12Charles Elton introduced the 'pyramid of numbers' in the late 1920s but this remarkable insight 13 into body-size dependent patterns in natural communities lay fallow until the theory of the biomass size 14 spectrum was introduced by aquatic ecologists in the mid-1960s. They noticed that the summed 15 biomass concentration of individual aquatic organisms was roughly constant across equal logarithmic 16 intervals of body size from bacteria to the largest predators. These observations formed the basis for a 17 theory of aquatic ecosystems, based on the body size of individual organisms, that revealed new insights 18 into constraints on the structure of biological communities. In this review we discuss the history of the 19 biomass spectrum and the development of underlying theories. We indicate how to construct biomass 20 spectra from sample data, explain the mathematical relations among them, show empirical examples of 21 their various forms, and give details on how to statistically fit the most robust linear and nonlinear 22 models to biomass spectra. We finish by giving examples of biomass spectrum applications to 23 production and fisheries ecology, and offering recommendations to help standardize use of the biomass 24 spectrum in aquatic ecology. 25 26

Developing the crustacean zooplankton community size spectrum into an indicator of change in lakes requires quantification of the natural variability in the size spectrum related to broad-scale seasonal, annual, and spatial factors. Characterizing seasonal patterns of variation in the size spectrum is necessary so that monitoring programs can be designed to minimize the masking effects that seasonal processes can have on detecting longer-term temporal change. We used a random effects model to measure monthly, annual, and interlake variability in the slope (i.e., relative abundance of small and large organisms) and centered height (i.e., total abundance) of the crustacean zooplankton normalized abundance size spectrum from 1981 to 2011 among eight Canadian Shield lakes. Consistent with theoretical predictions, the slope was a relatively stable characteristic of the zooplankton community compared with the height, which varied significantly among lakes. We identified a seasonal signal in height and slope and used a mixed effects model to characterize the linear rate of change from May to October; there was an overall decline in height and an overall increase in slope. Seasonal variance was greater than annual variance for both the height and the slope, suggesting that long-term monitoring of lakes and interlake comparisons using zooplankton size spectra should be based on temporally standardized sampling protocols that minimize the effects of seasonal processes. We recommend sampling the zooplankton community in midsummer because this results in size spectrum estimates close to seasonal mean values.

We evaluated the crustacean zooplankton size spectrum as an indicator of lake characteristics and ecosystem change. First, we used time-series from seven Canadian Shield lakes to identify the factors associated with among-lake and among-year variability in the spectrum slope (relative abundance of small and large zooplankton) and centered height (total abundance). Second, we used time-series from an invaded and three control lakes to assess change in mean and variability in slope and height due to a Bythotrephes invasion. We found that the slope and the height reflected among-lake predictors related to morphometry. The slope was responsive to long-term declining lake phosphorus levels, whereas the height reflected both increases in dissolved organic carbon and decreases in ice duration. We detected a significant increase (i.e. flattening) in mean slope and substantial (up to 120%) increases in the CV of height after Bythotrephes invaded Harp Lake. Thus, the zooplankton size spectrum was responsive to long-term environmental change and a strong top-down perturbation can be detected through regular and frequent monitoring programs.

Rivers historically played, and continue to play, a fundamental role in supporting humanity through provisioning numerous resources and services. Through time, research has aimed at understanding rivers through hydrological, geomorphological, and energic lenses to determine how such river dynamics combine to structure aquatic ecological communities. This research has led to the development of various conceptual models to describe river dynamics and ecological community structure. However, as many urban regions are often built around water sources, rivers are heavily altered as hydrological, geomorphological, and energic dynamics changed as land use intensified and human populations increased. Such changes ultimately altered the structure of ecological communities, and the services provided by rivers in urban regions. Here, we review and synthesize natural river concepts and urban river concepts, while emphasizing the importance of considering more natural river dynamics as a guide for river restoration in urban 2 regions. Novelly, we connect river dynamics to their terminal receiving waters, as changing dynamics in rivers can ultimately alter receiving water dynamics. Moreover, rather than focus solely on the main river channel and terminal water body, we consider river dynamics and urban impacts to river associated wetlands, riparian zones, and hyporheic zones. Through linking river dynamics from headwaters to receiving waters, we synthesize and extend historical river concepts with more modern understanding of urban river dynamics across numerous aquatic zones. In this work, we highlight broad implications of urbanization and restoration for both academic research and applied management. Finally, we emphasize the potential of urban rivers in facilitating connections to nature for urban residents. With the importance of urban blue space recognized in the recently agreed upon Kunming-Montreal Global Biodiversity Framework, increasing access to, and ecological integrity in, urban blue spaces will require understanding river energy dynamics across the entire river course, from headwaters to receiving waters.