Freshwater Wetland Ecosystems Final

Aquatic vs Hydraulic civilizations

Aquatic: Adapt to water abundant floodplains and deltas, working within the aquatic landscape

Hydraulic: Control water flow with dikes, dams, pumps, etc. seeking to control the natural world

U.S. Historical view on wetlands

• seen as wastelands

• often viewed as areas with pests and threats

• were often hydrologically altered

How this influenced wetland policies:

• for over 120 years, it was US policy to drain wetlands

  • swamp lands act → drained wetlands used for agruculture

Direct effects on wetlands

• Agriculture, forestry, and mosquito elimination practices

• stream chanellization/dredging (flood control)

• filling → roads and development

• water pollution

• wetland mining

• groundwater withdrawl

Indirect effects on wetlands

• sediment retention by dams

• hydrologic alteration by roads, canals, etc

• land subsidence due to resource extraction & river alterations

Natural effects on wetlands

• subsidence

• sea level rise

• drought

• hurricanes/storms

• erosion

• biotic effects

Conversion

Draining, dredging, and filling

• mostly due to conversion to agriculture

  • most notable in the midwest bottomland hardwood forests

  • for urban and industrial development

  • loss trongly correlated with population density

Hydrologic modifications

• Flood control:

  • draining wetlands and adjacent uplands → mosquito control, limiting riparian area flooding

• Navigation and transportation:

  • improved transport among ports

  • canal formation

  • hydrologic isolation from highway construction

• Industrial activity:

  • canals dredged for oil well access and pipelines

Peat mining

• 75% of peat harvest occurs in Ireland and northeastern Europe

• peat is harvested for fuel, horticulture, and agriculture

• sustainable practices are almost impossible given how slow peat accumulates

Water pollution

• Eutrophication: changes in species composition and oxygen content of water

• Toxic inputs: acutely harm wetland communities

“No Net Loss”

National Wetlands Policy Forum (1988)

• Interim goal: no net loss of wetland area and function

• Future goal: net gain of wetland area and function

Clean Water Act (1972 Ammendments)

Considered the “primary vehicle” for wetland protection in the US

• Section 404 of the CWA: Dredging or filling of “waters of the US” (WOTUS) requires a permit from the US army corps of engineers

• 404 permit screening seeks 3 things, in this order:

  • 1) Avoidance: avoid wetland impacts where possible

  • 2) Minimization: minimize the potential impacts on wetlands

  • 3) Mitigation: provide compensation for any remaining, unavoidable impacts through wetland restoration and creation

Swampbuster (1985)

Provision within Food Security Act: Denies federal subsidies to any farm owner who knowingly converts wetlands to farmlands

• prior to this provision, normal ag. and sivilculture activities were exempt from section 404 permit requirements

• emphasizes soils component of wetland designation

Wetland Deliniation

USACE → developed guidelines to determine regulatory (jurisdictional) wetlands, 1987

• this process = wetland deliniation

• USACE publishes regional supplements and some states have more specific wetland policy, which affects deliniation

Four realities of the Millenium Ecosystem Assessment

1) Humans have changed Earth’s ecosystems over the last 50 years of the twentieth century more than any other period in human history

2) These changes have contributes to substantial gains in wellbeing and economic development, but at the cost of losing many ecosystem services.

3) The ecological degradation is expected to grow significantly worse in the first half of the twenty-first century

4) reversing this degradation will involve significant changes in policies, practices, and institutions that are not yet in place

Ecosystem Services (broad definition)

The benefits people obtain from ecosystems

Supporting ecosystem services

Benefits of biodiversity that allow ecosystems to exist

• primary production

• soil formation

• nutrient cycling

Provisioning ecosystem services

Benefits of biodiversity that provide products for human use

• animals harvested for pelts

• waterfowl and other birds

• fish and shellfish (as habitat and nurseries)

• vegetation and building materials, fiber, and food

• peat harvest

Regulating ecosystem services

Benefits of biodiversity that mitigate disturbance or disaster

• flood mitigation

• storm abatement and coastal protection

• climate regulation

• aquifer recharge

• water quality

Cultural ecosystem services

Benefits of biodiversity that provide aesthetic, spiritual, or recreational value

Effects of wetlands on climate change → Sequestration and Storage

• Sequestering carbon is not the same as storing carbon

• 20-30% of C in Earth’s soils is stored in wetlands

• boreal peatlands store an enormous amount of C → they are considered true carbon sinks

Effects of wetlands on climate change → Emissions

• wetlands emit CH4 (methane) and N2O (nitrous oxides) via natural processes. These are potent greenhouse gasses

• disturbance of wetland soils turns carbon sinks into carbon sources via CH4 release.

Effects of wetlands on climate change → Thermal Buffering

• “Hydrologic setting mediates local growth sensitivity to changes in ambient climate conditions” (Raney et al. 2016)

• water has a higher specific heat capacity than does air, so it changes temperature more slowly

• groundwater flow is particularly stable in terms of amount and temperature

Effects of climate change on wetlands → Sea Level Rise

• If sea level rise is not met with equivalent sediment accreation, coastal wetlands will disappear due to Increased inundation, erosion, and saltwater intrusion

Effects of climate change on wetlands → Inland Wetland Function & Distribution

• changes in precipitation and evapotransporation alter wetland function and distribution

  • temperature increases and precipitation decreases produce the most dramatic wetland loss

• permafrost (boreal peatlands) melting = wetland loss and carbon emissions

Ecological valuation

Quantifies wetland values based on the functional services and biological components

Economic valuation

Quantifies wetland values based on the dollar amount the public is willing to pay for the good or service rather than be without it (e.g. “replacement value”)

Problems with quantifying ecosystem services

• terms “value” and “service are anthropocentric and don’t acknowledge ecological etities’ intrinsic value

• value of a wetland depends on its landscape context

• most valuable wetland products are “common” recources

• large scale ecosystem services (nutrient cycling, carbon sequestration, etc.) are hard to fully characterize and harder to quantify

The Faustian Bargain

The need to justify conservation with economic reasons, while knowing that conservation is important for reasons beyond economic or material benefit.

Intrinsic Value

Value of ecosystems (their components and functions) is not tied to economic benefit or judgement of human worth

• ex: they provide a habitat for various biota

The Precautionary Principle

Biodiversity elements (species, genes, etc.) with potential use should not be lost simply because we currently do not know their value

• Loss of biodiversity is generally irreversible

Why is wetland management subjective?

• before protective legislation → draining, dredging, and filling was considered “managing”

• currently → “management” refers to maintaining or enhancing wentland functions and values

Ecosystem perspective

• Focuses on function

  • water recharge

  • Nitrogen sink

• “Self design”

• species relatively less important than valued functions

• wetland functions primarily a product of hydrologic setting

Community perspective

• Focuses on natural community patterns

  • species composition and structure

• Characteristic species patterns suggest characteristic functions also being performed

• recognition that species can be important drivers of ecosystem functions

General perspective on wetland management

• Sound management for wetlands considers both ecosystem perspective AND community perspective

• The site context (landscape, social, political, economic) affects whether one takes more of an ecosystem or community perspective

Human Impacts Model

Considers broad categories of human alterations to wetlands:

• hydrologic modification

  • hydroperiod

  • water source

  • flow rate

• Biogeochemical modification

  • nutrient loading

  • pH modification

  • salinization

  • freshening

  • thermal alteration

• Disturbance Regime modification

  • type

  • frequency

  • duration

  • intensity

  • timing

• Species pool modification

  • Invasion

  • extinction

  • habita fragmentation/dispersal limitation

  • exhaustion from seed bank

Water level management guidelines

Water level should…

• vary from year to year and/or within-year

• be lowest during the growing season

Nutrient inputs management guidelines

Restrict nutrient inputs because…

• the more kinds of infertile (marginal) habitats available, the more plant species can coexist

• eutrophication generally reduces species richness

Monitoring

The key to success and flexibility, which is adaptive management

Ecological restoration

Process of assisting the recovery of an ecosystem that has been damaged, degraded, or destroyed

Main takeaways:

• many restored ecosystems needs active management for some time after recovery

• some restoration involves the creation of new wetlands

• recovery of hydrology, biogeochemistry, community adaptations and traits, and succesional processes

• restoration may be incomplete or incapable of completely reversing anthropogenic impacts

Reference ecosystem

• ecosystem that is a model for a degraded system’s restoration → a target

• must incorporate a range of conditions, and mechanisms of resistance and resilience

Threshold approach

• restoration efforts (and decisions) initially based on which threshold(s) a degraded ecosystem has crossed

• If the threshold is controlled by abiotic limitations, recovery is longer and harder

Directing succession

Land managers take advantage of successional pathways or stages to restore ecosystem function

Habitat heterogeneity

A variety of habitat types

• causes: natural legacy effects, natural disturbances, human activity

• can generate species diversity at local and regional scales

Habitat fragmentation

Large expanse of habitat is transformed into many smaller patches of habitat

General effects:

• total amount of habitat decreases

• number of patches increases

• amount of edge habitat increases

• patch isolation increases

effects of fragment size:

• smaller fragment size = lower spp. diversity

• smaller fragment size = increased trophic cascades

effects of fragment edges:

• ecotones form along edges

• edges change the abiotic conditions and spp. composition of the habitat

Corridors, connectivity, and conservation:

• metapopulation: regionally connected populations of a spp.

• corridors → allow connectivity between habitat patches

• conservation efforts often week to protect metapopulations w/ corridors

Biodiversity hotspots

• Biodiversity is not evenly distributed across earth

• Norman Myers (1988) established regions of conservation priority based on endemism and vulnerability → these are hotspots

• Hotspot criteria:

  • irreplaceable (ex: at least 1500 endemic spp. of vascular plants)

  • Threatened (lost at least 70% of original habitat)

SLOSS

Single Large Or Several Small → two different approaches to conservation

Given the same total amount of land area…

• single large favors one sizeable, contiguous preserve

• several small favors multiple smaller areas of land

Swamp Land Acts 1849, 1850, 1860 (Drainage Acts)

Up until the 1970’s, US army corps of engineers promoted wetland drainage thru the Natural Resources Conservation Service

Wetland mitigation

offsets for unavoidable impacts to wetlands under a permit

• mitigation bank → built ahead of impacts

• in lieu fee program → built within 3 years of credit sale

• Permittee responsible → built concurrent with impacts

Sources used by Dr. Landis

• Paleoecology

• archaeology

• missionary records

• maps/surveys

• oral history

• ethnobotany

What communities did Dr. Landis find?

• shrub swamp

• cedar swamp

• inland salt marsh

• rich fen

• beech-maple forest

General impacts of flooding on plants

• Changed hormone levels

  • Ethylene → structural adaptations

  • Abscisic acid → stomatal closure

• Reduced gas exchange

• reduced water uptake

• altered nutrient uptake

Morphological (structural) plant adaptations to flooding

• Aerenchyma:

  • allows oxygen to diffuse to flooded plant parts

  • decreases respiratory demand → reduced cellular density

• Adventitious roots:

  • new root growth from stems or leaves

  • above the anaerobic zone

• Stem hypertrophy:

  • swelling of lower stem

  • buttressing, helps with stability

• Stem elongation

  • rapid vertical stem growth

  • keeps photosynthetic organs out of the water → think lillypad

• Lenticels:

  • small pores on woody plant surfaces

  • conduits to aerenchymous tissue

• Root adaptations:

  • shallow root systems

  • pneumatophores or “knees”

Physiological (funcional) plant adaptations

• Pressurized gas flow:

  • pushes oxygen to roots

  • pressure gradient driven by temp. differences

• Rhizosphere oxidation:

  • extra oxygen pushed out of plant roots

• Decreased water uptake:

  • intolerant of anaerobic conditions

  • flooding limits root metabolism

• Altered nutrient absorption:

  • sybiotic plant root+fungi relationship

  • carnivory → increased nitrogen intake

• Sulfide avoidance:

  • oxidation of sulfide to make it safer

  • metabolic tolerance

• Anarobic respiration:

  • less efficient, and causes toxic byproducts

Whole plant strategies

• Timing of seed production:

  • delayed or accelerated flowering

  • seeds made in non-flood season

• Buoyant seeds and seedlings:

  • float until they reach high or unflooded ground

  • viviparous seedlings

• Persistent seed banks:

  • cache of dormant seeds in soil

  • wait for non-flooded conditions for germination and establishment

• Resistant roots, tubers, and seeds

  • can survive long periods of submergence

• Evergreen sclerophyllus foliage:

  • tough, leathery leaves → protection from wilting and herbivory

• Brittle twigs:

  • rapid twig breaking protects main trunk/stem

  • twigs also often propagules

Facilitation

the presence of one species alters the environment in a way that enhances the growth, survival, or reproduction of another species

Interspecific competition

Individuals from one species consume or drive down the abundance of a resource or defend the resource, to the point that individuals from another species cannot persist

Clementsian community

• Communities are “superorganisms” with each association of species being an interacting, integrated component of a larger unit.

• species in association rise to max abundance at the same point

• transitions between communities are narrow or sharp

• Autogenic

• interdependent species assembly

Gleasonian community

• Community continuum concept: species coexist in communities due to similarities in their tolerance and requirements, but are not exclusive to that association

• changes in species abundance and transition along a gradient are gradual and difficult to identify.

• allogenic

• Independent species assembly

Modern community boundaries summary

Clementsian and Gleasonian views both accepted, but Gleasonian view (community continuum concept) is considered the most broadly accurate.

Zonation

changes in physical and biological structures of communities as one moves across the landscape. It manifests by changes in species composition and/or diversity

• often driven by:

  • physical processes (sediment deposition, flooding)

  • abiotic gradients (salinity, pH)

  • competetive heirarchies

Life History Strategies (C-S-R model) (Grime)

There are tradeoffs to being a good competitor, or stress-tolerator, or disturbance-tolerator.

• competetively dominant spp. can outcompete and exclude weaker competitors

• less competitive spp. often occupy niches that are physiologically suboptimal

Centrifugal Organization Model (Keddy)

Dominant spp. occupy core habitat and exclude weaker competitors to “peripheral” habitats that are more stressful/more disturbed.

• greater species richness in peripheral habitats

• peripheral or marginal habitats are important for conservation → higher densities of rare spp.

Environmental Sieve Model (Van der Walk)

Vegetation patterns in a community are predicted by 3 traits:

• propagule longevity (in the seedbank)

• plant lifespan (annual or perrenial)

• propagule establishment requirements (drawdown)

The “sieve” selects for particular traits

How does the bog climax hypothesis counter hydrarch succession?

• Allogenic factors such as precipitation play a major role in the bog climax

• persistence of wet conditions

• sphagnum moss dominance

• Classical Hydrarch Succession = Predictable, linear progression from water → land.

• Bog Climax Hypothesis = Wetland may reach a stable, non-forested climax, contradicting the idea that succession always ends in upland forest.