Issues for coastal marshes and pondsJudith S. WeisRutgers UniversityRI Natural History Survey 2011

SALT MARSHES AND COASTAL PONDS: MANAGEMENT ISSUES

JUDITH S. WEIS RUTGERS UNIVERSITY

RHODE ISLAND NATURAL HISTORY SURVEY

APRIL 2011

Functions of Salt Marshes• Breeding grounds for: Fish (menhaden, striped

bass, summer flounder, alewife, shad) shrimp, crabs, birds. Two-thirds of all marine species depend on tidal wetlands for a portion of their life cycle.

• Stopping place for migratory birds.

• Habitat for mammals: Racoons, muskrats, etc.

• High productivity – comparable to coral reef or rain forest - supports lots of life

Other Ecosystem Services

• Fisheries – source of food for humans

• Removing pollutants

• Sequestering carbon

• Flood control – shoreline protection

MARSHES vs HURRICANES• Storm protection - buffer• Emergent wetlands greatly diminish wind

penetration and wave strength• Maintain elevation by trapping sediments• Economic damage inversely proportional to

amount of wetland area

Human Impacts on Salt Marshes: Physical Changes

Mosquito ditching. By the 1930s, most salt marshes ditched for mosquito control. Impacts - drainage of marsh pools, lowered water table, vegetation changes. Ditching drains all standing water. Not very effective in controlling mosquitoes, but reduced populations of birds and fish that used marsh pools

Open marsh water management (OMWM).

Creating or restoring natural shallow pools, allowing water to remain on marsh at low tide; fish stay and eat mosquito larvae. Birds attracted to the pools and also eat mosquito larvae. More effective in controlling mosquitoes.

These deep marshes were filled in for homes and lawns. Many acres filled during development of East Coast cities. Major airports on filled marshes.

FILLING

Residential land-use change impacts run-off. More impervious surface --> more runoff - impairs water quality.  

LAND USE

Bridges and culverts built over creeks restrict water flow

Areas became less saline since less seawater reaches them, allowing less salt-tolerant plants to invade, like common reed, loosestrife, and cattails.

ROADS AND RAILROADS

Bulkheads - vertical structures to control erosion

Revetments - large rocks or boulders.

Remove shallow water habitat and prevent marshes from

migrating inland as sea level rises.

Straightened creek channel makes currents run faster, narrower and deeper, preventing sediments from settling in nearby wetlands.

Shoreline Hardening: Bulkheads

CCA-TREATED WOOD IN ESTUARIES

(From Weis, J.S., and P. Weis (1992). J. Exp. Mar. Biol. Ecol. 161: 189-199.)

EPIBIOTA:

• UPTAKE BY RESIDENT ORGANISMS• TOXIC EFFECTS IN OYSTERS – GENOTOXIC

AND HISTOPATHOLOGICAL• SETTLEMENT OF EPIBIOTA ON

EXPERIMENTAL PANELS DELAYED• UPTAKE AND EFFECTS GREATEST FROM

NEW WOOD AND IN POORLY FLUSHED CONDITIONS

SEDIMENTS & BENTHOS • GRADIENT OF METALS IN SEDIMENT (FINE

FRACTION) AND IN BENTHOS GOING OUT FROM BULKHEAD

• REDUCED BENTHIC COMMUNITY – ABUNDANCE, SPECIES RICHNESS AND DIVERSITY – BY CCA BULKHEADS

• BY 10 M AWAY, COMMUNITY IS COMPARABLE TO REFERENCE SITE (BULKHEADS OF OTHER MATERIALS)

• TROPHIC TRANSFER FROM ALGAE GROWING ON WOOD TO SNAIL GRAZERS – TOXIC TO SNAILS

CURRENT SALT MARSH PROBLEMS

• Subsidence = sinking

• Channelling rivers (levees) to prevent flooding deprives marshes of new soil to build up its elevation, so marsh sinks (Louisiana)

• Sea level rise

LESS MARSH, MORE OPEN WATER.

Healthy Marsh

Normal

ErodingMarsh

Booming(more edge habitat)

DepletedMarsh

Busting

Marsh Dieback in Cape Cod

The culprit Sesarma reticulatum, a native marsh crab that is growing out of control, probably because of depletion of its natural predators

Global sea level rises due to thermal expansion of the oceans, and melting of glaciers. The rate of sea-level rise during the 20th century was about 10 times higher than the average rate during the last 3,000 years and is accelerating.

INTERTIDAL SALT MARSHES MUST INCREASE ELEVATION, MOVE INLAND, OR BE SUBMERGED.

MARSH MIGRATION INLAND• WILL THEY RUN INTO ROUTE 1, MAIN

STREET, AND PARKING LOTS?

• IRONICALLY, THE INVASIVE PLANT PHRAGMITES, WHICH IS OFTEN REMOVED, INCREASES ELEVATION, AND MAY ALLOW MARSHES TO KEEP UP WITH SEA LEVEL.

Biomagnification. Concentration of some contaminants, such as mercury, increases as it moves up the food chain. Organisms higher in the food web have higher concentrations, represented by size of the dot.

Chemical Changes - Pollution

EUTROPHICATION• EXCESSIVE INPUTS OF NUTRIENTS

• CAN BE FROM POINT SOURCES – SEWAGE TREATMENT PLANTS

• CAN BE FROM NON-POINT SOURCES – INTERMITTENT

RUNOFF- AGRICULTURE AND

URBAN ENVIRONMENTS

Excess nutrients lead to algal blooms.

When blooms die and sink, their decomposition uses up the oxygen in deeper water.

HARMFUL ALGAL BLOOMS• Some algal blooms are toxic. Toxins they produce

can make their way up the food chain, causing animal mortality.

• Algal toxins are taken up by shellfish (mussels, oysters), that humans can eat.

“Red tide”

Alexandrium, the cause of PSP

3. BIOLOGICAL ALTERATIONS: INVASIVE SPECIES – COMMON REED

PRESENT IN HIGH MARSH FOR 1,000 YEARS BUT IN ’60S STARTED SPREADING AND MOVING DOWN

NEW VARIETY INVADING EAST COAST BRACKISH MARSHES, REPLACING CORDGRASS IN LOW MARSH, GREATLY REDUCING PLANT DIVERSITY IN HIGH MARSH.

Research Sites

Saw Mill Creek:Spartina alternifloraPhragmites australis

Mill Creek:Restored Spartina

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Creek Bank Habitat

Edge of the Vegetation Habitat

Benthic Community

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HABITAT CHOICE

A. LABORATORY MICROCOSMS:

GRASS SHRIMP, FIDDLER CRABS, OR MUMMICHOGS PUT INTO CENTER OF TANK WITH PHRAGMITES ON ONE SIDE AND SPARTINA ON THE OTHER. COLLECT ANIMALS FROM BOTH SIDES AT END OF EXPERIMENT

??

HABITAT CHOICE: RESULTS

1. NO DIFFERENCE IN SELECTION OF EITHER PLANT SPECIES BY GRASS SHRIMP OR FIDDLER CRABS

2. MUMMICHOG CHOICE DEPENDED ON FISH SIZE AND MICROCOSM SIZE – NOT CONSISTENT

HABITAT REFUGE VALUE

MICROCOSMS – METHODS• GRASS SHRIMP PUT IN MICROCOSMS

OF EITHER PHRAGMITES OR SPARTINA

• MUMMICHOG PREDATORS ADDED

• AFTER 8 HOURS, SURVIVING GRASS SHRIMP COUNTED

HABITAT- REFUGE VALUE

MICROCOSM RESULTS:

• EQUIVALENT SHRIMP SURVIVAL IN PHRAGMITES AND SPARTINA MICROCOSMS

HABITAT: REFUGE VALUE

FIELD STUDY: TETHERED GRASS SHRIMP ON BOTH

SIDES OF SMALL TIDAL CREEK IN SAW MILL CREEK IN HACKENSACK MEADOWLANDS, WHICH HAS PHRAGMITES MARSH ON ONE SIDE AND SPARTINA MARSH ON OTHER

Results: Equivalent survival on both sides

HABITAT: NEKTON

• SAMPLE MONTHLY AT SITES WHERE PHRAGMITES AND SPARTINA ARE CLOSE TO EACH OTHER - FLUME NETS AND KILLIE TRAPS

HABITAT - NEKTON

• MUMMICHOGS LESS ABUNDANT ON PHRAGMITES; MAYBE BECAUSE THEY ARE MOSTLY YOUNG OF THE YEAR (KNOWN TO PREFER SPARTINA)

• ALL OTHER SPECIES EQUIVALENT

FOOD VALUE

• PUREE LEAVES TO MAKE DETRITUS

• FEED 6 TYPES OF DETRITUS TO ANIMALS, MONITOR SURVIVAL AND GROWTH

• FIDDLER CRABS – UCA PUGILATOR AND U. PUGNAX, GRASS SHRIMP PALAEMONETES PUGIO

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U. PUGILATOR

All types of detritus equally good

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All types of detritus equally bad

Excretion

Sediment Storage & Porewater Flux

Plant Uptake

Trophic Transfer

Roles of Plants in Metal Fluxes of Salt Marshes

Litterfall

Phragmites australis Spartina alterniflora

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Hg Cr

Field study

Leaf Tissue Concentrations

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ControlPhragmites

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abab aaab

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Greenhouse - Pb dosing study

High PbLow Pb

Seasonal Mercury (Hg) Release

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Field - Excretion of metals from leaves

Mercury Release vs. Leaf Concentration

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Mercury Concentration in Leaves (ng g-1)

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Linear (Spartina)

Linear (Phragmites)

Excretion of Hg from leaves correlates with leaf Hg concentration

Findings• Phragmites provides equivalent habitat for

most fishes and marsh invertebrates (but not killifish)

• Phragmites detritus gets into food webs the same as Spartina detritus and is equally nutritious (or non-nutritious)

• Phragmites sequesters metal pollutants more efficiently than Spartina by keeping more belowground in roots rather than moving into leaves where it can cycle in the ecosystem

Marsh Restoration• Many efforts--but still in early stages, not yet a science

• Mitigation for “no net loss”—newly created marsh may not be equivalent to old one

• What are endpoints for success? – Species composition? – Vegetation? – Canopy architecture? – Fish? – Diversity? – Productivity?

Restoration Issuesproviding proper tidal flushing and topography –

tidal creeks

elevation is critical to desired plants

substrate - soil texture/amount of organic matter

salinity-if too low, converts to different vegetation

eutrophication and contaminants

disturbance - trampling by people

invasive exotics

Bridges and culverts often too small for tidal flow. Original 12-inch culvert under a road provided inadequate tidal exchange. New culvert of four 24-inch pipes allows better tidal exchange.

RESTORATION BY INCREASING TIDAL FLOW

prior to restoration Saltmarsh planting

OTHER TECHNIQUES INVOLVE HERBICIDES TO KILL PHRAGMITES, BULLDOZERS TO LOWER THE MARSH LEVEL, AND REPLANTING SPARTINA

IMPROVEMENT OVER TIME• PLANTS RETURN QUICKLY, BUT MAY HAVE LOWER STEM DENSITY &

HEIGHT• SOIL ORGANIC MATTER SLOW INCREASE• GRADUAL INCREASE IN INVERTEBRATE DENSITY, AND DIVERSITY • TAXA WITH DISPERSED LARVAL STAGES SLOWER TO RETURN • ~15-20 YEARS FOR IT TO APPROACH “NORMAL” LEVELS OF

BIODIVERSITY AND ECOSYSTEM FUNCTION

TAKE-HOME MESSAGESIF YOU WANT TO RESTORE A MARSH BY REPLACING

PHRAGMITES WITH SPARTINA, YOU SHOULD EITHER:• 1. CHOOSE SITES WITH LOW LEVELS OF

CONTAMINATION, OR• 2. CLEAN UP THE SITE BEFORE OR WHILE

RESTORING IT• REMEMBER: PHRAG MARSHES ARE NOT

ECOLOGICALLY USELESS BUT ARE FUNCTIONING ECOSYSTEMS THAT CAN BE MANAGED, RATHER THAN ALWAYS DESTROYED AND REMOVED

AND REMEMBER• Plan for Sea Level Rise lest your marsh

turn into a coastal pond in 10 or 20 years