ABSTRACT

Reconstruction of modern fresh water sedimentary environments from both the sediment record and historical documents provides valuable insight into aquatic ecosystem change in time-frames of human occupation and water management. Lake deposits are particularly suited, as this environment intercepts and receives most sediment transported through a watershed. Such an approach is used in the historically well-documented Caddo Lake region of northwestern Louisiana and northeastern Texas to reconstruct its 200-year history and origin as a raft lake associated with the Great Raft of the Red River.

Sediment thickness measurement and description plus time-line establishment for 1800, t873, and 1963 indicate the lake's 19th-century depositional history was strongly influenced by Red River backflow westward through the old flooded Cypress Bayou tributary, opposite of today's dominantly eastward flow from the Texas side. Sedimentation rates were at least 10 times greater in eastern Caddo Lake prior to the final 1873 log-jam removal on the nearby Red River. Higher sedimentation rates have always existed in the topographically-low flooded channel versus the shallower-water old floodplain. Pre-1873 sediment accumulation rates approached 2-3 cm/yr, falling to 0.3-0.4 cm/yr after log-jam breakup and return to pre-raft river and tributary flow. Extrapolation of average 2Oth-century sedimentation rates into the future suggest complete filling of the deeper Louisiana lake region would require around 1000 years.

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