The distribution of biogenic thiols in surface waters of Galveston Bay

Thiolic compounds are important metal-complexing ligands as well as importa nt components of the global sulfur biogeochemical cycle. A lack of informat ion on the concentration and distribution of thiols in natural waters, espe cially in the dissolved fraction, is still a major impediment to a complete understanding of the role of thiols in these biogeochemical processes. The concentrations of dissolved, colloidal, and particulate thiols were measur ed along a salinity gradient in estuarine waters off of Galveston Bay, Texa s. The majority of thiols were present in the dissolved fraction, although more thiolic species were detected in the particulate phase. Dissolved glut athione was present at higher concentrations (0.23 to 6.23 nM) than was the particulate glutathione (0.094 to 0.72 nM). Most gamma-glutamylcysteine wa s present in the particulate phase, with concentrations as high as 2.24 nM in the middle of the estuary. Phytochelatin-2 was ubiquitous in surface wat ers, with chlorophyll a-normalized concentrations of up to 6.3 mu mol g Chi a(-1). A major thiol peak was present in Lower Galveston Bay and a minor p eak in Upper Galveston Bay, and in both regions, 5-6 mol of gamma-glutamylc ysteine were produced per mole of glutathione. This bimodal distribution in dicates in situ production of thiols from two different phytoplankton commu nities in Galveston Bay during this period.