In situ and Instantaneous Determination of Primary Production in Representative in by Using a New Method Kazuhiro KOMATSU*, Noriko TOMIOKA*, Akio IMAI*, Ayato KOHZU*, Shinichiro MATSUZAKI*, Megumi NAKAGAWA*, and Kazuhide HAYAKAWA** * National Institute for Environmental Studies, Japan, ** Biwa Environmental Research Institute, Japan

What is primary production (PP)? What is Fast Repetition Rate PP is the organic matter produced through Fluorometry (FRRF)? photosynthesis. PP plays an important role in the Applied FRRF is a powerful method for estimating PP in situ based carbon cycle and other ecosystem functions in the on chlorophyll fluorescence in response to pulsed irradiation. inland waters and will likely be influenced by global warming. 8000 7000 ・ ・ ・ 6000 P*O2(E)= E σPSII nPSII 5000 ・ ・ PP distribution in in May 2018 f qP(E) φe(E) 4000 Fluorescence yield (relative) 0 30 60 90 120 150 PP Number of flashlets

1.2 Advantage & Disadvantage 1.0 Unlike traditional methods (e.g., 13C and 14C methods),

/day) 0.8 2 0.6 FRRF does not require incubation and can instantaneously 0.4 estimate PP in situ. FRRF measurements do not use 0.2 PP (gC/m 0.0 radioisotopes. 12A 12B 12C 15A 15B 15C 17A 17B 17C FRRF detects weak chlorophyll fluorescence; consequently, Chl.a PP/Chl.a it is difficult to estimate PP in the surface layer of lakes under strong sunlight conditions. 4.0 0.08

3.0 0.06 Overcoming the disadvantage 2.0 0.04 The wavelength of chlorophyll fluorescence detection is

1.0 PP/Chl.a 0.02

Chl.a (μg/L) around 680 nm. To measure PP in the surface layer by

0.0 (C-mol/Chl.a-mol) 0.00 FRRF, over the sensor we installed a short-pass filter that 12A 12B 12C 15A 15B 15C 17A 17B 17C 12A 12B 12C 15A 15B 15C 17A 17B 17C cut sunlight with wavelengths longer than 650 nm.  PP was higher at the middle stations (12B, 15B, 17B), and was lower near the lakeside. Conclusion  PP was higher at the southern stations (12A‒C) than at those in In Lake Biwa, PP was higher toward the south; conversely, the north (17A‒17C). PP/Chl a was higher toward the north. Those differences  PP/Chl a was, conversely, higher to the north. might be related to . Correlation analysis and PCA results show that TP and UV254 affect PP. In , PP was mainly affected by The relationship between PP anthropogenic activities in rural areas, especially in May. and water quality

10.0 y = 361.2x + 0.2464 10.0

‐6 PP distribution in Lake 8.0 R² = 0.7846 ‐6 8.0 y = 18.166x ‐ 0.8872 )×10 )×10

2 R² = 0.2614 6.0 2 6.0 Kasumigaura in 2016 5 4 3

PP/PAR 4.0

PP/PAR 4.0 2

St.1 St.9 St.3 St.12 2.0 2.0 /day) (C‐g/L)/(E/m 2

(C‐g/L)/(E/m St.7 PP vs. T‐P PP vs. T‐N 1 0.0 0.0 0.00 0.01 0.02 0.03

0.00.10.20.30.4 PP (gC/m T‐P (mgP/L) T‐N (mgN/L) 0 No Data  PP was affected by total phosphorus (TP) rather than total Feb. May Aug. Nov. nitrogen (TN).  PP was highest in May, except at Station 7.  PP was also affected by some organic matter, which absorb  Stations 1 and 3 were affected by rural areas, and Station ultraviolet light at 254nm, (UV254 absorbance) but not affected 7 was affected by an urban area by the total concentration of organic matter.  cultivation starts in May, and a large load of  These results were generated by principal component analysis nutrients flowed into the lake then, potentially affecting (PCA). PP at Stations 1 and 3. Lake Biwa Lake Kasumigaura  Largest lake in Japan (670 km2)  Second largest lake in Japan (220 km2)  Average depth around 41 m  Average depth around 4 m  The NIES Lake Biwa Branch  The main campus of NIES is near this Office is near this lake lake. St.1 Survey St.3 Survey • The stations were 12A, 12B, • The stations were 1, 3, 7, 9, and 12. St.7 St.9 12C, 15A, 15B, 15C, 17A, 17B, • The survey was conducted monthly St.12 and 17C. 5km from 2016 to 2018. • The survey was conducted in Mar., May, Jul., and Nov. 2018