Science Inventory

MICROTOPOGRAPHY AND GRAZING IN DESERT RANGE LAND: A LESSON IN STATISTICS VERSUS REALITY IN THE FIELD

Citation:

Nash, M S. MICROTOPOGRAPHY AND GRAZING IN DESERT RANGE LAND: A LESSON IN STATISTICS VERSUS REALITY IN THE FIELD. Presented at Landscape Ecology Branch (LEB) Seminar Series, Las Vegas, NV, November 12, 2003.

Impact/Purpose:

Overarching Objectives and Links to Multi-year Planning

This research directly supports long-term goals established in ORD's multi-year research plans related to GPRA Goal 2 (Water Quality) and Long Term Goal WQ-2 Assessment of aquatic systems impairment. Relative to the GRPA Goal 2 Water Quality multi-year plan, this research will "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors" and "provide the tools to restore and protect aquatic ecosystems and to forecast the ecological, economic, and human health outcomes of alternative solutions" (Water Quality Long Term Research Goals 2 and 3).

Subtask 1 - Impervious Surface Evaluation

This subtask addresses the development of impervious surfaces estimators for local to regional scale assessments of watersheds and their landscape relationship to stream ecology. The amount of impervious surface area in a watershed is a key indicator of landscape change. As a single variable, it serves to integrate a number of concurrent interactions that directly influence a watershed's hydrology, stream chemical quality, and in-stream habitat. It is our working hypothesis that impervious surface area within a watershed, as an independently mapped predictor variable, can be used to generally track a range of watershed ecological parameters (e.g., NPS pollution, biological integrity, TMDLs) that are of concern to local, state and federal environmental managers. The specific objectives of this research are: 1) to quantitatively evaluate the varying remote sensing methods used in mapping impervious surfaces at multiple scales (local to regional), and 2) to relate the varying levels of impervious surface area in watersheds to the environmental condition of multiple water resource endpoints such as streamflow, temperature, and biota.



Subtask 2 -- Landscape Assessments and Evaluations of Best Management Practices: Watershed Demonstrations

Best Management Practices (BMP) encompass a range of strategies to reduce water pollution related to urban and agricultural activities. EPA, through Section 319(h) of the Clean Water Act [PL 92-500], provides grants to states to implement BMPs in areas with suspected or known water-quality problems. Grants for implementation of BMPs have not been tracked or monitored to document their effectiveness. Although effectiveness can be measured in many different ways, one straightforward but important measure is existence. Implementation of BMPs is a voluntary process and actual implementation is not always executed (Nowak 1992). The primary objective of this project is to assess the feasibility of using high-resolution aerial photography and other remotely sensed data to identify the existence of BMPs that were planned under the 319 program. An additional objective is to evaluate the effectives of BMPs implemented by examining monitoring data from about 5 sites in the OW National NPS monitoring system.

There are several potential benefits to determining the feasibility of using the aerial photography for identifying BMPs: 1) since BMP implementation is voluntary and some may not be implemented due to a variety of social and economic factors (Nowak 1992), remote detection of BMPs can provide data to estimate the ratio of BMPs implemented to BMPs planned; 2) remote detection of BMPs provides validation data that can be input into EPA's Grants Reporting and Tracking System (GRTS), and 3) remote monitoring of BMPs over time could be used to develop data on BMP lifespans, providing important data related to social- and cost-effectiveness.

Subtask 3 -- TMDL Non-point Source Assessment Tool

This subtask involves the development of a software tool to assess the potential risks of water bodies to exceed TMDL threshold values established by States. When completed, the tool will allow the user to evaluate watersheds over entire regions. The too

Description:

This presentation summarizes two experiments on the effects of grazing on soil microtopography in a Chihuahuan Desert rangeland. In the first experiment, we measured the effect of three consecutive years of short duration <48 hours per year) intense grazing (20--40 yearling cows per hectare) and shrub removal on microtopography. Microtopography were measured in 18 plots (treatments). Treatments were a combination of two factors: (I) three levels of grazing (winter-grazed, summer-grazed, and not grazed), and (2) two levels of habitat structure (shrubs-removed and shrubs-intact). Mesquite (Prosopis glandulosa) shrubs were removed from half of the plots (9 out of 18 plots ). In the second experiment, three grazing gradients from water point, measurements were made using a modified erosion bridge at three distances (50 m, 450 m, and 1050 m) from water points.

From Experiment I, we found that the average height of the micromounds, the average depths of intermound depressions, and the number of micromounds were significantly reduced on the grazed plots. There were significant differences in average micromound heights and intermound microdepression depths attributable to the season of grazing. Microtopography was significantly reduced on grazed plots from which shrubs were removed, compared to ungrazed plots, and grazed plots with shrubs present. Grass canopy reduction, and destruction of the micromound structure in a short duration, plus intense grazing, results in erosion of micromounds and in-filling of intermound depressions. The loss of microtopography coupled with reduction in vegetation height and cover resulting from short.
From Experiment 2, we found that microtopography of plots at 450 m from water was not significantly different from that recorded at 50m. Microtopography of plots that were 1050 m from water points was significantly different from that of plots nearer water points. Strong correlation between microtopography and the cover of long-lived perennial grasses (R 2 = 91% ) was found, such dependence could be used assessing the trend in organic matter content that is in concordance with that of microtopography .Loss of microtopography from the impact of livestock in biospheres exacerbates erosion processes and contributes to desertification.

Record Details:

Record Type:DOCUMENT( PRESENTATION/ ABSTRACT)
Product Published Date:11/12/2003
Record Last Revised:06/06/2005
Record ID: 74946