Biology ETDs

Publication Date

4-5-1996

Abstract

In most climatic regions, the growth of ecological knowledge for terrestrial and limnological components of landscapes have roughly occurred in tandem. But at a time when the world's deserts are increasingly used for human development, and particularly so along water courses, knowledge of how stream ecosystems function within semi-add landscapes has seriously lagged the productive history of terrestrial research there. How terrestrial and limnological components interact within semi-arid landscapes will elude a useful scientific understanding of semi-arid landscapes and will preclude wise landscape management policies as long as semi-arid fluvial ecosystems in general, and ephemeral streams in particular, remain poorly understood. In Chapter One, I characterize a thunderstorm-generated spate that occurred on July 17, 1991 through an ephemeral stream channel that drained a 76 ha portion of the Sierra Ladrones Study Basins (SLSB), located at the Sevilleta LTER site. Ammonium-N concentration in stream water remained near that in rain water throughout the spate. Nitrate-N concentration was higher in stream water than in rain water; peak concentrations occurred at the onset of flow. Soluble reactive phosphorus concentrations in stream water peaked later during high flow. Stream pH was higher than rain pH and tended to increase during the spate. Dissolved organic forms of carbon, nitrogen, and phosphorus; totals of dissolved solids, nitrogen and phosphorus; conductivity; and sulfate-S all showed a pronounced pulse in the organic-rich bore water. In Chapter Two, I describe how rainfall properties and geomorphic factors over a five year period combined to produce gradients in flow extent and in flow frequency along ephemeral channels draining areas of less than 1 ha to about 190 ha within the SLSB. And I describe how this underlying hydrologic template affects the downstream movement of organic materials. Rain occurred on only 19% of all days between 1990 and 1993. With a bias for light rain, 95% of the storms in the SLSB were not productive or intense enough to produce streamflow. Flow was highly episodic, more frequently occurring in channels draining rocky, headwater source areas than in lower channels where surface flow was usually absorbed before it reached the base of the 190 ha SLSB. CPOM retention along the ephemeral stream profile was greater in rocky, upstream reaches than in sandy, middle reaches, where doweis traveled nearly 300 rn. Retention was complete in downstream reaches where surface flow ceased. In Chapter Three, I investigated hydrologic and suspended sediment responses of the Rio Puerco basin, a 1.6 million hectare tributary basin of the Rio Grande that intersects the Sevilleta L TER site in central New Mexico, to changes in global atmospheric circulation related to the Southern Oscillation phenomenon. Responses generally depended on the magnitude of the Tahiti - Darwin Southern Oscillation Index. Precipitation during October - May increased in El Niño years and decreased in La Niña years. Discharge in the upper portions of the river increased by 900% during October-January of El Niño years, declined to near normal during February - May, and declined further to 23% of normal during the July - September thunderstorm season. Concurrently, discharge and suspended sediment load near the confluence with the Rio Grande remained near normal during October -January, while discharge increased 790% of average and suspended sediment load increased to 400% of average during February - May. Discharge returned to normal levels during the following summer, while suspended sediment load decreased to 22% of normal. During October - January of La Niña years, discharge remained near normal throughout the river. But, in the near absence of spring snow melt during February - May of La Niña years, discharge in both the upper and lower basins decreased by 93%, while suspended sediments entering the Rio Grande decreased by over 99%. Discharge and suspended sediments returned to normal by the summer of La Niña years. In summary, variability in cool season precipitation - a product of changes in global atmospheric circulation patterns - is followed by complex, seasonal evolution of discharge and suspended sediment responses in the Rio Puerco basin.

Project Sponsors

The Sevilleta LTER Program (NSF Grant BSR 88-11906), the Sevilleta Research Experiences for Undergraduates Program (NSF Grant BBS-9100740), the Sevilleta L TER Program (NSF Grant BSR 88-11906), the Sevilleta Research Experiences for Undergraduates Program (NSF Grant BBS-9100740), Sigma Xi - the Scientific Honor Society, the Sevilleta LTER Program (NSF Grant BSR 88-11906), and the Sevilleta Research Experiences for Undergraduates Program (NSF Grant BBS-9100740)

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Manuel Carl Molles, Jr.

Second Committee Member

Clifford N. Dahm

Third Committee Member

Clifford Smeed Crawford

Fourth Committee Member

MIchael E. Campana

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