Geology, Land-use, and Water Quality: Lessons from Big Spring Bob Libra – State Geologist of Iowa Iowa Geological & Water Survey Iowa D.N.R. The rock sequence in the Turkey River Watershed: All units are aquifers except the Maquoketa Shales. The Cedar Valley, Silurian, and Galena rocks are particularly karst-prone. Karst Aquifers move LOTS of water! Geography and Geology of Big Spring ? BTLUW BTLUE VD24 BTLD BOOGD ? L23S L22T Dc05 T17 F08 F47 GL01 ? RC02 JSW TR01 N USA BIG SPRING BASIN 0 6 miles 0 10 km CLAYTON COUNTY GEOLOGIC MAP UNITS EXPLANATION SILURIAN Silurian dolomites (Blanding, Tete des Morts, Mosalem Fms.) Private well ORDOVICIAN Surface-water site Maquoketa Formation (Brainard Shale Member) Gaged tile-line site Maquoketa Formation Big Spring (Ft. Atkinson, Clermont, Elgin Members) Groundwater-basin divide Galena Carbonates (Dubuque, Wise Lake, Dunleith Fms.) Cross section C A B Groundwater ro Elevation G undwater Divide in Divide meters feet 400 1200 Q 1150 S nk o SU Sinkhole Area i h le Area Q k k e 1100 e Q Omf k e e r r Q e e C C r s Omf d C t r 1050 350 r r Q a e e w b Q v l o o mf i O H R 1000 S a Og w Omf n o le alluvium 950 l a f G Og r e of G ric t p al met 900 a To ena entio 300 w pot d n u o ocks 850 r ate r carbon G haly Og s shale 800 dp na O e le Sandston Ga St. Peter 250 750 of se p Ba Os 700 Osh 650 1 1/2 0 1 mile GEOLOGIC UNITS 1 1/2 0 1 kilometer Decorah, Platteville, Holocene alluvium Omb Maquoketa Formation Odp (stream deposits) Brainard Shale Member and Glenwood Fms. St. Peter Sandstone Q Quaternary deposits Omf Maquoketa Formation Osp undiferentiated loess, till, etc. Ft. Atkinson, Clermont, and Elgin Members Shakopee Formation SU Silurian dolomites Og Galena carbonate rocks Osh NO3 in water and N-Inputs to Big Spring Basin mg/L 3000 60 Payment-in-Kind 3000 set-aside program 2500 Fertilizer-N 50 2500 10 Big Spring 2000 40 Groundwater NO3 2000 3 -N 1500 30 3 NO Metric Tons-N Metric 1500 NO Tons-N 5 1000 20 1000 500 10 500 Manure-N (and Soil-N) 0 0 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 Graph with event at different watershed scales Big Spring Water Years 1982-2000 cm inches 50 NO3-N load 120 Annual Basin mg/L kg Precipitation 45 14 900,000 110 Annual FW Mean NO -N 40 3 100 12 750,000 Annual NO3-N Load 90 35 600,000 10 80 30 450,000 70 8 25 300,000 60 6 150,000 50 20 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01 4 0 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01 mcm ac-ft Atrazine load 60,000 µg/L kg 70 Annual Groundwater 10.0 70 Annual FW Mean Atrazine Discharge 60 50,000 5.0 60 Annual Atrazine Load 50 50 40,000 40 40 1.0 30,000 30 30 0.5 20 20,000 20 10 10 10,000 0.1 0 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01 Nitrogen Input Reductions Basin average fertilizer-nitrogen rates Average Yield Rotation All corn 1st-year corn 2nd-year corn Continuous Continuous after alfalfa after alfalfa corn corn yields Year .......................................lbs N/Acre........................................ Bushels/Acre 1981 174 123 160 178 128 1982 174 123 ... 178 138 1984 158 115 155 169 130 1986 147 96 ... 153 149 1987 149 84 121 157 141 1988 141 84 124 151 79* 1989 138 82 125 148 147 1990 123 66 121 145 145 1991 117 59 112 131 138 1992 117 ... ... 128 165 1993 115 55 117 124 110** * drought lowered yields in the basin and across Iowa ** frequent rains lowered yields in the basin and across Iowa Nitrate – Big Spring Groundwater Row – Crop: 45% 57% 64% 71% (1982) (1992) (2002) (2009) .