Todd V. Royer

Inter-annual patterns in macroinvertebrate communities of wilderness streams in idaho, U.S.A.

This study examined the inter-annual variation in macroinvertebrate assemblages in six wilderness streams in central Idaho over a 6-year period (1990–1995). Benthic macroinvertebrates and associated environmental correlates were sampled during baseflow each summer. Little environmental change, as assessed using coefficients of variation (CVs) for substrate size and embeddedness, width, depth and periphyton standing crops, occurred in the streams over the period of study. There was also little temporal change in macroinvertebrate assemblages based on the relative abundance of the 10 most abundant taxa, all shredder taxa and all plecopteran taxa. CVs for individual taxa were substantially greater than those of most community measures, with rare taxa contributing 30–50% of the variation for any one stream. Frequency distributions for taxa CVs excluding rare taxa were more normally distributed. Differences in assemblage structure among streams were attributed to stream size (shift in shredder assemblages) and temperature (shift in plecopteran taxa). These data indicate a long-term (multi-year) persistence in the macroinvertebrate composition of these pristine streams, thus supporting the premise that such streams are excellent references for use in long-term biomonitoring programs.

Controls on leaf processing in streams from spatial-scaling and hierarchical perspectives

The importance of leaf litter to streams is well known, as is the series of events involved in leaf decay (leaf processing). What is currently missing, however, is an understanding of how the numerous, interacting variables controlling leaf-processing rates in streams can be organized. We suggest that leaf processing is scale-dependent and that factors controlling processing rates will largely depend on the spatial scale of study. Such factors may interact across spatial scales, creating problems in extrapolating results beyond the scale at which the study was conducted. We present a hierarchical framework that relates constraints on leaf processing to specific spatial scales. This framework reveals a predictable structure regarding the factors controlling leaf processing, providing a means for explicit incorporation of spatial scale into studies of leaf processing. Our framework also allows for developing scale-specific predictions of how various environmental changes might affect rates of leaf processing in streams.

Processing of native and exotic leaf litter in two Idaho (U.S.A.) streams

The Russian olive tree (Elaeagnus angustifolia L.) was brought to the western United States from Eurasia during the early to mid-1900s, and has since become a common member of many riparian communities in Idaho. We compared leaf chemistry and in-stream processing of Russian olive leaves (exotic) and various species of native leaves in one hardwater and one relatively softwater Idaho stream. Measurements using air-dried leaves showed that Russian olive contained the greatest concentration of nitrogen, approximately 1.6% of the dry mass, whereas the native species each contained less than 1.0% nitrogen. The C/N ratio of Russian olive was <30, whereas the natives each had C/N ratios greater than 40. Results from the hardwater stream indicated no difference in 30-day loss of AFDM between Russian olive and the native leaves (dogwood and aspen). In the relatively softwater stream, the Russian olive leaves were processed significantly slower than the native leaf species (cottonwood). The results indicate that a replacement of native riparian trees by exotics, such as Russian olive, may result in slower rates of leaf processing in Idaho streams but that the effect may vary among streams. When comparing the processing of native and exotic leaf litter, initial nitrogen concentrations and initial C/N ratios of the leaves did not appear to be accurate indicators of relative decay rates.

Rapid breakdown of allochthonous and autochthonous plant material in a eutrophic river

Carbon/nitrogen ratios and breakdown of leaves of Populustremuloides (allochthonous) and the aquatic macrophytes, Ceratophyllum demersum and Potamogeton pectinatus(autochthonous), were investigated in a eutrophic river. Theallochthonous material had a C/N ratio 5–6u2009× greaterand decayed slower than either of the macrophytes. The decay ratesmeasured for these species were greater in this eutrophicsystem than has been reported for the same species in moreoligotrophic systems. The rapid breakdown of the plant material and theeutrophic condition of the river suggest the microbialdecomposer community may have been limited, at least in part, by theavailability of detrital organic carbon, rather than dissolvednutrients only.

Estimated Historical and Current Nitrogen Balances for Illinois

The Midwest has large riverine exports of nitrogen (N), with the largest flux per unit area to the Mississippi River system coming from Iowa and Illinois. We used historic and current data to estimate N inputs, outputs, and transformations for Illinois where human activity (principally agriculture and associated landscape drainage) have had a dominant impact. Presently, approximately 800,000 Mg of N is added each year as fertilizer and another 420,000 Mg is biologically fixed, primarily by soybean (Glycine max L. Merr.). These annual inputs are greater than exports in grain, which results in surplus N throughout the landscape. Rivers within the state export approximately 50% of this surplus N, mostly as nitrate, and the remainder appears to be denitrified or temporarily incorporated into the soil organic matter pool. The magnitude of N losses for 1880, 1910, 1950, and 1990 are compared. Initial cultivation of the prairies released large quantities of N (approximately 500,000 Mg N year(-1)), and resulted in riverine N transport during the late 19th century that appears to have been on the same order of magnitude as contemporary N losses. Riverine flux was estimated to have been at a minimum in about 1950, due to diminished net mineralization and low fertilizer inputs. Residual fertilizer N from corn (Zea mays L.), biological N fixed by soybean, short-circuiting of soil water through artificial drainage, and decreased cropping-system diversity appear to be the primary sources for current N export.