Ecosystem Engineering Impacts of Water Primrose in the Sacramento-San Joaquin Delta

Science Center Objects

Many non-native fish, invertebrates, and plants have colonized the Sacramento-San Joaquin Delta (Delta) of California, the landward most region of the San Francisco Estuary. Included among these invasive species is the water primrose (Ludwigia spp.), an aggressive floating aquatic plant that is native to South and Central America and parts of the US, but invasive in California. Water primrose is such a highly disruptive invader in the Delta, that it has been categorized as an ecosystem engineer. Currently, it is expanding its range from the marsh edge to the marsh interior and causing mortality of key wetland plants including bulrushes and cattails. The reason for this marsh mortality is currently unknown. Such a gap in knowledge prevents the development of management actions that could protect and improve marsh habitat in the Delta.

The aim of this three-year project is to better understand the mechanisms involved in water primrose invasion in the Delta. We will chiefly be investigating allelopathic chemicals exuded by water primrose and whether or not they could be causing the mortality of marsh plants.This information will enable management actions to be focused on protecting marshes most vulnerable to invasion and controlling water primrose in marshes already affected.

Map of a large river delta with many rivers and streams, with two additional maps to show its location.

The Sacramento-San Joaquin River Delta covers the right half of the bottom image. Bottom image credit: Wikimedia, by English Wikipedia user Decumanus.

Science Plan and Objectives

The main objective of this project is to determine the allelopathic chemicals (polyphenols) present in water primrose growing in and adjacent to Delta marshes and at what concentrations these chemicals are found in leaf samples, ambient water samples, and sediment samples.  By studying the allelopathic chemicals exuded by water primrose and their concentrations in the environment, we will determine whether allelopathic chemicals could be the cause of marsh mortality in infested areas of the Delta.
Results and benefits

The ultimate benefit of this work will be an improved understanding of water primrose invasion processes in the Delta, which are key to conserving and restoring marsh habitat. This project will also improve our general understanding of the ecosystem engineering properties of water primrose and how it may transform other aquatic habitats in California and beyond. Acquiring new knowledge about water quality and the links between ecosystem science and water resources are important goals of the USGS strategic plan.