Can phytoplankton maintaina positive carbon balance in a turbid, freshwater, tidal estuary?

Abstract

An analysis of phytoplankton primary production in the tidal freshwater portion of the Hudson River estuary suggests that net primary production is strongly limited by light and mixing regime. In this turbid, well-mixed system, cells spend from 18 to 22 h d-l below the 1% light level. Autotrophic dark respiration, conservatively estimated at 5% of pb,,,, is of sufficient magnitude to make positive algal growth impossible over much of the river and much of the year. It is particularly difficult to explain the observed increase in algal biomass during blooms in spring and summer. We hypothesize that such blooms can occur only in a small fraction of the river where depth is 54 m.

Enzymatic analysis of riverine bacterioplankton production

“…Large-scale relationships with reduced carbon abundance, measured as bulk DOC or as algal productivity, have been documented (Cole et al 1988;Tranvik 1990). These rela- tionships are valuable for intersystem comparisons and for making global predictions, but their resolution does not extend below the ecosystem level.…”

“…Samples from the Hudson River were collected from a well-studied station near Kingston, New York (Cole et al 1992;Findlay et al 1991). This location is tidal (range, l-2 m) but well above any influence of salt water.…”

“…Dissolved organic carbon (DOC) is assimilated into the microbial loop through heterotrophic bacterial production. Among ecosystems, bacterial production can be correlated with DOC concentration or, more indirectly, with primary production (Cole et al 1988). Within an ecosystem the trophic basis of bacterial production is more difficult to discern (Findlay et al 1991), partly because other physicochemical [UV radiation (Herndl et al 1993), nutrients (Meyer-Reil 1987), temperature (Hudson et al 1992;Shiah and Ducklow 1994)] and biological factors [grazing (Gonzalez et al 1990;Bott and Kaplan 1990), growth efficiency (Kroer 1993;Biddanda et al 1994)] play a role in regulating productivity.…”

Tidal and spring‐neap variations in horizontal dispersion in a partially mixed estuary

“…A surface release of fluoroscein would be significantly compromised by the nonconservative effect of photodecay. However, the Hudson estuary is so turbid that the 1% light level occurs between 2 and 3-m depth [Cole et al, 1992], so significant photo-decay would only occur if the dye reached the upper 2 meters of the water column. In order to minimize the problem of photo-decay, only nearbottom dye releases were performed.…”

An empirical model of the phytoplankton chlorophyll : carbon ratio‐the conversion factor between productivity and growth rate

“…If the smaller respiration losses described here under low-light conditions are realistic, then this approach may help resolve the paradox between observed and calculated C balances of phytoplankton populations in turbid waters (e.g. Cole et al 1992). Our model is not the ultimate solution to the challenging problem of how we define population growth responses of phytoplankton to changing light and nutrient availability.…”