| heal.abstract |
Flow regime and total suspended solids (TSS), along with chemical and biological parameters associated with urbanization and intensive agriculture/aquaculture, impact benthic organisms, which represents the food chain foundation in aquatic systems. We designed this experiment to begin the integration of physical flow regime effects along with chemical and biological indicators on periphyton, an important benthic organism indicator, towards a goal of using periphyton (live biomass containing chlorophyll a) and pheophytin (dead chlorophyll-containing biomass) in assessments of stream health. Physical flow regimes in a laboratory flume were created using multiple roughness conditions and an in-channel weir. Results suggested that one could model the hydraulic regime with a hydraulic model, HEC-RAS, to within 2% to 11% of measured velocity values. Thus, one may roughly but not precisely move computed velocities from the flume to the field. Significant interactions between biological response and hydraulic and TSS factors were observed, and the study suggested several indicators of periphyton-pheophytin response that are potentially relevant to ecological engineering applications featuring a channel. Increased mean velocities significantly reduced (P < 0.05) live periphyton and filament length. The 200 mg L -1 TSS level significantly reduced (P < 0.05) biomass and filament development. The effect of TSS was least where velocity was highest and depth was most shallow, which had the least effect on light absorption and resulted in the least sediment deposition. The intermediate TSS level (100 mg L -1) appeared to stimulate a growth response based on periphyton and filament length, although the effect was less noticeable where velocities were higher. Pheophytin tended to he highest in conditions resulting in lower periphyton values, consistent with the notion that regimes imparting physical stress would harbor the highest concentration of pheophytin. The periphyton/filament length ratio tended to be lowest in velocities less than 0.75 m s -1 except in the high TSS case, where both periphyton and filament length were low. Low velocities and low to moderate TSS would provide the most biomass for grazing organisms and would result in the most effective nutrient filtering due to long filament length. High periphyton/pheophytin ratios were associated with high TSS, velocities exceeding ∼0.5 m s -1, or both. Sloughing could occur in systems with a pulsing velocity where the pulse period was long enough for growth to occur in the quiescent interval. © 2007 American Society of Agricultural and Biological Engineers. |
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