Grantee Research Project Results
2010 Progress Report: Modeling of the Hydrochemical Response of High Elevation Watersheds to Climate Change and Atmospheric Deposition
EPA Grant Number: R834188Title: Modeling of the Hydrochemical Response of High Elevation Watersheds to Climate Change and Atmospheric Deposition
Investigators: Driscoll, Charles T. , Campbell, John L. , Pourmokhtarian, Afshin , Hayhoe, Katharine , Wu, Wei
Current Investigators: Driscoll, Charles T. , Campbell, John L. , Pourmokhtarian, Afshin , Hayhoe, Katharine , Wu, Wei , Dong, Zheng
Institution: Syracuse University , University of Southern Mississippi , USDA , Towson University
Current Institution: Syracuse University , Towson University , USDA , University of Southern Mississippi
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2009 through July 31, 2012 (Extended to July 31, 2014)
Project Period Covered by this Report: August 1, 2009 through July 31,2010
Project Amount: $800,000
RFA: Consequences of Global Change for Water Quality (2008) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Climate Change , Watersheds , Aquatic Ecosystems , Water
Objective:
Our overarching goal for this proposed study is to compare model calculations across high elevation watersheds in the U.S. with a range of climatic conditions to better understand and quantify how the quantity and quality of surface waters might respond to changing climate.
To achieve this goal, we are using the hydrochemical model, PnET-BGC, driven by both past and future simulated climate, to assess the impact of climate change on water quantity and quality. Climate input scenarios are generated with a well-documented statistical downscaling procedure based on simulations from the latest AOGCM outputs available from the Intergovernmental Panel on Climate Change (IPCC) Working Group 1. Using these climate input data, PnET-BGC are being run at the 14 high elevation watersheds. This approach will enable us to evaluate hydrochemical responses intensively at local scales and more broadly at regional and national scales. We are working with cooperating scientists from the intensive study sites to interpret model results and design additional analyses.
Progress Summary:
The modeling results for Hubbard Brook Experimental Forest (HBEF), New Hampshire, suggest that under future climatic conditions peak discharge in spring will transition from April to March due to higher temperature and less snowpack development and growing season will extend longer through the spring-fall period. Higher temperatures and a decrease in the ratio of snow to rain, regardless of overall increase in total precipitation, will cause a shift in snowpack development. Over the summer period, higher rates of evapotranspiration will decrease streamflow. Hydrologic simulations suggest substantial changes in the HBEF water budget, with shifts in seasonal and annual hydrology. Changes in the seasonality of runoff can influence the frequency of flooding and summer drought. Under scenarios of climate change with CO2 effects on vegetation, the average annual run off at Hubbard Brook is predicted to increase slightly in comparison with climate change alone. Under elevated CO2, changes in stomatal conductance decreases canopy transpiration, which offset higher evaporation associated with higher temperature. Although modeling results suggest increases in annual runoff, higher temperatures and an extended season of enhanced growth offset this increase to some extent due to increases in evapotranspiration.
The model simulations indicated that climate change alters the hydrologic cycle and the seasonality of stream discharge. Because drainage strongly influences element transport, seasonal changes in discharge also alter the seasonal patterns of chemical constituents. We assessed changes in seasonal patterns of concentrations of NO3-, SO42-, Ca2+, DOC, pH, and ANC under all climate change scenarios with and without CO2 effects on vegetation over the period of 2070-2100 and compared these with the seasonal patterns of measured values from 1970-2000. Although there were changes in the total concentrations and fluxes of different elements, as well as the acid-base characteristics of streamwater (pH, ANC), seasonal patterns for elements simulated by the model were similar to patterns for 1970-2000. These results suggest that even though climate change will likely alter the overall element concentrations and fluxes, the relative seasonal patterns will not be highly altered.
Model simulations suggest that elevated temperature will increase N mineralization and nitrification leading to a condition of N saturation in northern forests. This may result in elevated leaching losses of NO3- resulting in soil and stream acidification. The modeled increase in NO3- concentration and loss was due to enhanced rates of N mineralization and nitrification associated with warmer temperatures and decreased uptake of NH4+ from water stress. The modeled increase in NO3- leaching caused acidification of the soil and surface waters. Under PCM-A1fi and B1 scenarios, lower rates of mineralization and nitrification delay the peak in streamwater NO3- concentration compared to HadCM3-A1fi, B1 and GFDL-A1fi, B1 scenarios. Under climate change with CO2 effects on vegetation, higher rates of photosynthesis and tree growth (increases in NPP and NEP) resulted in increases in plant nutrient uptake, and mitigated leaching losses of NO3-. The rates of NH4+ and NO3- uptake under the four low and moderate climate change scenarios with CO2 effects considered were able to keep the pace with mineralization and nitrification rates caused by warmer air temperatures. Model results for HadCM3-A1fi and GFDL-A1fi (scenarios of largest temperature increase) suggest that N saturation and elevated NO3- leachate occur, although to a lesser extent due to enhanced tree uptake of N associated with CO2 fertilization. Increases in atmospheric CO2 resulted in increased tree growth and limited NO3- leaching over the first half of the 21st. century, while tree growth remained constant or decreased over the second half of the century because of water stress. Over time, and especially under higher CO2 emission scenarios and warmer temperatures, the CO2 fertilization effect declines and N saturation occurs, as temperature becomes the dominant driver of N cycling.
The watershed responses of other major elements such as Ca2+ and chemical characteristics such as pH to changes in climate follow the same patterns as NO3-. The PnET-BGC simulations suggest that DOC will decrease over the century under all climate change scenarios without considering CO2 effects on vegetation. The trends in streamwater DOC were different under climate change in the presence of CO2 fertilization. The higher productivity of the forest (NPP and NEP) due to CO2 fertilization increased litterfall in comparison to values from model simulations without CO2 effects on vegetation. An increase in the decomposition of soil organic matter triggered by higher temperatures results in higher DOC concentrations in streamwater. Model projections also suggest marked decreases in soil exchangeable calcium, magnesium and potassium with simultaneous decline in soil base saturation and Ca/Al ratio over this century due to changing climate. These changes are attributed mainly to elevated leaching losses of nitrate.
In addition to the HBEF, model simulations also are being conducted for Huntington Forest, New York; Sleepers River, Vermont; Cone Pond, New Hampshire and Noland Divide, Tennessee.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 26 publications | 7 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Campbell JL, Driscoll CT, Pourmokhtarian A, Hayhoe K. Streamflow responses to past and projected future changes in climate at the Hubbard Brook Experimental Forest, New Hampshire, United States. Water Resources Research 2011;47(2):W02514 (15 pp.). |
R834188 (2010) R834188 (2011) R834188 (2013) R834188 (Final) |
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Supplemental Keywords:
RFA, Air, climate change, Air Pollution Effects, Atmosphere, environmental monitoring, hydrologic models, atmospheric modelsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.