For years, PNNL researchers have been part of a wide scientific effort to study how land and water interact. From soils at the pore scale to regions at the watershed scale, they have investigated the interface between terrestrial and aquatic systems, which are ecologically critical and biogeochemically dynamic.

Around the world, aquatic ecosystems dominated by water include streams, rivers, ponds, lakes, estuaries, and oceans. They interact with terrestrial ecosystems beginning with vegetated wetlands in carbon-rich hybrid zones of water and land.

These terrestrial-aquatic zones are relatively small in size, but they have monumental consequences for Earth systems. They capture, store, transform, and release carbon, nitrogen, water, energy, and other entities that influence feedback loops with aquatic environments, land ecosystems, the atmosphere, and climate.

Carbon cycles and more

Some scientists at PNNL specialize in the carbon cycle of soils, which sequester much of the Earth’s carbon, and—depending on conditions of wetting and drying—release it back into the atmosphere as carbon dioxide.

Others monitor biogeochemical exchanges that occur in riverine hyporheic zones, where fresh water and groundwater mix in reactive regions of sediment and rock.

Still others at the lab specialize in studies of permafrost, which can be fairly described as sites of terrestrial-aquatic interchange.

PNNL-Sequim is the only coastal research site within the national laboratory system of the Department of Energy (DOE). Researchers there support DOE missions related to sustainable energy (including algal biofuels and ocean-wave energy), coastal hazards risks, wetlands health, marine chemical transport hazards, and biofouling.

Other researchers at PNNL were part of recent studies sponsored by the DOE’s Terrestrial Ecosystem Science program, including a six-year effort investigating soil carbon biogeochemistry.

One ecologist at the lab inspired and now directs an international consortium of researchers called the Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems (WHONDRS). In a world where thousands of dams are emplaced on rivers annually, WHONDRS researchers collectively aim to understand the hydrologic, biogeochemical, and microbial impacts of the high-frequency water level fluctuations that dams engender.

The TAI Gap

Still other scientists at PNNL are part of a growing effort to incorporate terrestrial-aquatic interfaces (TAIs) into Earth systems models. TAIs are where fully terrestrial ecosystems transition to those that are fully aquatic—the largely coastal areas of the planet that some scientists say go from “boots to boats.”

To date, Earth system models only include static fractions of dry land and open water. That approach misses much of what is in between: an ecologically critical hybrid of wet-to-dry features that mark coastal areas and that are global hotspots of biological, biogeochemical, and ecological activity. In 2016, DOE sponsored a landmark workshop to correct what it called the “TAI gap” in Earth system models. The resulting report on research priorities was co-authored by a PNNL soil microbiologist.