Bloom-forming cyanobacteria are known to produce a wide variety of toxic secondary metabolites that can yield fish kills, threaten wildlife and result in shutdown of water treatment facilities. Moreover, harmful algal bloom (HAB) biomass forms surface scums that result in losses in tourist revenue, property valuation and general quality of life in coastal communities. Notably, cyanobacterial HABs are becoming more widespread globally due to factors that include climate change (both temperature and rainfall) and anthropogenic nutrient loadings (Ho et al., 2019). Regarding the Laurentian Great Lakes, while HABs were once viewed a threat restricted to eutrophic embayments and western Lake Erie (Bullerjahn et al., 2016), they are now observed in oligotrophic systems such as coastal Lake Superior (Sterner et al., 2020). Mitigation and management of HABs is a major priority going forward that must engage scientists, social scientists, coastal residents and policy makers.

Resources: (click the link)

NOAA Great Lakes Environmental Research Laboratory (GLERL). Great Lakes Harmful Algal Blooms (HABs) and Hypoxia

Cyanobacterial Assessment Network (CyAN)

Great Lakes Commission, HABs Collaboratory

CIGLR Harmful Algal Blooms (HABs)

Great Lakes water levels have undergone considerable variation over centuries, decades, and even within a single year or two (Lenters, 2001; Wilcox et al., 2007; Gronewold et al., 2013). Although the water levels of Lakes Superior and Ontario are weakly “regulated” at their outflow by dams (Clites and Quinn, 2003; Clamen and Mcfarlane, 2018), the vast majority of Great Lakes water level variability is due to changes in weather and climate. These changes, in turn, alter the Great Lakes water balance through components such as precipitation, terrestrial evapotranspiration, snowmelt, streamflow into the lakes, interconnecting channel flow, and over-lake evaporation (Wilcox et al., 2007). The interplay of these components in driving lake level variability is especially evident on seasonal timescales (Lenters 2004), since each of the lakes typically rise in the spring when evaporation is low and runoff is high, but decline in the autumn when rates of evaporation increase. On longer timescales, interannual to decadal variability in precipitation can lead to changes in lake level on the order of 4-6 feet (Wuebbles et al., 2019), dwarfing the rates of sea level rise along the coastal oceans (Gronewold et al., 2013). Ongoing and future climate change is expected to lead to warmer Great Lakes water temperatures and increased lake evaporation, but higher annual precipitation and a greater frequency of heavy rain events may lead to an overall rise in lake levels in the coming decades (Lofgren and Rouhana, 2016; Wuebbles et al., 2019).

Helpful Links:

The Great Lakes Dashboard - NOAA

Great Lakes Water Level Forecast - US Army Corps of Engineers

Great Lakes Water Levels - Great Lakes Environmental Research Laboratory

Lake-Level Variability and Water Availability (Report) - USGS

Great Lakes Region - General Information - NOAA

Water loss from the Great Lakes occurs primarily through open-water evaporation and outflow from connecting channels (Lenters, 2004). Lake evaporation is a particularly important process since it not only affects seasonal to interannual variations in lake level, but it also modulates lake temperature and ice cover through the process of latent heat flux (Woolway et al., 2020), while also contributing to lake-effect precipitation (Minder et al., 2020). Atmospheric and limnological drivers of lake evaporation include solar radiation, wind speed, air and lake surface temperature, ice cover, and atmospheric humidity (Lenters et al., 2005), with highest evaporation rates on the Great Lakes generally occurring during the autumn and winter (Blanken et al., 2011). Climate change is altering many of these evaporation drivers, and the Great Lakes’ continued decline in winter ice cover and warming of summer water temperatures are of particular concern (Van Cleave et al., 2014). Such effects are known to cause an earlier start to the evaporation season (Woolway et al., 2020) and higher cumulative water loss from the Great Lakes following warm, low-ice years (Spence et al., 2013).

Helpful Links:

The Great Lakes Evaporation Network

Superior Watershed Partnership

Great Lakes Monthly Hydrologic Data (1860-Present) - GLERL

Assessing the Impacts of Climate Variability and Change on Great Lakes Evaporation

Ice cover represents one of the most important physical variables for alpine, temperate, and high-latitude lakes (Vavrus et al., 1996). The presence of ice on the surface of a lake greatly alters its interaction with the overlying atmosphere by trapping heat and moisture (e.g., inhibiting evaporation), altering wind mixing, and reflecting solar radiation that would otherwise be absorbed by darker, open water (Zhong et al., 2016). Large lakes such as the Great Lakes have the added complexity of spatially variable ice cover (Wang et al., 2012), with the most extensive ice tending to form in shallow, nearshore waters, providing a protective, coastal barrier against winter storms. Lake Erie typically sees the most extensive areal ice coverage (often exceeding 90%), while deeper lakes such as Lakes Michigan and Ontario rarely see annual maximum ice coverage in excess of 70% (Wang et al., 2017). The deepest lake (Superior) is also the most northern, leading to high year-to-year variability in ice cover (~10-95%) that is strongly dependent on early winter air temperatures (Spence et al., 2013). In addition to the large interannual variability in Great Lakes ice cover, which is often related to atmospheric teleconnection patterns (Van Cleave et al., 2014; Bai et al., 2015), recent climate change and associated warmer winters have led to a dramatic, 71% drop in overall Great Lakes ice coverage since 1973 (Wang et al., 2012). In the case of Lake Superior, much of this decline in winter ice cover occurred in conjunction with a step change following the warm, El Niño winter of 1997-98 (Van Cleave et al., 2014), after which time the lake has mostly persisted in a low-ice state.

Helpful Links:

Great Lakes Ice Cover - GLERL

Great Lakes Ice Coverage - GLISA

Great Lakes Ice Climatology - NOAA