A novel approach for estimating ecosystem production and respiration in estuaries: Application to the oligohaline and mesohaline Hudson River

Most estimates of metabolism in estuaries are based on water samples incuba ted in bottles. Such approaches may severely underestimate rates of both gr oss primary production (GPP) and respiration for a variety of reasons, incl uding reduced turbulence, unnatural light fields, respiration of C-14-label ed organic matter, and altered grazer communities. These problems may be pa rticularly intense in turbid and deeply mixed estuaries. The measurement of metabolism from in situ changes in dissolved oxygen (DO) concentration ove r a diel time period offers a potential solution to these problems, but com plicated patterns of water advection and mixing in estuaries have limited t he use of such open-water approaches. Here, we describe a method of using d iel changes in oxygen concentrations in the oligohaline and mesohaline Huds on River estuary to estimate GPP, whole-ecosystem respiration (ER), and net ecosystem production (NEP). For this approach, concentrations of DO at any given time for several stations are described as a function of salinity an d depth, providing a surface in the three-dimensional space of oxygen, dept h, and salinity. The change in this "response surface" for oxygen over time , once corrected for atmospheric exchange, allows the estimation of metabol ism rates. The regression procedures used allow an estimate of the standard error associated with the metabolism measures. For the mesohaline Hudson R iver estuary, these standard errors are reasonably small. Similarly, any po tential errors associated with the estimation of atmospheric exchange in ox ygen are small for the Hudson. The technique should be useful for estimatin g GPP, NEP, and ER in other partially mixed estuaries without the biases as sociated with incubations in bottles.