Putah Creek hydrology affecting riparian cottonwood and willow tree survival
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Creating or recruiting new riparian forests to improve Lower Putah Creek (LPC) ecosystem functions is challenging under the modified stream flow regime developed after historic gravel mining and installation of Monticello Dam upstream. Hydrologic connectivity between riparian trees, shallow groundwater, and the low flow channel is essential towards maintaining these forests and related habitats through the annual summer and multi-year drought periods typical in this Sacramento Valley region of California. Despite increased average summer flows, significant mature cottonwood and willow tree mortality along the LPC riparian areas below the Putah Creek diversion dam in 2014 raised concerns over the soil and hydrologic factors affecting riparian vegetation survival. A forensic analysis was conducted combining annual canopy coverage fractions and tree ring studies with daily soil-water balances, low flow records, and available groundwater level Information from the past few decades to determine the key hydrologic factors affecting riparian tree survival along the LPC. The 2011–2016 drought was linked with greater than prior average soil-water deficits in 2012–2015 and lower initial soil-water storage on March 1 of 2012 and 2014 that would be expected to stress the trees. However, such stress was not apparent in decreased tree ring spacing during this period from mature (40–50 years old), deceased, and living trees. Tree canopy coverage declined dramatically (by as much as 50% as compared to the previous decade average) only in the summer of the 2014 despite a ~ 35% increase in average summer flows from 2011 to 2014. However, the regional water table aquifer levels declined at an average rate of ~ 35 mm/day in 2014 (as compared to ~ 17 mm/day in previous decade) and by several meters overall between 2011 and 2016 suggesting that deceased trees lacked access to the water table aquifer or lateral stream seepage. The increased rates of water table decline and overall depth may be associated with a large increase in adjacent irrigated almond orchard areas in 2014–2016. Knowledge of the dynamic hydrologic factors controlling sustainability of riparian trees should better inform and guide future tree restoration efforts along the LPC.
KeywordsSoil-water balance Hydrology Restoration ecology Groundwater Riparian trees
The Solano County Water Agency (SCWA) with personal aid from the Lower Putah Creek Council and the Putah Creek Streamkeeper supported this research while various landowners along the Creek also provided insights and access to their property for measurements and observations.
- Barbour, M.G. & Whitworth, V. (2001). Natural vegetation of the Putah-Cache. http://bioregion.ucdavis.edu/book/00_Entering/00_03_vegetation.html.
- Brayshaw, T. C. (1996). Catkin-bearing plants of British Columbia. Victoria: Royal British Columbia Museum.Google Scholar
- Gordon, N. D., McMahon, T. A., & Finlayson, B. L. (1992). Stream hydrology, an introduction for ecologists. Toronto: John Wiley and Sons Inc..Google Scholar
- Horton, J. L., & Clark, J. L. (2000). Water table decline alters growth and survival of Salix gooddingii and Tamarix chinensis seedlings. Forest Ecology and Management, 140, 243–251.Google Scholar
- Hortscience. (1997). Putah creek riparian vegetation summary. Prepared for the SCWA.Google Scholar
- Irmak, S., Kabenge, I., Rudnick, D., Knezevic, S., Woodward, D., & Moravek, M. (2013). Evapotranspiration crop coefficients for mixed riparian plant community and transpiration crop coefficients for common reed, cottonwood and peach-leaf willow in the Platte River Basin, Nebraska-USA. Journal of Hydrology, 481, 177–190.CrossRefGoogle Scholar
- Katz, G. (2017). How riparian hydrology affects riparian trees on the rivers of the Great Plains. Colorado Water, p. 3–6.Google Scholar
- Krasny, M. E., Vogt, K. A., & Zasada, J. C. (1988). Establishment of four Salicaceae species on river bars in interior Alaska. Holarctic Ecology, 11, 210–219.Google Scholar
- Millers, L., Lachance, D., Burkman, W.G. & Allen, D.C. (1991). North American maple project cooperative field manual. USDA Forest Service General Technical Report NE-154.Google Scholar
- Nagler, P.L., Shafroth P.B., LaBaugh, J.W., Snyder, K.A., Scott, R.L., Merritt, D.M. and Osterberg, J. (2010). The potential for water savings through the control of salt cedar and Russian olive. In Shafroth, P.B., Brown, C.A., Merritt, D.M., (Eds.), Salt cedar and Russian olive control and demonstration act science assessment. U.S. Geological Survey Scientific Investigations Report 2009-5247. 143 pages.Google Scholar
- Norton, A.G. Katz, A., Eldeiry, R., Waskom, R. & Holtzer, T. (2016). SB14-195 Report to the Colorado Legislature South Platte phreatophyte study. Colorado Water Institute Special Report No. 30. December. http://cwi.colostate.edu/publications/SR/30.pdf.
- Rood, S. B., & Mahoney, J. M. (2000). Revised instream flow regulation enables cottonwood recruitment along the St. Mary River, Alberta, Canada. Rivers, 7, 109–125.Google Scholar
- Sanford, R.A. (2005). Conceptual framework of the lower Putah Creek riparian water availability forecasting model. Report prepared for the SCWA.Google Scholar
- Sanford, R.A. (2009). Update 2009, Lower Putah Creek Riparian water availability forecasting model. Report prepared for the SCWA.Google Scholar
- Sanford, R.A. (2011). Lake Solano seepage loss investigations 1958-2009. Report prepared for the SCWA.Google Scholar
- Shafroth, P. B., Stromberg, J. C., & Patten, D. T. (2000). Woody riparian vegetation response to different alluvial water table regimes. Western North American Naturalist, 60(1), 6.Google Scholar
- Stromberg, J. C. (1993). Fremont cottonwood-Goodding willow riparian forests, a review of their ecology, threats, and recovery potential. Journal of the Arizona–Nevada Academy of Science, 26, 97–111.Google Scholar
- Stromberg, J. C., Patten, D. T., & Richter, B. (1991). Flood flows and Sonoran riparian forests. Rivers, 2, 221–235.Google Scholar
- Thomasson, H.G., Olmsted, F.H. & LeRoux, E.F. (1960). Geology, water resources and usable ground-water storage capacity of part of Solano County, California. USGS Water Supply Paper No. 1464.Google Scholar
- Turner, R.M. (1974). Quantitative and historical evidence of vegetation changes along the upper Gila River, Arizona. USGS Professional Paper 655-H.Google Scholar