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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

The status of physical, natural and cultural resources of the Colorado River affected by Glen Canyon Dam are summarized here to provide relevant information to the Adaptive Management Work Group and the public. In addition, this June 1999 State of the Colorado River Ecosystem report summarizes long-trends in resource conditions, and focuses on scientific insights gained through analyses of previous and on-going scientific studies.

Physical resources reported here include climate, flow, changes in sediment transport, sandbar morphology, and campsite availability. Glen Canyon Dam discharge was reduced during winter and spring, but high flows, near or exceeding 20,000 cfs, resumed in the summer of 1999, as Lake Powell reservoir reached near full-pool stage. Flood-triggering flow criteria have not been met in 1999 as of June 21 1999. Several large Paria River flows in late summer 1998 increased sediment supplies in the Marble Canyon reach to the highest levels since 1980. Sediment inflow from the Little Colorado River was also substantial in 1998; however, continuing high flows in 1999 are exporting sediment, and may limit the effectiveness of planned flooding in the year 2000 for sand bar rejuvenation.

The water quality data reported here includes the limnology of Lake Powell, as well as downstream water temperature, water clarity and water chemistry. Data on water quality are contributed by the Lake Powell Monitoring Program, which has collected, synthesized and analyzed changing water quality since 1965 in Lake Powell, and since 1990 in the Colorado River downstream from Glen Canyon Dam.

Aquatic biological resources include the aquatic foodbase and fisheries in the Glen Canyon Reach (trout) and in Grand Canyon (native fish). High mainstream flows from 1996 through 1998 resulted in extensive colonization of the 8,000 cfs to 20,000+ cfs zone by benthic macrophytes and invertebrates, which comprise the aquatic foodbase for trout in the Glen Canyon (tailwaters) reach. Flows below 10,000 cfs in the winter and spring of 1999 reduced the extent of the aquatic foodbase, but recent resumption of high flows is expected to result in recolonization at higher stages in the summer of 1999. Further downstream, tributary inflows in 1997-1998 somewhat reduced benthic algal and invertebrate colonization in Grand Canyon. The general conclusion from 8 years of benthic analyses in this ecosystem is that high, steady flows enhance the aquatic foodbase, while lower, fluctuating flows reduce the benthos to the lowest normally achieved stage. Analysis of the relationship of the aquatic foodbase to higher aquatic trophic levels is underway.

The Glen Canyon reach supports a blue-ribbon rainbow trout fishery, of which >70% are naturally produced. The condition of this fishery in 1999 thus far appears to be near-normal with respect to the past decade.

Endangered humpback chub (HBC) exist in 9 mainstream populations in Grand Canyon but are restricted to breeding in the lower Little Colorado River (LCR, CR Mile 61L). The status and health of this population have been difficult to determine from previous studies; and concern exists regarding HBC condition factor and population size. Initially dry, warm winter conditions were replaced by very wet spring weather in 1999. The intensity of the HBC spawn has yet to be determined for 1999. A new finding from 1998 was the presence of more subadult HBC in the mainstream than had previously been reported. Reasons for this finding are related to gear type: the subadult size class (200-400 mm) is better sampled using mini-hoop nets, and is undersampled using electroshocking equipment. The distribution and abundance of the other three native fish species appears to be normal, but detailed time series monitoring data on their condition or population trends have yet to be developed.

The non-native Asian tapeworm infestation in HBC is widespread. This parasite was probably vectored by non-native carp or other cyprinid minnows, and remains a concern to HBC management. Also, Lernia (a copepod) is a common ectoparasite in the warm water of the LCR. Two fisheries topics are being studied in the warm water of the LCR studied by the Arizona Game and Fish Department (T.L. Hoffnagle, Principal Investigator): parasite distribution and abundance, and predator distribution and diet.

Other non-native fish populations (e.g., red shiner) appear to be increasing, but time series analyses of these non-native fish populations have yet to be developed.

Terrestrial biological resources include wetland and riparian soils, vegetation and fauna, including several species of concern. The homogenization of fine sand riparian soils resulting from the 1996 Bureau of Reclamation experimental flood has continued to influence vegetation recovery from that event. Fluvial marsh vegetation is well developed in large return current channel backwaters, and wetland vegetation has slowly recovered from the scouring effects of the 1996 experimental flood. Marshes associated with two historical southwestern willow flycatcher breeding sites (Mile 50.5L and 65.3L) that had been scoured by the 1996 flood are gradually recovering, while the other two marshes (51.5L and 71L) were little damaged by the experimental flood and have fully recovered. Gradual recovery of some (especially channel margin) marsh patches has remained slow, possibly because of increased soil grain size. The timing of the 1996 BHBF (March) and the 1997 HMF (November) limited saltcedar seedling establishment during those two planned floods, but steady high flows from 1995-1998, and again beginning in May 1999, have allowed additional establishment of saltcedar downslope from the 30,000 cfs stage.

Terrestrial species of concern are being monitored to determine long-term population trends and responses to dam operations:

Kanab ambersnail (KAS): This endangered landsnail exists at Vaseys Paradise in native and non-native herbaceous vegetation and in two known populations near Kanab, Utah. Habitat and population recovery at Vaseys Paradise from the 1996 planned flood was virtually complete in 1998, and 1999 cover and population size are at or above the pre-1996 BHBF levels below the 45,000 cfs stage. Decision making regarding population size and the extent of habitat that may be taken in planned flows is complicated by climate-driven variation in watercress (a primary KAS host plant) cover and by seasonal variation in KAS distribution on its host plants. Preliminary results from the May 1999 habitat survey indicate that 81.5 m2 (approximately 11.8%) of the KAS habitat exist below the 45,000 cfs stage.

Southwestern Willow Flycatcher: This endangered Neotropical migrant bird nests preferentially in saltcedar in Arizona across a broad elevational gradient (<500' to 8000'), and Mile 46 to 74 has been designated as critical habitat for SWWF in Grand Canyon. Four historic southwestern willow flycatcher (SWWF) territories have been occupied in that reach since 1974, in riverside saltcedar stands at Miles 50.5L, 51.5L, 65L and 71L. Nest trees at these sites typically lie upslope from the 45,000 cfs stage and the nests 4-7 m above the ground. SWWF commonly forage out into adjacent shoreline and wetland habitats. Only a single SWWF pair was detected in Grand Canyon during 1997 and 1998, at Mile 50.5L. This SWWF pair did not breed successfully in 1997 or 1998 because of brown-headed cowbird brood parasitism and loss of nests to high winds. A single SWWF singing male has been identified in 1999 in Glen Canyon, and the 50.5L Mile pair has returned; however, no information on nesting success was available at the time of this report.

The four marshes associated with territories in upper Grand Canyon were reduced in area by the 1996 BHBF. Two of the 4 marshes (including the 50.5L site) have recovered slowly from the 1996 test flood and are still smaller than they were prior to the flood. The other two sites, which were not strongly affected by the experimental flood, have largely recovered or increased in area.

The Lower Colorado River office of the Bureau of Reclamation supported SWWF inventories in the headwaters of Lake Mead in 1998. An analysis of 24 sites revealed an estimated 16 SWWF territories between Spencer Canyon (Colorado River

Mile 246) to the Park boundary at Mile 278, including observation of several sets of fledglings (P. Arroyava, personal communication). The status of SWWF in lower Grand Canyon in 1999 is presently unknown.

The -9L Spring population of Niobara ambersnail survived the 1996 BHBF, and appeared to be little affected by the November 1997 31,000 cfs habitat maintenance flood. Flows in excess of 20,000 cfs through the summer of 1998 eliminated most of the habitat of the Niobrara ambersnail, and it was not evident in late summer 1998; however, snails were observed in April 1999. Resumption of high flows in May 1999 has again reduced snail habitat area at that site.

Northern leopard frogs continue to be abundant at he -9L Spring, and a possible leopard frog tadpole was reported by the NPS in Spring Canyon (Mile 204R) in May 1999.

No flow-related impacts on peregrine falcons, bald eagles, osprey or belted kingfishers were reported in 1997, 1998 or 1999, and 1999 populations appear reasonably robust.

Cultural resources include: archaeological sites and traditional cultural resources such as springs, landforms, sediment and mineral deposits, and traditional plant locations and animals. These resources have the potential to be affected by the operations of Glen Canyon Dam. The ultimate goal of the cultural resource efforts related to Glen Canyon Dam operations is in-situ preservation, with minimal impact to the integrity of the resources and when preservation is not possible data recovery efforts, as appropriate.

Hydroelectric power production data are compiled from Bureau of Reclamation SCADA data. These data are related to flow releases, and show normal daily and seasonal variation of power production in relation to the Glen Canyon Dam Record of Decision criteria and experimental flows (e.g., the November 1997 habitat maintenance flow). Discharge since 1995 has remained elevated, except during the late winter and spring of 1999, when flows were briefly decreased to more normal levels.

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