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Headwater streams have some of the best quality water in the country (Dissmeyer 2000). Because headwaters eventually flow into other downstream water bodies like rivers and lakes, they are important places to focus research and conservation efforts. All streams in this study had good water quality based on several assessments of macroinvertebrate communities. 1. Judging from metrics of abundance, richness, EPT, and HBI, all study streams had very good water quality. Thirty-nine total families were observed among the three streams. Whittier Stream was the least healthy of the three, most likely as a result of human disturbances such as a road crossing, fishpond, and mill remnants. It is probable these habitat alterations are having an effect on downstream benthic communities. 2. The riparian zone of each stream was forested and stable, but there were some eroding banks at some points along the study reaches. The abundance of sensitive macroinvertebrates (measured using representative Orders Ephemeroptera, Plecoptera, and Trichoptera) increased with increasing percent canopy cover and decreased with high percentages of sand characterizing the streambed. 3. Macroinvertebrates can be categorized into functional feeding groups based on feeding behavior. Shredders should hypothetically be in high abundance in headwater streams due to high riparian organic matter inputs. However, observed shredders were limited. This may be due to seasonal changes in functional feeding group ratios. In addition, all study streams had a predator/prey ratio that was higher than the ratio expected for a typical stream, which suggests that there might be an abundance of prey biomass in the study stream headwaters. 4. Based on results from stable isotope analysis of carbon and nitrogen, most macroinvertebrates within the study streams seem to be omnivorous. The most complex food web was observed at Stony Brook. Food webs of Beaver Brook and Stony Brook showed similar trophic clustering, a pattern that might be indicative of streams with excellent water quality.
Lonicera maackii, an invasive terrestrial shrub that is dominant in riparian zones, may have substantial impacts on the structure and function of aquatic systems. We investigated linkages between this terrestrial invader and the aquatic community structure in headwater streams by assessing in situ leaf breakdown and the colonization of leaf packs by macroinvertebrates in three 3rd order headwater streams of southwestern Ohio, Possum Run, Fecher Park, and Black Oak Park. Leaf breakdown and colonizing macroinvertebrate taxa richness, density, and functional feeding group relative abundance were assessed using three types of in-stream leaf packs: L. maackii, native (Fraxinus spp., Platanus occidentalus), and a mixture of native and invasive leaves. Invasive leaf breakdown rates were up to 4x faster than native leaves, and significantly less organic matter remained for invasive compared to other leaf types on all sampling days. There were specific macroinvertebrate taxa unique to particular treatments. For instance, invasive leaf packs were dominated by collector-gatherers for the duration of the study and Chironomidae, in particular, was the most important taxon colonizing invasive leaf packs. In contrast, Oligochaeta colonized native leaf packs in greater densities at Possum Run stream and mix leaf packs in Fecher Park stream. Collector-gatherers also dominated mix leaf packs across stream sites and native leaf packs located within Possum Run. In summary, our results demonstrate that L. maackii leaves breakdown significantly faster in headwater streams compared to native leaves, and that macroinvertebrate densities and functional feeding group colonization are influenced by invasive leaf litter input. These results support the hypothesis that L. maackii invasion in riparian zones can have direct and significant impacts on aquatic ecosystems by influencing organic matter processes.
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.
Effectively valuing the contribution of small headwater streams to the functioning of river networks requires an understanding of how physical and biological drivers are linked to ecosystem functions, and of how drivers and functions vary, both within and among stream networks. Despite a large body of work on individual 1st and 2nd order streams, fewer studies have examined patterns in structure or function across different sized streams within a network. Here, I combined field experiments and cross-biome syntheses to link stream structure and function through two focal lenses; the quantity and quality of basal resources, and the role of stream consumers. When developing quantitative relationships between drivers and rates of ecosystem respiration (ER), gross primary production (GPP), and ammonium (NH4) uptake, I found that within a headwater stream network, coarse and fine benthic organic matter standing stocks were positively correlated with ER, while light availability was a strong driver of GPP. Based on extrapolation to the stream network, small 1st and 2nd order streams are expected to play a substantial role in ER and NH4 uptake compared to larger streams. Across four distinct stream networks, benthic organic matter carbon to nitrogen and phosphorus ratios were lower in fine than course fractions. This higher relative nutrient content in fine benthic organic matter suggested that macroinvertebrates feeding on coarse and fine organic matter could be broadly macronutrient or carbon limited, respectively, with implications for in-stream resource cycling. Stream consumers had limited detectable effects on measured metrics of structure and function, both within and among headwater networks. Larval salamanders did not initiate top-down trophic cascades, but reduced stream NH4 uptake rates, potentially through nitrogen excretion. We also did not detect significant consumer effects across stream networks from five biomes, despite differences in consumer biomass and trophic position. However, across biomes, basal resources were strong drivers of both ER and GPP, which indicated that study networks were bottom-up, rather than top-down controlled. Collectively, these four studies highlight the importance of linking measurements of structure and function in headwater streams, to quantify their role in larger stream networks, and as such, advocate for their protection.
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.
This textbook provides a unique and thorough look at the application of chemical biomarkers to aquatic ecosystems. Defining a chemical biomarker as a compound that can be linked to particular sources of organic matter identified in the sediment record, the book indicates that the application of these biomarkers for an understanding of aquatic ecosystems consists of a biogeochemical approach that has been quite successful but underused. This book offers a wide-ranging guide to the broad diversity of these chemical biomarkers, is the first to be structured around the compounds themselves, and examines them in a connected and comprehensive way. This timely book is appropriate for advanced undergraduate and graduate students seeking training in this area; researchers in biochemistry, organic geochemistry, and biogeochemistry; researchers working on aspects of organic cycling in aquatic ecosystems; and paleoceanographers, petroleum geologists, and ecologists. Provides a guide to the broad diversity of chemical biomarkers in aquatic environments The first textbook to be structured around the compounds themselves Describes the structure, biochemical synthesis, analysis, and reactivity of each class of biomarkers Offers a selection of relevant applications to aquatic systems, including lakes, rivers, estuaries, oceans, and paleoenvironments Demonstrates the utility of using organic molecules as tracers of processes occurring in aquatic ecosystems, both modern and ancient
Farmers have been encouraged to adopt more sustainable farming practices (BMPs) that mitigate adverse agricultural effects on the natural environment. However, the ability of BMPs to protect or restore riverine systems continues to be questioned due to limited evidence directly linking BMP use with improved ecological conditions. The exclusion of hydrological pathways in previous field studies may explain why a direct link has not yet been established. The goal of this study was to assess the association between benthic macroinvertebrate community structure and the number and location of agricultural BMPs. Macroinvertebrates and water chemistry were sampled in 30 headwater catchments in the Grand River Watershed. Catchments exhibited gradients of BMP use and location as measured by the degree of hydrologic connectedness. Stepwise ordination regressions and variance partitioning were used to determine which environmental variables (i.e., BMP metrics, water chemistry parameters, habitat characteristics, and land use variables) were associated with benthic macroinvertebrate community structure. Water chemistry parameters were negatively associated with BMP metrics suggesting BMPs were mitigating losses of nutrients and sediments. However, BMP abundance and location explained minimal variation in benthic macroinvertebrate structure within the 30 sampled catchments. The absence of a strong association between BMPs and benthic macroinvertebrates may indicate a need for greater numbers and targeted siting of BMPS to improve water quality beyond a threshold point that would allow recolonization of intolerant invertebrate taxa. Focusing of conservation goals on ecological conditions and the promotion of BMPs that enhance in-stream habitat may also be required.