Primary production by suspended and benthic microalgae in a turbid estuary:time-scales of variability in San Antonio Bay, Texas

Abstract

The within-day, between-day and month-to-month variability of light attenuation and microalgal chlorophyll a (chl a ) and photosynthetic response was measured in San Antonio Bay, Texas, USA. Waters were shallow (<2 m) and turbid (attenuation coefficients of 0.7 to 15.3 m"), yet daily rates of primary production (0.1 to 2.5 g C d-') were comparable to those in much deeper and clearer estuaries. Chl a concentrations in the sediment (459 to 7837 mg m-3 in the surficial millimeter) were much higher than those In the water column ( 4 to 48 mg m-'). The benthic assemblages were photosynthetically competent, but dally benthic primary productivity was low (0.00 to 0.09 g C m-' d-'; an average of 2'Lb of productivity in the water colun~n) because of the very low irradiances at the sedimentwater interface. The high rates of production by the suspended mlci-oalgae were largely due to high chlorophyll-specific light-saturdted rates of photosynthesis. P:,:' 13.0 to 24.4 g C (g chl a)-' h -' ] , which were correlated positively wlth temperat~lre and inversely with the mean irradiance in the water column. The between-day and temperature-~ndependent variation in P$! was also correlated with F,,Chl-l, a n index of the proportion of functional photosystem 11 reaction centers. In turn, within-day variability in F,,Chl-l was inversely correlated with the mean irradiance in the water column in 8 of 10 observations, a pattern consistent with photoinhibition. A depression of P : ! ' caused by photoinhibition throughout the water column may therefore b e responsible for the inverse trend of P$' with mean irradiance in the water column. Short-term (h) variability in suspended chl a and turbidity was high (coefficient of variation = 13 to 7 5 % ) , but estimates of daily productivity could be predicted with reasonable fidelity (mean error 2 7 % ) from a single midday determination of chl a, the photosynthesis versus lrrad~a n c e response and the attenuation coefficient, along with daily incident radiation. The predictive power of a single observation was due to coherence in the variation of chl a, P: :' and the attenuation coefficient In the water column-the decrease in mean irradiance caused by resuspension was compensated for by concomitant Increases in Pc,hland suspended chl a Between-day variability in productivity of 15 to 5 2 % approached month-to-month differences, so the optimal use of resources in monitoring productivity would be to take slngle samples daily.

Control of phytoplankton production by physical forcing in a strongly tidal, well-mixed estuary

“…In particular, the coupling between primary production and sediment dynamics has been overlooked in the past, partly because the study of these processes pertains to scientific disciplines that have largely evolved independently. Many authors have studied the correlation between phytoplankton production and turbidity, using the composite parameter BZE: biomass B, euphotic depth Z and solar irradiance E (Cole and Cloern, 1984;Harding et al, 1986;Cole and Cloern, 1987;Keller, 1988;Cole, 1989;Boyer et al, 1993;MacIntyre and Cullen, 1996). This empirical model may explain a large part of the variability of phytoplankton production in many estuaries, especially at the seasonal scale.…”

Critical events in the Ariake Bay ecosystem: Clam population collapse, red tides, and hypoxic bottom water

“…MacIntyre et al (1996) emphasized the importance of the benthic micro-algae that grow on the sediment surface in the primary production on the tidal flats. Montani et al (2003) estimated the primary production by the benthic micro-algae as 434 gC/m 2 /day on the tidal flats facing Seto Inland Sea, western Japan, and showed that the amount of primary production on the tidal flats was approximately double that by the phytoplankton in the whole water column offshore from the tidal flats, and the production was concentrated at the thin layer of the sediment surface only 5 mm in depth.…”

Modeling photosynthesis‐irradiance curves: Effects of temperature, dissolved silica depletion, and changing community assemblage on community photosynthesis

“…We will call this the two-step approach. Usually, simple linear techniques (ANOVA, regression, principal components analysis [PCA]) are used to study the variation in the α and P m estimates and their relation with abiotic factors (e.g., Kromkamp and Peene 1995;MacIntyre and Cullen 1996;Goebel and Kremer 2007). In contrast, we propose to extend the Webb model (Eq.…”

“…Next the spatiotemporal properties of the parameters of the P-I curve, of plankton production, and of the trophic status of the ecosystem are studied (e.g. Alpine and Cloern 1988;Keller 1988;Cole 1989;Kromkamp and Peene 1995;MacIntyre and Cullen 1996;Goosen et al 1999;Gazeau et al 2005;Goebel and Kremer 2007). Whereas the former approach elucidates the mechanisms underlying algal growth, the performance of the models under (changing) ambient conditions is difficult to assess, since it is virtually impossible to replicate all occurring natural situations in the laboratory.…”