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Among the dozens of researchers involved with the Brown Marsh Project, the theory that the phenomenon had been caused by some combination of causative agents soon became the general consensus. Despite this consensus, however, one single factor receiving prominent focus prior to the project's start was that of the heightened marsh salinity that accompanied the drought of 2000-01.
Although some early studies reported that soil salinity levels during the period were within tolerance limits for smooth cordgrass, other studies had found that they were marginally high. More significant, perhaps, was what these initial studies agreed upon, namely that salinity levels in the region's bayous and bays had been higher than average for a far greater period than had been witnessed in the past 40 years.
| "You have to go back to 1963-64 to find a gulfwide drought as severe as that of 2000-01, and even then, it was not nearly so prolonged." |
Several researchers, then, began to suspect a direct connection between the reduced rainfall, lowered water levels, increased salinity, and the marsh dieback. Although it would not prove the sole cause, salinity's role as a chief stressor-that is, one of the key players in the multi-causal scenario-could not be overlooked. And no matter one's opinion on this possible causal chain brought on by the drought, all agreed that the role that climate had played, especially with respect to its alteration of the salinity regime, needed to be investigated.
One of the central tasks in the "Causes" subproject, then, is a thorough examination of climate and hydrological data. This includes not only a thorough accounting of the climatic factors running concurrent to the brown marsh dieback, but an investigation into how the turn-of-the century drought deviated from both the norm and previous drought periods. Heading this task are LSU's Eric Swenson, a specialist in field hydrology, and John Grymes, the state climatologist. The baseline datasets they have to work with, compared to the lack of baselines confronting some of the other researchers in the project, amount to an embarrassment of riches. The gulf coast-the large-scale context in which they are examining the dieback-not only contains 20 climate divisions, but has climate data such as temperature, rainfall, wind, and humidity dating back to 1895.
Given the gulfwide nature of the drought that they observed, Swenson and Grymes asked themselves why the brown marsh phenomenon appeared to be concentrated only in certain portions of coastal Louisiana. Part of the answer had to do with the length of the drought. As Swenson notes, "You have to go back to 1963-64 to find a gulfwide drought as severe as that of 2000-01, and even then, it was not nearly so prolonged."
More important in terms of the impact on coastal Louisiana, however, was that this prolonged dry period in the gulf was occurring at the same time as an extremely low flow rate in the Mississippi River, a rate that in turn affected the salinity of the coastal waters. In addition to these conditions, they are investigating what role, if any, that wind may have played. Preliminary reviews of the data suggest that winds were more westerly (i.e., drier and warmer) than usual across the period in question, a factor that may have contributed to above normal evaporation rates, thereby furthering the hydrological drawdown and salinity concentrations in the marshes.