Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material

The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0–1 cm) and three times lower in the middle layer (1–3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3–10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We␣conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were␣no␣indications of any group adjusting their vertical position behaviourally as a response to predation threat.     

Colonizing macroinvertebrates in the Upper Mississippi River with a comparison of basket and multiplate samplers *

SUMMARY. Colonizing aquatic macroinvertebrates were collected from two kinds of artificial substrate placed on wing dams in Pool 13 of the Upper Mississippi River in September 1978. Thirty-one taxa were collected from basket samplers containing cement spheres and twenty-one taxa from multiplate samplers constructed from tempered hardboard. Hydro-psychidae (Trichoptera), especially Cheumatopsyche sp., Potamyla flava and Hydropsyche sp., were the dominant macroinvertebrates which colonized both samplers. Basket samplers had a significantly greater macroinvertebrate density, biomass and number of taxa compared with multiplate samplers. Precision of the arithmetic mean for density, biomass and number of taxa was 19.9, 18.3 and 8.1% for basket samplers and 18.8, 18.7 and 8.5% for multiplate samplers. The number of sampling units required for a precision of 20% for macroinvertebrate density, biomass and number of taxa was 13, 11 and 2 for basket samplers and 11, 11 and 2 for multiplate samplers. Basket samplers with 7.5-cm cement spheres are recommended for use instead of multiplate samplers.     

Structure and composition of benthic macroinvertebrates of a tropical forest stream, River Nyamweru, western Uganda

Benthic invertebrates from River Nyamweru, a tropical forest stream in western Uganda were sampled bimonthly between April and December 1997 using a modified Hess Sampler. A total of 3708 benthic fauna from thirteen taxonomic orders were collected. Benthic samples were dominated by Diptera (mainly Chironomidae) representing over 60% of all the organisms, followed by Ephemeroptera. Benthic invertebrate densities ranged from 63 ± 9.03 organisms/m² to 300 ± 33.36 organisms/m², with higher densities occurring during the dry season and lower densities during the wet season. The benthic community structure in River Nyamweru reflected mainly collectors and scrapers as the most important groups (83%), while predators were very rare (3.1%). River discharge influenced benthic abundance, with more invertebrates at lower discharge and fewer invertebrates at higher discharge. The applicability of the River Continuum Concept to tropical forest stream situation is discussed.     

长江口及东海春季底栖硅藻、原生动物和小型底栖生物的生态特点

利用Ludox-QPS方法并结合沉积环境因子的综合分析,研究了2011年4月采自长江口及东海10个站位以底栖硅藻、纤毛虫和异养小鞭毛虫为代表的微型底栖生物及小型底栖生物的组成、丰度和生物量、分布及生态特点。结果表明,底栖硅藻的丰度 (5.92 ? 104 ind/10 cm2) 和生物量 (83.29 ?g C/10 cm2) 远高于纤毛虫 (丰度为1036 ind/10 cm2,生物量为3.33 ?g C/10 cm2)、异养小鞭毛虫 (丰度为4451 ind/10 cm2,生物量为2.51 ?g C/10 cm2) 和小型底栖生物 (丰度为1947 ? 849 ind/10 cm2,生物量为49.01? 22.05 ?g C/10 cm2)。在鉴定出的11个小型底栖生物类群中,线虫占小型底栖生物总丰度的90%和总生物量的37%。底栖硅藻生物量在长江口及东海海域呈由近岸向外海逐渐降低的分布特点,而底栖纤毛虫、异养小鞭毛虫及小型底栖生物的分布则正相反。在垂直分布上,76%的硅藻和80%的线虫分布在0–2 cm沉积物表层,仅1%的硅藻和6%的线虫分布在5–8 cm分层。统计分析表明,底栖硅藻的现存量与沉积物中叶绿素a含量呈极显著的正相关,与底层水温度呈弱的正相关;该海域底栖原生动物和小型底栖生物的分布受多个因子而非单一环境因子的共同作用。对比分析表明,长江口及东海单位体积沉积物中的硅藻丰度较水体中的硅藻丰度高2个数量级,沉积物中相当部分的叶绿素a含量可能系底栖硅藻所贡献;表层8 cm沉积物中纤毛虫的丰度约是上层30 m水柱中纤毛虫丰度的30倍,生物量约是后者的40倍。尽管纤毛虫在生物量上远小于小型底栖生物,但其估算的生产力约是后者的3倍;而异养小鞭毛虫由于个体更小,其周转率可能较纤毛虫更高。长江口及东海陆架区原生动物和小型底栖生物的高现存量及生产力预示着其在该海域生态系统中的重要作用。     

Benthic macro- and meso-invertebrates of a sandy riverbed in a mountain stream, central Japan

Quantitative samples of benthic invertebrates were collected from a sandy riverbed of a mountainous stream (Kozu site of Takami-gawa stream, Nara Prefecture), central Japan by core samplers in five sampling occasions through the years 2008–2009. A total of 120 taxa were identified, representing 55 families and 97 genera. Insects formed about 92% of the total recorded taxa and 88% of individuals’ abundance. A total of 111 taxa of aquatic insects, belonging to 49 families and 92 genera, were identified and represented by ten orders. Oligochaeta and Acari were dominant non-insect invertebrates. Diptera was the most diverse insect group, followed by Trichoptera and Ephemeroptera. Dominant taxa were mesoinvertebrates, younger stages of macroinvertebrates, both of which predominantly inhabit the interstitial zone of a sandy riverbed. Both taxon richness and invertebrate abundance were higher in February 2009 and lower in April and August 2008. A few major invertebrate taxa demonstrated distinct seasonal trends; i.e. Nymphomyia alba, Rheosmittia, and Corynoneura were abundant in February 2009. Newly hatched larvae of Larcasia akagiae were abundant in May 2008. This study also demonstrated the effectiveness of core samplers to collect small-sized benthic fauna that inhabit the interstitial or hyporheic zone of the sandy riverbed.     

A new quantitative air-lift sampler for collecting macroinvertebrates on stony bottoms in deep rivers

SUMMARY. 1. As three previous comparative studies of deep-water samplers for benthic macroinvertebrates in rivers highlighted the need for a quantitative sampler for use on stony substrata, a new air-lift sampler was developed. It can be operated from a small boat by two people, weighs 13.5–20.0 kg, depending on the length of riser used, and extends the maximum range of substrata that may be sampled quantitatively from 16–32 mm to 128—256 mm. The sampling area is isolated by forcing a collecting cylinder into the substratum, and rapid evacuation of the contents is assisted by a vibrator.
2. All the major specifications of the sampler were determined experimentally in a large tank using three sizes of substrata and plastic pellets to represent invertebrates. The sampler performed accurately to a depth of at least 8 cm on substrata ranging from gravel (2–4 mm) to large stones (32–36 mm long).
3. The performance of the sampler was compared with that of a Ponar grab and Pearson el at. air-lift sampler at two sites on a large river and also with a Naturalist's dredge and a diver-operated Hess-Waters sampler at one of the sites where there were large stones up to 280 mm long. In terms of both mean taxa per sample and mean numbers m⁻², samples taken using the new air-lift sampler provided estimates comparable to or belter than those obtained with the other samplers.     

Vertical distribution and diversity of sulfate-reducing prokaryotes in the Pearl River estuarine sediments, Southern China

The vertical distribution and diversity of sulfate-reducing prokaryotes (SRPs) in a sediment core from the Pearl River Estuary was reported for the first time. The profiles of methane and sulfate concentrations along the sediment core indicated processes of methane production/oxidation and sulfate reduction. Phospholipid fatty acids analysis suggested that sulfur-oxidizing bacteria (SOB) might be abundant in the upper layers, while SRPs might be distributed throughout the sediment core. Quantitative competitive-PCR analysis indicated that the ratios of SRPs to total bacteria in the sediment core varied from around 2–20%. Four dissimilatory sulfite reductase ( dsrAB) gene libraries were constructed and analyzed for the top layer (0–6 cm), middle layer (18–24 cm), bottom layer (44–50 cm) and the sulfate-methane transition zone (32–42 cm) sediments. Most of the retrieved dsrAB sequences (80.9%) had low sequence similarity with known SRP sequences and formed deeply branching dsrAB lineages. Meanwhile, bacterial 16S rRNA gene analysis revealed that members of the Proteobacteria were predominant in these sediments. Putative SRPs within Desulfobacteriaceae, Syntrophaceae and Desulfobulbaceae of Deltaproteobacteria , and putative SOB within Epsilonproteobacteria were detected by the 16S rRNA gene analysis. Results of this study suggested a variety of novel SRPs in the Pearl River Estuary sediments.     

An ecological investigation of the Portneuf River, Idaho: a semiarid-land stream subjected to pollution

The Portneuf River (mean monthly discharge near mouth 1.4-15.4 m³/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156-km course, during the period 1967-1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil-conservation practices. However, the stream also is affected by wastes from a sewage-treatment plant, phosphate-processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip-net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of reduced habitat.     

Invertebrate seedbanks: rehydration of soil from an unregulated river floodplain in the south-eastern U.S.

1. We investigated the responsiveness of aquatic invertebrates to rehydration of floodplain soil in a south‐eastern U.S. river floodplain. Non‐inundated soil divots containing invertebrate seedbanks were collected from three floodplain elevations with different inundation histories (inundated for 2, 38, and 78% of a year), and subjected to rehydration (experimental inundation) in aquaria for 10 weeks. 2. Before rehydration, samples were collected to assess the initial density and composition of invertebrates in non‐inundated soil at each elevation. After rehydration, benthic samples were collected biweekly and emergence of aquatic insects was collected weekly from aquaria. 3. The surviving invertebrates were classified as aquatic, semi‐aquatic and terrestrial. Some aquatic invertebrates survived the non‐inundated period in an active state (e.g. Chironomidae and Ceratopogonidae), while others appeared to be dormant (e.g. Heptageniidae, microcrustaceans and Chironomidae). The response for several invertebrates (e.g. Chironominae, Oligochaeta, Collembola and terrestrial invertebrates) depended on the length of rehydration and inundation history. 4. The capacity of aquatic invertebrates to survive and recover was greatest at the most frequently inundated site. Despite variation in floodplain environments, both active and dormant invertebrates persisting in non‐inundated floodplain soil contributed to the floodplain assemblage during flooding. Thus, maintaining the connection between river and floodplain appears to be important in sustaining the invertebrate seedbank and its capacity to recover during inundation. River channelisation and regulation that severs this connection may result in a loss of diversity and abundance.     

Vertical distribution and abundance of invertebrates within the sandy substrate of a low-gradient headwater stream

SUMMARY. 1 The vertical distribution of invertebrates (>0.053 mm) was studied in a sandy-bottomed, first-order stream on the Coastal Plain of Virginia, U.S.A. Invertebrate species composition, abundance and bio-mass were determined monthly over one year at sediment depth intervals of 0–1, 1–5, 5–15,15–30 and 30–40 cm.
2. The subsurface community was numerically dominated by species of Chironomidae, Nematoda and Crustacea, while much of the biomass was due to early instars of several species of Trichoptera.
3. Invertebrate density and biomass decreased significantly with depth in the substrate (ANOVA; P <0.05). Annual mean density decreased from 1,346,844 individuals m⁻³ at the surface to 13,578 individuals m⁻³ at 15–30 cm. Annual mean biomass decreased from 66.30 g m⁻³ at the surface to 0.44 g m⁻³ at 15–30 cm.
4. Dissolved oxygen decreased markedly from the surface to the 5 cm depth in the substrate, anaerobic conditions often occurring below 10 cm. Density and biomass both showed a significant positive relationship with dissolved oxygen concentration (Linear regression; P <0.05).
5. Physical forces were important in structuring the subsurface invertebrate community. Besides low dissolved oxygen concentration, sediment scouring resulting from storm discharge dramatically reduced density and biomass     

The vertical distribution of macrobenthos within the substratum of the Brazos river,Texas

Vertical stratification samplers were developed for sampling the grave-sand substrate of a Brazos River, Texas riffle. Fifteen of 25 species recovered, occurred below 10 cm. Mean percentages of total organisms recovered were 66.4%, 20%, 6.1% and 7.5% per 10 cm level, respectively, from the surface down. Dominant insects were Neochoroterpes mexicanas naiads and chironomid, Simulium, Cheumatopsyche and Stenelmis larvae. Seasonal population peaks of these five groups in the top 10 cm correspond with observed emergence peaks. The smaller size classes were generally predominant in the 0–10 cm level. Larvae of Stenelmis were the most evenly distributed among the various 10 cm levels in all size classes. A movement of Cheumatopsyche and Neochoroterpes to lower levels was observed following a large flood, suggesting an escape response to increased silt load and scouring.Dissolved oxygen ranged from saturation at the surface down to 0.4–0.7 ppm at 30–40 cm, indicating that it was possibly limiting at lower levels. Maximum temperature difference between to cm levels was only 3 C. Flow was negligible below to cm.The vertical stratification sampler recovered significantly greater populations in the surface 20 cm, but not in the total 40 cm, than a modified Hess sq. ft. sampler.Study supported in part by the Faculty Research Fund and Institute for Environmental Studies of North Texas State University.     

Benthic foraminifera off West Africa (1°N to 32°S): Do live assemblages from the topmost sediment reliably record environmental variability?

Recent benthic foraminifera (> 125 μm) were investigated from multicorer samples on a latitudinal transect of 20 stations between 1°N and 32°S along the upper slope off West Africa. Samples were selected from a narrow water depth interval, between 1200 and 1500 m, so that changes in water masses are minimized, but changes in surface productivity are important and the only significant environmental variable. Live (Rose Bengal stained) benthic foraminifera were counted from the surface sediment down to a maximum of 12 cm. Dead foraminifera were investigated in the top 5 cm of the sediment only. Five live and five dead benthic foraminiferal assemblages were identified using Q-mode principal component analysis, matching distinct primary productivity provinces, characterized by different systems of seasonal and permanent upwelling. Differences in seasonality, quantity, and quality of food supply are the main controlling parameters on species composition and distribution of the benthic foraminiferal faunas.To test the sensitivity of foraminiferal studies based on the uppermost centimeter of sediment only, a comparative Q-mode principal component analysis was conducted on live and dead foraminiferal data from the top 1 cm of sediment. It has been demonstrated that, on the upper slope off West Africa, most of the environmental signals as recorded by species composition and distribution of the “total” live and dead assemblages, i.e., including live and dead foraminifera from the surface sediment down to 12 cm and 5 cm, respectively, can be extracted from the assemblages in the top centimeter of sediment only. On the contrary, subsurface abundance maxima of live foraminifera and dissolution of empty tests strongly bias quantitative approaches based on the calculation of standing stocks and foraminiferal numbers in the topmost centimeter.     

Seasonal changes in vertical distribution, biomass and faecal production of tubificids in the profundal region of a shallow Japanese lake

Two tubificid species Limnodrilus hoffmeisteri and L. claparedeianus formed more than 93% of the total number of oligochaetes in the profundal. Limnodrilus spp. worms were found down to 33 cm in the sediment but in great numbers in the upper zone in June and October. Worms confined to the top 15 cm of sediment accounted for 53-92% of the total number. There were two annual maxima in population density and biomass, one in late spring (66000 inds m⁻², 17 g wet wt m⁻²) and the other in mid autumn (97000 inds m⁻², 176 g wet wt m⁻²). Two regression lines describing the effect of temperature on faecal production rate were obtained; Log F = 0.0604 T (°C) −0.7660 (below 15°C), Log F = 0.0266 T – 0.2170 (above 15°C). In total 26.8 kg dry wt m⁻² of sediment was defecated annually by Limnodrilus spp. The sediment in the 0–10 cm stratum may pass through the guts of the worms 2.3 times a year. Sedimentation rates in profundal region were very low with respect to the faecal production rates of the tubificids.     

欧美108杨细根形态及垂直分布对水氮耦合措施的响应

合理高效的水肥集约经营是有效地提高速生丰产林生产力的重要途径。细根是植物吸收水肥和维持生长的主要器官, 了解细根形态及其分布对水肥耦合措施的响应机制有助于解释树木生长和吸收水肥能力的差异性。该文基于水氮耦合措施对欧美108杨(Populus × euramericana ‘Guariento’)幼林表土层(0–30 cm)细根形态及分布的影响研究, 在连续两年的水氮管理后, 开展了欧美108杨0–60 cm土层细根形态及垂直分布对水氮耦合响应的研究。田间设计3个灌溉水平(灌溉土壤水势起始阈值为–75 kPa、–50 kPa、–25 kPa)和3个养分水平(施N 150 g·tree^–1·a^–1、300 g·tree^–1·a^–1、450 g·tree^–1·a^–1), 组合成9个水氮耦合处理, 另设1个对照处理(CK)。研究结果表明: (1)垂直方向上, 各处理细根生物量密度、表面积和平均直径均表现为10–20 cm土层最大(该层生物量密度占0–60 cm土层总生物量的27%–37%), 随后在30–60 cm土层逐层递减; 根长密度则随土壤深度的加深而逐层递减, 0–10 cm土层显著大于其他土层(该层根长密度占0–60 cm土层总根长密度的33%–45%)。(2) 6个土层的细根生物量密度、根长密度和平均直径均表现为高水高氮(D3F3)和中水高氮(D2F3) 2个处理间差异不显著, 但均显著高于其他处理, 其中, D3F3处理6个土层生物量密度是对照的3.12–47.74倍; 细根表面积则是D3F3处理显著高于其他处理, 是CK的4.36–30.57倍。(3)连续的水氮耦合管理措施不会改变细根的垂直分布格局(各处理均具有与CK一致的分布格局), 但在第二个生长季, 欧美108杨细根的整体分布随着林龄的增加趋于深层化; 另外, 中水高氮的耦合处理也可有效地促进细根的生长, 这种水氮需求水平与第一个生长季内需高水高氮才可显著促进其生长的特性不同。欧美108杨细根在第2个生长季主要分布于0–20 cm土层, 9个水氮耦合处理中, 除低水低氮处理外, 其他处理各细根形态指标值均显著高于CK, 这种差异性在浅土层更为显著, 而在深土层表现出相对较小的差异。当灌溉量一定时(尤其中、高灌溉水平), 增加施氮量可显著促进细根生长, 但当施氮量一定时(尤其低、中氮水平), 增加灌溉量对细根生长的促进效果不显著, 即欧美108杨细根生长趋肥性强于向水性。     

Responses of the fine root morphology and vertical distribution of Populus × euramericana ‘Guariento’ to the coupled effect of water and nitrogen

Aims Irrigation and fertilization have great potentials to enhance yield in forest plantations. The integrated effect of water and nitrogen management on fine roots morphology and distribution of Populus × euramericana ‘Guariento’, however, remains unclear. The objective of this study was to evaluate the effect of water and nitrogen addition on fine root morphology and distribution in poplar plantations for developing the best water and nitrogen strategy for promoting fine root. Methods The soil core method was used to quantify the morphology and distribution of fine roots in the 0–60 cm in a poplar plantation with surface dripping irrigation and fertilization technologies. The experiment included nine treatments, which were a combination of three irrigation treatments where dripping irrigation was applied when soil water potential (ψ_soil) reached –75, –50, or –25 kPa, and three fertilization treatments at nitrogen additions of 150, 300, or 450 g·tree–1·a–1, respectively). A control plot with non-irrigation and non-fertilizationtreatment in growing season (CK) was also included in the study. Important findings The fine roots biomass density, fine root surface area density, average root diameter in all treatments were mainly found at 0–10 cm and 10–20 cm depths, with root biomass density in the 10–20 cm of 1.03 to 1.21 times of that in the 0–10 cm, 1.25 to 1.80 times of that in the 20–30 cm, 1.62 to 22.10 times of that in the 30–40 cm, 2.77 to 54.35 times of that in the 40–50 cm, and 6.48 to 293.09 times of that in the 50–60 cm. The root biomass density in the 10–20 cm accounted for 27%–37% of the total biomass density in the top 60 cm. For root biomass density and average diameter, there were no significant differences between 0–10 cm and 10–20 cm depths, and between 40–50 cm and 50–60 cm depths. Fine roots in the irrigation and fertilization treatments were significantly higher than that of the CK, except the D1F1 treatment (i.e., with low water and low nitrogen level). Additionally, fine roots in the D2F3 treatment (i.e., with intermedia irrigation and high nitrogen level) and the D3F3 treatment (i.e., with high water and high nitrogen level) were significantly higher than those in other treatments, but not significantly different between D2F3 and D3F3. Compared with the CK, the fine roots biomass density in six soil layers were significantly enhanced at 359%, 388%, 328%, 3823%, 4774% and 2866%, respectively, for the treatment with high water and high nitrogen levels. The vertical distributions of fine roots appeared not affected by the interaction of irrigation and nitrogen addition. However, the surface dripping irrigation and fertilization treatments increased fine roots significantly. Finally, we found that the response of fine root growth and distribution was stronger to fertilization than to the irrigation in this poplar plantation.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.     

Wind dispersal of soil invertebrates in the McMurdo Dry Valleys, Antarctica

Dispersal of soil organisms is crucial for their spatial distribution and adaptation to the prevailing conditions of the Antarctic Dry Valleys. This study investigated the possibility of wind dispersal of soil invertebrates within the dry valleys. Soil invertebrates were evaluated in (1) pockets of transported sediments to lake ice and glacier surfaces, (2) wind-transported dust particles in collection pans (Bundt pans) 100 cm above the soil surface, and (3) sediments transported closer to the surface (<50 cm) and collected in open top chambers (OTCs). Invertebrates were extracted and identified. Nematodes were identified to species and classified according to life stage and sex. Three species of nematodes were recovered and Scottnema lindsayae was the most dominant. There were more juveniles (∼71%) in the transported sediments than adults (29%). Tardigrades and rotifers were more abundant in sediments on lake and glacier surfaces while nematodes were more abundant in the dry sediment collections of Bundt pans and OTCs. The abundance of immobile (dead) nematodes in the Bundt pans and OTCs was three times greater than active (live) nematodes. Anhydrobiosis constitutes a survival mechanism that allows wind dispersal of nematodes in the McMurdo Dry Valleys. Our results show that soil invertebrates are dispersed by wind in the Dry Valleys and are viable in ice communities on lake surfaces and glaciers.     

Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105°30'; latitude 40°35').
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.     

新疆天山中段巴音布鲁克高山草地碳含量及其垂直分布

对新疆天山中段巴音布鲁克高山草地(高山草原和高山草甸)的生物量和土壤有机碳进行了测定。结果表明积分和分层两种估算方法得到的土壤有机碳含量没有显著差异,但积分算法的优势在于能推算不同深度的土壤有机碳含量,便于与以往的研究进行比较;高山草甸的生物量和土壤有机碳含量均大于高山草原;其地上生物量分别为71.4和94.9 g C·m^-2,地下生物量分别为1 033.5和1 285.2 g C·m^-2; 1 m深度的土壤有机碳含量分别为25.7和38.8 kg·m^-2;地上生物量呈现较为明显的垂直分布格局,即随着海拔的增加,地上生物量先呈增加趋势,但当海拔超过一定界限后生物量突然下降;土壤含水率是导致南坡(阳坡)土壤有机碳含量空间分异的重要因素,但北坡(阴坡) 土壤有机碳含量还可能与地形、土壤质地等其它因素有关;两种高山草地(高山草原和高山草甸)的根系集中分布在40 cm以内,0~20 cm根系分别占其总量的76%和80%;土壤有机碳集中分布在60 cm以内,0~20 cm土壤有机碳分别占其总量的55%和49%;高山草原根系分布比高山草甸深,但较低的地下/地上比使得其有机碳分布比高山草甸浅。