively nonpolluted site. At a more polluted site, poliovirus T-99 was increased from approximately 1 h to 4925 days by virus adsorption to sediment. This study demonstrates that under field conditions virus association with estuarine sediment acts to prolong its survival in the marine environment.     

Influence of estuarine sediment on virus survival under field conditions.

The survival of poliovirus 1 (LSc) and echovirus 1 (Farouk) in estuarine water and sediment was studied in Galveston Bay, Texas. Viruses were suspended in estuarine water and sediment both in dialysis tubing and in chambers constructed with polycarbonate membrane walls. Virus inactivation rates in seawater were similar in both types of chambers. Virus adsorption to sediment greatly increased survival time. The time required to inactivate 99% (T-99) of poliovirus increased from 1.4 days in seawater alone to 6.0 days for virus adsorbed to sediment at a relatively nonpolluted site. At a more polluted site, poliovirus T-99 was increased from approximately 1 h to 4925 days by virus adsorption to sediment. This study demonstrates that under field conditions virus association with estuarine sediment acts to prolong its survival in the marine environment.     

Phosphorus cycling in urban aquatic ecosystems: connecting biological processes and water chemistry to sediment P fractions in urban stormwater management ponds

Phosphorus (P) dynamics in urban landscapes may differ from that in natural landscapes due to different P sources and unique environmental conditions. However, many aspects of P cycles in urban areas, especially within engineered aquatic ecosystems, remain largely unknown. Through this work, we aim to contribute to better understanding of P cycling in urban aquatic ecosystems by investigating P fractions in sediment and their relationship with ambient chemistry in surface water from six urban stormwater management ponds located in Ontario, Canada. We found that organic P contributed up to 75% of total P in pond sediment, but this percentage decreased significantly between our two sampling events in June and September 2012. This decrease coincided with increased rates of extracellular enzyme (especially phosphatase) activities, which is indicative of fast mineralization processes in these ecosystems. Moreover, the decreased sediment organic P was matched by increased water column P concentration. This inverse relationship suggests that the large organic P pool in pond sediment, and its fast decomposition, contributed to internal release of P from sediment and increased water column P concentrations. The dominance of organic P in sediment and the putative role of relevant biological processes (i.e., decomposition and productivity) in urban ponds found in this study strongly contrast with classic water management expectations of physicochemically controlled P dynamics and long-term P storage in sediment of aquatic ecosystems. This difference suggests that urban stormwater ponds may perform poorly in terms of P retention and thereby contribute to poor water quality in terms of P pollution to downstream urban watersheds. Thus, stormwater pond design and future management strategies should consider these biogeochemical features of urban ponds, including internal P release, to help prevent eutrophication of downstream ecosystems.     

The influence of Corophium volutator abundance on resuspension

Two experiments were performed to test the hypothesis that Corophium volutator affects the turbidity of water in estuaries through active resuspension of sediment. One experiment was done in a flume system under different flow velocities, and one in aquaria. A diatom film developed at the sediment surface in both experiments before Corophium was added. This diatom film was supposed to have a stabilising effect on the sediment. In both experiments, the concentration of suspended solids in the water column increased with the density of Corophium individuals. No effect of flow velocity on suspended solids concentration was found. This indicates that, in our flume experiment, active resuspension by Corophium was more important than physical resuspension, at least at low flow velocity (<20 cm s^-1) and in the presence of a diatom film. The critical erosion threshold decreased with increasing Corophium density in the aquarium experiment, indicating that indirect effects of Corophium grazing may become more important at high levels of bottom shear stress. The implications of our findings for suspended solids concentration in estuarine systems are discussed.     

Effect of Sorption on Mineralization of Low Concentrations of Aromatic Compounds in Lake Water Samples

Montmorillonite-benzylamine complexes were formed immediately upon addition of 20 pg to 20 μg of amine per ml of suspensions containing the clay. The extent of amine sorbed was a linear function of equilibrium amine concentration in lake water. Increases in the clay concentration decreased the percentage of the organic compound that was mineralized at amine levels of 20 pg to 200 ng, but not at 20 μg/ml. A larger percentage of the chemical was released from the complex during mineralization in the presence of high clay concentrations than in the presence of low clay concentrations. The rates of desorption and mineralization increased linearly with benzylamine levels up to 200 ng/ml. Montmorillonite did not enhance mineralization rates at amine levels of 200 ng/ml or lower, but it was stimulatory at 20 μg/ml. Except at high amine and clay concentrations, mineralization was more rapid than desorption during the early periods of decomposition when the amine concentration in solution was relatively high. However, relative to the microbial demand, desorption was more rapid during later periods of decomposition when the amine level in solution was very low. Mineralization of benzoate was not usually affected by montmorillonite, kaolinite, or glass beads. More than 90% of the carbon from benzylamine and benzoate was often mineralized when the substrate concentration was 250 ng/ml or less. After incubation of the chemical in lake water, none of the radioactivity from benzylamine was in the particulate fraction containing natural sediment and microbial cells. The data indicate that clay may have a significant effect on the microbial decomposition of low concentrations of certain organic compounds.