Global estimates of methane (CH 4 ) emissions from reservoirs are poorly constrained, partly due to the challenges of accounting for intra-reservoir spatial variability. Reservoir-scale emission rates are often estimated by extrapolating from measurement made at a few locations; however, error and bias associated with this approach can be large and difficult to quantify. Here, we use a generalized random tessellation survey (GRTS) design to generate unbiased estimates of reservoir-CH 4 emissions rates (695% CI) for areas below tributary inflows, open-waters, and at the whole-reservoir scale. Total CH 4 emission rates (i.e., sum of ebullition and diffusive emissions) were 4. 2011), partly due to the large range of CH 4 emission rates reported for reservoirs. Some of the variability in reported emission rates among systems can be attributed to differences in water temperature, reservoir age, and productivity (Barros et al. 2011;West et al. 2012), but another potentially large source of variability among studies is differences in how intra-reservoir spatial patterns in emission rates are assessed and incorporated into system-scale estimates. This source of variability is attributable to methodology, rather than true differences in emission rates, and therefore obscures spatial and temporal patterns in emission rates and adds uncertainty to emission rate estimates. The factors that govern CH 4 production and emission from aquatic systems can lead to pronounced spatial patterns in CH 4 emission rates. Methane is produced in reservoirs from the degradation of organic matter under anoxic conditions, therefore one factor that governs CH 4 production rates is the quantity and quality of carbon delivered to the sediments (Sobek et al. 2012). Sediment deposition rates in reservoirs are often greatest in the transition zone between tributaries and open waters where water velocities rapidly decrease and suspended solids consequently settle (Thornton 1990). Also,

Streams, riparian areas, floodplains, alluvial aquifers and downstream waters (e.g., large rivers, lakes, oceans) are interconnected by longitudinal, lateral, and vertical fluxes of water, other materials and energy. Collectively, these interconnected waters are called fluvial hydrosystems. Physical and chemical connectivity within fluvial hydrosystems is created by the transport of nonliving materials (e.g., water, sediment, nutrients, contaminants) which either do or do not chemically change (chemical and physical connections, respectively). A substantial body of evidence unequivocally demonstrates physical and chemical connectivity between streams and riparian wetlands and downstream waters. Streams and riparian wetlands are structurally connected to downstream waters through the network of continuous channels and floodplain form that make these systems physically contiguous, and the very existence of these structures provides strong geomorphologic evidence for connectivity. Functional connections between streams and riparian wetlands and their downstream waters vary geographically and over time, based on proximity, relative size, environmental setting, material disparity, and intervening units. Because of the complexity and dynamic nature of connections among fluvial hydrosystem units, a complete accounting of the physical and chemical connections and their consequences to downstream waters should aggregate over multiple years to decades.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Most amphibian species with an aquatic larval stage use one of two types of breeding habitats: ephemeral or permanent water bodies. A common assumption is that, once a minimum developmental threshold has passed, tadpoles of species that use temporary ponds can respond adaptively to a drying larval habitat by hastening development to metamorphose before the pond dries. We investigated how different pond drying regimes affected the timing of metamorphosis and body size at metamorphosis of two closely related species of hylid treefrogs, one of which commonly breeds in temporary ponds (Hyla gratiosa) and the other in permanent ponds (Hyla cinerea). We experimentally manipulated the water level in cattle-tank communities, exposing tadpoles of each species to a slow drying treatment, a fast drying treatment, and a constant water level treatment. There was no direct effect of pond drying on the larval period or body size at metamorphosis of either species. The drying treatments indirectly affected these traits by increasing larval densities, which extended the larval period and produced smaller sizes at metamorphosis. The timing of metamorphosis and body size at metamorphosis of H. gratiosa were more plastic than the corresponding traits in H. cinerea, but this greater plasticity cannot be interpreted as adaptive. Our results emphasize the utility of the comparative approach in interpreting the potential adaptive responses of species to environmental variation.The distinctive distributions of different species of larval amphibians among ponds of different duration (due to the species-specific breeding habitat choice of their parents) represent an excellent system in which to examine the relationship between habitat variability and adaptive phenotypic plasticity. Ponds with characteristically different hydroperiods create different selective pressures on two larval life-history traits, the larval period and the size at metamorphosis. Both traits are under active, demonstrable selection, but the direction of their relationship with fitness changes with pond duration. In favorable conditions (low predation risk, no risk of desiccation) longer larval periods result in larger body size at metamorphosis; larger size enhances male mating success, increases the probability of overwinter survival, decreases the time to first reproduction, and increases female fecundity (Howard 1978, Berven 1981, 1982, Berven and Gill 1983, Pough and Kamel 1984, Smith 1987). In less favorable conditions (high predation risk, habitat drying), shortened larval periods will minimize the cumulative r...