Biogeochemistry is the study of how essential nutrients—such as carbon, nitrogen and phosphorus—move through different components of the ecosystem. Nutrients are continually cycling between soil, water, living organisms (including plants, animals and microbes), and the atmosphere. Studying these fluxes provides insights into ecological processes and the way ecosystems respond to changes in climate, land use or other human activities or disruptive natural events such as floods or forest fires.
Biogeochemical measurements quantify the storage and movement of nutrients through the biological, hydrological and geological systems of the ecosystem. These measurements focus on:
- Inputs: How nutrients are entering an ecosystem component (atmospheric deposition, groundwater nutrient content, carbon uptake)
- Outputs: How nutrients are leaving an ecosystem component (stream nutrient export, respiration, evapotranspiration)
- Stocks: The volume of carbon and other nutrients stored in different components of the ecosystem (e.g., biomass, soil carbon, nutrient pools)
- Fluxes: How nutrients are cycling between different ecosystem components (stream nutrient fluxes, carbon exchange, evapotranspiration, plant litter)
- Processes: The ecological processes that drive nutrient fluxes (decomposition, biomass production, microbial activity, stream metabolism)
Nutrients naturally move through the ecosystem through the water cycle and activities of organisms (e.g., respiration, consumption, excretion and decomposition). Human activities also impact nutrient fluxes. Energy production and industrial activities remove stored carbon from the earth and add it to the atmosphere as carbon dioxide (CO2). Modern agriculture relies on fertilizers that artificially add nitrogen, phosphorus and other nutrients back the soil; these nutrients can migrate through the ecosystem and make their way into streams, lakes and oceans through runoff. These and other human activities are changing the balance of nutrients stored in the atmosphere, soil and water and the availability of nutrients for living organisms. Rising levels of CO2 and other greenhouse gases in the atmosphere are a primary driver of global anthropogenic climate change. At a smaller scale, nutrient fluxes in soil and water can disrupt local ecosystems—as seen in the "algae blooms" that result from nutrient pollution in lakes caused by agricultural runoff.
The NEON Observational Sampling System includes the collection of biogeochemical data from:
- Soils and sediments
- Terrestrial plants, aquatic plants and microalgae
- Surface and groundwater
These data products can be used to examine complex ecological questions, such as:
- What are the factors that influence the ability of an ecosystem to sequester carbon from the atmosphere?
- How is the distribution of carbon in biomass changing over time and in different ecosystems?
- How are changes in nutrient availability interrelated with microbial activity and decomposition rates in soils and sediments?
- How does nutrient pollution impact aquatic microbes, microalgae and aquatic invertebrates?
Soils and Sediments
Soil and sediment biogeochemistry focuses on the concentrations of carbon and nutrient pools, stable isotopes of carbon (C) and nitrogen (N), and targeted measurements of N transformation rates. Nutrient concentrations in soils and sediments are a major constraint on plant growth, influence microbial activity and provide insights into the overall health of the ecosystem.
Soil biogeochemical data products include:
- Soil chemical properties (Megapit)
- Soil chemical properties (distributed initial characterization)
- Soil chemical properties (distributed periodic)
- Soil staple isotopes (distributed periodic)
- Soil inorganic nitrogen pools and transformations
Sediment biogeochemical data products include:
- Sediment chemical properties
Biogeochemical analysis of plant tissues—including foliar canopy, roots and litter—provides valuable information about nutrient intake and storage by plants in terrestrial ecosystems. Plants take in carbon from the atmosphere (as CO2) and take in carbon and other nutrients from the soil. By looking at carbon and nutrient contents in living foliar tissue, roots and litter, researchers can see how nutrients are cycling between above- and belowground processes.
Biogeochemical analysis of terrestrial plant tissues produces six data products:
- Plant foliar physical and chemical properties
- Plant foliar stable isotopes
- Litter chemical properties
- Litter stable isotopes
- Root chemical properties
- Root stable isotopes
Aquatic Plants and Microalgae
Aquatic plants and microalgae store and cycle carbon and other nutrients in the aquatic ecosystem, taking in nutrients from water and sediments and cycling them back through the ecosystem as they are consumed or die and decompose. The NEON project conducts chemical analysis of aquatic plants and microalgae collected at lakes and streams at the NEON aquatic field sites.
Biogeochemical analysis of aquatic plants and microalgae produces two data products:
- Aquatic plant bryophyte chemical properties
- Periphyton, seston, and phytoplankton chemical properties
Surface and Groundwater
Monitoring carbon and nutrient content of surface and groundwater allows researchers to assess the role of hydrological cycles in fluxes of nutrients between air, soil, water and living organisms. Nutrients make their way into surface water through precipitation, runoff from surrounding land and decomposition of aquatic organisms. Carbon and nutrients filter into groundwater through the soil or from surface water.
Surface water and groundwater data products include:
- Chemical properties of groundwater
- Stable isotope concentrations in groundwater
- Chemical properties of surface water
- Stable isotope concentrations in surface water
- Dissolved gases in surface water
- Nitrate in surface water