Low latitude, seagrass-dominated coastal bays, such as Shark Bay, Australia, are potential sources of chromophoric dissolved organic matter (CDOM) to coastal regions. Dissolved organic matter (DOM) is known to influence aquatic nutrient dynamics, microbial community structure, and depth of light penetration in estuarine systems. Shark Bay is a sub-tropical ecosystem with limited freshwater inputs and restricted tidal flushing. As such, much of the DOM is expected to be seagrass-derived. However, combining excitation/emission fluorescence spectroscopy and parallel factor analysis (EEM-PARFAC) with 13C stable isotope analysis of DOM, we found evidence for DOM inputs from terrestrial (riverine and possibly groundwater), autochthonous plankton, macroalgae, and seagrass sources. Isotopic analysis of 13C in DOM supports the idea that seagrass inputs contribute substantially to the DOM pool in Shark Bay, whereas, EEM-PARAFAC data suggests that much of this input is derived from decomposing seagrass detritus and to a lesser extent due to exudation during primary production. We also report increases in DOM concentrations and changes in DOM characteristics with increasing salinity in surface water samples, indicating that evaporation is an important control on DOM concentration and photo-degradation may play a critical role in transforming DOM within the system.
A primordial 15N-depleted organic component detected within the carbonaceous chondrite Maribo
