Horizontal variability and regulation of bacterial production in a
large, temperate lake
Abstract
To clarify horizontal variability and regulation of bacterial production
(BP), we investigated BP and environmental variables along three
east-west transects (Lines 12, 15, and 17) covering inshore/offshore
stations in Lake Biwa, Japan, during four seasons. In winter, surface BP
along Line 12 (southern transect) was higher than Lines 15 and 17
(central and northern transects) and reflected the water-temperature
distribution. Additionally, any nutrients and dissolved organic carbon
did not correlate to BP, suggesting water temperature regulated BP in
winter. In spring, BP was higher at eastern inshore stations, near large
agricultural fields, and was correlated with phosphorus concentration
rather than water temperature, suggesting that the limitation shifted to
nutrient availability. As well as spring, surface BP in autumn was
correlated with phosphorus. Additionally, a negative correlation with
water temperature in autumn suggested that nutrient loadings through
river and groundwater contributed to enhancing BP. In summer, surface BP
at offshore stations along Lines 15 and 17 was notably lower than the
other stations. Summer BP was correlated with phosphorus concentration,
suggesting that allochthonous nutrient loading determines horizontal BP
variations. Moreover, summer depth-integrated BP (DBP) at offshore
stations was lower (32-52 mgC m-2 d-1) than inshore stations (43-110 mgC
m-2 d-1) regardless of water depth. The average DBP at inshore stations
in summer was 2.1 times that offshore stations, and the inshore/offshore
DBP ratio was higher than the other seasons (0.58-1.0). The results
suggest that inshore BP significantly contributes to whole-lake BP in
productive seasons.