Tracing the Movement of Irrigated Effluent into an Alluvial Gravel Aquifer

Abstract

Three microbial tracers -Escherichia coli J6-2, a somatic coliphage (ØESR1) and endospores of Bacillus subtilis var. niger NCIB 8649 tracer strain JHI -were added to effluent flood irrigated onto border dyke strips at a sewage treatment plant near Christchurch, New Zealand. All three tracers, and three effluent indicators -faecal coliforms, F-RNA phages, and chloride -were recovered in a bore, approximately 100 m downstream. A simple spatial model was applied to the breakthrough curves (BTCs) in the bore, using a series of hypothetical "entry points" in the strips. This analysis indicated effluent transport velocities through the 16.8 m deep vadose zone of between 15.7 and 39.2 m hr −1 . The shapes of the BTCs for the microorganisms and chloride were very different, suggesting that they reached the groundwater table via two pathways: -both underwent rapid transport to the groundwater though macropores, but chloride also underwent far slower (matrix) transport though micropores. The BTC shapes also suggested transport velocities in the vadose zone of E. coli J6-2 > B. subtilis JH1 endospores > phage ØESR1, which is consistent with the theory of pore size exclusion, based on particle size. Reductions in microbial concentrations were ≈100 times greater than for chloride, and occurred rapidly, suggesting that up to 99% of the microorganisms underwent early exclusion from macropore flow and were removed during matrix flow. Nevertheless, the results show that substantial numbers of bacteria and viruses will still reach the groundwater through macropores beneath effluent irrigation schemes located on alluvial gravel formations.

Biodiversity, functional roles and ecosystem services of groundwater invertebrates

“…Some microbes reached the aquifer 30 m down-gradient of the disposal site within 10 h of irrigation. Highest concentrations of the tracers reached this well after 15 h, and persisted for 80 h (Sinton et al 1997(Sinton et al , 2005. Horizontal transport of these tracers indicated groundwater velocities of up to 8 m/h (Martin and Noonan 1977).…”

“…Using bacteria and bacteriophages as tracers, effluent and its associated POM and DOC was found to percolate from the ground surface through highly porous, poorly sorted alluvial gravels into the aquifer some 12 m below the ground surface (Sinton et al 1997(Sinton et al , 2005. Some microbes reached the aquifer 30 m down-gradient of the disposal site within 10 h of irrigation.…”

“…Sinton et al 2005), groundwater ecosystem services also are implicated in this natural, downstream remediation of groundwater due to the very high numbers of typically rare stygofaunal species along this gradient. Large numbers, notably crustaceans up to 20 mm long, occurred in these wells at Templeton, with numbers more than ten times higher immediately downstream of the effluent disposal area, compared with upstream or further downstream (Sinton 1984;Scarsbrook and Fenwick 2003).…”

Spatially Resolved Characterization of Water and Ion Incorporation in Bacillus Spores

“…A number of studies have suggested that nongenetic identifiers, such as elemental and isotopic signatures, can potentially be used to identify the means, geographic location, and approximate date of production of biological agents (13,21,25,26,41,55). Such nongenetic markers can also extend the utility of bacterial spores as environmental tracers to study the fate and transport of biological materials in natural environments (23,24,46). In order to establish the utility of elemental and isotopic signatures for microbial forensics and environmental microbiology, it is necessary to know if and how the elemental and isotopic compositions of bacterial spores can be altered during and after production.…”

Animal Waste, Water Quality and Human Health

“…The phages were easily remobilised, however, by enhanced flow which suggests continued viability whilst adsorbed to the sandy aquifer matrix. Sinton et al (2005) reported vertical microbial tracer transport from areas of slurry spreading to a 16.8 m deep aquifer in New Zealand. The breakthrough curves suggested travel speeds of between 15.7 and 39.2 m.hr Table 5.6).…”