Amy L. Hetherington

Rapid and highly variable warming of lake surface waters around the globe

In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global mean = 0.34°C decade−1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factors—from seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decade−1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decade−1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.

A global database of lake surface temperatures collected by in situ and satellite methods from 1985–2009

Global environmental change has influenced lake surface temperatures, a key driver of ecosystem structure and function. Recent studies have suggested significant warming of water temperatures in individual lakes across many different regions around the world. However, the spatial and temporal coherence associated with the magnitude of these trends remains unclear. Thus, a global data set of water temperature is required to understand and synthesize global, long-term trends in surface water temperatures of inland bodies of water. We assembled a database of summer lake surface temperatures for 291 lakes collected in situ and/or by satellites for the period 1985–2009. In addition, corresponding climatic drivers (air temperatures, solar radiation, and cloud cover) and geomorphometric characteristics (latitude, longitude, elevation, lake surface area, maximum depth, mean depth, and volume) that influence lake surface temperatures were compiled for each lake. This unique dataset offers an invaluable baseline perspective on global-scale lake thermal conditions as environmental change continues.

Effect of Temperature on Feeding and Survival of Mysis relicta

During their diel vertical migration, Mysis relicta can experience temperatures from 4°C to about 15°C. High temperatures may limit the ascent due to direct effects on survival or through decreased feeding rates. Mysis relicta survival (over 8 hours) was high up to 17°C (93%) and decreased with an increase in temperature over 18°C to 0% at 26°C. Feeding rates on newly hatched nauplii of Artemia salina were measured in 4-hour experiments at temperatures between 4 and 20°C. Feeding rates for 13 to 16 mm mysids were highest at 12°C and decreased at both higher and lower temperatures to 40% of peak feeding rates at 18 to 20°C and to 75% of peak feeding rates at 4°C. Smaller mysids (average length 10.5 mm) had peak feeding rates at 14°C. These results are consistent with field observations. Mysids seldom occur in temperatures above 15°C and smaller mysids are often found higher in the water column than larger animals. Consumption rates at both higher and lower temperatures were higher relative to peak consumption than assumed in a published bioenergetics model for Mysis (Rudstam 1989).

The importance of lake-specific characteristics for water quality across the continental United States.

Lake water quality is affected by local and regional drivers, including lake physical characteristics, hydrology, landscape position, land cover, land use, geology, and climate. Here, we demonstrate the utility of hypothesis testing within the landscape limnology framework using a random forest algorithm on a national-scale, spatially explicit data set, the United States Environmental Protection Agencys 2007 National Lakes Assessment. For 1026 lakes, we tested the relative importance of water quality drivers across spatial scales, the importance of hydrologic connectivity in mediating water quality drivers, and how the importance of both spatial scale and connectivity differ across response variables for five important in-lake water quality metrics (total phosphorus, total nitrogen, dissolved organic carbon, turbidity, and conductivity). By modeling the effect of water quality predictors at different spatial scales, we found that lake-specific characteristics (e.g., depth, sediment area-to-volume ratio) were important for explaining water quality (54-60% variance explained), and that regionalization schemes were much less effective than lake specific metrics (28-39% variance explained). Basin-scale land use and land cover explained between 45-62% of variance, and forest cover and agricultural land uses were among the most important basin-scale predictors. Water quality drivers did not operate independently; in some cases, hydrologic connectivity (the presence of upstream surface water features) mediated the effect of regional-scale drivers. For example, for water quality in lakes with upstream lakes, regional classification schemes were much less effective predictors than lake-specific variables, in contrast to lakes with no upstream lakes or with no surface inflows. At the scale of the continental United States, conductivity was explained by drivers operating at larger spatial scales than for other water quality responses. The current regulatory practice of using regionalization schemes to guide water quality criteria could be improved by consideration of lake-specific characteristics, which were the most important predictors of water quality at the scale of the continental United States. The spatial extent and high quality of contextual data available for this analysis makes this work an unprecedented application of landscape limnology theory to water quality data. Further, the demonstrated importance of lake morphology over other controls on water quality is relevant to both aquatic scientists and managers.

Insights from the Global Lake Ecological Observatory Network (GLEON)

The Global Lake Ecological Observatory Network (GLEON) is a grass-roots network of people, data, and observatories. The network represents a unique effort to bring together a diverse community of scientists, engineers, information technology experts, and engaged stakeholders to understand, conserve, and predict the state of lakes and reservoirs globally. Individuals and teams in GLEON have generated a range of scientific, educational, and outreach products, from software tools to scientific publications to education modules and programs. This special issue of Inland Waters brings together a series of papers generated from the network. Here, we discuss the foundations of GLEON that have facilitated these publications and others like them in terms of network structure, research areas, and the threads that tie the network together. GLEON is underpinned by sophisticated analytical tools and a network of high-frequency in situ observatories that exploit advanced sensors and associated technologies. This approach expands the space and time domains available to inquiry and analysis of lake processes. Using team science, the network has also established a culture of collaboration, sharing, and trust. This flexible framework allows GLEON members to advance research on a range of topics and has led to an increasing number of collaborative cross-site products. Future success will depend on the network’s ability to continue to facilitate the successes of its members while also being responsive to evolving member needs, technologies, and societal priorities.