loading page

Influence of Anthropogenic Nutrient Inputs on Rates of Coastal Ocean Nitrogen and Carbon Cycling in the Southern California Bight, USA
  • +6
  • Karen McLaughlin,
  • Meredith Howard,
  • George Robertson,
  • Carly Beck,
  • Minna Ho,
  • Faycal Kessouri,
  • Nikolay Nezlin,
  • Martha Sutula,
  • Stephen Weisberg
Karen McLaughlin
Southern California Coastal Water Research Project

Corresponding Author:[email protected]

Author Profile
Meredith Howard
Southern California Coastal Water Research Project
Author Profile
George Robertson
Orange County Sanitation District
Author Profile
Carly Beck
Southern California Coastal Water Research Project
Author Profile
Minna Ho
Southern California Coastal Water Research Project
Author Profile
Faycal Kessouri
Southern California Coastal Water Research Project
Author Profile
Nikolay Nezlin
Southern California Coastal Water Research Project
Author Profile
Martha Sutula
Southern California Coastal Water Research Project
Author Profile
Stephen Weisberg
Southern California Coastal Water Research Project
Author Profile

Abstract

Coastal nitrogen (N) enrichment is a global environmental problem that can influence acidification, deoxygenation, and subsequent habitat loss in ways that can be synergistic with global climate change impacts. In the Southern California Bight, an eastern boundary upwelling system, modeling of wastewater discharged through ocean outfalls has shown that it effectively doubles N loading to urban coastal waters. However, effects of wastewater outfalls on biogeochemical rates of primary production and respiration, key processes through which coastal acidification and deoxygenation are manifested, have not been directly linked to observed trends in ambient chlorophyll a, oxygen and pH. In this paper, we compare observations of nutrient concentrations and forms, as well as rates of nitrification, primary production, and respiration, in areas within treated wastewater effluent plumes compared to areas spatially distant from ocean outfalls where we expected minimum influence of the plume. We document that wastewater nutrient inputs have an immediate, local effect on nutrient stoichiometry, elevating ammonium and nitrite concentrations and increasing dissolved nitrogen: phosphorus ratios, as well as increasing rates of nitrification within the plume. We did not observe a near plume effect on nitrate assimilation into the biomass, primary production, chlorophyll a, respiration, or dissolved oxygen concentration, suggesting any potential impact from wastewater on these processes is moderated by offshore factors, notably mixing of water masses. These results indicate that a “reference-area” approach, wherein stations within or near the zone of initial dilution (ZID) from the wastewater outfall are compared to stations farther afield (reference areas) to assess contaminant impacts, is insufficient to document regional scale impacts of nutrients. Understanding of the complex interactions between local, regional, and global drivers on coastal eutrophication requires coupled observational-numerical modeling approaches where numerical models are carefully validated with observed state and rate data to develop effective, evidence-based solutions to coastal eutrophication.