The Scientific Basis for Protecting Wetland Buffers

Robert Buchsbaum Massachusetts

Audubon Society

Scott JacksonUniversity of Massachusetts

Wetland Functions Affected by Buffers

• Pollution prevention– Surface– Groundwater

• Storm damage prevention

• Fish and shellfish habitat

• Wildlife habitat

• Aesthetic and scenic values

Selected Definitions of Vegetated Buffers

• Transitional area between two different land uses where one mitigates the impact from the other.

• Zones of undeveloped vegetated land along a water body that trap pollutants.

• Riparian zone: The interface between terrestrial and aquatic ecosystems. Encompasses sharp gradients

From Desbonnet et al. 1994 and Gregory et al. 1991

Buffers are particularly important for protecting Critical Areas

• Drinking water supplies

• ACEC’s

• Wildlife refuges

• Rare plant/ animal habitats

• Regionally significant ecological communities

• Shellfish beds

Pollution Prevention

Types of pollutants affected by buffers

• Particulates– Total suspended solids (TSS) and sediments– Toxic organics and metals associated with

particles– Pathogens: bacteria and viruses

• Soluble– Nitrogen– Phosphorus

Characteristics of buffers that affect pollution attenuation capacity

• Slope• Width• Soil characteristics• Surface “roughness” (to slow down flow)

– e.g., vegetation cover

• Surface hydrology– Channelization v sheet flow– Fracturing of underlying rocks

Landscape factors• Relative size of wetland, buffer, and surrounding

watershed• Position of wetland within watershed

Possible groundwater flow paths: 1

Possible groundwater flow paths: 2

Lots of variation in the relationship of pollution

attenuation to buffer widths

From Wenger 1999

Effects of soils and drainage are obvious

From Wenger 1999

Effect of slope

From Wenger 1999

Relationships of buffer widths to pollutants

Sediments

From Desbonnet et al. 1994

Total Suspended Solids

From Desbonnet et al. 1994

From Wenger

1999

Interaction of Width and Slope

Total Nitrogen

From Desbonnet et al. 1994

Nitrate

Denitrification is the key process in nitrate removal

From Desbonnet et al. 1994

Phosphorus

From Desbonnet et al. 1994

Modeled removal of Sediments and TSS

From Desbonnet et al. 1994

Modeled Removal of Nutrients

From Desbonnet et al. 1994

Fecal Coliforms

• Bacteria behave somewhat like particles with a limited lifespan outside a warm-blooded intestine

• Buffers “buy time”, allowing bacteria to die off naturally before reaching a sensitive area.

Die-off rates of fecal coliforms

• Typically 90% die off at ca. 48 hrs in freshwater• Typically 90% die off at ca. 1 day or less in salt

water• But lots of variation depending on type of

bacteria and characteristics of the sediment• Survival times of over a month and travel

distances greater than 2000 feet have been recorded.

Freshwater die-off rates of coliform bacteria

0

1

2

3

4

5

6

7

Frequency

20 40 60 80 100 120 >120

Hours for 90% loss

From Mitchell and Chamberlain, 1978

Relationship of housing density within 100 foot buffer to fecal coliform

concentrations

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200

400

600

800

1000

1200

1400

1600

0 5 10 15 20 25 30 35

Housing Density within 100 foot buffer

Mea

n fe

cal c

olif

orm

s pe

r 10

0 m

l

Data from Bochman 1990 (Cape Ann salt marsh creeks)

General Conclusions: Buffers and Water Quality

• On average, a 100 foot buffer will remove in the neighborhood of 70% of the pollutants

• A small buffer (e.g., 25 feet) is still very worthwhile – removes over 50% of pollutants

• Going from 300 to 600 feet gives you only an additional 10% of pollutant removal

• Scientifically, nothing is better than site-specific information.

Wildlife Habitat Function of Buffers

• Ecological link to both wetlands and upland

• Nesting sites for wetland animals

• Hibernation sites for wetland animals

• Refuge during times of very high water

• Migration corridor

• Shade for cold water fish

Wildlife Habitat Functions (2)

• Ameliorates the effects of disturbance• Improves water quality• Provides a buffer from invasive and generalist

animals• Woody debris from buffer provides a habitat for

wetlands invertebrates• Provides an energy source to invertebrates in the

form of detritus• A habitat for “buffer specialists”

New England Animals likely to be sensitive to activities within wetland buffers

• Waterfowl – particularly during nesting• Herons and egrets – feeding and nesting• Shorebirds – during migration• Semiaquatic mammals – e.g., mink, otter• Semiaquatic reptiles – e.g. turtles• Vernal pool-breeding amphibians• Cold water fish – e.g., trout• Fish spawning in clear running water – e.g., smelt• Buffer species, e.g., yellowthroat

Shade regulates water temperature

Buffer supplies woody debris to the stream

Freshwater Wetland-Dependent Wildlife with Upland Requirements (MA)

Wetland-Dependent

Species

Species with

Upland Requirements

% Wetland-Dependent

with Upland Requirements

Amphibians 20 19 95%

Reptiles 10 9 90%

Mammals 14 14 100%

Birds 42 23 55%

TOTAL 86 65 76%

Boyd, 2001: Report available at: http://www.umass.edu/umext/nrec/pages/biodiver_resrc.html

A number of birds do best where wetlands are interspersed with forests

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Scale 1:12,000

20012001 2002

Movements

95% Kernel50% Kernel

95% Kernel 50% Kernel

(X Locations(X LocationsMovements

Male #306 Home Range

. il m te60. 0 0 6 K o e rs

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Blanding’s Turtle Home Range

Vernal Pool Setbacks

d

d=?

d'

d

Vernal Pool Setbacks

Appropriate Habitat

d'

Vernal Pool Setbacks

d Adult Upland Habitat use

d'

d

Vernal Pool Setbacks

Adults

juveniles

Differences in bird numbers in a relatively developed v undeveloped salt marsh creek

0

5

10

15

20

25

Waders

Divers

Ducks

Gulls/Terns

Shorebirds

Num

ber of Birds

Farm Creek - undeveloped

Walker Creek - developed

R. Buchsbaum unpublished data, Essex Bay, MA

Buffer vs pannes as an explanation for wader density of different marsh sites

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0 20 40 60 80 100 120

Percent of Site Border with No Houses

Av

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Number of pannes per km2

Ave

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Buffers help protect against invasive species

Mark Bertness and coworkers have shown an association between Phragmites australis at the upper edges of salt marshes and houses along the upland edge.

Bertness, M.D., P. Ewanchuck, and B.R. Silliman. 2002. Anthropogenic modification of New England salt marsh landscapes. Proceedings of the National Academy of Science. 99: 1395-1398

Roads reduce wildlife habitat value

A study in a forested area of Ontario showed:

• bird diversity lower within 1 km of roads• plant diversity lower within 1-2 km of roads

• herp and mammal diversity lower within 2 km of roads

• 1-2 km buffer from road needed to maintain maximum diversity

Findlay, C.S. and J. Houlahan. 1997. Anthropogenic correlates of species richness in southeastern Ontario wetlands. Conservation Biology 11:1000-1009

Buffers from Disturbance

• Great Blue Herons – 300 feet

• Great Egret – 60 feet

• Black Duck – 240 feet for nesting

• Bald Eagle – 1500 feet

• Various shorebirds – 180-300 feet

• Muskrat – 33 feet

• Mink – 330 feet

• Loss of all surrounding upland habitat will result in significant impacts to wetland wildlife

• Science cannot answer the question: what size buffer?

• Setbacks and buffer zones are political decisions that can be informed by science

• Regulatory buffers are insufficient for protecting many wetland wildlife species

General Conclusions:Wildlife and Buffer Zones

Ranges of buffer widths recommended for wildlife habitat protection

From Wenger 1999

Recommended buffer widths from avian studies

From Wenger 1999

From Desbonnet et al. 1994

Recommended buffer widths from literature for wildlife habitat protections

Decision-matrix for Buffers

Special cases

Set buffer at 200-300 feet

•water supply

•Rare species habitat

•ACEC

•Outstanding resource water

•Colonial waterbird nests

•Exemplary natural community

•Resource extraction activities

•Wastewater treatment facility

Decision-matrix for Buffers

Not a special case?

Evaluate and score wetland functions

Evaluate and score potential for impacts including cumulative impacts

e.g., evaluate soils, slope, etc.

Calculate combined scoreSet buffer distance

50-300 feet

+

Multiple use buffers recommendationsfrom Desbonnet et al. 1994

General Conclusions: Buffers, Water Quality, and Wildlife

• Our current regulatory buffers (100-200 feet) is more effective in protecting a wetland from pollutants than from loss of wildlife habitat function.

• Other approaches, such as creative land use planning, is needed to maintain wildlife habitat functions