Research
Developing Models for Advancing Ecology
Sparse modeling approaches for timeseries prediction and forecasting
Bayesian models for missing data in ecology
Process Guided Deep Learning to Predict Dissolved Oxygen
River Ecosystem Energetics
Linking Carbon Fluxes to Biomass Building in Rivers
Understanding Autotrophy in Rivers at a Continental Scale
The Impact of Climate Change on River Carbon Cycling
Much like forests, streams have annual ecosystem energy cycles. Stream algae and moss and other primary producers require light for photosynthesis, just like plants. In small streams, this means that peak productivity occurs in the early spring, before trees have all of their leaves that shade the stream. At the scale of a year, streams break down more organic carbon than they produce, and this additional fuel comes from plants and soils. In the fall, carbon consumption is high in streams as microbes and stream insects break down all of the leaves that fall from trees. Climate Change is altering the timing and the rates of these fundamental ecosystem processes in streams. In my research, I am studying stream energetics in New Hope Creek, which is the site of the first ever study of annual stream energetics in 1972. This stream flows through a protected watershed in the Duke Forest, and little about it has changed in the fifty years since this foundational study except for the global change in climate leading to warmer water and more extreme floods and droughts. In comparison to fifty years ago, carbon and energy in New Hope Creek cycle faster, and hotter, drier falls have shifted the timing of most of this cycling. This means that organisms in the stream have less food available to them in the winter and that substantial release of greenhouse gasses and depletion of oxygen may become more common in the late summer and Fall. This research demonstrates that changing climate will exacerbate the consequences to streams that we have observed in modified landscapes.
Past Research Projects
River Hypoxia
Hypoxia is when oxygen in an aquatic ecosystem is severely depleted, which can lead to fish kills, release of toxic metals from sediments, and production of atmospheric pollutants . Most research on hypoxia has focused on coastal areas and algal blooms in lakes, but in my research, I have observed extensive hypoxia throughout the rivers in the North Carolina Piedmont. My findings build on those from previous studies out of our research group that indicate that changes in river channel shape caused by urbanization including channel erosion from intense bursts of storm water flowing into culverts and flatter stream beds upstream of road impoundments are causing large portions of river networks to alternate between high storm flows and low flow leading to hypoxia (Carter et al. in press). This is a global problem of expanding concern as increasingly human modified and polluted landscapes interact with warming climate and more extreme hydrologic cycles.
Element cycles in aquatic sediments are strongly linked to the presence or absence of oxygen. This determines what type of microbial breakdown of organic carbon occurs and what molecules are released into the water.
Greenhouse gas flux from rivers
Most of the energy that fuels food webs in streams and rivers comes from breaking down plant matter and organic carbon that comes from outside of the ecosystem. The most efficient way to break down this carbon is using oxygen, through aerobic respiration. However, when oxygen is low, microbes can break down carbon through other, anaerobic metabolic pathways. Both aerobic and anaerobic respiration lead to the release of carbon dioxide into the atmosphere, anaerobic pathways are additionally responsible for removal of reactive nitrogen through denitrification, the mobilization of heavy metals and contaminants, and release of organic carbon as methane, a potent greenhouse gas. When rivers are hypoxic, rates of anaerobic metabolism are high, but many observations indicate these pathways are active in the sediments even when the water column is oxygenated. In my research, I have found measurable rates of anaerobic metabolism at every location that I have looked for it.
I am studying the release of greenhouse gasses, and the conditions that lead to this, in streams in Durham, North Carolina. I have found that flow and temperature both determine rates of carbon dioxide and methane production in streams. Importantly human modification of river networks are creating conditions that deplete oxygen and favor anaerobic metabolism , resulting in more greenhouse gas pollution in the atmosphere.
Oceanic Flux Program at the Bermuda Institute for Ocean Sciences
Before beginning work in streams, I worked with Dr. Maureen Conte as a research assistant for the Oceanic Flux Program. We worked to understand the rates and composition of oceanic particles that sink from the surface water, driving the distribution of organic matter and other elements in the deep ocean. Sinking particles undergo dynamic transformations as they are influenced by eddies and ocean currents, decomposition, secondary production and chemical processes. The particles that are observed at depth thus have a very complex temporal and chemical relationship with those formed in the surface ocean. I studied phosphorus phase partitioning and the trace element geochemistry of marine particles sinking through the water column at our field site in Bermuda. I found that iron and opal are important carriers of phosphorus to ocean sediments. Our research demonstrated that many trace elements have seasonal cycles at different depths in the ocean (Chemical Geology Paper: Conte et al 2019).
Toolik Lake Long Term Ecological Research Station
I worked under the guidance of Dr. Anne Giblin as the nutrient chemistry research assistant at Toolik Lake Long Term Ecological Research (LTER) site in northern Alaska. For two summers, I was part of a team conducting long term monitoring of Arctic lake ecosystems to understand how they respond to climate change and the nutrient loading that results when permafrost thaws.
Proyecto Costa Escondida - Sea level reconstruction in a Maritime Maya Site
The Proyecto Costa Escodida was an interdisciplinary team of geologists, ecologists and archeologists researching the occupation of an antient Maya port city, Vista Alegre, on the Yucatan Peninsula in Mexico. I worked with hydrogeologist Dr. Patricia Beddows to reconstruct the patterns of sea level inundation in relation to the times of Maya inhabitation of the city. I analyzed sediment cores from shallow estuaries, constructing a stratigraphic record with δ18O and δ13C to look at sea level fluctuations during the Holocene. I found that periods of low sea-level indicated fresh water availability and correlated with times of site occupation by the Maya residents (Water WIRES paper: Beddows et al 2016)