SALT-MARSH FORAMINIFERA FROM THE GREAT MARSHES, MASSACHUSETTS - ENVIRONMENTAL CONTROLS

By using sites in the Great Marshes at Barnstable (Massachusetts. USA) this study examines the effects of a set of environmental parameters on the foraminiferal distribution. The studied parameters are: elevati on above mean high water: salinity of the porewater: various sediment characteristics: vegetation: and food source. Relations between the en vironmental parameters and foraminiferal properties (frequencies. dens ities and diversities) are quantified with correlation coefficients. F or the first time Siphotrochammina lobata and Balticammina pseudomacre scens are documented in the New England region. The following species show a significant correlation with one or more of the studied paramet ers and are designated as key-species: Haplophragmoides manilaensis. J adammina macrescens. Balticammina pseudomacrescens, Milammina fusca an d Tiphotrocha comprimata. Based on cluster analysis and the presence. absence or dominance of the key-species characteristic associations ar t: distinguished. The distribution of three associations is indicative of specific marsh environments: the marsh fringe, the middle marsh an d the marsh edge. These three marsh units are separated by their own s alinity regime. flooding and sediment characteristics. The marsh fring e is typified by the H. manilaensis, Association and experiences fresh water input (seepage, surface runoff and rainwater) and only slight ma rine influence. resulting in low salinity values (2.5-20 parts per tho usand). The width of the marsh fringe is variable, dependent on the am ount of seepage which in turn is controlled by the permeability of the basement and the peat. The J. macrescens Association characterizes th e middle marsh where salinities are controlled by infiltration of sea- and rainwater and by evaporation. Salinity values are higher than 20 parts per thousand while temporarily salinity can reach extreme high v alues during periods without flooding and high evaporation rates (e.g. , 44 parts per thousand). The fully marine M. fusca Association occupi es the daily hooded marsh edge where,:he salinities have the same valu es as Cape Cod bay water (ca. 28 parts per thousand). Unlike many othe r salt marshes the distribution of foraminiferal assemblages in the Gr eat Marshes does not show a vertical zonation with respect to mean hig h water. This shows that a worldwide applicable model for paleoenviron mental studies in salt marshes based on foraminifera is not feasible. Each salt marsh has its own characteristics. Regional factors such as climate play an important role in the salinity regime. while the local upland characteristics determine if seepage takes place. Thus each ma rsh has its own foraminiferal fingerprint showing the opportunistic be haviour of the salt marsh agglutinants. A surface study is an indispen sable first step in assessing the value of foraminifera as paleo-ecolo gical indicators. (C) Elsevier Science B.V.