Beneath the rushing waters of any stream, there is a deposit of sediment called the hyporheic zone. Water from the stream, as well as groundwater, seeps into this nutrient-rich sediment, allowing a cornucopia of fish, plants, and other organisms to thrive. Furthermore, most of the chemical changes in a stream’s ecosystem take place in the hyporheic zone. Water flowing into the zone carries nutrients, pollutants, and dissolved oxygen, and water flowing back out carries transformed products into the stream, a process called hyporheic exchange.
Of these, dissolved oxygen plays a particularly important role in aquatic ecosystems: It regulates environmental pollutants, metabolic waste, and nitrogen and carbon cycling and promotes respiration, which is necessary for many organisms to survive. All of these processes affect the water quality, habitability, and carrying capacity of the hyporheic zone. For these reasons, the concentrations and consumption rates of dissolved oxygen are two of the biggest indicators of a hyporheic zone’s health and ability to support life. However, these interactions are complex, and scientists do not yet know enough about them to be able to predict future outcomes.
Past studies have mainly treated the consumption rate of dissolved oxygen as static and unchanged by organisms’ behavior. In a new study, Reeder et al. show how these variables can change over time. By comparing direct measurements of dissolved oxygen to mathematical models, the team was able to show that they could improve the accuracy of dissolved oxygen predictions. They also found that the consumption of carbon had an effect on microbes’ respiration rates over time.
The results of this study highlight the important chemical and physical relationships between the water, sediment, and organisms in a stream’s hyporheic zone and provide a solid foundation for improving existing models of these processes. (Water Resources Research, https://doi.org/10.1002/2017WR021388, 2018)
—Sarah Witman, Freelance Writer