Slide1: Chapter 14: Wetlands and Land Drainage Homework: 2, 6, 7 Due 19 November


Slide2: Wetlands: Once considered a nuisance, to be drained and farmed Now recognized for their value: Wildlife habitat Groundwater recharge Flood control Recreation A large percentage of wetlands have already been lost and strict laws in the US protect the remainder


Slide3: Table 16-1 14-1


Slide4: Wetland drainage: Much prime farmland is on former wetlands: 10% of world croplands 33% of US croplands Also has been much peatland drainage in Finland for forest plantations Crop growth on drained wetlands is good because soils are fertile


Slide5: Wetland trends and laws: Since the late 18th century, 22 states have lost at least half their wetlands and 10 states have lost 70% of them “Swampbuster” provisions added to the Farm Bill starting in 1985 to protect remaining wetlands President George H. Bush issued a directive that three be “no net loss of wetlands in the future” in 1990 on authority of the 1977 Clean Water Act However, defining wetlands can be difficult - where is the boundary?


Slide6: Wetland definition: The US Army Corps of Engineers has jurisdiction over wetlands under the Clean Water Act. It defines wetlands as: “Areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do supppr, a prevalence of vegetation typically adapted for life in saturated soil conditions”


Slide7: Wetland trends and laws: From 1993 to 2000, 9,700 ha of wetlands have been drained while 17,000 ha have been reconstructed or restored 1.8 ha gained for every 1 ha lost


Slide8: Wetland definition: The US Army Corps of Engineers has jurisdiction over wetlands under the Clean Water Act. It defines wetlands as: “Areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do supppr, a prevalence of vegetation typically adapted for life in saturated soil conditions”


Slide9: Wetland definition: The US Army Corps of Engineers definition is based on the presence of: Hydric (saturated) soils Hydrophitic plants Ponding or high water table


Slide10: Wetland definition: These lands can still be used but cannot be drained without a permit: Converted wetland: former wetland drained before 23 Dec 1985 Farmed wetland: former wetland farmed before 23 Dec 1985 Prior converted cropland: Drained and cropped before 23 Dec 1985 Exempt from Swampbuster law unless allowed to unfarmed for 5 years and wetland characteristics return, in which case they become protected


Slide11: Wetlands goals: The national goal is to take grandfathered wetlands now farmed out of production and back to wetlands. Three options: Permanent easement: USDA pays the cost of restoration and buys the easement; land is still owned by the farmer 30-year easement: USDA pays 75% of restoration cost and 75% of permanent easement cost Restoration cost-sharing: Farmer agrees to restore and maintain wetland for 10 years, USDA pays 75% of restoration cost; no easement.


Slide12: Wetland Characteristics: Just being waterlogged after rains, floods does not make a wetland. Wetlands can be dry for part of the year Wetlands are defined by hydric soils: “Soils formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part.”


Slide13: Table 16-2 14-2


Slide14: Chemistry of wetlands: Reducing conditions Organic matter + microbes --> O2 is consumed --> Anerobic conditions Iron and Manganese are good indicators (recall that they undergo redox reactions easily): Fe3+ + e- --> Fe2+ Mn4+ + 4e- --> Mn2+ Fe is more abundant than Mn Also, sulfur reduces to sulfide and carbon dioxide is reduced to methane: SO42- --> S- (Rotten egg smell) CO2 --> CH4


Slide15: 14-2


Slide16: Chemistry of wetlands: Reducing conditions induce mottling (patchy bluish-gray colors), rotten egg smell, characteristic plants (e.g., cattails).


Slide17: Types of wetlands: Aquatic wetlands: Permanently inundated (under water) Shallow surface water systems Swamp: Stable, perrennial vegetation Permanently wet Underwater at least part of the year Marsh: Ephemeral vegetation or periodic fluctuations of vegetation Seasonal water table on surface from groundwater Can be salty in coastal areas (salt water marsh) Areas inundated by tides are tidal flats


Slide18: Types of wetlands: Bogs or fens: Stable, perrenial vegetation Not inundated for more than part of a year Landscape position: Bog: Receiving inputs from rain Water drains away Low nutrient inputs (rain) Fen: Receiving water from upslope positions via groundwater Higher nutrient and salt input


Slide19: 14-3


Slide20: Types of wetlands: Vernal pools: Small depressions that fill with water from snowmelt, autumn rain, or groundwater Temporary Lack fish and therefore are richer in aquatic organisms Frogs and salamanders can inhabit them


Slide21: Functions of wetlands Biodiversity Water supply Flood protection (store water and dissipate energy) Pressure against saline intrusion into aquifers coastal areas Buffer effects of high winds, hurricanes, waves Catch sediment from upslope positions (have seen this personally in the Gondola fire) Products: peat, timber, fruit, cane, reeds, medicinal herbs Sequester huge amounts of carbon on a global scale Wildlife habitat Specialized croplands (e.g., cranberries, rice)


Slide22: p. 481


Slide23: Draining to improve soil conditions Pros: Crop use of fertile soils Warmer in spring More uniform moisture Reduces N losses by denitrification Reduces toxic buildups (salts, methane, sulfides, etc) Deeper plant rooting Construction, roads Mosquitoes Reduced frost heaving


Slide24: Draining to improve soil conditions Cons: Wildlife habitat (this would prevent draining in most cases where it applies) Reduce water table Reduce capillary rise Oxidize pyrite and cause extreme acidification (do not drain soils with pyrite!) Finland still does a fair amount of wetland drainage because they have extensive bog soils; however, It seems doubtful that much wetland drainage will occur in the US in the near future.


Slide25: Drainage systems – keep for future reference