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1.
To examine the biogeochemistry of amino acids (AAs) in the sediment of Lake Taihu, surface sediments (0–3 cm) and deeper sediments (18–21 cm) were collected at 21 sites from different ecotype zones of the lake. AAs were extracted from the sediments, and the total hydrolyzable amino acids (THAA) were determined by high-performance liquid chromatography instrument. The THAA contents in Taihu sediment were much lower than that in marine sediments, ranging from 6.84 to 38.24 μmol g−1 in surface sediments and from 2.91 to 18.75 μmol g−1 in deeper sediments in Taihu, respectively. AAs were a major fraction of the organic matter (OM) and organic nitrogen in Taihu sediments. The AAs on average contributed 8.2% of organic carbon (OC) and 25.0% of total nitrogen (TN) from surface sediments, and 5.9% of OC and 20.5% of TN in deeper sediments, respectively. AA composition provided very useful information about the degradation of OM. Glycine (Gly) and lysine (Lys) were the predominant forms of AAs in the sediments, irrespective of lake regions, followed by alanine, glutamic acid, serine (Ser), and aspartic acid (Asp). The high concentrations of Gly, Lys, and Ser suggested that these forms of AAs were relatively refractory during OM degradation in sediments. The relationship between the Asp/Gly ratio and Ser + Thr [mol%] indicated that OM in surface sediment was relatively fresher than that in deeper sediments. The AAs-based degradation index (DI) gave a similar conclusion. The composition and DI of AAs in surface sediments are markedly different across different zones in Taihu. The percentages of AAs to organic carbon (AA-C%) and total nitrogen (AA-N%) were higher in phytoplankton-dominated zones than those in macrophyte-dominated zones. These results suggest that DI could provide useful information about the degradation of OM in shallow lakes such as Taihu.  相似文献   

2.
太湖沉积物中微生物多样性垂向分布特征   总被引：2，自引：0，他引：2  
运用化学分析方法和PCR-DGGE技术,从沉积物化学及分子生物学角度对太湖沉积物理化性质(pH、Eh)、营养盐及微生物多样性的垂向分布及相关性进行研究。结果表明:沉积物-上覆水接触界面处于轻度还原状态,在表层8.0cm左右以下,Eh随沉积深度的增加迅速下降,还原性逐渐增强,到15.0～22.5cm深度区间内,Eh值基本稳定,还原性最强,之后随深度的进一步增加,Eh呈"之"型缓慢升高。沉积物pH随深度的增加先降低后缓慢升高,pH在整个剖面上变化幅度不大,在7.2～7.6变动。沉积物中含有丰富的营养盐,总氮(TN)、总磷(TP)最高含量分数和有机质(OM)的最高百分比分别为2.436mg/g、0.731mg/g和3.817%,其剖面特征表明,沉积物表层TN和OM远高于底层,其含量随深度增加而降低。TP随着沉积深度的增加呈"之"型缓慢减少。不同深度沉积物的微生物群落呈现出明显的空间分布多样性差异,不同深度沉积物的微生物群落结构之间的相似性和动态性存在差异。多元相关分析结果显示,TN与OM显著相关,理化指标、营养盐中任一指标含量与微生物群落多样性指标之间存在相关性,但不显著,微生物多样性是营养盐及环境物理、化学和生物等多方面共同作用的结果。  相似文献   

3.
哈素海沉积物中氮和有机质的分布特征   总被引：5，自引：0，他引：5  
沈丽丽  何江  吕昌伟  孙英 《沉积学报》2010,28(1):158-165
针对哈素海富营养化日趋严重的现实,系统开展了湖泊沉积物中不同形态氮及有机质的空间分布和污染特征研究。结果表明,表层沉积物中TN、Org N、NH+4 N及有机质的水平分布均表现经向分异特征,Org N的分布特征主导了TN的水平分布格局,有机质与TN具有强相关性。沉积柱芯中TN随深度增加而递减,有机质和Org N与TN的垂向分布相似,尽管 NH+4 N的垂直变化分异较大,但仍表现于表层富集的特点。Org N为表层沉积物和沉积柱芯中氮的主导形态,NH+4 N为无机氮的主导形态,成岩过程中,沉积物中TN只有极少部分在发生矿化。沉积物中有机质主要来源于湖中芦苇等大型挺水植物及陆源输入。哈素海表层沉积物的氮污染对底栖生物已经产生了严重的生态毒性效应,对底栖生物群落及整个水生生态系统构成了严重威胁。  相似文献   

4.
Phosphorus (P) is the limiting macronutrient for primary production in most lakes. Sediment characteristics are strongly correlated to the internal P loading in lakes. This study investigated speciation of P, Fe, Al, and Ca in sediments of six sampling sites with varying trophic status in Baiyangdian Lake of North China during the period of July 2008 and March 2009. The results of sequential extraction experiments of the top sediments showed that total extractable P ranged approximately from 13 to 28 μmol g−1 for all sampling sites and the rank order of P-fractions was HCl–P > NaOH85–P > NaOH25–P > BD–P > NH4Cl–P. BD–P and BD–Fe had a consistent change with seasons. Their concentrations were both much higher in early spring and mid-autumn. BD–Fe, Al extracted with NaOH at 25°C and 85°C affected corresponding P concentration in sediments, while high concentration of extractable Ca from sediments showed no direct effects. According to the Kopáček et al. model of the molar ratios of Al:Fe and [NaOH25–Al]:[NH4Cl–P + BD–P], there was potential P release from sediments twice a year for some hypereutrophic sites in early spring and mid-autumn, especially in the former season.  相似文献   

5.
潮白河是京津冀地区的重要河流。本研究以潮白河中游段为研究区,针对该区段沉积物有机质、氮磷污染程度不明的问题,通过对研究区130个采样点表层沉积物中有机质(OM)、总氮(TN)和总磷(TP)的测定,分析了表层沉积物中有机质和氮磷的分布特征及污染来源,将有机指数和有机氮污染指数评价法相结合开展污染及生态风险评价。结果表明:(1)潮白河中游表层沉积物中OM含量变化范围为0.17%~13.15%,平均含量为5.32%; TN的含量为0.005~1.028 g/kg,平均含量为0.192 g/kg;TP的含量为0.367~4.825 g/kg,平均含量为1.662 g/kg。(2)相关性分析表明,OM与TP、OM与TN均呈弱相关,而TN与TP呈强相关。这是因为TN和TP来源相近,主要来自外源,与OM来源有一定差异。根据TOC/TN特征分析,OM主要受藻类、浮游植物和非纤维束植物等影响。(3)有机指数评价结果显示,潮白河中游段表层沉积物监测点中60%为清洁,33.85%为较清洁,4.62%为尚清洁,1.54%为有机污染。有机污染点主要位于运潮减河入潮白河口和田贾庄排干渠入潮白河口。区域有机氮评价结果以清洁级别为主,整体较好。  相似文献   

6.
The interacting effect of pH, phosphate and time on the release of arsenic (As) from As-rich river bed sediments was studied. Arsenic release edges and kinetic release experiments (pH range 3–10), in the absence and presence of phosphate, coupled with sequential extraction procedures, SEM/EDX analyses and geochemical calculations, were carried out to evaluate As remobilisation and to elucidate the mechanisms involved. The results showed that As release underwent pronounced kinetic effects, which were strongly influenced by pH and phosphate. Remobilisation of As after 24 h was low (between ~1 and 5%) and varied slightly with pH, whereas alkaline conditions generally promoted As remobilisation after 168 h, with up to 12–21% of total As released. The results showed that depending on the pH and sediment considered, the release of As increased dramatically after ~48–72 h, suggesting that different processes are involved at different reaction periods. The addition of phosphate (1 mM) increased both the amount of As released (between 2 and 8 times) and the rate of As release from the sediments within the entire pH range (3–10) and period (168 h) studied. Moreover, in some cases, it also affected the shape of the As release edges and kinetic profiles. The similarities in the release profiles and the positive correlations between As and some sediment components, especially Fe and Al hydroxides, and organic matter—which appears to play a key role at high pH—suggest that As release from the studied sediments may be associated with solid phase dissolution processes under both acid and alkaline pH, whereas desorption plays a key role in the short term and at natural pH conditions, especially in the presence of phosphate, which acts as an As-displacing ligand. Evaluation of As mobility based on short-time leaching experiments may seriously underestimate the mobilisation of As from sediments.  相似文献   

7.
Potentially mineralizable N (PMN) in sediments is an important N source to aquatic ecosystems. However, there are few studies on PMN in lake sediments. The main N fraction in lake sediments is organic, and mineralization is through benthic metabolism in sediments rather than in the water column in most shallow lake systems. It is shown that PMN contents in the studied sediments were higher than the inorganic N in the shallow lakes in the middle and lower reaches of the Yangtze River area, China, and were also higher than those in soils from the same region. PMN constituted 3–26% (14%, on the average) of total N (TN) in sediments. Amino-acid N was the major contributor to the organic N pool in PMN. Potentially mineralizable N, TN, total P, organic matter, cation exchange capacity and fine-grain size were significantly correlated. With TN increasing in the slightly polluted sediments, PMN increased more rapidly in the heavily polluted sediments. The results suggest that more attention should be paid to organic N mineralization both in heavily and in less polluted sediments.  相似文献   

8.
Organic matter in sediments, for instance, carbon, nitrogen and phosphorus, can be used to reconstruct the paleoecological and pollution history of lakes and their catchment basins. In this paper, the contents of allochthonous organic carbon (allochthonous OC) and autochthonous organic carbon (autochthonous OC) in sediment cores taken from Wuliangsuhai Lake and Daihai Lake in northern China are quantified by using a binary model, and phosphorus forms in the sediment cores from the two lakes are extracted by sequential extraction techniques. The results indicate that the palaeoenvironment and paleoclimate of Daihai Lake and its catchment basin in the recent 250 years can be well reconstructed based on the content of allochthonous OC. The climate was relatively humid and warm in the period of 1865–2005, while relatively dry and cold in the period of 1765–1865. The sedimentary information of allochthonous OC in the 22–42-cm portion of the sediment cores in Daihai Lake corresponds to the final cold fluctuation of the Little Ice Age that occurred since the Middle Holocene. The difference of phosphorus forms in the sediment cores between the two lakes indicates that phosphorus input to the lakes and the correlation between phosphorus forms and distribution and the changes of environment are influenced by the eutrophication mechanisms and environmental conditions of the two lakes.  相似文献   

9.
Vertical distribution patterns of organic geochemical constituents and the enzymes aminopeptidase and β-glucosidase provide insights about the nature and reactivity of sediment organic matter in the sandy sediments of two shallow “South Texas” estuaries. Sediment total organic carbon (TOC) δ13C values indicated that the organic matter (OM) was derived more from a mixture of seagrass and phytoplankton than from terrigenous OM. Down-core amounts of TOC and total nitrogen (TN) were <0.2% of dry weight, respectively. Enzyme activities were highest near surface and ranged from 25 to 1 μM/h for aminopeptidase as compared to 5 to 0.2 μM/h for glucosidase. In Aransas Bay, aminopeptidase activity correlated with sediment TN content (r s = 0.30) and β-glucosidase with TOC content (r s = 0.27). In Copano Bay, aminopeptidase correlated with TOC, TN, and carbohydrate content (r s = 0.89, 0.90, and 0.83, respectively). Variations of glucosidase activity also related positively to TOC, TN, and total carbohydrate content (r s = 0.68, 0.77, and 0.48, respectively). Overall, enzyme activities in these low OM, sandy sediments resembled those for other benthic marine environments.  相似文献   

10.
Metal fluxes to the sediments of the Moulay Bousselham lagoon,Morocco   总被引：2，自引：0，他引：2  
The metal content in surface sediments (0–2 cm, 26 samples), in a sediment core (120, 1 cm slices), taken from Moulay Bousselham (Morocco) was investigated. Concentrations of Al, Fe, Mn, Pb, Zn, Cu, Ni, Cr, Cd, As, and Hg were evaluated in surface and cored sediments of Moulay Bousselham lagoon. Significantly high concentrations in μg g−1 dw of Pb (31.7–6.2), Zn (758.9–167), Cu (310.7–22), Ni (96–10.5), Cr (113–18.9), Cd (0.84–0.02), As (1–0.1), and Hg (0.61–0.02) were found in sediment samples from Moulay Bousselham lagoon. Calculated enrichment factors [EFMe = (Me/Al)sample/(Me/Al)background], using Al as a normalizer, and correlation matrices showed that metal pollution in Merja Zerga of Moulay Bousselham lagoon was the product of anthropogenic sources, while the metal content in Merja Kehla was of natural origins. The results suggest that a major change in the sedimentary regime of the lagoon, associated with internal trapping and re-distribution of heavy metal, has been occurring in the past few decades. The cause would appear to be the construction of a Nador Canal at the lagoon. Probable effects concentrations (PEC) were often exceeded for heavy metals in the lagoon sediments, especially for Zn, Cu, Ni, and Cr, and four stations, stations MZ-11, MZ-12, MZ-13, MZ-14, MZ-16, and MZ-17, had multiple metals at presumptively toxic levels. These comparisons suggest that sediment metal levels in the river are clearly high and probably pose an environmental risk at some stations. The levels of most of the metals were not greatly enriched, a consideration that is of the utmost importance when contamination issues are at stake. Metal concentrations found in Moulay Bousselham lagoon were comparable to aquatic systems classified as contaminated from other regions of the world.  相似文献   

11.
 The Yamuna River sediments, collected from Delhi and Agra urban centres, were analysed for concentration and distribution of nine heavy metals by means of atomic adsorption spectrometry. Total metal contents varied in the following ranges (in mg/kg): Cr (157–817), Mn (515–1015), Fe (28,700–45,300), Co(11.7–28.4), Ni (40–538), Cu (40–1204), Zn (107–1974), Pb (22–856) and Cd (0.50–114.8). The degree of metal enrichment was compared with the average shale concentration and shows exceptionally high values for Cr, Ni, Cu, Zn, Pb and Cd in both urban centres. In the total heavy metal concentration, anthropogenic input contains 70% Cr, 74% Cu, 59% Zn, 46% Pb, 90% Cd in Delhi and 61% Cr, 23% Ni, 71% Cu, 72% Zn, 63% Pb, 94% Cd in Agra. A significant correlation was observed between increasing Cr, Ni, Zn, and Cu concentrations with increasing total sediment carbon and total sediment sulfur content. Based on the Müller's geoaccumulation index, the quality of the river sediments can be regarded as being moderately polluted to very highly polluted with Cr, Ni, Cu, Zn, Pb and Cd in the Delhi and Agra urban centres. The present sediment analysis, therefore, plays an important role in environmental measures for the Yamuna River and the planning of these city centres. Received: 21 June 1999 · Accepted: 1 October 1999  相似文献   

12.
Mercury concentrations (HgT) in fine-grained fraction (<63 μm) of core sediments of the Hugli–Matla–Bidyadhari estuarine complex, India were analyzed. Results revealed a wide range of spatial variations (<4–93 ng g−1 dry weight) with a definite enhancement level at the lower stretch of the estuarine complex infested with mangrove plants, which might act as a sink to HgT. An elevated concentration of Hg was encountered in surface/subsurface layer of the core in majority of the cases resulting from physical, biogenic and postdepositional diagenetic processes that remobilized and resuspended the metal from deeper sediments. A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while the correlations of Hg with Al, Fe and Mn were poor. Based on the index of geoaccumulation (I geo) and effects range-low (ER-L) value, it is considered that the sediments are less polluted and thus there is less chance of ecotoxicological risk to organisms living in sediments.  相似文献   

13.
李敏  成杭新  李括 《地学前缘》2018,25(4):276-284
利用中国150余个淡水湖泊表层沉积物和深层沉积物的地球化学数据,采用中位数绝对中位差的方法统计获得了中国主要淡水湖泊沉积物的As、Cd、Cr、Cu、Hg、Ni、Pb、Zn、TN、TP、TOC及pH的地球化学背景值,为我国湖泊沉积物环境质量基准的建立和湖泊生态环境质量监管提供了重要依据。统计结果表明,我国表层湖泊沉积物中的As、Cd、Hg等重金属元素以及TP、TOC等发生了显著富集,显示出强烈的人类活动对湖泊沉积物环境质量的改变。在探讨国外环境质量基准值对我国淡水湖泊沉积物环境质量评价适应性的基础上,提出直接采用国外相关标准还不能客观评价我国湖泊沉积物的污染程度和生态风险,应充分考虑我国湖泊沉积物的地球化学背景,建立适应我国情况的沉积物环境质量基准。  相似文献   

14.
Mineralization of organic matter (OM) in sediment is crucial for biogeochemical cycle of nitrogen (N) and phosphorus (P) in lake ecosystem. Light fraction OM (LFOM) is a reactive pool in sediment and is considered as labile fraction contributing to N and P cycling. In our study, the effect of LFOM on the process and characteristics of N and P mineralization in sediments of Taihu Lake were investigated with 77-day waterlogged incubation plus intermittent leaching at 27°C. Sediments from Yuantouzhu (Y) and Gonghu (G) were used, which were removed the LF. Results indicated that the organic nitrogen mineralized ranged from 14.3 to 19.5% of total nitrogen (193.49–378.93 mg kg−1 sediment) and the organic phosphorus mineralized ranged from 5.7 to 7.9% of total phosphorus (19.86–60.65 mg kg−1 sediment). The heavily polluted sediment had a higher mineralization rate and net mineral-N and mineral-P than slightly polluted sediment. LF stimulated the initial amounts of inorganic N and P and also can be the potential source for mineralization. After the LFOM removal, the net mineral-N of Y and G decreased 116.47 mg kg−1 sediment and 48.03 mg kg−1sediment, respectively, and the net mineral-P decreased 2.67 mg kg−1sediment for Y and 4.82 mg kg−1sediment for G. Two models were used to fit the observed mineral-N data vs. incubation days using a non-linear regression procedure: one is the effective cumulated temperature model, a thermodynamic model which assumes that N mineralization is affected by temperature; the other is the single first-order exponential model, which is a dynamic model. Based on root mean square error values for the two models, the effective cumulated temperature model made a better prediction of N mineralization than the other model for all the four treatments. The single first-order exponential model underestimated N mineralization during the first 14 days and the last 21 days, and overestimated it in the other days during the 77-day incubation. This indicated that temperature was the primary factor influencing N mineralization and the amount of mineral-N were correlated significantly with the effective cumulated temperature (T ≥ 15°C) and incubation time when waterlogged incubation plus intermittent leaching was used.  相似文献   

15.
 Acidification is the most common water quality problem in lakes created from previous open cast lignite mines. Aeration of aquifers and dump materials from mining activities causes pyrite oxidation. Pyrite oxidation products are stored in pore water, minerals and at the exchange complexes of the aquifers and dump sediments. Rainfall runoff transports sediments on the dump slope into the lakes. Elutriation of these sediments whithin the lakes releases either acid-producing or acid-neutralizing agents. At a test site south of Leipzig, the annual erosion rates were quantified by water erosion models (RUSLE, EROSION 2D, PEPP) and field measurements. They ranged from 300 up to 900 tons per hectare. Hydrogen ion equivalent release or binding at the sediment elutriation was computed from laboratory analysis of the pore-water quality, ion exchange complex and mineral composition of the sediment. Two of the three investigated sediments contained 3 mmol (eq) acidity per 100 g dry sediment and revealed saturation with respect to jarosite, jurbanite and gypsum. In the third sediment, 6 mmol (eq) alkalinity per 100 g dry sediment was obtained. The annual net acidity influx was calculated to be about 0.5 million mol (eq) for the lake of the test site. Received: 2 November 1998 · Accepted: 26 January 1999  相似文献   

16.
Phosphorus (P) fractions and their bioavailability in the sediments from the middle and lower reaches of the Yangtze River region were investigated using different chemical extraction methods. The results show that the contents of bioavailable P in the sediments extracted by different extraction procedures varied greatly. But their rank order was similar. Potentially releasable P (PRP) was the largest, followed by algal available P (AAP), NaHCO3 extractable P (Olsen-P), water soluble P (WSP), and readily desorbable P. PRP contributed approximately 60% to total P (TP) in most sediments, AAP 20%, Olsen-P 15%, WSP 2%, and readily desorbable P (RDP) 0.5%. For the heavily polluted sediments, their bioavailable P extracted from TP mainly originated from inorganic P (IP), IP mainly originated from NaOH–P, the bioavailable P concentrations can be evaluated by measuring the concentrations of TP, NaOH–P, and IP. For the slightly polluted sediments, the bioavailable P can only be evaluated by different chemical extractable methods.  相似文献   

17.
太湖东部湖湾水生植物生长区底泥氮磷污染特征   总被引：6，自引：0，他引：6  
向速林  朱梦圆  朱广伟  许海 《沉积学报》2014,32(6):1083-1088
为了解太湖东部湖湾(贡湖湾、光福湾、渔洋湾)表层底泥中氮、磷的污染特征及其与水生植物生长的关系,采集了各湖湾滨岸带水生植物生长区的表层底泥,探讨了水生植物的生长与分布对表层底泥中总氮(TN)、总磷(TP)及总有机碳(TOC)等含量的影响,并对表层底泥进行营养评价.结果表明,水生植物生长密集区底泥中TN、TP、TOC的含量均显著低于水生植物零星生长区,说明水生植物的生长对太湖东部湖湾表层底泥中营养盐与有机碳含量具有较为明显的影响;相关性分析显示,表层底泥中TOC与TN含量呈显著相关性(R2=0.832 8),而与TP的相关性则较弱(R2=0.166 5),反映了TOC在湖泊底泥中的沉积可能成为湖泊氮的重要来源,而对磷的影响较小.利用有机指数与有机氮指数两种方法分别对东部各湖湾底泥进行污染评价,贡湖湾、光福湾、渔洋湾底泥有机指数平均值分别为0.142 7、0.228 6与0.208 6,均属较清洁与尚清洁水平,而各湖湾有机氮指数平均值均为Ⅲ与Ⅳ级,说明底泥已遭受了一定程度的氮污染.因此,对水生植物零星生长区表层底泥中氮含量的控制与削减有利于湖泊富营养化的预防与治理.  相似文献   

18.
Understanding the mechanism of arsenic mobilization from sediments to groundwater is important for water quality management in areas of endemic arsenic poisoning, such as the Hetao Basin in Inner Mongolia, northern China. Aquifer geochemistry was characterized at three field sites (SH, HF, TYS) in Hangjinhouqi County of northwestern Hetao Basin. The results of bulk geochemistry analysis of sediment samples indicated that total As concentrations have a range of 6.8–58.5 mg/kg, with a median of 14.4 mg/kg. The highest As concentrations were found at 15–25 m depth. In the meanwhile, the range of As concentration in the sediments from background borehole is 3–21.8 mg/kg, with a median value of 9 mg/kg. The As sediments concentrations with depth from the SH borehole were correlated with the contents of Fe, Sb, B, V, total C and total S. Generally, the abundance of elements varied with grain size, with higher concentrations in finer fractions of the sediments. Distinct lithology profile and different geochemical characteristics of aquifer sediments indicate the sediments are associated with different sources and diverse sedimentary environments. Up to one third of arsenic in the sediments could be extracted by ammonium oxalate, suggesting that Fe oxyhydroxides may be the major sink of As in the aquifer. Sequential extraction results indicate that arsenic occurs as strongly adsorbed on and/or co-precipitated with amorphous Fe oxyhydroxides in sediments accounting for 35 and 20%, respectively, of the total contents of arsenic. The release of As into groundwater may occur by desorption from the mineral surface driven by reductive dissolution of the Fe oxide minerals. Furthermore, small proportions of As associated with iron sulfides occur in the reductive sediments.  相似文献   

19.
 A total of 121 bed sediment samples were collected from a 5.8-km stretch of Manoa Stream, Hawaii. Samples were physically partitioned into two grain-size fractions, <63 μm and 63–125 μm, acid digested and analyzed by ICP-AES and FAAS. Non-parametric matched-pair statistical testing and correlation analysis were used to assess differences and strengths of association between the two fractions for Al, Ba, Cu, Fe, Mn, Ni, Pb, Ti and Zn. Results indicated statistically significant differences between fractions for all elements except Mn. Concentrations were significantly greater in the <63 μm fraction for Al, Cu, Pb, Ti and Zn, while Ba, Fe and Ni were higher in the 63–125 μm fraction. Though some elements had statistically significant differences between fractions (Al, Ba, Fe and Zn) percentage differences were in the range of analytical precision of the instrument and thus differences were not practically significant. Correlation analysis indicated strong positive associations for all elements between the two fractions (p<0.0001). Three contamination indices indicated similar degrees of pollution for each size fraction for four elements having an anthropogenic signal (Ba, Cu, Pb and Zn). The environmental information obtained from the 63–125 μm fraction was essentially equivalent to that from the <63 μm fraction. In this system it is clear that both bed sediment fractions indicate anthropogenic enrichment of trace metals, especially Pb, and further supports previous research that has found that aquatic sediments are critical median for tracing sources of pollution. Received: 17 August 1998 · Accepted: 30 October 1998  相似文献   

20.
We examined the effects of seasonal salinity changes on sediment ammonium (NH4 +) adsorption and exchange across the sediment–water interface in the Parker River Estuary, by means of seasonal field sampling, laboratory adsorption experiments, and modeling. The fraction of dissolved NH4 + relative to adsorbed NH4 + in oligohaline sediments rose significantly with increased pore water salinity over the season. Laboratory experiments demonstrated that small (∼3) increases in salinity from freshwater conditions had the greatest effect on NH4 + adsorption by reducing the exchangeable pool from 69% to 14% of the total NH4 + in the upper estuary sediments that experience large (0–20) seasonal salinity shifts. NH4 + dynamics did not appear to be significantly affected by salinity in sediments of the lower estuary where salinities under 10 were not measured. We further assessed the importance of salinity-mediated desorption by constructing a simple mechanistic numerical model for pore water chloride and NH4 + diffusion for sediments of the upper estuary. The model predicted pore water salinity and NH4 + profiles that fit measured profiles very well and described a seasonal pattern of NH4 + flux from the sediment that was significantly affected by salinity. The model demonstrated that changes in salinity on several timescales (tidally, seasonally, and annually) can significantly alter the magnitude and timing of NH4 + release from the sediments. Salinity-mediated desorption and fluxes of NH4 + from sediments in the upper estuary can be of similar magnitude to rates of organic nitrogen mineralization and may therefore be important in supporting estuarine productivity when watershed inputs of N are low.  相似文献   

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