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1.
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2.
The objective of this study was to measure the effects of invertebrates on the physical characteristics and microbial processes in hyporheic sediments. We investigated the impacts of an assemblage of three taxa (asellids, chironomid larvae, and tubificid worms) on sediment distribution, water fluxes, sediment organic carbon, biofilm (attached bacteria) characteristics, and O2, dissolved organic carbon NO3?, NO2?, and NH4+ concentrations in slow filtration sand–gravel columns. The results showed that invertebrates clearly modified the distribution of particles in the sediment column, probably because of the structures (tubes, macropores, and faecal pellets) produced by the three taxa in the sediment. Our assessment of water fluxes indicated that invertebrate activities led to an increase in the porosity of the sediment columns. In addition, aerobic (O2 consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) microbial processes occurring in the sediment were stimulated in the presence of invertebrates. Finally, the present study demonstrates that invertebrates can act as ecosystem engineers in heterogeneous sediments that are under the influence of an advective flux of water. The solute residence time increased in columns containing the faunal assemblage. Micro‐organisms used more dissolved organic matter and nutrients in the presence of invertebrates because invertebrate activities increased the contact between the biofilm and water. We conclude that engineering by invertebrates in natural conditions modifies characteristics of the hyporheic zone and thereby enhances both the porosity of the sediment and the solute transport across the benthic interface. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

3.
Mercury, with its reactive forms being the most deleterious for the trophic chains, has been identified as a major pollutant in a few confined bodies of the coastal zone. Due to feeding, burrowing, and bioirrigation activities, infauna are known to play a crucial role in the biogeochemical processes of contaminants. The main goal of the present study is to evaluate the effects of Hediste diversicolor bioturbation on mercury fluxes from estuarine sediments in a mesocosms laboratory experiment. Additionally, an attempt was made to establish a relationship between the amount of remobilised mercury to the water column and the degree of contamination of the sediments using a mercury contamination gradient. The present experiment demonstrated that the bioturbation activity caused by the gallery-diffuser H. diversicolor did not influence the remobilisation of mercury (in dissolved reactive forms) from the sediment to the water column. The concentration of dissolved reactive mercury in the water column also did not reflect the degree of contamination in the sediments. The results obtained were in accordance with the sediment characteristics of the Mondego Estuary and Ria de Aveiro (Portugal), since they are very rich in organic matter content, iron/manganese total and hydrous oxides. These physicochemical characteristics of the sediments may partially justify the retention of mercury by these systems, even when they are subjected to bioturbation. In conclusion, sediments with high organic matter content and a high concentration of iron/manganese hydrous oxides allowed for efficient retention of mercury, and the bioturbation process did not seem to affect the system. Another conclusion from this study is that the remobilisation of mercury by bioturbation to the water column is not a fast process, requiring more than 24h. This study constitutes an important work in the area of the effects of bioturbation on mercury remobilisation. Considering the toxicity of mercury for the biota, it is essential to evaluate the real magnitude of mercury processes occurring in estuarine systems in order to obtain essential information on metal behaviour.  相似文献   

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

5.
Copper-based antifoulant paints and the sea lice treatment Slice® are widely used, and often detectable in the sediments beneath farms where they are administered. Ten-day, whole sediment mesocosm experiments were conducted to examine how increasing sediment concentrations of copper or Slice® influenced final water column concentrations of ammonium-nitrogen (NH4-N), nitrate + nitrite-nitrogen (NOX-N) and phosphate-phosphorus (PO4-P) in the presence of the non-target, benthic organisms Corophium volutator and Hediste diversicolor. Nominal sediment concentrations of copper and Slice® had significant effects on the resulting concentrations of almost all nutrients examined. The overall trends in nutrient concentrations at the end of the 10-day incubations were highly similar between the trials with either copper or Slice®, irrespective of the invertebrate species present. This suggests that nutrient exchange from the experimental sediments was primarily influenced by the direct effect of copper/Slice® dose on the sediment microbial community, rather than the indirect effect of reduced bioturbation/irrigation due to increased macrofaunal mortality.  相似文献   

6.
: Lake Neuchâtel (Switzerland) has been recovering from human-induced eutrophication since 1982. Oligochaetes and chironomid larvae were used to monitor the recovery of sediment at a depth of 40 m. In oligochaete communities, the mean proportion of individuals belonging to species indicative of oligotrophic conditions (mostly Spirosperma velutinus and Stylodrilus heringianus) increased from 16 % in 1984 to 33 % in 1992, but decreased to 11 % in 1997. Based on oligochaetes, benthic conditions deteriorated in 1997 whereas, based on the increase of oligotrophic chironomids (mostly Micropsectra), they improved. This difference was attributed to the impact of large planktonic algae whose sedimentation had altered oxygen concentrations at the water-sediment interface. Oligochaetes were more affected than chironomids because they are less mobile and they depend more on the inner sediment for their food and reproduction than the latter. However, based on the combined response of oligochaetes and chironomids, benthic recovery was stalled in 1997 but was not reversed.  相似文献   

7.
This work deals with the potential influence of benthic communities on the sediment dynamics of the coastal zone, and specifically with the modifications to bottom roughness caused by communities and their effects on wave propagation across the coastal profile. Time-series of video observations of the sea bottom on the Ebro delta coast were analysed in order to estimate the bottom roughness associated with physical and biological morphological components and the sediment reworking rates caused by epifaunal organisms. Biological roughness was mainly caused by ophiuroids and tanatocenosis of bivalve and gastropod shells, which changed their abundance during the study period. The total biological roughness (Kbio) ranged between 0.27 and 0.81 cm and represented a significant part (<20%) of the total form drag roughness. Flattening of ripples caused by bioturbation was observed under low-energy conditions. Surface sediment perturbation and bioturbation rates were also estimated. Based on these observations a wave propagation model was applied in order to carry out a sensitivity analysis of the significance of biological roughness on wave dissipation in the study area under different wave conditions.  相似文献   

8.
Microbial activity, abundance and biomass, and biogeochemical cycling of iron, sulphur and carbon were studied in the extremely acidic (pH 2.5-4.3), meromictic, nutrient-rich pit lake Cueva de la Mora in Spain. The goal was to find out (1) if the relatively high nutrient content influenced plankton abundance in the water column and alkalinity-producing microbial processes in the sediments compared to other acid pit lakes, and (2) if sediments in the shallow, mixed and the deep, stagnant parts of the lake exhibited differences in microbial activities and geochemical sediment composition related to meromixis. We hypothesised that redox cycling was more intense in the mixed part and higher amounts of reduced components would accumulate in the stagnant part. Especially phytoplankton biomass, CO2 production, and sulphate reduction were indeed higher than reported from typical acid pit lakes and were rather within the range of neutral or weakly acidic lakes, which can be attributed to the relatively high nutrient contents of Cueva de la Mora. Even in the monimolimnion, anaerobic processes occurred mainly in the sediments. Sediments from the mixed and stagnant parts of the lake differed markedly in their biogeochemistry. Mixolimnetic sediments showed high iron and sulphate reduction rates, and they appeared to undergo substantial recycling, as supported by reactive Fe, relation between gross sulphate reduction rate and net accumulation of reduced sulphur, and viable counts of iron and sulphur bacteria. Monimolimnetic sediments exhibited lower anaerobic microbial activities, and surprisingly they accumulated more Fe(II) than mixolimnetic sediments, but less reduced sulphur and carbon. This might be explained by a strong separation of the two water bodies, resulting in comparably less input of energy (light) and allochthonous matter into the monimolimnion. Regarding the total extent of alkalinity-generating microbial processes, their net effect is not sufficient to neutralise the lake within decades.  相似文献   

9.
Sedimentation and sediment metabolism was measured at eight active milkfish fish pens and at one abandoned site in the Bolinao area, Philippines in order to examine the interactions between sediment and water in this shallow coastal zone. The rates of sedimentation were high in the area due to siltation, but the activities in the fish pens also contributed to enhanced sedimentation as indicated by the difference between the abandoned and active sites. The sediment metabolism appeared to decrease with increasing rates of sedimentation indicating that the microbial activity reached a saturation level in the fish pen sediments. Anaerobic processes dominated the organic matter decomposition, and sulfate reduction rates are among the highest measured in fish farm sediments. The rates decreased with increasing organic loading despite high concentrations of sulfate (>10 mM) at all sites. Presence of methane bubbles in the sediments suggests that sulfate reduction and methanogenesis were coexisting. The sediment metabolism was significantly reduced at the abandoned site indicating that the stimulation of microbial activities is due to active fish production. The anaerobic activity remained high at the abandoned site indicating that the sediment biogeochemical conditions remain affected long time after fish production has ceased.  相似文献   

10.
Streambed hydraulic conductivity (K) and vertical K (K v) are key controls on groundwater and surface water exchange and biogeochemical fluxes through the hyporheic zone, but drivers of transient hydraulic properties in different fluvial environments are poorly understood. This study combines hydrogeology, geophysics, and sedimentology to reveal mechanisms of K and K v transience in the upper 0.5 m of a sandy streambed during low discharge. Hydraulic tests (44 slug tests, 130 falling-head permeameter tests) and 130 grain-size analyses were repeated three times over 8 weeks on a 1,200 m2 grid spanning: (a) a channel with continuously flowing water and mobile bed load; (b) an adjacent mid-channel bar that was stationary and infrequently submerged. Aerial photographs and ground-penetrating radar show scour and complete reworking of fluvial sediments in the channel. Bar sediments below the water table remained immobile, but infrequent flows of moderate discharge reworked the uppermost few centimetres of the bar top. Despite differences in sediment mobility and stream flow characteristics across environments, K and K v exhibited order-of-magnitude differences in spatial heterogeneity and temporal variability in both the channel and bar. Mean K and K v values in the channel were comparatively stable over time. In the immobile bar, mean K declined 20% and K v declined 26% after increased discharge temporarily inundated the bar. Grain-size distributions were steady across both environments over time, but repeat geophysical surveys of the bar show a decrease in electrical conductivity, likely from porosity reduction. These findings suggest that sediment dynamics and stream flow characteristics in different streambed environments are important drivers of K transience during low discharge conditions. Specifically, pore clogging can be an important mechanism of transience over short durations (weeks to months) in immobile sediments subject to infrequent flows and minor reworking.  相似文献   

11.
Sediment characteristics influence the distribution and bioavailability of phosphorus (P) in river sediments. In this study, we analyzed different P fractions in the sediments of the Bronx River, New York City, NY, using sequential extraction. The results showed that the average P pool rank order was HCl?P > NaOH?P > NaHCO3?P > residue?P, and their relative proportions were 3.7: 2.0: 1.4: 1 in sediments collected in 2006, while HCl?P > NaOH?P > residue?P > NaHCO3?P, with their relative proportions of 27.8:6.2:2.7:1 in the sediments obtained in 2007. The strong correlation between microbial P and organic P (OP), along with the changes in microbial P over time indicate that most of the OP in the river bed sediments is potentially bioavailable. The sediment transport, deposition, assimilation, the exchange of P between sediments and water columns, the land use changes, raw sewer discharge, gas spill, construction, fertilizer application, etc., as well as the hydro‐climatic changes could result in the spatial and temporal variations in P bioavailability in the river bed sediments. The estimations of P pools and their bioavailability in river bed sediments could help determine the spatial and temporal variations in P transport and impacts of land use on water quality, in turn, help regulate P in the river's watershed.  相似文献   

12.
泥炭地是一种水-陆过渡型的湿地生态系统。水体沼泽化过程中,植被等生物群落也随之改变,进而影响泥炭地碳埋藏和发育过程。作为泥炭地生态系统重要的次级生产者,摇蚊群落结构变迁可以为追溯泥炭地环境演变和发育历史提供关键线索。泥炭地在发育过程中将经历各种不同阶段,然而,现有的泥炭地摇蚊群落调查仅限于泥炭生境或泥炭地中开阔水域,较短的生境梯度不足以提供更为全面的摇蚊群落变化信息。神农架大九湖湿地包含泥炭地、湖泊、临时性水体等多种生境,本研究选择该湿地公园作为研究区域,通过采集不同生境的表层沉积物及水体样品,提取底泥亚化石摇蚊头壳,分析大九湖湿地中不同生境下的摇蚊群落结构差异,并对其与环境因子间的关系进行探讨。结果表明:1)大九湖湿地不同生境中摇蚊优势种迥异,泥炭藓藓丘生境中Limnophyes、Psilometriocnemus、Pseudosmittia等半陆生种类为主要优势种,湖泊生境中则以典型静水种Polypedilum nubeculosum-type为主要优势种,而过渡性水域(泥炭地洼地、沟渠及水洼生境)中,静水种与半陆生种共存;2)烧失量、水位埋深和pH是塑造不同生境类型下摇蚊群落结构的显著环境因子,水文条件主要通过改变碳积累过程等其他环境条件间接影响生物群落组成;3)沿水生-半陆生生境梯度,有机质含量和类型均发生显著变化,而摇蚊群落也由静水种、静水/半陆生共存转变为以半陆生种为主,摇蚊群落对生境变化表现出良好的响应过程。本研究揭示了不同生境条件下摇蚊群落的结构差异及影响摇蚊群落结构的潜在因子,为未来基于摇蚊的长时间尺度上泥炭地发育过程分析提供参考依据。  相似文献   

13.
To investigate vertical changes of bacterial communities from living plants to the associated sediments and bacterial biogeochemical roles in peatland ecosystem,samples of different part of individual Sphagnum palustre and the different layers of the underlying sediments were collected from Dajiuhu Peatland in central China.All samples were subject to 16S rRNA gene clone libraries and quantitative PCR analysis.Even though bacteria vary in abundance at the same order of magnitude in all samples,they show great profile difference in composition from the top part of S.palustre to the low layer of the sediments.Cyanobacteria and alpha-Proteobacteria dominate at the top part whereas Acidobacteria at the middle part of S.palustre.Alpha-Proteobacteria and Acidobacteria are the dominant phyla at the bottom part of S.palustre and in the surface peat sediment.In contrast,bacterial communities in the subsurface sediments are dominated by Acidobacteria.These profile distributions of different bacterial communities are closely related to their ecological functions in the peatland ecosystem.Specifically,most Cyanobacteria were observed at the top green part of S.palustre,a horizon where the active photosynthesis of the moss occurs,which infers their endosymbiosis.In contrast,Acidobacteria,dominant in the subsurface sediments,are able to decompose the specific compounds on the cell wall of Sphagnum moss and thus might play an important role in the formation of the peatland,including the acidic condition.Methane oxidizing process might have been underestimated in Sphagnum peatland due to the identification of Methylocystaceae in all parts of the moss investigated here.The vertical difference in bacterial composition and bacterial ecological functions presented here sheds light on the understanding of biogeochemical processes,in particular the CH4 flux,in peat ecosystems.  相似文献   

14.
The Markermeer is a large and shallow man-made freshwater lake in the Netherlands, characterized by its high turbidity. As part of a study aiming to mitigate this high turbidity, we studied the water–bed exchange processes of the lake’s muddy bed. The upper centimeter’s–decimeter’s of the lake bed sediments mainly consists of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of this soft anoxic mud. This oxic layer, which is much easier to be eroded than the anoxic mud, is believed to be related with Markermeer’s high-turbidity levels. Our hypothesis is that the thin oxic layer develops from the anoxic mud, enhanced by bioturbation. Actually, we will demonstrate that it is the bioturbated state of the bed that increases its erodability, and not the oxidation state of the sediments. In particular, we will refer to bioturbation caused by meiobenthic fauna. The objective of this study is therefore to determine the influence of the development of the thin oxic layer on the water–bed exchange processes, as well as to establish the role of bioturbation on those processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the rate at which Markermeer sediments are eroded by almost an order of magnitude. The short-term fine sediment dynamics in Markermeer are found to be driven by the complex and highly dynamic interactions between physics, chemistry, and biology. Finally, the long-term fine sediment dynamics are driven by the erosion of the historical deposits in the lake’s bed, which is only possible after bioturbation, and which leads to an increase of the stock of sediments in the lake’s muddy bed.  相似文献   

15.
210Pb- and137Cs-measurements, and varve counting have been used to date sediment cores from Lake Zurich (Switzerland). Two cores from different water depths were dated with210Pb/210Po and revealed sediment accumulation rates of (0.055±0.015) g·cm?2·y?1 and (0.09±0.03) g·cm?2·y?1, respectively. A comparable rate of (0.07±0.01) g·cm?2·y?1 has been obtained from137Cs measurements. These rates were confirmed by annual layer (varve)-counts which lead to rates of 0.07 g·cm?2·y?1. Constant210Pb activities were observed in the top 6 cm of the sediment cores. This constancy is generally explained in the literature by mixing processes caused by bioturbation and by distortion during coring operations of the uppermost water-rich fluffy sediments. However the distinct137Cs-maxima and the regular and undisturbed varve lamination of the top sediment observed in the cores of Lake Zurich contradict this assumption. In addition, measurements of7Be at the water/sediment interaces proved complete sediment core recovery and mechanically undisturbed sediments. Remobilization processes are assumed to cause the observed constant210Pb activities. Remobilization may also be the reason for an incomplete210Pb inventory in the sediments which contain only about 50% of the fallout from atmosphere. The results of the210Pb dating should therefore be considered with some care. If existent, varve counting represents the easiest and most reliable means for dating lake sediments.  相似文献   

16.
Research on the sediment‐surface water transition zone in three study site regions, different in hydrological conditions, was conducted to estimate to which extent nitrate in surface water can contribute to riverbed sediment oxidation and thus prevent release of sediment phosphorus to surface water. Consequently, the Du tch Flow Model (DUFLOW) based water quality model “Spreewald” and results from the emission model “ Mo delling N utrient E missions in Ri ver S ystems” (MONERIS) were used to estimate to which extent wastewater treatment plants (WWTPs) could contribute to the NO3– concentration in surface waters if they were operated without denitrification. It is demonstrated that an effective phosphorus retention in sediments by means of surface water NO3– is possible only under specific conditions, i. e. (i) a sufficient supply of surface water to the sediment by advective fluxes, (ii) a sufficient amount of sediment iron to provide phosphorus binding sites in the case of sediment oxidation, (iii) a redox system not leading to a rapid NO3– and FeOOH depletion and to phosphorus release from organic pools by high microbial activities. Model results show that in‐stream denitrification processes counteract a significant increase of NO3– surface water concentrations from WWTPs operated without denitrification during summer, when eutrophication risk through phosphorus is highest. The increase of NO3– surface water concentrations in winter due to decreased denitrification in the surface water is of minor relevance for phosphorus release from sediments.  相似文献   

17.
Slag material was dumped in two sites off southwestern Taiwan by the China Steel Corporation during 1984–1995. By geochemically analyzing four sediment cores, we investigated the impact of slag on the sediment chemistry. Elemental profiles from the dumping sites show a strong depletion in detrital elements and enrichment in alkaline and redox-sensitive elements, especially for the top ～20 cm of sediments. The relative enrichment factor (EFrel) exhibits wider range for Ca (0.73–13.33), Fe (0.88–3.03), Mg (0.94–9.58) and Mn (1.22–33.30) due to contamination of sediments by slag. Sediment weathering indicators also show a distinct change with lower values in sediments influenced by dumping due to Ca and Sr addition. Higher EFrel for As, Cd and Pb in the top sections of the cores indicate an additional modern/industrial input of these elements since ～1950. Our study suggests that slag dumping may have a localized effect on biogeochemical processes by inducing the diagenetic remobilization of certain elements.  相似文献   

18.
The distribution of benthic invertebrates and their subfossil remains was examined within the basin of De Waay, a dimictic, eutrophic lake in the Netherlands. We focused on Chironomidae, but also report the abundances of 11 invertebrate groups that potentially produce chitinous remains that are preserved in the fossil record, although their remains could only be identified at a coarser taxonomic resolution. Most living invertebrates sampled in different seasons were constrained to the littoral zone, with the exception of a few taxa (Ceratopogonidae, Chaoborus flavicans, and Chironomus) that are adapted to low oxygen conditions in the seasonally anoxic profundal zone. In contrast, assemblages of invertebrate remains in lake surface sediments were similar in the entire lake basin, suggesting that considerable numbers of invertebrate remains are transported and redeposited off-shore in Lake De Waay, due to its steep bathymetry. These results indicate that a single sediment sample obtained from the centre of this lake contains subfossil invertebrate remains originating from the entire lake basin. In Lake De Waay, the majority of taxa found in the living assemblages were identified as remains in lake surface sediments, at least for the Chironomidae that could be identified at a similar taxonomic level in living and subfossil assemblages. Of the total 44 chironomid taxa found in Lake De Waay, 35 taxa occurred in the living assemblages and 34 taxa occurred in the subfossil assemblages. Thirty chironomid taxa occurred both as living and subfossil specimens, and on average these 30 taxa represent 94% of the specimens encountered in a sediment sample. Five rare chironomid taxa present as living larvae were not detected in the subfossil assemblages. Conversely, eight rare and four common chironomid taxa were found in subfossil remains, but not in living assemblages. Our results indicate that subfossil assemblages in surface sediment samples provide spatially integrated and representative samples of the living assemblage. However, a combined approach examining both the living benthic invertebrate fauna and invertebrate remains in lake surface sediments will potentially give a more complete and detailed overview of benthic invertebrates in a lake ecosystem than an approach based exclusively on one of these groups.  相似文献   

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20.
Subarctic marine sediments amended with various organic compounds were exposed to fresh Cook Inlet crude oil at a concentration of 50 ppt for either 6 or 8 months. After the sediments were initially treated, they were returned to the approximate location where they were collected and left to be exposed to natural environmental conditions until they were retrieved for analysis. As a result of crude oil treatment, the activities of the enzymes that hydrolyse structural polysaccharides were reduced and the activities of the enzymes that hydrolyse storage polysaccharides were stimulated. In addition to these changes, we observed changes in phosphatase activity, nitrogen fixation rates, potential denitrification rates, methane concentrations, CO2 production rates, and the glucose uptake and mineralization rates. The effect of the crude oil perturbation was different depending on the organic compound used in the amended sediments. Many of these differences could be explained by the effect of crude oil on the hydrolases which were responsible for degrading the compound in question. The results of this study suggest the effect of crude oil on microbial processes may be affected by the type of organic material present in the impacted marine sediment. This study also illustrates the value of measuring hydrolase activity in studies designed to determine the effects of this or any other pollutant on microbial processes in marine sediments.  相似文献   

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