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

Emergent

(

Panicum hemitomon

)

Floating-leaved

(

Nymphaea odorata

)

Submerged

(

Hydrilla verticillata)

Native to Asia, first introduced into the U.S. ~1960

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 surface floating 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

Cross-section of water hyacinth root showing aerenchyma tissue

Paspalum repens

Echinochloa polystachya

(creeping river grass) Very fast growth rates.

Annual net production among highest for all plants.

Important food source for grazers such as capybaras, manatees, turtles, herbivorous fish.

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 Herbicides Mechanical removal 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 160 Contracting Parties to the Ramsar Convention on Wetlands (shaded; February 2011) 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.

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 (H 2 O, 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, non-

point-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

Honors rain garden Lot-10 rain garden New UT treatment wetlands (aka “rain gardens”)