Research

Our work focuses on the interactions and feedbacks among surface hydrology, vegetation, and the atmosphere. Our approach begins with pattern analysis of processes at the point scale and progressively moves up to the landscape scale, investigating the organized heterogeneity and physical fingerprints imposed by the structure of watersheds.  Here is a summary of our current research projects here in the Carbonshed Lab at Carolina:

1. CAREER: The Role of Small Wetland Connectivity in Controlling Greenhouse Gas Emissions and Downstream Carbon Fluxes from Headwater Tropical Streams. (Funding: NSF Hydrologic Sciences, NSF Education & Human Resources). A growing body of work recognizes inland waters as fundamental players in the carbon cycle. This study seeks to quantify the role of hydrologic connectivity across multiple landscape elements (i.e., uplands, floodplains, wetlands, and streams) on regulating the partitioning between atmospheric and downstream carbon losses. The study will be conducted in an ecosystem where both water fluxes and carbon storage per unit area are among the highest on Earth: the Andean Paramos of Ecuador. Results from this research will provide a comparison of carbon dioxide effluxes across terrestrial and aquatic landscape elements on a per unit area (or per unit time) basis and as a function of the hydrologic wetness status of the year. The broader impacts of this project include the design and implementation of educational activities directed at large and diverse audiences, including populations that are traditionally underrepresented in the sciences. After successfully completing field, outreach, and professional development activities, participating undergraduate students will receive a research designation on their transcript and graduate as Carolina Research Scholars. Materials from this work will be used to develop teaching lectures for different audiences, including K-12, undergraduate and graduate students, and the general public.

2. Effects of Land Use and Stream Network Dynamics on Water Quality across Urban-Rural Transitions. (Funding: State of North Carolina). Nutrient loading to headwater streams strongly mediates water quality downstream. This project seeks to characterize the spatial and temporal contributions of different land uses in headwater streams to nutrient loading in the Jordan Lake watershed, located in the Research Triangle of North Carolina. This rapidly developing area consists of a wide range of urban development and sanitary infrastructure, including marked differences in sanitary sewer density, parcel density, impervious surface cover, and geology. We seek to evaluate the range of hydrologic and water quality conditions that currently predominate upstream of Jordan Lake and quantify nutrient loading (including N and P) to the stream network and to the lake. The ultimate goal of this project is to devise strategies to optimize nutrient management for urban watersheds and reservoirs in rapidly urbanizing watersheds and across urban-rural transitions.

3. Impacts of Extreme Flooding on Hydrologic Connectivity and Water Quality in the Atlantic Coastal Plain and Implications for Vulnerable Populations. (Funding: NSF Hydrologic Sciences, NSF CBET).  Hurricane Matthew (October 2016) and Hurricane Florence (September 2018) brought extreme rainfall that led to severe flooding across eastern North Carolina. Land use in this region is dominated by large-scale crop-cultivation and includes some of the highest densities of concentrated animal feeding operations (CAFOs) and processing facilities in the United States. This RAPID projects seek to conduct an assessment of the near-term impacts of regional flooding on water quality in the Lumber River watershed in an effort to better understand flood-driven connectivity between upland contaminant sources and hydrologic systems (surface water, shallow groundwater, public water supplies) and its water quality implications for vulnerable populations. This project evaluates the post-hurricane spatial variability of biological (microbial community markers in wastewater), chemical (non-targeted high-resolution mass spectrometry screening), and physical (d18O, d2H, specific conductance) water quality characteristics of surface water, shallow groundwater, and the confined aquifer. Investigators: Diego Riveros-Iregui and Jill Stewart (UNC); Ryan Emanuel, Katie Martin, Josh Gray, Elizabeth Nichols, Angela Harris, Natalie Nelson (all NCSU).

4. Disturbance and Water Crises in the Tropics: The Galápagos Islands as a Case Study. (Funding: Two NSF Graduate Research Fellowships, two NSF-CZO SAVI Awards, Geological Society of America, CUAHSI student grant, National Geographic Young Explorers Grant, Faculty for the Future Fellowship, and Fulbright Fellowship).  The tropics are currently inhabited by 40% of the world’s population, and 55% of the world’s children under the age of five, yet by 2050 those proportions will increase to 50% and 60%, respectively. This projected growth makes the tropics of particular interest for global sustainability studies, as tropical regions will inevitably experience climbing pressures and demands for essential ecosystem services. The Galapagos Islands offer a unique example of a tropical environment that has a distinct, sharp microclimate zonation imposed by varying precipitation inputs at altitude. A layer of dense fog cloaks the humid highlands during the cool season each year, imparting seasonality on island hydrology. Increased demand on freshwater resources due to population growth, land use change, contamination, and increased tourism impose major challenges for the future sustainability of the Islands.

PAST PROJECTS:

5. Using a drought-enhanced nitrate pulse to understand stream N retention and processing (Funding: NSF – DEB).  Nitrogen (N) fertilization is a cornerstone of modern agriculture, but the practice also has led to eutrophication, hypoxia, and harmful algal blooms in both inland and coastal waters. Several studies identify Iowa, Illinois and Indiana as major sources of N discharged by the Mississippi River to the Gulf of Mexico where large-scale hypoxia develops annually. However, N reaching the Gulf is only a fraction of the N flushed from Midwestern agricultural landscapes or the N applied as fertilizer due to significant losses (physical and biological) during transport. This project seeks to understand how climate, precipitation patterns, and watershed morphology control the magnitude and timing of nitrate flushing from agricultural landscapes.  Investigators: Amy Burgin, Terry Loecke and Steven Thomas (all UNL), Diego Riveros-Iregui (UNC), Marty St. Claire (Coe College), and Adam Ward (Indiana University).

6. Agriculture at the Edge: Hydrologic Dynamics in the Tropical Andes.  (Funding: The World Bank).  Páramos, or alpine grasslands occurring right above the forest tree-line (2,800 – 4,700 m), are among the most transformed watersheds of the humid tropics. In the Tropical Andes, Páramos mark the highest altitude capable of sustaining vegetation growth (i.e., ‘the edge’), where they form an archipelago-like pattern from Central Peru to Northern Colombia, effectively capturing precipitation and atmospheric moisture originated in the Amazon-Orinoco basin. This project investigates the effects of land use and land fragmentation on fluxes of water, energy, and nutrients across a mountainous watershed in the Tropical Andes of Colombia.

7. Soil carbon transformation in heterogeneous landscapes: Implications for soil, water, and air (Funding: USDA).  This project addresses the poorly understood relationship between watershed geomorphic form, vegetation structure, and the spatial variability of soil carbon (C) stocks and fluxes. Despite growing knowledge of C cycle dynamics within heterogeneous landscapes, it remains less known how landscape complexity and the spatial arrangement of variables such as soil moisture and soil temperature, affect soil C balance on an ecosystem scale. The project seeks to understand how physical and biological dynamics intersect at the local scale to influence soil C stocks and fluxes, and how these processes integrate over complex landscapes. This project investigates landscape-scale patterns of soil C transformation and fluxes, including their 13C isotopic composition, and their relevance to soil C losses to the streams and the atmosphere.