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At least 595 records · Page 33Linked to original sources
USGS1975

Chemical and biological quality of water in part of the Everglades, southeastern Florida

A comprehensive monitoring network was established in a part of the Everglades to evaluate the quality of water being delivered to Everglades National Park. Physical, chemical, and biological parameters were determined in surface water, bottom sediment, and bulk precipitation (rainfall and dry fallout). The geology of the area, bottom sediment, bulk precipitation, natural, urban, and agricultural runoff, and the characteristics of the hydrologic system in the Everglades influence the type and concentration of each chemical constituent and how it affects the water quality. The quality of surface water in the agricultural area between Lake Okeechobee and the water conservation areas is markedly different from that of other surface water in southeastern Florida. In general, the water in this area is higher in concentrations of most chemical constituents. Man has engaged in cultural activities, both agricultural and urban, which have affected the water quality in the northern and eastern segments of the area of investigation. The quality of the water improves, however, as it flows to the south and east because there is minimal input from man's activities and many of the constituents are assimilated by plants, sorbed on organic material and clay in the bottom sediments, and entrapped within the sediments. Dilution by rainfall and concentration by evapotranspiration are also important factors that influence the quality of surface water in the area of investigation. The area of investigation in the Everglades is a sink for macronutrients, trace metals, and chlorinated-hydrocarbon insecticides. These constituents do not move through the system freely. They become tied up in various complexes and for that reason, the water being delivered to Everglades National Park is of better quality than the water entering the northern edge of the water conservation areas. The various physical and biological processes and chemical reactions combine to improve the water quality as the water flows southward. The data presented in this report may be used as a baseline for determination of future changes in water quality at the several places in the Everglades where recurrent sampling of rainfall, surface water, and bottom sediments was undertaken during the course of the investigation.

Florida↗
USGS2012

Increased temperature and altered summer precipitation have differential effects on biological soil crusts in a dryland ecosystem

Biological soil crusts (biocrusts) are common and ecologically important members of dryland ecosystems worldwide, where they stabilize soil surfaces and contribute newly fixed C and N to soils. To test the impacts of predicted climate change scenarios on biocrusts in a dryland ecosystem, the effects of a 2–3 °C increase in soil temperature and an increased frequency of smaller summer precipitation events were examined in a large, replicated field study conducted in the cold desert of the Colorado Plateau, USA. Surface soil biomass (DNA concentration), photosynthetically active cyanobacterial biomass (chlorophyll a concentration), cyanobacterial abundance (quantitative PCR assay), and bacterial community composition (16S rRNA gene sequencing) were monitored seasonally over 2 years. Soil microbial biomass and bacterial community composition were highly stratified between the 0–2 cm depth biocrusts and 5–10 cm depth soil beneath the biocrusts. The increase in temperature did not have a detectable effect on any of the measured parameters over 2 years. However, after the second summer of altered summer precipitation pattern, significant declines occurred in the surface soil biomass (avg. DNA concentration declined 38%), photosynthetic cyanobacterial biomass (avg. chlorophyll a concentration declined 78%), cyanobacterial abundance (avg. gene copies g −1 soil declined 95%), and proportion of Cyanobacteria in the biocrust bacterial community (avg. representation in sequence libraries declined 85%). Biocrusts are important contributors to soil stability, soil C and N stores, and plant performance, and the loss or reduction of biocrusts under an altered precipitation pattern associated with climate change could contribute significantly to lower soil fertility and increased erosion and dust production in dryland ecosystems at a regional scale.

Global Change Biology↗
USGS2026

Recent scientific contributions by the U.S. Geological Survey in the San Francisco Bay and Sacramento–San Joaquin Delta Estuary

Introduction The San Francisco Bay and Sacramento–San Joaquin Delta Estuary (hereafter, Bay-Delta) is the largest estuary on the West Coast of the United States. The Bay-Delta covers more than 1,600 square miles and drains a watershed of more than 75,000 square miles, which is greater than 40 percent of California. The region surrounding the Bay-Delta is home to about 10 million people, and its habitats (fig. 1) support more than 800 plant and animal species. The waterways of the Bay-Delta are the central hub of California’s extensive freshwater delivery system, supplying water to more than 27 million Californians and 4 million acres of farmland in the Central Valley. The U.S. Geological Survey (USGS) is the primary science agency of the U.S. Department of the Interior, providing a broad range of Earth, water, biological, and mapping data and expertise to inform natural resource management across the country. This fact sheet focuses on research conducted by the USGS in the Bay-Delta region, mostly within the past 5 years. The fact sheet is organized across five major themes: water flow and water quality, fish and wildlife, wetland restoration, invasive species, and hazards. In each of these areas, the USGS works closely with Federal, State, and local agencies; academia; and non-governmental organizations to provide objective, evidence-based science. The data and knowledge gained from USGS research and monitoring are publicly available and are routinely used by agencies, including the U.S. Bureau of Reclamation, U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, California Department of Water Resources, California Department of Fish and Wildlife, California State Water Resources Control Board, Delta Stewardship Council, and many additional organizations and stakeholders to inform management of the Bay-Delta region and its resources.

California↗
USGS2018

Natural resource condition assessment: Olympic National Park

The Natural Resource Assessment Program aims to document condition and trends of selected park resources while identifying emerging issues and information needs. This information is intended to serve as a platform for natural resource managers to use in developing future resource stewardship priorities and planning. Olympic National Park (OLYM) on Washington’s Olympic Peninsula protects remarkable examples of several Pacific Northwestern ecosystems, including the glacier-capped Olympic Mountains, oldgrowth temperate rainforests, pristine river systems, and wild Pacific coastline and islands. The park provides habitat for numerous plants and animals, including at least 16 animal and eight plant taxa endemic to the Olympic Peninsula. The park’s lakes and rivers support over 70 stocks of Pacific salmonids and 29 native freshwater fish species. The rocky intertidal community is one of the most complex and diverse shorelines in the United States. Although we conducted in-depth assessments on a limited number of resources, the general condition of several other physical and biological components of OLYM ecosystems is described in Chapter 2, along with an overview of park history and ecology. In Chapter 3, we describe how we chose our focal resources and measures, as well as our protocol for conducting the assessment. In Chapter 4, we provide a detailed assessment of each resource, with a summary of condition and trends. In Chapter 5, we further interpret and discuss the implications of each focal resource status, highlighting future areas for monitoring and research. We summarize the general findings from our assessments below.

Washington↗
USGS2002

Hydrologic variability and the application of Index of Biotic Integrity metrics to wetlands: a Great Lakes evaluation

Interest by land-management and regulatory agencies in using biological indicators to detect wetland degradation, coupled with ongoing use of this approach to assess water quality in streams, led to the desire to develop and evaluate an Index of Biotic Integrity (IBI) for wetlands that could be used to categorize the level of degradation. We undertook this challenge with data from coastal wetlands of the Great Lakes, which have been degraded by a variety of human disturbances. We studied six barrier beach wetlands in western Lake Superior, six drowned-river-mouth wetlands along the eastern shore of Lake Michigan, and six open shoreline wetlands in Saginaw Bay of Lake Huron. Plant, fish, and invertebrate communities were sampled in each wetland. The resulting data were assessed in various forms against gradients of human disturbance to identify potential metrics that could be used in IBI development. Our results suggested that the metrics proposed as potential components of an IBI for barrier beach wetlands of Lake Superior held promise. The metrics for Lake Michigan drowned-river-mouth wetlands were inconsistent in identifying gradients of disturbance; those for Lake Huron open embayment wetlands were yet more inconsistent. Despite the potential displayed by the Lake Superior results within the year sampled, we concluded that an IBI for use in Great Lakes wetlands would not be valid unless separate scoring ranges were derived for each of several sequences of water-level histories. Variability in lake levels from year to year can produce variability in data and affect the reproducibility of data collected, primarily due to extreme changes in plant communities and the faunal habitat they provide. Substantially different results could be obtained in the same wetland in different years as a result of the response to lake-level change, with no change in the level of human disturbance. Additional problems included limited numbers of comparable sites, potential lack of undisturbed reference sites, and variable effects of different disturbance types. We also evaluated our conclusions with respect to hydrologic variability and other major natural disturbances affecting wetlands in other regions. We concluded that after segregation of wetland types by geographic, geomorphic, and hydrologic features, a functional IBI may be possible for wetlands with relatively stable hydrology. However, an IBI for wetlands with unpredictable yet recurring influences of climate-induced, long-term high water periods, droughts, or drought-related fires or weather-related catastrophic floods or high winds (hurricanes) would also require differing scales of measurement for years that differ in the length of time since the last major natural disturbance. A site-specific, detailed ecological analysis of biological indicators may indeed be of value in determining the quality or status of wetlands, but we recommend that IBI scores not be used unless the scoring ranges are calibrated for the specific hydrologic history pre-dating any sampling year.

Wetlands↗
USGS2004

Density and success of bird nests relative to grazing on western Montana grasslands

Grassland birds are declining at a faster rate than any other group of North American bird species. Livestock grazing is the primary economic use of grasslands in the western United States, but the effects of this use on distribution and productivity of grassland birds are unclear. We examined nest density and success of ground-nesting birds on grazed and ungrazed grasslands in western Montana. In comparison to grazed plots, ungrazed plots had reduced forb cover, increased litter cover, increased litter depth, and increased visual obstruction readings (VOR) of vegetation. Nest density among 10 of 11 common bird species was most strongly correlated with VOR of plots, and greatest nest density for each species occurred where mean VOR of the plot was similar to mean VOR at nests. Additionally, all bird species were relatively consistent in their choice of VOR at nests despite substantial differences in VOR among plots. We suggest that birds selected plots based in part on availability of suitable nest sites and that variation in nest density relative to grazing reflected the effect of grazing on availability of nest sites. Nest success was similar between grazed plots and ungrazed plots for two species but was lower for nests on grazed plots than on ungrazed plots for two other species because of increased rates of predation, trampling, or parasitism by brown-headed cowbirds ( Molothrus ater ). Other species nested almost exclusively on ungrazed plots (six species) or grazed plots (one species), precluding evaluation of the effects of grazing on nest success. We demonstrate that each species in a diverse suite of ground-nesting birds preferentially used certain habitats for nesting and that grazing altered availability of preferred nesting habitats through changes in vegetation structure and plant species composition. We also show that grazing directly or indirectly predisposed some bird species to increased nesting mortality. Management alternatives that avoid intensive grazing during the breeding season would be expected to benefit many grassland bird species.

Montana↗
USGS2025

Waterfowl endozoochory: Traits drive plant-bird dispersal interactions in North America

Plant biogeography and ongoing changes in plant distributions are influenced by long-distance dispersal (LDD) of seeds, and migratory waterfowl (Anatidae: Ducks, geese and swans) are particularly important for the dispersal of plants in and around wetlands through gut passage (endozoochory). However, this dispersal is not contemplated by classical dispersal syndromes; hence, currently we have limited understanding of what angiosperm traits predict seed dispersal by waterfowl and any differences due to avian trait variation among waterfowl species. We conducted a literature search for data on the presence of seeds in the alimentary canal or faeces of North American waterfowl as a proxy for dispersal interactions, since an important fraction of these seeds survives gut passage. We present a list of North American flowering plant species ( N = 536) from 95 families potentially dispersed by 38 waterfowl species, together with traits of these plants and their vectors. Owing largely to limited sampling effort, 47% of plant species and 35% of plant genera recorded were only found in a single waterfowl species. A suite of analytical approaches revealed major differences in the traits of plants whose seeds are ingested and likely dispersed between foraging groups (guilds) and in relation to other waterfowl traits. Diving ducks and sea ducks are associated with sublittoral plants that have submerged or floating leaves, and hence with the classical hydrochory syndrome. Dabbling ducks and herbivorous waterfowl (notably geese) are associated with terrestrial herbaceous plants, and also with the unspecialised dispersal syndrome common in terrestrial plants. Plants with larger seeds or of greater height are more likely to be dispersed by dabbling ducks, whereas shorter plants are more likely to be dispersed by geese than by other waterfowl. Network analyses of interactions between waterfowl species and plant traits were generally consistent with these results, but also provided evidence that not all geese, dabbling ducks, or sea duck species are alike in their interactions with plants along the terrestrial–aquatic gradient, but instead occupy distinct dispersal niches. The traditional classification of waterfowl into guilds therefore does not accurately reflect their differing roles in the ingestion and dispersal of plant seeds. Aquatic plant species had more vector species than terrestrial ones. Detailed studies of waterfowl endozoochory and more trait determinations for North American plants are needed to facilitate predictions of LDD as waterfowl population sizes and migration patterns vary in the future with climate change.

Freshwater Biology↗
USGS2008

Algal and water-quality data for Rapid Creek and Canyon Lake near Rapid City, South Dakota, 2007

This report summarizes the results of algae and water-quality sampling on Rapid Creek and Canyon Lake during May and September 2007. The overall purpose of the study was to determine the algal community composition of Rapid Creek and Canyon Lake in relation to organisms that are known producers of unwanted tastes and odors in drinking-water supplies. Algal assemblage structure (phytoplankton and periphyton) was examined at 16 sites on Rapid Creek and Canyon Lake during May and September 2007, and actinomycetes bacteria were sampled at the Rapid City water treatment plant intake in May 2007, to determine if taste-and-odor producing organisms were present. During the May 2007 sampling, 3 Rapid Creek sites and 4 Canyon Lake sites were quantitatively sampled for phytoplankton in the water column, 7 Rapid Creek sites were quantitatively sampled for attached periphyton, and 4 lake and retention pond sites were qualitatively sampled for periphyton. Five Rapid Creek sites were sampled for geosmin and 2-methylisoborneol, two common taste-and-odor causing compounds known to affect water supplies. During the September 2007 sampling, 4 Rapid Creek sites were quantitatively sampled for attached periphyton, and 3 Canyon Lake sites were qualitatively sampled for periphyton. Water temperature, dissolved oxygen, pH, and specific conductance were measured during each sampling event. Methods of collection and sample analysis are presented for the various types of biological and chemical constituent samples. Diatoms comprised 91-100 percent of the total algal biovolume in periphyton samples collected during May and September. Cyanobacteria (also called blue-green algae) were detected in 7 of the 11 quantitative periphyton samples and ranged from 0.01 to 2.0 percent of the total biovolume. Cyanobacteria were present in 3 of the 7 phytoplankton samples collected in May, but the relative biovolumes were small (0.01-0.2 percent). Six of seven qualitative samples collected from Canyon Lake and retention ponds during May and September also contained cyanobacteria. Geosmin and 2-methylisoborneol concentrations were less than detection limits (0.005 ug/L) in all five of the Rapid Creek samples collected in May. Actinomycetes bacteria were present at the water treatment plant intake in May 2007, at a concentration of 6 colonies per milliliter. During this study, no taste-and-odor problems with the drinking water within the study area were reported. However, the presence of cyanobacterial taxa known to contain taste-and-odor producing strains (such as Leptolyngbya, Phormidium, and Anabaena) indicates the potential for taste-and-odor problems under certain physical and chemical conditions.

South Dakota↗
USGS2011

Toward a community coastal sediment transport modeling system: the second workshop

Models for transport and the long-term fate of particles in coastal waters are essential for a variety of applications related to commerce, defense, public health, and the quality of the marine environment. Examples include: analysis of waste disposal and transport and the fate of contaminated materials; evaluation of burial rates for naval mines or archaeological artifacts; prediction of water-column optical properties; analysis of transport and the fate of biological particles; prediction of coastal flooding and coastal erosion; evaluation of impacts of sea-level or wave-climate changes and coastal development; planning for construction and maintenance of navigable waterways; evaluation of habitat for commercial fisheries; evaluation of impacts of natural or anthropogenic changes in coastal conditions on recreational activities; and design of intakes and outfalls for sewage treatment, cooling systems, and desalination plants.

Eos, Transactions, American Geophysical Union↗
USGS2009

A burning story: The role of fire in the history of life

Ecologists, biogeographers, and paleobotanists have long thought that climate and soils controlled the distribution of ecosystems, with the role of fire getting only limited appreciation. Here we review evidence from different disciplines demonstrating that wildfire appeared concomitant with the origin of terrestrial plants and played an important role throughout the history of life. The importance of fire has waxed and waned in association with changes in climate and paleoatmospheric conditions. Well before the emergence of humans on Earth, fire played a key role in the origins of plant adaptations as well as in the distribution of ecosystems. Humans initiated a new stage in ecosystem fire, using it to make the Earth more suited to their lifestyle. However, as human populations have expanded their use of fire, their actions have come to dominate some ecosystems and change natural processes in ways that threaten the sustainability of some landscapes. ?? 2009 by American Institute of Biological Sciences.

BioScience↗
USGS2005

Aniakchak sockeye salmon investigations

Aniakchak National Monument and Preserve provides unusual and dramatic landscapes shaped by numerous volcanic eruptions, a massive flood, enormous landslides, and ongoing geological change. The focal point of the monument is Aniakchak Caldera, a restless volcano that embodies the instability of the Alaska Peninsula. This geological instability creates a dynamic and challenging environment for the biological occupants of Aniakchak and unparalleled opportunities for scientists to measure the adaptability of organisms and ecosystems to change. The sockeye salmon (Oncorhynchus nerka) is one member of the Aniakchak ecosystem that has managed to adapt to geologic upheaval and is now thriving in the park. Aside from just surviving in the harsh environment, these salmon are also noteworthy for providing essential marinederived nutrients to plants and animals and as a source of food for historic and present day people in the region.

Alaska↗
USGS2023

Association of excessive precipitation and agricultural land use with honey bee colony performance

Context: From landscape variables to weather, multiple environmental factors affect honey bees and other pollinators. Detailed honey bee colony assessments in a variety of landscape and weather conditions offer the opportunity to develop a mechanistic understanding of how landscape composition, configuration, and weather are associated with colony nutrition, demography, and productivity. Objectives: Our objective was to test if weather and landscape characteristics (e.g., agricultural versus forested land use) are associated with different honey bee colony outcomes (foraged nectar mass, foraged pollen mass, pupal population size, and adult population size change). Methods: We collected detailed colony measurements on over 450 honey bee colonies over four years across an agricultural-to-forested land use gradient in Michigan, USA. Results: We found that higher than normal precipitation in the preceding spring and fall was negatively correlated with colony size change and with foraged nectar mass, respectively. Sites surrounded by less agricultural land and more forested land also had fewer pupae by the end of summer. Conclusions: These inter-dependent colony metrics offer insights into environmental-plant-pollinator dynamics. Our finding that extreme weather events, associated with climate change, are negatively correlated with colony performance point to likely lagged effects of weather on pollinator floral resources. Landscapes managed with climate-resilient, temporally continuous floral resources are likely to support pollinators. Capturing extreme weather phenomena in field studies is a valuable way to investigate the associations between land use, climate change and biological systems. However, caution should be taken in overinterpreting observational studies, so further research is needed.

Landscape Ecology↗
USGS2007

Water-quality and ancillary data collected from the Arroyo Colorado near Rio Hondo, Texas, 2006

The Arroyo Colorado is in the lower Rio Grande Valley of southern Texas and extends from near Mission, Texas, eastward to the Laguna Madre estuarine and coastal marine system, which separates Padre Island from the Texas mainland. Streamflow in the Arroyo Colorado primarily is sustained by effluent from municipal wastewater-treatment plants along the stream banks. Since 1986, the tidal segment of the Arroyo Colorado from the port of Harlingen to the Laguna Madre has been designated by the State of Texas as an impaired water body because of low dissolved oxygen concentrations. Efforts to develop predictive water-quality models for the tidal segment of the Arroyo Colorado have been hampered by a lack of physical, biological, and biochemical data. Specifically, data on primary algal productivity, nutrient cycling, sediment deposition rates, and the relations between these processes and dissolved oxygen dynamics in the stream have been inadequate to support water-quality modeling efforts. The U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality, did a study in 2006 to collect data associated with primary algal productivity, nutrient cycling, and dissolved oxygen dynamics in the tidal segment (2201) of the Arroyo Colorado near Rio Hondo. Specific objectives of the study were to (1) characterize water quality by measuring basic properties; (2) characterize the concentrations of carbon and nutrients, biochemical oxygen demand, total organic carbon, total suspended solids, and volatile suspended solids; (3) measure the seasonal differences of nutrient-dependent algal growth and algal production in the water column; (4) measure oxygen respiration or production rates; and (5) measure rates of sediment deposition.

Data Series↗
USGS1926

Shore phases of the Green River formation in northern Sweetwater County, Wyoming

For the last two years the writer has been engaged in a detailed study of the Green River formation and its oil shale. In order to arrive at an intelligent interpretation of this great series of lacustrine beds, the field study has been focused upon the marginal phases of the deposits and the associated formations, to determine, first, so far as possible from the geologic and biologic evidence recorded there, the environmental conditions that prevailed when these beds were laid down, such as the geologic history and physical configuration of the basin of deposition the mode of filling, the sources and nature of the materials, and the climatic conditions under which the deposits accumulated. From the same evidence the writer has also endeavored to determine the kinds and relative abundance of both plant and animal life that existed in the Green River lake and on the adjacent land. Such evidence is fragmentary, as was to be expected, but it serves well as a basis for fur her study and interpretation.

Wyoming↗
USGS2024

New uses for ancient middens: Bridging ecological and evolutionary perspectives

Rodent middens provide a fine-scale spatiotemporal record of plant and animal communities over the late Quaternary. In the Americas, middens have offered insight into biotic responses to past environmental changes and historical factors influencing the distribution and diversity of species. However, few studies have used middens to investigate genetic or ecosystem level responses. Integrating midden studies with neoecology and experimental evolution can help address these gaps and test mechanisms underlying eco-evolutionary patterns across biological and spatiotemporal scales. Fully realizing the potential of middens to answer cross-cutting ecological and evolutionary questions and inform conservation goals in the Anthropocene will require a collaborative research community to exploit existing midden archives and mount new campaigns to leverage midden records globally.

Trends in Ecology and Evolution↗
USGS2024

Review of the life history and conservation of federally endangered plant species of the Lower Rio Grande Valley, Texas, U.S.A.

This review aims to summarize information critical to the conservation of the federally listed endangered species of South Texas, which occur along the border of Texas and Mexico. This paper describes the characteristics, habitat, population status, distribution, life history, threats, and restoration of endangered plant species of the Lower Rio Grande Valley, Texas, which includes Cameron, Willacy, Hildago, and Starr County. Seven federally listed species are considered including Ambrosia cheiranthifolia, Asclepias prostrata, Astrophytum asterias, Ayenia limitaris, Manihot walkerae, Lesquerella thamnophila (syn. Physaria thamnophila), and Thymophylla tephroleuca. An eighth species, Physostegia correllii is under consideration for federal listing by the U.S. Fish and Wildlife Service. This paper assembles information on the background, biological status, major threats, and conservation to aid managers and the scientific community in restoring and managing these species.

Texas↗
USGS2013

Challenge theme 1: Understanding and preserving ecological resources: Chapter 3 in United States-Mexican Borderlands: Facing tomorrow's challenges through USGS science

The notable biodiversity within the United States–Mexican border region is driven by the wide variety of natural landscapes in the area and its biologically unique transition zone of habitats for xeric, temperate, and subtropical species. Six diverse ecoregions cover the length of the border (fig. 3–1): California Coastal Sage, Chaparral, and Oak Woodlands; Sonoran Desert; Madrean Archipelago; Chihuahuan Desert; Southern Texas Plains; and Western Gulf Coastal Plain. The unique geology and many of the distinctive geographic features and climatic conditions that have given rise to the diverse populations of plants and animals found in the Borderlands also attract human populations. The number of people living in the Borderlands has increased dramatically over recent years, from about 7 million in 1980 to almost 12 million in 2003; the population is estimated to be more than 18 million by 2020 (Peach and Williams, 2003). The human population increase and associated change in land use have contributed to habitat fragmentation and habitat loss for native species, thus threatening their survival. Some ways in which humans negatively affect plants and animals in the Borderlands include dewatering of aquatic ecosystems, water pollution, introduction and spread of invasive species, outdoor lighting, military and border enforcement activity, and energy development and transmission.

United States-Mexico Borderlands↗
USGS1988

The ecology of the soft-bottom benthos of San Francisco Bay: a community profile

This profile, part of a series of profiles concerning coastal habitats of the United States, is a detailed examination of the soft-bottom benthos of San Francisco Bay. A U.S. Fish and Wildlife Service and California Department of Fish and Game report (1979) entitled "Protection and Restoration of San Francisco Bay Fish and Wildlife Habitat" provides clear recognition of the importance of intertidal and subtidal soft-bottom habitats and their associated organisms to the bay's birds and fishes and to the overall functioning of the estuary. The purpose of this profile is to provide a description of the structure and functioning of the benthic community in San Francisco Bay (exclusive of its tidal marshes, which are discussed by M. Josselyn [1983] in another profile). The habitats covered in this volume include all nonvegetated soft-bottom intertidal and subtidal areas of the bay between the Golden Gate and the mouths of the Sacramento and San Joaquin Rivers to the northeast, and to the southern extremity of the bay. The profile provides a reference to the scientific information concerning the animals and plants of the bay's benthic communities, their importance to the bay ecosystem, and their value as a resource measured in human terms. Because there have been few process-oriented studies of the benthos of San Francisco Bay (e.g., field and laboratory rate-measurement experiments), the material presented herein is largely descriptive. Nonetheless, we have described the processes that interconnect the various physical, chemical, and biological components of the benthic environment, and the important couplings between this environment and the water column above, with reference to research results from other estuaries where necessary. We consider the role of the benthic community as a food source for fish, aquatic birds, and humans; as a consumer or degrader of organic materials including wastes; as a recycler of minerals and nutrients; and as an accumulator of pollutants.

California↗