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In situ allelopathic expression by the invasive amphibious plant, Ludwigia hexapetala (water primrose) across habitat types, seasons, and salinities

Biological Invasions (Springer Link) | August 17th, 2024

Summary

Broad infestations of invasive, non-native vegetation have transformed wetlands around the world. Ludwigia hexapetala is a widespread, amphibious invasive plant with a cr

Broad infestations of invasive, non-native vegetation have transformed wetlands around the world. Ludwigia hexapetala is a widespread, amphibious invasive plant with a creeping growth habit in open water and an erect growth habit in terrestrial habitats. In the upper San Francisco Estuary of California, L. hexapetala is increasingly terrestrializing into marshes and this expansion may be facilitated by allelopathy. We conducted the first field-based study on L. hexapetala allelopathy to determine whether (1) three allelochemicals known to be exuded by L. hexapetala are expressed in situ, (2) the allelochemicals are detectable in leaves, soil, and water, and (3) allelopathic expression varies by season, salinity, and growth habit (open water “patch” vs. terrestrial marsh “interface” locations). Water, soil, and L. hexapetala leaves were collected in two freshwater sites and two oligohaline sites in the upper San Francisco Estuary in summer 2021, fall 2021, and spring 2022. Myricitrin and quercitrin, known allelochemicals, and salipurposid, a newly identified polyphenol, were detected in water, soil, and leaves. There were significant differences in allelochemical concentrations under fresh versus oligohaline conditions in water and soil, but not leaves. All three allelochemicals generally had higher concentrations in patch versus interface locations, suggesting that L. hexapetala allelopathy plays a greater competitive role in open water than terrestrial habitats. Leaf concentrations of each allelochemical varied seasonally; however, both myricitrin and salipurposid had heightened concentrations in spring. These results suggest that herbicide application in early spring may be most effective in controlling L. hexapetala terrestrialization from open water to marshes.

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Incorporating Wetlands into Watershed Planning

U.S. Environmental Protection Agency (EPA) | February 26th, 2013

Summary

The purpose of this Supplement is to encourage the inclusion of proactive wetland management into watershed plans because wetlands play an integral role in the healthy fu

The purpose of this Supplement is to encourage the inclusion of proactive wetland management into watershed plans because wetlands play an integral role in the healthy functioning of the watershed. This Supplement promotes using a watershed approach that not only protects existing freshwater wetlands but also maximizes opportunities to use restored, enhanced, and created freshwater wetlands to address watershed problems such as habitat loss, hydrological alteration, and water quality impairments. The primary audiences for the Supplement are members and staff of watershed organizations and local/state agencies. This document is a Supplement to the U.S. Environmental Protection Agency’s (EPA) Watershed Planning Handbook. It conveys information on recently developed approaches and tools for assessing wetland functions and conditions, the results of which assist decision makers in determining where in a watershed existing and former wetlands can best be restored or enhanced, or where wetlands can be created to optimize their functions in support of water quality and other watershed management plan goals. The Supplement also discusses wetland restoration, enhancement, and creation techniques and reviews the considerations involved in deciding how best to undertake a wetlands project. EPA’s Watershed Planning Handbook and other scientific resources emphasize the importance of the watershed as a management unit in which elements and processes operate over different spatial and temporal scales. The literature also emphasizes the importance of planning and implementing projects aimed at protecting or restoring water quality (or meeting similar goals) within the context of the watershed.

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Insights into estuary habitat loss in the western United States using a new method for mapping maximum extent of tidal wetlands

PLOS | August 14th, 2019

Summary

Effective conservation and restoration of estuarine wetlands require accurate maps of their historical and current extent, as well as estimated losses of these va

Effective conservation and restoration of estuarine wetlands require accurate maps of their historical and current extent, as well as estimated losses of these valued habitats. Existing coast-wide tidal wetland mapping does not explicitly map historical tidal wetlands that are now disconnected from the tides, which represent restoration opportunities; nor does it use water level models or high-resolution elevation data (e.g. lidar) to accurately identify current tidal wetlands. To better inform estuarine conservation and restoration, we generated new maps of current and historical tidal wetlands for the entire contiguous U.S. West Coast (Washington, Oregon, and California). The new maps are based on an Elevation-Based Estuary Extent Model (EBEEM) that combines lidar digital elevation models (DEMs) and water level models to establish the maximum historical extent of tidal wetlands, representing a major step forward in mapping accuracy for restoration planning and analysis of wetland loss. Building from this new base, we also developed an indirect method for mapping tidal wetland losses, and created maps of these losses for 55 estuaries on the West Coast (representing about 97% of historical West Coast vegetated tidal wetland area). Based on these new maps, we estimated that total historical estuary area for the West Coast is approximately 735,000 hectares (including vegetated and nonvegetated areas), and that about 85% of vegetated tidal wetlands have been lost from West Coast estuaries. Losses were highest for major river deltas. The new maps will help interested groups improve action plans for estuarine wetland habitat restoration and conservation, and will also provide a better baseline for understanding and predicting future changes with projected sea level rise.

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Land Reclamation Impacts on Tidal Landscape Evolution

American Geophysical Union (AGU) | August 21st, 2025

Summary

Fertile and low-lying coastal landscapes are often densely populated due to food supply (agriculture, aquaculture, and fisheries) and easy navigability (shipping lanes).

Fertile and low-lying coastal landscapes are often densely populated due to food supply (agriculture, aquaculture, and fisheries) and easy navigability (shipping lanes). Much of the low-lying land that is regularly inundated by the sea has been converted to agricultural land or urban environments to meet the need for land. This reclamation of land influences the tidal dynamics of the coastal environment, which in turn modifies its morphology. Through various complex tide-topography interactions identified in this paper, we explore how the location and extent of land reclamation influences tides and bed levels in various tidal environments. We especially point to the key role of sediments herein, introducing feedback mechanisms that lead to large impacts on tidal landscapes, but also long adaptation times. This is especially the case for estuaries due to their confinement and the typically large availability of sediments.

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Leveraging Wetlands for a Better Climate Future

San Francisco Estuary Institute (SFEI) | July 15th, 2022

Summary

Managing Natural and Working Lands (NWL) to enhance carbon sinks and limit greenhouse gas (GHG) emissions is a key component of California’s ambitious strategy to achie

Managing Natural and Working Lands (NWL) to enhance carbon sinks and limit greenhouse gas (GHG) emissions is a key component of California’s ambitious strategy to achieve net carbon neutrality by 2045. The California Air Resources Board (CARB) Climate Change Scoping Plan includes 7 NWL categories in its GHG emission reduction scenarios, one of which is wetlands. Coastal wetlands in California are a high- leverage NWL type for GHG management relative to their small spatial footprint. These ecosystems have high rates of carbon sequestration and can accumulate large stocks of carbon, due to high productivity, efficient sediment trapping, and low decomposition rates (Chmura et al. 2003, Mcleod et al. 2011). In the absence of management interventions focused on wetland conservation, however, conversion of coastal wetlands to other land uses such as agriculture, grazing, development, impounded wetlands, or subtidal or upland habitat can halt or reverse carbon sequestration, and can shift these ecosystems from long-term GHG sinks to large GHG sources (Hatala et al. 2012, Tan et al. 2019). Filling of wetlands for infrastructure and development was a common practice throughout the early 20th century (Goals Project 1999), dramatically reducing the state’s coastal wetland area and associated carbon sink.

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Managing California’s Freshwater Ecosystems: Lessons from the 2012-16 Drought

Public Policy Institute of California (PPIC) | November 16th, 2017

Summary

The 2012–16 drought caused unprecedented stress to California’s ecosystems and pushed many native species to the brink of extinction. It also tested the laws, policie

The 2012–16 drought caused unprecedented stress to California’s ecosystems and pushed many native species to the brink of extinction. It also tested the laws, policies, and institutions charged with protecting the environment. Eight case studies on environmental water management during the drought reveal both strengths and weaknesses in federal, state, and local response that can inform how California addresses future droughts. Three areas of reform hold promise for improving ecosystem conditions and reducing conflict: * Improve water accounting. Drought management requires accurate and timely information about water use and availability and about likely environmental response to changes in water supply. But California’s current tracking systems are neither timely nor transparent. To address these gaps, environmental water accounting and ecosystem monitoring systems need an overhaul. * Prepare for drought. With a few significant exceptions, environmental water managers were unprepared for the environmental consequences of an extended drought, and were forced to make ad hoc decisions during a crisis. Developing watershed-level plans that set ecosystem priorities and identify trade-offs would help managers anticipate drought and drive implementation of habitat investments and water allocation. Annual watering plans that guide management under different types of water years would better engage and inform water users. * Develop ecosystem water budgets. Current methods of allocating water to support ecosystem health rely on minimum flow standards that are unevenly enforced and often insufficient during drought. Ecosystem water budgets, which allocate a portion of water to the ecosystem within watersheds, could enable more flexible and effective water management during dry times. Although state and federal agencies have important

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Marsh Sediment in Translation: A Review of Sediment Transport Across a Natural Tidal Salt Marsh in Northern San Francisco Bay

University of California, Davis (UC Davis) | March 15th, 2025

Summary

Deposition of inorganic sediment is essential for the sustainability of tidal salt marshes. Understanding variability in sediment sources and the processes of sediment de

Deposition of inorganic sediment is essential for the sustainability of tidal salt marshes. Understanding variability in sediment sources and the processes of sediment delivery to salt marshes are high priorities for decision-makers responsible for managing sediment and conserving and restoring marshes.

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Mercury on a landscape scale—Balancing regional export with wildlife health

U.S. Geological Survey (USGS) | June 26th, 2018

Summary

The Cosumnes River watershed requires a 57–64 percent reduction in loads to meet the new Delta methylmercury (MeHg) total maximum daily load allocation, established by

The Cosumnes River watershed requires a 57–64 percent reduction in loads to meet the new Delta methylmercury (MeHg) total maximum daily load allocation, established by the Central Valley Regional Water Quality Control Board. Because there are no large point sources of MeHg in the watershed, the focus of MeHg load reductions will fall upon non-point sources, particularly the expansive wetlands considered to be a primary source of MeHg in the region. Few management practices have been implemented and tested in order to meet load reductions in managed wetlands, but recent efforts have shown promise. This project examines a treatment approach to reduce MeHg loads to the Sacramento-San Joaquin River Delta by creating open-water deep cells with a small footprint at the downstream end of wetlands to promote net demethylation of MeHg and to minimize MeHg and Hg loads exiting wetlands at the Cosumnes River Preserve. Specifically, the deep cells were were located immediately up gradient of the wetland’s outflow weir and were deep enough (75–91 centimeter depth) to be vegetation-free. The topographic and hydrologic structure of each treatment wetland was modified to include open-water deep cells so that the removal of aqueous MeHg might be enhanced through (1) particle settling, (2) photo-degradation, and (3) benthic microbial demethylation. These deep cells were, therefore, expected to clean MeHg from surface water prior to its discharge to the Cosumnes River and the downstream Delta.

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Mercury, Monomethyl Mercury, and Dissolved Organic Carbon Concentrations in Surface Water Entering and Exiting Constructed Wetlands Treated with Metal-Based Coagulants, Twitchell Island, California

U.S. Geological Survey (USGS) | August 30th, 2015

Summary

Coagulation with metal-based salts is a practice commonly employed by drinking-water utilities to decrease particle and dissolved organic carbon concentrations in water.

Coagulation with metal-based salts is a practice commonly employed by drinking-water utilities to decrease particle and dissolved organic carbon concentrations in water. In addition to decreasing dissolved organic carbon concentrations, the effectiveness of iron- and aluminum-based coagulants for decreasing dissolved concentrations both of inorganic and monomethyl mercury in water was demonstrated in laboratory studies that used agricultural drainage water from the Sacramento–San Joaquin Delta of California. To test the effectiveness of this approach at the field scale, nine 15-by-40-meter wetland cells were constructed on Twitchell Island that received untreated water from island drainage canals (control) or drainage water treated with polyaluminum chloride or ferric sulfate coagulants. Surface-water samples were collected approximately monthly during November 2012–September 2013 from the inlets and outlets of the wetland cells and then analyzed by the U.S. Geological Survey for total concentrations of mercury and monomethyl mercury in filtered (less than 0.3 micrometers) and suspended-particulate fractions and for concentrations of dissolved organic carbon.

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National hydrologic connectivity classification links wetlands with stream water quality

Nature Portfolio (Springer Nature) | April 6th, 2023

Summary

Wetland hydrologic connections to downstream waters influence stream water quality. However, no systematic approach for characterizing this connectivity exists. Here usin

Wetland hydrologic connections to downstream waters influence stream water quality. However, no systematic approach for characterizing this connectivity exists. Here using physical principles, we categorized conterminous US freshwater wetlands into four hydrologic connectivity classes based on stream contact and flowpath depth to the nearest stream: riparian, non-riparian shallow, non-riparian mid-depth and non-riparian deep. These classes were heterogeneously distributed over the conterminous United States; for example, riparian dominated the south-eastern and Gulf coasts, while non-riparian deep dominated the Upper Midwest and High Plains. Analysis of a national stream dataset indicated acidification and organic matter brownification increased with connectivity. Eutrophication and sedimentation decreased with wetland area but did not respond to connectivity. This classification advances our mechanistic understanding of wetland influences on water quality nationally and could be applied globally.

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