Effects of municipal wastewaters on aquatic-nearshore food webs

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Terrestrial and aquatic ecosystems are tightly linked through the runoff of materials from land to water and the return of these materials via emergent aquatic insects to nearshore (riparian) predators. However, these energetic links can be disrupted by contaminants because they impact the abundance of aquatic insect larvae and subsequent prey available to riparian predators. Our understanding of how contaminants disrupt aquatic-riparian linkages is mainly limited to highly contaminated, industrial sites. Municipal wastewaters are the largest human inputs by volume to Canadian surface waters and contain excess nutrients and a wide range of contaminants including antimicrobials (antibiotics, disinfectants). Our previous work at wastewater-impacted sites revealed that fish, larval insects and riparian spiders have altered microbiomes but it is unclear whether these effects occur at other sites and the mechanisms behind these shifts (i.e., exposures to antimicrobials, shifts in dietary habits). Given that the microbiome is critical for energy provision, immune function, etc., in their hosts, changes in its diversity and composition may lead to adverse effects in individuals. In addition, the excess nutrients and contaminants may impact aquatic food web structure and aquatic-terrestrial linkages, which can be assessed because the unique isotopic values of nitrogen in these effluents are incorporated into the downstream food web. The long-term objective of my Discovery program is to understand the ecological risks posed directly or indirectly by contaminants in aquatic and riparian environments. This will be met through short-term objectives that determine how municipal wastewater effluents and the antimicrobials they contain affect: 1) microbiomes, tissue antimicrobials, and energy sources of diverse aquatic species; 2) water-land subsidies via emergent aquatic insects to riparian spiders and their microbiomes and antimicrobial levels; and 3) biofilms, leaf litter decomposition and macroinvertebrate microbiomes. For Obj. 1 and 2, food web sampling will be done upstream and downstream of effluent discharges to assess changes in its structure and reliance of macroinvertebrates, fish and spiders on wastewater-associated nutrients using stable C and N isotope ratios. Biological samples and surface water will be analyzed for antibiotics to assess their fate. Host microbiomes are characterized using the 16S rRNA gene of the V3-V4 region and Illumina sequencing and assessed for changes in diversity and relative abundance and the presence of wastewater-derived bacteria. Mesocosm experiments (Obj. 3) using mixtures of antimicrobials will determine effects on the microbiomes and growth of macroinvertebrates and ecosystem functions (e.g., decomposition). Overall, the program will address how these substantial discharges into Canadian surface waters are affecting key ecosystem processes and advance knowledge on the fate and effects of antimicrobials.