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Results do not support the contention of textbook publishers, presidential commissions, and some educators that the reading difficulty level of English, science, or social studies textbooks has eased considerably in recent years. (FL)

1. Primary consumers play important roles in the cycling of nutrients in headwater streams, storing assimilated nutrients in growing tissue and recycling them through excretion. Although environmental conditions in most headwater streams and their surrounding terrestrial ecosystems vary considerably over the course of a year, relatively little is known about the effects of seasonality on consumer nutrient recycling these streams. In this study, we measured nitrogen accumulated through growth and excreted by the grazing snail Elimia clavaeformis (Pleuroceridae) over the course of 12 months in Walker Branch, identifying close connections between in-stream nitrogen processing and seasonal changes in the surrounding forest. 2. Nitrogen processing rates were positively correlated with ecosystem respiration, which was driven by leaf phenology on streamside trees. Snail nitrogen assimilation, growth and excretion were relatively high in spring before leaf emergence, low in summer when canopy shade was extensive and high again in autumn after leaf-fall. During the time that snails grazed primarily on epilithon (winter, spring and summer), growth and excretion rates followed changes in light and epilithon biomass. In autumn, when snails primarily grazed fallen leaves, leaf-associated microbes provided large subsidies of nitrogen for the snails. Nitrogen accumulation in snail biomass was greater in the 2 months following leaf-fall than at any other time of the year. 3. Snails were less important as nitrogen sinks than as sources of recycled nitrogen in Walker Branch. Over the course of the year, snails excreted approximately 12 times more nitrogen than they accumulated in biomass. Nitrogen accrued during growth in spring was subsequently lost in summer when primary production declined and snails underwent tissue loss. Catabolic losses represented >40% of the nitrogen excreted by the snails in summer. Net nitrogen growth efficiency (growth/assimilation), which varied with food availability, was only 8% for the entire year. Neither growth nor excretion was positively correlated with nitrogen concentrations in grazing substrata. 4. Snails achieved high standing crops and were significant contributors to nitrogen spiralling in Walker Branch. On an areal basis, nitrogen in snail biomass (mgN m-2) was two to five times greater than that in epilithon biomass, depending on the season. Snails assimilated and excreted up to 50% of the nitrogen initially taken up by autotrophs and leaf microbes, and they were likely to have additional effects on nitrogen spiraling through egestion and the cropping of assimilative biomass. Primary consumers like Elimia are important catalysts of nutrient movement through headwater streams, decreasing residence times and facilitating fluxes to downstream waters [ABSTRACT FROM AUTHOR]

1. This study investigated the combined effects of light and phosphorus on the growth and phosphorus content of periphyton. To investigate the potential for colimitation of algal growth by these two resources, diatom-dominated periphyton communities in large flow-through laboratory streams were exposed under controlled conditions to simultaneous gradients of light and phosphorus. 2. Periphyton growth rate was predictably light-limited by the subsaturating irradiances (12–88 μmol photons m−2 s−1) used in this experiment. However, phosphorus concentration also limited growth rate: growth increased hyperbolically with increasing soluble reactive phosphorus (SRP), reaching a threshold of growth saturation between 22 and 82 μg L−1. 3. Periphyton phosphorus content was strongly and nonlinearly related with SRP, reaching a maximum at 82 μg L−1 SRP. Contrary to the Light : Nutrient Hypothesis, periphyton phosphorus content did not decrease with increasing light, even at the lowest concentrations of SRP. Periphyton phosphorus was highly correlated with periphyton growth rate (Spearman's ρ = 0.63, P < 0.005). 4. Multiple regression analysis reinforced evidence of simultaneous light and phosphorus limitation. Both light and periphyton phosphorus content were significant variables in multiple regressions with growth parameters as dependent variables. Light alone accounted for 67% of the variance in periphyton biomass, and the addition of periphyton phosphorus as an additional independent variable increased the total amount of variance explained to 81%. 5. Our results did not support the hypothesis that extra phosphorus is required for photoacclimation to low light levels. Rather, the effect of additional phosphorus may have been to accommodate increased requirements for P-rich ribosomal RNA when growth was stimulated by increased light. The potential colimitation of periphyton growth by phosphorus and light at subsaturating irradiances has important implications in both theoretical and applied aquatic ecology. [ABSTRACT FROM AUTHOR]

Nutrient-diffusing substrates were used to investigate nutrient limitation of attached algal assemblages in a shaded stream and an unshaded stream in northern California. Water front both streams contained low levels of nitrogen (<14 μg · L[SUP-1] and very low N:P ratios (<2). After 31 days of colonization and growth, attached algal biomass on nitrate-diffusing substrates was significantly greater than on control substrates in the unshaded stream. Nitrate-diffusing substrates also supported larger numbers of grazing insects in the unshaded stream. The prostrate diatoms. Achnanthes lanceolata Bech. and Cocconeis placentula Ehr. displayed the most consistent positive responses to nitrate enrichment. Nutrient enrichment did not increase the accrual of algal biomass in the shaded stream, but algal biomass was significantly greater at sites located under openings in the tree canopy, implicating light as a limiting factor in this stream. Several Navicula and Nitzschia species, and one unidentified Gomphonema species, were positively associated with higher light levels in the shaded stream. Shade appears to be the primary factor limiting algal growth in small northern California streams, but when its effect is reduced by logging, the inherently low levels of nitrogen in these streams can become limiting. [ABSTRACT FROM AUTHOR]

Current external criticism of American schooling includes an assumption that content textbooks used in upper grades fail to challenge the abilities of pupils. To investigate this assumption, the multiformula readabilities of 111 content textbooks currently employed in grades six through nine in 30 middle or junior high schools were obtained. Five and six formula, same sample readability data were collected and analyzed by 37 teacher researchers. Two or more formulas placed 49% of these texts one or more grade levels above grade of use. The results also were analyzed in light of current concerns about the accuracy and use of readability formulas. Readability placements varied notably and significantly between‐texts and within‐texts for each content area and grade level of use. Significant mean differences occurred in grade placement by formulas differing in comprehension criteria and in word count procedures. Extending sample selection from three to six and nine within‐text samples did not change readability estimates notably or significantly. Teacher researcher procedural error occurred rarely. Teacher participants preferred the formulas combining realistic school estimates with efficiency in estimation. [ABSTRACT FROM PUBLISHER]