Hydrogen is a type of element that can have different types called isotopes. Biogeochemistry is the study of the way that living things interact with the environment around them. People who study hydrogen isotope biogeochemistry want to know more about how living things use and change different types of hydrogen isotopes.
It's kind of like how you can have different types of money, like pennies, nickels, dimes, and quarters. Some of these have different values, and people might use them in different ways depending on what they're trying to do. Hydrogen isotopes are like different types of money that living things can use in different ways.
Scientists who study hydrogen isotope biogeochemistry might look at things like how different types of plants absorb different types of hydrogen isotopes from the soil, or how animals might use different types of hydrogen isotopes to make their body parts. They might also be interested in how different types of hydrogen isotopes can tell us about the environment itself, like where water might have come from or how it has moved around over time.
By studying hydrogen isotope biogeochemistry, scientists can learn a lot about how living things interact with the world around them, and how those interactions can tell us more about our planet's past, present, and future.