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.

Understanding the factors that affect water quality and the ecological services provided by freshwater ecosystems is an urgent global environmental issue. Predicting how water quality will respond to global changes not only requires water quality data, but also information about the ecological context of individual water bodies across broad spatial extents. Because lake water quality is usually sampled in limited geographic regions, often for limited time periods, assessing the environmental controls of water quality requires compilation of many data sets across broad regions and across time into an integrated database. LAGOS-NE accomplishes this goal for lakes in the northeastern-most 17 US states. LAGOS-NE contains data for 51 101 lakes and reservoirs larger than 4 ha in 17 lake-rich US states. The database includes 3 data modules for: lake location and physical characteristics for all lakes; ecological context (i.e., the land use, geologic, climatic, and hydrologic setting of lakes) for all lakes; and in situ measurements of lake water quality for a subset of the lakes from the past 3 decades for approximately 2600–12 000 lakes depending on the variable. The database contains approximately 150 000 measures of total phosphorus, 200 000 measures of chlorophyll, and 900 000 measures of Secchi depth. The water quality data were compiled from 87 lake water quality data sets from federal, state, tribal, and non-profit agencies, university researchers, and citizen scientists. This database is one of the largest and most comprehensive databases of its type because it includes both in situ measurements and ecological context data. Because ecological context can be used to study a variety of other questions about lakes, streams, and wetlands, this database can also be used as the foundation for other studies of freshwaters at broad spatial and ecological scales.

Lake surface water temperatures are warming worldwide, raising concerns about the future integrity of valuable lake ecosystem services. In contrast to surface water temperatures, we know far less about what is happening to water temperature beneath the surface, where most organisms live. Moreover, we know little about which characteristics make lakes more or less sensitive to climate change and other environmental stressors. We examined changes in lake thermal structure for 231 lakes across northeastern North America (NENA), a region with an exceptionally high density of lakes. We determined how lake thermal structure has changed in recent decades (1975–2012) and assessed which lake characteristics are related to changes in lake thermal structure. In general, NENA lakes had increasing near-surface temperatures and thermal stratification strength. On average, changes in deepwater temperatures for the 231 lakes were not significantly different than zero, but individually, half of the lakes experienced warming and half cooling deepwater temperature through time. More transparent lakes (Secchi transparency >5 m) tended to have higher near-surface warming and greater increases in strength of thermal stratification than less transparent lakes. Whole-lake warming was greatest in polymictic lakes, where frequent summer mixing distributed heat throughout the water column. Lakes often function as important sentinels of climate change, but lake characteristics within and across regions modify the magnitude of the signal with important implications for lake biology, ecology and chemistry.

Rudstam, L. G., Parker-Stetter, S. L., Sullivan, P. J., and Warner, D. M. 2009. Towards a standard operating procedure for fishery acoustic surveys in the Laurentian Great Lakes, North America. – ICES Journal of Marine Science, 66: 1391–1397. Acoustic surveys are conducted annually in all five of the Laurentian Great Lakes and Lake Champlain to assess forage-fish abundance. The main target species are rainbow smelt (Osmerus mordax), alewife (Alosa pseudoharengus), and several coregonine species (Coregonus spp.). The Great Lakes Fishery Commission sponsored an Acoustic Study Group from 2002 to 2006 to discuss common problems and suggest standardized methods across these lakes. The study group produced a set of recommendations, available as a Great Lakes Fishery Commission Special Publication and on the web, that use in situ target strength (TS) to scale volume backscattering. Here, we review these recommendations with special attention to four often-overlooked topics of interest to all acoustic users, namely issues associated with first, the choice of thresholds for both TS and volume-backscattering strength, second, different settings for single-echo detection algorithms for measures of in situ TS, third, those taking account of measuring in situ TS in dense fish concentrations, and finally, detection limits.

We developed a bioenergetics model for bloater Coregonus hoyi based on a synthesis of studies on the energetics of bloater and other coregonines. This model was applied to the Lake Michigan population with information on water content, gonad weight, energy density, diet, and thermal history. Water content (inversely correlated with energy density) of nonspawning Lake Michigan bloaters decreased linearly with increasing weight for fish smaller than 155 g. Model results indicated comparatively small seasonal changes in consumption, a result of high consumption by bloaters at low temperatures and relatively small differences in the temperatures of occupied water between winter and summer. Growth rates and food conversion efficiencies of bloater estimated from the model were higher by factors of 2–4 than comparable values for the alewife Alosa pseudoharengus, indicating that Lake Michigan could support a higher biomass of native coregonines than of the introduced alewife. Bioenergetics estimates of a...