The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

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Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 μm, <3 μm, <8 μm, <10 μm, <40 μm, <64 μm, <112 μm and <200 μm) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 μm are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 μm, <10 μm and <3 μm in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l−1 d−1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l−1 d−1, respectively. The average production of phytoplankton corresponding to micro- (10–112 μm), nano- (3–10 μm) and pico- (<3 μm) were 1.61, 8.30 and 0.33 mgC l−1 d−1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l−1 d−1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 μm, <10 μm and <3 μm in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l−1 d-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l−1 d−1, respectively. The average production of phytoplankton corresponding to micro- (10–200 μm), nano- (3–10 μm) and pico- (<3 μm) plankton was 0.11, 1.86 and 0.22 mgC l−1 d−1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l−1 d−1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 μm), nano- (3–10 μm) and pico- (<3 μm) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 μg l−1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 μm), nano- (3–10 μm) and pico- (<3 μm) plankton in enclosures were 1.7, 34.3 and 3.0 μg l−1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.