NSF Results

We found that photosynthesis was strongly negatively affected 12 days after the oil exposure in the heavy and medium oiled sites compared to the control. However, 88 days after the oil exposure most of the leaves sampled had recovered photosynthesis to levels comparable to the control. This did not change in any of the subsequent samplings done until 1 year had passed since the initial oiling. 

Figure 1: Average Light- and Dark-adapted chlorophyll fluorescence yield (s.e. bars) measured using a Walz Mini-PAM on the same first mature leaf of Spartina (n=10) at 3 sites (control = no oil; medium oil; and heavy oil impact) during 5 sampling events over the course of 1 year.

Figure 2: Average Light-adapted chlorophyll fluorescence yield (s.e. bars) measured on 10 randomly selected individuals of Spartina at 3 sites (control = no oil; medium oil; and heavy oil impact) during 5 sampling events over the course of 1 year (left panel). The difference in yield compared to the control site highlights the reduction in yield from oil impacts at the medium and heavy site 2 weeks after initial oiling, but rapid recovery to yields similar to the control in all subsequent dates (right panel).

Observations in the field suggested that the leaves measured 3 months after the oiling were new growth on shoots that had grown to replace those coated by the oil. This suggests that Spartina alterniflora at Marsh Point was able to recover primarily by growing new shoots and leaves to replace those impacted by the oil. 

Additional observations over the course of the sampling, indicates that Marsh Point is an eroding shoreline, and that much of the area initially affected by the oil in July 2010, was either covered by sand as the "dune" migrated inland, or became open water as the sediment was eroded away in front of the sand "dune" (see Photos). This is typical of many exposed marsh shores in Mississippi and Louisiana, and is expected to continue as sea-level begins to rise with global climate change.