Water Resources Research Act Program

Principal Investigators: Jose Sanchez Ruiz

Abstract: Increasing anthropogenic disturbance (e.g., land-use, pollution, climate change) poses asignificant threat to freshwater ecosystem structure (e.g., diversity, abundance) and function (e.g.,nutrient cycling, production, and energy flow). Mining has been a pervasive disturbance in the westernUS and represents a major source of heavy metal pollution in freshwater systems (Miller et al. 1993,Canfield et al. 1994, Poulton et al. 1995, Moore and Langner 2012, Langner et al. 2012). Miningactivities often lead to decreases in species richness and abundance (Canfield et al. 1994, Poulton et al.1995, Hogsden and Harding 2012), and freshwater communities in heavily contaminated sites typicallyharbor a small subset of the potential species pool. To date, relatively very few studies have consideredthe consequences of these changes on ecosystem function (Hogsden and Harding 2012). Yet, suchinformation is critical for the management and restoration of freshwater communities and associatedecosystem services (e.g., fisheries production).Food webs can provide a powerful way to assess the impact of disturbance on ecosystems. In thecontext of heavy metal contamination, food webs may be simplified due to loss of sensitive species, adecrease in the number of interactions between species, and extirpation of top predators (Hogsden andHarding 2012, Pomeranz et al. 2019). Additionally, heavy metals can bioaccumulate or biomagnify upthe food chain depending on the metal, the species, and trophic pathways (Miller et al. 1993,Woodward et al. 1995, M. Besser, W. G. Brumbaugh, T. W. M 2001). Indeed, metal-contaminated diets,more than the basic occurrence of metals in the system, contribute to chronic toxicity in trout in theClark Fork River in Montana (Miller et al. 1993, Woodward et al. 1995).The Clark Fork River watershed, due to historical mining activities (1880 - 1972), has been polluted withan estimated 14.5 million m3 of tailings and heavy metal (Cu, Cd, Pb, Mn, Zn, and As) sludge (Canfield etal. 1994). The concentrations of metals decrease downstream from Butte MT, producing a steepenvironmental pollution gradient. As a consequence, brown trout fisheries have decreased fromdensities of up to 1250 fish/km to 21 to 125 fish/km in some locations (Woodward et al. 1995). Somehave attributed this decline to low recruitment and poor water quality; however, there is considerableuncertainty about the specific mechanism (Woodward et al. 1995). At the base of the food web, it islikely that bioavailability of metals, and the consequent transfer of metals to higher trophic levels (i.e.,fish), is influenced by redox conditions in river biofilms and the functional composition of microbialcommunities (M. Besser, W. G. Brumbaugh, T. W. M 2001, Nimick et al. 2011, Fashola et al. 2016).Explicit consideration of these communities in consumer guts may allow a mechanistic understanding ofhow metals enter and influence river food webs, including the Clark Fork.Efforts to understand trophic ecology and impacts on ecosystem function has led to the development ofnext-generation molecular techniques such as eDNA and metabarcoding (Roslin and Majaneva 2016,Pawlowski et al. 2018). DNA metabarcoding techniques can provide broad taxonomic resolution (i.e.,~1000% more ids per sample and ~600% more ids total in fish; JakubaviÄiÅ«tÄ— et al. 2017) in comparisonto traditional methods, and the potential for estimating proportions of biomass (i.e., method such asMNI; Corse et al. 2017); this approach has the potential to produce highly resolved ‘maps’ of food webinteractions in ecosystems (Roslin and Majaneva 2016) . Here, as a component of my broader Ph.D.research, I propose to use metabarcoding techniques to disentangle the influence of microbialcommunity structure on the flux of metals to higher trophic levels.