Collaborative Research: Quantifying terrestrial riparian-stream carbon connections across a salt gradient

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Forests and streams are intimately connected by the sharing of carbon as vegetation and animal biomass, such as leaf litter inputs to streams. Still, the land and the stream are often studied in isolation, which can lead to fundamental misunderstandings of how changes in one system impact one or both systems. Globally, salinization is a current major change in both terrestrial soil and freshwater systems. Salinization can change water quality and drinking water suitability, carbon storage and quality, and plant productivity. Freshwater salinization often begins through terrestrial salinization from human activities like urbanization, agricultural practices, and road salting. Yet, predicting how salinization alters carbon inputs across riparian-stream boundaries is not yet possible. This research will quantify how salinization, which can both subsidize and stress organisms, alters carbon processing across terrestrial-aquatic boundaries, through field work and experiments. The project will also examine the relationship between terrestrial and aquatic salinity in part from the collaborations of crowd-sourced k-12 teacher data. This project will also support three female PIs, mentorship of three graduate and four undergraduate students, support three REU students, and incorporate public participation and awareness through citizen science. This research will identify fundamental principles about how aquatic and terrestrial systems will respond to increased salinization. This project will quantify how sodium chloride inputs to riparian zones and streams interact to alter decomposition, secondary production, gross primary productivity, ecosystem respiration, and net ecosystem production in both terrestrial riparian and aquatic stream ecosystems using experimentally paired riparian-stream mesocosms and a field decomposition study across a sodium gradient. The responses are expected to follow a subsidy-stress model. Sodium chloride (NaCl) should act as a subsidy and increase these processes up to some optimal threshold because Na is a biologically essential nutrient. After which, these processes should decrease as Na becomes a stressor at sub-lethal levels and a toxicant at higher levels. The primary objectives are to 1) measure and quantify field terrestrial-stream relationships using a decomposition study that concurrently measures soil and stream chemistry across a large salinization gradient (electrical conductance ranging from 30-1200 micro Siemens per centimeter), 2) experimentally determine how soil salinization impacts terrestrial-aquatic carbon exchange across a gradient of salinization in novel paired terrestrial riparian-stream mesocosms, and 3) quantify the field-mesocosm relationship to determine the congruence of experimental mesocosm- and field-measured decomposition rates across a salinity gradient. Using a combined terrestrial-aquatic approach is essential to understanding, predicting, and ultimately mitigating negative salinization impacts on terrestrial and aquatic ecosystem structure and function. 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.