No abstract

A study of 16 streams in eastern North America shows that riparian deforestation causes channel narrowing, which reduces the total amount of stream habitat and ecosystem per unit channel length and compromises in-stream processing of pollutants. Wide forest reaches had more macroinvertebrates, total ecosystem processing of organic matter, and nitrogen uptake per unit channel length than contiguous narrow deforested reaches. Stream narrowing nullified any potential advantages of deforestation regarding abundance of fish, quality of dissolved organic matter, and pesticide degradation. These findings show that forested stream channels have a wider and more natural configuration, which significantly affects the total in-stream amount and activity of the ecosystem, including the processing of pollutants. The results reinforce both current policy of the United States that endorses riparian forest buffers as best management practice and federal and state programs that subsidize riparian reforestation for stream restoration and water quality. Not only do forest buffers prevent nonpoint source pollutants from entering small streams, they also enhance the in-stream processing of both nonpoint and point source pollutants, thereby reducing their impact on downstream rivers and estuaries.

This literature review addresses how wide a streamside forest buffer needs to be to protect water quality, habitat, and biota for small streams (≤~100 km 2 or~5th order watershed) with a focus on eight functions: (1) subsurface nitrate removal varied inversely with subsurface water flux and for sites with water flux >50 l/m/day (~40% avg base flow to Chesapeake Bay) median removal efficiency was 55% (26-64%) for buffers <40 m wide and 89% (27-99%) for buffers >40 m wide; (2) sediment trapping was~65 and~85% for a 10-and 30-m buffer, respectively, based on streamside field or experimentally loaded sites; (3) stream channel width was significantly wider when bordered by~25-m buffer (relative to no forest) with no additional widening for buffers ≥25 m; (4) channel meandering and bank erosion were lower in forest but more studies are needed to determine the effect of buffer width; (5) temperature remained within 2°C of levels in a fully forested watershed with a buffer ≥20 m but full protection against thermal change requires buffers ≥30 m; (6) large woody debris (LWD) has been poorly studied but we infer a buffer width equal to the height of mature streamside trees (~30 m) can provide natural input levels; (7, 8) macroinvertebrate and fish communities, and their instream habitat, remain near a natural or semi-natural state when buffered by ≥30 m of forest. Overall, buffers ≥30 m wide are needed to protect the physical, chemical, and biological integrity of small streams.

We employ molecular methods to profile the diet of the little brown bat, Myotis lucifugus, and describe spatial and temporal changes in diet over their maternity season. We identified 61 prey species of insects and 5 species of arachnid. The largest proportion of prey (∼32%) were identified as species of the mass-emerging Ephemeroptera (mayfly) genus Caenis. Bats roosting in agricultural settings had lower dietary richness than those occupying a roost located on a forest fragment in a conservation area. We detected temporal fluctuations in diet over the maternity season. Dipteran (fly) species dominated the diet early in the season, replaced later by species of mayfly. Because our methodology provides species-level identification of prey, we were able to isolate environmental indicator species in the diet and draw conclusions about the location and type of their foraging habitat and the health of these aquatic systems. The species detected suggested that the bats use variable habitats; members of one agricultural roost foraged on insects originating in rivers or streams while those in another agricultural roost and the forest roost fed on insects from pond or lake environments. All source water for prey was of fair to good quality, though no species detected are intolerant of pollution thus the habitat cannot be classified as pristine. Our study outlines a model system to investigate the abiotic and biotic interactions between habitat factors through this simple food chain to the top predator.

Adult body size and fecundity of a number of hemimetabolous aquatic insects depend largely on thermal conditions during the larval period. Small adults and reduced fecundity result when temperatures are either warmed or cooled with respect to more optimal thermal conditions. Temperature apparently affects adult size by altering the larval growth rate and the timing and rate of adult tissue development for each larva. The data suggest a new interpretation for the geographic distribution of aquatic insects.

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The reestablishment of riparian forest is often viewed as “best management practice” for restoring stream ecosystems to a quasi‐natural state and preventing non‐point source contaminants from entering them. We experimentally assessed seedling survivorship and growth of Quercus palustris (pin oak), Q. rubra (red oak), Q. alba (white oak), Betula nigra (river birch), and Acer rubrum (red maple) in response to root‐stock type (bare root vs. containerized), herbivore protection (tree shelters), and weed control (herbicide, mowing, tree mats) over a 4‐year period at two riparian sites near the Chester River in Maryland, U.S.A. We started with tree‐stocking densities of 988/ha (400/ac) in the experimental plots and considered 50% survivorship (i.e., a density of 494/ha [200/ac] at crown closure) to be an “acceptable or minimum” target for riparian restoration. Results after four growing seasons show no significant difference in survivorship and growth between bare‐root and containerized seedlings when averaged across all species and treatments. Overall survivorship and growth was significantly higher for sheltered versus unsheltered seedlings (49% and 77.6 cm vs. 12.1% and 3.6 cm, respectively) when averaged across all species and weed control treatments. Each of the five test species exhibited significantly higher 4‐year growth with shelter protection when averaged across all other treatments, and all species but river birch had significantly higher survivorship in shelters during the period. Seedlings protected from weeds by herbicide exhibited significantly higher survivorship and growth than seedlings in all other weed‐control treatments when averaged across all species and shelter treatments. The highest 4‐year levels of survivorship/growth, when averaged across all species, was associated with seedlings protected by shelters and herbicide (88.8%/125.7cm) and by shelters and weed mats (57.5%/73.5 cm). Thus, only plots where seedlings were assisted by a combination of tree shelters and either herbicide or tree mats exhibited an “acceptable or minimum” rate of survivorship (i.e.,>50%) for riparian forest restoration in the region. Moreover, the combined growth and survivorship data suggest that crown closure over most small streams in need of restoration in the region can be achieved most rapidly (i.e., 15 years or less) by protecting seedlings with tree shelters and controlling competing vegetation with herbicides.

Egg development, growth, and emergence 01 lsonychiu bicolor were observed in White Clay Creek (Pennsylvania) at ambient temperatures and in fluctuating experimental regimes with diel minima ranging from 12"-12.9"C and maxima between 12" and 2O.l"C. Development rate of both eggs and nymphs was correlated positively with increased magnitude of the diel temperature pulse. Adult metamorphosis was most successfIll in regimes with diel maxima >16"C.Subimago body size and fecundity for winter generation females were about double those for the summer generation.Reducing spring and summer water temperatures lowered the fecundity of winter and summer subimagocs.Weight-specific respiration rates of nymphs measured at 14 constant temperatures (range, lo-2l'C) increased with temperature but were inversely related to body size at a given temperature. Metabolic response to short term (1 h) changes in temperature was immediate; thermal acclimation or compensation was not observed. Energy budgets were calculated for male and female nymphs reared in various thermal regimes. Growth rates, net growth efficiencies, and production:rcspiration ratios of female nymphs were about twice those of males at all temperatures.Overall net growth efficiencies for 1. hicolor averaged 44.16% and P:R ratios 0.84 for the combined sexes.