Land use and soil erosion

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

http://www.metacafe.com/watch/yt-x2CiDaUYr90/u_s_dust_bowl_of_1930s/



Type of Erosion • Geological (natural) Erosion

- continuous slow rate of erosion- 0.02 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)

Rill Erosion

Gully Erosion

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

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

Tolerable Soil Loss

• USDA – erosion loss of 1 to 5 tons/A/yr without impacting crop production

• No scientific basis for this measure

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

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)

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

Erosion Factors (water) green manure:

plowing under of cover crop in order to increase soil fertility (N fixation), increase organic matter, reduce erosion

Erosion Factors (water) 3) Topography

• Slope grade and length

Controlling Water Erosion of Soil

clean tillage: crop residues turned into soil soon after harvest; often fall plow

1) contour farming2) Strip cropping3) Terracing4) Gully reclamation5) Conservation tillage6) Cropland Reduction Programs

Moldboard Plow

Contour Farming • Farming perpendicular to slope (across

slope) -- Jefferson• Reduces water runoff (65%), erosion,

and siltation • Link to Strip Cropping

Contour-Strip Cropping

Corn

Strip Cropping • Alternate strips of crops across a slope• Rotate crops (crop rotation), i.e., rotate

strips• Example:

Corn-Oats-AlfalfaOats

Alfalfa

Waterways

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

Channel Terracing

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

Minimum Tillage Equipment

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)

No Till Equipment

No Till

No-Till with Crop Residue

Pesticidespesticide: chemical that kills pests (animal

& plant)

herbicide – weedsinsecticide – insectsrodenticide – rodentsSilent Spring – Rachel Carson (1960s)1960s to present (6X > herbicide)

No-Till vs. Minimum Till

Alternative Agriculture Systems conventional farming: agrochemicals, new

crop varieties, bigger equipmentalternative agriculture: use organic,

biodynamic, integrated, low-input or no-till concepts

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

The Ecology of Farming• Native communities = dynamic

equilibrium• Human-altered systems = monocultures,

ecosystem simplification

“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)

Precision Farming

Soil Properties • comprised of: minerals

organic matter water air

• Properties = texture, structure, organic matter, life, aeration, moisture content, pH, fertility

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

Adsorption

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)

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)

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

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 (CaCO3) – Ca+ ions reduce acidity

- fertilizers (N, P) – with water… acidic

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

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

Soil Formation Five Factors:3) Organisms (macro and micro)

4) Topography – relation to water movement & soil condition/type

5) Time *4.5 - 3.5 billion yrs before present(ybp)* relation to other 4 factors

Soil Profile • soil profile: cross-section view of soil

horizons• horizon: layers of soil that share

attributes of texture, structure, etc…

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)

Water Resources Water Shortage?1) Human Population2) Consumption - ag.,industry,resident

3) Efficiency4) Distribution Problems5) Pollution (air, soil, water)

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

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

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?

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, $$

Dams - Alqueva Dam (Portugal)

Irrigation water but destroys critical habitat for Iberian lynx

• World’s most endangered cat

• Less than 600• Spain & Portugal

• Distribution of Iberian lynx

• Know populations Iberian lynx

• 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.

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

Types of Pollution 1) Sediment2) Inorganic Nutrient3) Thermal4) Disease-Producing Microorganisms5) Toxic Organic Chemicals6) Heavy Metals7) Organic Wastes

Managing Pollution pollution control: (output control)

manage pollutant post hoc- pollutant dispersion

pollution prevention: (input control)avoid pollution a priori

1) Sediment Pollution

- linked to soil erosion /poor land useSources: agriculture, logging,

construction, strip minesCosts: $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

Controlling Sediment Pollution

- input control includes:conservation tillagecontour-strip farmingshelter beltsterracingcover crops/increase OM

- output control includes: $$$$$sediment filtration systems (artificial &

natural)dredging

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

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

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

4) Disease-Producing Organisms

- infectious organisms introduced to water; cholera, typhoid fever, dysentery, polio, Cryptosporidium

- better sanitation & water treatment can reduce diseasee.g., chlorination for bacteria and

oxygenation for enteric disease (intestine-dwelling; anaerobic)

- coliform bacteria count: index of microorganism-based water pollutioncoliform = usually harmless bacteria in human gut

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

Water Pollutants

1) Review Table 11.4, p 2682) 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; andd) explain its effects on human health

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

7) Organic Waste: reduce available oxygen

- decomposition of wastes by bacteria uses oxygen; release of nutrients -- cyclic

- Oxygen-demanding organic wastesbiological 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)

Eutrophication

Gulf of Mexico - Watershed


• hypoxic zone • dissolved oxygen

concentration less than 2 mg/L, or 2 ppm

Gulf of Mexico - Watershed• 22,000 km2 in mid-

summer • Size of New Jersey or

the states of Rhode Island and Connecticut combined

Land use and soil erosion

Environment

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