Date of Award

2013

Document Type

Thesis

Degree Name

Master of Science (MS) in Biology

Department

Biology

Abstract

"Riparian areas (floodplains) provide key ecological functions that are linked to the ecohydrology however; they are particularly susceptible to invasion by alien species. In much of the western United States, riparian zones are shifting from native woody and herbaceous species to invasive grass dominated ecosystems that may alter hydrology, including changes to stream flow. Compared to the woody species they often replace, dense grass stands may have higher rates of growth (productivity) and water loss through leaves (transpiration), yet may access shallower water sources and thus reduce stream flow. In eastern Washington, many streams experience low flow that degrades water quality, concentrates pollutants, and reduces habitat. Most of these streams' riparian zones have extensive stands of reed canary grass (Phalaris arundinacea). Reed canary grass was historically planted for erosion control and as a forage crop, but its ability to invade and create monotypic stands has allowed it to out compete native vegetation in riparian areas throughout much of the temperate United States. My goal is to determine the effect of reed canary grass on the ecohydrology of riparian zones along low order streams in a semi-arid region. I conducted vegetation, groundwater, and stream flow surveys at nine sites along four watersheds to determine community composition and hydrologic regime measured the length of the growing season for nine riparian species. I measured the amount of biomass and calculated the amount of photosynthetic surface for dense stands of nine riparian species. The amount of water used by different species was determined by measuring transpiration rates of reed canary grass and other riparian species throughout the growing season. Hydrogen and oxygen isotopes from different water sources (stream water and deep groundwater) were used to determine the proportion of water sources use by different plants species. Reed canary grass was found with greater cover than other riparian species on low elevation geomorphic positions in the riparian zone. It had the longest growing season by two weeks. Although its transpiration rates per unit leaf area are not exceptional compared to other species, its high specific leaf area and ability to produce dense stands of photosynthetic biomass results in more photosynthetic surface through which to transpire water than any other riparian species. Reed canary grass was found to rely heavily on surface water sources along different elevations in the riparian zone. My results implicate reed canary grass as a major factor in the regional low stream flow during the growing season. Although the presence of reed canary grass can add some benefits to a riparia buffer, I present strong evidence that it is altering the ecohydrology of these ecosystems. The management of this grass, particularly in a semi-arid region, could improve water quality and quantity"--Document.

Comments

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