Wetlands Analysis ~ Waterbudget Exam

hydrology suggests

• water depth

• water flow

• frequency and duration of flooding or saturation

hydrology affects plant communities

• groundwater fed species (yellow birch, eastern hemlock)

• surface water species (timothy, stinging nettle, dandelion, multiflora rose, poison ivy)

• daily tidal inundation (tall smooth grass)

• disturbed hydrology (common reed, cattails, black cherry)

• consistent tidal water levels (short smooth cordgrass)

• permanent flooding/bogs (white water lily, yellow cow lily, pond weeds, water milfoil)

• seasonally flooded (rice cutgrass, golden ragwort, sweet flag, black willow, tear thumb)

• temporarily flooded (garlic mustard, sycamore, eastern cottonwood, bitternut hickory, box elder)

• saturated (white break rush, large cranberry, coast sedge)

types of hydrology changes

• tide restrictions

• reservoirs and ponds with stabilized water levels

• drained eastern forests

controls on wetness

sources, throughflows, outputs, hydroperiod

hydroperiod

the amount of time water is present in a habitat (flood duration) and the timing and frequency of flood events

• depth of water at the surface, to water table

• frequency - time between wet episodes

• duration - how long water persists

US Army Corps of Engineers’ wetland

an area saturated or inundated by surface or groundwater at a frequency and duration sufficient to support and that under normal circumstances do support a prevalence of vegetation typically adapted for life in saturated soil conditions

hydrology indicators

• evidence of surface water (ex: creek)

• evidence of saturated soils (ex: hydrogen sulfide)

• microtopography (small-scale terrain change), drainage

• persistence waters influence soils and vegetation

how persistent waters influence soils and vegetation

• climatology - precipitation and storms

• physical oceanography - limnology

• geology - groundwater and stratigraphy

• soil - infiltration and percolation

• ecology - water usage and storage

water budget

is an accounting of the rates of water movement and the change in water storage in all or parts of the atmosphere, land surface, and subsurface

input - output = change in storage

gains - losses = changes to water level

water cycle

• oceans are the global bulk storage water of water by gravity

• evaporation and precipitation remove and redistribute water back to the continents

• direct monitoring of water level

evaporation

change the energy state of water molecules from high energy (condensed) to low energy (dispersed)

• cooling, heat must be absorbed

precipitation

heat is released to condense water from a low energy to high energy state

• opposite of evaporation

• cry when you’re low in energy

• happens by: cooling during uplift (convection), tropical convection, cold front (cold air rising over warm air), warm front (warm air rising over cool air), occluded front (air of diff temps collide), orographic effect (air lifting over a physical feature), low pressure (cyclonic lifting air, depression hurricane)

cold climate rain processes

• snowpack accumulation

• ice formation and glacial processes

• meltwater and glacial outwash

• sublimation to water vapor

warm climate rain processes

• infiltration (precipitation soaks into the soil)

• surface runoff

• percolation/permeability

• groundwater processes and recharge

• downward and later flows

• capillary forces

• Darcy’s law and gradient flow

Darcy’s law

a constitutive equation that defines the flow of a fluid through a porous medium; the flow between two points is directly proportional to the pressure differences between the points, the distance, and the connectivity of flow within rocks between the points

ecological processes of hydrology

root uptake and plant use

• partly a function of evaporation - stomates, turgor pressure regulation to slow water losses

water cycle water budget

P = precipitation

ET = evapotranspiration

G = groundwater flow

S = surface water flow

T = tides

t = time

H = water level

water budget precipitation

wetlands dominated by P have large dh/dt (fluctuating water levels)

• prairie potholes, vernal pools, wet meadows, closed depressions

• physical measurements: rain gauge

• remote measurements: estimate from weather radar

rain gauge

physical precipitation measurement

• manual - read from stick or side gauge

• automatic - tipping bucket, read triggers (tips)

  • calibrated for reservoir: collection surface

weather radar estimates

remote measurement of precipitation

• vertical profiles of reflectivity

• gauge to radar statistical adjustment (NWS method)

managing rainfall data

record precipitation data as depth (in or mm)

volume of precipitation = depth x area = acre of feet of water

• a 1in rain over a 24 acre reservoir: 1/12 ft x 24 acres = 2 acre feet of water

• metric might make more sense (m³)

transpiration

the passive process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers

varies by plant type (shallow vs deep root system)

• shallow: similar ________ rates to a soil film’s evaporation rate

• deep: have access to water tables = higher ________ rate

evapotranspiration

the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants

Pan evaporation

daily measure of water loss/replacement in an open pan

• doesn’t measure plant use - usually much larger than open pan for moist soils and tall vegetation, less for short vegetation on dry soils

• lysimeter = weighed system

Penman Monteith equation

physical calculation to estimate evapotranspiration using an observed reference surface, removing the need to define parameters for each crop and stage of growth

• evapotranspiration rates of different crops are related to the evapotranspiration rate from the reference surface through the use of crop coefficients

Hargreaves equation

equation to estimate evapotranspiration from min, max, & mean air temp, solar radiation; temperature-based method

• underestimates ET in windy conditions

• overestimates ET in extremely humid or dry air

Thornthwaite equation (1948)

estimate of daily potential evapotranspiration (PET) based on air temperature and latitude

• measured multiple sites, fitted equation

specific yield of aquifers, ponds

in unique circumstances, ET can be calculated by daily changes in water level

• overnight, a closed waterbody receives groundwater, but ET is near zero = water level rises overnight

• during the day, groundwater inflow is about the same as overnight, but ET is high

• simplify water budget equation

specific yield estimate of ET

comparing estimates of ET

Pan evaporation = overestimates ET

Penman Monteith = great at estimating evaporation, underestimates ET in wetlands (surface area of plants)

Thornthwaite = ok, least costly to implement

surface water flows (S)

wetlands dominated by S have large dh/dt (fluctuating water levels), especially related to river flooding

• duration may be short as floodwaters rapidly rise but flow through

• significant sedimentation = disturbances

• physical measurements: stream gauge

• remote measurements: estimate from weather radar

stream gauge

physical measurement of surface water flow

• a “yardstick” for how deep the water is

• USGS network of stream gauges

• pressure transducers for automation

ratings curve

water level coupled with discharge measurement

• multiple measures of water depth (stage) and discharge (water flow)

• curve-fit equations allow to calculate discharge from stage (measured by pressure transducer)

timed gravimetric

capture and weigh method to measure discharge for ratings curve

area-velocity

method to measure discharge for ratings curve

• cross-sectional area of flow (L x W)

• velocity (by propeller or otherwise)

• open channel or pipe

Manning’s equation

method to measure discharge for ratings curve

• area

• slope

• depth of water

• bottom roughness

hydraulic structures

method to measure discharge for ratings curve

• engineered flow channel

• height ~ flow

• transducers or floats

estimating surface flow (S) from rainfall

divide rainfall into “rations,” and estimate runoff from each storm (as a fraction) = hydraulic coefficient c

• values 0.05-0.5 = permanent vegetation and permeable soils to urban areas

• storm monitoring - get rainfall amount from single storm, find receiving waterbody (pond) and measure water volume change and watershed area; assume G+ET is small in a 2-day period

groundwater flows (G)

hard to directly monitor without specialized equipment, so measure all other components and any difference is this

• must be measured as a gradient - change in water level between distance = dH/L

• gaining streams, losing streams (saturated, unsaturated)

gaining streams

surface water gains from groundwater upwelling (aquifer discharge)

losing streams

surface water is lost from stream to groundwater (aquifer recharge)

• B saturated contact

• C unsaturated contact

network of monitoring wells

G must be measured as a gradient change in water level between distance (dH/L)

• follow Darcy’s law

• estimate regional flow with depth of aquifer and 1D or 2D flow (radial flow to a pond?)

seepage meters/ hydraulic potentiomanometer

measure change in head from the open water to a depth below the lake (dH/L)

• groundwater flow across lakebed = where discharge happens

• measure hydraulic gradient across sediment bottom (dH/L)

• trap inflow across bottom in a barrel (Q)

• solve for K

• Darcy’s law

putting it all together

ecosystem function

• water level change controls some plant communities (dh/dt)

• water chemistry controls some plant communities (G_i vs S_i)

• nutrient cycling is often pulse dependent for infiltration, biological interactions

• organic matter - peat accumulation/decomposition

hydroperiod

depth of flooding (inundation)

may alter vegetation composition

• enhance/limit species richness

• flowing water = enhances plant diversity

• flow action stimulates new niches

• disturbances to seed bank

primary productivity

increased by water flow

• stagnant water = lower productivity, low oxygen, low nutrient imports

• flowing water = higher nutrient loads, higher oxygen, higher productivity

organic matter accumulation and export

• accumulation rates

• decomposition rates

• anoxia

• dystrophic water (fulvic acid and tannins; nutrient starved, acidic)

• eutrophic water (rapid algae growth; nutrient rich, likely alkaline)

nutrient cycling - water outflow

• nutrient inflows, exports

• nutrient transformations (anoxia)

• P more soluble in anaerobic conditions

• NH₄ more stable in anaerobic conditions

• denitrification and conversion of NO₃ to N₂

nutrient cycling - pH changes

• soils that are anaerobic will have stable NH₄ and sulfides (HS^-)

• soil dries during drought, O₂ enters and oxidizes N to nitrate and S to sulfate, releasing H⁺ (acid forming)

• dry soils that flood during high water become anaerobic (alkaline forming reactions)

flooding key concepts

• different species have different physiological responses to flooding

• large trees generally more tolerant to flooding than seedlings

• flooding has major control over which species become established

• plant succession depends on environmental/hydrologic change (deposition/erosion)

water budget important facts

• faster water flows increase plant diversity; stagnant waters have little (monocultures)

• water scour (sediment removal) opens new niches and creates habitat

  • river flooding → sandbars, gravel, silt deposits, natural levies

• ecosystem productivity increases with water velocities in flow-through systems

  • aeration, removal of toxins, dilution of hormones, N and P supply and transformation

• hydrology is a primary control over nutrient imports

• organic matter accumulation and preservation is a key component of wetland systems

  • repeated wetting/drying accelerated decomposition

  • stagnant water improves accumulation

  • slow waters have faster decomposition than fast (detritivores)

• nutrient cycling - chemical reactions are unique, but O₂ generally speeds up all biological reactions

• intermittent wet/dry cycles slow reactions that need either O₂ or anaerobic conditions (foster biodiversity and chemical diversity)

growing season

the definition of wetlands requires that anaerobic conditions be present during the growing season

types of hydrology observation

• direct observation of surface water or saturated soils (Group A)

• evidence of prior inundation or ponding (surface water) (Group B)

• evidence of soil saturation, present or recent (Group C)

• landscape, vegetation, and soil features that suggest contemporary hydrology (not relic) (Group D)

primary hydrology indicators

reliable evidence of long-lasting saturation or inundation; need one to indicate the presence of wetland hydrology

• presence of water (A1 surface water; A2 high water table; A3 saturation, B1 water marks, B13 aquatic fauna, etc., C3 oxidized rhizospheres along living roots, etc.)

• presence of saturated soils (B2 sediment deposits, B5 iron deposits, C1 hydrogen sulfide)

• clear evidence of flow channels and deposition

secondary hydrology indicators

less reliable evidence of wetness; must be supported by at least two

• vegetation patterns (B16 moss trim lines, B8 sparsely vegetated concave surface, D1 stunted or stressed plants)

• microtopography (looks like a low spot) (B6 surface soil cracks, D2 geomorphic position, D4 microtopographic relief)

• crayfish burrows (C8)