The effect of tidally induced changes in the creekbank water table on pore water chemistry

Water moved into the creekbank sediments in direct response to the changing levels of the water table caused by the tides. The net water loss of the sediments was 3–30% on each low tide and this loss was confined to within 4 m (horizontal) of the creek. The replacement of this water by incoming tidal water could not supply sufficient nutrients for the growth of creekbank Spartina. However, during ebb tide there was a replacement of water in the creekbanks with nutrient-rich water from the marsh interior as demonstrated by the large changes in pore water chemistry over a tidal cycle. The concentration and the range of a chemical parameter depended upon the stage of the tide, the tidal range, the time of year and (for salinity) the rainfall patterns of the month preceding sampling. Over a single tidal cycle the maximum ranges were: salinity ‰, 26–33; alkalinity, 2·5–13·6 med 1^?1, ammonia, 2–400 μm, sulfate, 23·5–29 mmol 1^?1. Measurable concentrations of sulfide were only found in a few samples. This high nutrient water can supply nitrogen and probably other nutrients to Spartina.