Transparent Exopolymer Particles (TEP) in a River-Dominated Estuary: Spatial–Temporal Distributions and an Assessment of Controls upon TEP Formation

Abstract

Transparent exopolymer particle (TEP) distributions were examined in North Carolina’s Neuse River Estuary (NRE) over a 1-year period, and experiments were conducted to examine controls upon TEP formation. TEP-carbon averaged 16% of the total organic carbon pool in the NRE. From May to early August 2007, TEP ranged from 805 to 1,801 µg xanthan gum (XG) L−1. A large phytoplankton bloom peaked in early August and then subsequently declined. Within 2 weeks of the bloom’s peak, TEP concentrations increased to >3,500 µg XG L−1 and remained elevated through mid-December. Decreasing water temperatures and enhanced retention due to drought conditions in Fall 2007 likely aided in the persistence of TEP concentrations during this timeframe. Thereafter, TEP decreased coincident with increased river flow and flushing of the estuary that began in January 2008, and TEP remained low (ranging from 991 to 1,712 µg XG L−1) until the end of April 2008. TEP was positively correlated with salinity, suggesting that cation availability (which co-varies with salinity and stabilizes the structural integrity of TEP) may play a role in estuarine TEP formation. In two cation addition experiments using water from the mesohaline region, TEP concentrations tended to be higher in treatments with vs. without cations added. Statistically significant relationships were also found between in situ TEP concentrations and pH, mixing, and temperature, suggesting that a complex suite of environmental parameters affect TEP formation and its distribution in estuaries.