Disconnect of microbial structure and function: enzyme activities and bacterial communities in nascent stream corridors

A fundamental issue in microbial and general ecology is the question to what extent environmental conditions dictate the structure of communities and the linkages with functional properties of ecosystems (that is, ecosystem function). We approached this question by taking advantage of environmental gradients established in soil and sediments of small stream corridors in a recently created, early successional catchment. Specifically, we determined spatial and temporal patterns of bacterial community structure and their linkages with potential microbial enzyme activities along the hydrological flow paths of the catchment. Soil and sediments were sampled in a total of 15 sites on four occasions spread throughout a year. Denaturing gradient gel electrophoresis (DGGE) was used to characterize bacterial communities, and substrate analogs linked to fluorescent molecules served to track 10 different enzymes as specific measures of ecosystem function. Potential enzyme activities varied little among sites, despite contrasting environmental conditions, especially in terms of water availability. Temporal changes, in contrast, were pronounced and remarkably variable among the enzymes tested. This suggests much greater importance of temporal dynamics than spatial heterogeneity in affecting specific ecosystem functions. Most strikingly, bacterial community structure revealed neither temporal nor spatial patterns. The resulting disconnect between bacterial community structure and potential enzyme activities indicates high functional redundancy within microbial communities even in the physically and biologically simplified stream corridors of early successional landscapes.     

宁波滩涂贝类养殖区沉积物中有机氯农药和多氯联苯残留及生态风险评估

利用GC-ECD对宁波市主要滩涂贝类养殖区表层沉积物中的多氯联苯(PCBs)和有机氯农药六六六(HCHs)、滴滴涕(DDTs)的残留量进行测定,研究其分布状况,并进行生态风险评估.结果表明:贝类养殖区表层沉积物中的总有机氯农药含量为0.80～32.40ng·g-1,多氯联苯含量为3.20～33.33 ng·g-1.HCHs主要来自远距离大气传输及历史残留,部分区域有DDTs输入,其来源可能是三氯杀螨醇的使用.大部分站位的p,p’-DDT和DDTs存在潜在的生态风险,其中墙头和西店海域的p,p’-DDT残留超过生物效应中值,对底栖生物毒害效应较高.大多数站位PCBs的生态风险较低.     

次降雨条件下坡度对坡面产流产沙的影响

以野外径流小区的次降雨产流产沙数据为基础,对不同次降雨条件下坡面产流产沙随坡度的变化规律进行研究.结果表明:降雨性质的差异对坡面产流随坡度而变化的影响较小,在研究区的6场次降雨中,坡面产流量随坡度的变化规律基本一致,坡面径流量均随坡度增大而增大,但坡面径流量随坡度增加而增加的趋势较弱,这主要由降雨量与入渗量之间的转化程度所决定;次降雨性质对不同坡度的坡面产沙规律有重要影响,一般情况下存在临界侵蚀坡度,但临界坡度不是唯一值,而是随着降雨特性的不同而不同,临界侵蚀坡度随径流量的增大而增大,临界坡度较大时,坡面产沙量随坡度变化而变化的趋势也往往较大.     

鲁中南山地丘陵区土壤侵蚀强度景观格局的动态变化

以鲁中南山地丘陵区为研究区,以TM影像和地形图为源数据,借助GIS和RS技术,获取1986、1995和2004年土壤侵蚀强度数据,分析鲁中南山地丘陵区近20年来土壤侵蚀强度景观格局动态变化。结果表明:微度和轻度土壤侵蚀面积增加,而中度以上土壤侵蚀面积具有明显减小的趋势,其中轻度、强度、极强度和剧烈4种土壤侵蚀类型的面积变化比较显著;较低级别(微度、轻度和中度)土壤侵蚀强度转移率较小,较高级别(强度、极强度和剧烈)的土壤侵蚀强度转移程度较大;在景观水平上,1986—1995年斑块数量和景观形状指数增加,蔓延度指数下降,表明这期间斑块破碎度增加,连接度降低,形状变得更为复杂;而1995—2004年各指数变化趋势恰好相反。     

Determination of Trace Phthalic Acid Monoesters in Sediments and Soils by GC-MS

A simple procedure for determining trace phthalic acid monoesters (PAMs) in sediments/soils was developed. The method used ultrasonic extraction, silylation derivatization, and GC-MS. After ultrasonic extraction, the supernatants were reextracted with dichloromethane, silylated, and did not require further clean-up before GC-MS analysis. Effects of parameters, such as extraction solvents, pH of water as extraction solvent and sediment/soil properties, on the recovery of PAMs were studied. Five sediments from Tianjin city and one red soil from Jiangxi province were used. The results showed that organic carbon (OC) content played an important role in the recovery of PAMs. The optimal extraction solvent for sediments/soils with >1% of OC content and high CEC was 0.01 M HCl aqueous solution and pure water was better for sediments/soils with <1% of OC content. In 5 g sediment/soil sample (dry weight), the method detection limit (MDL) was below 0.04 ng/g for mono-n-butyl phthalate (MBP) and 0.02 ng/g for mono-(2-ethylhexyl)-phthalate (MEHP). Average recoveries of MBP and MEHP were 81.6%?105.2% and 76.0%?95.6%, respectively, with relative standard deviations ≤ 6.6%. MBP and MEHP in the sediment and soil samples studied were detected at levels of 9.2–57.1 and 13.0–166.7 ng/g, respectively.     

Using SPMDs to Assess Natural Recovery of PCB-contaminated Sediments in Lake Hartwell,SC: I. A Field Test of New In-Situ Deployment Methods

Results from the field testing of some innovative sampling methods developed to evaluate risk management strategies for polychlorinated biphenyl (PCB) contaminated sediments are presented. Semipermeable membrane devices (SPMDs) were combined with novel deployment methods to quantify the availability of PCBs at the Sangamo-Weston Lake Hartwell Superfund Site in SC. Three locations in Lake Hartwell were examined: a background site (BKG) with little detectable contamination and two contaminated sites (T-M/N and T-O). PCB availability was quantified using sediment surface samplers designed to hold SPMDs in contact with surface sediments, benthic dome samplers designed to enclose and suspend SPMDs at the sediment-water interface, and commercially obtained SPMD cages suspended in the water column. A two-way analysis of variance showed significant effects by sampler type (P < 0.0001) and site (P < 0.0001) for mean time-weighted average (TWA) total PCBs (t-PCBs). Regardless of the SPMD sampler used, mean TWA t-PCBs were directly proportional to the level of contamination present (BKG < T-M/N < T-O). Water column and surface sediment sampler t-PCB uptake patterns were described by a significant linear fit of the data (r² = 0.9625, p < 0.0001, and r² = 0.8188, p < 0.0001, respectively). Dome and sediment surface SPMD samples had a higher percentage of higher chlorinated PCBs compared to water column samples.     

Concentrations and Distribution of Trace Metals in Water and Streambed Sediments of Orogodo River,Southern Nigeria

The distribution of Cd, Pb, Ni, Cr, Cu, Mn, Fe, and Zn in sediment and surface water, and some physico-chemical characteristics of Orogodo river sediments, were evaluated. The sediment pH ranged from 5.1–7.3; conductivity values ranged from 34.5 to 389.0 μScm^?1. Total nitrogen values ranged from 0.06–0.10%, NH₃-N values ranged from 0.25–0.44 mgkg^?1, percent total organic carbon ranged from 0.21–1.68%, and total phosphorus values ranged from 0.004–0.02% for dry and wet seasons. The sand fraction consists of 87–95%, silt fractions ranged from 0–2%, and clay fraction between 4–13%. The mean concentrations of metals (dry weight basis) in the streambed sediments ranged from 1.92–17.37 mgkg^?1 for Cu, 0.98–4.78 mgkg^?1 for Ni, 0.01–32.98 mgkg^?1 for Mn, 353.22–2045.64 mgkg^?1 for Fe, 69.96–100.16 mgkg^?1 for Zn, 0.21–1.32 mgkg^?1 for Cr, and Cd was less than 0.001 mgkg^?1 for wet and dry seasons. The mean concentrations of metals in the surface water ranged between 0.01–0.05–0.05 mg/L for Cu, nd-0.11 mg/L for Ni, 0.001–0.31 mg/L for Pb, 0.001–1.82 mg/L Mn, 0.01–3.52 mg/L for Fe, 0.16–0.61 mg/L for Zn, nd-0.007 mg/L for Cr, and <0.001 mg/L for Cd. Based on principal component analysis, two main sources of metals in the Orogodo River can be identified: (i) Cr, Cu, Pb, and Fe are mainly derived from industrial sources; (ii) Mn, Zn, and Ni associated with traffic activities. No element examined had a contamination/pollution index value greater than unity (pollution ranges). This implies that the multiple pollution indices obtained from the analysis showed that Orogodo River sediments were not polluted with heavy metals.     

Spatial Variation and Fractionation of Bed Sediment-Borne Copper,Zinc, Lead,and Cadmium in a Stream System Affected by Acid Mine Drainage

An investigation was conducted to examine the spatial variation and fractionation of bed sediment-borne Cu, Zn, Pb, and Cd in a stream system affected by acid mine drainage. The pH had a major control on the spatial variation pattern of soluble, exchangeable, and carbonate-bound Cu, Zn, and Cd. There was a prominent concentration peak of carbonate-bound, oxide-bound, and organic-bound metals at the 29 km station, as controlled by the abundance of organic C, carbonate C, and oxides of manganese and iron. In general, the residual fraction was the dominant form for all four investigated metals. It was likely that oxide-Mn played a more important role in binding Zn and Cd than oxide-Fe did. In contrast, Cu had a higher affinity for iron hydrous oxides than for manganese oxide. Pb had a higher affinity for oxides of iron and manganese than for carbonates and organic matter. The presence of organic-bound metals in both the acidic upstream reach and non-acidic downstream reach suggests that the binding of these metals by organic matter was not markedly affected by pH, while the correspondence of organic C peak and organic-bound metal peaks at the 29 km station indicates a strong control by organic matter abundance on the quantity of organic-complexed metals.     

Sediment suppresses herbivory across a coral reef depth gradient

Sediments are a ubiquitous feature of all coral reefs, yet our understanding of how they affect complex ecological processes on coral reefs is limited. Sediment in algal turfs has been shown to suppress herbivory by coral reef fishes on high-sediment, low-herbivory reef flats. Here, we investigate the role of sediment in suppressing herbivory across a depth gradient (reef base, crest and flat) by observing fish feeding following benthic sediment reductions. We found that sediment suppresses herbivory across all reef zones. Even slight reductions on the reef crest, which has 35 times less sediment than the reef flat, resulted in over 1800 more herbivore bites (h⁻¹ m⁻²). The Acanthuridae (surgeonfishes) were responsible for over 80 per cent of all bites observed, and on the reef crest and flat took over 1500 more bites (h⁻¹ m⁻²) when sediment load was reduced. These findings highlight the role of natural sediment loads in shaping coral reef herbivory and suggest that changes in benthic sediment loads could directly impair reef resilience.     

Waterfalls drive parallel evolution in a freshwater goby

Waterfalls may affect fish distribution and genetic structure within drainage networks even to the extent of leading evolutionary events. Here, parallel evolution was studied by focusing on waterfall and the landlocked freshwater goby Rhinogobius sp. YB (YB), which evolved from amphidromous R. brunneus (BR). The fish fauna was surveyed at 30 sites in 11 rivers on Iriomote Island, Japan, the geography of which was characterized by terraces/tablelands with many waterfalls. We found that all YB individuals were distributed only above waterfalls (height 6.8-58.7 m), whereas BR, and other fishes, were mostly distributed below waterfalls. Mitochondrial DNA analysis showed that every YB local population above the waterfall was independently evolved from BR. In contrast, cluster analysis of nine morphological characters, such as fin color and body pattern, showed that the morphology of YB individuals held a similarity beyond the genetic divergence, suggesting parallel evolution has occurred relating to their morphology. Genetic distance between each YB local population and BR was significantly correlated with waterfall height (r(2) = 0.94), suggesting that the waterfalls have been heightened due to the constant geological erosion and that their height represents the isolation period of YB local populations from BR (ca. 11,000-88,000 years). Each local population of BR was once landlocked in upstream by waterfall formation, consequently evolving to YB in each site. Although the morphology of YB had a high degree of similarity among local populations, finer scale analysis showed that the morphology of YB was significantly correlated with the genetic distance from BR. Consequently, there could be simultaneous multiple phases of allopatric/parallel evolution of the goby due to variations in waterfall height on this small island.