A limnological investigation of the relationship between the Navasota River, Texas, and a selected floodplain

Abstract

A limnological investigation was conducted between January 1971 and September 1971 in the Navasota River and an adjacent floodplain in Grimes County, south-central Texas. The study centered upon the physico-chemical and biological dynamics associated with a sudden spring flood (spate). Analyses were made of water samples taken from the river and floodplain, including two small ponds. The early stages on the river were found to have higher concentrations of organic materials, as well as other chemical constituents, than did stages which followed. This was attributed to the flushing action of those early stages, followed by the dilution of subsequent runoff water. Rainfall runoff was shown to carry rather large quantities of nitrate and phosphate into floodplain ponds. Phosphorus uptake by pond organisms was rapid. Calorific energy equivalents of the benthos found in the floodplain pools was much greater (per square meter) than the benthos in riffle areas of the river. As drying of the ponds occurred, a rapid decrease of pond organism occurred. Predation and emergence are both likely to have contributed to this decrease. Analyses of soil core samples taken before and after flooding along transects across a ponded area on the floodplain and across the high-water line on the floodplain showed no statistically significant variation in the concentrations of constituents measured. It is proposed that floodplain ponds, which are often flooded several times each year, are important physico-chemcially and biologically for the maintenance of the chemical and biological diversity of the river which they are found.