Climate impacts on freshwater resources and ecosystems

The impacts of climate change on freshwater resources (both surface and groundwater) will be one of the most important and far reaching impacts felt by individuals, ecosystems, and institutions. As noted by the Intergovernmental Panel on Climate Change in their Fourth Assessment Report, “observed warming over several decades has been linked to changes in the large-scale hydrological cycle such as: increasing atmospheric water vapor content; changing precipitation patterns, intensity and extremes; reduced snow cover and widespread melting of ice; and changes in soil moisture and runoff.” Recent extreme weather events (e.g., inland flooding, hurricanes, and droughts) in the US cannot be directly attributed to climate change; however, these events are consistent with events that climate change models suggest will be more frequent in the future. 
 

There is a diversity of important freshwater resources in the Northeast CSC region. These include the Laurentian Great Lakes ecosystems, which contain myriad habitat types from open-lake, to coastal wetlands and tributaries (Dodge and Kavetsky, 1995), to other smaller freshwater lakes (e.g., Lake Champlain), ponds, and vernal pools. Also of high importance are wetlands and their intrinsic mosaic of hydric soils, as well as multifaceted stream and river systems. Together, these freshwater resources support numerous ecologically, economically, and culturally important species and ecosystem services, including clean drinking water, agriculture, fisheries, and recreational activities. 
 

Changes in snowpack depth and extent, seasonal shifts in the timing and volume of runoff, transitions in the peak and base stream flows, and changes in stream and river temperatures are extremely important throughout watersheds and ecosystems. This is especially true in the Northeast where precipitation and extreme storm events are increasing flow extremes and impacting hydrologic networks. Timing and volume shifts will significantly impact species that rely on hydrologic regimes for important transitions in their life cycle. In addition, increasing stream, river, and lake temperatures will impact water quality, stream, river, and lake chemistry, as well as the composition and vulnerability (Theme 5) of aquatic species ranging from microorganisms to commercially important fishes and other associated riparian flora/fauna. The combined impacts of climate change and anthropogenic activities (e.g., agricultural practices and urban development) will bring about shifts in the hydrological cycle that effect the transfer of sediments and nutrients, production and transport of pollutants including pesticides and heavy metals (e.g., methyl-mercury), and influence salinity concentrations of lower watersheds and coastal habitats (Theme 4) (Groisman et al., 2004). These changes in hydrological and thermal regimes may increase the risk of disease outbreaks in aquatic systems, impact eutrophication, hypoxic and dead zones, as well as lead to community transitions that alter ecosystem structure and function. Recent and future climate changes are occurring on a backdrop of historical geologic influences such as glacial-related events and physiographic effects (such as slope and mass wasting). Consequently, paleoclimate studies may be useful in assessing long-term fluxes and responses of stream networks to modern changes in the environment. 
 

The Great Lakes will be a particular focus for the NE CSC. Containing 84% of North America's surface freshwater, the Great Lakes region supports a variety of resources such as agricultural lands, coastal marshes, mineral deposits, forests, fens, wetlands, dunes, and other ecosystems unique to the region. Considering that the Great Lakes supply drinking water to more than 26 million people, and have billions of dollars in economic impact, climate change impacts on the Great Lakes will reverberate throughout the region. Projected increases in temperature, changes in precipitation, fluctuating ice cover, and water levels possibly accompanied by increasing prevalence of drought, will lead to a variety of impacts. Concurrent and interrelated impacts from invasive species, eutrophication, and other environmental stressors, could directly affect the lakes, but also have indirect effects on streams, wetlands, forests, and agriculture as well as ecological and human communities across the region. Although there are issues unique to the Great Lakes system, research into issues that will affect coastal, limnological, and fisheries systems can help inform the impacts of climate change throughout the greater region. For example, the link between climate change, eutrophication, and harmful algal blooms (HABs) are important emerging issues in the Great Lakes as well as for regional inland lakes, and Atlantic and Gulf of Mexico coastal environments (Theme 4) (Nelson et al., 2013b). 
 
Also of particular interest are the impacts of climate change on the headwaters of watersheds. Studies of headwaters in the NE CSC region are particularly effective in identifying the potential impacts of climate impacts on (inherent and downstream) vulnerable aquatic communities. As an area of maximum terrestrial/aquatic interaction, headwaters are an ideal location to assess how land management affects persistence of aquatic and riparian species under a changing climate. These habitats have already been noted as critical priorities by several of the Center’s LCC partners. 
 
Evaluating current and future climate changes on freshwater resources is an important theme not only for the NE CSC, but a range of federal agencies and other partners in the region (e.g., NOAA Great Lakes Integrated Sciences and Assessments Center, EPA Great Lakes Restoration Initiative (GLRI), Upper Midwest and Great Lakes LCC). The NE CSC will work collaboratively with existing efforts to develop protocols for assessments of the impacts of climate change on freshwater fisheries, lake level fluctuations, hydrology, water quality, and water availability. 
 
Recommendations 
  • Identify the impacts of climate (Theme 1) and land use/land cover change (Theme 2) on freshwater resources including the occurrence, magnitude, and frequency of flooding events across varying elevation, soil types, and other scales; susceptibility to drought, and changes in seasonal water availability. 

  • Identify the impacts of climate (Theme 1) and land use/land cover change (Theme 2) on freshwater quality, including agricultural runoff, nutrient loading, methyl-mercury production and transport, and waterborne disease outbreaks across the region. 

  • Identify the impacts of climate change on freshwater ecosystems, particularly regional headwaters, ephermal wetlands and other intermittent habitats (e.g. seasonal and temporary wetlands; vernal pools), and the temperature ranges of coldwater streams. 

  • Characterize potential consequences of hydrological and thermal regime changes on water resource budgets, requirements for ecological flows, and the implications of widespread loss of (vulnerable) habitats on biodiversity and ecosystem services. 

  • Characterize the resulting vulnerabilities from the combined impacts of climate and land use/land cover change, particularly in the form of habitat degradation and increased exposure to pollution, on human health, economic, fish, wildlife, and cultural resources. 

  • Assist partners that collect and monitor water quality data to better understand landscape changes across the region. 

  • Collaborate with partners (e.g., NOAA GLERL, GLISA, RISA) to improve models and predictions of climate impacts on physical processes unique to the Great Lakes, particularly the direction and magnitude of lake level fluctuations, fluctuating seasonal ice cover, and how changes affect ecological, socio-economic and cultural interests. 

  • Use decision analysis frameworks to identify major risks and uncertainties in model predictions for freshwater resources across the region and develop alternatives for management decisions that are focused on different outcomes (e.g., decisions effected by the direction and magnitude of seasonally, and annually fluctuating lake levels and ice cover). 

  • Work with partners and stakeholders to develop adaptation strategies that decrease vulnerabilities from the impacts of climate and land use/land cover change, and increase the resilience of changing water resources.