Exploring the distribution of groundwater Crustacea (Copepoda and Ostracoda) to disentangle aquifer type features—A case study in the upper Tajo basin (Central Spain)

Abstract

One of the most challenging questions in the assessment of groundwater ecosystem health is whether assemblages of groundwater biota can be used reliably as biomarkers. In this study, we aimed to (a) explore the diversity, distribution, and ecological composition of groundwater Crustacea, Copepoda, and Ostracoda communities from six aquifers in Central Spain and (b) relate the structure of the species assemblages to the aquifers' hydrogeological conditions, habitat features, and hydrochemistry. The datasets were simultaneously collected from 24 boreholes drilled in six unconfined aquifers from the upper part of the Tajo catchment. Our results show that the assemblages are primarily influenced by the specific hydrogeological conditions of the aquifer, determined by groundwater flow, supply of organic matter from the surface, and habitat features, whereas the aquifer's hydrochemistry has only a marginal effect. The assemblages from the Tertiary detrital aquifer were the most diverse, containing a mixture of stygobiont and nonstygobiont species distributed preferentially in the recharge area of the aquifer, characterized by medium hydraulic conductivity, high surface input and relatively high water renewal. The Quaternary alluvial aquifer type was found to have a moderate richness with several hyporheic dwellers, indicating an active surface/groundwater exchange with the adjacent stream channel.In contrast, the carbonate aquifer type was less diverse but markedly distinct owing to the high occurrence of stygobionts. Our results provide a step forward in exploring the groundwater biodiversity of aquifers in Spain and towards incorporating an ecological perspective into overall assessments of groundwater status.

Potential of A Trait-Based Approach in the Characterization of An N-Contaminated Alluvial Aquifer

“…The taxonomic richness of VO_GWB was high and consistent with previous studies in other European and non-European alluvial aquifers [60,64,66,68,69], both at the local and the regional scales [15,70]. However, the number of species collected in VO_GWB is surprisingly high if considering the persisting N-compound contamination which occurred in 90% of the aquifer.…”

“…The traditional taxonomy-based approach showed that most taxa were collected only in a few bores and showed, therefore, restricted distributions as already observed in other studies (e.g., [64,66]). The most widespread species in VO_GWB, D. cosanus, is known to be highly tolerant to elevated values of salinity and electrical conductivity, being collected in other N-contaminated alluvial aquifers, in brackish coastal groundwater in southern Italy, and in sulfidic saturated karst [21].…”

“…The occurrence of epigean species in the deeper sectors of VO_GWB is recurrent in alluvial aquifers, especially in those polluted by contaminants of organic origin (e.g., [22,64]). The weak correlations of the environmental and biological variables are a common result in groundwater studies, in particular, in aquifers that are highly homogeneous from a physicochemical point of view [22,66,73]. In this study, the variance explained by the univariate models was low and this indicated that further factors, in addition to those already investigated, must be taken into account in the future to better explain the observed biological patterns.…”

Effect of Temperature Rising on the Stygobitic Crustacean Species Diacyclops belgicus: Does Global Warming Affect Groundwater Populations?

“…Groundwater ecosystems are generally poorer in nutrients and oxygen than surface water ecosystems [12][13][14][15][36][37][38][39][40]. In order to reduce energetic costs, groundwater ectotherms have evolved metabolic rates that are lower than those of their close epigean relatives [20,[41][42][43][44].…”

“…This limits the number of replicates and sometimes prevents performing a trial. Most importantly, the abundances are very low and "the one well to one species" is the rule of thumb [12,14,15,40].…”