Phytoplankton structure and dynamics in a semiarid wetland, the National Park "Las Tablas de Daimiel" (Spain).
Rojo, C.; Ortega-Mayagoitia, E.; Rodrigo, M. A.; Álvarez-Cobelas, M.
published: Jun 14, 2000
ArtNo. ESP141014803010, Price: 29.00 €
We have studied a hypertrophic wetland in the semiarid National Park "Las Tablas de Daimiel" Five areas were sampled monthly from March 1996 to December 1998. Following an increasing level of eutrophication, increases in both total species richness and Euglenophyte populations were observed, as well as a progressive substitution of Oscillatoriean Cyanophytes by Nostocalean ones. The dominant species were Planktothrix agardhii (Gomont) Anagnostidis & Komárek, Peridinium willei Huitfeldkaas, Cryptomonas erosa Ehrenberg, Cyclotella meneghiniana Kutzing and Anabaena sphaerica Barnet & Flahault. The only similarities between areas were the extremely eutrophic conditions and the algal flora, but the structural features of these assemblages lacked a common pattern among sites. The Shannon-Wiener diversity index embraced one of the widest ranges yet noted for wetlands (10-2 and 4 bits/mm3, average in different areas was 1.6-2.2 bits/mm3). Phytoplankton biomass tended to increase in humid years (1997-1998). Biovolume average ranged from 4-14 mm3/L and peaked in late summer, with the lowest values in winter-spring. No relationships were found among nutrient concentrations, zooplankton abundance and phytoplankton biovolume. Only two areas (the more isolated, so the less disturbed) showed a clear-cut pattern: the first, a eutrophic euryhaline pond with the highest diversity in winter-spring, supporting small pennate diatoms and cryptophytes followed by big blue-green filaments in summer and colonial chorophytes in autumn; the second was a perturbed pond with the highest diversity in summer-autumn, when a miscellany of large-sized algae occurred, followed by blooms of Cryptomonas in winter. Phytoplankton assemblage dynamics displayed quite stochastic trajectories due to grazing, allelopathy and alternating self-organization processes, resulting from interaction between the hydrology and shallow morphology of a semiarid wetland. Phytoplankton dynamics in a wetland are more complex than in lakes due to the large number of interacting factors. A conceptual ecological model for algal dynamics follows.