As expected, lead release from coupons increased with water temperature. Raising the cell temperature from 4 to 21°C caused a 120% increase in geometric mean lead release (Figure ). That is, [𝑃𝑏] ,'˚1 /[𝑃𝑏] 2˚1 -1 = 1.2. But while temperaturedependent lead release has been described elsewhere, the solubilities of several common lead minerals do not appear to be temperature-sensitive. It is not clear whether changes in solubility, dissolution, complex formation, or particle mobility are primarily responsible for temperature-driven seasonality. Adding 1 mg PO4 L -1 decreased total lead release by 34% (Figure ), while aluminum had the opposite effect; increasing the aluminum concentration from 20 to 500 µg L -1 increased total lead release by 41%. Adding orthophosphate and increasing aluminum concentration accompanied a further 61% increase in lead. That is, the combined effect of aluminum and orthophosphate was larger than would be expected based on the main effect of each factor. This may be due to formation of particulate aluminum and phosphorus-perhaps as aluminum phosphate. Particulate phosphorus was highest at the high aluminum level, and in this form it would presumably be less available to react with lead in a way that immobilized lead at the scale-water interface (Figure and Figure ). Consistent with this interpretation, substantially less phosphorus was lost to the system at the high aluminum level (i.e., more remained in the water phase).