1,721,012 research outputs found
Effects of light and substrate on the benthic diatoms in an oligotrophic lake: a comparison between natural and artificial substrates
No full textBenthic diatoms form a particularly important community in oligotrophic lakes, but factors influencing their distribution are not well known. This study reports the depth distribution of living motile and total diatoms (living plus dead diatoms) on both natural (from sand to fine organic mud) and artificial substrates in an oligotrophic lake. On artificial substrates, motile diatom densities peaked in abundance (24–30 cells · mm?2) between 0.6 and 1.9 m depth; on natural sediment surfaces, motile diatoms were generally more numerous and peaked in abundance (925 cells · mm?2) at 1.3 m depth. Total diatom densities on artificial substrates were highest (1260 valves · mm?2) at 0.6 m depth, with very low values below 3 m depth; on natural sediment surfaces, total diatom abundances were generally much higher (21600 valves · mm?2) at 3 m depth and declined gradually with depth. Significant relationships were found between light and diatom densities on the artificial substrate. Ordination analysis indicated that substrate type significantly correlated with the variation of diatom composition on artificial and natural substrates. Our results suggest that in oligotrophic lakes, light influences benthic diatom abundance, whereas substrate type has more influence on benthic diatom composition
A portable hand-operated sampler for shallow-water surface sediments with special reference to epipelic communities
No full textA convenient, portable, hand-operated surface-sediment sampler for use in shallow water is described. Collection of replicable, undisturbed surface sediment samples from shallow-water locations is made simple. The sampler is highly portable for use at remote sites and can be operated by one person. It is especially useful for sampling in the 0.3–1.3 m water depth range where other samplers are often unsuccessful. This sampler consists of a PVC tube (about 33-cm length, 7.1-cm diameter) attached to a 1-m-long supporting rod. A lever system is used to close off the PVC core tube. In the open position, the core tube is inserted into the sediment to an optimal depth (typically 1-cm) so that a 1-cm disc of surface sediment is enclosed. This disc is then isolated by operating the lever and tube closure plate. The sampler and sediment sample (with an intact epipelon biofilm) are removed carefully so that most of the enclosed water drains away and the sample is retained intact. <br/
Rural factories won't fix Chinese pollution
No full textChina's green movement is awakening and starting to receive global attention (see, for example, Q. Wang et al. Nature 489, 502; 2012). The municipal governments of Qidong and Shifang should be applauded for suspending two planned industrial plants likely to cause widespread pollution (Nature 488, 261–262; 2012). But there may be plans afoot to relocate these to rural areas.Moving factories from cities to rural areas is becoming more common. The relocation by local government of a US$1.4-billion paraxylene plant from Xiamen City in Fujian province to the less-developed Gulei Town was not welcomed by residents (T. Ma China Environ. Ser. 10, 33–49; 2008/2009). Their protests received little media attention or help from non-governmental organizations (NGOs), and the new plant is now almost complete.Shifting pollution from urban to rural areas can only be a short-term fix. For example, rural and semi-rural factories trebled their contribution to the national wastewater discharge between 1990 and 2007 (see go.nature.com/kdgsh3; in Chinese), and there are more than 200 cancer-cluster villages in China where pollution is suspected as the major cause of death.More local NGOs are needed to support rural populations in suing polluting industrialists. To ensure sustainability of the country's huge production system, industrialists must embrace the green economy and tackle factory pollution at source.<br/
An improved coverslip method for investigating epipelic diatoms
No full textThe traditional coverslip method for harvesting motile diatoms was improved and standardized by determining optimum times for diatom harvesting; by using opaque Petri dish bases as experimental chambers; and by preparing coverslips by burning. Three experiments were conducted to evaluate the harvesting efficiency of the coverslip method. Experiment 1 was performed to reveal the spatial distribution of epipelic diatoms on the coverslips after exposure periods ranging from 2 to 36 h. The transect count results were supplemented using an Inverse Distance Weighted algorithm and showed that after 8 h exposure the epipelic diatoms began to accumulate at the coverslip margin. Therefore, 8 h was identified as the optimum time for the coverslip method to capture epipelic diatoms efficiently for the samples. However, the optimum time could vary between sites because of differences in diatom composition, light intensity and other environmental conditions. Experiment 2 revealed that the numbers of epipelic diatoms harvested from opaque chambers were 15.6% higher than those harvested from transparent chambers, indicating that opaque sides and base reduce multi-directional diatom migration. Experiment 3 indicated that the burning method was more efficient than the traditional method (directly counting fresh diatoms) because it makes identification easier and yields higher densities of diatoms. All experiments demonstrated that the coverslip method harvested more epipelic diatoms, made identification easier than the traditional method, enabling permanent slides to be created. In addition, the method makes it possible to estimate in situ epipelic cell densities, if the sediment area is known
Influence of environmental and spatial variables on the distribution of surface sediment diatoms in an upland loch, Scotland
Full text linkThe spatial distribution of surface sediment diatoms was analyzed using ArcGIS in the Round Loch of Glenhead, an acid upland lake in south-west Scotland. The assemblages were composed almost entirely of benthic species. Tabellaria quadriseptata was fairly evenly distributed across the loch but some species (Navicula madumensis, Brachysira brebissonii, Aulacoseira perglabra and Eunotia vanheurckii var 1) showed rather patchy distributions. Ordination analysis was performed to assess the influence of environmental and spatial variables on the diatom composition of the samples. Loss of ignition was significantly negatively correlated with redundancy analysis species axis 1 (r = –0.77), indicating the influence of substrate on the diatom assemblages. The positive relationship between theoretical bottom shear stress resulting from wind stress and redundancy analysis (r = 0.31) suggests wind stress also influences the spatial distribution of diatoms within the loch. Spatial variables [(principal coordinates of neighbour matrices (PCNM 1 and PCNM3) positively correlated with redundancy analysis axis 2], indicated that spatial variables, ignored in former studies, are a further influence on diatom distribution. Unique environmental and spatial variables explained 27.3% and 8.6% of diatom variability respectively. Environmental and spatial interactive variables combined explained 4.8% of variation. Although the pure contribution of spatial variables was only 8.6%, the study highlighted the importance of differences in the spatial distribution of different benthic diatom species in this upland lake
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