Riparian Zones in Glen Canyon: Condition of the Park's Streamside Lands

What riparian zones are

Riparian zones are the lands along rivers, streams, lakes and other waters — streambanks, riverbanks, flood plains. Water shapes their soils and plants, setting them apart from the uplands around them. In the southwestern United States they cover less than two percent of the land, yet hold the highest density and abundance of plants and animals of any habitat.

They:

• give wildlife habitat, migration routes and corridors;
• protect water quality, as streamside plants strip excess nutrients and sediment from runoff;
• stabilize banks and slow floodwater;
• shade streams, keeping water cooler for fish;
• offer recreation and scenery.

A riparian area in Harris Wash. NPS photo.

Glen Canyon's waterways

More than 3,000 miles of waterways run through Glen Canyon National Recreation Area — farther than from Los Angeles to Washington, D.C.

Flow depends mostly on mountain snowpack and how fast it melts in spring and summer, plus monsoon rains and other precipitation. Riparian plants range from cattail, rush and sedge marshes and streamside willows to deciduous forest.

The biggest threats

• Climate change: warmer, drier conditions and shifts in the amount and timing of precipitation — the zone's key driver — stress native plants and favor some invasive ones.
• Invasive plants: among the largest stressors. The park and partners have worked to control them along the Escalante River, but others, such as the Dirty Devil River, are heavily invaded.

The assessment

A Natural Resource Condition Assessment (NRCA) under the NPS NRCA Program looked at water-related resources away from Lake Powell and the main-stem Colorado River. The riparian zone was one of five focal resources.

• Where: four major Colorado River tributaries (Dirty Devil, Escalante, Halls Creek, Lake Canyon), two Escalante tributaries (Coyote Gulch, Harris Wash) and one San Juan tributary (Wilson Creek).
• Who and how: ecologists at Utah State University used three indicators — water quantity and availability, stream and watershed health, and vegetation — drawn from literature describing healthy Colorado Plateau riparian systems as those with highly variable flow and mostly native plants.

What it found

• Water quality: no impairments reported for the streams studied.
• Intactness: some subwatersheds rated low or very low for aquatic intactness, reflecting water demand, dams, diversions and development.
• Flow: no significant decline in annual discharge on the Escalante (1943–2020) or Dirty Devil (1948–2020). But the Escalante shows a moderate drop in average annual flow and in yearly and monthly variability.
• Vegetation: fairly stable, but non-native species make up many of the plants along some corridors, especially the Dirty Devil — including some of the park's worst invaders.

What managers can do

Control of some invaders, such as tamarisk (Tamarix ramosissima), has worked, but non-native plants remain a serious threat and climate change will add stress. The assessment named continued invasive plant control and research on non-native plants as management needs.

More: non-native species and water quality in the park; the 2022 Glen Canyon NRCA project.

Sources

Based on "Riparian Zones—It's all about the Water," part of the series NRCA 2022: Condition of Glen Canyon's Tributary Rivers and Associated Resources, National Park Service, summarizing Albright J and others, 2022, Natural resource conditions at Glen Canyon National Recreation Area: Findings & management considerations for selected resources, Natural Resource Report NPS/SCPN/NRR—2022/2374, National Park Service, Fort Collins, Colorado, DOI; a work of the United States government in the public domain.