Sediment Concentration Ratios Research Articles

Propagation characteristics of the flow and suspended sediment peaks in the three gorges reservoir, China: Insight from numerical simulations and measured data

AbstractEffective management of reservoir sedimentation necessitates the characterization of flood events, especially in relation to the propagation of the flow peak (Qpeak) and the suspended sediment concentration peak (SSCpeak). This study, based on a one‐dimensional river network hydro‐sediment model together with field data, presents an exploration of the flood events in the Three Gorges Reservoir (TGR) with focus on the propagating characteristics of Qpeak and SSCpeak. The findings reveal that the main flood season (from July to September) contributed over 80% of the annual sediment load into the TGR, with the mainstream Yangtze and its tributary, the Jialing River, being the primary sediment sources. After the impoundment of the TGR, the propagation time of Qpeak decreases with the raise of the water level in front of dam (WLdam). The increases in Qpeak discharge extends the range of river reach dominated by kinematic wave, resulting in an increase trend in Qpeak propagation time. The propagating speed of SSCpeak is closely related to the ratio of sediment concentration to flow discharge and WLdam. Finally, the propagating durations of Qpeak and SSCpeak in the TGR are compared, and empirical formulas are proposed for quantifying their difference.

The role of algae in fine sediment flocculation: In-situ and laboratory measurements

The precise interactions between organic and inorganic particles in the context of flocculation is an on-going topic of research. The suspended particulate matter (SPM) found in estuaries is composed of both organic and inorganic particles with specific particle size distributions (PSD's). These PSD's are a function of the hydrodynamic conditions, suspended sediment concentration (SSC), organic matter composition, salinity and seasonal variations. A field campaign was carried out in August 2015 in the turbidity maximum zone of the Yangtze Estuary, where the SPM dynamics were recorded. The concentration of algae in the water column was indirectly measured through the chlorophyll-a concentration (CC). We show that there is a strong correlation between SSC and CC in the whole water column, for the whole tidal cycle. Additional flocculation experiments in the laboratory confirm that the largest observed flocs are predominantly organic-based, and that salinity alone could not induce the flocculation of the Yangtze mineral particles. A key parameter for the maximal floc size is the algae concentration to sediment concentration ratio. When this ratio is high, the D50 is high and vice-versa.

Experiments on critical judgment parameter of heavily silt-laden fluid mud

In the heavily silt-laden river, density current belongs to an excellent method for flushing the input sediment without water level drawn down. Heavily silt-laden fluid mud in reservoir comes from heavily silt-laden density current. Density current comes into being in the reservoir and may reach the front of the dam with certain flood duration in addition. And the flood also needs to meet a certain sediment concentration and discharge. That makes water and sediment input need to provide density current with energy to overcome the energy loss during the forming process. For example, in a density current creeping process, the current energy shortage often can unsuccessfully reach the front of the Xiaolangdi dam, the stop makes a muddy pond before the dam. Another situation occurs during the density current flushing process. When the input flood ends without subsequent enough energy retention, the foremost density current creeps slowly and suspends before the dam. In these two cases, the muddy layer along the vertical section in front of the reservoir dam will be called fluid mud in this paper. On the basis of understanding the mixing characteristics of hyper-concentrated flow settlement characteristics, viscoelastic and Bingham fluid in the Yellow River, under the flume experiments combined with theoretical analysis method, the formula which concludes high sediment rheological properties of mud and sediment particle size, the volume ratio of sediment concentration, is established and fluid mud layer theoretical analysis had been carried out and flume experiments had been combined to carry out about the effect between density currents and fluid mud. It is found that the difference between the fluid mud with the Bingham shear stress and the flow shear stress due to different sediment concentration, which can divide the movement regime into 2 types, named invasive and interface. The heterogeneous density flow of different sediment does not only affect the muddy water thickness and blending extent, but also determine the movement regime of the head. The flow discharge mainly affects the muddy water thickness and the velocity of the density current. The density of fluid mud increased from fast to slow with the time lasting, which is formed due to settlement. Through the theoretical deduction, the critical judgment parameter of the fluid mud layer incipient motion is obtained. The calculation formula which concluded volumetric sediment concentration, slope and density current thickness is proposed based on the experiments. Obviously, timely opening the desilting tunnel or with the help of the subsequent flood, this will enable the fluid mud incipient motion and flushing out of the reservoir to achieve the purpose of efficient sediment transport. With the adhesion of the fine sediment mud layer in group settlement mechanism and process, conditions on follow-up density current occurrence, and fluid mud layer motion possibility, and its interaction are the basis and key technology of efficient way flushing sediment out of the reservoir in the heavily silt-laden river. The research results can enrich the contents of river sediment dynamics and provide technical reference for the operation and planning of sediment-laden river reservoir

Sedimentation of overbank floods in the confined complex channel–floodplain system of the Lower Yellow River, China

AbstractThe channel boundary conditions along the Lower Yellow River (LYR) have been altered significantly since the 1950s with the continual reinforcement and construction of both main and secondary dykes and river training works. To evaluate how the confined complex channel–floodplain system of the LYR responds to floods, this study presents a detailed investigation of the relationship between the tempo‐spatial distribution of sedimentation/erosion and overbank floods occurred in the LYR. For large overbank floods, we found that when the sediment transport coefficient (ratio of sediment concentration of flow to flow discharge) is less than 0.034, the bankfull channel is subject to significant erosion, whereas the main and secondary floodplains both accumulate sediment. The amount of sediment deposited on the main and secondary floodplains is closely related to the ratio of peak discharge to bankfull discharge, volume of water flowing over the floodplains, and sediment concentration of overbank flow, whereas the degree of erosion in the bankfull channel is related to the amount of sediment deposited on the main and secondary floodplains, water volume, and sediment load in flood season. The significant increase in erosion in the bankfull channel is due to the construction of the main and secondary dykes and river training works, which are largely in a wide and narrow alternated pattern along the LYR such that the water flowing over wider floodplains returns to the channel downstream after it drops sediment. For small overbank floods, the bankfull channel is subject to erosion when the sediment transport coefficient is less than 0.028, whereas the amount of sediment deposited on the secondary floodplain is associated closely with the sediment concentration of flow. Over the entire length of the LYR, the situation of erosion in the bankfull channel and sediment deposition on the main and secondary floodplains occurred mainly in the upper reach of the LYR, in which a channel wandering in planform has been well developed.

Shaping and maintaining a medium-sized main channel in the Lower Yellow River

This paper studies relations between bankfull discharge, lateral cross section variation and the incoming flow and sediment condition in the Lower Yellow River using measured data from 1950 to 2003. Since 1950 the bankfull discharge has obviously decreased and the ratio of channel width to flow depth has increased. The critical annual average incoming sediment coefficient (defined as the ratio of sediment concentration to discharge) and discharge at the Huayuankou station are approximately 0.012 and 1,850 m3 s−1, respectively, for no accumulative deposition occurring in the reach from Huayuankou to Lijin. On this basis, a mathematical model is used to study the scale of the main channel in the Lower Yellow River and its corresponding bankfull discharge under possible incoming flow and sediment conditions in the near future. The main factors influencing the scale of the main channel are analyzed, and measures to shape and maintain a medium-sized channel are discussed. The results show the effect of various water and sediment combinations released from the Xiaolangdi Reservoir on the shaping of the main channel and suggest that under recent incoming flow and sediment conditions, it is possible to shape and maintain a medium-sized channel with a bankfull discharge of approximate 4,000 m3 s−1.

Investigating step‐pool sequence stability

Step‐pool units, common features in steep, narrow streams, are highly dynamic systems that adjust during high flows and active sediment transport conditions. Consecutive step pools in a reach form a step‐pool sequence, and though these features are prevalent in nature, quantifying the stability of such systems is challenging. This study focuses on the statistical relationships between 445 stable sequences of three or more steps and nine geometric and resistance‐based parameters. Step sequence stability is parameterized through a sequence stability parameter, a metric of how long a given step‐pool sequence exists relative to the total run time. Despite variability in the strength of the statistical relationships, the results allow identification of dominant trends between sequence stability and both roughness and geometric parameters. The sediment concentration ratio provides a means for comparing the relative strength of these statistical relationships. As sediment concentration ratios increase, the relations between flow resistance parameters and step stability change from dominantly inverse to dominantly direct. Thus, at higher sediment concentration ratios, sequence stability is more likely to increase with flow resistance, but the reverse is more likely at low sediment concentration ratios. A connection exists between bed morphology, flow resistance, and stability. For the majority of stable step sequences, resistance parameters increase over time, indicating some sequences adjust their geometry to increase stability during flood events. The influence of sediment concentration over the stability‐geometric and stability‐resistance parameter relationships may enable the use of the sediment concentration ratio as a predictor of step sequence stability during a flow event.

Channel adjustments in response to the operation of large dams: The upper reach of the lower Yellow River

The Yellow River in China carries an extremely large sediment load. River channel-form and lateral shifting in a dynamic, partly meandering and partly braided reach of the lower Yellow River, have been significantly influenced by construction of Sanmenxia Dam in 1960, Liujiaxia Dam in 1968, Longyangxia Dam in 1985 and Xiaolangdi Dam in 1997. Using observations from Huayuankou Station, 128km downstream of Xiaolangdi Dam, this study examines changes in the river before and after construction of the dams. The temporal changes in the mean annual flow discharge and mean annual suspended sediment concentration have been strongly influenced by operation of theses dams. Observations of sediment transport coefficient (ratio of sediment concentration to flow discharge), at-a-station hydraulic geometry and bankfull channel form observed from 1951 to 2006 have shown that, although variations in flow and sediment load correspond to different periods of dam operation, changes in channel form are not entirely synchronous with these. The channel has been subject to substantial deposition due to the flushing of sediment from Sanmenxia Dam, resulting in a marked reduction in bankfull cross-sectional area. Flows below bankfull had a greater impact on channel form than higher flows because of very high sediment load. At-a-station hydraulic geometry shows that the variation of channel cross-sectional area below bankfull in this wide and relatively shallow system largely depends on changes in width. Such at-a-station changes are significantly influenced by (1) events below bankfull and (2) overbank floods. Bankfull depth is the main component of channel adjustment in that depth adjusts synchronously with channel area. The channel adjusts its size by relatively uniform changes in depth and width since 1981. Channel morphology is not the product of single channel-forming flow frequency. It is determined by the combination of relatively low flows that play an important role in fine sediment transport and bed configuration as with relatively high flows that are effective at modifying the channel's morphology. The sediment transport coefficient is a useful index for efficiently guiding the operation of the dams in a way that would minimize channel changes downstream. Sedimentation over the nearly 60years of study period caused the lower Yellow River to aggrade progressively, the only significant exception being the two years following completion of Sanmenxia Dam.

Comparative distribution, sourcing, and chemical behavior of PCDD/Fs and PCBs in an estuary environment

PCDD/F and PCB field data (1041 samples) in five media (dissolved, suspended sediment, bed sediment, catfish, and blue crab) were studied to explore dual contaminant patterns in the Houston Ship Channel, Texas, USA. PCDD/Fs showed greater concentration than PCBs in suspended sediments while PCBs were higher in apparent dissolved (truly dissolved + DOC-associated), fish, and crab. PCDD/Fs at nearly all locations contributed more strongly to dioxin-like toxicity. The fraction of PCB TEQ was, however, enriched in biotic over abiotic media due in large part to the presence of PCB 126, which was mostly undetected in water and sediment and yet exhibited a BAF three times greater than 2,3,7,8-TCDD. Dissolved-suspended sediment and suspended-bed sediment relationships showed that (1) observed apparent dissolved concentration differences (as fraction of total water were mean 10% PCDD/Fs and 63% PCBs) can reasonably be explained by a four-phase partition model (truly dissolved, DOC-associated, suspended OC, and suspended BC) for PCBs but not for PCDD/Fs and (2) the contaminants behaved similarly in bed to suspended sediment concentration ratios ( C bed/ C susp) upstream of a major confluence but not downstream. PCA-cluster analysis pointed to the possibility that suspended sediment PCB contamination originates from resuspended bed sediment while PCDD/Fs in suspended sediment originates more probably from other sediment sources such as upstream wash load or air deposition. Finally, examinations of a congener marker ratio (PCB 209/206) seemed to indicate that a source of pure PCB 209 may exist in bed sediment near Patrick Bayou though the source was not completely localized.

Antibiotic Transport via Runoff and Soil Loss

Research has verified the occurrence of veterinary antibiotics in manure, agricultural fields, and surface water bodies, yet little research has evaluated antibiotic runoff from agricultural fields. The objective of this study was to evaluate the potential for agricultural runoff to contribute antibiotics to surface water bodies in a worst-case scenario. Our hypothesis was that there would be significant differences in antibiotic concentrations, partitioning of losses between runoff and sediment, and pseudo-partitioning coefficients (ratio of sediment concentration to runoff concentration) among antibiotics. An antibiotic solution including tetracycline (TC), chlortetracycline (CTC), sulfathiazole (STZ), sulfamethazine (SMZ), erythromycin (ERY), tylosin (TYL), and monensin (MNS) was sprayed on the soil surface 1 h before rainfall simulation (average intensity = 60 mm h(-1) for 1 h). Runoff samples were collected continuously and analyzed for aqueous and sediment antibiotic concentrations. MNS had the highest concentration in runoff, resulting in the highest absolute loss, although the amount of loss associated with sediment transport was <10%. ERY had the highest concentrations in sediment and had a relative loss associated with sediment >50%. TYL also had >50% relative loss associated with sediment, and its pseudo-partitioning coefficient (P-PC) was very high. The tetracyclines (TC and CTC) had very low aqueous concentrations and had the lowest absolute losses. If agricultural runoff is proven to result in development of resistance genes or toxicity to aquatic organisms, then erosion control practices could be used to reduce TC, ERY, and TYL losses leaving agricultural fields. Other methods will be needed to reduce transport of other antibiotics.

Experimental results on bioaccumulation of metals and organic contaminants from marine sediments

A test-system for the assessment of bioavailability and bioaccumulation of metals and organic contaminants in marine benthic organisms is described and results from studies where this system has been applied are assessed. Sediments tested were polluted harbour sediment (from Norway), and clean sediments spikes with metal containing weight materials for drilling muds. Contaminants that may bioaccumulate under relevant conditions are indicated. The test-system uses two species of ecological relevance ( Nereis diversicolor and Hinia reticulata). Interspecies differences in bioaccumulation were found for several compounds, which show the importance of using species with different modes of living in such tests. Compared to other PAHs, pyrene was found to bioaccumulate to a high degree (BioAccumulation Ratio, BAR = 213.5 > sediment concentration ratio, SCR = 97.4; bioaccumulation factor, organism dw. conc. to sediment dw. conc., BAF = 1.02), which shows that extrapolating bioaccumulation results between different substances is difficult. When assessing bioavailability of specific compounds, it is most adequate to perform direct measurements on exposed organisms, such as the experiments described here. The high bioaccumulation of compounds such as pyrene and nickel may in some cases be attributed to manipulation of the sediments and (for pyrene) lack of subsequent aging, thereby overestimating bioavailability.

IMPACT OF COAL SURFACE MINING AND RECLAMATION ON SURFACE WATER CHEMICAL CONCENTRATIONS AND LOAD RATES IN THREE OHIO WATERSHEDS1

ABSTRACT: Information is lacking on the watershed scale effects of mining and reclaiming originally undisturbed watersheds for coal on surface water chemical concentrations and load rates for a variety of constituents. These effects were evaluated on three small, geologically dissimilar watersheds subjected to surface mining in Ohio. Comparisons were made between phases of land disturbances using ratios of average concentrations and load rates: Phase 1 (natural), subphases of Phase 2 (mining and reclamation), and subphases of Phase 3 (partial reclamation and final condition) using 4,485 laboratory analyses of 34 constituents. Average concentration and load rate ratios were categorized into three classes—minor, moderate, and substantial. Mining and reclamation (M/R) affected flow duration curves in different ways‐baseflow changes were variable, but high flows generally increased. The average concentration ratios for all sites were classified as 15 percent “minor,” 36 percent “moderate,” and 49 percent “substantial” (average ratio of 2.4.) Generally load rate ratios increased due to mining and reclamation activities (average ratio of 3.3). Minor, moderate, and substantial impacts were found on average for 7 percent, 23 percent, and 70 percent, respectively, of load rate ratios. The impact of M/R on average load rates was not necessarily the same as on average concentrations due to changed hydrology and can be opposite in effect. The evaluation of the impacts of M/R requires knowledge of changing hydrologic conditions and changing supplies and rates of release of chemicals into streams. Median sediment concentration ratio is an indicator of average constituent load rate ratio of a wide variety of chemical constituents and is useful for development of best management practices to reduce chemical loads. The site at which diversion ditches were not removed during final reclamation sustained large chemical load rates, and removal of diversions at the other mined site reduced load rates. Revegetation of poorly reclaimed areas decreased chemical load rates. Chemical load rates were sensitive to geology, mining, and reclamation methods, diversions, and changing hydrology, concentration flow rate regressions, and watershed areas.

Concentrations and Spatial Variations of Polybrominated Diphenyl Ethers and Several Organochlorine Compounds in Fishes from the Northeastern United States

Fish from four lakes, two small lakes in the northeastern United States and two of the Great Lakes, were analyzed to determine the concentrations and spatial variations of polybrominated diphenyl ethers (PBDE) in this region. Three of the lakes were considered to have background levels of PBDEs; one lake was close to a suspected source. The PBDE concentrations were compared to organochlorine pesticide and PCB concentrations. Age and trophic position did not influence the organohalogen concentrations in the fish collected from the four locations. At the three background locations, the sum of PBDE concentrations ranged from 6.9 +/- 1.4 to 18 +/- 1 ng/g wet weight, or 150 +/- 9 to 300 +/- 80 ng/g lipid, and these values were similar to those of some of the organochlorine pesticides, such as total chlordane, but lower than sum of PCB concentrations. At the lake near the suspected source, the sum of PBDE concentration was 65 +/- 8 ng/g wet weight, or 2,400 +/- 600 ng/g lipid, and it exceeded the sum of PCB concentration. The hexabrominated congeners made up 43% of the total mass of PBDEs at this lake, and 7% at the background locations. Fish to sediment concentration ratios indicated that the tetra- through hexa-substituted congeners have a similar bioavailability, while the deca-substituted congener does not seem to be bioavailable at all.

Experimental Study of Changes in Channel Slope at Stream Confluences

Flume experiments are conducted to evaluate the change in channel slope at a stream confluence. The rate of change in the slope of the main channel at the confluence is only weakly related to the discharge ratio of two tributaries, but exhibits a strong positive relationship with the sediment concentration ratio of the confluent flows. This finding indicates that the slope adjusts basically to sediment transport through bed shear stress and the sediment content of the incoming flows plays a primary role in slope change at a stream confluence.

Lacey Divergence Equations for Alluvial‐Canal Design

Besides discharge Q and sediment characteristics (size D50 and concentration C), the third physical factor governing hydraulic geometry of an alluvial canal is resistance to erosion of bank material. Lacey formulas provide one set of the parameters of hydraulic geometry through the wetted perimeter P, hydraulic mean radius R, and slope S, with implied values of sediment concentration C and maximum safe boundary shear stress t\ds. But with varying values of C and t\ds, many other sets of P, R, and S are possible. Defining Lacey divergence as the ratio of actual value to value obtained with the Lacey formula and designating this ratio by subscript r, Lacey Divergence relations were obtained for velocity V and C. Velocity ratio V\dr was found related only to slope ratio S\dr, whereas sediment concentration ratio C\dr was related to both S\dr and boundary shear stress ratio t\dr. Equations were then derived for P\dr, R\dr and S\dr in terms of C\dr and t\dr, which permit determination of P, R, and S when design data in respect of Q, D50, C, and t\ds are given.

Uptake of uranium and thorium series radionuclides by the waterlily, Nymphaea violacea

The waterlily Nymphaea violacea is a major aquatic macrophyte in the waters of the Alligator Rivers Region, Northern Teritory, Australia. It is also a traditional Aboriginal diet item, and is considered to be potentially one of the main contributors to the effective dose equivalent arising from consumption of so called ‘bush’ food in the region. Because of the proximity of the Ranger Uranium Mine (RUM), the activity concentrations of the U and Th series radionuclides have been studied in water, sediment and waterlily during different seasons at five sites downstream of the mine site. The objectives of the study are: 1. 1. To identify the major source of radionuclide uptake by the plant; i.e. water or sediment. 2. 2. To assess the concentration factors/ratios needed for predicting the radiation exposure of the critical group resulting from any discharge of water to the aquatic environment from the Ranger uranium mine. 3. 3. To estimate the natural radiation exposure of the public arising from consumption of waterlilies. Results show that sediment is the major source of U and Th series radionuclides to waterlily roots, rhizomes and foliage. Waterlily to sediment concentration ratios, based on wet weights, are of the order of 0·01–0·03 for roots and rhizomes and 0·005–0·015 for foliage. The naturally occurring committed effective dose equivalent (CEDE) from an estimated annual intake of 3 kg waterlily rhizomes from the forage areas are of the order of 0·02 mSv.

A Semiportable Multislot Divisor for Erosion and Runoff Measurements1

When comparing the effects of cropping systems on runoff and erosion characteristics, it is important to collect samples representative of the treatment area while minimizing variance due to other factors. To meet these requirements a multislot divisor for runoff and sediment collection from small plots was constructed and its feasibility for use in field experiments assessed. The collection system was designed to handle a 20.3-cm, 24-h rainfall event resulting in a soil loss of 33.5 Mg/ha. The divisor ratio was found to be 0.1111 ± .0003 for flow rates ranging from 0.2 to 4.9 L/s. The sediment concentration ratio for nonsampled to sampled runoff was 0.9969 ± .05, and was close to unity for each particle size separate. The compact size of this equipment facilitates easy installation and removal of the device with minimum disturbance to the site.

Simultaneous exposure of English sole ( Parophrys vetulus) to sediment-associated xenobiotics: Part 1—uptake and disposition of 14C-polychlorinated biphenyls and 3H-benzo[a]pyrene

English sole ( Parophrys vetulus) were exposed to environmentally realistic levels of sediment-associated 3H-benzo[a]pyrene (3 μg BaP/g sediment, dry weight) and 14C-Aroclor 1254 (1 μg PCBs/g), separately and together, for up to 10 days. BaP and its metabolites in tissues reached steady-state concentrations by the first day of the exposure, whereas PCBs did not approach steady-state concentrations until the tenth day of exposure. Simultaneous exposure of sole to BaP and PCBs, relative to separate exposure to the xenobiotics, significantly increased the concentrations of BaP-derived radioactivity and decreased the concentrations of PCB-derived radioactivity in some tissues and bile. Accumulation of PCB-derived radioactivity, estimated as the burden in tissues, was significantly greater (4- to 13-fold) than that of BaP-derived radioactivity throughout the experiments and regardless of the type of exposure. The rank of the concentrations of PCB-derived radioactivity in tissues and bile was: bile ∼ liver > brain > kidney ∼ gill > skin ∼ blood ∼ muscle and for BaP-derived radioactivity the order was: bile > liver > gill > kidney > skin ∼ blood > muscle > brain. BaP-derived radioactivity in liver and bile was present primary (85–99%) as metabolites, whereas PCB-derived radioactivity was present equally as parent compounds and metabolites in bile and primarily (98 %) as parent compounds in liver. Hydrolysis of bile from PCB/BaP-exposed sole with β-glucuronidase/arylsulfatase released 35 % of the BaP-derived radioactivity and 32 % of the PCB-derived radioactivity as primary metabolites. A much higher proportion of the BaP-derived radioactivity (64 %) than the PCB-derived radioactivity (13 %) in bile was unaffected by the enzyme treatment, indicating differences in the conjugation of the primary metabolites of PCBs and BaP. The results suggest that in contaminated environments the tissue to sediment concentration ratios for PCBs would exceed that for BaP and its metabolites; however, BaP would be continually absorbed and metabolized by sole to potentially carcinogenic and mutagenic compounds. In addition, the tissue levels of these toxic compounds may be increased by simultaneous exposure to PCBs.

TRACE METAL CYCLING IN THE U.S. COASTAL ZONE: A SYNTHESIS

This synthesis of trace element research in estuarine communities of the U.S. coastline and the Caribbean provides a summary applicable to the shoreline of the tropical and temperate regions of the world which have mangroves, kelp beds, riverine marshes and seagrass communities. An inventory of sediments and leaf tissues shows Mn and Fe to be the most highly concentrated elements with Hg and Cd present in lowest concentrations. Generally, trace element concentrations in roots are much higher than in leaves and other tissues above the sediment. Tissue to sediment concentration ratios show that Cd is most likely to be bioamplified and that Cu, Hg, Sr and Zn may have relatively high concentration ratios which can exceed unity. A conceptual model was constructed to integrate the forcing functions, compartmental couplings, and dynamics common to these estuarine systems. Seasonality is important for changes in some trace element concentrations in plants and litter. Trace element additions to water or sediment increased certain trace element concentrations in plants and dead organic matter. It is clear that estuarine plant communities serve as living filters of estuarine trace elements. However, increased knowledge of trace element cycling in estuarine systems and relationships between trace element concentrations in plants and the estuarine food chain is needed, particularly food chains to man. There is a need for structured long‐term estuarine research to allow direct comparison of results among estuarine study sites, to identify the similarity of population and system processes among estuaries and to define the geographical scale over which estuarine research results may be generalized.