Date of Award:

1993

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Range Science

Advisor/Chair:

James Dobrowolski

Abstract

Microphytic crust influences on selected physical and hydrologic soil properties were examined at one location in Capitol Reef National Park, Utah. Designed experiments were conducted in a sandy loam soil where microphytic crusts were present without the concomitant development of confounding physical or chemical soil conditions. Three treatments were used for all experiments: control, chemically killed (microphytes killed but left in place), and scalped (microphytic crusts mechanically removed).

A portable wind tunnel was used to deter-nine if microphytic crusts contribute to soil stability and reduce the erosive effect of wind. Significantly lower threshold friction velocity and greater wind-entrained material were recorded in the scalped treatment than in the control or chemically killed treatments. These results are evidence that microphytic crusts significantly contribute to reducing the erosive force of wind at this site.

A dripper system was used in situ to determine if microphytic crusts influence effective saturated hydraulic conductivity. There were no significant differences among treatments. This result is evidence that microphytic crusts have a minimal influence, if any, on effective saturated hydraulic conductivity at this site.

Rainfall simulation was used to determine if microphytic crusts influence hydrologic properties of time to ponding, time to runoff, and infiltration capacity. Rainfall was simulated for 90 minutes after runoff began. Simulated rainfall also was used to determine if microphytic crusts influence interrill erosion. Time to ponding and time to runoff were significantly shorter in the control and chemically killed treatments than in the scalped treatment. However, infiltration capacity was not significantly different among treatments during any five-minute period within the 90 minutes that runoff occurred. Microphytic crusts apparently reduce initial entry of water into the soil profile; however, once infiltration has begun, they do not inhibit or enhance infiltration capacity at this site.

Interrill erosion was nearly constant from the control treatment throughout simulated rainfall events. Significantly greater interrill erosion occurred in the chemically killed treatment compared to control and scalped treatments. Interrill erosion in the scalped treatment was significantly greater than in the control treatment after 30 minutes and through 90 minutes. These results are evidence that microphytic crusts, when composed of living, undisturbed microphytes, resist the erosive effect of rainfall and contribute to the soil stability of this site.