L. Maurice

The ancient Britons: groundwater fauna survived extreme climate change over tens of millions of years across NW Europe

Global climate changes during the Cenozoic (65.5–0 Ma) caused major biological range shifts and extinctions. In northern Europe, for example, a pattern of few endemics and the dominance of wide‐ranging species is thought to have been determined by the Pleistocene (2.59–0.01 Ma) glaciations. This study, in contrast, reveals an ancient subsurface fauna endemic to Britain and Ireland. Using a Bayesian phylogenetic approach, we found that two species of stygobitic invertebrates (genus Niphargus) have not only survived the entire Pleistocene in refugia but have persisted for at least 19.5 million years. Other Niphargus species form distinct cryptic taxa that diverged from their nearest continental relative between 5.6 and 1.0 Ma. The study also reveals an unusual biogeographical pattern in the Niphargus genus. It originated in north‐west Europe approximately 87 Ma and underwent a gradual range expansion. Phylogenetic diversity and species age are highest in north‐west Europe, suggesting resilience to extreme climate change and strongly contrasting the patterns seen in surface fauna. However, species diversity is highest in south‐east Europe, indicating that once the genus spread to these areas (approximately 25 Ma), geomorphological and climatic conditions enabled much higher diversification. Our study highlights that groundwater ecosystems provide an important contribution to biodiversity and offers insight into the interactions between biological and climatic processes.

Using boreholes as windows into groundwater ecosystems.

Groundwater ecosystems remain poorly understood yet may provide ecosystem services, make a unique contribution to biodiversity and contain useful bio-indicators of water quality. Little is known about ecosystem variability, the distribution of invertebrates within aquifers, or how representative boreholes are of aquifers. We addressed these issues using borehole imaging and single borehole dilution tests to identify three potential aquifer habitats (fractures, fissures or conduits) intercepted by two Chalk boreholes at different depths beneath the surface (34 to 98 m). These habitats were characterised by sampling the invertebrates, microbiology and hydrochemistry using a packer system to isolate them. Samples were taken with progressively increasing pumped volume to assess differences between borehole and aquifer communities. The study provides a new conceptual framework to infer the origin of water, invertebrates and microbes sampled from boreholes. It demonstrates that pumping 5 m3 at 0.4–1.8 l/sec was sufficient to entrain invertebrates from five to tens of metres into the aquifer during these packer tests. Invertebrates and bacteria were more abundant in the boreholes than in the aquifer, with associated water chemistry variations indicating that boreholes act as sites of enhanced biogeochemical cycling. There was some variability in invertebrate abundance and bacterial community structure between habitats, indicating ecological heterogeneity within the aquifer. However, invertebrates were captured in all aquifer samples, and bacterial abundance, major ion chemistry and dissolved oxygen remained similar. Therefore the study demonstrates that in the Chalk, ecosystems comprising bacteria and invertebrates extend from around the water table to 70 m below it. Hydrogeological techniques provide excellent scope for tackling outstanding questions in groundwater ecology, provided an appropriate conceptual hydrogeological understanding is applied.

A tracer methodology for identifying ambient flows in boreholes

Identifying flows into, out of, and across boreholes is important for characterizing aquifers, determining the depth at which water enters boreholes, and determining the locations and rates of outflow. This study demonstrates how Single Borehole Dilution Tests (SBDTs) carried out under natural head conditions provide a simple and cheap method of identifying vertical flow within boreholes and determining the location of in-flowing, out-flowing, and cross-flowing fractures. Computer simulations were used to investigate the patterns in tracer profiles that arise from different combinations of flows. Field tracer tests were carried out using emplacements of a saline tracer throughout the saturated length of boreholes and also point emplacements at specific horizons. Results demonstrated that SBDTs can be used to identify flowing fractures at the top and bottom of sections of vertical flow, where there is a change in vertical flow rate within a borehole, and also where there are consistent decreases in tracer concentration at a particular depth. The technique enables identification of fractures that might be undetected by temperature and electrical conductance logging, and is a simple field test that can be carried out without pumping the borehole.

Stygobitic Invertebrates in Groundwater — A Review from a Hydrogeological Perspective

Abstract Groundwater-adapted species (known as stygobites) provide animportant contribution to biodiversity. Groundwater ecosystems are some of the oldest on earth, and contain many endemic species adapted to live in an environment with no light and limited resources. The controls on stygobite distributions are not yet fully resolved because of the complex interaction between many processes operating at different scales. Many of these processes are geological or hydrogeological in nature and therefore more detailed geological and hydrogeological studies could provide improved understanding of stygobite distributions. Hydrogeologists can assist ecologists by providing expertise on both general geological characteristics of sampling sites, and how groundwater at sampling sites relates to the wider aquifer setting. Geological input would be especially useful in stygobite dispersal studies because dispersal depends upon habitat continuity associated with geological dispersal corridors, and is limited where rocks that do not provide a suitable habitat form geological barriers. Stygobite studies are of benefit to hydrogeology because stygobite distributions can provide information on ground-water-surface water interaction and aquifer connectivity over a range of spatio-temporal scales. Future studies using DNA analysis of stygobites may provide much more detailed information on hydraulic connectivity within and between aquifers. There is also potential for the development of stygobites as indicators of groundwater quality. The biogeochemical function of stygobites is of interest to both hydrogeologists and ecologists. Studies have demonstrated that stygobites graze biofilms and bacteria but their role in biogeochemical cycles is still not fully understood. Ecosystem services provided by groundwater fauna depend upon their abundance and biomass. Future studies using hydrogeological data (e.g. borehole packer techniques) may provide an improved understanding of where in aquifers stygobites live and how many there are, which would be an important step towards assessing the significance of their role in biogeochemical cycling of nutrients and carbon.

Regional-scale drivers of groundwater faunal distributions

Freshwater aquifers are a major source of drinking water. They also possess unique assemblages of organisms. However, little is known about the distributional drivers of obligate groundwater organisms at the regional scale. We examined the distribution and composition of stygobiont assemblages in a complex geological setting and explored the relationship between groundwater fauna, hydrogeology, and water chemistry. In the study area, we grouped similar geologies into 5 hydrogeological formations (hydro-units [HUs]) within which habitats for groundwater fauna were broadly similar. The occurrence of stygobionts differed significantly between HUs. Stygobionts were significantly less likely to be recorded in mudstone/siltstone and sandstone aquifers than in carbonate or igneous/metamorphic rocks. Variance partitioning indicated that HU explained a greater proportion of the variance (7.52%) in the groundwater community than water chemistry (5.02%). However, much of the variation remained unexplained. The macrofaunal stygobiont species in our study area formed 3 groups: 1) Niphargus glenniei was recorded in a range of HUs but only in the western part of the study area. 2) Niphargus kochianus, Niphargus fontanus, Proasellus cavaticus, and Crangonyx subterraneus were predominantly recorded in carbonate aquifers in the eastern part of the study area. 3) Niphargus aquilex and Microniphargus leruthi were found throughout the study area and in a range of HUs. We hypothesize that physical barriers prevent some stygobiont taxa from colonizing apparently suitable geologies. The low-permeability deposits dividing the western and eastern parts of the study area may partly explain the observed distributions.

Defining geo-habitats for groundwater ecosystem assessments: an example from England and Wales (UK)

Groundwater ecosystems comprising micro-organisms and metazoans provide an important contribution to global biodiversity. Their complexity depends on geology, which determines the physical habitat available, and the chemical conditions within it. Despite this, methods of classifying groundwater habitats using geological data are not well established and researchers have called for higher resolution habitat frameworks. A novel habitat typology for England and Wales (UK) is proposed, which distinguishes 11 geological habitats (geo-habitats) on hydrogeological principles and maps their distribution. Hydrogeological and hydrochemical data are used to determine the characteristics of each geo-habitat, and demonstrate their differences. Using these abiotic parameters, a new method to determine abiotic habitat quality is then developed. The geo-habitats had significantly different characteristics, validating the classification system. All geo-habitats were highly heterogeneous, containing both high quality habitat patches that are likely to be suitable for fauna, and areas of low quality that may limit faunal distributions. Karstic and porous habitats generally were higher quality than fractured habitats. Overall, 70% of England and Wales are covered by lower quality fractured habitats, with only 13% covered by higher quality habitats. The main areas of high quality habitats occur in central England as north–south trending belts, possibly facilitating dispersal along this axis. They are separated by low quality geo-habitats that may prevent east-west dispersal of fauna. In south-west England and Wales suitable geo-habitats occur as small isolated patches. Overall, this paper provides a new national-scale typology that is adaptable for studies in other geographic areas.RésuméLes écosystèmes des eaux souterraines comportant des micro-organismes et des métazoaires contribuent fortement à la biodiversité globale. Leur complexité dépend de la géologie, qui détermine l’habitat physique disponible et son état chimique. Malgré cela, les méthodes de classification des habitats des eaux souterraines à l’aide de données géologiques ne sont pas bien établies et les chercheurs appellent à des cadres pour une détermination de plus haute résolution des habitats. Une typologie innovante pour l’Angleterre et le Pays de Galles (Royaume-Unis) est proposée, distinguant 11 habitats géologiques (géo-habitats) basés sur des principes hydrogéologiques. La distribution de ces habitats est également cartographiée. Des données hydrogéologiques et hydrochimiques sont utilisées pour déterminer les caractéristiques de chacun des géo-habitats, et démontrer les différences entre habitats. En utilisant ces paramètres abiotiques, une nouvelle méthode pour déterminer la qualité abiotique de l’habitat a ainsi été développée. Les géo-habitats ont des caractéristiques suffisamment différentes pour permettre la validation du système de classification. Tous les géo-habitats sont fortement hétérogènes, contenant à la fois des îlots d’habitats de très bonne qualité pour la faune et des secteurs de faible qualité pouvant limiter le développement de la faune. Les habitats karstiques et poreux sont généralement de meilleure qualité que les habitats fracturés. En tout, 70% de l’Angleterre et du Pays de Galles sont couverts par des habitats fracturés de faible qualité, avec seulement 13% couverts par des habitats de haute qualité. Les principaux secteurs d’habitats de haute qualité se situent au centre de l’Angleterre s’étendant du nord au sud, facilitant sans doute une certaine dispersion le long de cet axe. Ces secteurs sont séparés par des géo-habitats de faible qualité qui limitent sans doute la dispersion de la faune selon un axe est-ouest. Au sud-ouest de l’Angleterre et du Pays de Galles les géo-habitat adéquats se retrouvent en petits îlots isolés. D’une manière générale, ce papier propose une nouvelle typologie à l’échelle nationale qui peut être adaptée à des études dans d’autres secteurs géographiques.ResumenLos ecosistemas de aguas subterráneas que comprenden microorganismos y metazoos proporcionan una contribución importante a la biodiversidad global. Su complejidad depende de la geología, que determina el hábitat físico disponible, y las condiciones químicas dentro de él. A pesar de ello, los métodos de clasificación de los hábitats de aguas subterráneas utilizando datos geológicos no están bien establecidos y los investigadores han demandado marcos de hábitat de mayor resolución. Se propone una nueva tipología de hábitat para Inglaterra y Gales (Reino Unido), que distingue 11 hábitats geológicos (geo-hábitats) sobre los principios hidrogeológicos y se mapea su distribución. Se utilizan datos hidrogeológicos e hidroquímicos para determinar las características de cada geo-hábitat y demostrar sus diferencias. Utilizando estos parámetros abióticos, se desarrolla un nuevo método para determinar la calidad del hábitat abiótico. Los geo-hábitats tenían características significativamente diferentes, validando el sistema de clasificación. Todos los geo-hábitats eran altamente heterogéneos, conteniendo tanto áreas de hábitat de alta calidad que probablemente sean adecuados para la fauna, como áreas de baja calidad que pueden limitar las distribuciones faunísticas. Los hábitats cársticos y porosos generalmente eran de mayor calidad que los hábitats fracturados. En general, el 70% de Inglaterra y Gales están cubiertos por hábitats fracturados de menor calidad, con sólo el 13% cubierto por hábitats de mayor calidad. Las principales áreas de hábitat de alta calidad se producen en el centro de Inglaterra como fajas de tendencia norte-sur, lo que posiblemente facilita la dispersión a lo largo de este eje. Están separados por geo-hábitats de baja calidad que pueden impedir la dispersión este-oeste de la fauna. En el suroeste de Inglaterra y Gales, los geo-hábitats adecuados se presentan como pequeñas áreas aisladas. En general, este documento proporciona una nueva tipología a escala nacional que es adaptable para estudios en otras áreas geográficas.摘要包含微生物和后生动物的地下水生态系统为全球的生物多样性做出了重要的贡献。其复杂性取决于地质状况,因为地质状况决定现有的栖息地以及栖息地内的化学条件。尽管如此,利用地质数据对地下水栖息地的方法还没有建立,研究人员需要更高分辨率的栖息地框架。这里提出了(英国)英格兰和威尔士一种新的栖息地类型学,这种类型学根据水文地质原则区分出11个地质上的栖息地(地质栖息地)及绘制出其分布图。利用水文地质和水化学数据确定每一个地质栖息地的特征,论证其差异。利用这些非生物参数,提出了一种新的确定非生物栖息地品质的方法。地质栖息地具有显著不同的特征,验证了分类系统。所有的地质栖息地高度异质,包含很可能适宜动物种群的高品质的栖息地地块以及可能限制动物种群分布的低品质区域。岩溶和多孔渗水的栖息地通常比断裂的栖息地品质要高。总的来说,70%的英格兰和威尔士被低品质断裂的栖息地所覆盖,只有13%的面积被高品质的栖息地所覆盖。高品质栖息地的主要区域位于英格兰中部,呈北-南走向带,可能促进沿这个轴散布。这些区域被可能阻止东-西向动物群分布的低品质地质栖息地所分隔。在英格兰和威尔士西南地区,有适宜的地质栖息地,以小的岛状地块分布。总的来说,本文提供了一种新的全国尺度的类型学,这种类型学也适合在其它地理区的研究。ResumoEcossistemas em águas subterrâneas incluindo microrganismos e metazoários fornecem uma importante contribuição para a biodiversidade global. Sua complexidade depende da geologia, que determina o habitat físico disponível, e as condições químicas dentro dele. Apesar disso, métodos para classificação de habitats em águas subterrâneas usando dados geológicos não são bem estabelecidos e pesquisadores tem requerido por arcabouços para habitats de maior resolução. Uma nova tipologia de habitat para Inglaterra e País de Gales (Reino Unido) é proposta, que distingue 11 habitats geológicos (geohabitats) em princípios hidrogeológicos e mapeia sua distribuição. Os dados hidrogeológicos e hidroquímicos são usados ​​para determinar as características de cada geohabitat e demonstrar suas diferenças. Usando esses parâmetros abióticos, um novo método para determinar a qualidade do habitat abiótico é então desenvolvido. Os geohabitats apresentaram características significativamente diferentes, validando o sistema de classificação. Todos os geohabitats foram altamente heterogêneos, contendo os dois fragmentos de habitat de alta qualidade que provavelmente serão adequados para a fauna e áreas de baixa qualidade que podem limitar as distribuições faunísticas. Os habitats cársticos e porosos geralmente eram de maior qualidade do que os habitats fraturados. No geral, 70% da Inglaterra e do País de Gales são cobertos por habitats fraturados de menor qualidade, com apenas 13% cobertos por habitats de maior qualidade. As principais áreas de habitats de alta qualidade ocorrem no centro da Inglaterra como cinturões de tendência norte-sul, possivelmente facilitando a dispersão ao longo deste eixo. Eles são separados por geohabitats de baixa qualidade que podem impedir a dispersão leste-oeste da fauna. No sudoeste da Inglaterra e do País de Gales, os geohabitats adequados ocorrem como pequenos fragmentos isolados. Em geral, este artigo fornece uma nova tipologia de escala nacional adaptável para estudos em outras áreas geográficas.

Microbial communities in UK aquifers: current understanding and future research needs

The presence and activity of microorganisms in aquifers can affect, amongst other things, nutrient cycling, contaminant degradation and water flow. The introduction of a pollutant or other changes in water chemistry can alter the microbial community composition and affect aquifer functioning. To understand the microbial response to anthropogenically induced changes, a better knowledge of baseline microbial communities in uncontaminated aquifers is needed. Here, we review the information on microorganisms in UK aquifers together with examples of research from other countries on this topic, and discuss how these communities might respond to disturbance. Research into microbial communities in UK aquifers has mostly been limited to bacteria and often reveals a community dominated by Proteobacteria. The community composition is influenced by factors such as mineralogy and water chemistry, and the natural baseline community may be altered by aquifer contamination. A UK-wide survey of aquifer microbes, similar to one recently carried out in New Zealand, would provide valuable information about the current state of UK aquifer microbiology. This would lead to a greatly improved understanding of the ecosystem services provided by the microbial communities present in aquifers, allow future monitoring and assessment of the effects of pollution, and assist in groundwater resource management.

The Influence of Flow and Bed Slope on Gas Transfer in Steep Streams and Their Implications for Evasion of CO2

The evasion of greenhouse gases (including CO2, CH4 and N2O) from streams and rivers to the atmosphere is an important process in global biogeochemical cycles, but our understanding of gas transfer in steep (> 10%) streams, and under varying flows is limited. We investigated gas transfer using combined tracer injections of SF6 and salt. We used a novel experimental design in which we compared four very steep (18.4-29.4%) and four moderately steep (3.7-7.6%) streams, and conducted tests in each stream under low flow conditions and during a high discharge event. Most dissolved gas evaded over short distances (~100 and ~200-400 m respectively), so accurate estimates of evasion fluxes will require sampling of dissolved gases at these scales to account for local sources. We calculated CO2 gas transfer coefficients (KCO2) and found statistically significant differences between larger KCO2 values for steeper (mean 0.465 min-1) streams compared to those with shallower slopes (mean 0.109 min-1). Variations in flow had an even greater influence. KCO2 was substantially larger under high (mean 0.497 min-1) compared to low flow conditions (mean 0.077 min-1). We developed a statistical model to predict KCO2 using values of streambed slope x discharge which accounted for 94 % of the variation. We show that two models using slope and velocity developed by Raymond et al. [2012] for streams and rivers with shallower slopes, also provide reasonable estimates of our CO2 gas transfer velocities (kCO2; m d-1). We developed a robust field protocol which could be applied in future studies.

A review of hydrogeology and water resources on the Isle of Wight

Abstract The Isle of Wight is a small, heavily populated island, where complex and careful management is required to ensure sustainable use of water resources. Much of the island is underlain by permeable strata and groundwater is an important source of supply. Many groundwater studies were undertaken by the water provider and regulatory authority from the 1970s onwards, but this work is not publicly available. This paper reviews these previous studies and provides an overview of the hydrogeology of the island with particular focus on the Lower Greensand Group and the Chalk–Upper Greensand aquifer. As one of the areas in the UK to experience water shortages during the 1976 drought, the Isle of Wight became the focus for new strategies for the sustainable development of water, which included the exploitation of more marginal aquifers, water metering and an engineering solution to provide water from the mainland. Ensuring future water demand is managed sustainably in an area where aquifers are fully exploited is likely to rely on the twin-track approach of both further demand-management and unconventional water resource development, such as wastewater reuse or desalination.

Tracer Investigations of the Nature and Structure of Subsurface Voids in Mildly Karstic Aquifers: an Example from the English Chalk

The Chalk in England is a mildly karstified fractured limestone with high matrix porosity. Chalk landscapes are predominantly a fluviokarst with an extensive dry valley network and with stream sinks and dolines developed in zones close to overlying strata. The nature and extent of subsurface dissolutional voids is poorly understood and field tests using artificial tracers were carried out to investigate their structure. Tracer testing from stream sinks demonstrated rapid groundwater flow (up to 5 km/day) confirming previous Chalk tracer studies. However tracer attenuation was variable with extremely low tracer recoveries at some sites indicating that not all flowpaths fed by stream sinks comprise fully connected conduit systems. A conceptual model of flow along multiple flowpaths comprising a distributary network around stream sinks and a tributary network around springs with variable connectivity between the two is presented. The proposed conceptual model of flowpath structure in the Chalk resembles previous models of the early stages of speleogenesis. It is suggested that groundwater flow in the Chalk and other mildly karstic aquifers occurs within complex small scale dissolutional networks, in which there is a high degree of connectivity between larger conduits, fissures, and a primary fracture network. Advection from karstic channels into smaller voids results in high attenuation of solutes and particulates providing a degree of protection to groundwater outlets that is not seen in more highly karstic aquifers.