Ecological Limits of Hydrologic Alteration: Environmental Flows for Regional Water Management

U.S. Environmental Protection Agency (EPA) | March 20th, 2008

Worldwide, water conflicts are escalating as cities, industries, agriculture, and energy producers compete for limited freshwater supplies. At the same time, there is a g

Worldwide, water conflicts are escalating as cities, industries, agriculture, and energy producers compete for limited freshwater supplies. At the same time, there is a growing awareness of the need to maintain adequate freshwater flows in rivers, lakes, floodplains, aquifers, and estuaries to sustain biodiversity and the many benefits derived from the healthy, functioning ecosystems upon which local communities and economies depend. Efficient, integrated water resource management systems help  governments provide for growing human populations while protecting and restoring healthy freshwater ecosystems. The integration of ecological considerations into water management has been hampered by the difficulty, cost, and time required for determining environmental flows -- the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well-being that depend on these ecosystems.  Environmental flow assessments scientifically evaluate tradeoffs between alteration of natural water flow patterns by humans and consequent changes in ecological health.

Ecological Studies of the Sacramento-San Joaquin Estuary, A Decennial Report 1961-1971

California Department of Fish and Wildlife (CDFW) | June 15th, 1972

Ecological winners and losers of extreme drought in California

Nature Portfolio (Springer Nature) | August 20th, 2018

An unprecedented era of climatic volatility is altering ecosystems across our planet. The potential scale, pace and consequences of this global change have been m

An unprecedented era of climatic volatility is altering ecosystems across our planet. The potential scale, pace and consequences of this global change have been modelled extensively, yet little empirical research has quantified the impacts of extreme climate events on the composition of contemporary ecological communities. Here, we quantified the responses of 423 sympatric species of plants, arthropods, birds, reptiles and mammals to California’s drought of 2012–2015—the driest period in the past 1,200 years for this global biodiversity hotspot. Plants were most responsive to one-year water deficits, whereas vertebrates responded to longer-term deficits, and extended drought had the greatest impact on carnivorous animals. Locally rare species were more likely to increase in numbers and abundant species were more likely to decline in response to drought, and this negative density dependence was remarkably consistent across taxa and drought durations. Our system-wide analysis reveals that droughts indirectly promote the long-term persistence of rare species by stressing dominant species throughout the food web. These findings highlight processes that shape community structure in highly variable environments and provide insights into whole-community responses to modern climate volatility.

Ecologically Functional Floodplains: Connectivity, Flow Regime, and Scale

American Water Resources Association (AWRA) | March 31st, 2010

This paper proposes a conceptual model that captures key attributes of ecologically functional floodplains, encompassing three basic elements: (1) hydrologic connectivity

This paper proposes a conceptual model that captures key attributes of ecologically functional floodplains, encompassing three basic elements: (1) hydrologic connectivity between the river and the floodplain, (2) a variable hydrograph that reflects seasonal precipitation patterns and retains a range of both high and low flow events, and (3) sufficient spatial scale to encompass dynamic processes and for floodplain benefits to accrue to a meaningful level. Although floodplains support high levels of biodiversity and some of the most productive ecosystems on Earth, they are also among the most converted and threatened ecosystems and therefore have recently become the focus of conservation and restoration programs across the United States and globally. These efforts seek to conserve or restore complex, highly variable ecosystems and often must simultaneously address both land and water management. Thus, such efforts must overcome considerable scientific, technical, and socioeconomic challenges. In addition to proposing a scientific conceptual model, this paper also includes three case studies that illustrate methods for addressing these technical and socioeconomic challenges within projects that seek to promote ecologically functional floodplains through river‐floodplain reconnection and/or restoration of key components of hydrological variability.

Ecosystem variability along the estuarine salinity gradient: Examples from long-term study of San Francisco Bay

Limnology and Oceanography (Wiley) | March 25th, 2017

The salinity gradient of estuaries plays a unique and fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes. We use

The salinity gradient of estuaries plays a unique and fundamental role in structuring spatial patterns of physical properties, biota, and biogeochemical processes. We use variability along the salinity gradient of San Francisco Bay to illustrate some lessons about the diversity of spatial structures in estuaries and their variability over time. Spatial patterns of dissolved constituents (e.g., silicate) can be linear or nonlinear, depending on the relative importance of river-ocean mixing and internal sinks (diatom uptake). Particles have different spatial patterns because they accumulate in estuarine turbidity maxima formed by the combination of sinking and estuarine circulation. Some constituents have weak or no mean spatial structure along the salinity gradient, reflecting spatially distributed sources along the estuary (nitrate) or atmospheric exchanges that buffer spatial variability of ecosystem metabolism (dissolved oxygen). The density difference between freshwater and seawater establishes stratification in estuaries stronger than the thermal stratification of lakes and oceans. Stratification is strongest around the center of the salinity gradient and when river discharge is high. Spatial distributions of motile organisms are shaped by species-specific adaptations to different salinity ranges (shrimp) and by behavioral responses to environmental variability (northern anchovy). Estuarine spatial patterns change over time scales of events (intrusions of upwelled ocean water), seasons (river inflow), years (annual weather anomalies), and between eras separated by ecosystem disturbances (a species introduction). Each of these lessons is a piece in the puzzle of how estuarine ecosystems are structured and how they differ from the river and ocean ecosystems they bridge.

Effects of high temperatures on threatened estuarine fishes during periods of extreme drought

Journal of Experimental Biology (The Company of Biologists) | March 1st, 2016

Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an in

Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an integrative approach to assess the impact of elevated water temperature on two fishes of immediate conservation concern in a large estuary system, the threatened longfin smelt (Spirinchus thaleichthys) and endangered delta smelt (Hypomesus transpacificus). Abundances have reached record lows in California, USA, and these populations are at imminent risk of extirpation. California is currently impacted by a severe drought, resulting in high water temperatures, conditions that will become more common as a result of climate change. We exposed fish to environmentally relevant temperatures (14°C and 20°C) and used RNA sequencing to examine the transcriptome-wide responses to elevated water temperature in both species. Consistent with having a lower temperature tolerance, longfin smelt exhibited a pronounced cellular stress response, with an upregulation of heat shock proteins, after exposure to 20°C that was not observed in delta smelt. We detected an increase in metabolic rate in delta smelt at 20°C and increased expression of genes involved in metabolic processes and protein synthesis, patterns not observed in longfin smelt. Through examination of responses across multiple levels of biological organization, and by linking these responses to habitat distributions in the wild, we demonstrate that longfin smelt may be more susceptible than delta smelt to increases in temperatures, and they have little room to tolerate future warming in California. Understanding the species-specific physiological responses of sensitive species to environmental stressors is crucial for conservation efforts and managing aquatic systems globally.

Effects of Hydraulic Conditions on Salvage Efficiency of Adult Delta Smelt at the Tracy Fish Collection Facility

U.S. Bureau of Reclamation (USBR) | February 29th, 2016

Effects of Tidal Wetland Restoration on Fish: A Suite of Conceptual Models

California Department of Water Resources (DWR) | November 2nd, 2017

Fishes native to the Sacramento-San Joaquin Delta and Suisun Marsh have historically had access to a complex mosaic of dendritic channels, large tule marshes, floodplain

Fishes native to the Sacramento-San Joaquin Delta and Suisun Marsh have historically had access to a complex mosaic of dendritic channels, large tule marshes, floodplains, and riparian woodlands. After the Gold Rush, that habitat was rapidly and drastically altered, and today several native fish species occur in record low numbers. Although many other stressors also contributed to population declines, habitat restoration is a major component of strategies to reverse the trend. Programs such as the Fish Restoration Program particularly emphasize restoration of tidal wetlands and associated shallow subtidal habitat and strive to restore and learn in an adaptive management context. Conceptual models, therefore, are necessary to plan both the restoration and the monitoring and evaluation of restoration actions.

Electrical Resistivity Investigation of Fluvial Geomorphology to Evaluate Potential Seepage Conduits to Agricultural Lands along the San Joaquin River, Merced County, California, 2012–13

U.S. Geological Survey (USGS) | ?

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage los

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydraulically connected to the river could act as seepage conduits, allowing rapid and widespread water-table rise during restoration flows. There is a need to identify the geometry and properties of these channel deposits to assess their role in potential increased seepage effects and to evaluate management alternatives for reducing seepage. Electrical and electromagnetic surface geophysical methods have provided a reliable proxy for lithology in studies of fluvial and hyporheic systems where a sufficient electrical contrast exists between deposits of differing grain size. In this study, direct-current (DC) resistivity was used to measure subsurface resistivity to identify channel deposits and to map their subsurface geometry. The efficacy of this method was assessed by using DC resistivity surveys collected along a short reach of the San Joaquin River in Merced County, California, during the summers of 2012 and 2013, in conjunction with borings and associated measurements from a hydraulic profiling tool. Modeled DC resistivity data corresponded with data from analyses of core samples, hand-auger samples, a hydraulic profiling tool, and aerial photographs, confirming that DC resistivity was effective for differentiating between silty and sandy deposits in this setting. Modeled DC resistivity data provided detailed two-dimensional cross-sectional resistivity profiles to a depth of about 20 meters. The distribution of high-resistivity units in these profiles was used as a proxy for identifying areas of high hydraulic conductivity. Estimates of the cross-sectional area of channel deposits from DC resistivity pseudosections can provide critical input for groundwater-flow models designed to simulate river seepage and evaluate seepage-management alternatives.

Elevation and Opportunity in the Delta: Restoring the Right Thing in the Right Place

San Francisco Estuary Institute (SFEI) | May 31st, 2022

A future Sacramento-San Joaquin Delta and Suisun Marsh (“Delta” herein) that supports healthy ecosystems and native species, while also meeting flood risk reduction,

A future Sacramento-San Joaquin Delta and Suisun Marsh (“Delta” herein) that supports healthy ecosystems and native species, while also meeting flood risk reduction, water supply, water quality, carbon sequestration, economic, and cultural objectives, requires that appropriate restoration and management actions be taken in the right place at the right time. Geographic setting affects the potential opportunities available—not all actions are suitable everywhere. Physical factors determining what types of activities are appropriate now and in the future include a site’s elevation, degree of tidal and fluvial influence, salinity, soil type, and local effects of climate change, which all vary spatially across the Delta. While there has been considerable progress over the last several decades, continued acceleration of the pace and scale of enhancement actions appropriate to landscape position is needed. Understanding the physical template is necessary for developing strategies that move beyond opportunistic restoration, support resilience over time, and have the potential to connect and magnify benefits across the larger landscape.