Size-fractionated chlorophyll a and phycocyanin temporal variations in a highly eutrophic lake and its isolated karstic springs

Abstract

Monthly variations of size-fractionated chlorophyll a and phycocyanin were studied in Lake Pamvotis between August 2016 and January 2017. Sampling was conducted at two sampling sites: in the main lake (Site 1: Lake) and in an adjacent man-made water ski lake with karstic springs (Site 2: Springs). Samples were fractionated into three size classes: 0.2–2 μm (pico), 2–20 μm (nano) and 20–180 μm (micro). According to chlorophyll a values, eutrophic to hypereutrophic conditions prevail at Site 1 and oligotrophic to mesotrophic conditions – at Site 2. Similarly, Site 1 was distinguished by higher concentration of phycocyanin compared to Site 2. Fractionated chlorophyll a showed monthly variations at Site 1 with alternations in the dominance between the two larger fractions. The maximum of the 0.2–2 μm fraction was observed in October but it contributed less to the total chlorophyll a content than nano- or microphytoplankton. Its contribution was higher at Site 2, reaching occasionally ~ 40% of the bulk chlorophyll a. However, nanophytoplankton was the fraction found to respond faster when disturbances occurred. At Site 1, phycocyanin correlated well with total chlorophyll a as well as with the micro- and nanophytoplankton fractions, indicating that cyanobacteria represent an important component of the large-sized phytoplankton in Lake Pamvotis.

Diversity of Bacteria in Lakes with Different Chlorophyll Content and Investigation of Their Respiratory Activity through a Long-Term Microcosm Experiment

“…Chlorophyll-a (chla) was determined as previously described in detail by Tsola et al [8]. Water (0.5-2 L) was filtered through 0.7 µm (Sartorius, MGF, Goettingen, Germany) and chla was extracted at 4 • C in 90% acetone.…”

“…In total 6-8 duplicate microcosms were prepared for each lake and each temperature. Microcosms were incubated long-term (~14 days) [27], at in situ temperature, which ranged between 3.8 and 27.9 • C during samplings at the two ecosystems, and at temperature increased by 2 • C. Every two days, duplicates from each incubation temperature were 'sacrificed' in order to determine the concentration of dissolved oxygen (DO) by the spectrophotometric Winkler method [33] as described in [8]. The method is suggested for suboxic to supersaturated with DO freshwaters.…”

“…Water 2019, 11, x FOR PEER REVIEW 4 of 14 experimental bottles contained the whole plankton heterotrophic community <180 µm. This was to avoid alterations of bacterial community composition caused by sequential filtrations [35] and in particular in high chlorophyll samples in which filter clogging interrupts flow rate at the initial steps of the filtration [8]. Nevertheless, we considered bacteria as the principal contributors to heterotrophic respiration [36,37] as well as that the encounter rate of bacteria and their predators in the 130 mL bottles would be low [3].…”

“…Chlorophyll-a is a parameter widely used to describe ecosystems and their trophic state since it is linked to the availability of nutrients and organic substrates and to the onset and decline of phytoplankton blooms [6][7][8]. Several studies have shown positive correlations between bacterial abundance and chlorophyll-a [9].…”