Natural versus human-caused variability of water clarity in the Southern California Bight

Conversi, Alessandra; McGowan, John A.

doi:10.4319/lo.1994.39.3.0632

Cited by 17 publications

(10 citation statements)

References 27 publications

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“…The few reports of increased Secchi depths were associated with bioremediation or efforts to reduce untreated sewage outfall. For example, Secchi depths increased at 0.05 m/year in Narragansett Bay, Rhode Island, coincident with reductions in anthropogenic total suspended solids (Borkman and Smayda, 1998), as at one of several sampled sites in the Southern California Bight (Convers and McGowan, 1994). Our measures show a much more rapid change in Secchi depths than these previous studies.…”

Section: Long-term Trend In Secchi Depthscontrasting

confidence: 55%

Proceedings of the Smithsonian Marine Science Symposium

Lang¹,

Macintyre²,

Rützler³

2009

Smithsonian Contributions to the Marine Sciences

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s m i t h s o n i a n c o n t r i b u t i o n s t o t h e m a r i n e s c i e n c e s • n u m b e r 3 8 SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTIONEmphasis upon publication as a means of "diffusing knowledge" was expressed by the fi rst Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Botany Smithsonian Contributions in History and Technology Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Museum Conservation Smithsonian Contributions to Paleobiology Smithsonian Contributions to ZoologyIn these series, the Institution publishes small papers and full-scale monographs that report on the research and collections of its various museums and bureaus. The Smithsonian Contributions Series are distributed via mailing lists to libraries, universities, and similar institutions throughout the world.Manuscripts submitted for series publication are received by the Smithsonian Institution Scholarly Press from authors with direct affi liation with the various Smithsonian museums or bureaus and are subject to peer review and review for compliance with manuscript preparation guidelines. General requirements for manuscript preparation are on the inside back cover of printed volumes. For detailed submissions requirements and to review the "Manuscript Preparation and Style Guide for Authors," visit the Submissions page at www.scholarlypress.si.edu. The paper used in this publication meets the minimum requirements of the American National Standard for Permanence of Paper for Printed Library Materials Z39. Foreword N early two-thirds of Earth's surface is covered by the ocean, a global system essential to all life. Impacts on one part of the ocean can have worldwide effects. The ocean moderates our climate, provides valuable resources, and produces at least half the oxygen we breathe: it makes our planet livable. We know little, however, about the physical, chemical, geological, and biological aspects of this crucial life support system. s m i t h s o n i a n c o n t r i b u t i o n s t o t h e m a r i n S M I T H S O N I A N C O N T R I B U T I O N S T O T H E M A R I N E S C I E N C E S MARINE BIODIVERSITY, EVOLUTION, AND SPECIATION S M I T H S O N I A N C O N T R I B U T I O N S T O T H E M A R I N E S C I E N C E S i i i • S M I T H S O N I A N C O N T R I B U T I O N S T O T H E M A R I N E S C I E N C E SThe Smithsonian Institution, in efforts to increase knowledge about the ocean, has established a ...

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Section: Long-term Trend In Secchi Depthscontrasting

confidence: 55%

Proceedings of the Smithsonian Marine Science Symposium

Lang¹,

Macintyre²,

Rützler³

2009

Smithsonian Contributions to the Marine Sciences

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“…In some enclosed coastal seas, long-term reduction in water clarity has been connected to human-caused nutrient emissions (Mankovsky et al 1996;Sanden and Hå kansson 1996). Conversi and McGowan (1994) examined the natural vs. human-caused variability of water clarity close to the coast in the Southern California Bight with particular emphasis on sewage discharges. Although their results did not provide a totally unambiguous picture, they indicated that most of the water clarity variability was driven by bight-wide natural phenomena.…”

Section: Forcing Parametersmentioning

confidence: 99%

Multi‐decadal shoaling of the euphotic zone in the southern sector of the California Current System

Aksnesa

Ohman

2009

Limnology & Oceanography

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We document a long-term reduction in Secchi depth of 0.06-0.13 m yr 21 in the southern California Current System (CCS) over the period 1969-2007, reflecting a long-term shoaling of the euphotic zone. Calibrated water clarity observations from 1949 to 1954 reinforce the results indicating a progressive shoaling. For the inshore area, 150 km off the coast, Secchi disk has shoaled 8.4 6 1.2 m since 1949. This change has been accompanied by a nitracline shoaling of 18.2 6 6.4 m since 1969 and an increase in chlorophyll a since 1978. These changes have occurred despite an increase in density stratification in the CCS. Increased stratification has been linked by others to decreased nutrient fluxes, reduced primary production, increased water transparency, and a deepening of the euphotic zone, contrary to our findings. We explore this apparent paradox with a simple steady-state model of the thickness of the euphotic zone. A sensitivity analysis suggests that the observed shoaling of the euphotic zone is consistent with a doubling in nutrient upwelling, but in this analysis we also consider alternative causes for such shoaling: water-column darkening caused by freshening, increased residence time of the phototrophic biomass in the euphotic zone, and supply of nutrients of anthropogenic origin.

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“…These methods provided us with a methodical approach to the analysis of ecological time series that has helped reveal causes of temporal variability in a number of different systems. Note that Secchi depth spatial structure can also be analyzed to reveal underlying mechanisms (Conversi and McGowan 1994), but our data have confined us largely to the time domain.…”

Section: S C ϩ Kmentioning

confidence: 99%

Origins and scale dependence of temporal variability in the transparency of Lake Tahoe, California–Nevada

Jassby

Goldman

Reuter

et al. 1999

Limnology & Oceanography

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Secchi depth has been measured in Lake Tahoe an average of every 12 d since July 1967. Because of the unusual clarity of the lake, Secchi depth measurement is responsive to small changes in light-attenuating particles, and the record exhibits strong variability at the seasonal, interannual, and decadal scales. Using recently developed methods of applied time-series analysis, the mechanisms of change were delineated at each scale. The seasonal pattern is a bimodal one, with two minima at approximately June and December. The June minimum is due mostly to cumulative discharge of suspended sediments following melting of the snowpack. The December minimum is probably a result of mixed-layer deepening as the thermocline passes through layers of phytoplankton and other light-attenuating particles that reach a maximum below the summer mixed layer. The interannual scale exhibits two modes of variability, one during the weakly stratified autumn-winter period and the other during the more stratified springsummer period. The first mode is a result of variable depth of mixing in this unusually deep lake, while the second results from year-to-year changes in spring runoff. A decadal trend also exists (Ϫ0.25 m yr Ϫ1 ), resulting from accumulation of materials in the water column. It is not yet understood, however, how much of this change is due to phytoplankton or recent phytoplankton-derived materials and how much is due to other materials such as mineral suspensoids. Based on the available measurements and physical considerations, both categories may play a significant role.

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Natural versus human-caused variability of water clarity in the Southern California Bight

Cited by 17 publications

References 27 publications

Proceedings of the Smithsonian Marine Science Symposium

Proceedings of the Smithsonian Marine Science Symposium

Multi‐decadal shoaling of the euphotic zone in the southern sector of the California Current System

Origins and scale dependence of temporal variability in the transparency of Lake Tahoe, California–Nevada

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