Significance: Blooms of cyanobacteria in lakes and reservoirs cause fish kills and pose toxicity risk for humans, livestock, and wildlife. Theory suggests that blooms may be anticipated in advance by calculating resilience indicators using high-frequency observations of pigments in lake water. However, it is not known whether management can prevent blooms once indicators are detected. We measured these indicators while gradually enriching a lake until a bloom was triggered. When indicators passed a preset threshold, nutrient input was stopped. This action reversed the bloom, showing that monitoring of resilience indicators followed by prompt action when limits are exceeded can be useful in management. However, in practice, the risk of blooms may best be prevented by reducing inputs of nutrients.

Heatwaves are increasing in frequency, duration, and intensity in ocean, coastal, and lake ecosystems. While positive water temperature trends have been documented in many rivers, heatwaves have not been analyzed. This study examined heatwaves in rivers throughout the United States between 1996 and 2021. Riverine heatwaves increased in frequency over the study period, with the most robust increases occurring in summer and fall, in mid‐ to high‐order streams, and at free‐flowing sites and sites above a reservoir. The increase in heatwave frequency was accompanied by an increase in moderate strength heatwaves as well as a doubling of the annual mean total number of heatwave days at a site. Riverine heatwaves were often associated with normal or below‐normal discharge conditions and at sites with a mean annual discharge ≤ 250 m³ s⁻¹. These results provide the first assessment of heatwaves in rivers for a large geographic area in the United States.

It is well established that lakes are typically sources of CO₂to the atmosphere. However, it remains unclear what portion of CO₂efflux is from endogenously processed organic carbon or from exogenously produced CO₂transported into lakes. We estimated high‐frequency CO₂and O₂efflux from three north temperate lakes in summer to determine the proportion of the total CO₂efflux that was exogenously produced. Two of the lakes were amended with nutrients to experimentally enhance endogenous CO₂uptake. In the unfertilized lake, 50% of CO₂efflux was from exogenous sources and hydrology had a large influence on efflux. In the fertilized lakes, endogenous CO₂efflux was negative (into the lake) yet exogenous CO₂made the lakes net sources of CO₂to the atmosphere. Shifts in hydrologic regimes and nutrient loading have the potential to change whether small lakes act primarily as reactors or vents in the watershed.

Organic carbon accumulation in the sediments of inland aquatic and coastal ecosystems is an important process in the global carbon budget that is subject to intense human modification. To date, research has focused on quantifying accumulation rates in individual or groups of aquatic ecosystems to quantify the aquatic carbon sinks. However, there hasn’t been a synthesis of rates across aquatic ecosystem to address the variability in rates within and among ecosystems types. Doing so would identify gaps in our understanding of accumulation rates and potentially reveal carbon sinks vulnerable to change. We synthesized accumulation rates from the literature, compiling 464 rate measurements from 103 studies of carbon accumulated in the modern period (ca. 200 years). Accumulation rates from the literature spanned four orders of magnitude varying substantially within and among ecosystem categories, with mean estimates for ecosystem categories ranging from 15.6 to 73.2 g C m⁻² y⁻¹ within ecosystem categories. With the exception of lakes, mean accumulation rates were poorly constrained due to high variability and paucity of data. Despite the high uncertainty, the estimates of modern accumulation rate compiled here are an important step for constructing carbon budgets and predicting future change.