Trace Element Concentrations in Soil,Sediments, and Waters in the Vicinity of Geita Gold Mines and North Mara Gold Mines in Northwest Tanzania

The “Geita Gold Mine” (GGM) and “North Mara Gold Mines” (NMGM) have developed large quarries in the middle of fertile agricultural lands. Possible hazardous impact on the natural recourse has warranted a study on the trace element concentrations in soils, sediments, and natural waters. Generally, the study shows a great variation in type of elements and intensity of their spill to soils, sediments, and waters. We found indications of acid mine drainage (AMD) of trace metals near the GGM waste rock tailings, but the data are inconclusive. The environmental impact at NMGM was, on the other hand, more extensive. Severe trace element contamination of sediments and waters near one of the mining facilities managed by NMGM is connected to an accidental acid spill in 2009. However, we found strong indication that, in addition to the accident, leakage of alkaline wastewater into surface soils and free water took place from a large wastewater reservoir. We found very high concentrations, especially of As in sediments and water samples downside this reservoir. Water from several sites contained As concentration in the free water at more than one order of magnitude higher than the WHO drinking water recommendations. The chemical speciation of water samples indicated high fraction of Free Ion Activity (FIA) in several samples and the change in pH had a significant impact on the FIA. Due to extensive alkaline and acidic runoff from these sites, more information about hydrological transport routes and the chemical speciation of the free water is of great importance for assessing potential risk of these mines.     

Occurrence,distribution and transport of pesticides into the Salton Sea Basin,California, 2001–2002

The Salton Sea is a hypersaline lake located in southeastern California. Concerns over the ecological impacts of sediment quality and potential human exposure to dust emissions from exposed lakebed sediments resulting from anticipated shrinking of shoreline led to a study of pesticide distribution and transport within the Salton Sea Basin, California, in 2001–2002. Three sampling stations—upriver, river mouth, and offshore—were established along each of the three major rivers that discharge into the Salton Sea. Large-volume water samples were collected for analysis of pesticides in water and suspended sediments at the nine sampling stations. Samples of the bottom sediment were also collected at each site for pesticide analysis. Sampling occurred in October 2001, March–April 2002, and October 2002, coinciding with the regional fall and spring peaks in pesticide use in the heavily agricultural watershed. Fourteen current-use pesticides were detected in water and the majority of dissolved concentrations ranged from the limits of detection to 151 ng/l. Diazinon, EPTC and malathion were detected at much higher concentrations (940–3,830 ng/l) at the New and Alamo River upriver and near-shore stations. Concentrations of carbaryl, dacthal, diazinon, and EPTC were higher in the two fall sampling periods, whereas concentrations of atrazine, carbofuran, and trifluralin were higher during the spring, which matched seasonal use patterns of these pesticides. Current-use pesticides were also detected on suspended and bed sediments in concentrations ranging from detection limits to 106 ng/g. Chlorpyrifos, dacthal, EPTC, trifluralin, and DDE were the most frequently detected pesticides on sediments from all three rivers. The number of detections and concentrations of suspended sediment-associated pesticides were often similar for the river upriver and near-shore sites, consistent with downstream transport of pesticides via suspended sediment. While detectable suspended sediment pesticide concentrations were more sporadic than detected aqueous concentrations, seasonal trends were similar to those for dissolved concentrations. Generally, the pesticides detected on suspended sediments were the same as those on the bed sediments, and concentrations were similar, especially at the Alamo River upriver site. With a few exceptions, pesticides were not detected in suspended or bed sediments from the off-shore sites. The partitioning of pesticides between water and sediment was not predictable from solely the physical–chemical properties of individual pesticide compounds, but appear to be a complicated function of the quantity of pesticide applied in the watershed, residence time of sediments in the water, and compound solubility and hydrophobicity. Sediment concentrations of most pesticides were found to be 100–1,000 times lower than the low-effects levels determined in human health risk assessment studies. However, maximum concentrations of chlorpyrifos on suspended sediments were approximately half the low-effects level, suggesting the need for further sediment characterization of lake sediments proximate to riverine inputs. Guest editor: S. H. Hurlbert The Salton Sea Centennial Symposium. Proceedings of a Symposium Celebrating a Century of Symbiosis Among Agriculture, Wildlife and People, 1905–2005, held in San Diego, California, USA, March 2005     

Pollution characteristics and ecological risk assessment of heavy metals in the surface sediments from a source water reservoir

Surface sediment samples were collected from a source water reservoir in Zhejiang Province, East of China to investigate pollution characteristics and potential ecological risk of heavy metals. The BCR sequential extraction method was used to determine the four chemical fractions of heavy metals such as acid soluble, easily reducible, easily oxidizable and residual fractions. The heavy metals pollution and potential ecological risk were evaluated systematically using geoaccumulation index (I_geo) and Hakanson potential ecological risk index (H′). The results showed that the sampling sites from the estuaries of tributary flowing through downtowns and heavy industrial parks showed significantly (p < 0.05) higher average concentrations of heavy metals in the surface sediments, as compared to the other sampling sites. Chemical fractionation showed that Mn existed mainly in acid extractable fraction, Cu and Pb were mainly in reducible fraction, and As existed mainly in residual fraction in the surface sediments despite sampling sites. The sampling sites from the estuary of tributary flowing through downtown showed significantly (p < 0.05) higher proportions of acid extractable and reducible fractions than the other sampling sites, which would pose a potential toxic risk to aquatic organisms as well as a potential threat to drinking water safety. As, Pb, Ni and Cu were at relatively high potential ecological risk with high I_geo values for some sampling locations. Hakanson potential ecological risk index (H′) showed the surface sediments from the tributary estuaries with high population density and rapid industrial development showed significantly (p < 0.05) higher heavy metal pollution levels and potential ecological risk in the surface sediments, as compared to the other sampling sites.     

Seasonal Variations of Chemical Composition of Water and Bottom Sediments in the Wetland of Wadi Gaza,Gaza Strip

Water and sediment samples were collected from 18 sampling stations in Wadi Gaza for two successive years in order to: (1) Establish a baseline condition of the geochemistry of surface water and sediments; (2) assess the impact of seasonal variation on distribution of heavy metals and major ions; and (3) identify possible natural and anthropogenic sources of pollution. The heavy metal concentrations in the sediments of the lake (downstream) were higher than those of the eastern eight stations(upstream) where the water was shallower. Shallower areas showed greater temporal variation than deeper areas. Several elements (P, Fe, Mn and As) showed the greatest temporal variability. For example, in the winter rainy season these elements decreased 2–10 times compared to their values in summer. Moreover, Ca, Na, Cl, PO₄, and NO₃ decreased3, 3, 5, 2, 4 times, respectively. Some of the trace metals were more abundant in these waters compared to the domestic wastewaters of the study area. The averages of Cd and Co were 6 and 43 μg/l, respectively and they were 50 times higher than the domestic wastewater results. The discharge of olive oil mill wastewater was recorded in the Ca, Na, Mg, K and P concentrations in sediments of one of the sampling stations.     

青山水库表层沉积物重金属污染特征及生态风险评价

在位于浙江省临安市的青山水库采集了具有代表性的8个样点的表层沉积物样品,分析比较了样品中As、Cr、Cu、Ni、Mn、Pb、Zn等7种重金属总量的差异,采用BCR连续提取法对重金属不同形态(酸提取态、可还原态、可氧化态、残渣态)进行分析.采用地积累指数法(I_geo)和Hakanson潜在生态风险指数法,对青山水库不同采样点表层沉积物中重金属的污染程度和潜在毒性与生态风险进行评价.结果表明: 青山水库表层沉积物重金属污染程度存在明显的空间差异,流经城区和工业园区的青山水库支流入库河口附近的表层沉积物重金属含量明显高于其他采样点.青山水库表层沉积物7种重金属中,Mn主要以酸提取态存在;Cu和Pb主要以可还原态形式存在;As主要以残渣态形式存在.流经城区的支流入库河口附近表层沉积物还原态和酸提取态重金属比例较高,对水生生物有一定的毒性风险.8个样点的表层沉积物7种重金属中,以As污染程度最高,潜在生态风险最大,其次是Cu、Ni、Mn、Pb和Zn,均处于轻度污染状态,而Cr处于清洁水平,潜在生态风险较低.不同采样点比较发现,分别流经城区的锦溪和工业园区的横溪入库河口附近表层沉积物重金属污染程度和潜在生态风险明显高于其他采样点.     

Exchange of Cu and Cd across the sediment-water interface in intertidal mud flats from Ria Formosa (Portugal)

Depth profiles of Fe, Mn, (HS)_t, Cu and Cd concentrations in pore water were determined on a seasonal scale in intertidal sediments of Ria Formosa. Concentrations of Cu and Cd were also determined in near-bottom water during the short period that water inundates the sediment. A maximum near the sediment-water interface was observed in depth profiles of Mn and Fe concentrations followed by a decrease with depth. Otherwise, depth profiles of (HS⁻)_t were irregular but peak concentrations was observed below Mn and Fe maximum. Although subsurface maximum was observed at deeper layers for Cu and Cd, the profiles shape varied among sites and sampling dates. This suggests site specificity and alterations associated with early diagenetic reactions. In order to assess exchanges of Cu and Cd across the sediment water interface, diffusive fluxes and advective transport were estimated. Both contribute substantially to the daily transfer of Cd from intertidal sediments to the water column of Ria Formosa. In the case of Cu, the flux associated with tidal flooding (advective flux) was the major contributor. Presumably, the exchange of trace elements between the sediment-water interface in intertidal areas of macro- and meso-tidal systems are underestimated since do not take into consideration the pulse contribution associated with tidal flooding.     

Seasonal changes in sediment and water chemistry of a subtropical shallow eutrophic lake

A field study was conducted (May 1981 to June 1982) to develop a data-base on seasonal changes of water and sediment chemistry of Lake Monroe (4 000 ha surface and ca. 2 m deep) located in central Florida, USA. This shallow eutrophic lake is a part of the St. Johns River. Quantitative samples of lake water and sediments were collected on a monthly basis from 16 stations and analyzed for various physico-chemical parameters. Relatively high levels of dissolved solids (mean electrical conductivity (EC) = 1832 µS cm¹) prevailed in the lake water, and seasonal changes in EC were probably associated with hydrologic flushing from external sources, such as incoming water from upstream as well as precipitation. Average monthly levels of total N and P during the study period were 1.82 and 0.21 mg l^–1, respectively. Nutrient concentrations in the water did not show any strong seasonal trends. Organic matter content of lake sediments ranged from 1 to 182 g C kg^–1 of dry sediment, reflecting considerable spatial variability. All nutrient elements in the sediments showed highly significant (P < 0.01) correlations with sediment organic C, though little or no significant relationship appeared at any sampling period between water and sediment chemistry of the lake. Temporal trends in water and sediment chemical parameters may have been concealed by periodic hydrologic flushing of the St. Johns River into Lake Monroe.Florida Agricultural Experiment Stations Journal Series No. 7836.     

Recent sedimentation in a freshwater reservoir in SW-Finland: The diatomological and chemical evidence of sediments on the development of the water body

A freshwater reservoir was dammed from the Baltic Sea in 1965. The recent sediments and the processes of accumulation in the reservoir have been investigated. The physical, chemical and diatom analyses of the sediments were carried out at 5 sampling points in order to dinstinquish the freshwater sediments from the underlying brackish sediments as well as to date the freshwater sediments. The pattern of sedimentation in the reservoir is described on the basis of these results and conclusions are drawn regarding the development of the water body. In interpretating the diatomological and the chemical results from the recent sediments certain common features are highlighted.     

Enumeration of faecal coliforms from recreational coastal sites: evaluation of techniques for the separation of bacteria from sediments

AIMS: To identify the most efficient techniques for the separation of micro-organisms from coastal sediments and, using these techniques, to determine the concentration of faecal indicator organisms in recreational coastal water and sediment. METHODS AND RESULTS: Sediment samples were taken from a range of recreational coastal sites and subjected to various physical techniques to separate micro-organisms from sediment particles. Techniques investigated included manual shaking, treatment by sonication bath for 6 and 10 min, respectively, and by sonication probe for 15 s and 1 min, respectively. The use of the sonication bath for 10 min was the most successful method for removing micro-organisms from sediment particles where sediments consisted mainly of sand. When sediments contained considerable proportions of silt and clay, however, manual shaking was most successful. Faecal coliforms were then enumerated by membrane filtration in both water and sediment from three recreational coastal sites, chosen to represent different physical sediment characteristics, over a 12-month period. Faecal coliform concentrations were generally greater in sediment compared with overlying water for all samples. This was most evident in sediment consisting of greater silt/clay and organic carbon content. CONCLUSIONS: This study demonstrated the importance of sediment characteristics in determining the most efficient method for the separation of micro-organisms from coastal sediments. Sediment characteristics were also found to influence the persistence of micro-organisms in coastal areas. SIGNIFICANCE AND IMPACT OF THE STUDY: Recreational coastal sediments can act as a reservoir for faecal coliforms; therefore, sampling only overlying water may greatly underestimate the risk of exposure to potentially pathogenic micro-organisms in recreational waters.     

Ecological synopsis for Chironomus flaviplumus (Diptera: Chironomidae) in the Jung-rang stream

In this study, we conducted field sampling to assess the relative influences of water and substrate quality on benthic macroinvertebrate communities living in the Jung‐rang stream, Korea. We collected macroinvertebrates and assessed physicochemical variables from three sites in the stream between May 2001 and January 2002. Sites were located approximately within 20 km from the headwater. The structure of the benthic macroinvertebrate communities may be strongly affected by the physical conditions inherent to the environment in which they live. In this stream, we detected profound differences in water temperature (18 ～ 19.75°C), the concentrations of suspended solids (3.935 ～ 7.87 mg/L), and demand for chemical oxygen (10.575 ～ 14.425 mg/L). Nonylphenol concentrations ranging from 0.375 to 0.55 ng/mL were found in the water, and the sediments were measured to contain between 2.45 and 3.425 ng/mL. We identified a total of 20 macroinvertebrate species, including seven species of Chironomidae, the most abundant of which was Chironomus flaviplumus. At none of the sites did we find any significant differences in the structure of the communities. Using canonical correspondence analysis for the relation of species and environmental variables, chemical oxygen demand and suspended sediment gradients (SS) had significant preferences for site 1 with SS. The results of our study suggest that physico‐chemical variables exerted complex effects on the structure of the benthic community in the Jung‐rang stream. This study supports the contention that physico‐chemical analyses as well as community analysis are valuable tools to assess the effect of pollution on the ecological condition of a stream. Chironomids, in particular, showed a high degree of tolerance against contaminants.     

The chemical character and burial of phosphorus in shallow coastal sediments in the northeastern Baltic Sea

The chemical composition and vertical distribution of sediment phosphorus (P) in shallow coastal sediments of the northeastern Baltic Sea (BS) were characterized by sequential extraction. Different P forms were related to chemical and physical properties of the sediments and the chemistry of pore water and near-bottom water. Sediment P composition varied among the sampling sites located in the Archipelago Sea (AS) and along the northern coast of the Gulf of Finland (GoF): the organic rich sites were high in organic P (OP), while apatite-P dominated in the area affected by sediment transportation. Although the near-bottom water was oxic, the sediments released P. Release of P was most pronounced at the site with high sediment OP and reduced conditions in the sediment-water interface, indicating that P had its origins in organic sources as well as in reducible iron (Fe) oxyhydroxides. The results suggest that even though these coastal areas are shallow enough to lack salinity stratification typical for the brackish BS, they are vulnerable to seasonal oxygen (O₂) depletion and P release because of their patchy bottom topography, which restricts mixing of water. Furthermore, coastal basins accumulate organic matter (OM) and OP, degradation of which further diminishes O₂ and creates the potential for P release from the sediment. In these conditions, an abundance of labile OP may cause marked efflux of P from sediment reserves in the long-term.     

Enrichment and Chemical Fraction of Copper and Zinc in the Sediments of the Daliao River System,China

Copper and zinc contents and their chemical forms in the surface sediments of the Daliao River system (DRS) were investigated to quantitatively assess their contamination, mobility, and potential bioavailability. Twenty-seven surface sediment samples were collected and analyzed for total contents of Cu, Zn, Al, Fe and Mn and for chemical forms of Cu and Zn. These results reveal that the total contents of Cu and Zn in the sediment of DRS mainly ranged from 4.5 to 86.1 and 17.7 to 1340.9 mg kg^?1, respectively. The enrichment factors (EFs) were generally lower than 1.0 at most sampling sites, while at T3, B5 and B7 sites of the Taizi River near Benxi, Liaoyang and Anshan cities, respectively, they were more than 2.0. The primary sources of Zn and Cu contamination at these three sites are considered to be iron mining and smelting and some chemical industries. Hence, the total contents of Cu and Zn in the sediments of the Daliao River system mainly ranged around background levels. In general, less than 2% and more than 60% of total Cu and Zn contents in the sediment at most sampling sites were associated to the exchangeable fraction and residual fraction, respectively, showing their low mobility and bioavailability. The major sink for anthropogenic Cu might be organic matter and Fe oxides, while for anthropogenic Zn it was carbonate and the easily reducible phase dominated by Mn and amorphous Fe oxides. Therefore, anthropogenic Cu and Zn have relatively high potential mobility and bioavailability. In comparison with the sediments of other rivers in China and in the world, the sediment of the DRS contained relatively low contents of Cu and Zn.     

Phytoplankton and bacterioplankton stress by sediment-borne pollutants

The effect of sediment-borne and released chemicals on the phytoplankton and bacterioplankton communities of a clay-turbid and shallow lake was examined. Water and sediments from the lake were collected at two sites. One site near the source of pollution input (Eastern Region) and the second site 40 km from the pollution input (Central Region). The Elutriate Test was used to find the impact of sediment-borne substances. Elutriation of the water for the bioassays was done under aerobic and anaerobic conditions. Two sources of phytoplankton and bacterioplankton were used. One was the native organisms for each sampling site, the other was from the opposite sampling site. The phytoplankton bioassays showed inhibition of growth with increasing concentration of sediments regardless of source of sediments or phytoplankton. The bacterial bioassays showed, in most cases, stimulation of¹⁴C-glucose uptake with the addition of sediments. Bacteria from the more polluted region when grown in less polluted region elutriate did not show any significant change in glucose uptake. When less polluted region bacteria were grown in more polluted region elutriate they showed a highly significant stimulation in uptake.     

Heavy metals in water,sediments and invertebrates from a metal-contaminated river free of organic pollution

A study was made of water, sediments and invertebrates in the R. Derwent, North-East England, at one site above and three sites below a stream bringing in high concentrations of Zn, Cd and Pb derived from an active fluorspar mine. The mean concentrations of these metals in filtrable water at the unpolluted site were 0.020, <0.0003, 0.005 mg l^-1, respectively, while those at the first polluted site were 0.29, 0.0006, 0.016 mg l^-1. The benthic macroinvertebrate fauna was dominated by insects; all taxa present at the unpolluted site were represented at one or more of the polluted sites. In almost all cases the elevated concentrations of metals in water and sediments at polluted sites were paralleled by higher concentrations in animals. Significant positive correlations were demonstrated between metal concentrations in certain taxa and those in their environment e.g. Ecdyonurus venosus and aqueous Pb. Mayflies tended to concentrate Zn, Cd and Pb to higher levels than other groups. Comparison of carnivorous species with other taxa revealed no indication of increased metal concentrations at higher trophic levels.     

Analyses of three native aquatic plant species to assess spatial gradients of lake trace element contamination

A bioaccumulation study was performed on Lake Averno, a volcanic lake close to Naples (southern Italy), to ascertain the degree of trace element contamination. Good information to assess spatial gradients of Cd, Cr, Cu, Fe, Ni, Pb, V and Zn contamination was provided by analysing Phragmites communis roots, Najas marina shoots, Potamogeton pectinatus leaves and surface sediments of Lake Averno collected from July 1999 to July 2000 at three sites in the littoral zone. The highest concentrations of the trace elements were measured in sediments and plants from the site where a nearby sewage outfall channel reaches the lake, the lowest at the site below woodland. Significant correlations were found between sediment and plant element concentrations. For almost all the elements, values 2–4-fold higher were found for the site affected by the sewage effluent. Among the plant species, Ph. communis is the most useful species in biomonitoring studies due to its ability to accumulate trace elements in the roots and its collectability throughout the year. Given the absence of systematic water quality monitoring, trace elements in plants, rather than sediments, provide a cost-effective means for assessing trace element accumulation in aquatic systems during plant organ lifespan.     

珠江三角洲池塘养殖中多氯联苯的环境归趋

对珠江三角洲4个不同地方的养殖池塘中水样,泥样和不同种类的鱼样分析,结果表明水产养殖中多氯联苯的分布和归趋在不同分配相中有很大差别,水相中含量较低(8.0～2 4 .0 3ng·L- 1 ) ,沉积相中较高(7.32～36 .2 3ng·g- 1 ,干重) ,特别是工业活动频繁的地方,而乡村相对较低。鱼类不同食性对多氯联苯的积累及其同分异构体的分布有很大影响,肉食性鱼类比草食性鱼类积累更多的多氯联苯.其中代表性同分异构体有IUPAC 118,138,81/ 87,15 3,180 ,5 2 ,4 9,99,4 4。珠江三角洲水产养殖中多氯联苯对生态环境的影响相对较低。     

Multi-Scale Controls on Water Quality Effects of Submerged Aquatic Vegetation in the Tidal Freshwater Hudson River

Patches of submerged vegetation can be important sites of primary production and habitat for organisms in many aquatic ecosystems. In the tidal freshwater Hudson River they make up about 6% of the river bottom area. Direct sampling of water masses passing through patches of vegetation and week-long continuous monitoring of water characteristics were used to determine plant effects on dissolved oxygen and suspended sediments. Vegetated areas could have dissolved oxygen concentrations substantially higher than in the main channel and suspended sediments and turbidity were frequently higher in vegetated areas. Patches of Vallisneria americana had variable capacity to maintain super-saturated oxygen concentrations; patch size accounted for some of the variability whereas larger-scale differences in main-channel influent water also contributed. Differences in turbidity among sites were harder to account for; width of plant beds and abundance of neighboring vegetated areas contributed weakly to predictions of local turbidity. Functional heterogeneity within ecosystems is common and attempts to explain variability may require understanding different controlling factors for different functions and appreciating that factors operate at multiple scales.     

Micro‐scale structure in the chemistry and biology of a shallow lake

1. Repeat sampling in daytime within a lily (Nuphar lutea) bed and in open water showed distinct heterogeneities in the three‐dimensional distributions of water chemistry and planktonic organisms on centimetre to decimetre scales. 2. Vertical gradients of physico‐chemical variables that did not exist at dawn developed during the day in both sites, as available nutrients were released from the sediments and were consumed towards the surface. 3. Distributions of algal standing crop suggest limitation by both nutrients and grazing. 4. Marked variability in distributions may question the assumptions often made about the homogeneity of plankton and available nutrient distributions in open water and in macrophyte stands of shallow lakes. Although simple sampling regimes for monitoring of water quality may be adequate for many purposes, they miss a fine structure in the water that is inherently interesting in understanding the underlying processes of plankton function.     

Spatial variation of phosphorus fractions in bottom sediments and the potential contributions to eutrophication in shallow lakes

Spatial variation of phosphorus fractions in bottom sediment, pore water and overlying water in three shallow eutrophic lakes, Nishiura, Kitaura and Sotonasakaura, Japan, and the contributions of the fractional P to mobilization of phosphorus from sediment were examined in this study. The vertical distributions of dissolved inorganic phosphorus (DIP) concentrations in overlying and pore water differed with lake and sampling site. In particular, DIP was high in pore water in the surface layer of the sediment for the middle to downlake areas of Lake Kitaura. DIP release flux calculated from a gradient of the concentrations at the sediment–water interface was high compared with other sites. The distribution of fractional P content in sediments was highly variable. The citrate–dithionite–bicarbonate–non-reactive phosphorus (CDB–NRP) fraction, in particular, differed greatly among the three lakes. According to correlation in the ratios between CDB–NRP and loss on ignition, sediments of these lakes were classified in three clusters. The CDB–NRP fraction was suggested to play a role in DIP release from sediment. The possibility of nitrate concentration playing a role in the control of DIP release was considered.     

干旱区石羊河流域河水孢粉组合特征

石羊河流域初春和仲夏两季不同地点 ,洪水期、平水期 30个河水样孢粉分析显示 ,没有人类影响的情况下 ,河水样孢粉组合是由河流上游径流区的植物孢粉和采样点附近植被孢粉组成的 ,前者在孢粉组合中至少占30 %～ 6 0 %。河水搬运孢粉的能力非常强 ,可长距离、大量地搬运孢粉。孢粉组合中河水贡献孢粉的含量较高 ,如 :云杉属 (PiceaDietr.)花粉河水的贡献率在中下游可达 16 .5 %和 7.7%。采样时间、地点影响河水的孢粉组合和浓度 ,洪水期是孢粉搬运的主要时期。河水经过水库后 ,其中孢粉绝大多数沉积在水库中。