Stream Order, Morphometry, Physico-Chemical Conditions, and Community Structure of Benthic Macroinvertebrates in an Intermittent Stream System

Morphometry, physico-chemical conditions, and community structure of benthic macroinvertebrates were quantitatively related to stream order in a 6th order, intermittent stream system located in north-central Oklahoma. Number of species and individuals, and species diversity and heterogeneity indices were used as measures of community structure. Average drainage area and average lengths of streams increased, and stream numbers and average gradient decreased exponentially as stream order increased. Physico-chemical fluctuations, mean annual turbidity and water temperature decreased, while mean annual flow, alkalinity, and conductivity increased as stream order increased. Numbers of individuals were maximum in 4th order streams throughout the year. Minimum numbers occurred in the 6th order stream during periods of stream flow, and in 3rd order streams during drought. Annual numbers of species and total community species diversity (H) increased in 3rd, 4th, and 5th order streams and decreased in the 6th order stream. Diversity per individual ($\overline$H) increased and redundancy (R) decreased as stream order increased. Species diversity was significantly different between and within stream orders at the 75% confidence level, diversity per individual at the 95% level, and redundancy at the 90% level. During autumn, winter, and spring diversity per individual increased and redundancy decreased as stream order increased. Diversity per individual was significantly different at the 95% confidence level during autumn and the 90% level during winter and spring. Significance of redundancy increased from the 25% level during summer and autumn to the 90% level during spring. Annual ranges of species diversity, diversity per individual, and redundancy decreased as stream order increased, indicating more uniform community structure in the higher stream orders. Mean annual heterogeneity (IH) decreased as stream order increased, indicating that similarity of community structure and faunal assemblages increased progressively with stream order. A station located in a 3rd order adventitious stream that flowed directly into the 6th order stream had a community structure and faunal assemblage more similar to stations in higher order streams than to other 3rd order stations. Drought and seepage of oil-field brines upset the stream ordercommunity structure relationship. During drought community structure was similar in all stream orders. Influx of low concentrations of oilfield