CLIMATE SCIENCE PORTAL CLIMATE SCIENCE 101
Climate change will affect our lakes, rivers and wetlands
How will climate change effect Maine's lakes and ponds?
When asked which attributes people value most about Maine lakes, ‘clear, clean water’ is always high on the list. However as the period of ice cover on Maine lakes shortens, lake water temperatures become warmer and the frequency of extreme weather events increases, enhancing the conditions for more turbidity, more algal growth and browner (more tea-colored) water.
Source: Roberta Hill, Kezar Lake, Waterford, Maine
Increased precipitation and more intense rain events means more stormwater runoff sweeping eroded soils, nutrients, and other pollutants into lakes and their tributaries. Longer annual growing seasons and shorter periods of ice cover not only extend the season for polluted stormwater runoff to occur, these climatic shifts also increase the potential for a more complete breakdown of organic matter in the watershed, making it more soluble and therefore more easily transported to lakes in stormwater runoff. More organic matter flowing into lakes generally increases the concentration of both phosphorus and humic acids in the water.
2011 was warmer than average across much of Maine, as was the following spring. Many Maine lakes experienced an early ice-out in the spring of 2012 and Lake Auburn was no exception. That May, six-inches (15 cm) of rain fell in the Auburn area, causing severe soil erosion in the Lake Auburn watershed. Nutrient-laden soils flooded into Lake Auburn with the stormwater, fueling a severe algal bloom in the lake. The following winter, dissolved oxygen levels in the deeper areas of the lake reached all-time lows, causing a major dieoff of the lake’s lake trout population.
It is important to note that drought (the lack of sufficient precipitation) may also negatively impact lakes and ponds, dewatering the biologically important littoral zone, and in some cases causing the water to become clearer. Uncommonly clearer water allows more ultraviolet light to penetrate into the lake. This increase in UV radiation can have an adverse impact on the native plankton communities that have become established in a less drought-prone climate. Since plankton are the base of the food web for many Maine lake dwellers, adverse impact on plankton would have ripple effect.
Other ways that Maine’s lakes and ponds are being impacted by a changing climate include a lengthening boating season, and the increased threat of invasive aquatic species.
How will climate change effect Maine's streams and rivers?
Increased precipitation and more intense rain events mean more stormwater runoff flooding into streams and rivers resulting in flash flooding. Flash flooding may not only erode streambanks and undermine culverts, threatening roads and other nearby human infrastructure, but also may wash soils, nutrients, and other pollutants from the watershed into streams and rivers. Fine eroded soil particles, such as silts and clays, may be carried into streams through this process, burying cobble and gravel habitat that is essential for many stream-bottom dwellers such mayfly larvae and crayfish. Since many of these invertebrate bottom-dwellers are, in turn, food for fish such as brook trout and salmon, impacts from a single climate-driven flood event may ripple through the entire stream food web.
Droughts, on the other hand, deprive streams and rivers of the very water that sustains them, impacting not only the wildlife but also the human communities that depend upon this water. For example, when critically important spawning streams run low or dry up all together, local fish populations, unable to successfully spawn, can be (at least temporarily) locally extinguished. If severe drought conditions are statewide and prolonged, the cumulative impacts on stream and river ecosystems may be catastrophic.
Source: Roberta Hill, East Outlet Kennebec River
Seasonal shifts associated with climate change (such as warm temperatures coming earlier in the spring and lasting later into the fall) have an impact on stream ecosystem phenology. For example, the timing of aquatic insect hatches that have been relatively stable since the end of the last ice age are now shifting. Not all stream-dwellers are responding to seasonal shifts at the same speed or in the same ways. This can disrupt the manner in which species interact with each other and with the stream ecosystems as a whole.
Longer and warmer summers can cause rises in water temperatures that are dangerous for fish species such as trout and salmon that are evolutionarily adapted to cold water. Warmer water can cause some fish species to become stressed and therefore more vulnerable to parasitic infections. Warmer water also holds less oxygen. Stream pools that provide critical refuge for a host of wildlife species may become too warm and depleted of oxygen to support even some warm water species.
How will climate change effect Maine's wetlands?
Altered hydrology and rising temperature can both negatively impact wetlands. For example, wetlands that become dry or flooded may not only lose their capacity to purify surface water, but they may also begin to have the opposite effect: decomposing and releasing nutrients into surface waters. If plants decompose faster than they grow through photosynthesis, wetlands may cease to function as a sink for CO2 and become sources of CO2.
Many of Maine’s rarest plant species occur in wetlands. If wetlands are altered by droughts or floods, rare wetland species will be increasingly endangered.
Source: Roberta Hill, East Outlet Kennebec River