Ecological Indicators 77 (2017) 314–322 Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Original Articles Physicochemical and microbiological indicators of surface water body contamination with different sources of digestate from biogas plants Isabelle Studer, Carolin Boeker, Juergen Geist ∗ Aquatic Systems Biology Unit, School of Life Sciences Weihenstephan, Technical University of Munich, Mühlenweg 22, D-85354 Freising, Germany a r t i c l e i n f o Article history: Received 15 December 2016 Received in revised form 14 February 2017 Accepted 15 February 2017 Keywords: Biogas Bacterial communities Indicators TRFs Hyporheic interstitial Digestate a b s t r a c t Transition from fossil energy sources to biogas production has resulted in a strong increase of leakage accidents from fermenters, but knowledge on the effects of fermentation product runoff into freshwater systems is currently restricted to direct toxicity due to oxygen depletion. This study provides first infor- mation about the influence of digestate runoff on the physicochemical habitat properties and the bacterial community composition of the hyporheic interstitial which is important in determining ecosystem func- tioning. We exposed natural stream beds to different concentrations of two different digestates from fermenters (corn and manure feedstock), hypothesizing that the digestate addition causes acute changes of the physicochemical parameters and has distinct effects on microbial community composition of the hyporheic interstitial depending on concentration and type of digestate. In line with the hypotheses, pH value, conductivity, redox potential and ammonium differed significantly from controls and among treatments after digestate addition, but only for a maximum of two days. pH values (controls: 7.8; corn: 7.9; manure: 7.9) and conductivity (controls: 813 S/cm; corn: 969 S/cm; manure: 1097 S/cm) increased, the redox potential (controls: 153 mV; corn: 145 mV; manure: 144 mV) decreased the first two days. A high peak of ammonium-N was detected in the corn and manure treatments (controls: 5 mg/l, corn: 80 mg/l; manure: 60 mg/l) at day 1. In contrast, changes in bacterial community composition were detectable for longer periods of time (>5 days). Seventeen unique T-RF fingerprints of bacterial commu- nity response to each of the different digestate treatments (11 unique T-RFs in manure and 6 unique T-RFs in corn treatments) were found, suggesting that this approach provides a suitable ecological indicator for source tracking, e.g. in case of a biogas power plant leakage accident. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Growing global energy demand, rapidly rising concentrations of greenhouse gases in the atmosphere, global warming and the security of energy supply are considered the most important global challenges of this century (Holm-Nielsen et al., 2009). In addition, the Fukushima accident has triggered intense discussion about safe and sustainable energy provision. In this context, biogas production is considered an important renewable energy source, particularly in central Europe. Biogas production can either use animal waste or crops for energy and heat generation, and is often referred to as a technology with limited environmental risk (Weiland, 2010). ∗ Corresponding author at: Chair of Aquatic Systems Biology, School of Life Sci- ences Weihenstephan, Technical University of Munich, Mühlenweg 22, D-85354 Freising, Germany. E-mail address: geist@tum.de (J. Geist). Germany has become the largest biogas producing country in the world. By the end of 2014, nearly 8000 biogas plants were operated on German farms (Fachverband Biogas, 2014). With an increasing number of biogas plants, the probability of accidents like technical faults, handling errors and disturbances during the fermentation process increases. Given the high number of such facilities, such incidents were reported to happen on average every two minutes (FNR, 2010). During the fermentation process, the anaerobic digestion of biomass, induced by a special acetogenic and methanogenic microbial community under high oxygen consump- tion (Weiland, 2010), results in an anaerobic byproduct (digestate). Möller (2015) defined digestates as a complex mixture of organic and inorganic substances, nutrients, degradable organic matter and water. Digestates are stored in tanks until they can be appli- cated to fields as fertilizers (Weiland, 2010). Tank leakages are often the reason for uncontrolled runoffs of digestate into freshwa- ters. Depending on the composition and dilution of such pollution in receiving aquatic ecosystems, the effects can vary widely: At high concentrations of digestates in relation to the affected aquatic http://dx.doi.org/10.1016/j.ecolind.2017.02.025 1470-160X/© 2017 Elsevier Ltd. All rights reserved.