Ecogeochemistry of the subsurface food web at pH 0–2.5 in Iron Mountain,California, U.S.A.

Pyrite oxidation in the underground mining environment of Iron Mountain, California, has created the most acidic pH values ever reported in aquatic systems. Sulfate values as high as 120000 mg l^–1 and iron as high as 27600 mg l^–1 have been measured in the mine water, which also carries abundant other dissolved metals including Al, Zn, Cu, Cd, Mn, Sb and Pb. Extreme acidity and high metal concentrations apparently do not preclude the presence of an underground acidophilic food web, which has developed with bacterial biomass at the base and heliozoans as top predators. Slimes, oil-like films, flexible and inflexible stalactites, sediments, water and precipitates were found to have distinctive communities. A variety of filamentous and non-filamentous bacteria grew in slimes in water having pH values <1.0. Fungal hyphae colonize stalactites dripping pH 1.0 water; they may help to form these drip structures. Motile hypotrichous ciliates and bdelloid rotifers are particularly abundant in slimes having a pH of 1.5. Holdfasts of the iron bacterium Leptothrix discophora attach to biofilms covering pools of standing water having a pH of 2.5 in the mine. The mine is not a closed environment – people, forced air flow and massive flushing during high intensity rainfall provide intermittent contact between the surface and underground habitats, so the mine ecosystem probably is not a restricted one.     

A review of diatoms found in highly acidic environments

A review is presented of 28 studies in the literature of diatoms in environments at pH 3.5, including natural and anthropogenic acid sources. A total of 124 diatom taxa have been reported, but many are likely to have been accidental occurrences, because only a few specimens were found. Approximately 19 taxa abundant in at least one study or common in several studies are considered true inhabitants of highly acidic waters. These include: Achnanthes minutissima, Eunotia exigua, E. tenella, E. septentrionalis, E. osoresanensis, E. arcus, E. glacialis, E. pectinalis, Frustulia rhomboides, F. rhomboides var. saxonica, Nitzschia capitellata/subcapitellata, Nitzschia communis, Nitzschia pusilla, Nitzschia vasta, Pinnularia acoricola, P. obscura, P. braunii var. amphicephala, P. subcapitata and P. terminitina. There are inconsistencies in the taxonomy of several of these species and possible synonymies could lower the number of taxa to less than 9. Compared to diatom species richness in environments at pH 4.5–5.0, there are many fewer taxa in environments pH 3.5, suggesting a threshold between pH 4.5 and 3.5 below which many species are unable to maintain a population.     

Reconciling patterns of genetic variation with stream structure, earth history and biology in the Australian freshwater fish Craterocephalus stercusmuscarum (Atherinidae)

We examined the consequences of barriers, stream architecture and putative dispersal capability on levels of genetic differentiation among populations of the freshwater fish Craterocephalus stercusmuscarum. Seven polymorphic allozyme loci and sequences of a 498-bp fragment of the ATPase 6 mitochondrial DNA (mtDNA) gene were used to assess patterns of genetic variation among 16 populations from upland and lowland streams of five drainages in northern Queensland, Australia. Concordant patterns at both genetic markers revealed that there were significant levels of genetic subdivision among all populations, while an analysis of molecular variation showed that the distribution of genetic diversity was not consistent with contemporary drainage structure. There were reciprocally monophyletic mtDNA clades and fixed or large frequency differences at allozyme loci either side of instream barriers such as waterfalls. This implied barriers were effective in restricting gene flow between upland and lowland populations separated by waterfalls. However, there were two genetically distinct groups in upland areas, even within the same subcatchment, as well as high levels of genetic subdivision among lowland populations, suggesting barriers alone do not explain the patterns of genetic diversity. The data revealed a complex phylogeographic pattern, which we interpreted to be the result of one or more invasion events of independent lineages to different sections of each drainage, possibly mediated by well documented geomorphological changes. Our results highlight the importance of earth structure and history in shaping population genetic structure in stream organisms where dispersal capability may be limited, and reveal that the contemporary structure of drainages is not necessarily a good indicator of genetic relationships among populations.     

黄土高原退耕还林(草)区旅游开发探讨

黄土高原退耕还林(草)区生态环境相对脆弱,经济发展较为落后,如何在多元化目标主导下寻求退耕还林政策的合理模式,关系到西部大开发政策的实施效果。在简要介绍区域概况,评价退耕还林(草)模式的基础上,认为生态保护型和生态经济型模式缺乏社区利益的考虑,可持续发展的动力不足,但生态旅游开发模式可以解决动力不足的问题。通过分析退耕还林(草)区生态旅游开发的资源、区位、政策、交通、接待设施等旅游开发的影响因子,提出了黄土高原退耕还林(草)区旅游开发的阶段及任务,并构建了该区域旅游开发的分区框架。     

Changing Global Climate: Historical Carbon and Nitrogen Budgets and Projected Responses of Ohio’s Cropland Ecosystems

As the evidence of global climate change continues to mount, its consequences for cropland productivity assume particular significance. Against the backdrop of past agricultural practices, simulation models offer a glimpse into the future, showing the effect of temperature changes on crop production. In this study, we first quantified the carbon (C) and nitrogen (N) budgets of Ohios cropland ecosystems using inventory yield data of corn for grain, oat, and all wheat for the period 1866–1996 and soybean for the period 1924–96. Then we explored the responses of Ohios continuous soybean croplands to changes in temperature, carbon dioxide (CO₂) concentration, initial soil organic C and N (SOC-N) pools, soil texture, and management practices by developing a simple cropland ecosystem model (CEM) and performing a long-term sensitivity analysis. Finally, CEM simulations were evaluated against independent observations of SOC values (0–19 cm) averaged over 470 northwest Ohio sites between 1954 and 1987 under conventional tillage and rotations of corn–soybean–winter wheat by using the historical yield data (r ² = 0.8). The C contents per hectare of crop harvests increased by 178% for oats, 300% for corn for grain, and 652% for all wheat between 1866 and 1996 and by 305% for soybean between 1924 and 1996. Ohio croplands acted as C–N sources, releasing average net ecosystem emissions (NEE), including the removal of harvested C–N, of 4,598 kg CO₂ ha^–1 and 141 kg N ha^–1 in 1886 and 205 kg CO₂ ha^–1 (except for the corn-for-grain cropland) and 39 kg N ha^–1 in 1996. The continuous corn croplands continued to become a C sink, sequestering 255 kg C ha^–1 in 1996. Results of the sensitivity analysis for Ohios continuous soybean croplands revealed that the SOC pool increased by 6.9% and decreased by 7.5% in response to a doubled CO₂ concentration and a temperature increase of 2.8°C over 100 years, respectively. The sequestration potential of the SOC pool increased by 6.5% at a rate of 24.6 kg C ha^–1 y^–1 for the same period with finer soil texture (loam to silty clay loam). The shift from conventional to conservation residue practice led to an 11% increase in the steady-state SOC storage at a rate of 42 kg C ha^–1 y^–1 for 100 years.     

帽儿山地区不同类型河岸带土壤的反硝化效率

以帽儿山地区森林背景下的森林、皆伐、草地河岸带和农田背景下的森林、裸地河岸带土壤为研究对象,采用硝态氮消失法,研究了不同背景下各类型河岸带的反硝化强度及其影响因素．结果表明：各类型河岸带中,农田背景下的森林河岸带土壤反硝化强度最大,其硝态氮消失率的变化范围为46．79％～91．13％,农田背景下的裸地河岸带土壤反硝化强度最小,其硝态氮消失率的变化范围为15．64％～81．84％;森林背景下土壤反硝化强度的大小顺序为皆伐河岸带〉森林河岸带〉草地河岸带,其硝态氮消失率的变化范围依次为42．06％～90．39％、28．24％～85．73％、21．44％～83．11％．研究区河岸带表层土壤的反硝化强度大于底层．河岸带土壤反硝化强度均受可利用碳、硝态氮的限制,各类型河岸带以农田背景下森林河岸带土壤反硝化潜力最大．     

蛙心包淋巴孔的发现

首次报道蛙心包淋巴孔 ,揭示心包腔淋巴转归途径。本实验应用扫描电镜和透射电镜观察心包淋巴孔的超微结构 ,并使用计算机图象处理技术对淋巴孔作定量分析。结果发现 ,正常蛙心包腔面有一些散在分布的心包淋巴孔和少量淋巴窦。构成淋巴孔的间皮细胞常出现粗大的胞质突起 ,伸入淋巴孔 ,形成瓣膜状结构。淋巴孔的平均直径为 0 72±0 33μm ,平均分布密度是 3 57± 2 0 7个 /0 0 1mm2 ;心包间皮淋巴窦的面积是 995 0 8±2 2 1 74μm2 /0 0 1mm2 。蛙心肌无血管 ,其血供仅由心腔内血液直接进入心肌的小梁间隙。心包脏层未发现有淋巴孔。结果表明 :间皮淋巴窦是心包膜正常“漏出”的形态依据。心包淋巴孔的发现 ,证明心包腔淋巴引流途径的存在。淋巴引流对于心肌组织间液的平衡 ,清除组织间液蛋白质 ,防止心肌间质水肿 ,有重要意义     

Long-term recovery from mine drainage disturbance of a macroinvertebrate community in the Ichi-kawa River,Japan

The effects of mine drainage on a benthic macroinvertebrate community and its recovery have been investigated for 25 years in the Ichi-kawa River in western Japan, focusing especially on change in community structure. Concentrations of arsenic, copper and zinc in the water were distinctly higher at sites just below the drainage than an upstream reference site before mine closure in 1973. Benthic communities there were severely damaged, as evidenced by reductions in the number of families and biomass. Chironomidae and a mayfly, Epeorus latifolium, predominated at the impacted sites, whereas stenopsychid caddisflies were dominant at the reference site. After mine closure, zinc concentrations significantly decreased downstream, although they remained higher than at the reference site. Following this, family richness and biomass of benthic communities clearly increased. In addition, the percentage of Trichoptera increased and, finally, Stenopsychidae became the dominant family in 1996 at all sites except just below the drainage. Therefore, the dominance of Stenopsychidae at the impacted sites is expected to be an indicator of complete recovery of the benthic community from the effect of mine drainage.     

A review of the ecological effects of river regulation in Australia

Responses to hydrologic change are an important theme in lotic ecology, and data for Australian rivers are accumulating in a rapid, butad hoc manner. Thia paper arranges recent contributions according to the major drainage divisions, which provide reasonably coherent environmental units. The east coastal rivers are exploited for storage, power generation and waste disposal, and Tasmanian rivers are regulated to serve hydro-electric power schemes. Most information refers to the Murray-Darling river system, which supplies irrigated agriculture in semi-arid inland areas of S.E. Australia, and is intensively regulated by dams, weirs and barrages. The Murray's flows are over-committed, if variability is taken into account, and there are environmental problems (e.g. erosion and salinity) associated with irrigation. The effects of regulation are seen also in the changed distributions of plants and animals associated with the Murray and its floodplain. In Australia the national effort is uncoordinated because research and management are developing independently of one another. Ecologists must become involved in the planning and implementation of strategies that are consistent, as far as possible, with offstream and instream needs.     

Inter‐basin exchange and repeated headwater capture across the Sierra Madre Occidental inferred from the phylogeography of Mexican stonerollers

Aim Geomorphic evolution of river basins can shape the structure and diversity of aquatic communities, but understanding the biological significance of basin evolution can be challenging in semi‐arid regions with ephemeral or endorheic conditions and complex drainage configurations such as the Sierra Madre Occidental (SMO) in North America. In this study, we characterized range‐wide patterns of genetic variation in the Mexican stoneroller (Campostoma ornatum) to infer how orogenic and erosional influences on river basin connectivity have given rise to the diverse and largely endemic freshwater communities across the SMO region. Location Twelve drainage basins across northern Mexico and the south‐western United States, centred on the SMO. Methods  We collected 202 specimens from 98 localities across the range of C. ornatum. We performed phylogenetic analyses of DNA sequences from one mitochondrial (cytochrome b) and one nuclear (intron S7) gene. Phylogenetic trees were estimated for each data set using maximum likelihood and Bayesian inference. Results Phylogenetic analyses consistently resolved a monophyletic C. ornatum composed of multiple evolutionary lineages within two markedly divergent clades that differentiate northern drainages from southern drainages in the SMO region. Within‐clade patterns of divergence corresponded to fine‐scale geographic structure within and among SMO drainage basins. However, the geographic distribution of evolutionary lineages within the northern and southern clades did not always correspond to the geographic configuration of drainage basins. Some subclades encompassed multiple drainages, and individuals from a single drainage were sometimes recovered in multiple subclades. Main conclusions Our findings indicate that a common ancestor of Mexican Campostoma is likely to have entered north‐west Mexico through an ancient Rio Grande system that extended as far south as the Rio Nazas and Rio Aguanaval. The geographic orientation of the two strongly divergent clades recovered within C. ornatum provides evidence of long‐standing isolation of southern basins from northern basins within the ancestral Rio Grande system, possibly due to the combined influence of tectonic events and increasing regional aridity. Geographic patterns of genetic variation also provide evidence of range expansion from Atlantic to Pacific drainages due to drainage evolution and river capture events, as well as further inter‐basin exchange via more recent headwater capture events, hydrological connections and possible anthropogenic introductions.