Phytoplankton and primary production in clear-vegetated, inorganic-turbid, and algal-turbid shallow lakes from the pampa plain (Argentina)

Shallow lakes often alternate between two possible states: one clear with submerged macrophytes, and another one turbid, dominated by phytoplankton. A third type of shallow lakes, the inorganic turbid, result from high contents of suspended inorganic material, and is characterized by low phytoplankton biomass and macrophytes absence. In our survey, the structure and photosynthetic properties (based on C-14 method) of phytoplankton were related to environmental conditions in these three types of lakes in the Pampa Plain. The underwater light climate was characterized. Clear-vegetated lakes were more transparent (K (d) 4.5-7.7 m(-1)), had high DOC concentrations (> 45 mg l(-1)), low phytoplankton Chl a (1.6-2.7 mu g l(-1)) dominated by nanoflagellates. Phytoplankton productivity and photosynthetic efficiency (alpha similar to 0.03 mgC mgChla (-1) h(-1) W-1 m(2)) were relatively low. Inorganic-turbid lakes showed highest K (d) values (59.8-61.4 m(-1)), lowest phytoplankton densities (dominated by Bacillariophyta), and Chl a ranged from 14.6 to 18.3 mu g l(-1). Phytoplankton-turbid lakes showed, in general, high K (d) (4.9-58.5 m(-1)) due to their high phytoplankton abundances. These lakes exhibited the highest Chl a values (14.2-125.7 mu g l(-1)), and the highest productivities and efficiencies (maximum 0.56 mgC mgChla (-1) h(-1) W-1 m(2)). Autotrophic picoplankton abundance, dominated by ficocianine-rich picocyanobacteria, differed among the shallow lakes independently of their type (0.086 x 10(5)-41.7 x 10(5) cells ml(-1)). This article provides a complete characterization of phytoplankton structure (all size fractions), and primary production of the three types of lakes from the Pampa Plain, one of the richest areas in shallow lakes from South America.