Consequences of Fluctuating Discharge for Lotic Communities

• DOI: 10.2307/1467776
• Publication Date: 2006-05-08T06:38:06Z
• Authors: W. Blinn; Joseph P. Shannon; Lawrence E. Stevens; Justin P. Carder
• Keywords: Cobble; Benthos; Cladophora; Periphyton; Dreissena

We used five in situ experiments to test the influence of fluctuations river discharge on structure and function tailwaters benthos associated with cobble substrata Colorado River downstream from Glen Canyon Dam, Arizona, USA. Periods daily desiccation freezing during fluctuation significantly limited community biomass energy. The permanently submerged channel supported 4-fold higher macroinvertebrate mass than varial zone. Daily harvests showed a 50% reduction Cladophora glomerata after 2 d repeated 12-h summer exposure. Five days exposure resulted >70% C. >50% epiphyton mass. observed ≥85% benthic only one One night time subzero winter air temperatures ≥50% loss chlorophyll ≥90% Gastropod densities resubmerged cobbles that were subjected long-term (∼6 mo) equalled control within 1 wk, whereas recolonization by glomerata, Gammarus lacustris, chironomid larvae was slower; i.e., ≤30% controls 4 mo. Hence, our data two periods may require >4 mo for recovery achieve benthos. Incremental increases energy (joules/m²) over increased base 142 793 m³/s result an increase trout approximately 42.5 kg/ha at Lees Ferry.