Long-term monitoring in Lake Kasumigaura

   We have been conducting monthly monitoring at Lake Kasumigaura, the second-largest lake in Japan, for nearly four decades. Many environmental variables have been monitored such as water temperature, light intensity, pH, dissolved oxygen, organic matter, nutrients, heavy metals, plankton (e.g., bacteria, heterotrophic nanoflagellates, ciliates, picoplankton, phytoplankton, zooplankton, mysids), primary production, benthos (chironomids and oligochaetes), and fish. All monitoring data are actively published on the web and provided to international databases such as GEMS/Water and JaLTER.

   We have been conducting monthly monitoring at Lake Kasumigaura, the second-largest lake in Japan, for nearly four decades. We have monitored many environmental variables including water temperature, light intensity, pH, dissolved oxygen, organic matter,, nutrients, heavy metals, plankton (e.g., bacteria, heterotrophic nanoflagellates, ciliates, picoplankton, phytoplankton, zooplankton, mysids), primary production, benthos (chironomids and oligochaetes), and fish.
   We are actively publishing all monitoring data on the Internet (http://db.cger.nies.go.jp/gem/moni-e/inter/GEMS/database/kasumi/index.html) and also providing the data to international observational networks such as GEMS/Water and JaLTER. In 2011 and 2012, we re-designed the Japanese website and created an English version to promote the availability of the data and to increase the number of users. We also published two papers in the international journal “Ecological Research.” In 2014, fish monitoring data were published through the Global Biodiversity Information Facility (GBIF).
   In addition to the data release, we are also developing effective monitoring methods and analyzing long-term changes in community structures and ecosystem states. We have developed a large-diameter (11 cm) core-sampling system to collect sediment cores without compaction and to monitor the sediment temperature, water quality of pore water, and structure of benthic habitats. Based on information retrieved using this system, it is suggested that heat accumulation occurs especially in winter, which affects the biological activities of benthic microorganisms. Furthermore, this system has been applied to the investigation of the dynamics of radioactive substances within the sediment of lakes.
   We have also continued to develop rapid in situ methods for measuring primary production and estimating the phytoplankton biomass of each taxonomic group (e.g., cyanobacteria). Fast repetition rate fluorometry (FRRF), which does not require labeling with a radioisotope and lengthy incubation, has been applied to monitor in situ primary production by phytoplankton within the water column. To assess the validity of the FRRF technique, we compared estimates of primary production rates derived from variable fluorescence by means of FRRF with those measured using a traditional method (¹³C method) under laboratory conditions. These comparisons indicate the high correlations (R² values were close to 0.9) between the results of the FRRF and ¹³C techniques; however, the slopes of the regression lines were found to be <1 (¹³C > FRRF). One of the reasons why FRRF underestimates the primary production rates compared with the ¹³C method is assumed related to the effect of the predominant algal species and thus, we will apply multiple FRRF to the measurement of primary production.