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 examine the distribution and composition of stygobiont assemblages in a complex geological setting and explore the relationship between groundwater fauna, hydrogeology and water chemistry. In the study area we grouped similar geologies into five hydrogeological formations (hydro-units) within which habitats for groundwater fauna were broadly similar. We found that the occurrence of stygobionts differed significantly between hydro-units. Stygobionts were significantly less likely to be recorded in mudstone/siltstone and sandstone aquifers compared with carbonate rocks or with igneous/metamorphic rocks. Variance partitioning indicated that the hydro-units 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 three groups: (1) Niphargus glenniei was recorded in a range of hydro- units but only in the west of the study area. (2) Niphargus kochianus , Niphargus fontanus, Proasellus cavaticus and Crangonyx subterraneus were predominately recorded in carbonate aquifers in the east of the study area. (3) Niphargus aquilex and Microniphargus leruthi, were found throughout the study area and in a range of hydro-units. We hypothesise that physical barriers exist that 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

Invasive species influence macroinvertebrate biomonitoring tools and functional diversity in British rivers

Biological invasions could have major implications for the management and conservation of freshwater systems if they lead to a misclassification of waterbodies. However, there is limited understanding of the sensitivity of existing biomonitoring tools to invasive species in rivers; and even less known regarding how they influence community taxonomic and functional measures. This research explores the response of freshwater macroinvertebrate communities to biological invasion using taxonomic and functional indices. Utilising a long-term dataset (spanning 2000–2019, 5,988 samples) from rivers in England, the performance of four biomonitoring tools (WHPT, WHPT-ASPT, LIFE and PSI) and two community functional indices (functional richness and redundancy) was examined before and after the colonisation of the invasive species, Dikerogammarus haemobaphes (Eichwald, 1841; Crustacea: Gammaridae). This species represents a recent (first record 2012) and highly successful invader, allowing its range expansion within waterbodies to be examined in detail. Spatial (national and basin level) and seasonal (spring and autumn) effects were investigated using a before–after control–impact (BACI) experimental framework and linear mixed effects models. Results indicated that invasion by D. haemobaphes resulted in significant reductions to the WHPT index and functional diversity metrics (richness and redundancy) while more subtle patterns were observed for other metrics. Analysis of seasonal and individual river basins (River Trent and R. Thames) identified largely consistent responses. The establishment of D. haemobaphes also resulted in some modifications to the functional composition of aquatic communities primarily associated with voltinism and resistance features. Synthesis and applications. Our findings indicate that Dikerogammarus haemobaphes should be considered a significant pressure to riverine communities. These results have implications for biomonitoring, which informs managerial actions as effects may not be detected using a single taxonomic index. Community functional measures are useful in characterising the effects of invasive species and may form a valuable part of the ‘toolbox’ used for studying biological invasions in rivers. The research illustrates the need to consider the wider threats posed by invasive species on the long-term integrity of freshwaters and the efficacy of freshwater biomonitoring tools

Distribution of macroinvertebrate communities across surface and groundwater habitats in response to hydrological variability

Macroinvertebrate communities are strongly influenced by hydrological variability in surface waters. However, the response of these communities in corresponding groundwater-dependent habitats is not well understood. This study characterised the macroinvertebrate fauna and physicochemical characteristics of a chalk aquifer and its rivers in southern England. Over one year, samples were collected from five paired benthic-hyporheic sites located in perennial or temporary rivers, and a further seven phreatic sites in the surrounding aquifer. The study was preceded by a period of below average rainfall, providing an opportunity to assess the response of macro-invertebrate communities to unseasonal declines in river discharge and groundwater levels. Benthic, hyporheic and phreatic habitats each supported a distinct macroinvertebrate community, with the hyporheic habitat support- ing both epigean taxa and stygofauna. As discharge declined, the composition of these communities changed. In particular, the abundance of the epigean amphipod Gammarus pulex was higher in hyporheic than benthic habitats during periods of low river discharge, suggesting potential refuge-seeking behaviour. Similarly, fluctuations in the abundance and distribution of two stygofauna, Crangonyx subterraneus and Niphargus fontanus, coincided with marked changes in groundwater levels, suggesting that the contraction of available habitat and changes in connectivity also influenced the phreatic community. The variable distribution of macroinvertebrates between these habitats, especially in response to hydrological variability, suggests a dynamic connection between the river and its aquifer. This connection is an important consideration for the assessment and conservation management of both surface and groundwater communities and may help underpin integrated, catchment-based management, especially in river systems with temporary reaches

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 examine the distribution and composition of stygobiont assemblages in a complex geological setting and explore the relationship between groundwater fauna, hydrogeology and water chemistry. In the study area we grouped similar geologies into five hydrogeological formations (hydro-units) within which habitats for groundwater fauna were broadly similar. We found that the occurrence of stygobionts differed significantly between hydro-units. Stygobionts were significantly less likely to be recorded in mudstone/siltstone and sandstone aquifers compared with carbonate rocks or with igneous/metamorphic rocks. Variance partitioning indicated that the hydro-units 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 three groups: (1) Niphargus glenniei was recorded in a range of hydro- units but only in the west of the study area. (2) Niphargus kochianus , Niphargus fontanus, Proasellus cavaticus and Crangonyx subterraneus were predominately recorded in carbonate aquifers in the east of the study area. (3) Niphargus aquilex and Microniphargus leruthi, were found throughout the study area and in a range of hydro-units. We hypothesise that physical barriers exist that 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