Abstract
Between February, 1976 and January, 1977, an ecological study was made of sandy riffle areas of Mill Creek, Newton County, Texas. Surface waters of the creek were found to be low in nutrients, specific conductance, and alkalinity; and moderately low in pH. Dissolved oxygen was usually at or near saturation in surface waters and decreased with depth in interstitial waters; however, interstitial waters remained oxygenated to a 30 cm depth. Interstitial conductivity and alkalinity did not vary with depth, while pH decreased rapidly from 0-5 cm, but changed little below depth. Mean temperature of the sand at 20-40 cm depth was cooler in the summer but warmer in winter relative to mean surface water. Temperature and chemical data suggest an active thermal density convective mechanism for interchange of surface and interstitial waters. The study revealed a psammonic community in the main channel of Mill Creek consisting of midges, oligochaetes, flatworms, micro-crustaceans, nematodes, and tardigrades. The six dominant psammonic organisms with their annual mean densities were Parakiefferiella spp. (11867 org./m3), Robackia demeijerei (7757 org./m3), Polypedilum spp. (7700 org./m3), Nematoda (18457 org./m3), Aeolosoma spp. (562700 counts/m3), and Rhychosocolex simplex (72633 counts/m3). The following organisms were also present in descending order of abundance: Eucyclops agilis, Macrobiotus sp., Rhynchataloma falcate, Hexagenia limbata, Tanytarsini and Parastenocaris sp. Psammon densities were, in general, lowest in summer and highest in winter. Densities were highest in mid-stream and just above the pools. Densities were lowest at the stream margins and just below the pools. Highest densities appear to be associated with more loosely packed sands, and with intermediate water velocities which are slow enough to permit adequate deposition of organic material, but fast enough to prevent silt clogging of sand interstices...
Whitman, Richard Lincoln (1979). Ecology of the sand dwelling community of an east Texas stream. Doctoral dissertation, Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -151756.