FENS David J' Cooper Rodney Chimner Joanna Lemly

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FENSDavid J. Cooper Rodney Chimner Joanna Lemly
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Wetland

• Any ecosystem that has saturated soils for at
  least 2 weeks during the growing season of most
  years, creates hydric soils, supports hydrophytes
• Many different wetland types due to stability of
  the water table, water depth, erosive power of
  moving water
• Riparian
• Marshes
• Wet Meadows
• Salt Marshes and Flats
• Peatlands

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Wetland Types of Interior West
Riparian
Marsh
Salt Flat
Peatland (fen)
Wet Meadow
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PEATLAND

• Production gt decomposition due to water-logging
• Saturated, anaerobic soils, lack free oxygen
  limits decomposition rates
• Organic matter (roots, rhizomes, mosses, woody
  stems) accumulates (20 cm/1000 yrs) and organic
  soils form
• Peat accumulation create landforms
• Plants are rooted entirely in peat body
• Plants derive all water nutrients from peat
• Isolated from mineral sediment inputs

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Simplified Peatland Carbon Budget
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Two types of peatlands
BOGS
Peatlands
FENS

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BOGS

• Ombrogenous and Ombrotrophic
• Usually raised, but also blanket bogs
• Sphagnum dominated, with low pH (lt4.2)
• Nutrient and mineral ion poor, Ca lt 2.0 mg/L
  in water
• Typically occur in humid regions with cool
  temperatures, but also in drier areas of C.
  Canada
• Some consider peatlands with pH lt5 to be bogs, gt6
  to be fens (Wheeler and Proctor 2000)
• No bogs in Rocky Mts of US or Sierra Nevada

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FENS

• Ground water, not precipitation provides main
  water source. Minerotrophic
• Fen characteristics determined by chemical
  content of source waters and water flux
• pH varies from lt4 to gt8
• Very sensitive to changes in ground water supply
  or flow paths
• Vegetation can be conifer forest, shrub, sedge,
  or moss dominated

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Fen Characterization and Identification

• Hydrologic regime
• Soils
• Vegetation

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Ground Water Flow Paths That Sustain Fens
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Water Table near Surface

• Air diffuses 10,000 times slower into saturated
  than in unsaturated soils
• Soils become isolated from atmospheric gasses
• Oxygen in soil is rapidly used up and anoxic
  soils develop and limit organic matter
  decomposition
• Ground water input keeps soils cooler
• Duration of water table near surface? All summer

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Ground Water Monitoring Well
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Natural Range of Variation-8 of 11 yearsnear
surface
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Rain and Water Levels in Fens
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What is peat or organic soil?30-40 cm thick
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Drepanocladus moss fibers
Sedge roots/rhizomes
Soil colors and fibers indicate organics vs.
color of mineral soils - as well as redox features
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No International Criteria

• For organic matter composition
• For organic carbon composition
• For presence of mineral soil layers
• For type of inorganic matter present

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• Boreal peatlands with little mineral sediment
  influx

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Mineral soil influx from mountains
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Organic Soil Criteria

• Hydrologic Regime
• Saturated with water for gt30d each year
• Composition ( OC that controls soil function
  the more clay present the less OC influences
  soils)
• Must be gt18 organic carbon if gt60 clay
• 12 organic carbon if 0 clay
• 12 (0.1 clay) so if 20 clay need 14 OC
• Horizon Thickness
• 40 cm of organic horizons in top 80 cm of soil
  (dominates root zone)
• Or, on lithic contact

ftp//ftp-fc.sc.egov.usda.gov/NSSC/Soil_Taxonomy/t
ax.pdf
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How determine OC or OM?

• Must be done in lab
• OC can be determined using a CHN analyzer, must
  first treat with acid to remove carbonates
• OM can be determined by loss on ignition in
  muffle furnace, but OM is not all C, and OM
  must be converted to OC

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Peat vs. Muck

• Soil taxonomy identifies 3 suborders of histosols
  (ist) fibrist, hemist, saprist, based upon the
  level of decomposition of the organic matter.
• Fibrist soils are considered peat
• Hemist and saprist soils are muck
• HOWEVER, from an ecological perspective any
  ecosystem with organic soil is a peatland

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Peat forming vegetation

• Most organic matter in western U.S. fens is
  produced by clonal sedges and mosses,
• deposited in anaerobic zones below the soil
  surface
• Litter on surface decomposes
• Woody peat in alder or willow fens, and some
  partially forested fens
• Carex, Eleocharis, Scirpus are the key vascular
  plant genera
• Moss peat from Drepanocladus, Sphagnum,
  Aulacomnium, Tomenthypnum
• California has unusual peat formers Narthecium
  (also in Britain), Darlingtonia

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How old are peatlands?
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Basal Ages of Rocky Mt fens

• Big Meadows 11,180
• Green Mt. Fen 11,650
• East Lost Park 11,200
• Cottongrass Fen 10,300
• Caribou Fen 10,500
• Zapfs Fen 4,800

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Some meadows have small fen area, others are
nearly all fen
Wet Meadow
Fen
Round fen Sequoia NF
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Several plant communities in most fens should
sample each
5
4
3
1
2
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Within fen variation
recharge
4
5
6
Carex limosa
Flow through
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3
2
discharge
1
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Processes Driving Variation Among Fens and Fen
Vegetation

• Water flow variation, high to low flow rates
  influences vegetation production peat accum.
  rate
• Standing water depth
• Stable pond water level supports floating mats
• Chemistry of source waters due to bedrock
• Climate, including elevation, patterns of
  precipitation, supports unique floristic elements
• Disturbance processes, including ditches,
  livestock grazing etc.

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Four major landform/hydrologic systems support
fens

• Basins
• Slopes
• Spring mounds
• Geological discontinuities

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Limnogenous or Basin fenssurface or ground water
fed
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Basin fens typically have floating mats, but
depending upon rate of succession, basin
infilling may have been completed have
distinctive flora
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Sloping Fens
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Poison Fen Sierra NF
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hillslope fens may support conifer trees
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Spring moundspecialized type of soligenous fen
with point discharge
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Geological discontinuity creates hillside flow
systems
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Chemistry of source waters rich to poor
gradient of Sjörs and DuRietz
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Southern Rocky Mt. Fens Geochemical Classes
Extreme Rich Fens
Transitional Rich to Rich Fens
Iron Fens
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Convict Creek Basin Inyo NFHanging Fen pH
7.87, EC 257 uS, Ca 49 mg/L
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St. Marys Fen Stanislaus NFpH 6.7, high Ca,
HCO3
Rich Fen
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Transitional Fens
Pat-Yore-Flat (Tahoe NF) (Butterfly valley
(Plumas) Narthecium californicum, Darlingtonia,
Rhynchospora alba, Carex echinata, Ledum
glandulosum
pH 6.1, EC 17.8 uS Ca 1.8 mg/L
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Transitional Fen McKinstry Fens - Eldorado NFpH
5.7, EC 28 uS, Ca 2.1 mg/L, Carex echinata,
Drosera rotundifolia, Sphagnum subsecundum
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Poorest fens Dinky Lake Sierra NFSphagnum
fuscum, Kalmia polifolia
pH 5.75, EC 13 uS, Ca 0.3 mg/L, K 1.8 mg/L
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Iron Fens
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Conclusions

• Many fens in most mountain regions
• Large range of fen landforms, hydrologic regimes,
  mineral ion and nutrient fluxes, vegetation
  types, flora, history during Holocene, land
  use/condition
• Community types unique to fens, disjunct species
  
• Many communities are similar throughout North
  America and Holarctic (Scirpus pumilus,
  Eleocharis pauciflora, Carex aquatilis, C.
  utriculata, C. limosa, Meesia triquetra,
  Sphagnum subsecundum)
• Others more localized Carex illota, Narthecium
  californicum, cushion plants in tropical alpine
• Many fens impacted by human uses

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Impacts few fens are pristine

• ON SITE IMPACTS
• Filling
• Hydrologic changes drainage ditches
• Snow compaction on ski runs
• Trampling livestock, humans
• Mining, metal and peat
• OFF SITE IMPACTS
• Timber operations
• Hydrologic changes diversions, ground water
  pumping
• N deposition?

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Drainage

• Common in agricultural areas
• Particularly wet meadows, marshes, to completely
  dry areas out
• May be cropped

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Water Diversions/Ditches
What are hydrological and ecological impacts and
how restore?
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Mason Fen
Rate of flow in open channel compared to ground
water flow through peat/muck
Exotic plant invasion
Plant death
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Dewatering allows pocket gopher and vole invasion
-- proliferates drainage and channel development
Digging exposes peat to oxidation, and digging
undermines plants
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Prospect Basin Fens
Pre-development air photograph
Ski runs
Watersheds
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Snow compaction changed thermal characteristics
of snow from insulation to conducting cold
allowing peat to freeze deeply
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Ground Water Withdrawal

• Daily, seasonal or permanent lowering of water
  tables
• May stop peat accumulation, and cause peat
  oxidation in fens
• May cause subsidence
• May dry out wetlands

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Ground Water Pumping
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Trampling from hikersLoss of vegetation and peat
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Livestock Grazing
Eliminates species with rhizomes and favors
taprooted and short-lived species
Hummocks formed in areas without caespitose
species indicate compaction and erosion, and
increase surface area and oxidation
Bare ground facilitates channel development and
head cutting
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RMNP established 1915
Vegetation changes
Fen dry in summer
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Ditch Blockage
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Water Table Changes Relative to Controls
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