Physical and chemical variability in tidal streams

This article focuses on the variability of major hydrologic parameters of tidal streams that occur on different temporal and spatial scales within an individual estuary. Rapid changes in water temperature and salinity take place on a timescale of <1 hour, as a strong function of the tidal state (e.g., low vs. high tide) and amplitude (e.g., spring vs. neap tide). Large day-night fluctuations of dissolved oxygen (DO) concentration are also demonstrated and discussed in relation to the extent of in situ biological processes. In addition, the variability of these parameters is evaluated seasonally at controlled low tide. Finally, the year-round distribution of nutrient concentrations (i.e., ammonium, phosphate, silicate, and nitrate+nitrite) in low tide ebbing water is presented and compared with the variability in nutrient concentrations in the sediment porewater of an adjacent exposed sandflat.