Despite decades of work on implementing best management practices to reduce the movement of excess nitrogen (N) to aquatic ecosystems, the amount of N in streams and rivers remains high in many watersheds. Stream restoration has become increasingly popular, yet efforts to quantify N‐removal benefits are only just beginning. Natural resource managers are asking scientists to provide advice for reducing the downstream flux of N. Here, we propose a framework for prioritizing restoration sites that involves identifying where potential N loads are large due to sizeable sources and efficient delivery to streams, and when the majority of N is exported. Small streams (1st–3rd order) with considerable loads delivered during low to moderate flows offer the greatest opportunities for N removal. We suggest approaches that increase in‐stream carbon availability, contact between the water and benthos, and connections between streams and adjacent terrestrial environments. Because of uncertainties concerning the magnitude of N reduction possible, potential approaches should be tested in various landscape contexts; until more is known, stream restoration alone is not appropriate for compensatory mitigation and should be seen as complementary to land‐based best management practices.
Data from the DOL show that EMTs and paramedics have a rate of injury that is about three times the national average for all occupations. The vast majority of fatalities are secondary to transportation related-incidents. Assaults are also identified as a significant cause of fatality. The findings also indicate that females in this occupational group may have a disproportionately larger number of injuries. Support is recommended for further research related to causal factors and for the development, evaluation and promulgation of evidence-based interventions to mitigate this problem.
We use narrow-band images of the [O III] X5007 emission line and adjacent continuum in the well-studied Seyfert galaxies NGC 4151 and NGC 5548 to produce models of the surface-brightness distributions of the narrow-line region and host-galaxy starlight distribution in these galaxies. We use these models to compute the expected magnitude of seeing-induced aperture effects that can lead to systematic errors in broad emission-line and continuum flux measurements made from spectra which are flux calibrated based on the narrow emission lines. We find that small spectrograph apertures (e.g., 2"X 10") are highly undesirable as photometric errors as large as 10%-20% can result. Moreover, photometric corrections based on image modeling are not likely to offer great improvement since the corrections are a sensitive function of the seeing. Use of larger apertures (e.g., 5"X7'.'5) can reduce photometric errors to the few percent range, and in principle seeing corrections based on models of the surface-brightness distributions of the narrow-line region and starlight from the host galaxy can reduce the errors to about the 1% level, at which point miscentering errors probably dominate. The limitation in application of seeing corrections is probably our inability to characterize with sufficient accuracy the point-spread function for the spectroscopic observations, although uncertainties in the surface-brightness models are also likely to play a role.
Population growth in cities has resulted in the rapid expansion of urbanized land. Most research and management of stream ecosystems affected by urban expansion has focused on the maintenance and restoration of biotic communities rather than their basal resources. We examined the potential for urbanization to induce bottom-up ecosystem effects by looking at its influence on dissolved organic matter (DOM) composition and bioavailability and microbial enzyme activity. We selected 113 headwater streams across a gradient of urbanization in central and southern Maine and used elemental and optical analyses, including parallel factor analysis of excitation-emission matrices, to characterize DOM composition. Results show that fluorescent and stoichiometric DOM composition changed significantly across the rural to urban gradient. Specifically, the proportion of humic-like allochthonous DOM decreased while that of more bioavailable autochthonous DOM increased in the more urbanized streams. In laboratory incubations, increased autochthonous DOM was associated with a doubling in the decay rate of dissolved organic carbon as well as increased activity of C-acquiring enzymes. These results suggest that urbanization replaces upstream humic material with more local sources of DOM that turnover more rapidly and may drive bottom-up changes in microbial communities and affect the quality and quantity of downstream DOM delivery.
[1] The inconsistent performance of stream rehabilitation projects has generated debates over the use of morphological templates rather than detailed hydraulic information for channel designs. A rehabilitation project conducted in a reach of Deep Run, Maryland (United States), was monitored in order to assess commonly used approaches to channel design that rely on classification systems to describe the channel form, empirical relations to predict channel dimensions, and a single design discharge to evaluate the hydraulic conditions. Results from field measurements and observations indicated that the morphological conditions created in Deep Run were unstable. The morphology of the constructed channel was altered by storm flows smaller than the designed bank-full discharge and by floods that extended the flow width to the limits of the created meander belt. Hydraulic conditions associated with stabilization practices, vegetation, and gravel deposits influenced stability and unplanned adjustment patterns during flows contained within the active channel. Stability during flooding was diminished by reductions in floodplain roughness from vegetation removal and a decrease in flow path sinuosity. These findings illustrate the need for enhanced consideration of the relations between channel stability and hydraulic conditions at multiple scales and over a range of flow conditions in stream rehabilitation projects.
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