MEPS 122:27-43 (1995)  -  doi:10.3354/meps122027

The winter/spring bloom of 1990 in Chesapeake Bay, USA, was prolonged and well developed, relative to other recent years, along the axis of the Bay. However, the bloom did not occur uniformly along the axis of the Bay, but rather developed and dissipated at different times in different regions of the Bay. The peak of the bloom progressed northward and was observed in late March in South Bay, early April in Mid Bay, and not until mid May in North Bay. We measured biomass and nutrient concentrations and the rates of carbon, nitrogen, phosphorus, and silicon utilization during the development and dissipation of the bloom, and compared ratios of these rates to the elemental ratios of the incoming nutrients and the resulting particulate material. In North Bay, bloom development was probably delayed due to light limitation of carbon uptake. Nitrogen was delivered and utilized in excess of stoichiometric proportions in the northern part of the Bay, eventually leading to phosphorus and/or silicon limitation. In the mid portion of the Bay, the mean stoichiometric proportions of the particulate nutrients were similar to Redfield proportions, but ratios of uptake of nitrogen and phosphorus exceeded Redfield proportions by more than 20-fold, reflecting both the high uptake rates of nitrogen and low uptake rates of phosphorus in that region. However, only at the peak of the bloom in mid April did transient phosphorus limitation of growth occur at Mid Bay. In contrast, ratios of nitrogen to phosphorus uptake rates in South Bay were considerably below Redfield proportions, primarily due to the low availability and low uptake rates of nitrogen. Concentrations of Si(OH)₄ in South Bay were also extremely low through the bloom period, and thus Si(OH)₄ and nitrogen, as well as PO₄^3-, limited growth there. In addition, temperature appeared to play a key role in the collapse of the diatom assemblage in mid May. During the early stages of the bloom in South Bay, NO₃^- + NO₂^- contributed >60% of the total nitrogen utilized, but by the end of the spring bloom period in May, over 50% of the nitrogen utilized was urea alone. These data underscore the need to understand how freshwater flow, ambient nutrient concentrations, temperature, and light differ along the axis of the Bay to understand the differential timing and magnitude of bloom development in different regions of the Bay.

Phytoplankton · Spring bloom · Chesapeake Bay · Nutrient dynamics · Nutrient ratios