APPLYING NEW YORK CITY BIOSOLIDS ON A WEST TEXAS RANCHEIGHT YEARS OF OPERATION AND RESULTS
Abstract:New York City biosolids have been transported by railcar to Sierra Blanca Ranch and beneficially land applied to arid rangeland since July 1992. The Sierra Blanca Ranch property, consisting of approximately 90,000 acres of native grassland and shrubland, was in a somewhat degraded condition when the biosolids application program was initiated. This was the result of long-term overgrazing, overhunting, drought, poor watering facilities and overall poor range management.
The primary goals of the Sierra Blanca Ranch biosolids-recycling project were:
To assess the benefits of land application of biosolids in arid environments.
To research environmental conditions and the effects of biosolids on air, water, soil and vegetation in arid environments.
To use biosolids as a means of arid grassland rehabilitation and improved productivity for enhanced wildlife and livestock production.
To significantly enhance the world's database on use of biosolids on arid and semiarid lands and to prove the environmental and economic advantages of such projects.
This project has shown that when properly managed, arid rangeland offers environmental benefits and lower risk potential for biosolids reuse than for most agronomic reuse projects in high rainfall or irrigated regions of the country. These advantages include:
Lower potential for surface runoff from application sites.
High soil temperatures, dry surface conditions and maximum sunlight offer rapid destruction of pathogens and other organic compounds.
High ET rates, low rainfall and deep groundwater minimize the potential for leaching of any pollutant to underlying aquifers.
High soil pH and cation exchange capacity maximizes heavy metal immobilization and minimizes plant availability.
Air quality issues such as wind erosion; airborne biosolids particulate and pathogen transport is often raised as potential health concerns in arid rangeland application projects. These issues were addressed at Sierra Blanca Ranch through research studies conducted by several university scientists. These studies concluded that:
Applying biosolids reduces wind erosion by roughening the soil surface and provides organic mulch and enhanced vegetative density, which act as windbreaks and filters of particulate matter.
Air samples collected downwind of biosolids application areas averaged 54.6 percent less organic matter and 17.6 percent less particulate matter than did sites unwind of the application areas.
The dry and intense sunlight conditions of the application areas minimize survival of microbial pathogens in applied biosolids and in airborne transmissions.
Biosolids application under these conditions should cause no significant changes in biological air quality at off-site locations near the application areas.
Biosolids have enhanced and rehabilitated arid rangeland at the site with no apparent adverse environmental consequences. After eight years of operation and four applications of biosolids, there have been no significant changes in soil quality. Biosolids have increased soil infiltration, reduced rainfall run-off and lowered soil temperatures by 20 to 30 percent during intense summer heat.
There has been no increase in heavy metal content of the vegetation treated with as much as 40 tons per acre of biosolids. Nitrate nitrogen increases slightly during the growing season but returns to background levels by the end of the season.
Vegetation production and plant quality have been significantly increased on the ranch with biosolids application. Increase in grass productivity of up to 150 percent has been measured on the ranch, even in years with below normal rainfall. This increase, along with improved forage quality, have significantly improved wildlife reproduction and survival rates at the site.
Research and studies conducted over the past eight years at Sierra Blanca Ranch have demonstrated the benefits and safety of biosolids recycling on arid rangeland. This project has shown that arid rangeland can be economically enhanced with biosolids while creating jobs and improving the tax base for local schools and governments.
Document Type: Research Article
Publication date: January 1, 2001
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