The State of Natural and Cultural Resources in the Colorado River Ecosystem:
JUNE 30, 1999 DRAFT REPORT
Grand Canyon Monitoring and Research Center
Flagstaff, AZ 86001
Updated: 30 June 1999
Table of Contents
- Executive Summary
- Introduction and Administration
- Physical Resources and Processes: Climate, Hydrology, Sediment
- Water Quality: Lake Powell and the Colorado River Downstream
- Aquatic Biological Resources: Foodbase, Habitat, Native Fish, Non-native Fish
- Terrestrial Biological Resources: Vegetation, Habitat, Wildlife
- Endangered Species and Species of Concern
- Cultural Resources: Archeological Sites; TCP's; Ethonobiology; Havasupai, Hopi, Hualapai, Navajo, Southern Paiute and Zuni Tribes
- Socio-economic Resources: River Running, Angling, Hydropower Production
- Acknowledgements
- Bibliography
Terrestrial Biological Resources
Species of Special Concern
-
- Endangered Species
- Non-Endangered Arizona State Species of Concern
Terrestrial Biological Resources
Research by Parnell et al. (1999) revealed that the 1996 test flood buried large quantities of sand bar vegetation, and decomposition of that material substantially increased soil and bank-stored groundwater nitrogen and carbon, but not ortho-phosphate, concentrations for more than a year following the flood. Their analyses of carbon and nitrogen dynamics indicate that bank storage may strongly influence mainstream nutrient concentrations. Springer et al. (1999) demonstrated that loading of sand bars with new sand reduced hydraulic conductivity, a process that governs bank-stored ground water movement and nutrient export from sand bars. This process is reversing as sand bars have eroded in the post-1996 period.
Hydro-Riparian Vegetation: Fluvial Marshes
Fig. TB1.1: Estimated number of wet marsh patches along the Colorado River from Lees Ferry to Diamond Creek, 1965-1998 (draft data from L. Stevens, GCMRC). Riverside marshes are a novel post-dam development in the Colorado River ecosystem (Stevens et al. 1995). The decrease in marsh number in 1982 is an artifact of photo scale, whereas the reductions in 1983 and 1996 are a result of flood-related scouring. Updated 23 June 1999.
Fig. TB1.2: Estimated area (ha) of wet marsh patches along the Colorado River from Lees Ferry to Diamond Creek, 1965-1998 (draft data from L. Stevens, GCMRC). Riverside marshes are a novel post-dam development, now occupying 1-2% of the riparian habitat in the Colorado River ecosystem (Stevens et al. 1995). The decrease in marsh area in 1982 is an artifact of photo scale, whereas the reductions in 1983 and 1996 are a result of flood-related scouring. Updated 23 June 1999.
Fluvial Marsh Development
Fluvial marshes are biologically diverse and highly productive
habitats that have developed in the post-dam Colorado River corridor (Stevens et
al. 1995). Fluvial marshes colonize low-lying, fine-grained habitats in
channel margin and return current channel settings, which are periodically
inundated. Stevens et al. (1995) distinguished between cattail/reed/sedge/rush
wet marshes
, and horsetail dominated dry marshes
. Wet
marshes integrate the interactions between flow and sediment grain size, and
channel margin marshes are particularly susceptible to scouring under high
flows. Dry marshes are characteristic of channel margin deposits throughout the
river corridor, and provide additional near-shore habitat for young fish and
nesting mallard ducks. Therefore, marshes may serve as an indicator of
flow-related habitat stability and productivity.
Stevens (unpublished data) recorded the number and estimated area of all fluvial marsh patches along the Colorado River from Lees Ferry to Diamond Creek from aerial photographs, and during annual summer or fall river trips in 1965, 1973, 1980, 1982, 1984, 1991, 1993, and annually from 1995 through 1998 (Figs. TB 1.1-1.2). An overall increase in the number and area of marsh patches was detected through the Interim Flows period, with a maximum number of 1,519 patches and total estimated area of 8.47 ha in 1995. The use of planned flooding as a sediment management strategy reduced the number and area of fluvial marshes by scouring or burial of patches that had developed during Interim Flows, and marsh recovery has been limited by increased grain-size which limits germination of marsh plant species. A total of 1,241 marsh patches were detected (18.3% fewer than in 1995) with an estimated total area of 5.59 ha (34.0% less area than in 1995). Most of the patches that were scoured by the 1996 test flow were channel margin or bar face settings, but few marshes established in return current channels were scoured (Ayers and Kearsley 1999). Narrow reaches lost greater proportions of marshes than did wide reaches. Post-1996 reestablishment of marsh patches has been gradual, probably because of increased mean grain size (which reduce germination success) on channel margin bars of wet marsh species) slow and area continued to decrease because of larger grain-size on bars. A total of 1,322 patches covering an estimated 4.6 ha were detected in 1997, and 1,215 patches, occupying 4.6 ha were detected in 1998.
Importantly, several large, established marshes associated with endangered southwestern willow flycatcher (Empidonax trailii extimus) breeding and foraging sites were reduced in area by more than 70% by the 1996 experimental flood (Stevens et al. in press).
Lower Riparian Zone Vegetation
Fig. TB2.1: Data in preparation, 23 June 1999.
The GCD-EIS and ROD emphasize the maintenance of riparian vegetation in an array of successional stages as wildlife habitat (T. Melis and L. Stevens, GCMRC Memorandum 23 November 1998). As a test of sediment transport, the 1996 test flood was expected to scour riparian vegetation, which did sustain some reduction in cover, particularly through the burial of ground-covering vegetation under up to nearly 2 m of new fine sand. However, in contrast to riverside marshes, established woody largely survived the 1996 flood, growing up through newly deposited sand and becoming reestablished (Ayers and Kearsley 1999). The newly deposited 1996 sediments were well sorted fine sand, with a reduced seed bank and bar surfaces are higher, and therefore drier, than those prior to the experiment. This reduces the potential for germination of many riparian species, despite the relatively rapid recovery of the seed bank. Depending on flow and grain size, the newly formed sand bars are less likely to be overgrown by germinating tamarisk, and more likely to become colonized by clonal or rhizomatous species (e.g., coyote willow, Salix exigua; arrowweed, Tessaria sericea; and non-native camelthorn, Alhagi camelorum).
An additional concern with the test flood was that non-native plant species would become more widely distributed by planned floods. The test flood was scheduled to allow sufficient time after the flood to dry out the sand bars and limit tamarisk germination. In this respect, the test flood was quite successful. While not wholly preventing tamarisk germination, relatively little establishment was observed at -6.5R, 43L, 44L, 55.5R, 65L and 194L by Stevens (personal observation). However, high flows in the summers of 1996-1998 have allowed an additional cohort of tamarisk seedlings to become established, particularly in the lower Grand Canyon. Among the other non-native plant species: camelthorn vigorously occupies many sites downstream from the Little Colorado River confluence; tumbleweed and lovegrass are widely distributed; and Ravenna grass distribution was greatly reduced prior to the 1996 test flow, and its populations continue to be monitored and controlled by the NPS.
The 1996 experimental flood affected the culturally significant landscapes along lower Grand Canyon and Lake Mead in a fashion similar to that which occurred in the upstream reaches (Phillips 1997, Christianson 1997). The high flows extended below Mile 250, indicating that potential impacts of planned flooding may occur a fair distance out onto Lake Mead.
Upper Riparian Zone Vegetation
Anderson and Ruffner (1988) examined growth rates of pre-dam
old high water zone
plants during and after the 1983-1986 high
flows from Glen Canyon Dam. They measured growth rates of mesquite and catclaw
acacia in the river corridor and in tributaries, using internode distances and
reproductive output of mature plants, and seedling and sapling growth rates.
They concluded that there was no detectable effect of the 1983 flow of 96,200
cfs on growth rates of these dominant pre-dam species. Similarly, a dendrochronological
(tree ring) analysis of netleaf hackberry trees in the river corridor and in
tributaries demonstrated no discernable impact of flow regulation on the growth
rate of these common pre-dam species (Salzer et al. 1996). Netleaf
hackberry trees may live to be more than 200 yr in age, and mesquite may live
to be more 700 yr in age in the pre-dam vegetation zone along the Colorado
River in Grand Canyon. These studies indicate that dam operations have had no
impact on tree growth on upper riparian zone terraces; however, Stevens and
Ayers (1994) found virtually no evidence of mesquite or hackberry recruitment
on those high terraces, but active recruitment by acacia. A gradual
compositional shift from mesquite and hackberry (obligate riparian species in
this system) towards increasing dominance by acacia (a facultative riparian
species in this system) may be underway.
Fig.TB3.1: Graphs in preparation, 23 June 1999.
- Species of Special Concern
NON-ENDANGERED ARIZONA STATE SPECIES OF CONCERN
Niobrara Ambersnail (Oxvloma h. haydeni) in this region is known from one site along the Colorado River (-9L, upstream from Lees Ferry) and at Indian Gardens. The ambersnail population at the riverside spring is unique and is associated with the Typha and other wetland vegetation. This population somehow persisted through the 1996 experimental flow. This snail population is not presently being monitored; however, some observations were made in 1998. Although the snail was abundant in May 1998 (Stevens, personal observation), and in March 1999, flows in excess of 20,000 cfs inundate the habitat. Flows exceeded 22,000 cfs for extended periods in the summer of 1998 and in May 1999, and no snails were found during habitat searches in those periods (L.Stevens and V. Meretsky, personal communications). This population is one of several under genetic analysis.
Northern Leopard Frog (Rana pipiens) in the Grand Canyon region is presently known from one site along the Colorado River (-9L, upstream from Lees Ferry), but a mature tadpole was recently reported from Spring Canyon (Mile 204R). The frog population at -9L is apparently native, and was monitored before and after the 1996 test flow. The population was active at the time of that flow, and apparently was little affected by the flow and recovered quickly (Spence 1997). The frog population appeared healthy through 1998 and in March 1999 (Stevens, personal observation). However, higher flows may affect this population.
Wintering passerines and waterbirds are a concern in lower Glen and Grand canyons, and are being monitored. Migratory osprey and belted kingfisher populations are additional species of concern in Arizona. Those populations were apparently not affected by the 1996 test flow, and migratory populations from April 1997-May 1999 appear to be approximately normal (Stevens et al. 1997a, J. Spence, Glen Canyon National Recreation Area, personal communication).