Aquatic macrophytes in the tropics
Functions
• Important primary producers
• Reduce shoreline erosion
• Habitat for invertebrates, fish, waterfowl, etc.
• Trapping of particles and nutrients
• Substrate for bacteria and periphyton
Aquatic Macrophytes
(“large” plants)
• Free-floating (very significant in tropics, particularly in
water bodies with fluctuating water levels)
- Lemna (duckweed), Salvinia (water fern),
Eichhornia (water hyacinth), Azolla (mosquito fern)
• Rooted (confined to the shallow water)
- Emergent: Typha (cattail), Phragmites (giant reed)
- Submergent: Hydrilla, Utricularia (bladderwort)
- Floating-leaved: Nymphaea (water lily), Victoria
amazonica (giant water lily)
Changes in vegetation with water depth:
Zonations commonly applied to lakes and rivers
Floating
Aquatic
Macrophytes
Lemna (duckweed)
Pistia (water lettuce)
May be native to SE U.S.
Eichhornia
(water hyacinth)
Native to Brazil
Azolla (mosquito fern)
Water hyacinth:
Eichhornia crassipes
Giant water lily:
Victoria amazonica
Floating-leaved
(Nymphaea odorata)
Submerged
(Hydrilla verticillata)
Native to Asia, first introduced
into the U.S. ~1960
Emergent
(Panicum hemitomon)
Complex
zonation in
tropics
Almost 40 species total
Haugaasen and Peres 2006
Seasonally inundated floodplain forest along Amazon River. Note white and
black water stretches (True-color Terra MODIS image; September 8, 2002).
One study recorded
387 species of
herbaceous plants on
the Amazonian
floodplain near
Manaus (Junk and
Piedade 1994).
This was attributed to
the great variety of
habitats associated
with the flood pulse
Cross-section through the middle Amazonian floodplain (Sioli 1984)
The flat topography of the lower Amazon basin and the large seasonal fluctuations
in discharge result in an extensive floodplain which is alternately flooded and
drained with the annual rise and fall of the river level. Some floodplain habitat
cycles between dry and wet phases; other habitat is always inundated.
Macrophyte adaptations to large seasonal
fluctuations in water level
• Well-developed aerenchyma
– improved bouyancy and gas transport
• Long petioles (stalks) attached to surfacefloating leaves which rise and fall with
changing water levels
• Fast vegetative reproduction
– colonize habitat exposed by falling water
levels (terrestrial plants) or by rising water
levels (aquatic plants)
• Rapid growth
– keep up with rising water levels
Paspalum repens
Cross-section of water hyacinth
root showing aerenchyma tissue
Important food
source for grazers
such as capybaras,
manatees, turtles,
herbivorous fish.
Echinochloa polystachya
(creeping river grass)
Very fast growth rates.
Annual net production among
highest for all plants.
During annual floods, over 200 species of fish consume fruits that fall
into the water of South American floodplain forests.
Colossoma macropomum
(blackfin pacu)
Pirarara catfish (redtail catfish)
eating the fruit of a jauari palm.
(Bottom-dwelling omnivorous fish that can reach up to 1.3m and 80kg)
Macrophyte problems?
Pistia stratiotes
pantropical
Lemna in a Louisiana swamp
Azolla caroliniana
Cultural eutrophication (due to sewage inflow,
nutrient runoff, soil erosion, etc) causes
conditions with either excessive macrophytes or
excessive algae. What factors determine whether
a lake will be dominated by plants or by algae?
• The pre-impact condition of the lake
• The extent of the littoral zone
• The nutrient loading rates
Aquatic macrophyte control
Mechanical
removal
Herbicides
Biological control
• Wetlands are among the most diverse ecosystems
• Wetlands have disappeared at alarming rates throughout
the developed and developing worlds
• Wetlands provide important environmental services (for
free) at the population, ecosystem, and global levels
What is a wetland?
Ramsar Convention definition
"For the purpose of this Convention wetlands
are areas of marsh, fen, peatland or water,
whether natural or artificial, permanent or
temporary, with water that is static or flowing,
fresh, brackish or salt, including areas of
marine water the depth of which at low tide
does not exceed six meters."
(http://www.ramsar.org)
The Ramsar Convention on Wetlands of
International Importance (1971) is an
intergovernmental treaty that provides for
national action and international cooperation
for the conservation and sustainable use of
wetlands and their resources.
The 160 Contracting
Parties to the Ramsar
Convention on Wetlands
(shaded; February 2011)
What do Contracting Parties do?
1. Work towards the wise use of all their wetlands through land-use
planning, policies and legislation, management and public education.
2. Designate suitable wetlands for the List of Wetlands of International
Importance ("Ramsar List") and ensure their effective management
3. Cooperate internationally on transboundary wetlands, shared
wetlands, shared species and projects that may affect wetlands.
Global distribution of Ramsar sites (Oct. 2010)
Distribution of 1923 listed Ramsar sites by region totaling
187 million hectares, designated for inclusion in the Ramsar
List of Wetlands of International Importance (March 2011)
Compare
with Table
5.2 (Moss)
Causes for wetland losses and degradation
• Direct human actions
– Drainage (farming, urbanization, forestry, mosquito control),
Groundwater withdrawal, stream channelization, filling
(waste disposal, roads, development), mining (peat), diking,
pollution
• Indirect Human actions
– Sediment retention by dams, hydrologic alteration by roads
• Natural causes
– Subsidence, sea-level rise, drought, hurricanes, erosion,
biotic effects
Why Protect Wetlands?
[note that most of these functions rely on the presence of macrophytes!]
•
Population values
Habitat (e.g., fish, shellfish, waterfowl and hundreds of
endangered and threatened species) and harvest (e.g., animal
pelts, timber, shellfish, waterfowl).
•
Ecosystem values
Flood mitigation, erosion control, aquifer recharge, water quality
protection, subsistence use, aesthetics.
•
Global values
Element cycling (H2O, C, N, S, and others)
Not all wetlands perform all functions nor do they perform all functions equally well.
What can be treated?
• Municipal wastewater
• Mine drainage
• Stormwater runoff, nonpoint-source pollution
• Landfill leachate
• Agricultural wastewater
(dairy, swine, feedlot)
How is wastewater treated?
How can wetlands transform pollutants in runoff?
• Sedimentation (including filtration,
adsorption, and precipitation)
• Volatilization
• Microbial decomposition
• Uptake by plants
Design requires attention to…
• Hydrology (“First, get the water right”)
– drawdowns, rates of inflow/outflow, detention times,
groundwater recharge
• Basin morphology
– gentle slopes (6:1 or better) to maximize the littoral zone,
(wetland plants)
– multiple inflow locations and avoid flow channelization
– variety of deep and shallow areas
• Chemical loading
– loading graphs, retention rates, empirical models
• Soil physics and chemistry
– organic content, soil texture, depth and layering
• Wetland vegetation
– establishment, growth form, species
After wetlands are constructed and wastewater
has been applied, management may include:
• Plant harvesting
– harvest multiple times per growing season.
• Wildlife habitat
– ancillary goal, but often welcomed
• Mosquito and pathogen control
– adjusting hydrology, introducing chemical or biological control agents
• Water-level management
– pulse stability
• Sediment dredging
– expensive; also removes seed bank and rooted plants. Best done
during drawdown
New UT
treatment
wetlands
(aka “rain
gardens”)
Honors rain garden
Lot-10 rain garden