Carbon cycling and food web energy transfer in salinized headwater streams

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Freshwater ecosystems are becoming salinized (or “salty”) across the globe from activities associated with agriculture, road de-icing, wastewater discharge, and mining. In central Appalachia, headwater stream ecosystems are particularly vulnerable to the impacts of salinization from surface coal mining, a widespread economic activity in the region. Increased salt concentrations stress aquatic organisms and can make headwaters unlivable for some microbes and animals. This is concerning because Appalachian headwaters are home to some unique organisms and collectively, have some of the most diverse aquatic insect communities in the world. Stream insects are especially adapted to cycling nutrients and distributing food energy from the surrounding forests into aquatic food webs. There is an urgent need to understand how salinization affects the freshwater insect community, stream productivity, and food web energy transfer. The consequences of salinization on freshwater animals in headwater streams will be shared with local K-12 teachers and trainees, scientists, and regional policy makers. New metrics for stream bioassessments will also be developed and shared. This research will assess salinity effects on carbon (C) processing in headwater streams through measurements of food web C production and transfer. Enhanced weathering of mining-exposed minerals can elevate major ions and salinity in headwater streams, with documented impacts to microbial and macroinvertebrate growth and community composition. Such organismal stress responses likely have cascading effects on stream food webs and ecosystem processes like decomposition and primary production. Salinization is predicted to alleviate salt limitation in primary producers and increase gross primary production (GPP). In contrast, subsidy-stress responses are predicted in heterotrophic production. Thus, along an increasing salinity gradient, similar subsidy-stress responses in trophic transfer efficiency could ultimately decrease food web C transfer at the highest salinities. To test these hypotheses, simultaneous measurements of C pools, transfers, and transformations will be taken in nine study streams that represent a salinity gradient. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.