Spatial and Temporal Patterns of Substrate Physicochemical Parameters in Different-aged Barrier Island Marshes

Abstract

Physicochemical substrate parameters were measured monthly from June to October 1990 in two young and two old barrier island marshes off the eastern shore of Virginia. Porewater salinity, substrate redox potential (EH), organic matter content, and sediment grain size were measured at three depths at high marsh and low marsh stations of all four sites. Porewater ammonium and phosphate, and extractable ammonium were also measured at one old and one young marsh site. Higher sand content, lower organic content, and lower elevation of the young sites relative to the old sites was representative of differences in development time between the different-aged sites. Porewater salinity peaked in mid-summer at higher levels at the old sites relative to the young sites and was higher at the high marsh stations compared to the low marsh stations of both old sites and one young site. Substrate EH was higher at the young sites, presumably as a function of better drainage related to a coarser-grain size and a steeper topographic slope relative to the old sites. Nutrient pools increased throughout the growing season in both the young and old sites, but peaked at higher levels in the old marsh below 10 cm which was consistent with the finer-grain size and higher organic content at depth of the latter site. Differences in physical substrate characteristics, EH, and nutrient pools, found in this study, generally agree with other age comparison studies which are usually between young, created marshes and older, natural marshes. Created marshes have been shown to develop inorganic nutrient pools comparable to established, natural marshes in 2-15 years. The results of this study, representing few comparisons of substrate nutrient concentration in natural, different-aged marshes, demonstrated that nutrient pools are comparable at 10 cm between 10-13-year-old marshes and marshes whose age is most likely in the hundreds of years. Nutrient pools at 30 and 50 cm of young marshes take longer than 10-13 years to reach levels comparable to older marshes at the same depths.