6 May 2025

Technical Recommendations for the Identification and Management of Potential Acid Sulfate Soils in an Ecological Restoration Context

Abstract: Restoration projects are being implemented to address natural and anthropogenic threats to coastal wetlands, including increased inundation and historic land use alterations. The US Army Corps of Engineers (USACE) and other organizations introduce dredged sediments into coastal environments to increase elevation and stabilize marsh platforms. However, some dredged sediments either contain iron sulfide compounds (i.e., iron monosulfide [FeS] and pyrite [FeS₂]) or form them after application. Under aerobic conditions, FeS and FeS₂ can rapidly oxidize, which generates acidity that can dramatically lower the soil pH, impacts plant establishment, and threatens the success of wetland restoration projects. Recommendations are needed to properly manage iron sulfide containing materials through project design, screening, monitoring, and adaptive management. Tools and techniques exist to evaluate dredged sediments for the presence of FeS and FeS₂ prior to and following marsh sediment applications, and project design and construction approaches can minimize associated acidification risks. This report provides a framework for properly identifying and managing sediments containing iron sulfide minerals during wetland restoration projects. These technical recommendations provide dredged sediment beneficial use practitioners a decision support tool for the successful management of iron sulfide containing dredged sediments to increase the ecological function and sustainability of coastal wetlands.

18 Feb 2022

Approaches to Identify and Monitor for Potential Acid Sulfate Soils in an Ecological Restoration Context

Purpose: Potential acid sulfate soils include materials with the capacity to generate acidity under certain environmental conditions. As such, these soils can pose challenges to ecological restoration projects occurring in wetlands and nearshore environments. To provide guidance for ecosystem restoration practitioners, the following technical note describes acid sulfate soil formation and distribution and then describes techniques for identifying and monitoring acid sulfate soil conditions prior to and following implementation of restoration activities. Finally, this technical note outlines a number of tools and recently published resources to help avoid unintended consequences of acid sulfate soil disturbance and achieve ecological restoration objectives.

1 Oct 2020

Acid Sulfate Soils in Coastal Environments: A Review of Basic Concepts and Implications for Restoration

Abstract: Acid sulfate soils naturally occur in many coastal regions. However, the oxidation of acid sulfate soils can decrease soil pH to <4.0, affecting vegetation and aquatic organisms. Acid sulfate soil oxidation typically occurs where anaerobic sediments or soils were exposed to aerobic conditions (for example, extended drought, artificial drainage, or dredged material placement in upland areas). Recently, field observations documented the formation of acid sulfate materials at multiple degraded marsh restoration locations (Rhode Island, New Jersey, California) following intentional dredged sediment placement into wetland environments designed to increase marsh elevation. Unlike previous studies of acid sulfate soils, the in situ dredged material did not contain acid sulfate–bearing materials at the time of placement; instead, the interaction between the marsh substrate and the overlying dredged material appears to have caused the formation of acid sulfate soils. These findings highlight the need for additional studies of acid sulfate soil formation and fate—especially within a marsh restoration context. In response, this report provides a review of literature related to acid sulfate soils, discusses preliminary data collected to evaluate acid sulfate material formation following marsh restoration, and identifies knowledge gaps requiring additional research and technical guidance.