#7 Wetland delineation

Wetland delineation

the process of mapping the types, boundaries, and extents of wetlands using formal, standardized criteria

Why is wetland delineation important? (first 2)

• To quantify how many wetlands remain

• For legal/regulatory purposes

  • determining protections and jurisdiction

Why is wetland delineation important? (last 3)

• land-use planning

  • guiding where development is feasible

• environmental protection and habitat management

• To assess site-level wetland characteristics and functions

What is the primary reason wetlands are delineated in the U.S.?

Regulatory compliance

• finds whether wetlands and required buffers fall under federal protection

Regulatory delineation

determines legal jurisdiction and protection

• Most formal delineations are regulatory

Scientific delineation

focuses on ecological characteristics for research

• (e.g., habitat studies)

Which agency has final authority to confirm whether an area is a wetland for regulatory purposes?

The U.S. Army Corps of Engineers (USACE)

Who typically performs on-the-ground wetland delineations?

Qualified professionals (often contractors) with state/region-specific certifications

• collect field data for USACE review

What are the 3 Materials common in wetland delineation?

• “Parent” manual (1987 manual)

• Regional supplements

  • help specialized the delineation techniques to the local area

• Data forms

  • What you fill out when delineatiating

Why were regional supplements added to the delineation manual?

Because wetland characteristics vary widely across the U.S., requiring region-specific guidance

What is recorded on the data sheets?

• delineation report

• soil/vegetation/hydrology descriptions

• mapped wetland boundaries

What are the three main parameters used to determine whether an area is a wetland?

• Hydric soils

• Hydrology indicators

• Hydrophytic vegetation

What soil characteristics indicate hydric soils? (first 4)

• Low chroma/grayish color due to reducing conditions

• High organic matter or presence of muck

• Stratified layers

• Oxidized rhizospheres

What soil characteristics indicate hydric soils? (last 3)

• Anoxic or saturated conditions

• Peat or high organic horizon content

• Distinct soil horizons with undecomposed litter

What tools are used to measure hydric soils?

• soil core sampler

• digging a soil pit

Why does soil color help identify hydric soils?

Because reduced (anaerobic) conditions alter iron and manganese chemistry, creating gray, blue, or low-chroma colors

What are some field indicators of wetland hydrology? (first 5)

• Surface water

• High-water marks

• Sediment or debris deposition

• Saturation within the upper soil profile

• Algal mats

What are some field indicators of wetland hydrology? (last 4)

• Aquatic macroinvertebrates

• Water-tolerant plant zonation (“bathtub rings”)

• Salt crusts

• Water-filled holes (after digging)

What is a simple method to check for near-surface saturation?

Dig a small hole and observe whether it fills with water

Hydrophytic vegetation

Plant communities dominated by species adapted to saturated soils and wetland conditions

Why is vegetation not assessed simply by presence/absence?

Because dominance—not mere presence—indicates whether the plant community functions as a wetland system

How is vegetation typically sampled during delineation?

Using quadrats or line-intercept methods

• measure percent cover by species in each vegetation stratum

  • (trees, shrubs, herbs, woody vines)

What are plant species categorized as? (first 2)

• OBL: Wetland obligates

  • Floating plants

• FACW: Facultative, but more often in wetlands

  • Can survive periods of drought

What are plant Species categorized as? (last 3)

• FAC: Equally likely to be found in wetlands/uplands

  • Mostly uplands, but can be in wetlands

• FACU: Facultative, only uplands

• UPL: Non flood-tolerant species

How is hydrophytic vegetation confirmed?

If wetland species (OBL, FACW, FAC) dominate the community using the wetland “dominance test”

Why are transects useful for wetland delineation?

Because they capture transitions between upland and wetland conditions

• essential for locating boundaries

Why is purely random sampling generally not useful for delineating boundaries?

Random points do not efficiently capture transition zones where boundaries occur

How does sampling resolution change near wetland boundaries?

More sampling points are added near transitions for finer boundary accuracy

How is field data used to generate an official wetland boundary?

The delineator maps boundaries using field measurements of soils, vegetation, and hydrology, then prepares a delineation report for USACE review

What is included in a delineation report? (first 3)

• Site description and methods

• Data forms for each sampling point

• Wetland boundary map

What is included in a delineation report? (last 2)

• Photographic documentation

• Notes on anomalies or problematic areas

National Wetlands Inventory

USFWS database mapping wetland extent across the U.S.

• Updated infrequently

• Not often ground-truthed and thus inaccurate at fine scales

still provides a good starting point for identifying likely wetland locations

What are the steps to conduct a wetland delineation in the field? (first 3)

• Record site location and variables

• Assess hydrology, soils, and vegetation

• Photograph sampling points, soil profiles, vegetation, hydrological indicators

What are the main steps in conducting a wetland delineation? (first 3)

• Classify each point (wetland, upland, transition)

• Map the boundaries

• Compile data forms and report for USACE

How does a delineation become an official ruling?

• Delineator submits a report and boundary map to USACE.

• A regulatory manager reviews it, may request more info, and issues an official jurisdictional determination.

• This determination guides permitting and land-use planning

Who most commonly performs delineations for landowners and developers?

Environmental consulting companies with certified wetland scientists or soil scientists