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Headwater streams dominate stream channel length in catchments. They are important sources of water, sediment and biota for downstream reaches and critical sites for organic matter and nutrient processing. Aquatic biodiversity in headwater streams has been overlooked in comparison to higher-order rivers, and few studies have considered spatial biodiversity patterns in headwater streams, or streams in general. I reviewed studies of macroinvertebrate diversity in headwater streams and found equivocal evidence to support the view that headwater streams harbour high biodiversity. Headwater streams might still make an important contribution to [gamma] (regional) diversity at the landscape (catchment) scale by virtue of high [beta] (among-assemblage) diversity. I studied eight headwater streams from three forested, upland catchments along the Great Dividing Range, Victoria, Australia to test my hypothesis of high [beta] diversity and to understand the spatial patterns and determinants of macroinvertebrate diversity in headwater stream networks.Diversity partitioning showed that reaches each had high [alpha] (within-assemblage) diversity, while [beta] diversity made only a small contribution to [gamma] diversity at both the reach and catchment scales. [beta] diversity may have been lower than hypothesized due to relatively small distances between sites and high levels of dispersal among reaches and catchments in the study area. Contrary to other studies that have found environmental factors to be important for explaining variation in macroinvertebrate assemblage structure in headwater streams, I found a limited role for environmental factors structuring macroinvertebrate assemblages in the study area.In one year (2008), spatial factors (independent of environmental factors) were the dominant factor structuring macroinvertebrate assemblages. Therefore, metacommunity structure in the study area aligns most closely with the neutral/patch dynamic metacommunity model. This pattern of spatial structuring, coupled with low [beta] diversity, suggests that high neighbourhood dispersal might be the main factor structuring macroinvertebrate assemblages in the study area. Flow permanence had only a seasonal effect on macroinvertebrate diversity and so there is a temporal component to the spatial diversity patterns in this system.The explicit recognition of stream ecosystems as spatially structured networks has increased our understanding of ecological patterns and processes, and provided the impetus for this research. Recent advances in the study of networks, particularly in the fields of physics and network theory, offer an opportunity to considerably extend the current application of the network concept in stream ecology.Determining the relative contributions of [alpha] and [beta] diversity to [gamma] diversity, and the scale dependence of [alpha] and [beta] components, provides vital information for conservation planning because optimal reserve designs will differ depending on the relative contributions of [alpha] and [beta] diversity. My finding of high [alpha] and low [beta] diversity indicates that each stream in the study area can be considered to have low irreplaceability and the capacity to contribute a large portion of species to regional conservation targets.Information on spatial patterns of diversity is urgently required for systematic conservation planning for freshwater reserves if we are to halt the rapid decline in global freshwater biodiversity.
Author's abstract: Variation in long-term temperature and precipitation patterns will likely influence the decomposition and export of benthic organic matter and influence aquatic macroinvertebrate consumer communities. Tropical systems are relatively understudied; therefore basal information is urgently needed. As part of an ongoing long-term study, we monitored macroinvertebrates in two shrimp-dominated and fishless headwater streams within the Luquillo Experimental Forest in Puerto Rico from 2009-2010. We combined growth rates with yearly biomass data to calculate secondary production and examined gut contents to develop quantitative food webs. Macroinvertebrate assemblages were dominated by a few insect taxa, with similar biotic composition across streams and habitats, but different structure amongst habitats. Biomass and abundance were generally greater in pools, suggesting that pools may provide habitat stability and shelter. Alternatively, shrimp may provide secondary benefits by removing fine sediments given their high density of in pools. Overall, aquatic insects had low biomass; therefore, their production was relatively low as is the case in most tropical areas. However, their turnover rates were not as high as expected. Secondary production appears to rely more on amorphous detritus and allochthonous organic matter rather than algal resources. These data are an important first step towards predicting the long-term effects that expected changes in rainfall and discharge will have in tropical stream communities.
The increase in new conifer forest cover in the Irish landscape over the last twenty years has caused much concern with regard to its potential impacts on catchment water quality. Most of the conifer plantations are situated in upland regions, drained by headwater streams. The impact of coniferous monocultures on stream hydrochemistry, particularly pH and related aluminium concentrations has been the focus of much research. However conifer plantations can potentially influence the energy supply riparian zone. Of specific concern in this study was the manner in which streams with coniferous riparian zones differ from those with mixed deciduous riparian vegetation. The characteristics of the detritivore assemblages of such streams were investigated. Initially the seasonal variation in suspended detritus in two streams of contrasting riparian vegetation was monitored using regularly emptied detritus traps. The stream flowing through the conifer plantation (Streamhill West) carried significantly lower concentrations of detritus than the deciduous stream (Glenfinnish R.). Woody fragments made the greatest annual contribution to detrital mass in both streams. In the coniferous stream, willow and birch were the only abundant deciduous leaves. Conifer needles, grasses and coarse particulate organic matter > 1 mm were also consistently present in the stream. In the deciduous stream, leaves dominated the non-woody detritus throughout the year, particularly oak, hazel, beech, birch and willow. During the summer, holly and coarse particulate organic matter >1mm were the most important fraction. This study found definite differences between the macroinvertebrate assemblages of the coniferous and deciduous streams. However the influence of stream hydrochemistry and land-use history at both sites complicate the question of whether the conifer plantations are having a deleterious impact on the stream macroinvertebrates.
With $2 billion spent annually on stream restoration worldwide, there is a pressing need for guidance in this area, but until now, there was no comprehensive text on the subject. Filling that void, this unique text covers both new and existing information following a stepwise approach on theory, planning, implementation, and evaluation methods for the restoration of stream habitats. Comprehensively illustrated with case studies from around the world, Stream and Watershed Restoration provides a systematic approach to restoration programs suitable for graduate and upper-level undergraduate courses on stream or watershed restoration or as a reference for restoration practitioners and fisheries scientists. Part of the Advancing River Restoration and Management Series. Additional resources for this book can be found at: www.wiley.com/go/roni/streamrestoration.