Salinity contributions to groundwater from animal farming are a significant concern worldwide, particularly in arid and semi-arid regions with irrigated forage crops and intense animal farming. We compare measured groundwater salinity contributions from animal manure storage lagoons, animal holding areas, and forage fields managed with animal manure to those from other agricultural crops for a semi-arid, irrigated region in California with a high density of dairy facilities. We compare groundwater salinity in different groundwater regions. Salinity from manured field recharge is comparable between regions at an average of 1.5 mS/cm, while lagoon and corral impacts are significantly lower in a deep groundwater table region than in the vulnerable very shallow groundwater table region. Field mass balance of salinity inputs and root zone salt modeling results provide acceptable bulk estimates of salinity contributions to groundwater, although such estimates tend to underestimate measured groundwater salinity. Salinity is also shown to be highly aquifer depth-dependent. Recent agricultural activities increase salinity levels in shallow groundwater five- to ten-fold compared to older, deeper groundwater. To assess long-term groundwater quality impacts, we have modeled an extensive alluvial basin to assess salinity changes in the deeper aquifer over the next millennia. Significant heterogeneity in the alluvial aquifer system was explicitly modeled. We show that the extensive interconnectedness of coarser-grained sediments can accelerate downward movement of shallow salinity, thus shortening the time to excessive salinization of deeper aquifer sediments that are currently pumped for irrigation, domestic, and municipal water use.
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