The Influence of Vegetation in Riparian Filterstrips on Coliform Bacteria: II. Survival in Soils

Survival of total and fecal coliform bacteria was measured in the 0 to 5, 5 to 15, and 15 to 30 cm soil depths at 1, 3, 7, 14, and 90 to 120 d after swine (Sus scrofa) wastewater application to riparian filterstrips in southern Georgia during each season of the year. Vegetative treatments evaluated were: (i) 20 m grass-10 m forest, (ii) 10 m grass-20 m forest, and (iii) 10 m grass-20 m maidencane (Panicum hemitomon Schuh.). During winter, spring, and summer vegetation type in riparian filterstrips did not affect survival of total and fecal coliform bacteria. Total and fecal coliform bacterial numbers were usually higher in the top 0 to 5 cm of soil than in the 5 to 15 and 15 to 30 cm soil depths in all treatments. Total and fecal coliform numbers in the 0 to 5, 5 to 15, and 15 to 30 cm depths declined approximately 10-fold every 7 to 14 d after waste application in all seasons of the year. At 90 to 120 d after waste application, total and fecal coliform numbers in the three soil depths did not differ from riparian filterstrips that did not have animal waste applied. Total coliform bacteria in the O to 5, 5 to 15, and 15 to 30 cm soil depths correlated with temperature and moisture in a curvilinear relationship (r2 = 0.80 , 0.77, and 0.64, respectively). Fecal coliform bacteria in 0 to 5, 6 to 15, and 16 to 30 cm of soil also correlated with temperature and moisture in a curvilinear relationship (r 2 = 0.56 , 0.53, and 0.53, respectively). T HE NUMBER AND SIZE of animal production operations in the USA has been steadily increasing for several decades. Large volumes of animal waste are generated as waste water from urine and animal washing and as semi-solid or solid manure. Because advanced waste water treatments are cost prohibitive for animal waste (USEPA, 1998; Thomas and Law, 1977; Pratt et al., 1977), the economically viable alternative for manure disposal is land application. Land application of animal waste is a means of disposing of the waste and using it as a fertilizer to supply nutrients to crops. Land application of animal waste is a major source of microorganisms pathogenic to humans (Fraser et al., 1998; Howell et al., 1996; 1995; Mawdsley et al., 1995). Liquidwaste discharge into soil follows natural ground water drainage patterns and may contaminate adjoining bodies of surface water. These same bodies of water may be used as sources of drinking water and/or for recreational activities. Therefore, it is critical to keep these lakes and streams free of intestinal pathogens. The movement of animal waste into surface and4ground water has been increasingly cited as a major James A. Entry, USDA-ARS, Northwest Irrigation and Soils Research Lab., 3793 North 36(X) East, Kimberly, ID 83443. Robert K. Hubbard, USDA-ARS, Southeast Watershed Research Lab., P.O. Box 946, Tifton, GA 31793-0748. Janice E. Thies, Cornell Univ., Dep. of Crop and Soil Science, 722 Bradfield Hall, Ithaca, NY 14853. Jeffry J. Fuhrmann, Dep. of Plant and Soil Sciences, Univ. of Delaware, Newark, DE 19717-1303. Received 14 June 1999. *Corresponding author ([email protected] ). Published in 29:1215-1224 (2000). factor contributing to movement of nutrients and pathogenic microorganisms into surface and ground water (Mawdsley et al., 1995; Khaeel et al., 1980). The potential for movement of pathogenic bacteria in surface runoff and ground water will in part depend on soil type, climatic and soil conditions, method and amount of manure disposal, and the amount and type of vegetation growing on the site (Entry et al., 2000; Howell et al., 1996; Maswdsley et al., 1995; Canale et al., 1993; Van Donsel et al., 1967). The companion study (Entry et al., 2000) found that land application of swine waste to riparian vegetation increased total and fecal coliform concentrations in soil water and shallow ground water from 10to 1000-fold. Time and expense in testing for microorganisms pathogenic to humans have led to the use of indicator bacteria of enteric origin to estimate die-off of pathogens in soil and water. It is generally accepted that total and fecal coliform bacteria will he affected in the same manner as human pathogens in soil and water (Fujioka, 1997; Toranzos and McFeters, 1997: Greenberg et al., 1992). Riparian vegetation acts as a natural filter and removes nutrients and other contaminants through both groundand surface-water pathways (Hubbard et al.. 1998; Snyder et al., 1998; Jordan et al., 1993). However, there has been little research on the effectiveness of forest riparian filterstrips in protecting stream waters from coliform bacteria. Coyne et al. (1998, 1995), Walker et al. (1990) and Young et al. (1980) concluded that 10 m wide grass filterstrips reduced the amount of fecal coliform bacteria in surface runoff from areas where poultry and dairy waste water have been applied by as much as 70%. These authors, however, concluded that 10 m wide grass filterstrips are often inadequate in bringing animal waste water contaminated with fecal coliform bacteria into compliance with water quality standards. The ability of pathogenic bacteria to survive in the soil environment increases the probability of water contamination after rainfall events. Pathogen survival time in the upper soil varies from 4 to 160 d (Abu-Ashour et al., 1994; Sjogren, 1994). Survival of pathogenic bacteria first reflects the organism's ability to respond to nonparasitic and adverse environmental conditions. Obligate parasites usually only live a few minutes outside the host, but many pathogenic organisms can live in the soil for months (Sorber and Moore, 1987). Several factors influence the survival of pathogens in soil after waste materials are applied. Soil moisture seems to be the most important of these factors (Sjogren, 1994; Crane and Moore, 1986). Survival of bacteria that are pathogenic to humans in soil increases when the soil is moist. Soil temperature also exerts a major influence on the survival of pathogenic bacteria. Extremely hot (>28°C)