Hydrologic Treatments Affect Gaseous Carbon Losses From Organic Soils, Twitchell Island, California, October 1995 - December 1997

By Robin L. Miller, Lauren L. Hastings, and Roger Fujii

U.S. Geological Survey
Water Resources Investigations Report 00-4042

Prepared in cooperation with the California Department of Water Resources
Sacramento, California 2000

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Executive Summary

Abstract

Introduction

Methods and Materials

Site Description and Study Design

Measurement of Gaseous Carbon Emissions

Measurement of Plant Carbon Inputs

Statistical Analysis

Results

Gaseous Carbon Emissions

Plant Carbon Inputs

Discussion

Study Limitations

Summary

References

FIGURES

1. Map showing location of the study site, Twitchell Island, Sacramento-San Joaquin Delta

2. Schematic showing enlargement of study site, Twitchell Island, Sacramento-San Joaquin Delta

3. Sketch showing vented static chamber with base used for collecting gaseous carbon emissions

4 - 12. Graphs showing:

4. Mean gaseous carbon emissions from the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997, as methane, carbon dioxide, and total gaseous carbon (carbon dioxide and methane)

5. Mean monthly total gaseous carbon emissions from the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

6. Mean monthly carbon dioxide emissions from the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

7. Mean monthly methane emissions from the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

8. Mean soil and air temperatures of the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

9. Mean monthly soil temperature, at 10-cm depth, from the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

10. Mean monthly air temperature from chambers in the four hydrologic treatments of organic soils on Twitchell Island, October 1995 to December 1997

11. Mean above- and below-ground plant biomass for the reverse flooding and the permanent shallow flooding treatments of organic soils on Twitchell Island during the 1997 growing season

12. Mean above-ground plant biomass, depicted by plant type, from the reverse flooding treatment of organic soils on Twitchell Island during the 1997 growing season

13. Mean total leaf length and mean standing live leaf length of Typha spp. In the reverse flooding and permanent shallow flooding treatments of organic soils on Twitchell Island, 1997

TABLES

1. Multiple regression model statistics for methane flux against soil and air temperature, soil moisture and water depth, including model significance and r², and significant explanatory variables with r²

2. Multiple regression model statistics for carbon dioxide flux against soil and air temperature, soil moisture and water depth, including model significance and r², and significant explanatory variables with r²

3. Mean biomass measurements from monthly harvests in 1997 for the reverse flooding and permanent shallow flooding treatments and statistical comparisons

Abstract

Subsidence of organic soils in the Sacramento-San Joaquin Delta, California, has increased the potential for levee failure and flooding in the region. Because oxidation of the peat soils is a primary cause of subsidence, reversion of affected lands to wetlands has been proposed as a mitigation tool. To test this hypothesis, three 10 x 10 meter enclosures were built on Twitchell Island in the Delta and managed as different wetland habitats. Emissions of carbon dioxide and methane were measured in situ from October 1995 through December 1997, from the systems that developed under the different water-management treatments. Treatments included a seasonal control (SC) under current island management conditions; reverse flooding (RF), where the land is intentionally flooded from early dry season until midsummer; permanent shallow flooding (F); and a more deeply flooded, open-water (OW) treatment.

Hydrologic treatments affected microbial processes, plant community and temperature dynamics which, in turn, affected carbon cycling. Water-management treatments with a period of flooding significantly decreased gaseous carbon emissions compared to the seasonal control. Permanent flooding treatments showed significantly higher methane fluxes than treatments with some period of aerobic conditions. Shallow flooding treatments created conditions that support cattail [Typha species (spp.)] marshes, while deep flooding precluded emergent vegetation. Carbon inputs to the permanent shallow flooding treatment tended to be greater than the measured losses. This suggests that permanent shallow flooding has the greatest potential for managing subsidence of these soils by generating organic substrate more rapidly than is lost through decomposition. Carbon input estimates of plant biomass compared to measurements of gaseous carbon losses indicate the potential for mitigation of subsidence through hydrologic management of the organic soils in the area.