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Terrestrial hydrological and nutrient cycles are subjected to major disturbances by agricultural operations and urbanization that profoundly influence freshwater resources. Non‐point source pollution is one of the primary causes for water quality deterioration, and thus an emerging imperative in limnology is establishing empirical models that connect watershed attributes and hydrological drivers with lake nutrient dynamics. Here, we compiled three nation‐wide nutrient, meteorological, and watershed‐landscape data sets, to develop Generalized Linear Models that predict lake phosphorus and nitrogen concentrations as a function of the surrounding watershed characteristics within various hydrological distances across 104 Chinese lakes and reservoirs. Our national‐scale investigation revealed that lake nutrient concentrations can be satisfactorily predicted by proxies of natural drivers and anthropogenic activities, reflecting the properties of the surrounding watershed. Counter to previous studies, we found that China's lake nutrient concentrations strongly depend on watershed characteristics within a hydrological distance of less than 45 km rather than the entire watershed. Furthermore, extensive human activities in watersheds not only compromise our predictive capacity, but also increase the hydrological distance that is relevant to predict lake nutrients. This national‐scale characterization can inform one of the most contentious issues in the context of China's lake management, that is, the determination of the extent of the nearshore area, where nutrient control should be prioritized. As far as we know, our study represents the first attempt to apply the concept of hydrological distance and establish statistical models that can delineate the critical spatial domain primarily responsible for the nutrient conditions along the watershed‐lake continuum. Plain Language Summary: Connecting watershed attributes with lake water quality at multiple scales is an emerging imperative in limnology. This study introduces the concept of hydrological distance and establish lake‐watershed relationships based on a comprehensive water quality data set from 2,424 sampling sites across China. Our key finding is that lake nutrient levels strongly depend on watershed features within a <45 km hydrological distance rather than the entire watershed. Activities related to agriculture and urbanization increase the relevant hydrological distance to modulate lake nutrient levels, and our national‐scale analysis provides evidence that areas with discernible impact can be located far from the vicinity of a given lake. Key Points: China's lake nutrient concentrations can be accurately predicted by watershed attributesChina's lake nutrient levels depended on watershed features within a <45 km hydrological distanceHuman footprint increases the relevant hydrological distance to predict water quality for China's lakes [ABSTRACT FROM AUTHOR]

Reservoirs and their morphological characteristics are expected to alter the continuity of matter, energy, and nutrient transfer, which can modify resource availability, food supply, and fish trophic structure. We studied 29 reservoirs in Southern Brazil to verify the main factors related to the structure of their fish trophic guilds. We tested the hypothesis that environmental and morphological variables influence the organization of fish trophic guilds more than spatial variables (i.e., hydrological distance between the reservoirs). Additionally, we tested which variables linked to environmental, morphological, and spatial characteristics are most associated with the predominance of herbivores, omnivores, detritivores, insectivores, invertivores, and piscivores fishes. To assess the influence of these predictors, we used variance partitioning with distance-based redundancy analysis. Contrary to our assumptions, the structure of fish trophic guilds revealed that the spatial features were the most important predictors. Still, associations between and with the other predictors also revealed significant explanations. Trophic guilds that showed spatial segregation were herbivores and omnivores which can be associated with the evolutionary processes from the locality of each reservoir in distinct ecoregions. Overall, environmental and morphological characteristics like concentration of total nitrogen, age, size, and water retention time are associated with a greater or lesser abundance of herbivores, detritivores, omnivores, and piscivores. Our findings have important implications for the management of reservoirs by helping to guide policies and actions involving fishing stocks. [ABSTRACT FROM AUTHOR]

Abstract Terrestrial hydrological and nutrient cycles are subjected to major disturbances by agricultural operations and urbanization that profoundly influence freshwater resources. Non‐point source pollution is one of the primary causes for water quality deterioration, and thus an emerging imperative in limnology is establishing empirical models that connect watershed attributes and hydrological drivers with lake nutrient dynamics. Here, we compiled three nation‐wide nutrient, meteorological, and watershed‐landscape data sets, to develop Generalized Linear Models that predict lake phosphorus and nitrogen concentrations as a function of the surrounding watershed characteristics within various hydrological distances across 104 Chinese lakes and reservoirs. Our national‐scale investigation revealed that lake nutrient concentrations can be satisfactorily predicted by proxies of natural drivers and anthropogenic activities, reflecting the properties of the surrounding watershed. Counter to previous studies, we found that China's lake nutrient concentrations strongly depend on watershed characteristics within a hydrological distance of less than 45 km rather than the entire watershed. Furthermore, extensive human activities in watersheds not only compromise our predictive capacity, but also increase the hydrological distance that is relevant to predict lake nutrients. This national‐scale characterization can inform one of the most contentious issues in the context of China's lake management, that is, the determination of the extent of the nearshore area, where nutrient control should be prioritized. As far as we know, our study represents the first attempt to apply the concept of hydrological distance and establish statistical models that can delineate the critical spatial domain primarily responsible for the nutrient conditions along the watershed‐lake continuum.