Wetland Availability and Salinity Concentrations for Breeding Waterfowl in Suisun Marsh, California

Carley Schacter,Mark Herzog,Joshua Ackerman,Sarah Peterson,C Alex Hartman,Michael Casazza

doi:10.15447/sfews.2021v19iss3art5

Abstract

Availability of wetlands with low salinities during the breeding season can influence waterfowl reproductive success and population recruitment. Salinities as low as 2 ppt (3.6 mScm–1) can impair duckling growth and influence behavior, with mortality occurring above 9 ppt (14.8 mScm–1). We used satellite imagery to quantify the amount of available water, and sampled surface water salinity at Grizzly Island, in the brackish Suisun Marsh, at three time-periods during waterfowl breeding (April, May, July) over 4 years (2016–2019). More water was available and salinity was lower during wetter years (2017, 2019) than during drier years (2016, 2018), and the amount of water in wetlands decreased 73%–86% from April to July. Across all time-periods and years, the majority (64%–100%) of wetland habitat area had salinities above what has been shown to negatively affect ducklings (> 2 ppt), and up to 42% of wetland area had salinities associated with duckling mortality (> 9 ppt). During peak duckling production in May, 81%–95% of available water had salinity above 2 ppt, and 5%–21% was above 9 ppt. In May of the driest year (2016), only 0.5 km2 of low-salinity water (< 2 ppt) was available to ducklings in the study area, compared to 2.6 km2 in May of the wettest year (2017). Private duck clubs own the majority of wetland habitat at Grizzly Island and consistently had a greater percentage of land flooded during summer than did publicly owned wetlands, but private wetlands generally had higher salinities than public wetlands, likely because they draw from higher-salinity water sources. By July, few wetlands remained flooded, and most had salinities high enough to impair duckling growth and survival. Local waterfowl populations would benefit from management practices that provide fresher water during peak duckling production in May and retain more water through July.

Highlights

Wetlands provide critical ecosystem services, including habitat for many species (Williams and Dodd 1978; Wilen and Frayer 1990)
Within wetland and canal habitat, 96.9% of duckling locations and 96.0% of hen locations were in units that we sampled for salinity at least once
We were confident that the wetlands and canals we sampled for salinity concentrations represented those available to and used by the majority of ducklings each year

Summary

Introduction

Wetlands provide critical ecosystem services, including habitat for many species (Williams and Dodd 1978; Wilen and Frayer 1990). VOLUME 19, ISSUE 3, ARTICLE 5 are among the habitats most vulnerable to anthropogenic change (Williams and Dodd 1978), with global wetland losses estimated as high as 87% (Davidson 2018). Wetlands are important for migratory waterfowl, which rely on them for both wintering and breeding habitat. Maintaining sufficient wetland habitat to sustain abundant waterfowl populations will require coordination between public entities and private land owners (Brasher et al 2019). Wetland conservation and management for waterfowl has focused more on migration stop-overs and wintering habitat and less on the availability and quality of wetlands during the spring and summer breeding season

Methods

Results

Conclusion