In situ measurement of productivity and respiration in aquatic systems by a new box incubation method

Abstract

Changes in productivity and community respiration rates were assessed hourly through 24 and 29-h periods in Lake Hinuma, and every 1.5 h in Hiroshima Bay through a 25-h period, using a newly developed box incubation and free water method. The design of the box included light and dark bottles, with simultaneous measurement of temperature, DO and pH of the water in light and dark boxes, in which the water was exchanged with outside water, at intervals of 1 h (Lake Hinuma) and 1.5 h (Hiroshima Bay), respectively. Most changes in DO and DIC, during their respective incubations, were better approximated by linear, rather than exponential, models. During daylight, increased rates of DO in the light box ranged from 0.34 to 45.0 μmol l−1h−1 (Lake Hinuma) and 0.11 to 4.1 μmol l−1h−1(Hiroshima Bay), compared with decreased rates of DO from 0.20 to 17.0 μmol l−1h−1 (Lake Hinuma) and 0.25 to 3.2 μmol l−1h−1 (Hiroshima Bay) in the dark box. In contrast, the DO decrease rates in both light and dark boxes during nighttime ranged from 1.3 to 7.7 μmol l−1h−1 and 0.38 to 9.6 μmol l−1h−1 (Lake Hinuma), and from 0.10 to 1.0 μmol l−1h−1 and 0.30 to 0.80 μmol l−1h−1 (Hiroshima Bay), respectively; they nearly coincided for almost all periods. Metabolic Quotients (the ratio of DO to DIC change) were in the range from 0.61 to 1.35 (the 25th to 75th) (period-1) and 0.99 to 1.86 (period-2), respectively, except for a few incubation periods in the early night and morning hours. Most of the changes in the light box coincided with those in free water, indicating that the rate of change in the box was equal to that in the lake. However, due to advection, the free water outputs sometimes differed from those of the box incubation. We conclude that the box method is capable of evaluating gross and net production, and respiration, in a wide variety of aquatics with limited effort and time.