污染土的工程性质研究进展

随着我国经济的持续发展,环境污染不断加剧,城市土地被污染亦屡见不鲜。因此,研究污染土的污染机制、勘察评价和处理措施,对保护环境有重要意义。对污染土的物理力学性质、污染机制、试验测试技术、风险评价的研究现状进行了总结,并提出今后的研究方向。     

The assessment of environmental pollution caused by mining and metallurgy wastes from highly polluted post-industrial regions in Southern Poland

Stored metallurgy and mining wastes contain relatively high amounts of potentially toxic elements. To monitor the distribution of contaminants originating from dumps, the chemical and physical properties of the wastes must be characterised. In this study, the chemical properties of wastes deposited in two different locations in Southern Poland (Szklary and Zloty Stok) were evaluated. Heaps located in Zloty Stok contain wastes from gold mineralisation comprising arsenic while wastes in Szklary originate from a factory that produced an iron-nickel alloy. In Szklary the total concentrations of Ca, Mg, Fe, Zn, Mn, Cr, Co, Cu, Ni, Tl, Ag, Cd and Pb were determined, while in Zloty Stok also As is an important contaminant. To assess the risk of contamination of the surrounding environment and to select the proper method for removing the contaminants, information on the distribution of elements between operationally defined phases must be obtained. For this purpose, a six-step sequential extraction was used. The mobility of most elements in the wastes from Szklary and Zloty Stok was relatively low; however, the large amount of As, 40–180 mg L^?1, that could be released to environment in case of Zloty Stok was high. The results of fractionation studies indicated that Ag, Cd, Tl, Co, Cu, Cr, Pb, Zn and Mn may be released into environment under low pH and low redox potential conditions, which can be induced by bacterial activity.     

Differential effects of salinity and soil saturation on native and exotic plants of a coastal salt marsh

In many southern California salt marshes, increased freshwater inflows have promoted the establishment of exotic plant species. A comparative study showed that a native, perennial, high marsh dominant,Salicornia subterminalis, and an invasive, exotic annual grass,Polypogon monspeliensis, responded differently to soil salinity and saturation.Salicornia subterminalis seeds and young plants were more salt tolerant, and the native grew best at high salinities (23 g 1^?1 and 34 g 1^?1) in greenhouse experiments. In contrast, the exotic had reduced growth at high salinities relative to nonsaline controls. The native,S. subterminalis, grew poorly as the duration of soil saturation increased from 2 wk to 32 wk, butP. monspeliensis grew equally well for all durations tested. The response ofS. subterminalis andP. monspeliensis to increased salinity indicated that salt applications might be used to protect native vegetation in salt marshes where salt-sensitive exotics are a problem. A field experiment verified that a salt application of 850 g m^?2 mo^?1 for 3 mo was sufficient to control the exotic, while not noticeably affecting the native. Thus, salt applications may be a practical method for controllingP. monspeliensis invasions in areas receiving urban runoff or other unwanted freshwater inflows.     

Ammonium and phosphate dynamics in a Virginia salt marsh

Experimental chambers were used in a Virginia salt marsh to partition the tidal flux of dissolved nutrients occurring at the marsh surface and in the water column. On five dates from June to October 1989, six replicate chambers in the short Spartina alterniflora zone were monitored over complete tidal cycles. When reservoir water, used to simulate tidal flooding in the chambers, was initially low in dissolved nutrients, the marsh surface was a source of both ammonium and phosphate to the water column. Calculations of the physical processes of diffusion and advection could not account for total nutrient release from the marsh surface. We hypothesize the primary source of nutrients was organic matter mineralization in surface sediments, which released nutrients into the flooding water column. Assimilation (uptake) of phosphate measured in water-column incubation experiments was nearly equal to phosphate released from the marsh surface. Surface release of ammonium, however, was somewhat greater than water-column uptake. In this salt marsh, benthic production and release of ammonium and phosphate is comparable in magnitude to pelagic consumption, thereby yielding only a small “net” transfer of these nutrients to the estuary.     

Freshwater requirements of a semi-arid supratidal and floodplain salt marsh

When rivers are impounded, the reduction in downstream flow can produce important and often adverse effects, especially in the estuarine environment. One or more dams have been proposed for the Olifants River system in the Western Cape, South Africa. This estuary has an extensive area of salt marsh that was examined to see whether it required occasional flooding with freshwater to wash out accumulated salts. The dominant salt marsh species,Sarcocornia pillansii, occurred in supratidal and floodplain areas where the water table was shallowest, the soil moisture highest, and the soil electrical conductivity lowest. Aerial photographs and simulated runoff data showed that no flood had covered the floodplain during the previous 80 years. The data indicate that salt marsh plants use saline groundwater during the dry months of the year in order to survive, but use the short season winter rainfall period with low salinity conditions to grow and reproduce. This study demonstrated that live roots ofS. pillansii reached the water table during the dry season. Tissue and soil water potentials, the relationship between vegetation cover, depth to the water table, and electrical conductivity of the groundwater support the conclusion that saline groundwater is the only source of water during the drier months of the year. Freshwater flooding of the river in winter may be important because it covers the supratidal area with less saline water and reduces the depth to the water table on the floodplain. This makes the groundwater more accessible to the halophytes growing on the floodplain.     

Environmental quality assessment on a river system polluted by mining activities

In this study, adverse impacts of heavy metal pollution, originating from mining, smelting and panning activities, on the aquatic ecosystem of the Lean River in south China, were evaluated by integrating the chemical, toxicological and ecological responses of single and multiple metals in overlying water, surface sediment and floodplain topsoil. The assessment results indicated that a highly localized distribution pattern was closely associated with the pollution sources along the river bank. Based on the combined indices, deterioration of local environmental quality was induced mainly by two sources. One was strong acidity and a large amount of Cu in the drainage from the Dexing Cu Mine. Another was high concentrations of Pb and Zn in the effluents released from many smelters and mining/panning activities in the riparian zone. Some possible suggestions on source control may be effective in dealing with these issues.     

The value of salt marsh edge vs interior as a habitat for fish and decapod crustaceans in a Louisiana tidal marsh

Flume nets of various lengths and a 3-m seine were used to sample the fishes and macrocrustaceans using a flooded Louisiana salt marsh and the adjacent tidal creek. The experiment allowed for species-specific comparisons of the flooded marsh at the creek edge versus the interior. Of the 37,667 organisms collected in flume nets from January through November 1989, 89% were decapods (nine species) and 11% were fish (29 species). An additional 18,539 organisms (75% decapods and 25% fish) were collected from concurrent seine samples taken from July through November. Comparison of catches among different flume lengths and low tide versus high tide seine collections revealed distinct patterns of marsh habitat utilization. Densities of most organisms were highest within 3 m of the water’s edge, but significant numbers of marsh-resident fish species used the interior marshes. The edge marshes appeared to be used by both transient and resident species; however, the interior marshes were used primarily by marsh-resident species (Cyprinodontiformes andPalaemonetes sp.) that are excellent food sources for adult transient-species. Four zonations of marsh use are described for transients, residents, and rare species.     

Methane release from soils of a Georgia salt marsh

A seasonal study of methane release from marsh soils to the atmosphere indicates that ebullition is a significant process varying both seasonally and spatially. Release rates are higher during summer months than winter months and ebullition is greatest in the short Spartina alterniflora marshes and least in the tall S. alterniflora marshes. The annual amounts of methane released in the short and tall marshes are 53.1 and 0.4 gm^?3 which represents a loss of 8.8 and 0.002% of the net carbon fixation in the two respective marsh types.In vitro experimentation shows that methane production is sensitive to changes in temperature and addition of H₂ and CO₂.     

Productivity of algal epiphytes in a Georgia salt marsh: effect of inundation frequency and implications for total marsh productivity

Primary production by algal epiphytes of dead Spartina alterniflora shoots in a Georgia salt marsh was measured using the ¹⁴C technique. A 2³ factorial design was used to quantify the effects of light intensity and inundation frequency (stem height) on carbon fixation at two sites along a salt marsh creek. Algae inundated daily fixed carbon more rapidly than those which had dried for several days, but this may have been the results of greater biomass on more frequently immersed stems. This result corroborates studies showing desiccation is not always a severe stress for intertidal algae. Similarity of epiphyte algal productivity to that of salt marsh benthic diatoms suggests that, given adequate substrate, the epiphytes may be an important source of primary production during some seasons of the year.     

Estimating the net flux of nutrients between a salt marsh and a tidal creek

Statistical aspects of estimating net fluxes of nutrients between a salt marsh and a tidal creek on a tidal cycle basis and an annual basis are explored. For individual tidal cycles, the instantaneous flux of a nutrient is written in a constrained linear model as a function of time. The model is rewritten as an unconstrained model, and net flux is shown to be a linear combination of the parameters of the model. Standard linear models techniques can be used to make inferences about net fluxes on a tidal cycle basis. Considering a year as a finite population of tidal cycles, annual net flux can be estimated using a regression estimator. In the case of the flux of dissolved nitrite plus nitrate, the marsh was found to be a statistically significant sink for nitrogen (in this form) from adjacent tidal creeks.     

Early use by fish of a mitigation salt marsh,Humboldt Bay,California

Fish numbers and biomass in a mitigation salt marsh, Humboldt Bay, California, were examined from July 1981 to October 1982 and were compared with a nearby established marsh to determine whether the restored marsh provided adequate mitigation for habitat lost due to construction of a nearby marina. The use by fish of channels adjacent to the two marshes and the channel at the Woodley Island Marina construction site, for which mitigation was required, were also compared. The mitigation marsh, adjacent to Freshwater Slough channel, was 5.2 km from the marina site. Fishes were sampled by otter trawl, ichthyoplankton net, fixed channel nets, drop traps, and beach seines. Thirty-one fish species and two crab species were collected. Wide ranges in seasonal salinities and water temperatures, and differences in marsh elevation influenced fish use of the mitigation marsh area. The intertidal area of the mitigation marsh, dominated by euryhaline sticklebacks and topsmelts, did not replace intertidal and subtidal habitat lost by marina construction, which had more stable salinities and water temperatures and was used extensively by juvenile English sole.     

Early diagenesis of fatty acids and hydrocarbons in a salt marsh environment

In a salt marsh environment, plant-produced fatty acids and aliphatic hydrocarbons undergo significant modification upon being deposited in sediment. The major changes include alteration of the distribution pattern of straight chain components, increase in the concentration of branched components and decrease in the concentration of unsaturated components. Changes are similar in both oxidizing and reducing environments. Carbon isotope measurements indicate that there is little horizontal movement of sediment organics. Spartina alterniflora has a δC¹³ = ? 12.5% (vs NBS 20) and Juncus romerianus has a δC¹³ = ?23.2%. Sediment organic matter taken from cores up to 60 cm in depth retains a δC¹³ value similar to the plant species growing at the core site. Microbial metabolism appears to be responsible for the observed in situ changes in sediment lipids. The in situ changes did not result in significant alteration of δC¹³ values.     

Seasonal patterns of nitrification and denitrification in a natural and a restored salt marsh

Seasonal patterns of microbially-mediated nitrogen cycling via the nitrification-denitrification pathway were compared between a natural and a restored salt marsh. Sedimentary denitrification rates, measured with a modification of the acetylene block technique, were approximately 44 times greater in the natural marsh relative to an adjacent transplanted marsh. Nitrification rates were similar at both sites. The difference in denitrification rates was attributed to oxygen inhibition at low tide and tidal flushing of porewater nutrients at high tide in the coarse sediments of the restored marsh. Denitrification was positively correlated with nitrification throughout the year in the natural marsh with a seasonal fall peak in denitrification corresponding to a maximum in porewater ammonia concentration. A weak correlation existed between the two processes in the restored marsh, where nitrification rates exceeded denitrification rates by a factor of 20. Transplanted marsh denitrification rates exhibited a spring peak, corresponding to elevated porewater ammonia concentrations. Our findings demonstrate functional differences in microbial nitrogen dynamics of a young (0–3 yr) restored marsh relative to a mature (>50 yr) salt-marsh system. *** DIRECT SUPPORT *** A01BY070 00008     

Effects of sediment slurry enrichment on salt marsh rehabilitation: Plant and soil responses over seven years

In deltaic marshes, mineral sediment promotes positive elevation change and counters subsidence and sea level rise. In many such marshes sediment deficits result in wetland loss. One new way to address sediment deficiency is to supply marshes with sediments in a slurry that deposits the sediment in a thin layer over a large area. The long-term effects of this strategy are poorly understood. In a rapidly submerging,Spartina alterniflora salt marsh, we tested how different amounts of sediment ameliorated the effects of sea level rise and subsidence over 7 yr (1992–1998). Sediment slurry enrichment likely affected plants and soils by two mechanisms. It increased elevation and soil bulk density, leading to increased plant vigor and soil condition. These effects were long lasting, such that by 1998 areas receiving moderate amounts of sediment (5–12 cm relative elevation) had better plant vigor and soil condition compared to areas not receiving sediment (55% cover versus 20%; bulk densities of 0.4–1.0 g cm⁻³ versus 0.2 g cm⁻³; 0 mM hydrogen sulfide versus > 1.0 mM). The sediment slurry also had high nutrient content, which resulted in a pulse of growth, especially in areas receiving the most sediment (areas > 12 cm relative elevation initially had >90% cover and canopy heights >1.6 m). This nutrient-induced growth spurt was short lived and faded after 3 yr, at which point the long lasting effects of increased elevation probably became the dominant factor promoting plant vigor and soil condition. Moderate levels of sediment generated the most beneficial and long lasting effects to the vegetation and soils. This degree of sediment slurry addition countered the effects of subsidence and sea level rise, but not so much as to surpass the intertidal position to whichS. alterniflora is best adapted.     

The ecological role of zooplankton in a Long Island salt marsh

The role of zooplankton in a salt marsh ecosystem was studied in Flax Pond, Old Field, N. Y., a 30-hectare tidal pond adjacent to Long Island Sound. Various marine crustaceans accounted for over 95% of the zooplankton caloric biomass in all but three months, in which ctenophores (Mnemiopsis leidyi) accounted for about 20%. Mass balance analysis of crustacean biomass showed a seasonal trend with increased “consumption” by the marsh from July to November. Analysis of groups (or species) for all months showed total numbers were reduced by passing through, or interacting with, the marsh. The most abundant group for each sample date also was significantly reduced from outflowing waters for all months, as were the group copepodids and miscellaneous calanoids from July to November. The energy requirements for the crustacean zooplankton community could have been supplied amply by the estimated standing crop of phytoplankton in the marsh. Phytoplankton net primary production was low, but it was ample to satisfy crustacean energy needs in all months. Crustaceans and phytoplankton alone were not enough to support estimated ctenophore nutrition requirements in summer. Therefore, detritus may also have been an important ctenophore food source.     

Direct counts of bacteria in the sediments of a North Carolina salt marsh

The number of bacteria in sediments of a North Carolina salt marsh was determined by direct counts with epifluorescent illumination and acridine orange stain. Cell number decreased from 8.36–10.90×10⁹ cells/cm³ of sediment at the surface to 2.19–2.58×10⁹ cells/cm³ of sediment at a depth of 20 cm. No significant difference was found among four stations located on a transect which crossed the marsh and spanned subtidal to intertidal sediments.     

Freshwater inundation effects on emergent vegetation of a hypersaline salt marsh

The coastal marshlands of the Nueces estuary, Texas depend upon periodic freshwater inundation to support current community structure and promote further establishment and expansion of emergent halophytes. Decades of watershed modifications have dramatically decreased freshwater discharge into the upper estuary resulting in hypersaline and dry conditions. In an attempt to partially restore inflow, the U.S. Bureau of Reclamation excavated two overflow channels re-connecting the Nueces River to the marshlands. Freshwater-mediated (precipitation and inflow) changes in tidal creek and porewater salinity and emergent marsh vegetation were examined over a 5-yr period at three stations in the upper Nueces Marsh with the aid of a Geographical Information System (GIS). Two stations were potentially subjected to freshwater inflow through the channels, while one station experienced only precipitation. Decreased tidal creek and porewater salinity were significantly correlated with increased freshwater at all stations (R²=0.37 to 0.56), although porewater salinities remained hypersaline. GIS analyses indicated the most considerable vegetation change following freshwater inundation was increased cover of the annual succulentSalicornia bigelovii. Fall inundation allowed seed germination and rapid expansion of this species into previously bare areas during the subsequent winter and following spring. The station affected by both inflow and precipitation exhibited greaterS. bigelovii cover than the station affected solely by precipitation in both spring 1999 (58. 7% compared to 27.9%) and 2000 (48.6% compared to 1.9%). Percent cover of the perennialBatis maritima temporarily increased after periods of consistent rainfall. The response was short term, and cover quickly returned to pre-inundation conditions within 3 mo. Prolonged inundation led to longterm (>2yr) decreases in percent cover ofB. maritima. Our results suggest that the timing and quantity of freshwater inundation strongly dictate halophyte response to precipitation and inflow. Brief periods of freshwater inundation that occur at specific times of year alleviate stress and promote seed germination and growth, but extended soil saturation can act as a disturbance that has a negative impact on species adapted to hypersaline conditions.     

Seasonal and topographic variations in porewaters of a southeastern USA salt marsh as revealed by voltammetric profilingdagger

We report electrochemical profiles from unvegetated surficial sediments of a Georgia salt marsh. In creek bank sediments, the absence of Sigma H2S or FeSaq and the presence of Fe(III)-organic complexes suggest that Mn and Fe reduction dominates over at least the top ca. 5 cm of the sediment column, consistent with other recent results. In unvegetated flats, accumulation of Sigma H2S indicates that SO42- reduction dominates over the same depth. A summer release of dissolved organic species from the dominant tall form Spartina alterniflora, together with elevated temperatures, appears to result in increased SO42- reduction intensity and hence high summer concentrations of Sigma H2S in flat sediments. However, increased bioturbation and/or bioirrigation seem to prevent this from happening in bank sediments. Studies of biogeochemical processes in salt marshes need to take such spatial and temporal variations into account if we are to develop a good understanding of these highly productive ecosystems. Furthermore, multidimensional analyses are necessary to obtain adequate quantitative pictures of such heterogeneous sediments.     

崇明东滩盐沼潮沟水动力过程观测与分析

2007年7月在上海崇明东滩盐沼内部采用复合测量手段进行了现场观测,对取得的盐沼水动力过程数据进行了较系统的分析。崇明东滩盐沼内部的观测及分析结果表明:(1)潮沟及盐沼表面对潮波产生严重阻尼作用,潮波传播至盐沼内部时,潮沟水位波动明显异于外海,水位上升极快,而下降慢。当潮沟有退水时,涨潮初期的当地水位上升并不是潮水进入潮沟的结果,而是流向相反的潮沟进口涨潮水和潮沟内退潮水形成的水位壅高;(2)潮波进入盐沼内部时,风具有一定作用,向岸风可抬高潮沟及盐沼内部水位,离岸风反之;(3)潮沟水流流速与潮沟水位变化率、外海潮位变化率都不存在相关关系;(4)潮沟水位低时,过流断面较小,涨潮水进入潮沟时,潮沟水一旦改变流向,就具备很高的流速并伴随流速峰值的出现。潮沟水向盐沼表面漫溢时,过流断面突变,潮沟流速出现峰值。由于潮沟退潮水位变化慢,盐沼表面水归槽时并没有产生潮沟流速峰值。根据崇明东滩观测结果,概括了盐沼水动力过程的影响因素,指出了以后研究应重视的问题。     

利用盐沼泥炭重建长江三角洲北部全新世中期海平面

根据对长江三角洲北部海安地区4个钻孔标志性沉积物(潮上带盐沼泥炭、高潮滩沉积)的年龄测定和高程测量,以及沉积物压实沉降量的分析研究,重建了本研究区全新世中期8.1～7.3 cal kyr BP和5.6～5.4 cal kyr BP的相对海平面位置。结果显示,8.1～7.3 cal kyr BP海平面缓慢上升1.46m,上升速率仅为0.2cm/yr, 与三角洲南部全新世早期海平面的快速上升(2cm/yr)形成鲜明对比,验证了冰盖控制下的全球海平面阶段性波动上升模式。对比长江三角洲地区海平面曲线发现,三角洲北部海平面曲线较南部低5～6m,长江三角洲海平面曲线与世界各地海平面曲线也存在明显差异,分析认为主要是由长江口地区的差异性沉降和中国东部边缘海的水均衡作用两个因素引起的。