Research Summaries

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Compiled by Alan Carpenter

Saunders, W. C. and K. D. Fausch.
2007. Improved Grazing Management Increases Terrestrial Invertebrate Inputs That Feed Trout in Wyoming Rangelands Streams. Transactions of the American Fisheries Society 136:1216-1230.

Research in forest and grassland ecosystems worldwide indicates that terrestrial invertebrates can be a significant source of prey for fish, providing about 50% of their annual energy. We examined whether input of terrestrial invertebrates to rangeland streams in western Wyoming provides an important prey resource for brown troutSalmo trutta and brook trout Salvelinus fontinalis and how it is modified by livestock grazing. During the summers of 2004 and 2005 we sampled falling invertebrate input and trout diets in five pairs of streams that had riparian zones under two different grazing systems: high-density, short-duration (HDSD) grazing versus season-long (SL) grazing. The biomass of riparian vegetation and the input of terrestrial invertebrates were two to three times greater in reaches with riparian zones under HDSD than under SL grazing management. Likewise, the afternoon diets of individual trout in HDSD reaches had, on average, about twice as much terrestrial invertebrate biomass during summer than those of trout in SL reaches, but this was statistically significant only during late summer due to high variability. Overall, 57% of the afternoon diets of trout in reaches under both grazing systems consisted of terrestrial prey. Diel diet sampling during August 2005 showed that fish in HDSD reaches also had consumed more aquatic invertebrate prey, primarily at night. Total trout biomass in HDSD reaches was more than twice that in SL reaches. These results suggest that in rangeland streams of the western United States, both terrestrial and aquatic invertebrates are important prey resources for trout and that improved grazing management has the potential to influence fish populations through multiple food web pathways.

 

Whittier, T. R., R. M. Hughes, J. L. Stoddard, G. A. Lomnicky, D. V. Peck, and A. T. Herlihy.
2007. A Structured Approach for Developing Indices of Biotic Integrity: Three Examples from Streams and Rivers in the Western USA. Transactions of the American Fisheries Society 136:718-735.

In the late 1990s the Environmental Monitoring and Assessment Program of the U.S. Environmental Protection Agency developed a structured set of tests to evaluate and facilitate selection of metrics for indices of biotic integrity (IBIs). These IBIs were designed to be applicable across multistate regions as part of a national assessment of all U.S. waters. Here, we present additional steps in, and refinements to, that IBI development process. We used fish and amphibian assemblage data from 932 stream and river sites in 12 western U.S. states to develop IBIs for Mountains, Xeric, and Plains ecoregions. We divided 237 candidate metrics into nine metric classes representing different attributes of assemblage structure and function. For each ecoregion we sequentially eliminated metrics by testing metric range, signal-to-noise ratios, responsiveness to disturbance, and redundancy to select the best metric in each class. The IBIs for the Mountains and Plains each had seven metrics and the Xeric IBI had five. In the Mountains, half of the estimated stream length that could be assessed had IBI scores greater than 62 (out of 100). In the Xeric and Plains, half the stream length had scores no greater than 50 and no greater than 37, respectively. An estimated 16% of Xeric stream length had scores greater than 62 (the median for the Mountains), while 5% of Plains stream length had scores that exceeded 62. This IBI development process is less subjective and more streamlined and has more clearly defined criteria for metric selection and scoring than those used in the past, while maintaining a strong ecological foundation.

 

Shah, J. J. Follstad and C. N. Dahm.
2008. Flood Regime and Leaf Fall Dymanics Determine Soil Inorganic Nitrogen Dynamics in Semiarid Riparian Forests. Ecological Applications 18:771-788.

Flow regulation has reduced the exchange of water, energy, and materials between rivers and floodplains, caused declines in native plant populations, and advanced the spread of nonnative plants. Naturalized flow regimes are regarded as a means to restore degraded riparian areas. We examined the effects of flood regime (short [SIFI] vs. long [LIFI] inter-flood interval) on plant community and soil inorganic nitrogen (N) dynamics in riparian forests dominated by native Populus deltoides var. wislizenii Eckenwalder (Rio Grande cottonwood) and nonnative Tamarix chinensis Lour. (salt cedar) along the regulated middle Rio Grande of New Mexico. The frequency of inundation (every 2-3 years) at SIFI sites better reflected inundation patterns prior to the closure of an upstream dam relative to the frequency of inundation at LIFI sites (=10 years). Riparian inundation at SIFI sites varied from 7 to 45 days during the study period (April 2001 – July 2004). SIFI vs. LIFI sites had higher soil moisture but greater groundwater table elevation fluctuation in response to flooding and drought. Rates of net N mineralization were consistently higher at LIFI vs. SIFI sites, and soil inorganic N concentrations were greatest at sites with elevated leaf-litter production. Sites with stable depth to ground water (1.5 m) supported the greatest leaf-litter production. Reduced leaf production at P. deltoides SIFI sites was attributed to drought-induced recession of ground water and prolonged inundation. We recommend that natural resource managers and restoration practitioners (1) utilize naturalized flows that help maintain riparian groundwater elevations between 1 and 3 m in reaches with mature P. deltoides or where P. deltoides revegetation is desired, (2) identify areas that naturally undergo long periods of inundation and consider restoring these areas to seasonal wetlands, and (3) use native xeric-adapted riparian plants to revegetate LIFI and SIFI sites where groundwater elevations commonly drop below 3 m.