Frog communities and wetland condition: relationships with grazing by domestic livestock along an Australian floodplain river

Frogs are in decline worldwide, and are known to be sensitive indicators of environmental change. Floodplains of the Murray-Darling Basin in southeastern Australia have been altered in many ways by livestock grazing, by the introduction of exotic fish, and by changes to flooding regimes. These changes have led to declines in wetland condition and hence to the availability of habitat for wetland frogs. This study examined relationships between frogs, wetland condition and livestock grazing intensity at 26 wetlands on the floodplain of the Murrumbidgee River. Frog communities, species richness, and some individual species of frogs declined with increased grazing intensity. Wetland condition also declined with increased grazing intensity, particularly the aquatic vegetation and water quality components. There were clear relationships between frog communities and wetland condition, with several taxa responding to aquatic and fringing vegetation components of wetland condition. Thus, grazing intensity appeared to influence frog communities through changes in wetland habitat quality, particularly the vegetation. Reduced stocking rates may result in improved wetland condition and more diverse frog communities. River management to provide natural seasonal inundation of floodplain wetlands may also enhance wetland condition, frog activity and reproductive success.     

Soil–landscape relationships at the lower reaches of a watershed at Bear Creek near Oak Ridge,Tennessee

The watersheds at Bear Creek, Oak Ridge, TN, have similar soil–landscape relationships. The lower reaches of many of these watersheds consist of headwater riparian wetlands situated between sloping non-wetland upland zones. The objectives of this study are to examine the effects of (i) slope and geomorphic processes, (ii) human impacts, and (iii) particular characteristics of soils and saprolite that may effect drainage and water movement in the wetlands and adjacent landscapes in one of these watersheds. A transect was run from west to east in a hydrological monitored area at the lower reaches of a watershed on Bear Creek. This transect extended from a steep side slope position across a floodplain, a terrace, and a shoulder slope. On the upland positions of the Nolichucky Shale, mass wasting, overland flow and soil creep currently inhibit soil formation on the steep side slope position where a Typic Dystrudept is present, while soil stability on the shoulder slope has resulted in the formation of a well-developed Typic Hapludult. In these soils, argillic horizons occur above C horizons on less sloping gradients in comparison to steeper slopes, which have Bw horizons over Cr (saprolite) material. A riparian wetland area occupies the floodplain section, where a Typic Endoaquept is characterized by poorly drained conditions that led to the development of redoximorphic features (mottling), gleying, organic matter accumulation, and minimal development of subsurface horizons. A thin colluvial deposit overlies a thick well developed Aquic Hapludalf that formed in alluvial sediments on the terrace position. The colluvial deposit from the adjacent shoulder slope is thought to result from soil creep and anthropogenic erosion caused by past cultivation practices. Runoff from the adjacent sloping landscape and groundwater from the adjacent wetland area perhaps contribute to the somewhat poorly drained conditions of this profile. Perched watertables occur in upland positions due to dense saprolite and clay plugging in the shallow zones of the saprolite. However, no redoximorphic features are observed in the soil on the side slope due to high runoff. Remnants of the underlying shale saprolite, which occur as small discolored zones resembling mottles, are also present. The soils in the study have a CEC of <10 cmol kg⁻¹, silt loam textures and Fe_d values of 0.5–4.3%. These soils are also mainly acidic and low in total carbon.     

Impacts of a Hawaiian marine protected area network on the abundance and fishery sustainability of the yellow tang, Zebrasoma flavescens

Marine protected areas can enhance fish stocks within their boundaries, but the circumstances in which they might also supplement stocks or enhance fisheries outside their boundaries are less clear. Using visual survey and fishery data, we assess the impacts of increasing fishing effort, and of the establishment in Hawaii of a network of areas closed to aquarium fishing, on the prime-target species, yellow tang (Zebrasoma flavescens), and draw conclusions about MPA impacts on long-term fishery sustainability. Between 1999, when 27.8% of the coastline was closed to collecting, and 2007, the number of active fishers and total catch of yellow tang doubled. Prior to MPA establishment, yellow tang densities were similar at sites open to fishing and those slated for closure. By 2007, closed areas had five times the density of prime targeted sized fish (5-10 cm), and 48% higher density of adults than open areas. Densities of adults in ‘boundary’ areas (open areas <1 km from nearest MPA boundary) were significantly higher than in open areas far from MPA boundaries, which was indicative of spillover at that scale. Given the long life-span of yellow tang (>40 years) relative to the duration of protection and the increasing intensity of fishing, the likelihood is that protected areas will become increasingly important sources for the adult fishes which will sustain stocks and the fishery over the longer term.     

Effects of Key deer herbivory on forest communities in the lower Florida Keys

Ungulate herbivory can have strong impacts on plant communities, but these impacts are rarely considered in recovery plans of endangered species. This study examined the effects of the endangered Key deer (Odocoileus virginianus clavium) on its environment in the lower Florida Keys. The Key deer population has increased to over 700 deer from approximately 50 deer in the 1950s; however, approximately 75% of the population resides on only a few islands (Big Pine, No Name, Big Munson) where Key deer herbivory on forest communities may be substantial. Effects of deer herbivory on plant densities were estimated on these islands using vegetation quadrats in hardwood hammock, buttonwood transition, and mangrove wetlands and compared to nine other islands with intermediate or low deer densities. On islands with high deer density, densities of preferred woody plant species <1.2 m tall (within Key deer reach) were significantly lower than islands with lower deer densities, while densities of some nonpreferred species were significantly higher. Deer exclosures established in hardwood hammock on a high-density deer island revealed a mean increase in abundance/height of preferred woody species inside exclosures, while nonpreferred species significantly increased in open plots. We conclude that on high deer density islands, highly preferred plant species might eventually fail to regenerate and unpalatable plant species may become dominant. Careful criteria need to be developed to maintain Key deer numbers above an endangered species status yet below levels that are destructive to local forest species.     

Using habitat models to determine conservation priorities for pond-breeding amphibians in a privately-owned landscape of northern Idaho, USA

As rural landscapes experience increasing levels of residential development, the persistence of species that rely on them will depend on informed planning and management decisions. An understanding of habitat requirements is essential for setting priorities and developing landscape-level plans for the survival of these species. In many temperate rural landscapes, artificially created ponds may be the only wetlands available for aquatic reproduction by amphibians. The introduction of non-native fish into these ponds reduces survival and prohibits successful reproduction of many native pond-breeding amphibians. We surveyed 105 randomly selected wetlands in a primarily privately-owned, rural landscape in north Idaho, USA, for pond-breeding amphibian larvae in 2004 and 2005. We used an information theoretic multimodel inference and an algorithmic (random forests) approach to model habitat for each species based on local and landscape characteristics. We also used a mail survey to quantify how landowners value fish in their wetlands and their plans for future wetland development and fish stocking. Sixty-seven percent of pond owners reported that fishing in their pond was at least slightly important to them and 36% of owners indicated that they were at least 50% likely to add fish to their ponds in the next 5-10 years. Landscape change predictions for this area indicate that forests will become more open due to thinning; habitat models indicated that this is likely to be detrimental to long-toed salamanders and beneficial to Pacific treefrogs. Habitat models also indicate that Columbia spotted frog breeding sites consist of wetlands on flat ground with high solar insolation and that this species is sensitive to nearby development, indicating that as this landscape becomes further developed, this species may require habitat protection for persistence.     

浙江省近海渔运船转载信息提取

渔运船是从事渔获物运输的专用船舶,能够提高捕捞渔船作业效率,增加捕捞渔船的作业强度。为掌握渔运船在海上的转载情况,从而间接了解捕捞渔船作业强度,该研究提出一种基于北斗船位数据的以设定航速阈值、距离阈值和时间阈值来提取渔运船转载信息的方法。如果渔运船和捕捞渔船距离小于50 m,且期间有持续3条以上的船舶监控系统(Vessel Monitoring Systems,VMS)记录,则认为可能发生了1次转载,并记录下相遇的时长、船名、空间位置。以浙江省为例,利用该方法从2018年浙江省的北斗船位数据中提取渔运船的海上转载信息,并进行统计分析。结果表明,有转载记录的渔运船808条,参与转载的捕捞渔船3 548条,共转载28 916次。渔运船停船转载占比21.0%,以1～1.4 m/s低速航行的作业状态转载占比53.7%,转载时长小于12.5 min的占比81.3%,同时得到渔运船转载的热点分布,转载累积时长最长的空间网格为122.5°E～123°E,31.5°N～32°N,转载累积时长187 h,其次为122°E～122.5°E,28°N～28.5°N,转载累积时长150h。通过分析渔运船海上转载位置和转载累积时长的空间分布情况可掌握捕捞渔船作业的时空变化特点,为渔业限额捕捞精细化管理提供依据。     

Environmental Mobility of Radiocaesium in the Pripyat Catchment,Ukraine/Belarus

Evidence from research in the Pripyat catchment, reviewed here, indicates that under the ecological conditions prevalent in this area, radiocaesium (137Cs) is highly mobile in both river water and poorly drained organic soils. Data collected at three different spatial and temporal scales demonstrate the effects of hydrological events on 137Cs mobility. During the period 1988–1994, 137Cs contamination in some poorly drained organic soils in the Pripyat catchment and in the milk from cows grazing on these soils are generally declining much faster than the radioactive half life. However, sharp increases in levels of 137Cs in both floodplain soils and milk to 2–3 times that observed immediately after the initial deposition have been measured immediately after summer floods. The processes causing these observed changes have not yet been fully explained but the sites where enhanced 137Cs mobility has been detected are clearly associated with the spatial patterns of organic soils and river flooding.     

降雨侵蚀力对河岸滩区耕地土壤养分流失的影响

河岸滩区的人类农业活动最为直接地影响着河流的水文生态.自1997年小浪底水利枢纽工程成功截流以来,下游孟津扣马黄河滩区1 955hm2的天然滨河湿地有72%常年出露.为当地农业开发提供了原生动力.在10 a期间滩区的土地利用状况也发生了明显的改变,其中28.8%转变成鱼塘-荷花塘等人工湿地,39.8%转变成小麦棉花等旱地农作物,剩下的328 hm2的河床湿地因受农业活动的影响,正发生着严重的退化和萎缩.通过野外定位观测,对孟津黄河滩区河岸耕地土壤养分随降雨径流流失的特征进行了研究.研究结果表明,次降雨侵蚀力(R)是影响径流量和土壤养分流失的重要因素.在弱侵蚀力下,产生的径流以蓄满产流为主;当降雨侵蚀力大于19.0,产生的径流以超渗产流为主.径流土壤养分流失量与次降雨侵蚀力之间存在明显的二次曲线关系.根据滩区土壤的渗透特征,在次降雨侵蚀力R=10.0～45.0之间的中等强度降雨将产生较为严重的土壤养分流失.并强调河岸带的水土保持工作应亟待加强.     

Apparent Rapid Loss of Endocrine Disruptors from Wetlands Used to Store Either Tertiary Treated Sewage Effluent or Stormwater Runoff

The disruption of endocrine systems due to environmental contaminants potentially impacts on the developmental, behavioural, regulatory and reproductive systems of animals. A major source of exposure of animals (terrestrial and aquatic) to endocrine-disrupting compounds is through contact with contaminated surface waters contaminated with sewage effluent and/or stormwater discharge. We studied the response to endocrine-disrupting compounds of Gambusia holbrooki mosquito fish resident of wetlands that were used for the storage of either treated sewage effluent or stormwater runoff. We found that fish from wetlands that received polluted waters directly from the source (treated sewage effluent or stormwater runoff) demonstrated a morphological response consistent with endocrine disruption. In contrast, fish in the second in the series of wetlands that housed treated sewage effluent did not show evidence of such response. However, those from the second in the series of stormwater receiving wetlands did display a morphological response, although it could be considered milder than was observed in fish from the first in this effluent stream. Fish were also smaller in the wetland that received sewage effluent directly from the sewage treatment plant than elsewhere. Although the differences were not statistically significant, the average size of fish in the first in the series of stormwater wetlands were also small and second only to those in the first sewage effluent wetland.     

The hydrological impacts and sustainability of wetland drainage cultivation in Illubabor,Ethiopia

Wetlands are critical resources in the highlands of southwest Ethiopia, where they perform numerous environmental functions and provide a range of benefits for local communities. In recent years, however, an increase in the drainage and cultivation of these areas and reports of wetland degradation have raised concerns over the sustainability of wetland agriculture. This paper presents the results of a study in which groundwater levels were monitored in a series of wetlands undergoing different stages of drainage and cultivation, to establish the hydrological changes taking place as a consequence. The results suggest that drainage and cultivation induce extreme spatial and temporal variations in the wetland watertable. This is linked in part to structural and chemical changes in the wetland soil which affect hydraulic conductivity. Statistical analysis of this variability revealed the existence of wetland subunits, exhibiting specific hydrological behaviour, which may reflect the influence of current and past land use. Although degradation of these wetlands does occur, many wetland users are aware of their impacts and have developed practices which, in most cases, prevent overdrainage to the extent that the wetlands cannot support agriculture. In this respect, it is argued that wetland use remains hydrologically sustainable, although this ultimately rests upon the ability of communities to continue to develop and apply their indigenous wetland management practices under rapidly changing environmental, socio‐economic and political conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Effectiveness of five small Philippines’ coral reef reserves for fish populations depends on site-specific factors, particularly enforcement history

Community-managed, no-take marine reserves are increasingly promoted as a simple, precautionary measure to conserve biodiversity and sustain coral reef fisheries. However, we need to demonstrate the effects of such reserves to those affected by the loss of potential fishing grounds and the wider scientific community. We surveyed changes in fish communities in five small marine reserves in the central Philippines and three distant Control sites over seven years. We conducted underwater visual censuses of 53 fish families within the reserve (Inside), with a kilometre of the boundary (Outside) and at Control sites. We found significant differences between fish communities Inside and Outside the reserve only at the two sites with strictest compliance with fishing prohibition, while there were significant differences to distant Control sites in all cases. The strongest responses to reserve protection were found in predatory fishes (groupers and breams) and in butterflyfish. Other abundant fish families showed weak effects of protection. For all taxa analysed, we found significant effects of reserve Site and Site × Treatment interactions. The detection of fish responses to reserves is complicated by potential spillover effects, site-specific factors, particularly compliance, and the difficulty of identifying appropriate control areas.     

Conservation value of variable connectivity: aquatic invertebrate assemblages of channel and floodplain habitats of a central Australian arid-zone river, Cooper Creek

Rapidly expanding water resource development in arid and semi-arid zones of Australia threatens the flow regime and ecological integrity of the few large dryland rivers and their immense floodplains. Efforts to manage and conserve the surface waters of these rivers are hampered by limited scientific data on the ecology of their flora and fauna and on their responses to the high natural variability of flow regime that typifies dryland rivers. Irregular floods connect channel and floodplain wetlands to differing degrees and for varying periods of time but the ecological significance of this connectivity is poorly understood. On Cooper Creek, a large dryland river in central Australia, we explored the degree to which assemblage composition varied with connectivity and hydrological regime. Shortly after protracted regional flooding, we sampled aquatic macroinvertebrate assemblages from the principal microhabitats in 12 channel and floodplain wetlands. Ephemeral and temporary lakes tended to have fewer taxa than semi-permanent channel or terminal lake habitats. Although hydrological connection had only recently been lost for some wetlands, there was already evidence of divergence in aquatic macroinvertebrate assemblage composition. Disruption of the natural variability in connectivity and hydrological regime by excessive water abstraction or river-flow regulation threatens the ecological integrity and aquatic macroinvertebrate biodiversity of dryland rivers. Preservation of the irregular flow regime and sporadic connectivity underpins conservation of the mosaic of floodplain wetlands that play such a crucial role in the ecosystem functioning of rivers such as Cooper Creek.     

Agricultural Diffuse Nutrient Pollution Transport in a Mountain Wetland Complex

Wetlands in mountain environments provide critical ecosystem services but are increasingly threatened by agricultural land use intensification. This study evaluates agricultural nonpoint source nutrient pollution transport in a wetland–stream–lake complex in a mountain, tussock grassland catchment in the South Island, New Zealand. Flow and water-quality monitoring in the Lake Clearwater catchment during three flow events from May to August 2010 (autumn high flow, winter low flow, and winter high flow) showed high concentrations and exceedances of water quality guidelines for total nitrogen (TN) and total phosphorus (TP) in small ephemeral streams draining agricultural land during high flows. Concentrations were attenuated through the wetlands to below guidelines, with the exception of TN which still remained slightly higher. Most TN was in the organic form above and below the wetland, suggesting N sources from animal waste/agricultural land and organic material and vegetation within the wetland. Most TP was particulate associated with suspended solids during high flows. Dissolved forms of N and P generally were below guidelines. Flows and loads (instantaneous and daily) increased at the lake outlet during winter high flow, indicating unaccounted sources to the lake from groundwater, the wetlands, or the lake sediments, and seasonal N saturation. Infiltration losses to shallow groundwater along the main perennial tributary likely re-appear as discharge to the wetlands and lake downstream. Surface–groundwater interactions play a dominant role in N transport to the wetland complex due to highly permeable soils and glacial alluvial deposits. Loads and unit loads of TN and TP were also elevated in the ephemeral streams. Results show that TN and TP concentrations and unit loads during high flows in ephemeral streams in this mountain grassland catchment are similar to, or higher than, values for impacted lowland pasture catchments. Although impacts to the wetland ecosystem have not been observed to date, the lake is shifting toward a mesotrophic state, and further research is needed to elucidate impacts of nutrient loads and help meet conservation and restoration goals.     

Evidence for a depth refuge effect in artisanal coral reef fisheries

Natural refuges can play a fundamental role in protecting species from overexploitation but have not been adequately quantified in the marine environment. We quantified the effect of a depth refuge on all fish species in an artisanal coral reef fishery in Zanzibar, Tanzania by comparing changes in fish species richness and relative abundance with depth at five fished and three unfished reefs across the region. Commercial species richness was depleted by 15.1% at shallow depths in fished reefs, but there was no difference between the reefs deeper than seven metres. Non-commercial species were not affected by fishing or depth. Evidence for similar patterns in fish communities in other countries and depth-limitations to artisanal fishing methods imply this effect is widespread. The depth refuge effect could be sustaining coral reef fisheries and should be taken in to account before implementing policies or subsidies that encourage or allow fisheries to exploit deeper waters.     

Fishers’ perception of a 35-year old exclusive Fisheries Management Zone

Fishers’ attitudes and perceptions are critical for the success of fisheries protection areas with their associated biota, and a failure to understand fishers’ behaviour may undermine the success of such fisheries management measures. In this study, we examine fishers’ perception of a long-established exclusive fisheries zone around Malta and to investigate if the perceptions depend on fishers’ demographic, economic, social characteristics and fishing activity of the fishers. A questionnaire survey was undertaken to evaluate the demographic characteristics, economic situation (costs and revenue) and fishers’ activity and behaviour, together with their perception of the Fisheries Management Zone (FMZ). A total of 241 interview responses were analysed which was a response rate of 60%. The perception of most fishers was that the establishment of the FMZ has had an overall negative impact on their fishing activity and that the zone is not important for the protection of local fish stocks. When asked about the beneficial effect of the zone for fishers, most fishers from all backgrounds said that the zone does not benefit commercial fishers, but benefits mainly recreational fishers. The most evident differences in the perceptions and attitudes were between the full-time, part-time and recreational fishers. Fishers that have been fishing for more than 35 years and fishers from the main fishing village also had different attitudes from other fishers towards the FMZ. The results of this study suggest that the proportion of individual income derived from fishing was the strongest factor that influenced attitudinal differences, with home port and fishing experience having less important effects. The main differences in attitude among fishers were related to the protection and conservation effects of the zone, enhancement of resources and conflicts among user groups. The heterogeneity among fishers’ attitudes revealed by the present study has important implications for the implementation of spatial closures. Some sectors of stakeholders may require additional incentives to accept restrictions on access if spatial management is to achieve its intended objectives.     

Natural versus artificial- wetlands and their waterbirds in Sri Lanka

As natural wetlands have disappeared around the world, artificial wetlands have increased. We found interesting differences in waterbird communities of two natural (Bundala Ramsar site) and seven artificial wetlands (irrigation tanks, salt ponds, rice paddies) in south-east Sri Lanka. Eight species exclusively used natural and one species artificial wetlands. Migratory species (shorebirds 64%, terns 47%) dominated species’ richness of natural lagoons, with densities of shorebirds 3-6 times greater than on artificial wetlands. Contrastingly, resident species (dabbling ducks, gallinules) contributed most to the diversity (59%) and density of waterbirds on artificial irrigation tanks. Cattle egrets dominated waterbird density (>70%) of rice paddies. Waterbird communities reflected physical and chemical character of wetlands: natural wetlands were shallow (<2 m) and saline (EC > 1000 msm⁻¹) compared to deep (>2 m) and freshwater (EC < 110 msm⁻¹) artificial wetlands. Artificial inputs of water drained into the natural Embilikala lagoon changing its physico-chemical profile and disrupting the natural seasonal drying. Consequently its waterbird community was similar to artificial irrigation tanks, with shorebird species particularly impacted: densities half that of the other natural lagoon. Artificial salt ponds had similar physico-chemical properties to the natural Bundala lagoon and a similar waterbird community. Even though artificial wetlands supported waterbirds, they were not adequate replacements for loss of natural wetlands, favouring some species. Imposed hydrological stability degraded habitat quality for migratory shorebirds on one of our Ramsar site lagoons.     

Spatial distribution characteristics of organic matter and total nitrogen of marsh soils in river marginal wetlands

Contents of soil organic matter (SOM) and total nitrogen (TN) in the surface soils and subsurface soils were measured in five types of floodplains classified with different flood frequencies in river marginal wetlands of Erbaifangzi, China, in 1999. Contour maps and profile maps were constructed to describe the spatial distribution of SOM and TN in order to identify the influences of flood frequency on them. Results showed that spatial distributions of both SOM and TN were very similar in soil profiles (0–120 cm) of the five areas, decreasing gradually with depth except an accumulation peak in the flooded floodplain (B area). Also, the accumulation peak in the soil profile of B area was relevant to water table, nitrogen leaching, denitrification and mineralization. However, their horizontal distributions in surface soils (0–10 cm) were different in the five areas. Although the flood could bring the deposit of nutrients and sands, the highest content of SOM or TN did not appear in B area but in the floodplain with certain flood frequency. For example, SOM content (6.76%) in 5-year floodplain wetland was highest, and the highest content of TN (3666.4 mg/kg) appeared in 1-year floodplain wetland. However, SOM and TN contents in soils of B area were 4.08% and 2605.4 mg/kg, respectively. Soil clay content, wetland plant (Phragmites australis) litter inputs, soil moisture and water table greatly affected the spatial distribution of SOM and TN in floodplain wetlands. The ratios of carbon to nitrogen of wetland soils in this region were relatively lower than those in paddy soils. SOM and TN contents were significantly correlated with total phosphorus (TP) contents in floodplain wetlands except the 100-year floodplain wetland, but they were significantly influenced by soil pH values only in B area. Denitrification and ammonia volatilization were the main mechanisms resulting in nitrogen loss of surface soils in B area. Flood frequency significantly influenced the ecological functions such as nutrient retention and water quality maintenance of floodplains.     

Effect of hydrologic regime and forest age on Collembola in riparian forests

The principal objective of the study was to assess factors of primary importance for collembolan community variability measured in riparian forest stands of different age after traditional clear cutting within natural and altered hydrologic regimes. The study was conducted in the Ukrainian part of the Latorica river floodplain where the largest stands of the highly protected medio-European Querco—Ulmetum minoris fluvial forests can be found. Six oak forest stands were investigated on the river floodplain: three in a natural section (inside levee) of the floodplain, which have their original features preserved with periodical inundation, and three in a section separated by a flood control embankment (outside levee) and subjected to serious damage by drainage. In each section the three stands sampled were represented by different ages regenerated with clear-cutting (>3 years, >8 years and >112 years).Differences in hydrologic regimes were central to identification of a predictable and explainable percentage of variation in species composition of Collembola communities in fluvial forests. The hydrologic regime factor was correlated with the basic structural attributes of collembolan communities, such as abundance, species richness and some ecological traits. Season accounted for a higher degree of variation in collembolan communities than did the age of forest stands. We conclude that differences in hydrologic regime are of much higher importance in structuring collembolan communities in riparian forests than are the ages of stands.     

Lowered water table causes species substitution while nitrogen amendment causes species loss in alpine wetland microbial communities

Alpine wetlands are hotspots of carbon (C) storage and methane emission, and they could be key contributors to global warming. In recent years, rapid warming has lowered the water table in alpine wetlands on the Tibetan Plateau, concurrent with intensified nitrogen (N) deposition via anthropogenic activities. We carried out a field experiment to investigate the ecological impacts of these two factors on soil bacterial and functional communities, which are essential drivers of greenhouse gas emissions. Nitrogen amendment alone decreased the phylogenetic alpha-diversity of bacterial communities which could be offset by lowered water table. In contrast, microbial functional alpha-diversity, revealed by a high-throughput microarray, remained unchanged. Both bacterial and functional beta-diversity responded to lowered water table, but only bacterial community responded to N amendment. The alpha-Proteobacteria, beta-Proteobacteria, and Bacteroidetes were the major responsive bacterial lineages, and C degradation, methanogenesis, alkaline shock, and phosphorus oxidation were the major responsive functional processes. Partitioning analysis revealed that N amendment changed bacterial community structure mainly via species loss processes but did not affect bacterial functional communities, with soil pH and ammonium as the key factors influencing changes in bacterial community structure. Conversely, lowered water table altered bacterial and functional communities through species substitution processes linked to soil pH and soil moisture. According to our results, the response mechanisms of microbial communities to lowered water table and N amendment are fundamentally different in alpine wetlands.     

Deforesting the riverscape: the effects of wood on fish diversity in a Venezuelan piedmont stream

While deforestation of tropical ecosystems has been shown to have significant impacts on terrestrial habitats, its effects on aquatic habitats are poorly studied. Deforestation dramatically reduces the input of woody debris to streams, and given the importance of large woody debris to fish communities in temperate streams, this might be one mechanism by which logging could affect aquatic ecosystems in the tropics. To examine the effects of large woody debris on the diverse fish assemblage of a tropical stream, we surveyed pools with and without wood at Rio Las Marias, Venezuela. Pools containing wood contained greater numbers of individuals and more species of fish than pools without wood, and the two types of pools differed in their composition. To test whether these results were due to the presence of woody debris, we conducted an experimental wood addition. Pools to which wood was added showed marked increases in both fish abundance and species richness relative to wood-free pools, and the composition of the fish assemblage in experimental pools approached that of pools with naturally occurring woody debris. These results demonstrate that large woody debris plays a major role in structuring fish communities in tropical streams. As a consequence, logging practices that reduce the input of woody debris to tropical streams or directly remove wood from streams could have serious impacts on aquatic habitats, affecting both the diverse fish communities and local economies dependent on stream fisheries.