Spatio-temporal impacts of dairy lagoon water reuse on soil: Heavy metals and salinity

Authors: Corwin, Dennis; AHMAD, HAMAD RAZA - University Of Agriculture - Pakistan

Submitted to: Environmental Science: Processes & Impacts
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 8/13/2015
Citation: Corwin, D.L., Ahmad, H. 2015. Spatio-temporal impacts of dairy lagoon water reuse on soil: Heavy metals and salinity. Environmental Science: Processes & Impacts. 17:1731-1748. doi: 10.1039/C5EM00196J.

Interpretive Summary: Greater urban demand for finite water resources, increased frequency of drought resulting from erratic weather, and increased pressure to reduce drainage water volumes have intensified the need for degraded water reuse. Dairy lagoon water is degraded water that is often in large supply on concentrated animal feeding operations (CAFOs), but the impact and sustainability of its reuse on soil has not been evaluated at field scale. The objective of this study is to monitor the impact of dairy lagoon blended with recycled water on a 32-ha field located near San Jacinto, CA, over a 4-year time period using a monitoring approach developed by Corwin and colleagues at the U.S. Salinity Laboratory referred to as apparent soil electrical conductivity directed sampling. Salinity, soil pH, trace elements (i.e., As, B, Mo, and Se), and heavy metals (i.e., Cd, Cu, Mn, Ni, and Zn) were monitored from 2007 to 2011.Results of the monitoring demonstrated the practicality of reusing dairy lagoon water for agricultural applications. No short-term environmental or agronomic threats were identified. However, the results focused attention on the potential long-term threat of Cu to detrimental impacts on groundwater and the accumulation of Cd, Mn, and Ni in the soil profile, providing a potential future source for leaching. Trace elements were not a concern, except B, which should be monitored for potential long-term agronomic impacts due to its accumulation in soil. Even though salinity, trace elements, and heavy metals did not accumulate or leach over the 4 years of the study in amounts that would be regarded as an immediate environmental threat, the long-term sustainability of dairy lagoon water reuse hinges on regular monitoring of salinity, sodium, B, Cd, Cu, Mn, and Ni to provide feedback for management. California Department of Food and Agriculture, land and water resource managers, producers, extension specialists, and Natural Resource Conservation Service field staff are the beneficiaries of this demonstration of the sustainability of dairy lagoon water reuse.

Technical Abstract: Diminishing freshwater resources have brought attention to the reuse of degraded water as a water resource rather than a disposal problem. Dairy lagoon water is degraded water that is often in large supply on concentrated animal feeding operations (CAFOs), but the impact and sustainability of its reuse on soil has not been evaluated at field scale. The objective of this study is to monitor the impact of dairy lagoon blended with recycled water on a 32-ha field located near San Jacinto, CA. Monitoring and assessment were based on spatial soils data collected at sample locations directed by variability in geo-referenced ECa measurements taken with electromagnetic induction equipment. Soil samples were taken at depth increments of 0-0.15, 0.15-0.3, 0.3-0.6, 0.6-0.9, 0.9-1.2, 1.2-1.5, and 1.5-1.8 m at each of 28 sample sites on 7-11 May 2007 and again after 4 years of irrigation with the blended degraded waters on 31 May – 2 June 2011. Chemical analyses of the soil samples focused on characterizing the initial spatial variability of salinity as measured by electrical conductivity of the saturation extract (ECe), pHe (pH of the saturation extract), SAR (sodium adsorption ratio), trace elements (i.e., As, B, Mo, and Se), and heavy metals (i.e., Cd, Cu, Mn, Ni, and Zn) and monitoring their change during the 4-year study (2007-2011). Complex vertical and horizontal spatial patterns were found for ECe, pHe, SAR, all trace elements, and all heavy metals, which were a consequence of complex water flow and chemical interactions. From 2007 to 2011 results indicated a decrease in the mean values of pHe at all depth increments (0-0.15, 0.15-0.3, 0.3-0.6, 0.6-0.9, 0.9-1.2, 1.2-1.5, and 1.5-1.8 m) and a decrease in ECe and SAR above a depth of 0.15 m, but an increase below 0.15 m (i.e., 0.3-0.6, 0.6-0.9, 0.9-1.2, 1.2-1.5, and 1.5-1.8 m). All trace elements decreased over time except B, which increased throughout the 1.8-m profile. The heavy metals Cd, Mn, and Ni accumulated at all depth above 1.8 m, while Cu was readily leached from the 1.8-m profile over the four years. Zinc showed relatively little overall change over the 4 years. These results focused environmental concern on the potential long-term threat of Cu to detrimental impacts on groundwater and the accumulation of Cd, Mn, and Ni in the soil profile, providing a potential future source for leaching. Trace elements were not a concern, except for B. Even though salinity and the heavy metals did not accumulate or leach in amounts from 2007 to 2011 that would be regarded as an immediate environmental threat, the long-term sustainability of dairy lagoon water reuse hinges on close continuous monitoring to provide spatial feedback for management. The use of ECa-directed soil sampling to assess spatio-temporal chemical impacts was shown to be a viable field-scale monitoring tool to provide spatial feedback for managing the sustainability of degraded water reuse.