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Abstract Humans increasingly dominate Earth’s natural freshwater ecosystems, but biomass production of modified ecosystems is rarely studied. We estimate potential fish total standing stock in USA reservoirs is 3.4 billion (B) kg, and approximate annual secondary production is 4.5 B kg y⁻¹. We also observe varied and non-linear trends in reservoir fish biomass over time, thus previous assertions that reservoir fisheries decline over time are not universal. Reservoirs are globally relevant pools of freshwater fisheries, in part due to their immense limnetic footprint and spatial extent. This study further shows that reservoir ecosystems play major roles in food security and fisheries conservation. We encourage additional effort be expended to effectively manage reservoir environments for the good of humanity, biodiversity, and fish conservation. 

Abstract Lakes play a significant role in the global carbon cycle, acting as sources and sinks of carbon dioxide (CO₂). In situ measurements of CO₂flux (FCO₂) from lakes have generally been collected during daylight, despite indications of significant diel variability. This introduces bias when scaling up to whole‐lake annual aquatic carbon budgets. We conducted an international sampling program to ascertain the extent of diel variation in FCO₂across lakes. We sampled 21 lakes over 41 campaigns and measured FCO₂at 4‐h intervals over a full diel cycle. Rates of FCO₂ranged from −3.16 to 4.39 mmol m⁻² h⁻¹. Integrated over a day, FCO₂ranged from −381.68 to 878.49 mg C m⁻²d⁻¹(mean = 76.54) across campaigns. We identified three characteristic diel patterns in FCO₂related to trophic status and show that for half of the campaigns, daily flux estimates were biased by > 50% if based on a single (daytime) measurement. 

Abstract Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.