Abstract
The assessment and monitoring of the ecological quality and status of groundwater is a timely issue. At present, various assessment tools have been developed that now await application and validation. One of these, the D‑A‑C index, evaluates the microbiological-ecological quality of groundwater based on of prokaryotic cell counts, microbial activity measurements, and the qualitative characterization of dissolved organic carbon (DOM). The purpose of this paper is to illustrate the different ways of application of the D‑A-(C) index making use of a recently collected data set (n = 61) from the river Mur valley, Austria. First, we present an extension of the D‑A-(C) index by including measurements of dissolved organic matter quality (DOM) derived from fluorescence spectroscopy as additional variables to supplement the analysis of microbial cell density and activity levels. Second, we illustrate how the definition of a reference status for a ‘good’ microbiological-ecological state can improve the analysis and allow for a more sensitive and accurate detection of impacts on groundwater ecosystems. Based on our results, we advocate that the analysis be performed by making use of expert knowledge for the definition of reference sites to which target sites are to be compared.
Highlights
Besides being a vital resource, groundwater is the largest, yet still mostly unexplored freshwater ecosystem on our planet, harboring a rich diversity of microbial and metazoan life (Gibert and Culver 2009; Griebler and Lueders 2009)
We explored the usefulness of dissolved organic matter quality (DOM) quality indices derived from fluorescence spectroscopy as promising additional parameters to be included in the D-A-(C) index
If we label the samples according to their affiliation to sub-regions or according to their origin from areas of different land use ‘post-analysis’, we see that sub-clusters are visible, which indicate that groundwater samples collected from the same sub-regions are more similar to each other than to those of other sub-regions
Summary
Besides being a vital resource, groundwater is the largest, yet still mostly unexplored freshwater ecosystem on our planet, harboring a rich diversity of microbial and metazoan life (Gibert and Culver 2009; Griebler and Lueders 2009). These organisms are key to ecosystem services provided by groundwater, including, among many others, the attenuation of anthropogenic contaminants and pathogens (Griebler and Avramov 2015; Herman et al 2001). At about 20–30% of the global land surface, shallow groundwater feeds surface waters, wetlands and the roots of plants (Ribeiro et al 2013). Surface waters that receive wastewater and are subject to hydrological extremes such as flood events may carry pollutants from the surface into aquifers, thereby seriously compromising groundwater quality (Corada-Fernández et al 2017)
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