Salt Marsh and Phytoplankton Bloom Influences on the Composition and Metabolism of Organic Matter in a Temperate Estuary, Delaware, USA
Monday, 15 December 2014
Low oxygen levels within the Murderkill Estuary, DE, are largely driven by organic matter (OM) metabolism and chemical oxygen demand within the fringing salt marshes. To assess how the connectivity to and inundation of salt marshes impact OM quality and cycling within the Estuary, fluorescence excitation-emission matrix (EEM) data were used to characterize both dissolved and particulate OM pools. Parallel Factor Analysis (PARAFAC) identified five fluorophores that illustrated greater tidal variation in the particulate (POM) than dissolved (DOM) OM pools. The terrestrial-wetland and marine OM sources were statistically separated using the fluorophores in conjunction with the elemental composition and isotopic signature of particulates, as well as dissolved water chemistry (e.g. salinity, dissolved nitrogen, carbon, silica, and phosphorus). DOM pools in the Murderkill and leaving the marsh are dominated by soil humics, while POM pools have greater contributions of protein-rich sources and are generally are less processed. Tidal survey results point to the salt marshes as a sink of fine particulates, in particular protein rich OM, and a source of coarse particulates and DOM dominated by humic substances. Results from dark 24-hour bioassays suggest that coarse and fine POM pools are larger drivers of oxygen consumption than DOM pools. Correlations between community respiration rates during ebb tide, water chemistry, and OM fractions suggest that biological oxygen demand in the Murderkill is driven, in part, by the metabolism of protein-rich, phytoplankton from Delaware Bay. Thus, while the bulk of oxygen drawdown occurs within the salt marshes, in-stream metabolism appears to be driven by marine OM pools.