Collaborative Research: MSA: Uncovering local and regional controls on organic matter processing in freshwaters using in situ optical sensors

Inland waters, including streams, rivers, wetlands, and lakes, are critically important to the global carbon cycle. A portion of the organic carbon produced on land by plants is eventually transported into inland waters. Organic carbon that enters waterways is processed by aquatic organisms and sunlight into carbon dioxide.

Aquatic plants and algae convert some of this carbon dioxide back to organic carbon via photosynthesis. These processes are well understood, but how environmental conditions such as temperature, salinity, and nutrient levels influence the relative importance of each process is not. Furthermore, the molecular composition of the organic carbon created and consumed in waterways remains unclear.

To fill this knowledge gap, the investigators will use a national network of water quality sensors to estimate organic carbon processing in streams, rivers, and lakes at a continental scale. The research team will build interpretive websites for interested individuals to view how organic carbon processing varies in streams and rivers across the United States.

This website will be used to communicate how such models can be used to predict the presence of harmful algae blooms or organic carbon compounds that cause harmful disinfection byproducts in water purification systems.

Alterations to carbon cycling by inland waters can negatively impact water quality. Therefore, up-to-date information is needed to prevent and manage emerging water quality problems. Models based on data from optical sensors provide a solution for rapid and automated analysis of aquatic carbon cycling.

The National Environmental Observatory Network (NEON) maintains a network of sensors in streams, rivers, and lakes that measure ultraviolet and visible light absorption of water, which can be used to estimate the amount and composition of organic carbon in water. To improve the reliability and accessibility of these datasets for the scientific community, the investigators will develop correction factors to convert raw sensor data to chemically relevant absorbance units.

To estimate how environmental conditions in streams, lakes, and rivers influence organic carbon production by photosynthesis and consumption by heterotrophic metabolism and photo-oxidative degradation, the investigators will analyze the calibrated sensor data entailing sunlight levels, water chemistry, temperature, and hydrology data from NEON. The research team will perform laboratory incubation experiments to measure actual rates of organic carbon consumption and production under controlled conditions, thereby disentangling the different processes influencing organic carbon production and consumption in freshwater ecosystems across North America.

All code produced for this project will be annotated and made publicly available via a GitHub repository. Resulting data products will be published and models will be integrated with existing data streams where possible. This project will support early-career investigators including one post-doctoral scientist and one research experience for undergraduates (REU) trainee.

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.