Annual patterns of phytoplankton density and primary production in a large, shallow lake: the central role of light.

TORREMORELL , ANA; LLAMAES, MARIA EUGENIA; PÉREZ, GONZALO; ESCARAY, ROBERTO; BUSTINGORRY, JOSÉ; ZAGARESE, HORACIO

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 54 p. 437 - 449

0046-5070

1. We studied the seasonal dynamics of suspended particulate matter in a turbid, largeshallow lake during an annual period (2005–06). We relate the patterns of sestonconcentration (total suspended solids), phytoplankton biomass and water transparency tothe seasonal pattern of incident solar radiation (I0). We also report the seasonal trends ofphytoplankton primary production (PP) and photosynthesis photoinhibition due tophotosynthetically active radiation (PAR) and ultraviolet radiation (UVR) (Ib and UV50).2. We first collected empirical evidence that indicated the conditions of light limitationpersisted during the study period. We found that the depth-averaged irradiance estimatedfor the time of the day of maximum irradiance (Imean–noon) was always lower than themeasured onset of light saturation of photosynthesis (Ik).3. We then contrasted the observations with theoretical expectations based on a lightlimitation scenario. The observed temporal patterns of seston concentration, both on avolume and area basis, were significantly explained by I0 (R2 = 0.39 and R2 = 0.37respectively). The vertical diffuse attenuation coefficient (kdPAR) (R2 = 0.55) and the depthaveragedirradiance (Imean) (R2 = 0.66), significantly increased with the I0; while theirradiance reaching the lake bottom (Iout) significantly decreased with the incidentirradiance (R2 = 0.49). However, phytoplankton biovolume maxima were not coincidentwith the time of the year of maximum irradiance.4. A significant positive relationship was observed between PP estimated on an area basisand I0 (R2 = 0.51, P < 0.001). In addition, the parameters describing the photosyntheticresponses to high irradiances displayed marked seasonal trends. The photosynthesisphotoinhibition due to PAR as well as to UV were significantly related to incident solarradiation (PAR: R2 = 0.73; UV: R2 = 0.74). These results suggest adaptation of thephytoplankton community in response to changes in incident solar radiation.