6-Soil_Water.pdf

Transcript

1. EES 140: Spring 2017 Kaizad F. Patel 1 EES 140 Spring 2017 Kaizad F. Patel Water Water potential Types of water Hydrologic cycle Erosion 2
2. EES 140: Spring 2017 Kaizad F. Patel 2 universal solvent soil air soil temperature evapo-transpiration (ET) biological utilization erosion 3 covalent bonds sharing of electrons 4 O: atomic number 8 8 electrons, 8 protons H: atomic number 1 1 electron, 1 proton
3. EES 140: Spring 2017 Kaizad F. Patel 3 Water is a polar molecule 5 electrons clustered around O partial charges Water is a polar molecule 6 hydrogen bonding
4. EES 140: Spring 2017 Kaizad F. Patel 4 Hydrogen bonding 7 cohesion attraction of water molecules for each other adhesion attraction of water molecules for other molecules 8 hydrophilic vs. hydrophobic
5. EES 140: Spring 2017 Kaizad F. Patel 5 Capillary Rise? 9 Capillary action height ∝ 1 radius 10 Soil texture and capillary action Greater capillary rise in clays Finer texture = smaller pores = more capillary action Capillary action is slower in clays than in sands
6. EES 140: Spring 2017 Kaizad F. Patel 6 11 potential energy of soil water difference in energy between soil water, and pure water at a reference elevation 12  t =  g +  h +  m +  o Gravitational potential Hydrostatic potential Weight of overlying water (positive potential) Matric potential Attractive forces (tension) between soil matrix and water (negative potential) Osmotic potential Effect of solutes; osmosis (negative potential) Dominant in saturated soils (below the water table) Dominant in unsaturated soils (vadose zone) Total water potential
7. EES 140: Spring 2017 Kaizad F. Patel 7 13 Water moves from a higher potential to a lower potential -0.1 bar -0.7 bar -0.75 bar -10 bar -200 bar 14 Soil Colloid Wilting Coefficient Oven-dry soil Water saturation -0.1 bar -31 bar -15 bar <-10,000 bar Macro and micropores filled with water Field Capacity Water from macropores drained Water present in micropores (capillary pores) Hygroscopic Coefficient Water held very tightly to soil colloid Moisture potential 0 bar Tension increases, Potential decreases
8. EES 140: Spring 2017 Kaizad F. Patel 8 15 Soil water: physical classification Soil Colloid Field Capacity Hygroscopic Coefficient Oven-dry soil Gravitational water Capillary water 16 Soil water: biological classification Soil Colloid Field Capacity Wilting Coefficient Superfluous water -0.1 bar -15 bar Available water Unavailable water
9. EES 140: Spring 2017 Kaizad F. Patel 9 Texture and water retention Superfluous water Coarse texture: more superfluous water Fine texture: Greater field capacity Fine texture: More unavailable water Organic matter and water retention
10. EES 140: Spring 2017 Kaizad F. Patel 10 19 Tension/ potential tensiometer probes Electrical resistance block 20 Gravimetric (weight) Soil moisture content (%) = weight of water weight of dry soil x 100 = loss in weight weight of dry soil x 100 Weigh moist soil Dry in oven for 24 hours Weigh dry soil Weight of moist soil = weight of dry soil + weight of water
11. EES 140: Spring 2017 Kaizad F. Patel 11 Soil Moisture Calculation Potential (bars) Soil weight (grams) -0.1 70 -1.0 59 -10 57 -15 55 -27 54 31 53 51 52 Air-dried 51 Oven-dried 50 21 What is the % moisture at field capacity? weight of water = moist weight – oven-dried weight % moisture = weight of water weight of oven−dried soil x 100 % moisture at FC = weight of water at FC oven−dried weight x 100 = (70 − 50) g 50 g x 100 = 40 % Field capacity = -0.1 bars 22 What is the % available water? Available water = water at FC – water at wilting point % available water = (70−50) − (55−50) g 50 g x 100 = (70 − 55) g 50 g x 100 = 30 % Soil Moisture Calculation Potential (bars) Soil weight (grams) -0.1 70 -1.0 59 -10 57 -15 55 -27 54 31 53 51 52 Air-dried 51 Oven-dried 50 Field capacity = -0.1 bars Wilting coefficient = -15 bars
12. EES 140: Spring 2017 Kaizad F. Patel 12 23 24
13. EES 140: Spring 2017 Kaizad F. Patel 13 25 Precipitation Stemflow Throughfall Evaporation Transpiration Evapotranspiration Runoff Infiltration Root uptake
14. EES 140: Spring 2017 Kaizad F. Patel 14 27 Geologic Erosion vs. Human-accelerated Erosion 28 Overgrazing Deforestation Plowing Tearing up land for construction
15. EES 140: Spring 2017 Kaizad F. Patel 15 29 Egypt: pyramids Industrial Revolution Rome: roads Construction, agriculture 30
16. EES 140: Spring 2017 Kaizad F. Patel 16 31 32 Detachment raindrop impact puddling freeze-thaw Transportation floating rolling dragging Deposition
17. EES 140: Spring 2017 Kaizad F. Patel 17 On-site degradation Loss of soil Loss of fertility Loss of OM Off-site effects Sediment deposited off-site Smothering of crops and vegetation Turbidity in streams and lakes Fish gills/ respiration Buildup of bottom sediment = flooding 33 34 Sheet Erosion
18. EES 140: Spring 2017 Kaizad F. Patel 18 35 Rill Erosion 36 Gully Erosion
19. EES 140: Spring 2017 Kaizad F. Patel 19 A = R * K * L * S * C * P A = annual soil loss per unit area R = rainfall factor K = soil erodibility factor L = length of slope S = gradient of slope (steepness) C = cover and management P = erosion-control practices Universal Soil Loss Equation (USLE) 37 Managing soil erosion 38 Litter layer Culverts Terrace farming Rip rap
20. EES 140: Spring 2017 Kaizad F. Patel 20 Soil Water 39