Linking ecological health to co-occurring organic and inorganic chemical stressors in a groundwater-fed stream system

Abstract

Freshwaters are among the most endangered ecosystems worldwide, due predominantly to excessive anthropogenic practices compromising the future provisioning of ecosystem services. Despite increased awareness of the role of multiple stressors in accounting for ecological degradation in mixed land-use stream systems, risk assessment approaches applicable in field settings are still required. This study provides a first indication for ecological consequences of the interaction of organic and inorganic chemical stressors, not typically evaluated together, which may provide a missing link enabling the reconnection of chemical and ecological findings. Specifically, impaired ecological conditions - represented by lower abundance of meiobenthic individuals - were observed in the hyporheic zone where a contaminant groundwater plume discharged to the stream. These zones were characterized by high xenobiotic organic concentrations, and strongly reduced groundwater (e.g. elevated dissolved iron and arsenic) linked to the dissolution of iron hydroxides (iron reduction) caused by the degradation of xenobiotic compounds in the plume. Further research is still needed to separate whether impact is driven by a combined effect of organic and inorganic stressors impacting the ecological communities, or whether the conditions - when present simultaneously - are responsible for enabling a specific chemical stressor's availability (e.g. trace metals), and thus toxicity, along the study stream. Regardless, these findings suggest that benthic meioinvertebrates are promising indicators for supporting biological assessments of stream systems to sufficiently represent impacts resulting from the co-occurrence of stressors in different stream compartments. Importantly, identification of the governing circumstances is crucial for revealing key patterns and impact drivers that may be needed in correctly prioritizing stressor impacts in these systems. This study further highlights the importance of stream-aquifer interfaces for investigating chemical stressor effects in multiple stressor systems. This will require holistic approaches for linking contaminant hydrogeology and eco(toxico)logy in order to positively influence the sustainable management of water resources globally.

Climate change adaptation in rural South Africa: Using stakeholder narratives to build system dynamics models in data-scarce environments

“…Water resources that are directly threatened by human activities also stand to be further affected by anthropogenic climate change, and devising interventions that will protect freshwater biodiversity and ensure the sustainability of water delivery systems requires frameworks capable of diagnosing the key threats to water security at a range of scales (Sonne et al, 2018;Vörösmarty et al, 2010). As such, there is a need for more systemic approaches that can incorporate the combinations of pressures and their potential intended and unintended consequences, especially where integrated water resources management (IWRM) is concerned (van den Belt & Blake, 2015).…”

Evidence of Spatio‐Temporal Variations in Contaminants Discharging to a Peri‐Urban Stream

“…It is also a convenient way to aggregate the different pathways from a single source in order to quantify multiple pathway contributions at a larger scale, as carried out with respect to source zone A in this study. This in‐stream approach is limited, however, by practical constraints for the discretization of an in‐stream control plane, and to dissolved contaminants with concentration levels high enough to be detected after dilution in the stream (Sonne et al ). We observed a substantial increase in CMD related to increases in stream flow.…”

“…Freshwater resources are particularly sensitive and the related ecosystems exhibit some of the highest decline rates in terms of biodiversity (Strayer and Dudgeon ; Sonne et al. ). The reasons for such a decline are many and possibly cumulative, including stream flow alteration, habitat degradation, pollution, invasive species, and more recently emerging contaminants and climate change (Sonne et al.…”

Revealing chlorinated ethene transformation hotspots in a nitrate-impacted hyporheic zone

“…Chlorinated ethenes (CEs) such as trichloroethene (TCE) and its metabolites cis-1,2dichloroethene (cDCE) and vinyl chloride (VC) are among the most common volatile organic contaminants (VOCs) detected in groundwater (Shapiro et al, 2004;Rivett et al, 2012, Palau et al, 2014. These organohalides are prominent chemical stressors in surface water ecosystems impacted by legacy industrial sources (Roy et al, 2018;Sonne et al, 2018). Dissolved-phase CE plumes often continue to migrate in aquifers with limited sorption capacity, and frequently discharge with groundwater baseflow to streams and rivers (Weatherill et al, 2018).…”