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 farming

2) Strip cropping

3) Terracing

4) Gully reclamation

5) Conservation tillage

6) Cropland Reduction Programs

Moldboard Plow

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 – weeds

insecticide – insects

rodenticide – 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 equipment

alternative 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

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 Population

2) Consumption - ag.,industry,resident

3) Efficiency

4) Distribution Problems

5) 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) Sediment

2) Inorganic Nutrient

3) Thermal

4) Disease-Producing Microorganisms

5) Toxic Organic Chemicals

6) Heavy Metals

7) 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 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

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

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, fishing3) 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 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

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 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

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 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)

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)

Eutrophication

Gulf of Mexico - Watershed

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

Gulf of Mexico - Watershed