Environmental forcing of phytoplankton floral composition, biomass, and primary productivity in Chesapeake Bay, USA

Modeling the seasonal autochthonous sources of dissolved organic carbon and nitrogen in the upper Chesapeake Bay

“…6) was lowest in the winter and peaked in the spring and again in late summer. The contribution to total primary production by the different size classes of phytoplankton changed seasonally with large phytoplankton dominating production in the spring and small phytoplankton dominating production in the late summer, a result that is consistent with studies of this area of the bay (Adolf et al, 2006). In the spring and early summer primary production was fueled by the uptake of nitrate, which was abundant at this time of year (Fig.…”

“…Since these results closely match the chlorophyll a concentrations reported at station CB3.3C (Fig. 3b) and the general patterns in phytoplankton composition and biomass reported for the Chesapeake Bay (Adolf et al, 2006;Malone et al, 1996) we believe that the model did a relatively good job of capturing the phytoplankton biomass dynamics at this station. The biomass of large zooplankton peaked in the spring following the springtime phytoplankton bloom and then leveled off with low biomass during the summer and very little biomass in the winter.…”

“…As our model was not embedded in a hydrodynamic model of the whole bay we could not easily reproduce this phenomenon and were therefore more reliant on temperature and light to trigger a spring bloom. In addition, our model did not account for the ability of mixotrophic species, which can be present at this station in high concentrations during the spring (Adolf et al, 2006;Keller, personal observation in 2007 and2008), to supplement their photosynthetic growth with grazing and, thus, grow better than strict phototrophs at low spring temperatures and light levels. The exponential temperature function that we used to set the maximum attainable daily growth rate of phytoplankton may have also contributed to the delay in the beginning of the spring bloom as it has often led models to underestimate primary production at lower temperatures (Brush et al, 2002;Cerco and Noel, 2004).…”

“…The chlorophyll a data that we used are based on the maximum chlorophyll a concentration in the water column and not just surface layer data. We did this because in the spring dinoflagellates, which migrate to the surface during the day and to just above or in the pycnocline at night, are often present and can represent most of the chlorophyll in the water column (Adolf et al, 2006;Keller, personal observation in 2007 and2008). As CBP sampling at this station often occurred early in the morning when the dinoflagellates were just starting to migrate from above the pycnocline, surface measurements underestimate the amount of chlorophyll that will be present in upper water column throughout most of the day (i.e., the chlorophyll a maximum is just above the pycnocline early in the morning and moves up toward the surface as the day progresses).…”

“…Therefore, we split (Table 3) inflowing chlorophyll between large and small phytoplankton based on research which shows that larger phytoplankton (mostly diatoms and large dinoflagellates) dominate both biomass and productivity in the winter, early spring, and late fall and that smaller phytoplankton (cyanobacteria, cryptophytes, flagellates and small diatoms) dominate production, but not necessarily biomass, in the summer (Adolf et al, 2006;Malone, 1980;Malone et al, 1996). The phytoplankton chlorophyll to carbon ratio is modeled (see Appendix A.18) as a function of temperature, light, and nutrient availability (Cloern et al, 1995).…”