Colorado river benthic ecology in Grand Canyon, Arizona, USA: dam, tributary and geomorphological influences

Abstract

The serial discontinuity concept (SDC; Ward and Stanford, in Ecology of River Systems, 1983) predicts that recovery of large regulated rivers over distance downstream from a dam is limited by relative tributary size; however, channel geomorphology may also influence the recovery process. We examined the spatial variation in water quality, benthic composition and ash‐free dry standing biomass (AFDM) among the bedrock‐defined geomorphological reaches in three turbidity segments of the Colorado River between Glen Canyon Dam and Diamond Creek, Arizona, including most of the Grand Canyon. This 387‐km long study area supported virtually no Ephemeroptera, Plecoptera or Trichoptera, probably because cold, stenothermic, hypolimnetic releases limited maximum aestival warming to 17·1°C. The benthos displayed abrupt, physically related decreases in AFDM over distance from the dam and in the varial zone. The 26‐km long clear water segment between the dam and the Paria River supported a depauperate Cladophora glomerata/epiphyte/chironomid/Gammarus lacustris/lumbricine/Physella sp. assemblage, and ooze‐dwelling oligochaetes. This segment contained 6·9% of the aquatic habitat below the 140 m3/s (normal minimum) discharge stage of the Colorado River study area, but supported 63·5% of the benthic primary producer AFDM and 87% of the benthic consumer AFDM in the entire study area. Turbidity increased and light penetration decreased immediately downstream from the confluence of the small, turbid Paria River, and further downstream from the Little Colorado River confluence. The benthos downstream from the Paria River was abruptly replaced by an Oscillatoria/Simuliium assemblage with a mean AFDM of <0·12 g C/m2. Dam‐related effects on water clarity, varial flow and water temperature overrode geomorphological influences on habitat availability. These results generally support the SDC, in that recovery of the benthos did not take place over distance in this large river ecosystem; however, geomorphological differences in substratum availability between reaches mediated dam and tributary effects on water clarity and benthic AFDM. Interactions between flow regulation and geomorphology produce a pattern of circuitous recovery of some physical river ecosystem characteristics over distance from the dam, but not of the benthos. Improving discharge management for endangered native fish populations requires detailed understanding of existing and potential benthic development, and trophic interactions, throughout the geomorphological reaches and turbidity segments in this river. © 1997 John Wiley & Sons, Ltd.

Effects of flow regulation, basin characteristics and land-use on macroinvertebrate communities in a large arid Patagonian river

“…Collier and Lill (2008) observed an increase in diversity at main channel sites with distance down river in a large New Zealand watercourse, most likely as a consequence of interplay between habitat patchiness and successional and hydrogeomorphic processes influencing macroinvertebrate community. In the middle Chubut river basin where turbidity and flood disturbance were high, benthic density was low as found below a tributary of the Colorado River in arid Arizona (Shaver et al 1997, Stevens et al 1997. In contrast, the upper main river channel and its tributaries had a more abundant benthic fauna and twice the number of species found in the middle basin.…”

“…The interactive effects of basin features and land use changes on macroinvertebrates have been studied in headwater streams of the cordillera (Miserendino and Pizzolón 2004), and the impact of land desertification on invertebrate assemblages of rivers has been documented (Miserendino 2004(Miserendino , 2006. Although a large number of scientific papers consider the ecology of whole river systems in moderate-rainfall, temperate regions, river ecology in arid/semiarid areas remain largely unexplored (Wais 1990;Stevens et al 1997).…”

Temporal and altitudinal variations in benthic macroinvertebrate assemblages in an Andean river basin of Argentina

“…The first objective of our study was to assess seasonal and spatial variability in benthic community structure along a large river in the Central West Andes Mountains of Argentina. The study of relationships between invertebrate assemblages and environmental features is also an important community ecology theme and enhances knowledge about the functioning of rivers in arid zones, taking into account that the ecology of arid and semiarid streams remains relatively unexplored (Stevens et al, 1997). For this reason, the second main objective of our research was to find out whether physical and chemical variables affect distribution of benthic communities and whether they characterise the ecological distribution range of each species.…”

Dam and geomorphological influences on colorado river waterbird distribution, Grand Canyon, Arizona, USA

“…Hunting was permitted on the uppermost 24 km of the river in Glen Canyon National Recreation Area (except near Glen Canyon Dam and at Lees Ferry) during this study, but not in Grand Canyon. Additional climate and geographical information, and the history of flow regulation are discussed in Sellers and Hill (1974), Howard and Dolan (1981), Schmidt and Graf (1990), Marzolf (1991), and Stevens et al (1995Stevens et al ( , 1997.…”

“…Total AARE was only 114 and 113-fold greater in wide versus narrow reaches within the VT and UT turbidity segments, respectively (p INTRODUCTION Flow regulation is an ubiquitous modification of fluvial ecosystems (Ward and Stanford, 1979;Lillehammer and Saltveit, 1984;Gore and Petts, 1989) that can influence the distribution of riverine waterbirds (aquatic and semiaquatic avifauna) through modification of habitats and food resources. The natural channel geometry of large, complex rivers also affects waterbird food and habitat availability (Hupp 1988;Stevens et al, 1995Stevens et al, , 1997, but the influences of flow regulation versus natural channel geomorphology on river waterbird distribution have not been differentiated. Such information is important for evaluating the extent to which flow regulation alters the trophic structure of river ecosystems.…”