The regulation of blue-green algae by iron availability and calcite precipitation

The objective of this research was to determine if changes in iron availability influence the periodicity of blue-green algal growth. A secondary goal was to resolve how iron availability was related to events such as calcite precipitation and sediment nutrient release.;The biogeochemical regulation of blue-green algal succession was studied in three eutrophic hardwater lakes located in south-central British Columbia. The experimental approaches included in situ bottle and limnocorral experiments, sediment core analysis, water chemistry changes, and whole-lake manipulation by hypolimnetic aeration, or calcium hydroxide addition. Growth and primary production bioassays were isolated from algal cultures and lake water, quantified by a chelation assay, and used to determine their in situ effects on algal productivity and bacterial heterotrophy.;Algal siderophore isolates were rapidly assimilated in lake water and they were highly specific for iron chelation. Algae excreted chelators that could suppress growth of some other species of algae by 90%, enhance the primary production of some other algal species by 30%, or suppress the heterotrophic activity of bacteria by 14-98%.;Iron limitation in Black Lake was more than ten-fold more intense in early summer than in late summer. Blue-green algae blooms occurred in Black Lake only after the iron content of the lake increased from 20 to more than 100 ug/L. An increase in iron concentration was caused by a midsummer sediment release.;Although sediment pyrite formation converted available iron into refractory iron in both Chain and Frisken lakes, the degree of iron limitation varied greatly. Unlike in Black Lake, the algae in Chain Lake were not limited by iron availability. Phosphorus solubility was a good index of iron availability. Black and Frisken lakes had too little iron for iron phosphate to precipitate, but the higher iron concentration in Chain Lake regulated phosphorus solubility.;When iron availability was increased in the epilimnion of Black Lake, algal productivity was enhanced which resulted in an increase in pH and the coprecipitation of more calcite and phosphorus. Calcite precipitation resulted in the removal of as much as 90% of the algae and 97% of the phosphorus from the epilimnion.