The Littoral Zone and Wetlands (with emphasis on aquatic macrophytes)


Littoral zone -- from high water area to area with no attached plants; interface between land and water; highly productive

I. Aquatic Macrophytes -- almost all were originally land plants and are secondarily aquatic.
    There are also some ferns, mosses, liverworts and large algae.
NOTE:  You only need to remember (recognize) genus names in bold (not others)
    A. Importance of macrophytes
        1. Structurally important
            a. Define the littoral zone
            b. Often considered nuisances
            c. Slow currents and increase sedimentation
            d. Habitat for invertebrates and fish
            e. Increased species diversity

        2. Functionally important
            a. Very productive
            b. Pump of nutrients from the sediments to the water
            c. High rates of evapotranspiration may decrease lake water levels
            d. Most of carbon fixed by macrophytes goes to the detrital/microbial food web

    B. Ecological types of macrophytes – biodiversity of macrophytes
        1. Rooted in sediment
            a. Rooted submersed
                (1) (Type 1) Long stems and compound leaves.  Flexible.
                    a) Potamogeton -- pond weed;
                        ~80 species in a variety of habitats; variable size and shape; wildlife food
                    b) Myriophyllum -- water milfoil
                        (M. spicatum – Eurasian water milfoil is exotic; native is M. sibiricum)
                    c) Najas -- bushy pond weed;
                    d) Elodea -- water weed (has invaded Europe from N. America)
                    e) Chara -- green algae, stoneworts, ‘musk grass’; precipitate calcium carbonate
                            reproduction -- sporangia
                    f) Nitella -- green algae; acidic and dilute waters
            (2) (Type 2) -- plants with stiff leaves in a close rosette or on short, rigid unbranched stems
                    a) Ranunculus (in part) -- water crowfoot
                        buttercup family; lodewort; rams foot; sometimes fed to animals
                    b) Elatine -- waterwort
                    c) Isoetes -- quillwort; club moss; often in oligotrophic lakes or deep in water
                    d) Eriocaulon – pipewort, hatpins;
                    e) Vallisneria - wild celery; tape grass; eel grass

            b. Rooted floating (Type 3) - leaves mostly or entirely floating on the surface; lots of wind stress
                a) Nymphaea -- water lily; nearly circular in shape; notched to the center
                b) Brasenia – watershield; oval and shield shaped leaves.  Stalk attached at center of leaf blades;
                    undersides covered with viscous jelly-like substance
                c) Nuphar -- yellow water lily; spatterdock; cow lily – heart-shaped leaves
                d) Potamogeton
                    again, pondweeds most totally submersed; some have floating leaves
                 e) Trapa -- "water chestnut"; exotic pest in Central N.Y.

            c. Rooted emergent – (Type 4) more supportive material, plenty of sunlight; very productive, but often a low species diversity
                a) Scirpus – bulrush
                b) Juncus – rushes
                c) Pontederia – pickerelweed
                d) Typha – cattail
                e) Eleocharis – spikerush
                    ~150 spp.; Some are cultivated as human food;  some are major food for birds and other animals

                f) Sagittaria – arrowhead; edible rhizomes

                g) Carex – sedge; heavily used by wildlife
                h) Equisetum -- horsetail/scouring-rush horsetail; consumed by wildlife

        2. Unrooted – (can not get nutrients from sediments)
            a. Unrooted submersed
                a) Ceratophyllum -- underwater flowers and mobile pollen; leaves are in whorls on the stem – ‘raccoon’s tail’
                b) Utricularia -- bladderwort; carnivorous

            b. Unrooted floating (Type 5 – entire plant floating)
                a) Eichornia – water hyacinth; exotic pest in S. U.S., S. America and Africa;
                    clogs waterways; increases rate of evaporation of water; not many things eat it;
                    floats into littoral zone and decomposes -- decreases oxygen, hurts fish breeding zones;
                    can block off light penetration

                b) Lemna – duckweed

                c) Spirodela -  largest of the duckweeds
                d) Salvinia - water fern; in waters with high organic content; has root-like structures that are actually modified fronds
                e) Pistia - water lettuce

    C. Zonation of macrophytes
        1. Physical --
            a. Temperature
            b. Light
            c. Pressure -- affects gas transport; limits distribution
            d. Wind and waves
            e. Substrate -- rocks and sand are difficult, do better in soft and organic sediments

        2. Biological (not as well studied)
            a. competition -- light, nutrients, space
            b. herbivory -- not as important compared to grazing on terrestrial plants or in the pelagic; << 25% of aboveground biomass

    D. Adaptations of macrophytes -- how they deal with mostly physical limitations
        1. Water is buoyant -- reduced amount of supportive tissue
        2. Reduced light
            a.  leaves only a few cells thick
            b. leaves are finely divided -- more surface area per volume
        3. CO2 availability -- diffusion slower than in air
            a. assimilation of HCO3- 
            b. lacunae
            c. finely divided leaves
            d. heterophylly -- plasticity of shape of plant -- leaves are more finely divided as get lower –
               CO2 concentrations or temperature
        4. Nutrient availability
            a. most uptake through roots
            b. increased leaf length increases turbulent flow; then can take up nutrients through leaves as well.
        5. Many can reproduce vegetatively -- turions (winter buds) or rhizome sprouting
        6. Produce secondary defense compounds to inhibit algae, epiphytes, and grazers

II. Filamentous algae
    - concentrated in the littoral zone
    - must grow in shallow water where there is adequate light, but can go deeper than macrophytes (no lacunae; extra 
        photosynthetic pigments)
    - no roots, no leaves
    - nutrients from sediments
    - can cause problems/nuisances in small ponds
    - often are chlorophytes (green algae; e.g. Spirogyra, Cladophora) or cyanobacteria

III. Periphyton – algae (and associated microbes) that live attached to other objects, including macrophytes
    - Aufwuchs -- plants and animals that live attached to something
    - can't be moved out of euphotic zone easily
   
    - macrophytes are leaky and release nutrients through stems and leaves; algae take up nutrients from macrophytes
 
   - If periphyton gets dense it will shade the macrophytes -- macrophytes keep growing to try to avoid shading

Wetlands (intermittently to permanently flooded regions)
I. Peat forming (accumulate partially decayed plant matter; ‘mires’)
    A. Bogs --
        o sphagnum-moss dominated communities
        o only water source is rainwater (ombrotrophic)
        o low in nutrients
        o low in primary production
        o form acidic peats (lack of decomposition allows peat to build up)
        o support acidophilic vegetation
    B. Fens
        o Receives nutrients from sources other than precipitation, usually from groundwater
        o may range from acidic to non acidic
        o can have grasses, sedges, or reeds
        o peat can develop due to lack of decomposition in acidic areas, or to high production in non-acidic areas
II. Non peat forming
        - swamps -- mineral soils rather than peat; ground permanently or seasonally submerged;
                vegetation dominated by trees or shrubs (in US common usage)
        - marshes – frequently or continually wet areas with herbaceous vegetation adapted to saturated soil conditions
        - wet meadows – grasslands with water-logged soil near the surface, but without standing water for most of the year

Wetland and Littoral Management

I. Wetland destruction
    · ~1/2 of all wetlands lost in the contiguous U.S. since 1780
    · agricultural drainage; health reasons
    · loss of birds, mammals and fish
II. Wetland restoration
    · resemblance to the original?
    · Peatlands
III. During eutrophication littoral plants are often outcompeted by phytoplankton (shading)

IV. Macrophyte control
    · Mechanical harvesting
    · Herbicides
    · Biocontrol – grass carp; insects
 
 

Interested in wetlands/macrophytes and wetlands?  Two good recent sources are:

Mitsch, W.J. and J.G. Gosselink. 2000.  Wetlands. 3rd edition. John Wiley & Sons, Inc. 920 pp.

Naiman, R.J., H. Décamps, and M.E. McClain. 2005. Riparia: Ecology, Conservation and Management of Streamside Communities  Elsevier Academic Press. 430 pp.

 

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