The Mobile-Tensaw River delta and Mobile Bay represent a Pleistocene incised valley that has filled in response to sea-level rise over the last 7000 years. The delta is composed of marsh, swamp, levee, and distributary channel environments. Each of the terrestrial environments is inhabited by a distinct plant community. Palynomorphs arrive in distributary channels either by air or by water, transported from areas in-and-around the wetlands or upstream. Taphonomic analysis of terrestrial palynomorphs in this system may provide insight into the palynological character of similar modern settings as well as similar ancient incised-valley fills. Water-column (surface and mid-depth) and sediment-water interface samples were recovered from twelve localities throughout the delta during six sampling excursions over the course of one year. These samples were analyzed for palynomorph concentration using standard palynological techniques. Water-column samples were also analyzed for salinity, whereas grain-size, total organic carbon, and total nitrogen analyses were performed on sediment-water interface samples. Kruskal-Wallis ANOVA, Pearson Product Moment Correlation, and regression analyses were performed on the data in an attempt to assess any statistical relationships between factors that may have influenced concentration or distribution.
Results show that palynomorphs hydrodynamically behave as medium-to-fine clastic silt grains and their concentration varies both temporally and spatially. Highest concentrations were recovered in the spring and autumn months; lowest concentrations were recovered in the winter months. Spatial and temporal variations are the result of many different factors including salinity, tidal bore, discharge (relative to rainfall), seasonality (related to flowering and pollination), deltaic geomorphology, and proximity of sampling sites to source vegetation. Each of these factors affect palynomorph concentration to various degrees depending on the time of year, syzygy/quadrature, geographical location in the delta, and depth of recovery in the water column. High salinities inhibit the deposition of palynomorphs. Reworking of previously deposited grains is highest during spring tides near equinoxes in relatively straight distributary channels, whereas reworking is lowest during neap tides near solstices in highly meandered distributary channels. High rainfall results in dilution of the water-column samples and inhibits deposition as a result of increased discharge. The proximity of source vegetation affects surface concentration, possibly mid-depth concentration, but not the concentration at the sediment-water interface. Kruskal-Wallis ANOVA results show that water-column samples statistically represent different populations because sampling events represent individual snapshots in time of palynomorphs in transit. Conversely, sediment-water interface samples statistically represent the same populations because they are time-averaged palynomorph accumulations.