CHASING VADOSE ZONE NITRATE: CASE STUDIES IN NEBRASKA. Daniel Snow, Ph.D. University of Nebraska Water Sciences Laboratory

Transcription

1 CHASING VADOSE ZONE NITRATE: CASE STUDIES IN NEBRASKA Daniel Snow, Ph.D. University of Nebraska Water Sciences Laboratory

2 Vadose zone monitoring provides an early warning and early detection Complimented by groundwater monitoring programs used to detect, observe, regulate, and control ground water quality University of Nebraska Vadose Core Site

3 OK JUST WHERE IS THIS VADOSE ZONE?

4 What questions need to be answered? Variation of nitrate-n concentrations with depth? Changes in vadose nitrate over time? Estimated transport rates? Relationship to nutrient-water management? -1 Effect of sediment lithology? Potential for nitrate transformation? Water Table vadose nitrate-n Sediment composition (hydraulic and mineral properties) Moisture, ph, ammonia-n, carbon -3-4 Ground water nitrate-n -5 VADOSE ZONE MEASUREMENTS Nitrate-N (mg/l)

5 -1 Water Table vadose nitrate-n -3-4 Ground water nitrate-n Nitrate-N (mg/l)

6 Irrigation Water Application plus Precipitation = ~26 Water -1 Water Table vadose nitrate-n VADOSE ZONE MEASUREMENTS -3-4 Ground water nitrate-n Look at each parameter individually and then put everything together Nitrate-N (mg/l)

7 MSEA Vadose Zone Nitrogen Fall 1994 Gravimetric Water Content (g/g) Vadose Zone NH4-N (µg/g) Dry Weight NO3-N (µg/g) Pore Water NO 3 N (mg/l) ~15 lbs/acre

8 HASTINGS WELLHEAD PROTECTION AREA

9

10

11

12

13 Hastings Wellhead Protection Area

14 COMPARISON OF 2-YEAR MODELED TIME OF TRAVEL TO EXTENT OF GROUNDWATER NITRATE

15 211 CORING LOCATIONS COMPARED TO EXTENT OF GROUNDWATER NITRATE

16 LAND USE IRRIGATION PRACTICES

17 Thirty-six 6 foot long cores collected using direct-push technology Sites selected based on availability, land use, and cropping history Provided an initial baseline of vadose zone in wellhead protection area to evaluate whether improved water and nutrient management effectively control nitrate leaching 211 SURVEY OF VADOSE ZONE NITRATE

18 Crops: estimated pore water nitrate-n ranged between 5-5 mg/l, or lbs/acre Residential/abandon livestock areas generally lower, 1-25 mg/l, or 1-4 lb/acre except for 1 yard Assumed average 2.5 foot/year transport rate to predict approximate time of loading/leaching event ~2-3 years 211 OBSERVATIONS

19 Residential Area HC-3A HC-3A ± ± ± ± NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) ±.5-1.2± ± ± Moisture Content (g/g) NH 4 -N (ug/g) Moisture Content (g/g) NH 4 -N (ug/g) Total NO 3 -N 29 lbs/acre Total NO 3 -N 6 lbs/acre Bulk Density assumed=1.33 g/cm 3 Average Bulk Density=1.57 g/cm 3

20 HC-11E Gravity Irrigated Corn Site HC-11E ± ± ± ± NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) ± ±.6.46± ± Moisture Content (g/g) NH 4 -N (ug/g) Moisture Content (g/g) NH 4 -N (ug/g) Total NO 3 -N 524 lbs/acre Top 6 = 23 lbs/acre Total NO 3 -N 41 lbs/acre Bulk Density assumed=1.33 g/cm 3 Average Bulk Density=1.35 g/cm 3

21 HC Pivot Irrigated Corn Site HC ± ±4.9 3.± ± NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) NO 3 -N (ug/g) Pore Water NO 3 -N (mg/l) ±.9.72± ± ± Moisture Content (g/g) NH 4 -N (ug/g) Moisture Content (g/g) NH 4 -N (ug/g) Top 45 NO 3 -N 56 lbs/acre Total NO 3 -N 315 lbs/acre Total NO 3 -N 83 lbs/acre Bulk Density assumed=1.33 g/cm 3 Average Bulk Density=1.41 g/cm 3

22 Central Platte NRD

23 Keech, C.F. and Dreezen, V.H Availability of ground water in Hall County, Nebraska. U.S. Geological Survey Hydrologic Investigations Atlas HA-131. Steele, G.V., Gurdak, J.J., and Hobza, C.M., 214, Water movement through the unsaturated zone of the High Plains Aquifer in the Central Platte Natural Resources District, Nebraska, 28 12: U.S. Geological Survey Scientific Investigations Report , 51 p., plus tables and app.,

24 DH-32 DH-32 NO3-N Pivot Irrigated, Corn/Soybean Rotation DH-32 Pore Water NO3-N Feet Below Surface Feet Below Surface Average = Average = NO3-N (ug/g) Porew Water NO3-N (mg/l) DH-32 Gravimetric Water Content DH-32 NH4-N Feet Below Surface -4-6 Feet Below Surface Average = Average = NH4-N (ug/g) 1996 NO 3 -N 68 lbs/acre 216 NO 3 -N 2 lbs/acre

25 DH-47 Pivot Irrigated, Corn/Soybean Rotation DH-47 NO3-N DH-47 Pore Water NO3-N Feet Below Surface -4-6 Feet Below Surface NO3-N (ug/g) Concentration (mg/l) DH-47 Gravimetric Water Content DH-47 NH4-N Average = Average = 28.8 Feet Below Surface -4-6 Feet Below Surface Average = Average = NH4-N (ug/g) 216 NO 3 -N 445 lbs/acre

26 DH-49 Gravity Irrigated, Corn/Soybean Rotation DH-49 NO3-N DH-49 Pore Water NO3-N Feet Below Surface -4 Feet Below Surface Average = Average = NO3-N (ug/g) Pore Water NO3-N (mg/l) DH-49 Gravimetric Water Content DH-49 NH4-N Feet Below Surface -4-6 Feet Below Surface Silty Clay Loam 1-1 Silty Clay Loam 1-14 Silt Loam 14-3 Silty Clay Loam 3-33 Clay Clay Loam 38-4 Sandy Loam 4-45 Sandy Clay Clay Average = Average = Sandy Loam NH4-N 67-7 Silty Clay 216 NO 3 -N 612 lbs/acre

27 35 Comparison of Average Vadose N Residential Gravity Irrigated Corn Pivot Irrigated Corn Pivot Irrigated Corn/Soybeans Pivot Irrigated Corn/Soybeans NO3N Average (ug/g) Porewater Average (mg/l) NH4N Average (ug/g) Gravity Irrigated Corn/Soybeans

28 NO3N versus Porewater NO3N (mg/l) y = 1.19x R² = Possible relation between sediment NO 3 N and porewater NO 3 N

29 DH-32 NO3-N Feet Below Surface Is this conversion helpful? NO3-N (ug/g) NO 3 -N Concentration Bulk Density µg NO 3 -N g soil g NO 3 -N 1 lbs NO 3 -N 1,233,481,855 cm 3 soil g soil cm 3 1,, µg NO 3 -N454 g NO 3 -N soil 1 acre-ft soil

30 1 216 Vadose Total N (lbs/acre) (Excluding DH19) Residential Gravity Irrigated Corn Pivot Irrigated Corn Pivot Irrigated Corn/Soybeans Pivot Irrigated Corn/Soybeans Gravity Irrigated Corn/Soybeans

31 Nitrate fate and transport occurs in a geologic framework Long term evaluation of changing N, H 2 O and land use practices Total N Loading = lost nitrogen + moisture + lithology +? Collecting and presenting measurements across time and space SUMMARY VADOSE WORK IN PROGRESS

32