Temporal Succession in a Desert Stream Ecosystem Following Flash Flooding

Recovery of a desert stream after an intense flash flooding event is described as a model of temporal succession in lotic ecosystems. A late summer flood in Sycamore Creek, Arizona, virtually eliminated algae and reduced invertebrate standing crop by 98%. Physical and morphometric conditions typical of the preflood period were restored in 2 d and the biota recovered in 2—3 wk. Algal communities responded rapidly and achieved a standing crop of nearly 100 g/m 2 in 2 wk. Community composition was dominated by diatoms early in succession and by filamentous greens and blue—greens later. Macroinvertebrates also recolonized denuded substrates rapidly, largely by immigration of aerial adults and subsequent oviposition. Growth and development were rapid and several generations of the dominant mayfly and dipteran taxa were completed during the 1st mo of recovery. Invertebrate dry biomass reached 7.3 g/m 2 in 1 mo. Gross primary production (P g ) measured as O 2 increased in a similar asymptotic fashion and reached 6.6 g°m — 2 °d — 1 in 30 d. P g exceeded community respiration (R) after day 5 and P g /R averaged 1.46 for the remainder of the 2—mo sequence. This ecosystem is thus autotrophic and exports organic matter downstream and by drying, laterally. Uptake of nitrate and phosphorus were proportional to net primary production and exhibited a marked downstream decline in concentration during both light and dark periods. Temporal trajectories of various community and ecosystem attributes are compared with those suggested by Odum (1969) to be diagnostic of successional status. Agreement was poor in attributes which are especially modified in open, frequently disturbed ecosystems such as streams.