Fig. 4.

Drivers of hypoxia in (A and B) Elkhorn Slough and (C) northeast Pacific estuaries. (A and B) Path analysis from results of SEM (SI Methods) showing the direct and indirect drivers of lower DO (i.e., degree of hypoxia measured in annual 10th percentile) in upper (A) (n = 15, χ² = 5.76, df = 6, P = 0.45) and lower (B) (n = 10, χ² = 6.90, df = 10, P = 0.74) Elkhorn Slough, respectively. Solid lines indicate significant correlations (P < 0.10); dashed lines indicate insignificant correlations (P > 0.10); line widths are proportional to regression coefficients, and only paths with significant effects on DO and their corresponding coefficients and R² are shown. Black lines indicate positive correlations and red lines indicate negative correlations. Gray lines were significant correlations that were not used in the final model because their paths did not lead to DO. (C) Hypoxia in northeast Pacific estuaries of the United States as a function of latitude and El Niño (n = 3) and non-El Niño (n = 3) years (SI Methods). Each point represents the mean among stations at each estuary.