TRACKING CHANGES IN SEA LEVEL ALONG THE ATLANTIC AND GULF COASTAL PLAINS OF NORTH AMERICA USING ATROTORQUATA LINEATA, A FUNGAL PROXY, TO LOCATE PAST POSITIONS OF HIGH LEVEL SALT MARSHES

Juncus roemerianus is the plant that occurs at the upper reaches of saltwater influence in coastal plain marshes from Delaware to Texas. As such, it is a good marker for sea level, (highest position of high tide). In 2006 a palynomorphic fingerprint to identify surface sediment from J. roemerianus marshes was discovered in a South Carolina study (Marsh, 2006). This fingerprint had four components, primary among them, the presence of Atrotorquata lineata, a very unique and distinctive fungal spore, the occurrence of which alone can be considered a proxy for the presence of a J. roemerianus depositional environment. The present study addressed four hypotheses: 1) A. lineata is present in all J. roemerianus marshes regardless of their geographic location; 2) A. lineata is present anywhere within a Juncus stand; 3) this spore type does not readily decompose with depth beneath the surface; 4) changes in the size and location of J. roemerianus stands can be tracked with depth using the Atrotorquata fungal proxy.

The hypotheses above were tested in the following manner: 1) 93 surface samples were obtained from Juncus roemerianus marshes throughout the geographic range of the plant. A. lineata was found in all surface samples from this range except for those from the northeastern edge of the range; 2) surface sediments from a 600-ft. transect across a Juncus stand were sampled at 50-foot intervals. A. lineata was found in all samples regardless of position in the stand. This study also confirms previous work by Marsh and Cohen (2008) that Atrotorquata is not readily transported out of Juncus marshes into juxtaposed Spartina or salt panne marshes; 3) to test the third hypothesis, six cores were obtained from James Island, SC, six from The Belle W. Baruch Institute in Georgetown, SC, one from Roanoke Island, NC, and one core was investigated from core records and a set of microtome thin sections from a previously studied core site in S. Florida (Spackman et al., 1976). In every case, well-preserved A. lineata was present with depth; and, in the Florida core it occurred at 250 centimeters (about 3000 yrs. b.p.); 4) using the James Island and Baruch cores, correlation of these cores clearly revealed evidence of expansion and contraction of J. roemerianus patches over time and further suggested recent past fluctuations in sea level.