The GW-Fauna-Index: A first approach to a quantitative ecological assessment of groundwater habitats

Between June 2001 and December 2002, 18 hyporheic and groundwater bores were sampled for fauna and environmental data using phreatic traps. The bores were situated in three different natural geographic regions in Palatinate, Southwestern Germany.Faunal data correlated with the relative amount of detritus, bacterial abundances and the standard deviation of temperature, while very few and weak correlations were found with physical–chemical variables. Dissolved oxygen was assumed to be a limiting factor for most metazoans with a critical concentration at around 0.5–1 mg l⁻¹.To quantify the strength of the hydrological exchange with surface water and its effects on fauna, a so-called GW-Fauna-Index was developed and calculated using the relative amount of detritus, standard deviation of temperature, and oxygen concentration. From all environmental data and on all spatial scales, this index best explained the total faunal abundance and taxonomic richness.To describe the availability of organic aliments in the groundwater, the terms of “alimonic” and “alimony” [from lat. alimonium=(food) supply] were proposed.Although stygofauna was different in the geographic regions investigated, the GW-Fauna-Index was independent from these regional particularities. Using the GW-Fauna-Index, three groups of groundwater habitats could be classified according to the alimonic conditions. From oligo-alimonic group I samples, fauna was mostly absent, while meso-alimonic group II samples were prevailingly populated by stygobites, and eu-alimonic group III samples by ubiquists and stygoxenes. Total abundances and taxonomic richness increased significantly from group I to group III. Group I samples were characterized by low index values, group II samples by intermediate and group III samples by high values.The GW-Fauna-Index provides promising perspectives for application, but needs some improvement. First of all, detritus should be analysed quantitatively and qualitatively, rather than semi-quantitatively. Also, a standard protocol for sampling has to be developed.     

A comparison of stygofauna communities inside and outside groundwater bores

Sampling stygofauna is both time consuming and labour intensive. The challenge is to get samples from as many bores as possible within a limited time. The essential assumption for this is that faunal communities inside bores are comparable and representative of the communities outside.To compare relative abundance, taxonomic richness and community composition of the fauna inside groundwater bores to the fauna of the surrounding aquifer, 20 monitoring bores in Palatinate, southwestern Germany, were sampled twice in 1 month. Initially, a sample of 4 l of water was collected from the bottom of each bore. A further sample of 51 l was collected from the groundwater surrounding the bore using a pneumatic piston pump with double packer sampler.Water chemistry inside and outside the bore was similar, but the relative amounts of sediments within the bores were higher compared to those from outside. Relative abundances of fauna inside the bores were higher than in the aquifer, but taxonomic composition was similar with the exception of the proportions of nematodes and amphipods, which were higher inside. As a result, the proportions of cyclopoids were lower inside. Higher nematode proportions are explained partially by the nearly complete extraction of bore sediment. A “habitat heterogeneity effect” states that in heterogeneous aquifers with few suitable habitats, faunal distribution is supposed to be extremely patchy. Thus, detritus accumulates in bores, attracting animals and providing “habitat islands” in the groundwater. This effect could explain the higher amphipode proportions inside the bores, which were generally more frequently populated than the surrounding groundwater. As a consequence, fauna is thought to be nearly absent from groundwater, where suitable habitats are lacking. In those sparsely populated aquifers, samples representative of the aquifer taxonomic richness and composition can only be collected by removing large volumes of water, or by sampling the bottom of bores. These findings also suggest that the use of unbaited colonisation chambers or traps in the groundwater, which are comparable with bores, would seem to be a promising approach.     

Unbaited phreatic traps: A new method of sampling stygofauna

(1) A new method of sampling stygofauna is presented, along with some data derived from applications in the field. Numerous bores were sampled for fauna, water and bacteria, down to a depth of 7.50 m. Two or 3 unbaited traps were fixed to a central pole within the bore. The traps consist of an inert plastic chamber with holes in the upper parts and gaskets near the bottom and near the lid of each trap. The content of the traps was emptied monthly using a pump.

(2) While the taxonomic composition of the trap samples seemed to be comparable to the surrounding groundwater, estimation of abundances in the traps might differ, with a potential over-estimation in the traps, in particular in sparsely populated aquifers. Detailed comparative studies on the performance of the method are, as yet, lacking.

(3) Trap data of invertebrate communities reflect hydraulic changes, and highest abundances and taxa richness were found near the water table. They decreased rapidly with depth, implying that small-scale stratified sampling is possible.

(4) The technique is cheap, reliable, simple and rapid to use, and allows simultaneous sampling of hydro-chemical, faunal and microbial samples. The method seems to be suitable for a wide range of sub-surface waters, where the water table is shallower than 8 m.

Distribution patterns of subsurface copepods and the impact of environmental parameters

The ecosystem dynamics in the vadose zone, the unsaturated layer between the surface and the groundwater table, was studied in five caves located in northwestern Romania. Hypogean and epigean copepod assemblages collected in drip water and in the associated pools were analyzed over a period of 12 and 7 months, respectively. The temporal variation of fauna in both habitats was related to a series of environmental parameters (pH, temperature, electrical conductivity, forest cover, precipitation, type of limestone, hydrographic basin, substrate and volume of the pools). Canonical Correspondence Analysis was used to explore the relationships. Over the year, total abundances in pools were much lower than the abundances observed in drips and showed steep raising values in December only. It is shown that forest cover might be one of the most important driving factor influencing the copepod diversity and abundance. Occurrence of epigean species underground was influenced by precipitation and drip rates. The occurrence of hypogean species was related to electrical conductivity, as an indicator of residence time of water in the vadose zone. Pools on limestone harbored a more diverse and abundant fauna than those with clay sediments. Pools with calcite precipitation were preferred by hypogean species.     

Shared microsporidian profiles between an obligate (Niphargus) and facultative subterranean amphipod population (Gammarus) at sympatry provide indications for underground transmission pathways

Only sparse knowledge exists on amphipod-infecting microsporidians in subterranean waters. Here, we DNA barcoded two sympatric amphipod populations (obligate subterranean Niphargus schellenbergi, facultative Gammarus fossarum) and their microsporidian parasites. Parasite prevalence was assessed by diagnostic PCR assays. Overall prevalence was 82.7 %. Both amphipod populations shared all four identified parasite species (Nosema granulosis, Microsporidium sp. I, Orthosomella sp., Microsporidium sp. BPAR3). Hence, we postulate underground transmission pathways of microsporidians mediated by subterranean amphipod hosts.     

Aquifers and hyporheic zones: Towards an ecological understanding of groundwater

Ecological constraints in subsurface environments relate directly to groundwater flow, hydraulic conductivity, interstitial biogeochemistry, pore size, and hydrological linkages to adjacent aquifers and surface ecosystems. Groundwater ecology has evolved from a science describing the unique subterranean biota to its current form emphasising multidisciplinary studies that integrate hydrogeology and ecology. This multidisciplinary approach seeks to elucidate the function of groundwater ecosystems and their roles in maintaining subterranean and surface water quality. In aquifer-surface water ecotones, geochemical gradients and microbial biofilms mediate transformations of water chemistry. Subsurface fauna (stygofauna) graze biofilms, alter interstitial pore size through their movement, and physically transport material through the groundwater environment. Further, changes in their populations provide signals of declining water quality. Better integrating groundwater ecology, biogeochemistry, and hydrogeology will significantly advance our understanding of subterranean ecosystems, especially in terms of bioremediation of contaminated groundwaters, maintenance or improvement of surface water quality in groundwater-dependent ecosystems, and improved protection of groundwater habitats during the extraction of natural resources. Overall, this will lead to a better understanding of the implications of groundwater hydrology and aquifer geology to distributions of subsurface fauna and microbiota, ecological processes such as carbon cycling, and sustainable groundwater management.

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Resumen Los entornos ecológicos en ambientes subsuperficiales están relacionados directamente con el flujo de agua subterránea, la conductividad hidráulica, biogeoquímica intersticial, tamaño de los poros, y vínculos hidrológicos con acuíferos adyacentes y ecosistemas superficiales. La ecología del agua subterránea ha evolucionado a partir de una ciencia que describe la biota subterránea única hasta alcanzar la forma actual que enfatiza estudios multidisciplinarios que integran hidrogeología y ecología. Este enfoque multidisciplinario busca clarificar la función de los ecosistemas de agua subterránea y sus roles en el mantenimiento de la calidad de agua superficial y subterránea. En ecotonos de agua superficial y de acuíferos, los gradientes geoquímicos y biopelículas microbiales median transformaciones de calidad de agua. La fauna subsuperficial (estigofauna) se alimenta de biopeliculas, altera el tamaño de los poros intersticiales mediante su movimiento, y transporta físicamente material a través del ambiente de aguas subterráneas. Además, los cambios en sus poblaciones aportan señales de decadencia de calidad de agua. La mejor integración de ecología de aguas subterráneas, biogeoquímica, e hidrogeología incrementará significativamente nuestro entendimiento de ecosistemas subterráneos, especialmente en términos de bioremediación de aguas subterráneas contaminadas, mantenimiento o mejoramiento de calidad de agua superficial en ecosistemas dependientes de agua subterránea, y protección mejorada de habitats de agua subterránea durante la extracción de recursos naturales. Sobretodo, esto conducirá a un mejor entendimiento de las implicaciones de la hidrología de aguas subterráneas y geología del acuífero, de las distribuciones de fauna subsuperficial y microbiota, procesos ecológicos tal como ciclado de carbono, y gestión sostenible de aguas subterráneas.

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Résumé Les contraintes écologiques dans les environnements de subsurface sont en relation directe avec les écoulements des eaux souterraines, la conductivité hydraulique, la biogéochimie des milieux interstitiels, la taille des pores, et les liens hydrologiques avec les aquifères et les écosystèmes adjacents. Lécologie des eaux souterraines a évolué dune science décrivant uniquement les biotopes souterrains à des études multidisciplinaires qui intègrent lécologie et lhydrogéologie. Lapproche multidisciplinaire cherche à élucider le fonctionnement des écosystèmes souterrains et leur rôle consistant à maintenir la qualité des eaux souterraines et de surface. Dans les écotones des eaux de la surfaces des aquifères, les gradients géochimiques et les biofilms microbiologiques contrôlent les transformations de la qualité de leau. La faune de subsurface (stygofauna) construisent les biofilms, altèrent la taille des pores interstitiels à travers leur mouvement, et transportent physiquement des matériaux à travers lenvironnement des eaux souterraines. Par ailleurs, les changements de leur population signalent un déclin de la qualité de leau.Une meilleure intégration de lécologie des eaux souterraines, de la biogeochimie, et de lhydrogéologie pourra faire avancer de manière efficace de notre compréhension des écosystèmes souterrains, et spécialement en terme de bioremédiation des eaux souterraines contaminées, de maintenance et damélioration de la qualité des eaux de surface dépendant des écosystèmes souterrains, et lamélioration de la protection des habitats des eaux souterraines durant lextraction des ressources naturelles. En général, cela conduira à une meilleure compréhension de limplication de lhydrogéologie et de la géologie des aquifères à la distribution de la faune de subsurface et aux microbiota, aux processus écologiques tels que les cycles du carbone, et la gestion durable des eaux souterraines.

     

Testing unbaited stygofauna traps for sampling performance

Unbaited phreatic traps are a promising new method for sampling subterranean limnofauna. The aim of this study is to evaluate whether such trap systems are suitable to gather representative samples of the physico-chemical parameters and the invertebrate fauna of the aquifer. Fifteen traps, installed in five groundwater bores, and four traps located in the hyporheic zone, were sampled twice monthly over a 1 year period (June 2003–June 2004). Water samples were removed in three separated fractions (hose, trap and aquifer water), analysed for physico-chemical and faunal characteristics and compared with one another. The study was carried out in the Nakdong River floodplain, Korea. Physico-chemical characteristics of trap and aquifer were similar, but differed greatly from the hose samples. Abundances of fauna inside the traps were higher than in the aquifer, whereas there were no differences in taxonomic composition of the trap and aquifer samples. Biases of abundances suspected due to the use of traps were negligible in the groundwater, though it is recommended that comparisons between groundwater and hyporheic abundances ascertained by traps be handled cautiously.     

What is groundwater and what does this mean to fauna? - An opinion

Many subsurface waters are considered groundwater but are influenced in shallow depths by hyporheic, parafluvial and/or soil interception water to such a degree that groundwater fauna (stygofauna) communities may be significantly altered. Recharge, even if spatially and temporally distinct, delivers input of dissolved oxygen, organic matter (OM), and nutrients that caters sustainably for ubiquists such as stygophiles and hyporheic fauna, but renders the life of uncompetitive stygobites difficult or impossible. The impact of recharge at shallow groundwater thus needs to be taken into account when determining groundwater fauna reference communities and when evaluating monitoring studies.One of the main characteristics of groundwater is low OM concentration. In contrast, high OM concentrations are typical of hyporheic or parafluvial waters, which are enriched by OM from the river, the riparian soils and from interflow, and which contribute significantly to river OM balance. Consequently, for ecological studies on subsurface waters, both the origin of the water and OM, and the intensity of surface water interactions should be considered. Here, we discuss how groundwater spatial and temporal heterogeneity translates into faunal distribution patterns. In terms of the origin of water and OM, and from an ecological point of view, we need to distinguish between (i) shallow groundwater characterized by infiltrating precipitation and soil recharge, (ii) shallow groundwater interacting with surface water bodies such as continuously flowing and ephemeral streams and rivers, and (iii) “old” groundwater which has no recent connections to the surface and is thus largely secluded from input of nutrients and carbon. Water in the first two groups is characterized by high amounts of OM of varying quality, while water in the third group is characterized by low amounts of low quality OM. Consequently, stygophiles dominate in groups 1 and 2, with hyporheic fauna taking up a considerable proportion in group 2, while stygobites only dominate in group 3. Thus, for studies aiming to assess impacts on groundwater, only sampling sites of the third group should be used for reference sites as these are the most likely sites to have little surface impact and a stygofauna representative of the deeper aquifer.