Looking at the bigger picture, we want to find out what land use change is doing to change the dynamics of carbon and nitrogen cycling. Ziegler cites dramatic changes in an isotope of the amino acid alanine that she studied in a freshwater marsh in the Chesapeake Bay watershed as an example. The stable carbon isotopic composition of alanine serves as an indication of the metabolic activity of phytoplankton. The researchers took samples throughout the day to create scientific snapshots of the stream in small intervals. They found an enriched carbon 13 signal from phytoplankton at the end of the day.
Plants usually use the lighter carbon dioxide first, before tapping into the heavier isotope.
This indicates a large draw down of carbon dioxide in the system during the day and an overall increase in primary production. They also found seasonal variations in isotopes, indicating that plants and microbes contribute differently to the ecosystem depending upon the time of year. This may offer some explanation as to why algal blooms, such as the one in the Gulf of Mexico, occur seasonally. Ziegler plans to use the isotope techniques in the Arkansas delta region of the Mississippi to explore the biochemical cycles in the water and how they might be altered by human actions. The Mississippi River drainage affects a large area starting in Minnesota and ending in the Gulf of Mexico, and changes in land use throughout the Midwest may have contributed changes to the entire ecosystem.