High‐resolution data are improving our ability to resolve temporal patterns and controls on river productivity, but we still know little about the emergent patterns of primary production at river‐network scales. Although it is well known that several factors are related to variation in gross primary production in rivers, it is not known how these factors combine to determine primary productivity at the scale of river networks. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley. The net primary productivity of vegetation reflects the total amount of carbon fixed by plants through photosynthesis each year. But despite the dismal forecast for the future of water on the Colorado, some conservationists are hoping to return at least a portion of the delta to its former glory. 2004). Dam construction on river systems worldwide has altered hydraulic retention times, physical habitats and nutrient processing dynamics. Productivity is important in economics because it has an enormous impact on the standard of living. Our modeled productivity regimes indicate how the biological properties of river networks respond to changes in network size. Our goal was to highlight how different expectations regarding the spatial and temporal structure of GPP in rivers define a range of network‐scale productivity regimes. 2019). We therefore did not explicitly model individual drivers of GPP such as light, temperature, nutrient supply, hydrology, or the community composition of primary producers. Introductions of invasive species (e.g., zebra mussels, Asian carps) can result in competition for important food resources thereby impacting native fish and mussel populations. 2). This production is important because some of it is used for food and some is valued for recreation, it is a direct measure of total ecosystem processes, and it sustains biological diversity. Implicit in the “spring peak” regime is that light constrains GPP for much of the year due to shading by the terrestrial canopy. In our simulated networks, streambed surface area accumulates faster than drainage area. Understanding the characteristic patterns and controls on annual, network‐scale productivity is therefore important to addressing fundamental questions in aquatic ecology because of the implications for food webs, nutrient cycling, and regional carbon budgets. For the Productive rivers and Unproductive rivers scenarios, the overall network pattern was sensitive to the number of river segments wider than 9 m, and therefore, to small differences in network shape (e.g., elongation) among subcatchments of equal size. We thank the editors and anonymous reviewers for their comments and suggestions that greatly improved the manuscript. Snake River Chinook Salmon. Increasing the proportion of small streams without riparian shading resulted in a shift in the timing of peak productivity toward a summer‐dominated regime at the network‐scale (Fig. Prior research has established that reach‐scale productivity regimes can be classified into characteristic functional types. In our simulated network, extending the vernal window by as much as 14 d weakly increased annual, network‐scale GPP by approximately 2%, 2%, and 5% for the Productive rivers, Stochastic, and Unproductive rivers scenarios, respectively (Supporting Information Table S3). Our goal was to explore the envelope of river‐network productivity regimes by deriving network‐scale estimates of GPP for clear end‐members of the likely distribution of productivity regimes in real networks. Together, these results suggest that network productivity regimes may be highly variable, but are also sensitive to factors affecting the amount or timing of GPP in small streams. We focused our analysis to explore how patterns in network‐scale productivity change with watershed size and differences in the spatial arrangement of reach‐scale GPP. Such classifications enable representation of the spatial heterogeneity in river ecosystems, and provide a framework for scaling ecosystem processes to network‐scales. Removing the light constraint from riparian vegetation in a subset of streams had a more appreciable effect on network‐scale GPP. A sound understanding of biological production is essential to the effective science-based management of ecosystems. The depth of light penetration, current, the availability of suitable substrate, nutrient availability, hardness, temperature, and forest canopy cover all combine to influence macrophyte growth in lotic systems. dam and the relative productivity of the Lower Bridge River aquatic and riparian ecosystem. 3). Such data sets highlight the tremendous variability in productivity observed both within and across streams (Bernhardt et al. Working off-campus? 2007). S2). (1992). The relative importance of freshwater and marine factors is seldom quantified because a long time series of life-stage-specific demographic data is required and often unavailable. Taylor River sites showed the highest P limitation (soil N:P > 60). At the scale of river networks, the seasonal dynamics of primary productivity determine the amount and timing of energetic inputs that feed mobile organisms and generate the export of labile carbon downstream. Rivers, in their natural state, are among the most dynamic, diverse, and complex ecosystems on the planet. In the Unproductive rivers scenario, the spring‐time GPP peak was driven by metabolic activity in small streams (Fig. The fractal nature and geomorphic scaling of river networks means that the number of small streams increases in larger watersheds (Horton 1945), and so their contribution to network‐scale GPP is substantial across a range in watershed size. These modeled scenarios therefore do not capture the local heterogeneity in light and GPP that is expected along a river continuum due to local variation in canopy cover, topography, and geomorphology (Julian et al. All rivers share these same constraints on productivity, but their relative importance differs among rivers as temporal fluctuations in various physical, chemical, and biological drivers act individually or in concert to determine the productivity regime for a river, that is, its characteristic annual pattern in GPP (Bernhardt et al. 1d). Provide scientific information about the diversity, life history and species interactions that affect the condition and dynamics of aquatic communities. Regional human influences on Hudson River habitats and proposed . S3a). However, assuming large rivers are productive, the distribution of network GPP shifted later in the year as watershed size increased and more large rivers were sampled (Fig. Without the river and its load of nutrients, marine productivity in the Gulf of California — where the Colorado River once ended — has fallen by up to 95 percent. 5 OECD Publications. The scaling transition from stream reaches to river networks thus requires quantifying and conceptualizing the heterogeneity, connectivity, and asynchrony (sensu McCluney et al. Therefore, while a substantial proportion of annual, network GPP is accumulated earlier in the year, spring‐time productivity in the Stochastic scenario reflects the metabolism of both small streams and larger rivers. Within this network, we sampled replicate subcatchments around four values of upstream area (40, 160, 450, and 2600 km2; Supporting Information Fig. Therefore, in this scenario, we randomly selected 20–100% of reaches originally characterized by the “spring peak” regime and reassigned them as “summer peak” streams to simulate removing canopy shading as a constraint on primary productivity over varying spatial extents. We quantified river‐network GPP (kg C d−1) by summing daily estimates of reach‐scale GPP across the individual stream reaches that comprise the river network. We find no ev-idence of any break in relative consumption growth rates but do find some evidence of a break in the relative price of consumer goods rela- ... are sorted according to their relative probability (P. R) of being the most Annual productivity growth, which has been 2.3% in 1946-73,fell to 0.9% in 1973-90. 2004; Datry et al. In small watersheds (e.g., 40 km2), river network GPP is limited to a short period in the spring when incident light reaching headwater streams is high prior to terrestrial leaf‐out. Values for rivers range from 10 to 200mgCm −2 d −1 to more than 1000mgCm −2 d −1. GROUND-WATER RESOURCES OF ... River and Esopus Creek valleys, do not contain sand and gravel aquifers but are filled with relatively impermeable clay and silt. Wide-spread application of agricultural fertilizers has dramatically increased nitrogen loading. 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