OAH model used to investigate effects of nutrient discharges in coastal waters

A research team that has been modeling how land-based nutrient discharges into California coastal waters influences ocean acidification and hypoxia (OAH) has demonstrated how to use the model for predicting how coastal OAH conditions would be affected if these discharges were reduced.

The modeling effort, described in a journal article published in December, tested multiple hypothetical management scenarios that involve reducing nitrogen discharges by 0%, 50% and 85% across 19 Southern California wastewater outfalls.

The modeling work predicted that nitrogen reductions would result in a reversal of subsurface oxygen and pH losses, an expansion of simulated habitat volume for shelled organisms that are sensitive to pH losses, and an expansion of aerobic habitat for fish.

The findings, which are undergoing review by an independent panel of scientific experts convened to review the OAH modeling work, mark a key first step toward answering management questions about the role of land-based nutrient discharges, if any, in exacerbating coastal OAH conditions.

The next step is to run modeling simulations with more realistic nutrient-reduction scenarios – scenarios informed by changes that managers at each outfall could realistically make to their water recycling and nutrient management practices. Researchers also need to weigh the potential benefits of taking short-term actions to reduce nutrients against the pace with which OAH is intensifying in Southern California coastal waters.