Fig. 4.

(A–D) Relationships between annual water and Hg runoff. Annual Hg yield (μg⋅m⁻²⋅y⁻¹) as a function of river runoff (cm y⁻¹) for North American (NA) and Eurasian (EA) watersheds to the AO and for the NA watershed to the larger Hudson Bay (HB). Year of observation is coded with rivers, which are abbreviated as follows: CH, Churchill; GW, G. Whale; MK, Mackenzie; NE, Nelson; SL, Saint Lawrence; SD, S. Dvina; and YE, Yenisei. The SL does not run off into the HB but is included in the linear regressions. The regressions were used to estimate annual THg (A), DHg (B), PHg (C), and DMeHg (D) fluxes for 112 pan-Arctic rivers for which discharge and watershed area are documented (Dataset S2).