Wetland Ecology and Dynamics Prof. Dr. Paul J. DuBowy Ecohydrology Associates, LLC Lovell, Wyoming 82431 USA ecohydrology.associates@gmail.com

Outline Hydrology Overview Hydrogeomorphic Approach Wetland Water Budgets Hydrogeomorphic Approach Hydrological Consequences to Wetland Ecosystems Biogeochemistry/Redox Reactions Hydric Soils Vegetation/Plant Indicators Animal Communities

What is a Wetland? Defined on the basis of three characteristics: presence of water at surface or in root zone (hydrology) unique soil conditions (hydric soils) vegetation adapted to wet conditions (hydrophytes)

Wetland Hydrology Pn ET dV/dt Si So T Gi Go

USGS Water Supply Paper 2425

USGS Water Supply Paper 2425

Hydrogeomorphic Approach Hydrogeomorphic (HGM) classification system (Brinson 1993) developed to assess physical, chemical and biological functions of wetlands HGM links hydrology and geomorphology with wetland functions in order to provide an index of environmental services that wetlands provide

Hydrogeomorphic Approach HGM based on three principal physical factors that differentiate wetlands: position of wetland in landscape (geomorphic setting) water source (hydrology) flow and fluctuation of water once in the wetland (hydrodynamics) Taken together, these factors separate wetlands into different functional groups Wetlands within each group share similar characteristics and, by extension, provide similar functions

Examples of Subclasses HGM Hydrogeomorphic Class Dominant Water Source Dominant Hydrodynamics Examples of Subclasses Eastern USA Western USA and Alaska Riverine Overbank flow from channel Unidirectional, horizontal Bottomland hardwood forests Riparian forested wetlands Depressional Return flow from groundwater and interflow Vertical Prairie pothole marshes California vernal pools Slope Return flow from groundwater Fens Avalanche chutes Mineral soil flats Precipitation Wet pine flatwoods Large playas Organic soil flats Peat bogs; portions of Everglades Peat bogs Estuarine fringe Overbank flow from estuary Bidirectional, horizontal Chesapeake Bay marshes San Francisco Bay marshes Lacustrine fringe Overbank flow from lake Great Lakes marshes Flathead Lake marshes Brinson et al. 1995

Depressional Wetlands Pn ET dV/dt Si So T Gi Go

Prairie Potholes

Recharge Wetlands Pn ET dV/dt Si So Gi Go

Discharge Wetlands Pn ET dV/dt Si So Gi Go

Vernal Pools

Organic Flats Hydrology Pn ET dV/dt Si So Gi Go

Quaking Bog

Everglades

Tropical Peatlands

Ecosystem Consequences Soil Texture coupled with elevation gradients Biogeochemistry hydric soils Vegetation Responses

Geomorphic Features Backwater deposits of fine sediments deposited between natural levees and along valley walls Terraces are earlier floodplains that may have been formed by river’s alluvial deposits, but are not connected hydrologically with present river (except during high floods) Low topographic relief deceptive  elevation change of few centimeters may produce quite different hydrologic conditions, soils, and plant communities

Saucier 1974

25 km

Biogeochemical Elements “See Hopkin's Cafe? Mighty good!” for plant nutrients: C, H, O, P, K, N, S, Ca, Fe, Mg, (plus Mn)

Wetland Redox Reactions Redox rxns different in wetlands than in lakes/ponds Wetlands are shallow no thermocline—no dense cold deoxygenated water some wetlands dry out—aerobic processes plants (or algae) can grow on bottom across wetland—aerobic root zone Anaerobic/aerobic wetland soil interface  leads to reductive/oxidative processes

Wetland Redox Reactions 2 Anaerobic environment (saturated soil): reduction processes e- are donated O atoms stripped off H atoms added Aerobic environment (root zone): oxidative processes

Wetland Redox Reactions 3 Oxidation  Reduction Fe+3  Fe+2 Mn+4  Mn+2 (Fe and Mn important for hydric soil determination) Organic N  NH3  NH4+ (ammonification; N mineralization) NO3-  NO2-  NH4+ (nitrification) NO3-  N2O  N2 (denitrification)

Wetland Redox Reactions 4 Oxidation  Reduction Organic P  SOP  PO4-3  HPO4-2  H2PO4-  insoluble inorganic P (complexes with Ca, Fe, Al; adsorption on clay/organic particles) CO3-2  HCO3-  CO2 C(H2O) (carbonate system) (methanogenesis) C(H2O)  CH4 SO4-2  S-2 ( H2S)

Wetland Soils In order to understand wetland soils, we need to know something about: sediment type/origin organic material hydrology/inundation soil drainage/water flux biogeochemical redox reactions soil color

Hydric Soils Defined (USDA-NRCS) as soils that formed under conditions of saturation, flooding, or ponding long enough during growing season to develop anaerobic conditions in upper part of soil (Federal Register, 13 July 1994)

Hydric Soil Identification Soil Color indirect measure of other soil characteristics Fe+3  Fe+2; Mn+4  Mn+2 red – unhydrated iron oxide yellow – iron oxides brown – iron oxides and organic matter grey – permanently saturated; reduced iron easy to measure Munsell color chart in temperate climates, dark soils are relatively higher in organic content

Hydric Soil Identification 2 Mottling refers to repetitive color changes that cannot be associated with compositional properties of the soil mottles are described by quantity, size, contrast, color, and other attributes in that order redoximorphic features are a type of mottling that is associated with wetness (alternating aerated and saturated conditions) these gray/brown/red spots are caused principally by migration, depletion or concentration of Fe and Mn within the soil

Hydric Soil Identification 3 Gleying condition that develops when soil is wet for most of the year soil matrix color is gray or bluish gray due to transformation of iron caused by prolonged reducing conditions characteristic of very poorly drained soils Specific soil ID often difficult palustrine wetlands may be young with flooding/deposition/erosion floodplain soils can have poorly developed characteristics

Vegetation Dynamics Floodwaters and subsequent groundwater levels determine type and productivity of vegetation in floodplain Hydroperiod (flooding duration, intensity, timing) limits species composition and influences ecosystem structure and function import nutrient-rich sediments to floodplain export organic and inorganic material timing important  flooding in growing season has greater effect on species survival and ecosystem productivity

Vegetation Gradients

Riparian Vegetation Zonation Zone I (open water river corridor) present day river channel; continuous flooding Zone II (river swamp forest; deep water alluvial swamps) have surface water throughout all or most of growing season, but water levels vary seasonally and annually Zone III (lower hardwood swamp forest; first bottom) do not stay wet during the entire growing season, nor do they flood every year

Vegetation Zonation 2 Zone IV (backwaters or flats; second bottom) typically has standing water during less than 25% of growing season; many spp. as in zone III, but more diverse Zone V (upper hardwood swamp) highest elevations of floodplain; encompass natural levees and terraces as well as very old ridges and dunes only covered with water for very brief periods during growing season, flood no more than 50% of years within a 100-year cycle, and have a water table which is below soil’s surface

Vegetation Dynamics Prairie potholes: fluctuating hydrologic regime dry marsh  regenerating marsh  degenerating marsh  open water  dry marsh vegetation composed of pronounced concentric rings length of time wetland holds water  complexity of zonation (number of zones) water permanence  species richness Estuaries: salinity gradients: fresh  salt water corresponding vegetation gradients

Prairie Potholes

Connecticut River

Salt Marsh Vegetation