However, stable isotope measurements are

much less expensive (<$10 US/sample for stable isotopes vs. >$500/sample for radiocarbon), so that we used stable isotope results to screen samples for radiocarbon analyses. Samples for planktonic respiration were collected along Barataria Bay and Breton Sound transects in late August and early October, 2010 (Fig. 1). Whole-water samples were used without filtration or size fractionation. Planktonic respiration was measured as oxygen decreases in dark bottles incubated 24 h at field temperatures (Wissel et al., 2008). Results are expressed in units of mmol oxygen consumed m−3d−1. Filter-feeding estuarine mussels (Geukensia demissa) were collected directly from oiled and unoiled marsh sites in May and September 2010. A size range of mussels (from Entinostat supplier 40 to 110 mm total length) was collected at each site to study any size-related oil uptake. Mussels were collected from among marshgrass (Spartina) root mats, typically from within 5 m of marsh edges. Animals were placed on ice in the this website field and later frozen whole. Marsh sites in Terrebonne Bay were located near Cocodrie, Louisiana, with an oiled site (site terr 50; oil visibly present) along the northwestern shore of Lake Barre and unoiled sites about 4 and 14 km to the southeast and nearer Cocodrie (sites terr 49 and terr

53 initial, respectively). Collections at one site (terr 53) were made in May before any oil entered the bay for an initial pre-spill baseline, with post-spill September collections at this site showing elevated aromatic find more hydrocarbon values in sediment samples from the edge (R.E. Turner, personal communication). Marsh sites in Barataria Bay were located in the north-central part of the bay, with an oiled site (site bar 66; visibly oiled but without elevated hydrocarbon readings in marsh edge sediment)

located across a bayou channel from a paired unoiled site (site bar 65; no visible oil and without elevated hydrocarbon readings in marsh edge sediment) in northeastern Wilkinson Bay. Two other unoiled sites (sites bar 67 and bar 68) were located respectively 3 km to the southwest in Wilkinson Bay and 5 km to the southeast along the north shore of Bay Jimmy. Barnacles were collected August 28–30, 2010, six weeks after the Deepwater Horizon well was capped. Most samples were collected along a long transect through western Barataria Bay (Fig. 1). For reference, pre-oil barnacle tissue samples from 10 years earlier (May 2000) were available from the same transect. Reference barnacle samples also were collected in late August 2010 in a second Louisiana estuary, Breton Sound, that also was close to the Deepwater Horizon spill site (Fig. 1). Introduction of Mississippi River water at the head of the Breton Sound estuary through a river diversion structure (Day et al., 2009) at Caernarvon, Louisiana, largely kept oil from entering this estuary.