High spatial heterogeneity and low connectivity of bacterial communities along a Mediterranean subterranean estuary

Abstract

Subterranean estuaries are biogeochemically active coastal sites resulting from the underground mixing of fresh aquifer groundwater and seawater. In these systems, microbial activity can largely transform the chemical elements that may reach the sea through submarine groundwater discharge (SGD), but little is known about the microorganisms thriving in these land-sea transition zones. We present the first spatiallyresolved characterization of the bacterial assemblages along a coastal aquifer in the NW Mediterranean, considering the entire subsurface salinity gradient. Combining

Comparative Study of Microbial Diversity in Different Coastal Aquifers: Determining Factors

“…As has been observed in other Spanish coastal aquifers [21,22], the four aquifers studied here show great heterogeneity in their microbiological content. There is significantly greater inter-aquifer than intra-aquifer diversity, despite all of them being close to each other.…”

“…In this sense, the existence of high microbial diversity, with many low abundant taxa, could be indicative of anthropogenic influence on soil microbiomes, i.e., many of these microorganisms are not active, but merely remnants of human-impacted microbiota in groundwater. Furthermore, the higher diversity could result from a higher connectivity with the surface, with little microbial connectivity between the aquifer and the sea, as has been reported in previous studies [22,105,106].…”

“…In general, coastal aquifers are environments with pronounced gradients of physicochemical parameters, particularly salinity, but also temperature, pH, eH, and dissolved oxygen shift from the top of the aquifer to the bottom, and along the flow direction from land to coast [15][16][17]. For that reason, this environment is an ecosystem where a high variety of specialist microorganisms can live [12,[18][19][20][21][22]. The activity of the microbiota also modifies the environment, generating new opportunities for new organisms [23].…”

“…The activity of the microbiota also modifies the environment, generating new opportunities for new organisms [23]. The study of microbial communities in coastal aquifers has increased in recent decades [14,21,22,[24][25][26][27][28], not only because of the wide diversity they comprise, as already mentioned, but also because of the concurrence of a series of characteristics, such as the existence of transition zones, affected by a wide range of conditions or important anthropogenic pressure [6,29], which make them habitats of special interest from a microbiological perspective. Despite this, the existing knowledge of their microbial diversity and associated biogeochemical processes is very limited in comparison with continental and marine waters [14,21].…”

“…These aquifers have been studied intensely from the hydrodynamic and hydrogeochemical points of view [46][47][48][49]. Although the microbial dimension of coastal aquifers has been less explored than their physico-chemical dimension, in the case of coastal aquifers in Spain, we can find a great number of works on the microbiological content of their waters, both in detrital aquifers [21,22,[50][51][52][53] and in carbonate aquifers [18,23].…”