Hydrogeomorphic Classification of Wetlands on Mt. Desert Island, Maine, Including Hydrologic Susceptibility Factors for Wetlands in Acadia National Park
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Publications—Scientific Investigations Report

Prepared in cooperation with the National Park Service

Hydrogeomorphic Classification of Wetlands on Mt. Desert Island, Maine, Including Hydrologic Susceptibility Factors for Wetlands in Acadia National Park

By Martha G. Nielsen



U.S. Geological Survey Scientific Investigations Report 2006-5162



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Plate 1 (76,884 KB)


Abstract

The U.S. Geological Survey, in cooperation with the National Park Service, developed a hydrogeomorphic (HGM) classification system for wetlands greater than 0.4 hectares (ha) on Mt. Desert Island, Maine, and applied this classification using map-scale data to more than 1,200 mapped wetland units on the island. In addition, two hydrologic susceptibility factors were defined for a subset of these wetlands, using 11 variables derived from landscape-scale characteristics of the catchment areas of these wetlands. The hydrologic susceptibility factors, one related to the potential hydrologic pathways for contaminants and the other to the susceptibility of wetlands to disruptions in water supply from projected future changes in climate, were used to indicate which wetlands (greater than 1 ha) in Acadia National Park (ANP) may warrant further investigation or monitoring.

The HGM classification system consists of 13 categories: Riverine-Upper Perennial, Riverine-Nonperennial, Riverine- Tidal, Depressional-Closed, Depressional-Semiclosed, Depressional-Open, Depressional-No Ground-Water Input, Mineral Soil Flat, Organic Soil Flat, Tidal Fringe, Lacustrine Fringe, Slope, and Hilltop/Upper Hillslope. A dichotomous key was developed to aid in the classification of wetlands. The National Wetland Inventory maps produced by the U.S. Fish and Wildlife Service provided the wetland mapping units used for this classification. On the basis of topographic map information and geographic information system (GIS) layers at a scale of 1:24,000 or larger, 1,202 wetland units were assigned a preliminary HGM classification. Two of the 13 HGM classes (Riverine-Tidal and Depressional-No Ground-Water Input) were not assigned to any wetlands because criteria for determining those classes are not available at that map scale, and must be determined by more site-specific information. Of the 1,202 wetland polygons classified, which cover 1,830 ha in ANP, 327 were classified as Slope, 258 were Depressional (Open, Semiclosed, and Closed), 231 were Riverine (Upper Perennial and Nonperennial), 210 were Soil Flat (Mineral and Organic), 68 were Lacustrine Fringe, 51 were Tidal Fringe, 22 were Hilltop/Upper Hillslope, and another 35 were small open water bodies. Most small, isolated wetlands classified on the island are Slope wetlands. The least common, Hilltop/Upper Hillslope wetlands, only occur on a few hilltops and shoulders of hills and mountains. Large wetland complexes generally consist of groups of Depressional wetlands and Mineral Soil Flat or Organic Soil Flat wetlands, often with fringing Slope wetlands at their edges and Riverine wetlands near streams flowing through them.

The two analyses of wetland hydrologic susceptibility on Mt. Desert Island were applied to 186 wetlands located partially or entirely within ANP. These analyses were conducted using individually mapped catchments for each wetland. The 186 wetlands were aggregated from the original 1,202 mapped wetland polygons on the basis of their HGM classes. Landscape-level hydrologic, geomorphic, and soil variables were defined for the catchments of the wetlands, and transformed into scaled scores from 0 to 10 for each variable. The variables included area of the wetland, area of the catchment, area of the wetland divided by the area of the catchment, the average topographic slope of the catchment, the amount of the catchment where bedrock crops out with no soil cover or excessively thin soil cover, the amount of storage (in lakes and wetlands) in the catchment, the topographic relief of the catchment, the amount of clay-rich soil in the catchment, the amount of manmade impervious surface, whether the wetland had a stream inflow, and whether the wetland had a hydraulic connection to a lake or estuary. These data were determined using a GIS and data layers mapped at a scale of 1:24,000 or larger.

These landscape variables were combined in different ways for the two hydrologic susceptibility factors, according to the purposes of each. For the contaminant delivery analysis, the variables related to the relative importance of direct precipitation, surface water, and ground water as a water source for each wetland were grouped, and the scaled scores summed for each wetland. Relatively few wetlands scored high on the relative importance of precipitation as a pathway for contamination. Many of the highest-scoring wetlands for surface water as a potential source of contamination are in the eastern part of the island. The distribution of wetlands scoring highest for ground water as a potential source of contamination are more evenly distributed across the island.

For the analysis of susceptibility to water-supply disruptions under potential future climate change (greater annual precipitation and warmer temperatures, particularly in the summer, which may result in increased evapotranspiration), variables related to greater susceptibility (more anticipated water-supply disruptions) were grouped and given a negative value. Variables related to less susceptibility (fewer anticipated water-supply disruptions) were grouped and given positive scores. The scaled negative and positive scores for each wetland were summed to determine the final score. The 20 lowest-scoring wetlands are those that are likely to be the most vulnerable and would experience the most water-supply shortages should predictions of future climate conditions hold true. Many of these wetlands have relatively small catchment areas compared to the size of the wetland itself, most have little or no opportunity for surface-water storage in the catchment, and some have a large amount of rock cropping out (areas with little to no soil cover) in their catchments. Wetlands with the highest scores (those likely to be least vulnerable) have soils relatively favorable to ground-water recharge, relatively large catchment sizes, and many have a hydraulic connection to a lacustrine or estuarine water body.

TABLE OF CONTENTS

Abstract

Introduction

Purpose and Scope

Previous Studies

Description of Study Area

Hydrogeomorphic Classification System for Wetlands on Mt. Desert Island

Riverine Wetlands

Riverine–Upper Perennial

Riverine–Nonperennial

Riverine–Tidal

Depressional Wetlands

Depressional–Closed

Depressional–Semiclosed

Depressional–Open

Depressional–No Ground-Water Input

Mineral Soil Flat

Organic Soil Flat

Tidal Fringe

Lacustrine Fringe

Slope

Hilltop/Upper Hillslope

Dichotomous Key for the Identification of Wetland Subclasses

Hydrogeomorphic Classification of Wetlands on Mt. Desert Island

Hydrologic Susceptibility Factors for Wetlands in Acadia National Park, Mt. Desert Island

Methods Used to Determine Variables for Susceptibility Factors

Scaling of Variables

Methods Used to Determine Susceptibility Factor Scores

Selection of Wetlands for Susceptibility Factor Scoring

Determining Catchment Areas for Wetlands

Hydrologic Pathways for Contaminants Entering Wetlands

Measures Indicating Dominant Pathways for Potential Contamination in Acadia National Park Wetlands

Potential Changes in Wetland Hydrologic Regime Considering Projected Future Climate Change

Projections for Climate Changes in Northeastern North America

Wetland Hydrology Implications of Projected Climate Changes

Variables Used for Analysis of Vulnerability to Wetland Water-Supply Disruptions

Results of Analysis for Hydrologic Pathways for Contaminants and Susceptibility to Disruptions in Water Supply from Future Changes in Climate

Wetland Scores for Hydrologic-Contamination Pathways

Precipitation

Surface Water

Ground Water

Wetland Scores for Vulnerability to Water-Supply Disruptions Under Possible Future Climate Change

Summary and Conclusions

Acknowledgments

References

Appendixes 1–3

  1. Steps in Assigning Hydrogeomorphic Classifications to Wetland Polygons.
  2. Hydrogeomorphic Classification of Wetlands on Mt. Desert Island, Maine.
  3. Susceptibility Scoring for Wetlands Greater Than 1 Hectare in Acadia National Park.

Plate

  1. Hydrogeomorphic classification of palustrine and estuarine wetlands greater than 0.4 hectares on Mt. Desert Island, Maine.

Figures

1–7. Maps showing—

  1. Extent of shallow-water, nonmarine wetlands on Mt. Desert Island, Maine.
  2. Hydrogeomorphic classification of wetlands greater than 1 hectare in size in Acadia National Park, Mt. Desert Island, Maine.
  3. Example of wetlands in relation to their catchment areas in Acadia National Park, Mt. Desert Island, Maine.
  4. Wetland scores for precipitation as a potential pathway for contaminant delivery.
  5. Wetland scores for surface water as a potential pathway for contaminant delivery.
  6. Wetland scores for ground water as a potential pathway for contaminant delivery.
  7. Wetland scores for susceptibility to disruptions in water supply from projected future climate change.

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For further information, contact:

Robert M. Lent, Director
U.S. Geological Survey
Maine Water Science Center
196 Whitten Rd.
Augusta, ME 04330

dc_me@usgs.gov

or visit our Web site at:
http://me.water.usgs.gov



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