Fine‐scale genetics of subterranean syncarids

相似文献   

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi‐arid coastal ecosystem

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi‐arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water‐use functional types? We examined a suite of physiological parameters and water‐uptake depths of the dominant, functionally distinct woody vegetation along a water‐table depth gradient in a Mediterranean semi‐arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water‐source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi‐arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi‐arid coastal ecosystems to groundwater drawdown.     

Impact of groundwater abstraction on a Banksia woodland, Swan Coastal Plain, Western Australia

Summary The Gnangara Groundwater Mound, centred 38 km north of Perth, Western Australia, is a large, shallow unconfined aquifer that is currently under abstraction as part of the public metropolitan water supply. To investigate the impact of lowering groundwater levels on a Banksia woodland on the Mound, vegetation monitoring near a groundwater abstraction bore (known as P50) began 1 year before becoming operational. In February 1991, 2 years after abstraction commenced, extensive death of the Banksia overstorey was observed within close proximity of the bore, following a short period of high summer temperatures. The site was subsequently revisited and the understorey floristic composition, abundance and vigour of overstorey species resurveyed, and compared with data collected from a site under long‐term monitoring and not currently influenced by abstraction. A lowering of groundwater level by 2.2 m at P50 between the summers of 1990 and 1991, resulting from the cumulative effects of abstraction and below average annual rainfall (low groundwater recharge), coincided with a loss of between 20 and 80% of adults of overstorey species and up to 64% of adults of understorey species within 200 m of the bore. Over a similar time period no significant decreases in the abundance of overstorey or understorey species were recorded in the monitored site not influenced by groundwater abstraction. Of the overstorey species, Holly‐leaf Banksia (Banksia ilicifolia) displayed the greatest susceptibility and lowest net recovery following the abstraction event at P50. The negative impact of groundwater drawdown on Holly‐leaf Banksia populations makes this overstorey species an important indicator of decreasing groundwater levels on the Gnangara Groundwater Mound. Water stress may have been the primary cause of vegetation death in close proximity to the P50 bore, although this would have been exacerbated by extreme summer temperatures (> 45°C) recorded during February 1991. The P50 scenario represents a localized response to an acute drawdown event, in association with other environmental factors, and provides invaluable information on the assessment of groundwater abstraction and poor groundwater recharge events on a Banksia woodland community. However, there are limitations in using the community response at P50 to manage the impact of drawdown events on other plant communities occurring on sandy, shallow aquifers.     

Dynamics of phreatophyte root growth relative to a seasonally fluctuating water table in a Mediterranean-type environment

While seasonal redistribution of fine root biomass in response to fluctuations in groundwater level is often inferred in phreatophytic plants, few studies have observed the in situ growth dynamics of deep roots relative to those near the surface. We investigated the root growth dynamics of two Banksia species accessing a seasonally dynamic water table and hypothesized that root growth phenology varied with depth, i.e. root growth closest to the water table would be influenced by water table dynamics rather than surface micro-climate. Root in-growth bags were used to observe the dynamics of root growth at different soil depths and above-ground growth was also assessed to identify whole-plant growth phenology. Root growth at shallow depths was found to be in synchrony with above-ground growth phenophases, following increases in ambient temperature and soil water content. In contrast, root growth at depth was either constant or suppressed by saturation. Root growth above the water table and within the capillary fringe occurred in all seasons, corresponding with consistent water availability and aerobic conditions. However, at the water table, a seasonal cycle of root elongation with drawdown in summer followed by trimming in response to water table rise and saturation in winter, was observed. The ability to grow roots year-round at the capillary fringe and redistribute fine root biomass in response to groundwater drawdown is considered critical in allowing phreatophytes, in seasonally water-limited environments, to maintain access to groundwater throughout the year.     

Systematic Conservation Planning for Groundwater Ecosystems Using Phylogenetic Diversity

Aquifer ecosystems provide a range of important services including clean drinking water. These ecosystems, which are largely inaccessible to humans, comprise a distinct invertebrate fauna (stygofauna), which is characterized by narrow distributions, high levels of endemism and cryptic species. Although being under enormous anthropogenic pressure, aquifers have rarely been included in conservation planning because of the general lack of knowledge of species diversity and distribution. Here we use molecular sequence data and phylogenetic diversity as surrogates for stygofauna diversity in aquifers of New South Wales, Australia. We demonstrate how to incorporate these data as conservation features in the systematic conservation planning software Marxan. We designated each branch of the phylogenetic tree as a conservation feature, with the branch length as a surrogate for the number of distinct characters represented by each branch. Two molecular markers (nuclear 18S ribosomal DNA and mitochondrial cytochrome oxidase subunit I) were used to evaluate how marker variability and the resulting tree topology affected the site-selection process. We found that the sites containing the deepest phylogenetic branches were deemed the most irreplaceable by Marxan. By integrating phylogenetic data, we provide a method for including taxonomically undescribed groundwater fauna in systematic conservation planning.     

Effects of management works on the interstitial fauna of floodplain aquatic systems (River Rhône, France)

Long-term changes in composition, structure and biodiversity (i.e. taxonomic richness, diversity index, species traits and habitat-affinity) of interstitial assemblages were studied in two floodplain systems: a restored backwater and an artificial drainage canal. Before restoration, the backwater, affected by both terrestrialisation and eutrophication, was weakly populated by a low diversified fauna dominated by walkers, macrofauna, detritivores, and stygoxenes (i.e. taxa that occur incidentally in ground waters) that reproduce biparentally and lack parental care. This backwater displayed an upstream–downstream gradient in response to restoration works. Upstream, the dredging of fine organic sediments favoured inputs of nutrient-poor groundwater and exchanges between groundwater and surface water that induced an increase in taxonomic richness (in both herbivores and stygoxenes). Downstream the deposition of fine sediment that was suspended in the water column by restoration work enhanced colmation that induced a decrease in herbivore and swimming taxa, and an increase in mesofaunal taxa, whilst phreatobites (i.e. taxa specialized to interstitial life) remained absent from the system. The drainage canal that was artificially hollowed-out to lower the surrounding water table, harbors mixed assemblages of epigean (i.e. taxa of surface-water habitats) and hypogean (i.e. taxa of groundwater habitats) taxa. The upstream part, which is weakly influenced by surface waters, was colonized by phreatobites as oligotrophic conditions increased. The intermediate part, which is fed by surface water and where mesotrophic conditions occurred as habitats progressively matured and diversified, showed diversification of its fauna. The downstream part of the drainage canal displayed the reverse dynamic – this suggests a reduction in groundwater supply due to the clogging of sediment interstices fine sediments, the deposition of which is linked to the Rossillon backwater restoration works.     

Groundwater dynamics along forest-marsh transects in a southeastern salt marsh,USA: Description,interpretation and challenges for numerical modeling

Long-term and spatially dense time series of total head measured alongthree forest-marsh piezometer transects across a finger marsh basin,together with bimonthly groundwater salinity measurements, reveal dynamicfeatures that present challenges to the interpretation and modeling of thisshallow water table aquifer. These include:1. Rapid response of forest water table to rain events.2. Daytime lowering (drawdown) of the water table in the forest and highmarsh due to evapotranspiration and its recovery due to rain, seepage ortidal inundation.3. Upward gradients in head along the western margin of the marsh butdownward gradients in the eastern, more seaward, high marsh and forest.4. Rapid head responses to the tide in parts of the high marsh andforest that are not actually inundated.5. Asymmetrical distribution of salinity with higher values in theeastern marsh and forest than in the west.6. Sharp salinity gradients across the tidal creek that bisects the basin. We discuss modeling issues related to these features because acomprehensive understanding of them may have a bearing on patterns ofbotanical zonation and primary production, the transport of nutrients andcontaminants, and the response of this system to sea level rise.     

光合有效辐射与地下水位变化对柽柳属荒漠灌木群落碳平衡的影响

全球气候变化和人类活动的加剧, 正导致古尔班通古特沙漠南缘原始盐生旱生荒漠地区的地下水位发生显著改变。大气污染导致该地区太阳辐射减少。以盐生荒漠建群种多枝柽柳(Tamarix ramosissima)为研究对象, 选择地下水位在2.9-4.5 m波动的典型原始生境, 观测了生长期内光合有效辐射和地下水位变化时的光合作用、蒸腾作用和叶水势等生理活动的季节变化, 调查了根系分布特征; 并利用涡度相关系统测定了生态系统碳水通量, 估算群落碳同化能力、蒸腾耗水量与叶面积指数的季节变化, 旨在揭示光合有效辐射和地下水位等环境因素对柽柳属(Tamarix)荒漠灌木群落光合作用的影响。研究结果表明: 降水造成的潜土层水分状况变化对多枝柽柳的碳平衡没有显著影响。深根系与气孔调节是多枝柽柳碳平衡适应荒漠环境水分状况的两个关键机制。特殊的气孔行为体现了多枝柽柳以高水分消耗为代价将其碳获取最大化的适应对策; 多枝柽柳生理与群落尺度的水分平衡和碳获取均依赖于深根系获取的稳定地下水源, 缓和的地下水位波动将不会扰动其现有的碳/水平衡, 地下水位剧烈下降将危及多枝柽柳的生存。此外, 光合有效辐射是另一个主要影响因素, 与群落碳获取呈显著正相关关系。群落碳同化能力的季节变化是光合有效辐射和地下水位共同影响下光合作用物候学特征的体现。过度开采地下水和直接破坏原生植被的行为, 将会严重地干扰多枝柽柳群落的生存, 进而破坏该区域现有的生态水文过程。     

Phreatophytic vegetation response to climatic and abstraction-induced groundwater drawdown: Examples of long-term spatial and temporal variability in community response

The influence of climatic drought and groundwater abstraction on phreatophytic vegetation dynamics was investigated in the southwest of Western Australia. Two contrasting examples of long-term phreatophytic plant community response to reduced water availability are presented. Multivariate analysis of vegetation and hydrological parameters determined depth to watertable as the dominant biophysical driver of floristic spatial and temporal patterns. Under lower rates of watertable drawdown (9 cm year^?1), a progressive change in floristic composition was observed over a 33-year period. The abundance of species with a preference for wetter sites was significantly reduced, whereas that of more drought-tolerant species increased. Higher rates of drawdown (50 cm year^?1) where groundwater abstraction exacerbated climatic drought resulted in a threshold response in vegetation and 33% dissimilarity to pre-abstraction floristics in 12 years. In the context of an ecohydrological state and transition conceptual model, it is suggested higher rates of groundwater drawdown result in a threshold breach and subsequent transition to an alternative ecohydrological state, whilst lower rates result in a progressive floristic transition.     

Taking eDNA underground: Factors affecting eDNA detection of subterranean fauna in groundwater

Stygofauna are aquatic fauna that have evolved to live underground. The impacts of anthropogenic climate change, extraction and pollution on groundwater pose major threats to groundwater health, prompting the need for efficient and reliable means to detect and monitor stygofaunal communities. Conventional survey techniques for these species rely on morphological identification and can be biased, labour-intensive and often indeterminate to lower taxonomic levels. By contrast, environmental DNA (eDNA)-based methods have the potential to dramatically improve on existing stygofaunal survey methods in a large range of habitats and for all life stages, reducing the need for the destructive manual collection of often critically endangered species or for specialized taxonomic expertise. We compared eDNA and haul-net samples collected in 2020 and 2021 from 19 groundwater bores and a cave on Barrow Island, northwest Western Australia, and assessed how sampling factors influenced the quality of eDNA detection of stygofauna. The two detection methods were complementary; eDNA metabarcoding was able to detect soft-bodied taxa and fish often missed by nets, but only detected seven of the nine stygofaunal crustacean orders identified from haul-net specimens. Our results also indicated that eDNA metabarcoding could detect 54%–100% of stygofauna from shallow-water samples and 82%–90% from sediment samples. However, there was significant variation in stygofaunal diversity between sample years and sampling types. The findings of this study demonstrate that haul-net sampling has a tendency to underestimate stygofaunal diversity and that eDNA metabarcoding of groundwater can substantially improve the efficiency of stygofaunal surveys.     

Stygofauna Abundance and Distribution in the Fissures and Caves of the Nardò (Southern Italy) Fractured Aquifer Subject to Reclaimed Water Injections

The demographic growth in developing countries and the increasing pressure of anthropological activities in industrialized states around the world, are leading to a gradual contamination of the natural habitats of our planet. Although the extent of these effects is unclear, the results can already seen in the quality of natural resources, which are intensely stressed by climate changes (greenhouse effect, nutrients load, water consumption, etc.) and by direct contamination of toxic wastes. This could progressively destroy the variety of faunal species and, indeed, recent warming has caused changes in species distribution and abundance. This paper presents an investigation into the possible effects of climate change and anthropological pressures on the ground water fauna present at the Nardò site (Salento peninsula, Southern Italy). Three ecological categories were examined: stygoxenes, stygophiles and stygobionts. The latter are anophthalmic, without pigment, measure up to 10–12 mm, and live in water which moves throughout fissures and karstic caves of carbonate aquifers. These stygofauna are very sensitive to changes, due to environmental stresses, such as water temperature, dissolved oxygen, water salinity, pH and chemical constituents, in their hypogeous habitat. The stygofauna categories are active organisms which contribute to the biodegradation of organic compounds in wastewater artificially (or naturally) injected in the fractured subsoil. Weak information has been available until now about Salento stygofauna ability to resist water pollution caused by human activities. At the Nardò site 12000 m³/d of 2 ^y effluent from municipal treatment plants have been injected since 1991 in a natural sinkhole. Here, the abundance of the stygofauna, recovered in three wells (Colucci, Brusca and Spundurata cave) at progressive distances from sinkhole, and their distribution have been correlated with ground water constituents. Groundwater quality was monitored on each occasion that stygofauna were collected, during the spring-autumn seasons.     

Is hydrological manipulation an effective management tool for rehabilitating chronically flooded,brackish‐water wetlands?

1. Reinstating more natural water regimes is often a priority intervention to rehabilitate wetlands that have been degraded through anthropogenic changes to their natural wetting and drying cycles. Hydrological interventions are often made in chronically desiccated wetlands but less commonly in wetlands that have been permanently inundated and that require a drawdown phase for rehabilitation. Reports on the effectiveness of reinstating a drawdown phase in chronically inundated wetlands are particularly rare. 2. We undertook a landscape‐scale, experimental drawdown of water levels at Dowd Morass, a large, Ramsar‐listed, brackish‐water wetland in south‐eastern Australia that had been artificially flooded for 30+ years. During the hydrological manipulation, c. 500 ha of the wetland was drawn down and re‐flooded, and the remaining c. 1000 ha was used as a control site. Fringing areas with a fluctuating water regime were used as a reference site. Results were analysed in terms of gradient analysis, by classifying the different water regimes created by the hydrological interventions. The response of wetland vegetation was measured along replicated transects over a 4‐year period, before, during and after drawdown. Wetland plants were assigned to plant functional groups for analysis. Assembly theory and knowledge of life‐history traits were used to predict that drawdown would promote recruitment of plant species that required exposed sediment for germination and seedling establishment. 3. Within‐wetland microtopography interacted with the hydrological interventions to generate three distinct water regimes, which were differentiated by the spatial extent of exposed sediment and duration of the dry period. Drawdown promoted limited recruitment of some plant species, and the survival of cohorts then depended strongly on the extent and duration of the dry period. Species richness and vegetation cover (understorey and overstorey) continued to decline in constantly flooded areas of the wetland. Increased salinisation of sediments and surface waters reduced the effectiveness of the drawdown and dramatically affected species richness and cover of aquatic vegetation, which did not recover fully when fresher conditions returned. 4. The capacity of vegetation to respond to the reinstatement of a drawdown cycle following chronic inundation was constrained by abiotic (e.g. salinity) and biotic (e.g. depauperate seedbanks) factors. Reinstating a dry phase in chronically inundated, brackish‐water wetlands is complex and risky and may not effectively improve vegetation condition in the short term. In the case of Dowd Morass, rehabilitation was most successful in sites that had been shallowly flooded prior to drawdown and that remained dry for longest.     

Subsurface Dwelling Crustaceans as Indicators of Hydrological Conditions,Oxygen Concentrations,and Sediment Structure in an Alluvial Aquifer

The relation between environmental conditions and the species composition and individual abundance of crustaceans was investigated in a shallow alluvial aquifer, located in the Danube wetlands (Lobau, Austria). Samples, consisting of groundwater, sediment, and fauna, were taken from permanent installed wells by means of a piston pump five times in a year cycle. The results show that the spatial and temporal distribution, individual abundance, and species richness of crustacean fauna is related to hydrological conditions, oxygen concentrations, and geologic structures in the alluvial aquifer. Therefore, crustaceans, divided in stygoxene, stygophile, and stygobite species, can be used as bioindicators of these environmental conditions in an aquifer. It is suggested that beside physicochemical analyses also the crustacean fauna should be considered to characterise a groundwater ecosystem.     

Rapid Response of Hydrological Loss of DOC to Water Table Drawdown and Warming in Zoige Peatland: Results from a Mesocosm Experiment

A large portion of the global carbon pool is stored in peatlands, which are sensitive to a changing environment conditions. The hydrological loss of dissolved organic carbon (DOC) is believed to play a key role in determining the carbon balance in peatlands. Zoige peatland, the largest peat store in China, is experiencing climatic warming and drying as well as experiencing severe artificial drainage. Using a fully crossed factorial design, we experimentally manipulated temperature and controlled the water tables in large mesocosms containing intact peat monoliths. Specifically, we determined the impact of warming and water table position on the hydrological loss of DOC, the exported amounts, concentrations and qualities of DOC, and the discharge volume in Zoige peatland. Our results revealed that of the water table position had a greater impact on DOC export than the warming treatment, which showed no interactive effects with the water table treatment. Both DOC concentration and discharge volume were significantly increased when water table drawdown, while only the DOC concentration was significantly promoted by warming treatment. Annual DOC export was increased by 69% and 102% when the water table, controlled at 0 cm, was experimentally lowered by −10 cm and −20 cm. Increases in colored and aromatic constituents of DOC (measured by Abs_{254 nm}, SUVA_{254 nm}, Abs_{400 nm}, and SUVA_{400 nm}) were observed under the lower water tables and at the higher peat temperature. Our results provide an indication of the potential impacts of climatic change and anthropogenic drainage on the carbon cycle and/or water storage in a peatland and simultaneously imply the likelihood of potential damage to downstream ecosystems. Furthermore, our results highlight the need for local protection and sustainable development, as well as suggest that more research is required to better understand the impacts of climatic change and artificial disturbances on peatland degradation.     

Persistence of Water within Perched Basins of the Peace-Athabasca Delta, Northern Canada

The Peace-Athabasca Delta (PAD) is one of the world’s largest freshwater deltas. Many of its shallow (<1.5 m) lakes and wetlands are perched above surrounding waterways. The delta has experienced a number of wetting and drying intervals. The latest drying trend ended in 1996 when high waters, generated under ice-jam and open-water conditions, recharged a number of the perched basins. The objective of this study was to determine the relative importance of hydroclimatic components on the persistence of water. A water-balance model was developed to simulate water-level responses following a flood event. Basin response was tested against a range of historical hydroclimatic conditions that have occurred in the delta during the 20th century. Ponded water duration in a 0.8 m deep perched basin was 5 years for the cool-dry period of the 1920s, slightly longer for the post-1974 flood era, and up to 9 years for the wet conditions of the 1940s and 1950s. Water drawdown occurred in almost every year and was almost exclusively due to evaporation exceeding precipitation. Net groundwater flux was minimal. Given the overlying importance of the floodwater component in the water balance of perched basins, the next step is to investigate the causes, spatial sources and frequency of flooding. This water balance model presented in this paper offers a useful tool for the management of the duration of water in perched wetlands of the PAD, which can help preserve essential habitat for wildlife.     

Biogeographic history of subterranean isopods from groundwater calcrete islands in Western Australia

Groundwater calcretes in arid central Western Australia contain a diverse invertebrate groundwater fauna (stygofauna). Surveys have uncovered a diverse oniscidean isopod subterranean fauna above the water table (troglofauna), including species of a recently described genus Paraplatyarthrus. The aim of this study was to investigate the biogeographic history of Paraplatyarthrus and the timing of transitions from surface to subterranean habitats. Phylogenetic relationships among the isopod troglofauna from 11 groundwater calcretes along three palaeodrainage systems were assessed using one mitochondrial gene, cytochrome c oxidase subunit 1 (COI), and two nuclear markers, lysyl‐tRNA synthetase (LysRS) and 18S rRNA (18S) genes. Phylogenetic analyses revealed multiple sister lineage relationships between troglophile and troglobite lineages and evidence for divergent mtDNA lineages within species, providing a range of nodes for dating evolutionary transitions from surface to subterranean habitats. Relaxed molecular clock analyses provided evidence that evolutionary transitions from surface to subterranean environments took place between 13.3 and 1.75 million years ago, coinciding with the onset of aridification of Australia from the late Tertiary. In cases where groundwater calcretes contained multiple species, the taxa were not closely related phylogenetically, suggesting that these calcretes were independently colonised by multiple ancestral species. The study further confirmed the role of late/post‐Miocene aridification as a key driver of the evolution of subterranean invertebrates in the calcrete islands of Western Australia, supporting the climatic relict hypothesis. Troglobites most likely evolved from the troglophile ancestors that were capable of dispersal among, and active colonisation of, calcretes.     

The boundaries of river systems: the metazoan perspective

1. This overview of metazoans associated with the riparian/groundwater interface focuses on the fauna inhabiting substratum interstices within the stream bed and in alluvial aquifers beneath the floodplain. The objective is to integrate knowledge of habitat conditions and ecology of the interstitial fauna into a broad spatiotemporal perspective of lotic ecosystems. 2. Most aquatic metazoans of terrestrial ancestry, secondarily aquatic forms including insects and water mites (Hydracarina), are largely confined to surface waters (epigean), most of the time penetrating only the superficial interstices of the stream bed. 3. Primary aquatic metazoans include crustaceans and other groups whose entire evolutionary histories took place in water. Some species are epigean, whereas other members of the primary aquatic fauna are true subterranean forms (hypogean ) , residing deep within the stream bed and in alluvial aquifers some distance laterally from the channel. 4. The hypogean/epigean affinities of interstitial animals are reflected in repetitive gradients of species distribution patterns along vertical (depth within the stream bed), longitudinal (riffle/pool), and lateral (across the floodplain) spatial dimensions, as well as along recovery trajectories following floods (temporal dimension). 5. Fluvial dynamics and sediment characteristics interact to determine hydraulic conductivity, oxygen levels, pore space, particle size heterogeneity, organic content and other habitat conditions within the interstitial milieu. 6. Multidimensional environmental gradients occur at various scales across riparian/groundwater boundary zones. The spatiotemporal variability of hydrogeomorphological processes plays an important role in determining habitat heterogeneity, habitat stability, and connectivity between habitat patches, thereby structuring biodiversity patterns across the riverine landscape. 7. The erosive action of flooding maintains a diversity of hydrarch and riparian successional stages in alluvial floodplains. The patchy distribution patterns of interstitial communities at the floodplain scale reflect, in part, the spatial heterogeneity engendered by successional processes. 8. Interstitial metazoans engage in passive and active movements between surface waters and ground waters, between aquatic and riparian habitats, and between different habitat types within the lotic system. Some of these are extensive migrations that involve significant exchange of organic matter and energy between ecosystem compartments. 9. The generally high resilience of lotic ecosystems to disturbance is attributable, in part, to high spatiotemporal heterogeneity. Habitat patches less affected by a particular perturbation may serve as ’refugia ‘; from which survivors recolonize more severely affected areas. Mechanisms of refugium use may also occur within habitats, as, for example, through ontogenetic shifts in microhabitat use. Rigorous investigations of interstitial habitats as refugia should lead to a clearer understanding of the roles of disturbance and stochasticity in lotic ecosystems. 10. Development of realistic ’whole river ‘; food webs have been constrained by the exclusion of interstitial metazoans, which may in fact contribute the majority of energy flow in lotic ecosystems. A related problem is failure to include groundwater/riparian habitats as integral components of alluvial rivers. A conceptual model is presented that integrates groundwater and riparian systems into riverine food webs and that reflects the spatiotemporal complexity of the physical system and connectivity between different components. 11. Interstitial metazoans also serve as ’ecosystem engineers, ‘; by influencing the availability of resouces to other species and by modifying habitat conditions within the sediment. For example, by grazing on biofilm, interstitial animals may markedly stimulate bacterial growth rates and nutrient dynamics. 12. Although there has been a recent surge of interest in the role of interstitial animals in running waters, the knowledge gaps are vast. For example, basic environmental requirements of the majority of groundwater metazoans remain uninvestigated. Virtually nothing is known regarding the role of biotic interactions in structuring faunal distribution patterns across groundwater/riparian boundary zones. Interstitial metazoans may contribute significantly to the total productivity and energy flow of the biosphere, but such data are not available. Nor are sufficient data available to determine the contribution of groundwater animals to estimates of global biodiversity. 13. Effective ecosystem management must include groundwater/riparian ecotones and interstitial metazoans in monitoring and restoration efforts. Evidence suggests that a ’connected ‘; groundwater/riparian system provides natural pollution control, prevents clogging of sediment interstices and maintains high levels of habitat heterogeneity and successional stage diversity. River protection and restoration should maintain or re-establish at least a portion of the natural fluvial dynamics that sustains the ecological integrity of the entire riverine–floodplain–aquifer ecosystem. Keywords: groundwater/riparian ecotones, hyporheic habitat, epigean, hypogean, interstitial fauna, biodiversity, food webs     

新疆塔里木河下游荒漠河岸(林)植被合理生态水位

 该文依据塔里木河下游地下水位多年监测资料, 将地下水位按不同埋深划分为0~2、2~4、4~6、6~8、8~10和>10 m 6个梯度, 并设置植 被调查样方进行连续监测, 以分析地下水位变化对植物物种多样性与种群生态位的影响。研究结果表明: 在地下水位2~4 m时, 物种多样性最高 , 其次为4~6 m, 再次为0~2 m; 当地下水位在6 m以下时, 物种多样性锐减, Hill多样性指数曲线变化趋势趋于平直化。荒漠河岸(林)植被主要 植物种群生态位随着地下水位的逐步下降而扩展, 并在地下水位4~6 m处达到最宽; 尔后, 生态位又显著变窄; 地下水位4~6 m时, 种群间生态 位重叠最不显著, 物种数较为丰富。因此, 该文分析得出结论: 塔里木河下游植被恢复的地下水位应确保达到6 m以上, 大部分地区地下水位应 维持在4~6 m, 而部分河道附近地区地下水位争取达到2~4 m。     

Biogeochemical processes in the groundwater discharge zone of urban streams

The influence of biogeochemical processes on nitrogen and organic matter transformation and transport was investigated for two urban streams receiving groundwater discharge during the dry summer baseflow period. A multiple lines of evidence approach involving catchment-, and stream reach-scale investigations were undertaken to describe the factors that influence pore water biogeochemical processes. At the catchment-scale gaining stream reaches were identified from water table mapping and groundwater discharge estimated to be between 0.1 and 0.8 m³ m^?2 d^?1 from baseflow analysis. Sediment temperature profiles also suggested that the high groundwater discharge limited stream water infiltration into the sediments. At the stream reach-scale, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations were higher in stream water than in groundwater. However, DOC and DON concentrations were greatest in sediment pore water. This suggests that biodegradation of sediment organic matter contributes dissolved organic matter (DOM) to the streams along with that delivered with groundwater flow. Pore water ammonium (NH₄ ⁺) was closely associated with areas of high pore water DOM concentrations and evidence of sulfate (SO₄ ^2?) reduction (low concentration and SO₄:Cl ratio). This indicates that anoxic DOM mineralization was occurring associated with SO₄ ^2? reduction. However the distribution of anoxic mineralization was limited to the center of the streambed, and was not constrained by the distribution of sediment organic matter which was higher along the banks. Lower sediment temperatures measured along the banks compared to the center suggests, at least qualitatively, that groundwater discharge is higher along the banks. Based on this evidence anoxic mineralization is influenced by groundwater residence time, and is only measurable along the center of the stream where groundwater flux rates are lower. This study therefore shows that the distribution of biogeochemical processes in stream sediments, such as anoxic mineralization, is strongly influenced by both the biogeochemical conditions and pore water residence time.     

若尔盖高寒草本沼泽木里薹草叶片碳氮磷化学计量特征对水位下降的响应

2020年6—9月,以若尔盖高原纳勒乔沼泽水位下降模拟控制实验平台为依托,在若尔盖县纳勒乔沼泽原位切割1 m×1 m原状土块,原位抬升20 cm,原位模拟水位下降20 cm,研究湿地植物木里薹草碳氮磷化学计量特征对水位下降的响应。结果表明: 在整个生长季,木里薹草叶片C含量没有显著变化,N、P含量随着生长季的推移逐渐下降。水位下降后,叶片C含量在生长季的变化并不一致,在生长初期、中期水位下降导致C含量增加,生长旺期无显著变化;叶片N含量对水位下降的响应为显著升高,叶片P含量则显著降低。叶片C∶N、C∶P、N∶P在整个生长季内均表现为随季节变化而上升,木里薹草的相对生长速率与叶片C∶N呈显著正相关,与C∶P和N∶P呈显著负相关。水位下降后,叶片C∶N显著降低,C∶P和N∶P显著上升,导致木里薹草的相对生长速率显著降低。水位下降后,叶片P含量降低是木里薹草单叶质量和比叶重下降的主要调控因子。