FROM MACRO- TO MICRONUTRIENT: TRACE ELEMENT DISTRIBUTIONS IN GREAT LAKES WATERS

Micronutrient trace elements—usually iron—limit primary productivity in some oceanic regions (so-called High Nutrient, Low Chlorophyll). As a result of iron limitation, available nitrate and phosphate go unused by phytoplankton. The Great Lakes, especially Lake Erie, have been heavily impacted by human activities, including receiving large amounts of fertilizer runoff containing nitrate and phosphate that can feed harmful algal blooms. However, the micronutrient status of the Great Lakes has thus far been unexplored, and micronutrient controls on Great Lakes primary productivity remain unknown. In this study we present novel trace element water column data from multiple sites in Lake Superior and Lake Erie. Trace element concentrations in Lake Erie are nearly always greater than those in Lake Superior, in some cases by as much as an order of magnitude. Concentrations of industrially useful metals, many of which are also micronutrients, are similar to or greater than oceanic concentrations in Lake Erie. These data suggest that trace elements may limit primary productivity in Lake Superior, and fail to limit phytoplankton growth in Lake Erie. Therefore controlling micronutrient input to the Great Lakes could potentially reduce unwanted phytoplankton blooms despite abundant bioavailable nitrate and phosphate.