Original paper

Relationships between carbon flow through freshwater phytoplankton and environmental factors in Lake Biwa, Japan

Goto, Naoshige; Tanaka, Yuka; Mitamura, Osamu

Abstract

Gross primary production (GP) and approximate net primary production [particulate organic carbon production (NPPOC) and extracellular dissolved organic carbon production (NPEDOC)] of freshwater phytoplankton were measured in order to determine the relationships between carbon flow through phytoplankton and environmental factors. Over the course of a yearlong study at sites located in Lake Biwa, Japan, GP and NPPOC were measured by in situ incubations of 24 h using rates of oxygen evolution/consumption and 13C-fixation, respectively. In addition, the response of GP and NPPOC to irradiance and water temperature were measured through in vitro experiments. NPEDOC was measured using 13C-tracer in both in situ and in vitro experiments. NPPOC:GP ratios determined from in situ experiments ranged from 0.24 to 0.73 (0.53 ± 0.16, mean ± SD) over the course of the year. NPEDOC:GP ratios ranged from 0.04 to 0.08 (0.06 ± 0.02) in both in situ and in vitro experiments. Based on the results of the present study, daily carbon flow through phytoplankton within the water column in the euphotic zone of Lake Biwa was estimated as follows: ratios of NPPOC to GP and NPEDOC to GP were 53 and 7%, respectively. Algal respiration (R) accounted for 40% of GP. In addition, R in vitro experiments increased linearly along with increasing water temperature, while R in situ experiments did not. It was concluded that irradiance was the main factor affecting the carbon flow through phytoplankton within Lake Biwa.

Keywords

carbon flowfreshwater phytoplanktonlakeprimary production