Field sampling wraps up for OAH study examining influence of wastewater nutrients in coastal waters

SCCWRP and its member agencies have finished collecting two years of field sampling data for a study that will assess the relative influence of anthropogenic vs. natural sources of nutrient inputs on biogeochemical cycling in the Southern California Bight.

The study is intended to ascertain whether there are differences in dissolved oxygen levels, pH and algal blooms along the coastline and/or offshore as a result of discharging nutrients, including nitrogen, in wastewater effluent.

Changes in biogeochemical cycling can trigger ocean acidification and hypoxia (OAH), but it is unclear if natural upwelling is the dominant driver of these processes or if nutrients in wastewater effluent also are driving OAH.

During field sampling, nitrogen and carbon cycling were measured in multiple ways, including primary production and respiration, nitrogen uptake by primary producers, and nitrification, in which the dominant form of nitrogen in effluent is biologically transformed into nitrite.

Stable isotope source tracking techniques also were applied to determine the contribution of distinct nitrogen sources to standing stocks of phytoplankton, zooplankton and water column nutrients.

The field data are being used to validate a new coupled physical-biogeochemical model of the Southern California Bight that will estimate the extent to which anthropogenic vs. natural sources of nutrients are impacting biogeochemical cycling.