A simple device has been developed to facilitate in situ incubations. The hydraulic in situ time-series sampler (HINTS) facilitates collection and incubation of a large volume of water (16 liters) without need of manipulating the sample at the surface. Injection of isotopic tracers and subsampling can be accomplished remotely via tubing connected to the incubation chamber. HINTS consists of a rigid, clear polycarbonate vessel with a gas-impermeable plastic incubation bag inside. A two-way valve permits the incubation chamber to be filled with ambient water or to communicate with the surface via a sampling and tracer-injection line. Opening and closing the two-way valve and filling and emptying the incubation chamber are done hydraulically. The HINTS is particularly useful for comparing isotopic and chemical-change methods of measuring productivity, obtaining time series of chemical properties, physiological rates or organism abundance, and determining net community PQ and C: N assimilation ratios. Preliminary tests suggest good agreement between O2- and SIGMACO2-based measurements of net community production. The community photosynthetic quotient averaged 1.4+/-0.3 (95% C.I.) in four late-fall and winter measurements.
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