Autotrophic Picoplankton: Community Composition, Abundance and Distribution across a Gradient of Oligotrophic British Columbia and Yukon Territory Lakes

Abstract

Autotrophic picoplankton communities were examined in eleven oligotrophic lakes from a broad geographic region of western Canada, representing a variety of physico-chemical and biological conditions. During our study, several of the lakes were treated with additions of inorganic nitrogen and phosphorus fertilizers. Picoplankton communities in most lakes were dominated (> 70 %) by unicellular or colonial coccoid cyanobacteria, provisionally identified by morphological and autofluorescence properties as Synechocuccus. Also common in some lakes were red-fluorescing cyanobacteria and Chlorellu-like eucaryotes. Autotrophic picoplankters contributed from 36-63 % to total chlorophyll, from c 2-26 % to total phytoplankton carbon, and from 29-53 % to total photosynthesis. Average populations ranged from < 5-10,OOO cells. ml-* in winter and early spring to 65-75,ooO cells.ml-1 in summer and fall. Peak densities in most lakes occurred in AugustSeptember and most populations were within the epilimnion or metalimnionhypolimnion boundary. Subsurface peaks were prevalent only in untreated, strongly stratified lakes. Eucaryotic picoplankters became dominant in acidic (pH < 6.2), humic lakes. ColoniaI picoplankters were more common in more productive interior lakes in August, and though present, were uncommon in coastal systems. Picoplankton populations exhibited large increases under ice in a Yukon lake, and their abundance and seasonal distribution showed little relation to temperature or to light. Fertilization of lakes resulted in picoplankton population increases (> 2 x) and the elimination of subsurface peaks. Nutrients were considered to be one of the major factors controlling population abundance in these oligotrophic lakes with average pH > 6.5.

Vertical distribution of phototrophs in the pelagic zone of three small Lobelia lakes

“…As reported by Kraska et al (2006), the characteristic feature of the pelagic zone of the lake was the acid reaction of water (pH 5.6 in the epilimnion), which confirms reports (e.g. Stockner and Shortreed 1991) about the elimination of picocyanophytes resulting from decreasing water pH. The picophytoplankton of the other lakes were dominated by cyanophytes.…”

Flow-cytometric mapping provides novel insights into the seasonal and vertical distributions of freshwater autotrophic picoplankton

“…It has recently been stated by Stockner et al (2000) that the abundance of microcolonies in many lakes is higher at the base of the euphotic zone than in surface waters (Stockner & Shortreed 1991, SimeNgando 1995. Schallenberg & Burns (2001), who reported highly significant positive correlations between the abundance of aggregated picocyanobacteria in Lake Wakatipu and concentrations of total phosphorus and total nitrogen, suggested that colonial picocyanobacteria respond positively to small increases in total nutrient concentrations and that colonial picocyanobacteria may contribute significantly to nitrogen fixation within the pelagial.…”

Microbial food web responses to phosphorus supply and solar UV radiation in a subarctic lake

“…Most of these waters are oligotrophic (Smith et al 1984, Stockner & Shortreed 1991, Milot-Roy & Vincent 1994 in which the plankton community is likely to be strongly nutrient-limited and dominated by microbial food web components. Ultraviolet radiation (UVR) penetrates deep into oligotrophic, low DOC (dissolved organic carbon) waters (Morris et al 1995), and microbial responses to changes in phosphorus supply in these lakes (e.g.…”