• The changing phenology of lake stratification: eutrophication, algae blooms, and fish die-offs- Dave Courtemanch
• The Effects of Extreme Climate Events on Lakewater Chemistry: Implications for “Brownification” in Maine Lakes – Kristin Strock
• Historical groundwater trends in northern New England and relations with streamflow and climatic variables – Robert Dudley
• Trends in runoff, precipitation, and evapotranspiration for river basins draining to the Gulf of Maine in the United States – Tom Huntington

The changing phenology of lake stratification: eutrophication, algae blooms, and fish die-offs
Dave Courtemanch, The Nature Conservancy; Linda Bacon, Maine DEP; Scott Williams, Maine Volunteer Lake Monitoring Program
Presentation available (pdf format)
Abstract: Lake stratification develops in the spring as surface water warms from increasing solar radiation and warming air temperatures relative to lake area and lake volume, persisting into the fall until declining surface temperatures equilibrate with subsurface temperatures. Therefore, the onset of stratification can be expected to occur earlier and last longer based on projections for warmer atmospheric temperatures, reduced snow cover, and a shorter duration and depth of ice cover. Early onset can increase the duration of stratification, thus increasing the extent and period of anoxia in subsurface waters, creating greater dissolution of iron-bound phosphate in sediments. Rapid warming can result in a shallower epilimnion with steeper thermocline gradient, decreasing the epilimnion to hypolimnion volume ratio thereby reducing the dilution capacity of diffused phosphorus released from the sediments into the phototrophic zone. In 2012, anomalous early spring weather provided a glimpse of how a warming Maine climate may affect lake water quality in the future. Two aberrant algae bloom events were documented on Georges Pond and Abrams Pond in Hancock County where such altered stratification characteristics were observed. Additionally, Lake Auburn in Androscoggin County experienced a die-off of lake trout when the entire thermocline and hypolimnion became anoxic at least a month earlier in the year, eliminating all coldwater refugia for this species.       

The Effects of Extreme Climate Events on Lakewater Chemistry: Implications for “Brownification” in Maine Lakes
Kristin Strock, University of Maine School of Biology and Ecology, Climate Change Institute; Jasmine Saros, Climate Change Insititute; Sarah Nelson, Senator George J. Mitchell Center
Presentation not available
Abstract: In the Northeast U.S., there has been a widespread decline in sulfur emissions and deposition as a result of Clean Air Act Amendments. Over this same time period, extreme precipitation events have increased in frequency in the Northeast by over 61 percent. Disentangling climate and anthropogenic drivers of change in the influx of watershed subsidies to surface waters is an ongoing concern that has important implications for lake management and environmental policy. Most notably, increased dissolved organic carbon (DOC) concentration, or “brownification,” has been observed in many regions of the Northern Hemisphere. These changes have been attributed to both declining sulfur deposition and climate-mediated drivers. Long term monitoring of Maine lakes documents variable trends in DOC over the past three decades. To explore the effects of extreme climate events on DOC trends, we paired weather data collected from watershed-scale climate models with surface water geochemistry collected by US-EPA monitoring programs over the past three decades. Multivariate statistical analyses described episodic changes in geochemistry and identified subsets of lakes that respond to specific events: episodic acidification during drought; increased input of DOC during wet years; and lakes that appear unaffected by climate extremes. Clarifying the response of DOC, a pivotal regulator of aquatic ecosystems, to extreme weather events across gradients of landscape position and atmospheric deposition, is increasingly important for policy and management decisions as the frequency of extreme events continues to increase in this region.

Historical groundwater trends in northern New England and relations with streamflow and climatic variables
Robert W. Dudley, Glenn A. Hodgkins, US Geological Survey New England Water Science Center
Presentation not available
Abstract: Water-level trends spanning 20, 30, 40, and 50 years were tested using month-end groundwater levels in 26, 12, 10, and 3 wells in northern New England (Maine, New Hampshire, and Vermont), respectively. Groundwater levels for 77 wells were used in interannual correlations with meteorological and hydrologic variables related to groundwater. Trends in the contemporary groundwater record (20 and 30 years) indicate increases in groundwater levels in all months for most wells throughout northern New England. The highest percentage of increasing 20-year trends were in February through March, May through August and October through November. Forty-year trend results were mixed, while 50-year trends indicated increasing groundwater levels. While most monthly groundwater levels correlate strongly with the previous month’s level, monthly levels also correlate strongly with monthly streamflows in the same month, and correlations of levels with monthly precipitation are less frequent and weaker than those with streamflow. Groundwater levels in May through August correlate strongly with annual (water year) streamflow. Correlations of groundwater levels with streamflow data and the relative richness of 50-100 year historical streamflow data suggest useful proxies for quantifying historical groundwater levels in light of the relatively short and fragmented groundwater data records presently available.

Trends in runoff, precipitation, and evapotranspiration for river basins draining to the Gulf of Maine in the United States
Thomas Huntington, U.S. Geological Survey; Michael Billmire, Michigan Tech Research Institute
Presentation not available
Abstract: Climate warming is projected to result in increases in total annual precipitation in northeastern United States. However, increases in precipitation will not necessarily result in increases in streamflow, because increasing evapotranspiration could counteract the effect of increasing precipitation. This study was conducted to examine these competing trends in the historical record for major rivers draining to the Gulf of Maine. Twenty two basins having > 70 years of measured runoff were included in the analysis. Annual average air temperature increased over the period of runoff record for 19 out of 22 basins. Precipitation increased in all basins, with increases ranging between 8 and 25 percent. Runoff increased in all basins, with increases ranging between 9 and 34 percent. Evapotranspiration (calculated as precipitation minus runoff) increased in 17 basins and decreased in 5 basins. Annual average temperature and annual average precipitation were positively correlated for most of the largest basins. Annual average evapotranspiration was weakly positively correlated with annual average temperature. The lack of a more consistent and steeper increase in ET over time was unexpected but could be explained by various factors including changes in wind speed, cloudiness, and (or) patterns of forest growth. For the period 1926-2010, for the 9 largest non-nested river basins precipitation increased by about 12% (1.5 mm yr-2) while runoff increased by about 24% (1.7 mm yr-2).

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