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.

Large reductions in sulphur emissions at the Sudbury, Ont., Canada, smelters in recent decades have resulted in decreased lake acidity, and biological improvements have followed. Lakes in the Sudbury area offer a very unique opportunity to develop our understanding of the processes regulating biological restructuring in aquatic ecosystems recovering from acidification. Here, we examine changes in crustacean zooplankton communities that have accompanied the chemical recovery of Whitepine and Sans Chambre lakes, near Sudbury, over the last two decades. In both these formerly acidic lakes, pH has increased to ~6.0, and some zooplankton community recovery has occurred. However, zooplankton communities have not completely recovered based on multivariate comparisons with the community composition of reference lakes. Although a number of acid-sensitive species have appeared, many did not persist, or did not achieve abundances typical of the reference lakes. This indicates that zooplankton community recovery will most likely depend on biotic and abiotic interactions within these lakes and not on factors affecting species dispersal. Both chemical and biological factors have large influences on biological recovery processes. Assessing biological recovery is very important since the restoration of healthy aquatic communities is a major objective of large-scale sulphur emission control programs.

In the mid-twentieth century, many lakes near Sudbury, Canada, were severely contaminated by acid and metal emissions from local smelters. For example, in the early 1970s, Middle Lake had pH of 4.2, and Cu and Ni levels both >0.5 mg L )1 . To determine if crustacean zooplankton could recover from such severe and chronic damage, Middle Lake was neutralized in 1973. A comparison of its zooplankton with that of 22 reference (pH > 6) lakes indicates that the planktonic Copepoda completely recovered by 2001. In contrast, the cladoceran assemblage improved but did not recover. Colonist sources existed -Cladocera and Copepoda occurred with equal frequency in area lakes -but six separate colonizations by cladoceran species failed. We argue that local factors, metal toxicity and predation by yellow perch, have, to date, prevented cladoceran recovery. Nonetheless, the complete copepod recovery is encouraging, given the severity and duration of pre-neutralization stress.

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