Concentrated dissolved minerals in naturally occurring water accessible to livestock grazing semi-arid landscapes can negatively influence animal productivity and well being. Twelve indicators of water quality (Ca, Cl, F, Fe, Mg, Mn, Na, Nitrate-N, pH, SO4, total dissolved solids (TDS) and temperature) were measured at 12 reservoirs accessed by livestock for water over 7 years from 2009 through 2015 at the 22,257 ha USDA-ARS Fort Keogh Livestock and Range Research Laboratory, Miles City, Montana to estimate variation. Samples were collected twice yearly in 2 seasons, May (wet) and September (dry). Year, season, and their interaction was analyzed as a 7?2 factorial arrangement of treatments. A year by season interaction (P < 0.05) was found for F, Fe, Mn, Nitrate-N, pH, and temperature. Concentrations of Na, SO4, and TDS differed by year and by season (P < 0.05). Concentrations were higher in the dry season in years 2011, 2012, and 2015 for SO4 and TDS and 2012 and 2015 for Na. Concentrations of Ca and Mg were different between years (P < 0.05). Concentrations were highest for Ca and Mg in 2011 and 2012. Chloride concentrations were not different between years and seasons. Higher and then lower precipitation in 2011 followed by below average precipitation in 2012 and below average precipitation in 2015 was associated with elevated mineral concentrations in the reservoirs. Average concentrations of Ca, Cl, Mg, nitrate-N, pH and TDS levels across sources did not exceed the upper maximum intake level for beef cattle. In contrast, concentrations of F, Fe, Mn, Na, and SO4 exceeded upper levels for beef cattle, implicating these minerals may negatively impact range beef cattle performance.
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