| Popis: |
A diel study of the deep chlorophyll maximum and its associated nitrite maximum showed that the nitrite maximum strengthens during the day and diminishes at night. A one-dimensional vertical model was used to differentiate physical from biological processes affecting the nitrite distribution. The rates of net production (or uptake) of nitrite, nitrate, ammonia, phosphate, and silicate were estimated at local dawn, noon, dusk, and midnight. The nitrite maximum at the base of the euphotic zone is produced mainly by phytoplankton during the day by reduction of nitrate. Daytime release of nitrite by phytoplankton occurs at a rate higher than the capacity of nitrifying microorganisms to oxidize it, and this leads to the nitrite maximum, which diminishes at night by nitrification. Nitrification rates were 0.2 to 0.5 μg-at. N1 −1 h −1 . The rates are one to three orders of magnitude higher than those based on the long-term (24-h) incubations of samples usually used to estimate nitrification rates. |
