Earthquakes trigger the loss of groundwater biodiversity

Abstract

Earthquakes are among the most destructive natural events. The 6 April 2009, 6.3-Mw earthquake in L'Aquila (Italy) markedly altered the karstic Gran Sasso Aquifer (GSA) hydrogeology and geochemistry. The GSA groundwater invertebrate community is mainly comprised of small-bodied, colourless, blind microcrustaceans. We compared abiotic and biotic data from two pre-earthquake and one post-earthquake complete but non-contiguous hydrological years to investigate the effects of the 2009 earthquake on the dominant copepod component of the obligate groundwater fauna. Our results suggest that the massive earthquake-induced aquifer strain biotriggered a flushing of groundwater fauna, with a dramatic decrease in subterranean species abundance. Population turnover rates appeared to have crashed, no longer replenishing the long-standing communities from aquifer fractures, and the aquifer became almost totally deprived of animal life. Groundwater communities are notorious for their low resilience. Therefore, any major disturbance that negatively impacts survival or reproduction may lead to local extinction of species, most of them being the only survivors of phylogenetic lineages extinct at the Earth surface. Given the ecological key role played by the subterranean fauna as decomposers of organic matter and "ecosystem engineers", we urge more detailed, long-term studies on the effect of major disturbances to groundwater ecosystems.

Figure 1. Diagram of the response of groundwater biodiversity to changes of the Gran Sasso aquifer (central Italy) hydrodynamics before and after the earthquake of 6 April 2009.

SEM micrographs of representative groundwater crustacean copepods (white bar = 200 μm) (a), schematic representation of pre-seismic (b, e), co-seismic (c, f), and post-seismic (d, g) groundwater flow from surface recharge areas through the aquifer (main conduit, lateral chambers and fracture network) to the spring discharge area, with obligate groundwater microcrustacean responses. Bottom panels report the discharge of the Tirino Springs (TS) during the March–June periods for each sampling year; mean annual discharges ± standard deviations also are reported.

Figure 2. Study area.

Location of the Gran Sasso Aquifer (GSA), its main recharge and discharge areas, including the Tirino Springs (TS) where sampling was carried out, and the epicentre of the earthquake of 6 April 2009 that hit L'Aquila and surroundings. The two red dots represent the main springs (Presciano and Capodacqua) within the TS system (software program CorelDRAW 11 (version 11.633), 2002 Corel Corporation).

Figure 3. Selected abiotic and biological variables recorded at the Tirino Springs before (1997, 2005) and after the 2009 earthquake (2012).

Boxplot representations of median (thick black line), upper and lower quartiles (box), 1.5× interquartile range (whiskers) and outliers (circles) for selected abiotic (green/blue) and biological (yellow/orange) variables at TS in the three sampling years. Post-seismic values in blue or orange. Different letters within each panel represent significantly different data distributions [Nemenyi comparisons after significant Friedman tests (Q, P; df = 2 for each)].

Figure 4. Pre- and post-seismic abundance patterns of dominant groundwater copepods at the Tirino Springs.

Nonmetric multidimensional scaling ordination of pre- and post- earthquake abundance of the obligate groundwater copepod species that accounted for ~90% of abundance changes; 2D stress = 0.16. Pre-earthquake replicate-specific abundance data in light blue, and post-earthquake abundances in red; circle size is proportional to abundance).