Breton Sound estuary water quality data, 7/2/2010 to 12/14/2011.

Water quality transects for this study were started shortly after the Macondo Oil Spill in April 2010, and have been carried out monthly since to measure water chemistry and related hydrographic parameters. Water samples were collected at 16 locations from a depth of 10-20 cm in acidwashed one-liter plastic containers (Greenberg et al. 1985). Samples were preserved in cold storage prior to analysis. Water quality parameters included nitrite+nitrate (NOx), ammonium (NH4), total nitrogen (TN), phosphate (PO4), total phosphorus (TP), silicon (SiO4) and chlorophyll a (CHL). Samples analyzed for NOx and NH4 were filtered prior to analysis using 0.45 um millipore filters. The following parameters were determined by the following methods: NOx by the automated cadmium reduction method, NH4 by the automated phenate method, PO4 by the automated ascorbic acid reduction method, and SiO4 by the automated molybdate reagent/oxalic acid method, all with an Alpkem© autoanalyzer (Greenberg et al. 1985). TN and TP were determined by the persulphate oxidation method (Valderrama 1981). CHL was determined using a modified version of the Strickland and Parsons (1977) technique; pigment extract was obtained using a 40:60 solution of dimethyl sulfoxide (DMSO):90% acetone (Burnison 1980), and measured with a Turner Designs model 10-AU fluorometer. Burnison, B. Modified dimethyl sulfoxide (DMSO) extraction for chlorophyll analysis of phytoplankton. Canadian Journal of Fisheries and Aquatic Sciences. 37:729-733; 1980 Greenberg, A.; Trussel, R.; Clesceri, L.; Franson, M. eds. Standard methods for the examination of water and wastewater (APHA, AWWA and WPCF)(ed.): Washington; 1985 Strickland, J.D.H.; Parsons, T.R. Practical handbook of seawater analysis: Fisheries Research Board; 1977. Valderrama, J.C. The simultaneous analysis of total nitrogen and total phosphorus in natural waters. Marine Chemistry. 10:109-122; 1981