Reservoir–river linkages: Lake Powell and the Colorado River, Arizona

Abstract

The effect of lotic-lentic interactions on the phytobenthic community was studied in the Colorado River below Glen Canyon Dam (GCD), Arizona. Major compositional changes in river phytobenthos occurred following high snowmelt inflows that filled the Lake Powell reservoir and resulted in high, steady discharges from GCD. Cladophora glomerata, the previously dominant alga, was partly displaced by a mixed mucilaginous phytobenthic assemblage consisting of miscellaneous algae, macrophytes, and bryophytes (MAMB). Relationships between abiotic parameters (discharge, conductivity, nutrient concentration, and season) and biotic responses (composition and biomass of filamentous and epiphytic algae, and invertebrate biomass) were analyzed from 1995 to 1998. In addition, the response of the phytobenthos to an experimental flood (1275 m3/s) was examined in the tailwaters below GCD. Significant compositional changes occurred within 3 mo of lake filling and the onset of elevated discharges in June 1995. Relative phytobenthic composition by biomass prior to June 1995 was: Cladophora glomerata = 91.5%, MAMB = 3.5%, and cyanobacteria = 5.0%, compared to 49.6, 47.9, and 2.5%, respectively, after the initiation of high discharges. Cladophora and MAMB had an inverse relationship that fluctuated seasonally. Cladophora was positively associated with increased nutrient concentrations and lower discharge during summer-autumn, whereas MAMB was positively correlated with decreased nutrients and higher discharge during winter-spring. Cladophora was positively associated with invertebrate biomass and also had greater epiphyton biomass and density than MAMB. The 1996 experimental flood resulted in a significant loss of MAMB biomass, in contrast to a minimal decrease in Cladophora and invertebrates. Interactions between inflow patterns, reservoir chemistry, and discharge regime have an important effect on benthic community structure below dams. Resource managers need to consider these relationships and regard water resources above and below impoundments as a connected system when making management decisions.

Effects of experimental floods on periphyton and stream metabolism below a high dam in the Swiss Alps (River Sp�l)

“…Moss cover on upper stone surfaces declines inversely with the stability of the substratum, which among other factors, also depends on stone size (McAucliffe, 1983). The experimental flood below the Glenn Canyon Dam (Colorado River) showed that bryophytes were more susceptible to high flow than the filamentous macroalga Cladophora glomerata (Benenati et al, 2000). The low frequency of high flow events in the Spöl before 1999 favored moss growth also on relatively small rocks, which were highly stable under the residual flows, but were moved or subject to abrasion by moving bed sediment during the experimental floods.…”

Residence‐time‐based classification of surface water systems

“…Basu and Pick [] observed rotifers to be more populous in lake environments and Benenati et al . [] expected declines in Cladocera with increased lotic velocity. Hoffsten and Malmqvist [] used predetermined lentic and lotic taxa assemblages to predict the sources of species measured in a glaciofluvial spring.…”

A global lake and reservoir volume analysis using a surface water dataset and satellite altimetry

“…The reservoir shows a consistent seasonal variation, with increases of around 10-20 km 3 during the first five months, and decreases over the last seven months of the year (Figure 6b). Moreover, the lake gained at least 45 km 3 of water from 1996 to 1999. , Lake Powell is the largest lake in the U.S. by water surface area (Barnett and Pierce, 2008;Benenati et al, 2000). Its maximum capacity of 33.3 km 3 is slightly less than that of Lake Mead (Benenati et al, 2000;Holdren and Turner, 2010).…”

“…Moreover, the lake gained at least 45 km 3 of water from 1996 to 1999. , Lake Powell is the largest lake in the U.S. by water surface area (Barnett and Pierce, 2008;Benenati et al, 2000). Its maximum capacity of 33.3 km 3 is slightly less than that of Lake Mead (Benenati et al, 2000;Holdren and Turner, 2010). The lake showed two periods of maximum capacity during 1984-1988 and 1995-2000 …”