An invasive riparian tree reduces stream ecosystem efficiency via a recalcitrant organic matter subsidy

A disturbance, such as species invasion, can alter the exchange of materials and organisms between ecosystems, with potential consequences for the function of both ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in stream ecosystem respiration or organic matter export. Thus, estimated stream ecosystem efficiency (ratio of ecosystem respiration to organic matter input) decreased 14%. These findings show that invasions of nonnative plant species in terrestrial habitats can alter resource fluxes to streams with consequences for whole-ecosystem functions

CHARACTERIZING BENTHIC MACROINVERTEBRATE COMMUNITY RESPONSES TO NUTRIENT ADDITION USING NMDS AND BACI ANALYSES

Nonmetric multidimensional scaling (NMDS) is an ordination technique which is often used for information visualization and exploring similarities or dissimilarities in ecological data. In principle, NMDS maximizes rank-order correlation between distance measures and distance in the ordination space. Ordination points are adjusted in a manner that minimizes stress, where stress is defined as a measure of the discordance between the two kinds of distances. Before and After Control Impact (BACI) is a classical analysis of variance method for measuring the potential influence of an environmental disturbance. Such effects can be assessed by comparing conditions before and after a planned activity. In certain ecological applications, the extent of the impact is also expressed relative to conditions in a control area, after a particular anthropogenic activity has occurred. In this paper, two statistical techniques are employed to investigate the effects of stream nutrient addition on a riverine benthic macroinvertebrate community. The clustering of sampling units, based on multiple macroinvertebrate metrics across pre-determined river zones, is explored using NMDS. BACI is subsequently used to test for the potential impact of nutrient addition on the specified macroinvertebrate response metrics. The combination of the two approaches provides a powerful and sensitive tool for detecting complex second-order effects in river food chains. Statistical techniques are demonstrated using eight years of benthic macroinvertebrate survey data collected on an ultra-oligotrophic reach of the Kootenai River in Northern Idaho and Western Montana downstream from a hydro-electric dam

LONGITUDINAL DEVELOPMENT OF MACROINVERTEBRATE COMMUNITIES BELOW OLIGOTROPHIC LAKE OUTLETS

Volume: 50Start Page: 303End Page: 31

Benthos and Macroinvertebrate Drift in Six Streams Differing in Alkalinity

The productive capacity of aquatic systems often is equated with the \u27chemical richness\u27 of the water. A primary objective of the present study was to relate macroinvertebrate benthos and drift to a streams\u27 productive capacity as indicated by absolute levels of alkalinity. We tested this relationship in six 2nd–3rd order tributaries of the Salmon River, Idaho that ranged in alkalinity from 50 to 360 mg 1−1. Benthic density and biomass, drift biomass, and benthic organic matter increased with increasing levels of alkalinity, although not all relationships were significant. The proportion of drift biomass to benthic biomass was similar among study streams suggesting that drift was primarily passive during the study period. The data suggest that spatial variations in landscape-scale geology may indirectly affect spatial patterns of macroinvertebrate benthic and drift standing crops among streams within a single river basin by mediating lotic chemical richness as found among tributaries of the Salmon River basin

United States Fish and Wildlife Service Biological Report 85(7.24)

"The purpose of this profile is to summarize the ecological information available for and relevant to stream and riparian habitats of the Great Basin. The Great Basin comprises the northern half of the Basin and Range physiographic province and covers most of Nevada and western Utah and portions of California, Oregon, and Idaho. The entire basin actually consists of numerous subbasins and mountain ranges which present an extremely diverse physical setting" (p. iii)