Nutrient enrichment and depletion on the shoreside of the spring thermal front

A thermal front was evident within the nearshore zone of the south shore of Lake Ontario near Oak Orchard Creek on 28 May 2008. Here, we characterize nutrient concentrations during thermal bar formation on the shoreside and lakeside of the thermal front within a 5 × 20-km polygon. We observed that total phosphorus levels and turbidity were elevated while silica and nitrate were reduced on the shoreside relative to the offshore of the thermal front. Phosphorus and suspended solid flux from Oak Orchard Creek contributed to elevated turbidity and phosphorus concentrations on the shoreside of the thermal front and were not transported to the lakeside of the thermal front. Two hypotheses, not mutually exclusive, are offered as potential explanations for the observed reduction in silica and nitrate: biological uptake by phytoplankton and benthic algae and long-shore transport of nutrient poor Niagara River water. This work not only demonstrates that nutrient entrapment may occur but also that biological mechanisms function to reduce nutrient levels within the shoreside of the thermal front.