EFFECTIVENESS OF ALUM IN A WEEDY,SHALLOW LAKE1

ABSTRACT: An alum treatment in Long Lake (mean depth, 2 m) in 1980 has been effective at controlling internal loading of phosphorus for four years. The fifth summer after treatment, the lake returned to its pro-treatment state. Lake P content decreased from a summer average of 65 μg/L during 1976–1978 to about 30 μg/L during four years following treatment. In 1985, summer P content was 61 μg/L. Algal abundance, species composition, and transparency have responded proportionately with P. Alum effectiveness apparently declined because the floe layer tended to sink and become dispersed at a deeper level in the sediment, as well as become covered with new, P-rich sediment. Iron-reduction may be the principal mechanism for internal P loading, although the lake is unstratified and anoxia is usually not pronounced.     

太湖不同水域沉积物甲烷释放潜力及其途径分析

为明确太湖不同湖区CH₄释放特征与释放潜力差异,采用水-气界面甲烷排放通量测定和室内厌氧培养,结合沉积物理化因子对太湖沉积物CH₄释放特征及其释放潜力差异进行研究。结果表明,不同湖区水-气界面CH₄排放通量存在显著差异;不同湖区、不同深度沉积物中CH₄释放潜力也存在明显差异,且CH₄释放潜力与含水率和总有机碳呈正相关,与盐度呈负相关;太湖沉积物产CH₄潜力最大的途径为甲基途径,且主要集中在沉积物10~35cm深度。由此可知,太湖是CH₄排放的净产生源,含水率、有机质和盐度等环境因子的差异以及沉积物深度均会影响沉积物甲烷排放和释放潜力,从而对太湖沉积系统的碳循环以及局部气候变化产生重要影响。     

A MODEL FOR PREDICTING LAKE SEDIMENT OXYGEN DEMAND FOLLOWING HYPOLIMNTETIC AERATION1

ABSTRACT: Hypolimnetic aeration is a widely used technique for lake restoration and fisheries enhancement. However, system design still depends on application of “safety factors” to observed oxygen demand rates, in large part because actual oxygen demand may be greater after aeration than before. Laboratory incubations of sediment show that sediment oxygen demand (SOD) rates follow mixed order kinetics, with an initial period of zero order reaction, followed by first order kinetics. The transition from zero to first order kinetics may correspond to the transition from laminar to turbulent flow. This suggests that SOD reaction kinetics are governed by thickness of the diffusive sublayer adjacent to the sediments. Therefore, zero and first order reaction regions correspond with oxygen diffusion limitation and substrate limitation, respectively. Such a mechanism would account for the induced oxygen demand observed following hypolimnetic aeration and would reconcile differences in SOD reaction orders noted in the literature. This paper describes development of equations based on laboratory SOD incubations for predicting induced oxygen demand following hypolimnetic aeration.     

西湖和东苕溪沉积物重金属化学形态分析

不同赋存形态重金属的环境行为和生态效应不同,水体沉积物中重金属的迁移转化及其潜在环境危害更大程度上取决于其赋存形态。本研究在西湖和东苕溪设置12个采样点采集沉积物样品,采用改进BCR分步提取法,提取了重金属污染物的4种化学形态,分别为弱酸提取态、可还原态、可氧化态及残渣态。结果表明:沉积物中Cd以弱酸提取态为主,对外界环境的变化极其敏感,并易于发生迁移转化,生态风险较高。Cu离子对有机质表现出极强的亲和力导致Cu的可氧化态含量较高也有一定的生态风险。Pb会被Fe-Mn氧化物所吸附导致Pb的可还原态含量较高,存在较高的潜在生态危害。Mn的弱酸提取态、可还原态和残渣态含量都较高,在迁移的过程中变化地较快,能够逐渐降低Mn对自然环境的危害。其他各重金属(As、Cr、Zn)则都以残渣态为主,潜在危害较低。     

LAKE RESTORATION BY SEDIMENT REMOVAL1

ABSTRACT: Fresh water lake sediment removal is usually undertaken to deepen a lake and increase its volume to enhance fish production, to remove nutrient rich sediment, to remove toxic or hazardous material, or to reduce the abundance of rooted aquatic plants. Review of more than 60 projects and five case histories reveals that the first three objectives are usually met through sediment removal. Dredging to control aquatic plants has not been well documented. Disadvantages of dredging include cost, temporary phosphorus release from sediment, increased phytoplankton productivity, noise, lake drawdown, temporary reduction in benthic fish food organisms, the potential for toxic material release to the overlying water and potential for environmental degradation at the dredged material disposal site. The technique is recommended for deepening and for long range reduction of phosphorus release from sediment. Sediment removal to control toxic materials is possible with minimal environmental impact when proper equipment is used, but it may more than double the cost. Lack of definitive information about rooted plant regrowth rates in dredged areas prohibits explicit recommendations on sediment removal to control plant growth.     

Characteristics of heavy metals and Pb isotopic signatures in sediment cores collected from typical urban shallow lakes in Nanjing, China

To investigate the contamination levels and sources for heavy metals that have occurred during the development of cities, sediment cores collected from typical urban shallow lakes (Xuanwu Lake and Mochou Lake) in Nanjing, China were analyzed for Cu, Pb, Zn, Cd, Cr, Ni, and for Pb stable isotopic ratios. No significant differences were found in the concentrations of Cu, Ni and Cd among sediment layers from Xuanwu or in the levels of Cr and Ni among sediment layers from Mochou. However, there were significant differences among the layers in the concentrations of Cr, Zn and Pb in Xuanwu and Cu, Zn, Cd and Pb in Mochou. Based on geoaccumulation indexes and enrichment factors, Cd was the primary pollutant at all depths in the sediment cores. The ratios of (206)Pb/(207)Pb and (208)Pb/(206)Pb differ significantly among sediment layers in Xuanwu. No significant differences were found on the ratios of (208)Pb/(206)Pb in Mochou, but the ratios of (206)Pb/(207)Pb differ significantly among some of the sediment layers in Mochou. The range of (208)Pb/(206)Pb and (206)Pb/(207)Pb ratios was found to be 2.098-2.106 and 1.170-1.176, respectively, for sediment cores from Mochou Lake and 2.091-2.104 and 1.168-1.183, respectively, for cores from Xuanwu Lake. The differences in heavy metal concentrations and the Pb isotopic ratios with depth for the cores from Xuanwu and Mochou confirmed that the contamination sources changed during the formation of the different sediment layers. Furthermore, the ratios of (206)Pb/(207)Pb demonstrated that gasoline and vehicular Pb were not the primary sources of Pb contamination at different depths in the sediment cores in Xuanwu Lake and Mochou Lake.     

Corer-reactors for contaminant flux measurement in sediments

Design details and operating instructions are provided for a sediment corer that can be converted into a reactor for the measurement of the fluxes of contaminants from sediments to overlying waters. The corer-reactor permits measurements, under controlled laboratory conditions, on intact, largely undisturbed sediment cores, without significantly perturbing the physical and chemical conditions found in the field. The design can be constructed in-house for around US dollar 240 (A dollar 400) (excluding motor and corer lid), making it a relatively inexpensive system.     

HISTORICAL TRENDS IN SEDIMENTATION RATES AND SEDIMENT PROVENANCE,FAIRFIELD LAKE,WESTERN NORTH CAROLINA1

Sedimentation rates and sediment provenance were examined for lacustrine sediments deposited in Fairfield Lake, western North Carolina, during the past 111 years. Stratigraphic, radionuclide, and cartographic data indicate that sedimentation rates have increased several fold during the past three decades in response to localized development. The magnitude of increased sedimentation was surprising given limited development within the basin: 0.12 to 0.68 buildings/ha in 2000 in those parts directly delivering sediment to the dated cores. Thus, the analysis illustrates the potential sensitivity of watersheds in the southern Appalachians to changes in land cover. An approach that combined geochemical fingerprinting with sediment mixing models was subsequently evaluated to determine its ability to accurately estimate the contribution of sediment from (1) major bedrock formations that underlie the watershed and (2) potential sources associated with four land cover categories. Sediment sources in both analyses proved difficult to geochemically fingerprint to greater than 90 percent accuracy using data on acid‐soluble metals and selected isotopes of lead (Pb). The relative contributions of sediment from delineated sources, estimated by the mixing models, generally corresponded with known temporal and spatial patterns of land cover. However, the models were plagued by two significant problems — the chemical alteration of sediments as they were transported through upland streams to depositional sites within the lake and the loss of elemental mass. Thus, future investigations using the fingerprinting approach in this area of intense weathering, and presumably others, will need to modify the existing methods to more accurately elucidate changes in sediment provenance related to development.     

Estimating bulk density in vertically exposed stoney alluvium using a modified excavation method

Despite many decades of education and refining land-use practices, accelerated stream bank erosion is still prevalent in the United States. Eroding stream banks produce a sediment load to the riverine system and can cause reduced water quality as a result of increased suspended sediment. As total maximum daily loads (TMDLs) for water bodies impaired by turbidity or suspended sediments become more numerous, a simple, in situ field technique will be needed to estimate the bulk density of readily erodible stream bank material so that reasonably accurate sediment loading rates can be estimated. In this study, the excavation/polyurethane-foam technique for estimating total bulk density was applied to vertically exposed alluvium with high coarse-fragment content. Though not previously attempted in vertically exposed alluvium with high coarse-fragment content, the excavation/polyurethane-foam technique appears to provide a reasonably accurate estimate of the total and soil (<2-mm size fraction) bulk density from vertically exposed, alluvial deposits with high coarse-fragment content (i.e., >70%) along eroding stream banks. Obtaining bulk density estimates using this method would facilitate calculation of sediment loading rates to riverine systems with actual field data.     

COVERING BOTTOM SEDIMENTS AS A LAKE RESTORATION TECHNIQUE1

ABSTRACT: Sediment covering to control macrophytes and sediment nutrient release is reviewed. It is concluded that fly ash application to control sediment phosphorus release presents more dangers to the lake than benefits and should not be used. Polyethylene sheeting has not had long term effectiveness due to macrophyte regrowth on its surface. PVC-coated fiberglass screen is expensive but nontoxic and appears to give long term macrophyte control. Similar results may be obtained with spun-bonded polypropylene. Sand, clay, and sheeting to retard nutrient release have received insufficient attention.     

DISTRIBUTION OF SEDIMENT PHOSPHORUS POOLS AND FLUXES IN RELATION TO ALUM TREATMENT1

ABSTRACT: The distribution of sediment physical characteristics, sediment phosphorus (P) pools, and laboratory‐based rates of P release from the sediments were used to identify regions and dosage for alum treatment in Wind Lake, Wisconsin. Using variations in sediment moisture content, we identified an erosional zone at depths < 1.4 m and an accumulation zone at depths > 2.6 m. Mean concentrations of porewater P, loosely‐bound P, iron‐ and aluminum‐bound P, and mean rates of P release from sediments under anoxic conditions were high in the accumulation zone compared to sediment P characteristics in the erosional zone, indicating focusing of readily mobilized sediment P pools from shallow regions and accumulation to deep regions. We determined that a future alum treatment for control of internal P loading would be most effective at depths > 2.6 in the accumulation zone. The mean rate of anoxic P release from sediments encountered in the accumulation zone (8.3 mg m^‐2 d^‐1) was used in conjunction with a summer anoxic period of 122 d, and a treatment area of 1.6 km² to estimate an internal P load of 1,600 kg to be controlled. Our results suggest that an understanding of the distribution of sediment P pools and P fluxes in lakes provides a strategy for estimating alum dosage and application areas.     

Sediment amendment with Phoslock® in Clatto Reservoir (Dundee, UK): Investigating changes in sediment elemental composition and phosphorus fractionation

Lanthanum-modified bentonite clay (Phoslock(?) is a lake remediation tool designed to strip dissolved phosphorus (P) from the water column and increase the sediment P-sorption capacity. This study investigated short term alterations in sediment elemental composition and sediment P-fractions based on sediment cores taken 2 days before and 28 days following the application of 24 t of Phoslock? to a 9 ha, man-made reservoir. Following the application, sediment lanthanum (La) content increased significantly (p < 0.05; n = 4) in the top 8 cm of the sediment, thereby theoretically increasing sediment P-binding capacity on the whole reservoir scale by 250 kg. Mass balance calculations were used to estimate the theoretical binding of release-sensitive P (P(mobile); sum of 'labile P', 'reductant-soluble P' and 'organic P' fraction) by La across the top 4 cm and 10 cm depth of sediment. The amended mass of La in the sediment had the potential to bind 42% of P(mobile) present in the top 4 cm or 17% of P(mobile) present in the top 10 cm. However, with the exception of a significant increase (p<0.05; n=4) in the 'residual P' fraction in the top 2 cm, sediment P-fractions, including P(mobile,) did not differ significantly following the Phoslock? application. Experimental P-adsorption studies indicated P-saturation values for Phoslock? of 21,670 mg P kg?1 Phoslock?. Sequential extraction of P from saturated Phoslock? under laboratory conditions indicated that around 21% of P bound by Phoslock? was release-sensitive, while around 79% of bound P was unlikely to be released under reducing or common pH (5-9) conditions in shallow lakes. Applying Phoslock? is, therefore, likely to increase the P-sorption capacity of sediments under reducing conditions.     

Using turbidity and acoustic backscatter intensity as surrogate measures of suspended sediment concentration in a small subtropical estuary

The suspended sediment concentration is a key element in stream monitoring, although the turbidity and acoustic Doppler backscattering may be suitable surrogate measures. Herein a series of new experiments were conducted in laboratory under controlled conditions using water and mud samples collected in a small subtropical estuary of Eastern Australia. The relationship between suspended sediment concentration and turbidity exhibited a linear relationship, while the relationships between suspended sediment concentration and acoustic backscatter intensity showed a monotonic increase. The calibration curves were affected by both sediment material characteristics and water quality properties, implying that the calibration of an acoustic Doppler system must be performed with the waters and soil materials of the natural system. The results were applied to some field studies in the estuary during which the acoustic Doppler velocimeter was sampled continuously at high frequency. The data yielded the instantaneous suspended sediment flux per unit area in the estuarine zone. They showed some significant fluctuations in instantaneous suspended mass flux, with a net upstream-suspended mass flux during flood tide and net downstream sediment flux during ebb tide. For each tidal cycle, the integration of the suspended sediment flux per unit area data with respect of time yielded some net upstream sediment flux in average.     

含油污泥的热解处理与利用

文章对油田和炼油含油污泥进行了热解处理室内实验,测定了回收油气组成、热解残渣含碳量和Al2O3含量,开展了热解残渣对沥青的吸附性能和再生处理的絮凝性能测试分析。结果表明,含油污泥热解处理具有较好的油气回收和残渣再生利用价值,可实现污泥“零排放”,具有显著的直接经济效益和社会效益。污泥热解的产油率一般可达10%以上,废白土可达20%～30%,油回收率高;污水处理污泥热解残渣的Al2O3含量可达20%以上,有较高的铝含量,初步再生评价对污水有较好的絮凝作用,可再生循环利用;废白土热解残渣的吸附性能与活性白土相当,可循环使用。     

Evaluation of compost blankets for erosion control from disturbed lands

Soil erosion due to water and wind results in the loss of valuable top soil and causes land degradation and environmental quality problems. Site specific best management practices (BMP) are needed to curb erosion and sediment control and in turn, increase productivity of lands and sustain environmental quality. The aim of this study was to investigate the effectiveness of three different types of biodegradable erosion control blankets- fine compost, mulch, and 50-50 mixture of compost and mulch, for soil erosion control under field and laboratory-scale experiments. Quantitative analysis was conducted by comparing the sediment load in the runoff collected from sloped and tilled plots in the field and in the laboratory with the erosion control blankets. The field plots had an average slope of 3.5% and experiments were conducted under natural rainfall conditions, while the laboratory experiments were conducted at 4, 8 and 16% slopes under simulated rainfall conditions. Results obtained from the field experiments indicated that the 50-50 mixture of compost and mulch provides the best erosion control measures as compared to using either the compost or the mulch blanket alone. Laboratory results under simulated rains indicated that both mulch cover and the 50-50 mixture of mulch and compost cover provided better erosion control measures compared to using the compost alone. Although these results indicate that the 50-50 mixtures and the mulch in laboratory experiments are the best measures among the three erosion control blankets, all three types of blankets provide very effective erosion control measures from bare-soil surface. Results of this study can be used in controlling erosion and sediment from disturbed lands with compost mulch application. Testing different mixture ratios and types of mulch and composts, and their efficiencies in retaining various soil nutrients may provide more quantitative data for developing erosion control plans.     

WIND GENERATED WAVES IN LAKE OKEECHOBEE1

ABSTRACT: The study of wind generated waves is important because waves affect sediment resuspension in lakes. Measurements of wind velocity and wave elevation were made at three different stations in Lake Okeechobee. Significant wave heights were computed using a direct count from the recorded data, and verified by the root-mean-square value approach. The correlation between wind stress and significant wave height also was analyzed. The data revealed a strong correlation. In addition to field measurements, a Boussinesq-type wind-wave model was developed to simulate wind-generated, long-propagating waves. This model included the effects of wind stress and bottom viscous dissipation. Wave elevation and velocity field were evaluated numerically. A six-day simulation using 1996 wind data was conducted. Simulated significant wave heights were found to agree reasonably well with measured values. A predictive wind-wave model provides information about wind generated waves, which is used to compute bottom shear stresses required for sediment resuspension studies.     

Sedimentary Causes and Management of Two Principal Environmental Problems in the Lower Yellow River

Flood and water shortage are two of the leading environmental problems around the world, and among the causes of the problems is sedimentation. The Yellow River brought disastrous floods in its lower reaches in Chinese history. Today, although floods caused by the river are still a formidable hazard hanging over China, it cannot provide the lower reaches with enough usable water. The ineradicable flood hazard and newly emerged water shortage problems of the river are proved to be closely associated with its immense sediment load. The over loaded flow of the river can quickly fill the reservoirs and unceasingly raise the riverbed, attenuating the capacity of reservoirs to suppress floods and provide more water for dry seasons and of river channels to convey floods. Also, the high sediment content pollutes the water and reduces the volume of usable water. In virtue of the intimate linkage between these problems and the formidable sediment load in the river, the solution to these problems should be based on sedimentation management. After reviewing the defects and merits of management measures implemented and proposed, a management scenario composed of multiple measures are recommended. Beside of persistent soil conservation to reduce the huge sediment load, more reservoirs to check sediment and regulate river flows, approaches to alleviating riverbed accretion, interbasin water transfer to mitigate water deficiency, and so on, an emphasis should be laid on use of muddy flows in order to scatter the sediment in a vast area, which was a natural process but has been interrupted by construction of embankments.     

CARBON CONTENT OF SEDIMENTS OF SMALL RESERVOIRS1

ABSTRACT: Carbon content was measured in sediments deposited in 58 small reservoirs across the United States. Reservoirs varied from 0.2 to 4000 km2 in surface area. The carbon content of sediment ranged from 0.3 to 5.6 percent, with a mean of 1.9 ± 1.1 percent. No significant differences between the soil and sediment carbon content were found using a paired t-test or ANOVA. The carbon content of sediments in reservoirs was similar to the carbon content of surface soils (0–10 cm) in the watershed, except in watersheds with shrub or steppe (desert) vegetation. Based on the sediment accumulation rates measured in each reservoir, the calculated organic carbon accumulation rates among reservoirs ranged from 26 to 3700 gC m^-2yr^-1, with a mean of 675 ± 739 gC m^-2yr^-1. The carbon content and accumulation rates were highest in sediments from grassland watersheds. High variability was found in carbon content, carbon accumulation, and sediment accumulation rates due to individual watershed and reservoir characteristics rather than to any broad physiographic patterns. The carbon accumulation rates in these reservoir sediments indicate that reservoir sediments could be a significant sink for organic carbon.     

Landscape metrics and estuarine sediment contamination in the mid-Atlantic and southern New England regions

In a previously published study, quantitative relationships were developed between landscape metrics and sediment contamination for 25 small estuarine systems within Chesapeake Bay. These analyses have been extended to include 75 small estuarine systems across the mid-Atlantic and southern New England regions of the USA. Because of the different characteristics and dynamics of the estuaries across these regions, adjustment for differing hydrology, sediment characteristics, and sediment origins were included in the analysis. Multiple linear regression with stepwise selection was used to develop statistical models for sediment metals, organics, and total polycyclic aromatic hydrocarbons (PAHs). The landscape metrics important for explaining the variation in sediment metals levels (R2 = 0.72) were the percent area of nonforested wetlands (negative contribution), percent area of urban land, and point source effluent volume and metals input (positive contributions). The metrics important for sediment organics levels (R2 = 0.5) and total PAHs (R2 = 0.46) were percent area of urban land (positive contribution) and percent area of nonforested wetlands (negative contribution). These models included silt-clay content (metals) or total organic C (organics, total PAHs) of sediments and grouping by estuarine hydrology, suggesting the importance of sediment characteristics and hydrology in mitigating the influence of the landscape metrics on sediment contamination levels. The overall results from this study are indicative of how statistical models can be developed relating landscape metrics to estuarine sediment contamination for distributions of land cover and point source discharges.     

Electroosmotic dewatering of dredged sediments: bench-scale investigation

The Indiana Harbor (Indiana, USA) has not been dredged since 1972 due to lack of a suitable disposal site for dredged sediment. As a result of this, over a million cubic yards of highly contaminated sediment has accumulated in the harbor. Recently, the United States Army Corps of Engineers (USACE) has selected a site for the confined disposal facility (CDF) and is in the process of designing it. Although dredging can be accomplished rapidly, the disposal in the CDF has to be done slowly to allow adequate time for consolidation to occur. The sediment possesses very high moisture content and very low hydraulic conductivity, which cause consolidation to occur slowly. Consolidation of the sediment is essential in order to achieve adequate shear strength of sediments and also to provide enough air space to accommodate the large amount of sediment that requires disposal. Currently, it has been estimated that if a one 3-foot (0.9-m) thick layer of sediment was disposed of at the CDF annually, it would take approximately 10 years to dispose of all the sediment that is to be dredged from the Indiana Harbor. This study investigated the feasibility of using an electroosmotic dewatering technology to accelerate dewatering and consolidation of sediment, thereby allowing more rapid disposal of sediment into the CDF. Electroosmotic dewatering essentially involves applying a small electric potential across the sediment layer, thereby inducing rapid flow as a result of physico-chemical and electrochemical processes. A series of bench-scale electrokinetic experiments were conducted on actual dredged sediment samples from the Indiana Harbor to investigate dewatering rates caused by gravity alone, dewatering rates caused by gravity and electric potential, and the effects of the addition of polymer flocculants on dewatering of the sediments. The results showed that electroosmotic dewatering under an applied electric potential of 1.0VDC/cm could increase the rate of dewatering and consolidation by an order of magnitude as compared to gravity drainage alone. Amending the sediment with polymers at low concentrations (0.5-1% by dry weight) will enhance this dewatering process; however, the optimal polymer concentration and the cost-effectiveness of using polymers should be investigated further.