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Land Use & Soil Erosion Agriculture = dominant land use Urban Sprawl = new land use threat Excessive soil erosion – soil components moved to new location.

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Presentation on theme: "Land Use & Soil Erosion Agriculture = dominant land use Urban Sprawl = new land use threat Excessive soil erosion – soil components moved to new location."— Presentation transcript:

1 Land Use & Soil Erosion Agriculture = dominant land use Urban Sprawl = new land use threat Excessive soil erosion – soil components moved to new location due to water or wind x2CiDaUYr90/u_s_dust_bowl_of_1930s/






7 Type of Erosion Geological (natural) Erosion -continuous slow rate of erosion to 0.25 mm /yr for bare rock -2 mm /yr on stable soil surface Accelerated Erosion – human-caused -10 tons/A/yr (natural replacement = 0.5 tons/A/yr) -splash, sheet, rill, & gully erosion -Dust Bowl (1930s)

8 Rill Erosion

9 Gully Erosion

10 Shelterbelt Program Response to Dust Bowl 1-5 rows of trees (preferable to have 12) ~ 70% reduction in wind speed Aesthetics, wildlife habitat, energy conservation (25% savings) Will we repeat History? - removing windbreaks to gain > field size





15 Managing Soil Erosion USDA – 3,000 Soil & Water Conservation Districts Are we controlling soil erosion? -rate today = rate during 1930s) -4 B tons /yr -mostly on farmland (50% water- based & 60% wind-based) -80% farmland > natural replace. rate

16 Tolerable Soil Loss USDA – erosion loss of 1 to 5 tons/A/yr without impacting crop production No scientific basis for this measure

17 Costs of Soil Erosion Lower soil fertility / crop production Air (dust) & water (sediments) pollution Estimates of on-site costs = $27 B/yr Estimates of off-site costs = $17 B/yr

18 Erosion Factors (water) 1)Rainfall Amount, Intensity, Seasonality 2)Surface Cover (erodibility) Soil structure (related to water-stable aggregates) water-stable aggregates: material that aids in soil particles clumping together in water (e.g., organic matter)


20 Erosion Factors (water) cover crops: vegetation grown before/after primary crop for protection of soil surface (e.g., clover, alfalfa, winter wheat) – related to green manure

21 Erosion Factors (water) green manure: plowing under of cover crop in order to increase soil fertility (N fixation), increase organic matter, reduce erosion

22 Erosion Factors (water) 3)Topography Slope grade and length

23 Controlling Water Erosion of Soil clean tillage: crop residues turned into soil soon after harvest; often fall plow 1)contour farming 2)Strip cropping 3)Terracing 4)Gully reclamation 5)Conservation tillage 6)Cropland Reduction Programs

24 Moldboard Plow


26 Contour Farming Farming perpendicular to slope (across slope) -- Jefferson Reduces water runoff (65%), erosion, and siltation Link to Strip Cropping

27 Contour-Strip Cropping


29 Corn Strip Cropping Alternate strips of crops across a slope Rotate crops (crop rotation), i.e., rotate strips Example: Corn-Oats-Alfalfa Oats Alfalfa

30 Waterways


32 Terracing Ancient practice from mountain cultures Create bench-like steps on steep slopes ridge terraces (broad- base or grass backslope) – broad flat steps in slope channel terraces – dig channel across slope; used in high runoff sites

33 Channel Terracing

34 Conservation Tillage Limit or restrict plowing (tilling) of soil in order to reduce soil erosion 1) Minimum Tillage – field cultivator & disc for working top few inches of soil (vs. moldboard plow turning 6+ inches) < 50% of US cropland 2) No Till – field machinery cuts narrow slit into soil & drops seed; maximal surface residue; maximal soil protection

35 Minimum Tillage Equipment

36 No-Till Farming Pros: - reduces labor, fuel consumption, soil erosion - increases crop yield Cons: - need special equipment - not universal - disease & crop pest problems (herbicide & pesticide use)

37 No Till Equipment

38 No Till

39 No-Till with Crop Residue

40 Pesticides pesticide: chemical that kills pests (animal & plant) herbicide – weeds insecticide – insects rodenticide – rodents Silent Spring – Rachel Carson (1960s) 1960s to present (6X > herbicide)

41 No-Till vs. Minimum Till


43 Alternative Agriculture Systems conventional farming: agrochemicals, new crop varieties, bigger equipment alternative agriculture: use organic, biodynamic, integrated, low-input or no- till concepts

44 Alternative Agriculture Systems organic farming: no agrochemicals; combats disease/insects via cultural treatments (e.g., crop rotation, green manures, compost) biodynamic farming: use soil preparations made from animal manure, silica, and plants low-input farming: minimize use of material from outside of farm

45 The Ecology of Farming Native communities = dynamic equilibrium Human-altered systems = monocultures, ecosystem simplification

46 “Cutting-Edge” Agriculture Integrated Pest Mgt (IPM): limit pesticide use by combating insect pests with broad-spectrum (integrated) approach (e.g., biological, chemical, cultural…) precision farming: use satellites (Global Positioning System = GPS) to map fields and spatial data (crop yield, fertilizer application); manage smaller units (i.e., field sub-units)

47 Precision Farming



50 Soil Properties comprised of: minerals organic matter water air Properties = texture, structure, organic matter, life, aeration, moisture content, pH, fertility

51 Soil Texture Coarse fraction (rock, gravel) vs. fine- earth fraction (sand, silt, clay) Sand > Silt > Clay textural classes (soil texture pyramid, p.105, fig 6.2) adsorption: process of forming chemical bonds (ionic bonds) between nutrients (+) and soil (clay -) – relates to leaching/fertility


53 Adsorption

54 Soil Structure arrangement/grouping of soil into aggregates (or clumps) Influenced by “natural” physical factors (e.g., freezing/thawing, burrowing) and human alterations (e.g., tilling) Affects soil permeability (air & water) and plant growth (roots)

55 Soil Organic Matter (OM) & Life OM = living & dead organisms in soil humus: top layer of soil produced via decomposition; improves structure, permeability, stability, fertility, habitat microorganisms vs. macroorganisms mycorrhizae (pl.): “fungus root” symbiotic relationship between plant & fungus – nutrient uptake from soil (e.g., conifers and fungi)

56 Aeration & Moisture Content pore space: space between soil particles filled with air or water; relation to structure & texture (sand vs. clay) Pore space (aeration/moisture content) increased by OM At soil saturation, all pores filled with water – correlated with surface runoff intensity / erosion

57 Soil pH (reaction) soil reaction: pH of soil (acid, neutral, basic) – depends on H+ or OH- ions wet & mesic soils – acidic to neutral dry soils -- basic pH & agriculture -lime (CaCO 3 ) – Ca+ ions reduce acidity -fertilizers (N, P) – with water… acidic

58 Soil Fertility soil fertility: capacity to provide all nutrients needed for maximum growth macronutrient vs. micronutrient - N vs Fe relation to pH some nutrient sources: fixation, decomposition, animal waste

59 Soil Formation Five Factors: 1)Climate (temp. & precipitation) physical & chemical changes in soil/rock (weathering) – clay, leaching 2) Parent material - weathering in place or transported - outwash plain, alluvial, lacustrine, dunes, tephra

60 Soil Formation Five Factors: 3) Organisms (macro and micro) 4) Topography – relation to water movement & soil condition/type 5) Time * billion yrs before present(ybp) * relation to other 4 factors

61 Soil Profile soil profile: cross-section view of soil horizons horizon: layers of soil that share attributes of texture, structure, etc…

62 Soil Profile Major Horizons: O horizon (organic layer) A horizon (topsoil, humus, life) E horizon (leaching zone) B horizon (subsoil, accumulation zone) C horizon (parent material, field stone) R horizon (bedrock)

63 Water Resources Water Shortage? 1) Human Population 2) Consumption - ag.,industry,resident 3) Efficiency 4) Distribution Problems 5) Pollution (air, soil, water)

64 Water Cycle? replacement period: time to complete cycle (9 days to 37,000 years) Unequal distribution of precipitation -US 102 cm -MI 81 cm -Death Valley 4 cm -Pacific NW 368 cm Evaporation & Transpiration

65 Surface Water & Groundwater Surface water (lakes, streams) -may be potable, municipal use Groundwater – water infiltrates into soil percolation into aquifer (porous soil stratum of sandstone or limestone) zone of aeration: plant roots, capillary water in pore spaces zone of saturation: pore filled from water table down to bedrock


67 Watersheds watershed: area drained stream/river U.S. Army Corps of Engineers Flood Control 1) Levees – raise river banks with earthen/stone dikes develop floodplains floods prevented, almost increase flood severity?

68 Flood Control (cont.) 2) Dredging – removal of sediments (Corps) – pollutants? 3) Channelization – straightening streams (NRCS) – floods & drainage, Everglades 4) Dams – water impoundment – public works projects potable water, irrigation, recreation, energy loss of habitat, evaporation, sedimentation, $$

69 Dams -Alqueva Dam (Portugal) Irrigation water but destroys critical habitat for Iberian lynx


71 World’s most endangered cat Less than 600 Spain & Portugal

72 Distribution of Iberian lynx

73 Know populations Iberian lynx

74 Alqueva Reservoir began filling February 8th 2002 behind the 96-m-high floodgates New proposals to reduce wall height by 13 m leading to a reduction of the submersed area from 29,636 ha to 14,696 ha.

75 Protecting Watersheds & Floodplains watershed protection as proactive & sustainable flood control mgt. USDA, BLM, Army Corps, TVA floodplain zoning & Federal Flood Disaster Protective Act of 1973 nonstructural flood control

76 Types of Pollution 1)Sediment 2)Inorganic Nutrient 3)Thermal 4)Disease-Producing Microorganisms 5)Toxic Organic Chemicals 6)Heavy Metals 7)Organic Wastes

77 Managing Pollution pollution control: (output control) manage pollutant post hoc - pollutant dispersion pollution prevention: (input control) avoid pollution a priori

78 1)Sediment Pollution - linked to soil erosion /poor land use Sources: agriculture, logging, construction, strip mines Costs: $1 million per day in US clog irrigation canals, hydro- electric turbines, harbors, life of dams shortened - carries toxins - turbid water & sedimentation “kills” coldwater fish/bivalve habitat

79 Controlling Sediment Pollution - input control includes: conservation tillage contour-strip farming shelter belts terracing cover crops/increase OM -output control includes: $$$$$ sediment filtration systems (artificial & natural) dredging

80 2) Inorganic Nutrient Pollution - aquatic systems require certain chemical elements to exist & support life -includes C, O, N, H, P among others -N & P often are limiting factors because of their reduced abundance; -P > N in importance as limiting factor -> N & P = > productivity of aquatic system

81 Lake Productivity Gradient 1)oligotrophic: nutrient-poor lake - low productivity - low plant/animal biomass - e.g., Lake Superior = young lake 2) mesotrophic: moderate nutrient base - swimming, fishing 3) eutrophic: nutrient rich - dense algal blooms - reduced dissolved oxygen, diminished fishery

82 3) Thermal Pollution - increase temperature of aquatic system -Harmful effects: -reduced dissolved oxygen -reduced fish reproduction -spread of disease -Benefits: -increase growth rate of some fish -heating homes -Use of coolant towers

83 4) Disease-Producing Organisms - infectious organisms introduced to water; cholera, typhoid fever, dysentery, polio, Cryptosporidium -better sanitation & water treatment can reduce disease e.g., chlorination for bacteria and oxygenation for enteric disease (intestine-dwelling; anaerobic) -coliform bacteria count: index of microorganism-based water pollution coliform = usually harmless bacteria in human gut

84 5) Toxic Organic Chemicals - Carbon-based compounds; synthetic derivatives such as Volatile Organic Compounds (VOCs) = toluene -Synthetic Organics = resist decomposition & therefore persistent -Disrupt normal enzyme function in organisms; interfere with normal chemical reactions in cells

85 Water Pollutants 1) Review Table 11.4, p 268 2) Your choice, pick 1 of the pollutants and, a) be able to name it; b) provide an explanation of its use; c) indicate its source & its prevalence in the Great Lakes; and d) explain its effects on human health

86 6) Heavy Metals e.g., lead, mercury, arsenic, cadmium (fundamental chemical elements) -Mines & contaminated groundwater -Mines & tailings (Clarks Fork of Yellowstone) -interfere with normal enzyme function -lead contamination (soil & water) from paint & plumbing pipe (solder) -mercury contamination (methyl Hg in air & water) from industry; in muscle tissue

87 7) Organic Waste: reduce available oxygen - decomposition of wastes by bacteria uses oxygen; release of nutrients -- cyclic -Oxygen-demanding organic wastes biological oxygen demand (BOD): index of amount of organic matter in water sample; indexed via rate of oxygen use by bacteria -aquatic indicator species (bio-sentinels or bio-indicators) – also application to other pollutants (may flies, trout, bullheads, carp, sludge worms, mink)

88 7) Organic Waste: reduce available oxygen - decomposition of wastes by bacteria uses oxygen; release of nutrients -- cyclic -Oxygen-demanding organic wastes biological oxygen demand (BOD): index of amount of organic matter in water sample; indexed via rate of oxygen use by bacteria -aquatic indicator species (bio-sentinels or bio-indicators) – also application to other pollutants (may flies, trout, bullheads, carp, sludge worms, mink)

89 Eutrophication

90 Gulf of Mexico - Watershed

91 hypoxic zone dissolved oxygen concentration less than 2 mg/L, or 2 ppm

92 Gulf of Mexico - Watershed 22,000 km2 in mid- summer Size of New Jersey or the states of Rhode Island and Connecticut combined

93 Gulf of Mexico - Watershed

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