Fig. 2.

(A) Subsurface (30 to 45 m) ammonium (${\mathrm{N}\mathrm{H}}_4^{+}$) concentration (mmol ${\mathrm{m}}^{-3}$) averaged during summer (June to August between 1997 and 2000) from the ANTH simulation (background color contours) and in situ observations (colored dots), showing the location and dispersal of ammonium-enriched wastewater plumes near the coast. Blue stars show the location of three large POTW outfalls. A detailed illustration of the coast-wide inputs is presented in SI Appendix, Fig. S1. Oceanic regions shallower than 30 m in the Santa Monica and San Pedro shelves are shown in white in A. (B and C) Dissolved inorganic nitrogen (nitrate plus ammonium, ${\mathrm{N}\mathrm{O}}_3^{-}$ + ${\mathrm{N}\mathrm{H}}_4^{+}$, in mmol ${\mathrm{m}}^{-3}$) averaged during winter along a cross-shore section in the Santa Monica Bay, shown by the solid black line in A, where B is the ANTH simulation and C is the CTRL simulation. Weak wintertime stratification allows shoaling of buoyant plumes and mixing, exposing anthropogenically enriched waters to the surface, evident in B.