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Tuolumne Meadows

Mountain Meadow Restoration with a Changing Climate

Supported by the National Science Foundation under Grant No. CBET-0729838

The Tuolumne Meadows project is in collaboration between the University of Wisconsin-Madison and  the University of Washington.  Additional information can be found on the University of Washington Meadow Restoration in a Changing Climate page.  The purpose of this collaborative project is to investigate hydrological and climatic processes at a range of  both spatial and temporal scales affecting a meadow ecosystem. This work includes modeling snowmelt and groundwater flow processes, linking groundwater and vegetation patterning and testing the feasibility of various restoration strategies subject to climatic shifts. Using the well-instrumented Tuolumne Meadows in Yosemite National Park, CA as our case study, we  1) run a distributed snowmelt and runoff model over the basin to determine how different areas respond to climatic shifts and which areas are most and least sensitive, 2) combine simulated runoff with a hydraulic routing model through the meadow to estimate how stream water levels will be affected by climate change with and without various restoration efforts, 3) model how groundwater levels throughout the meadow will respond to shifts in stream level, and 4) model how vegetation communities are most likely to shift in response to projected water table changes. The development and implementation of this multifaceted model is designed to answer a basic question: Which riparian meadow restoration practices are most effective, sustainable, and appropriate given the scientific consensus on climate change? The new modeling techniques and linkages we have developed are not only applicable to mountain meadow systems in the Western US, but are also the framework for a transferable methodology that can be used to investigate the interrelated effects of climate, hydrology, and vegetation dynamics in other regions and ecosystems.

 

 

Site Description

Tuolumne Meadows is located on the eastern side of Yosemite National Park in the Sierra Nevada Mountains of California.  Tuolumne Meadows, at an elevation of 2600 meters, represents one of the largest subalpine meadows within the Sierra Nevada Mountains.  The upstream watershed has an area of approximately 234 km2.   Mean annual precipitation is approximately  1000 mm with a majority (>80%) of the precipitation falling in the form of snow during the winter months (California Department of Water Resources Station ID TUM). 

 

The meadow aquifer consists of fine grained overbank deposits overlying coarser sands and gravels.   As a result of these coarse grained deposits the meadow aquifer has a strong hydrological connection with the Tuolumne River which flows from east to west.  Four ephemeral tributaries feed the Tuolumne River (Budd Creek, Delaney, Creek, Dog Creek and Unicorn Creek) within the meadow boundaries, and are also hydrologically connected to the meadow aquifer.

Site Instrumentation

The field site is instrumented with a network of monitoring wells, stream stage recorders, soil moisture probes and two weather stations.  Water levels are recorded at 80 monitoring wells along five transects within the meadow.  Manual measurements are collected bi-weekly during the growing season at each of the wells in addition to hourly water level at 21 wells that contain pressure transducers. Soil moisture is recorded in three stations within the meadow with probes at 15, 30, 50, 75 and 100 cm.  Stream stage recorders measure water levels at five locations along the Tuolumne River as well as one location at each of the tributary streams.  Meteorological data is collected from weather stations maintained by the National Park Service (TMM) and the California Department of Water Resources (TUM).

 

Publications

 

Loheide, S. P., II, R. S. Deitchman, D. J. Cooper, E. C. Wolf, C. T. Hammersmark, and J. D. Lundquist, 2009. Hydroecology of impacted wet meadows in the Sierra Nevada and Cascade Ranges, CA. Hydrogeology Journal, 17:1, p. 229-246, doi: 10.1007/s10040-008-0380-4

 

Loheide S. P. II, J. D. Lundquist, 2009. Snowmelt-induced diel fluxes through the hyporheic zone, Water Resour. Res., 45, W07404, doi:10.1029/2008WR007329

 

Li, Q., K. Ito, Z.S. Wu, C.S. Lowry, S.P. Loheide II, 2009. COMSOL Multiphysics: A Novel Approach to Groundwater Modeling. Ground Water. (DOI:10.1111/j.1745-6584.2009.00584.x)

 

Lowry CS, Deems JS, Loheide SP, Lundquist JL, 2010. Linking snowmelt derived recharge and groundwater flow in a high elevation meadow system, Sierra Nevada Mountains, California, Hydrologic Processes, doi:10.1002/hyp.7714

 

Lowry, C.S., and S.P. Loheide II., 2010. Groundwater dependent vegetation: quantifying the groundwater subsidy. Water Resources Research, 46: W06202. doi:10.1029/2009WR008874.

Sediment Type and Root Water Uptake

The amount of soil moisture available for root water uptake within the unsaturated zone is dependent on the type of sediments with the meadow and the position of the water table.  Fine grained over bank deposits within the meadow are slow to drain and provide water for root water uptake late into the growing season.  Whereas the coarse grained sediments drain quickly and provide little water for plants at the end of the growing season.  In order to quantify the impact of the change in sediment thickness and variation in the water table on root water uptake a representative one-dimensional Richards equation model was created based on laboratory grain size analysis of the sediments and measure water levels.  Results show the importance of connection between the shallow water table and fine grain sediments on root water uptake as well as quantifying the additional water available to plants under different hydrologic settings.  For additional information see:

 

Lowry, C.S., and S.P. Loheide II., 2010. Groundwater dependent vegetation: quantifying the groundwater subsidy. Water Resources Research, 46: W06202. doi:10.1029/2009WR008874.

Linking Watershed Scale Hydrology to Meadow Scale Groundwater Flow

A watershed scale hydrologic model is linked to a meadow scale groundwater flow model in order to quantify the impact of timing and distribution snowmelt and watershed processes on seasonal groundwater fluctuation within Tuolumne Meadows.  Groundwater flow within Tuolumne Meadows is simulated with a two-dimensional groundwater flow model, using Comsol Multiphysics (Comsol, Inc. Burlington, MA), which is a general-purpose finite element software package that has recently been used to simulate groundwater flow (Li et al. 2009).  The groundwater flow model is linked at the boundary of the meadow to a Distributed Hydrology Soil Vegetation Model (DHSVM; Wigmosta et al. 1994), which is a watershed scale hydrologic model representing the water balance within the contributing watershed.  DHSVM is a physically-based distributed hydrology model, which simulates the energy and water balance over the basin contributing to Tuolumne Meadows.  Results from the linked watershed and meadow scale model demonstrate the importance of both the timing and distribution of snowmelt on water levels within Tuolumne Meadows from the surrounding watershed.  Timing of both snowmelt within the meadow as well as snowmelt within the surrounding hillslope create a unique signature on water levels within the meadow.  For additional information see:

 

Lowry CS, Deems JS, Loheide SP, Lundquist JL, 2010. Linking snowmelt derived recharge and groundwater flow in a high elevation meadow system, Sierra Nevada Mountains, California, Hydrologic Processes, doi:10.1002/hyp.7714

Snowmelt Induced Hyporheic Exchange

Fluctuations in stream stage as a result of daily changes in snowmelt causes water from the stream to propagate into the meadow aquifer. This diel snowmelt driven process has implications for filtering sediment, cycling nutrients, and promoting biogeochemical processes in the hyporheic zone. 

For additional information see:

 

Loheide S. P. II, and J. D. Lundquist, 2009. Snowmelt-induced diel fluxes through the hyporheic zone, Water Resources Research, 45, W07404, doi:10.1029/2008WR007329

Plant Communities and Hydrology

Tuolumne Meadows contains a mosaic of plant communities that are thought to be controlled by both availability of soil moisture as well as tolerance to oxygen stress.  Using our calibrated groundwater flow model linked to a one-dimensional Richards equation model we are investigating the relationship between vegetation and hydrology.  Relationships between vegetation and hydrology are based on seven years of historical data.  Using these relationships we run future climate scenarios through the linked snowmelt and groundwater flow models to predict vegetation patterning.  Finally, restoration scenarios are simulated in combination with the future climate scenarios in order to determine the impact on vegetation within Tuolumne Meadows.