Single most important determinant of the establishment and maintenance of specific types of wetlands & wetland processes

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1 Wetland Ecology Lectures 12 & 13 Wetland Hydrology Hydrology Single most important determinant of the establishment and maintenance of specific types of wetlands & wetland processes Starting point of hydrological processes is the climate & geomorphology Creates the unique conditions which differentiates wetland ecosystems from well-drained terrestrial & deep water systems What factors affect Pathway A? What factors affect Pathway B? Ecological Processes & Hydrology As previously stated Wetlands are transitions between terrestrial uplands & open-water aquatic ecosystems Wetlands are transitional in terms of Spatial arrangement & amount of water they store & process Hydrologic conditions can directly modify or change chemical and physical properties Nutrient availability Degree of soil anoxia Soil salinity Sediment properties ph when flooded tendency to move ~7 Inputs: Major source of nutrients to wetlands Outflows: Remove biotic & abiotic material from wetlands Biotic Control of Hydrology Biotic components, especially vegetation control their water conditions through a variety of mechanisms Peat building Sediment Trapping Nutrient retention Water shading Transpiration Animals contribute as well

2 Tidal Hydrology studies Explore relationships between hydrologic variables (depth) and wetland productivity or species composition Few comprehensive studies have described the hydrologic characteristics within specific wetland types Hydroperiod (H 2 O residency) Seasonal pattern of water levels in a wetland Integrates inflows & outflows of water Duration refers to the amount of time that wetland is in standing water Frequency the average number of times that a wetland is flooded in a given period Definitions of Hydroperiods (Cowardin et al. 1979) Subtidal permanently flooded with tidal water Irregularly exposed surface exposed by tides less often than daily Regularly flooded alternately flooded & exposed at least once daily Irregularly flooded flooded less often than daily Nontidal Permanently flooded flooded throughout the year in all years Intermittently exposed flooded throughout the year except in years of extreme drought Semipermanently flooded flooded during the growing season in most years Seasonally flooded flooded for extended periods during the growing season Saturated substrate is saturated for extended periods during the growing season, lacks standing water Temporarily flooded flooded for brief periods during the growing season, water table well below surface Intermittently flooded surface is usually exposed with surface water present for variable periods with no detectable pattern Year Year Fluctuations The hydroperiod is not the same each year but varies statistically according to climate and antecedent conditions Pulsing Water Levels Water levels in most wetlands are generally not stable but fluctuate: 1. Seasonally: High-order riparian systems

3 2. Daily or semi-daily: Tidal wetlands 3. Unpredictably: Wetlands in low-order streams; coastal wetlands with wind-driven tides Pulse-fed wetlands Productive High exporters of materials, energy + biota Land managers (waterfowl managers) want stable H 2 O levels Why? Counteract seasonal droughts + restrict H 2 O level fluctuations Water Budget Balance is a result of the following factors: Balance between inflows & outflows of water This is the actual water budget Surface contours of the landscape Subsurface soil, geology, & groundwater conditions Major components of water budgets Precipitation Wetlands typically occur where precipitation exceeds water losses ET Surface runoff Interception + Throughfall Interception: The amount of precip that is retained in the vegetation canopy Throughfall: The portion of precip that passes through the vegetation to the water or substrate below Interception depends on: 1. total amount of precip 2. intensity of precip 3. character of the vegetation Stage of development Vegetation type Deciduous ~ 13% Coniferous ~ 28%

4 Strata of vegetation Tree, shrub, or emergent macrophyte Stemflow: refers to water that passes down the stems of the vegetation (minor component of the water budget) P = I + TF +SF P = total precip I = interception TF = throughfall SF = stemflow Net precip = total amount of water that actually reaches the water surface or substrate of a wetland Pn = TF + SF Pn = P I Surface flow Wetlands can be receiving systems for surface flows (inflows) or surface water streams can originate in wetlands to feed downstream systems (outflows) Inflows Overland flow Channelized streamflow Those located in wide shallow expanses of river channels Coastal salt & brackish wetlands influenced by freshwater runoff & streamflow Seasonal or episodic pulses of flood flow from adjacent streams Read in book describing coefficient determination Groundwater Recharge-Discharge Wetlands Inflows Outflows When surface water (or groundwater) level of a wetland is lower hydrologically than the water table or the surrounding land When the water level in a wetland is higher than the water table of its surroundings (recharge wetland) Perched wetland

5 When a wetland is well above the groundwater of an area Also called a surface water depression wetland Evapotranspiration Refers to the water that vaporizes from water or soil in a wetland plus moisture that passes through plants to the atmosphere Rate of ET is proportional to the difference between the vapor pressure at the water surface (or leaf surface) and the vapor pressure in the air (solar radiation or surface temperature) Transpiration: physiologically controlled by plants through stomatal closure Evapotranspiration: determined with any number of empirical equations that use meteorological variables or by various direct measures Does vegetation increase or decrease the loss of water? Tides Results are conflicting Effects of tides Submergence, Saline soils + anaerobiosis Removing excess salts, reestablish aerobic conditions, nutrients Shift/alter sediment patterns in coastal wetlands uniform surface develops Specific effects of Hydrology Unique vegetation composition Limit or enhance species richness 1 productivity is enhanced by flowing conditions + pulsing hydroperiod but are depressed by stagnant conditions OM accumulation is hydrologically controlled Nutrient cycling + availability are significantly influenced by hydrologic conditions Species Richness Different species have different tolerances Large trees have greater tolerance to flooding than seedlings Establishment depends on seed tolerance to flooding Succession depends on geomorphic evolution of the floodplain Sediment deposition Stream downcutting 1 Productivity

6 Amount of new biomass/time Ex: Wetlands in stagnant water have low productivity Net biomass production of forested freshwater wetlands Flowing water swamps sluggish flow still water OM accumulation + export Excess OM accumulates as a result of: Increased 1 productivity Decreased decomposition and export Nutrient Cycling Nutrients are carried into wetlands by: Hydrologic inputs of precip River flooding Tides Surface and/or groundwater inflows Measurement of Hydrology Precip/TF: rain gauges in random locations throughout the wetland or weather station data Groundwater inflows: few shallow wells will help indicate the direction of groundwater flow Hardest to measure