Cell death in lake phytoplankton communities

1. The fraction of living and dead phytoplankton cells in seven Florida lakes was assessed by using the cell digestion assay, a non-staining membrane permeability test. The cell digestion assay is an effective method to analyse cell viability in complex natural phytoplankton communities. 2. The lakes examined ranged widely in phytoplankton abundance and community composition. The variability in the percentage of living cells (% LC) was high among the taxonomic groups forming the different phytoplankton communities, ranging from 19.7% to 98% LC. 3. All cells within single cyanobacteria filaments were determined to be either dead or alive, suggesting physiological integration of the cells within colonies. 4. Within each lake, the dominant taxa generally exhibited the highest proportion of living cells. A high proportion of living cells was found to be a characteristic of the different taxa forming the communities of eutrophic lakes. The average value for the % LC for all groups comprising the phytoplankton communities in each of the lakes ranged from 29.9 ± 7.2 to 80.4 ± 4.0 (mean ± SE) and varied strongly and positively with chlorophyll a concentration. 5. These results suggest phytoplankton cell death to be an important process structuring phytoplankton communities in lakes, particularly in oligotrophic ones. © 2006 The Authors.Peer Reviewe

Rapid accretion of dissolved organic carbon in the springs of Florida: the most organic-poor natural waters

7 páginas, 2 figuras, 3 tablas.The concentration of dissolved organic carbon (DOC) in groundwater emanating as spring discharge at several locations in Florida, USA and the net increase in DOC in the downstream receiving waters were measured as part of a larger investigation of carbon dynamics in flowing waters. Springs with high discharge (>2.8 m3 s−1) were found to be the most organic-poor natural waters yet reported (13 ± 1.6 μmol C L−1), while springs with lesser discharge exhibited somewhat higher DOC concentrations (values ranging from 30 to 77 μmol C L−1). DOC concentrations increased rapidly downstream from the point of spring discharge, with the calculated net areal input rate of DOC ranging from 0.04 to 1.64 mol C m−2 d−1 across springs. Rates of DOC increase were generally greater in those springs with high discharge rates. These input rates compare favorably with values reported for gross primary production in these macrophyte-dominated spring systems, assuming that 17% of macrophyte primary production is lost, on average, as DOC. The measures reported here are possible only because of the remarkably low DOC levels in the up-surging groundwaters and the short residency times of the water in the spring-runs themselves.Esta investigación ha sido financiada mediante subvenciones del Carl S. Swisher Endowment for Water Resources y Natural Sciences and Engineering Research Council of Canada.Peer reviewe