Developing standards and indicators for aquatic invertebrates for VERP planning in the Zion National Park Narrows

Project Number: 9716003PZ
Cooperating Agency: National Park Service
Project Chief: Anne Brasher, USGS Salt Lake City, Utah
Period: 2004-2007

Problem: The General Management Plan for Zion National Park commits the park to an impact-based approach to park management using the Visitor Experience Resource Protection (VERP) process. VERP is an approach to managing visitor use that applies the concept of Limits of Acceptable Change, where key indicators of visitor impact to natural or cultural resources are identified and monitored, and thresholds for management action are established. The approach is similar to current efforts to establish “vital signs” indicators of ecosystem health, except that it is applied specifically to impacts from park visitors. In this case, aquatic invertebrates are thought to be responsive to human disturbance of the riverbed, and would thus provide a quantifiable measure of actual human impact. Based on the findings, indicators and standards for aquatic invertebrates in the Zion National Park Narrows can be established for VERP management.

Objectives: Principal study objectives include ( 1) document the current aquatic invertebrate community with the identification of species, density, and diversity, (2) understand and quantify the current levels of impact including physical impacts of people walking through the river, (3) quantify the association between habitat characteristics and aquatic communities for streams with different levels of impact, and (4) Determine if the measured relationships are sufficiently consistent to be used as a predictor of response to evaluate proposed management actions.

Relevance and Benefits: The number of people engaged in water-based recreation in several of the park’s desert streams is high during the spring, summer and fall, with unknown consequences for aquatic species. With the large volume of visitors using these areas, management actions that would curtail these popular uses will be controversial and must be supported by scientifically credible monitoring techniques and well-documented impacts.

Approach: Aquatic invertebrates will be collected seasonally in order to develop as complete a taxa list as possible. Additional sampling will be conducted in the summer during periods of maximum visitor use. Invertebrates will be sorted and identified using standard procedures. Immature insects will most often be identified to genus and adult insects to species. In addition to aquatic invertebrate sampling, measurements of chlorophyll a, turbidity, substrate type, and temperature will be made at each site. Stream flow will be noted at the time of sampling, and past flows that may have lingering effects will be noted. Water velocity measurements will accompany drift net samples. Available GIS data will facilitate the incorporation of other potentially important variables such as canyon width, watershed topography, and light availability. Diversity and richness indices will be used to compare each site. Statistical analyses will be used to determine between-site differences and the effects of several variables on these differences.

Products: A final report will be prepared and presented to the National Park Service, detailing results and selection of standards and indicators. We will make recommendations for additional research, suggested management approaches and monitoring protocols based on our findings.

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