The impact of flash floods on microbial distribution and biogeochemistry in the parafluvial zone of a desert stream

Abstract

Summary 1. The impact of flash flooding on microbial distribution and biogeochemistry was investigated in the parafluvial zone (the part of the active channel lateral to the surface stream) of Sycamore Creek, a Sonoran Desert stream in central Arizona. 2. It was hypothesized that subsurface bacteria were dependent on the import of algal‐derived organic matter from the surface stream, and it was therefore predicted that microbial numbers and rates of microbially mediated processes would be highest at locations of surface to subsurface hydrologic exchange and at times when algal biomass was high. 3. Prior to a flash flood on 19 July 1994, chlorophyll a was high (≈ 400 mg m–2) in the surface stream and microbial numbers were highest at the stream–parafluvial interface and declined along parafluvial flowpaths, supporting the hypothesized algal–bacterial linkage. Immediately following the flash flood, chlorophyll a was low (≈ 7 mg m–2), and microbial numbers were reduced at the stream–parafluvial interface. 4. Counter to expectations, parafluvial functioning (in terms of nitrate production and dissolved oxygen decline along flowpaths) re‐established immediately after the flood receded. Therefore, material other than algal exudates supported parafluvial metabolism immediately postflood, and terrestrially derived dissolved organic matter is the likely source. 5. Algae in the surface stream recovered quickly following flooding, but recovery of parafluvial bacteria lagged somewhat behind. These results highlight the importance of surface–subsurface interaction to stream ecosystem functioning and show that the nature of these interactions changes substantially in successional time.

Heterogeneity in ground water–surface water interactions in the hyporheic zone of a salmonid spawning stream

“…The hyporheic element of the stream context and its functional characteristics are not readily apparent from a reading of superficial bed features (Edwards, 1998). However, the hyporheic zone is demonstrably important in an ecological context, and potentially limiting in some respects (Holmes et al, 1998). Because of this it merits greater prominence in relation to the reinstatement of function in streams (Naiman et al, 1998).…”

Direct and indirect effects of central stoneroller (Campostoma anomalum) on mesocosm recovery following a flood: can macroconsumers affect denitrification?

“…Results of a study of microbial recovery from flooding in a southwestern USA desert stream (Holmes et al 1998) indicate that algal recovery is more rapid than heterotrophic microbial recovery. However, transplanted substrata adjusted to local nitrification rates within 6 d in a prairie stream (Kemp and Dodds 2002), a result suggesting rapid microbial colonization following disturbance in prairie streams.…”

Importance of Extracellular Enzymes for Biogeochemical Processes in Temporary River Sediments during Fluctuating Dry–Wet Conditions

“…These events can severely impact microbial distribution as river discharges can increase by several orders of magnitude with respect to their regular flow (Holmes et al 1998).…”