Skip to Main Content
Book Chapter

Phytoplankton Production in the Mississippi Delta1

By
William H. Thomas
William H. Thomas
La Jolla, California, and Rockport, Texas
Search for other works by this author on:
Ernest G. Simmons
Ernest G. Simmons
La Jolla, California, and Rockport, TexasScripps Institution of Oceanography. We are in debted to the following persons for help on various aspects of this investigation—Robert Holmes and David Contois, who initiated the work and carried out the first three field trips; Freda M. H. Reid, who identified and counted some of the phytoplankton; Parke Richardson and Eugene F. Corcoran, who made chemical analyses of water and sediment samples; E. W. Fager, who introduced us to nonparametric methods of statistical analysis.
Search for other works by this author on:
Published:
January 01, 1960

Abstract

At 138 stations in the eastern Mississippi Delta area measurements were made of phytoplankton production (C14O2 uptake), chlorinity, temperature, suspended solids, Secchi disc depth, inorganic phosphate, soluble silica, and soluble Kjeldahl nitrogen. In addition, the phytoplankton in the water were identified and enumerated. These stations were generally located inshore of those taken by G. A. Riley (1937). The following results were obtained.

  1. 1.

    Surface phytoplankton production off the delta is equal to or greater than that of highly productive tropical or subtropical pelagic or neritic areas.

  2. 2.

    Surface production is quite variable; variation can be as much as seven-fold from one day to the next, at a given location.

  3. 3.

    Although seaward traverses made on single days showed that production generally increased at seaward locations, there were no over-all statistical differences between river, plume, and gulf areas at any given season.

  4. 4.

    During the period of high river discharge (May), surface production at the most seaward locations (gulf) was significantly greater than during the fall months. Phosphate and Kjeldahl nitrogen were also significantly greater in May than during the fall months in this area.

  5. 5.

    Integrated production in the water column was three to six times that occurring at the surface. Measured in situ water column production agreed within 20 per cent with that calculated by Ryther’s (1956) method in three out of six determinations. In the other determinations, the measured value was three to six times greater than the calculated value.

  6. 6.

    Rough calculations of the rate of sedimentation of organic carbon off the delta were compared with phytoplankton production. This comparison showed that it is unlikely that production contributes much organic carbon to pro-delta slope sediments. Production would have to proceed at the maximum rate throughout the year without losses of phytoplankton carbon to equal the rate at which carbon is deposited in these sediments. In the bottom-set beds farther seaward we cannot estimate from the present data the relative contribution of organic matter by phytoplankton to these sediments.

  7. 7.

    Theoretical calculations indicate that nitrogen is a more likely limiting nutrient in these waters than phosphate. Silicate may limit phytoplankton only in highly saline water, where no silicate could be detected.

  8. 8.

    Two hundred species of phytoplankton were identified from the delta, of which 86 per cent were diatoms. Two associations of primary species were recognized. One of these, consisting of species of Cyclotella, Melosira, and Navicula, was found in the river plume, and Blind Bay. The other consisting of species of Nitzschia, Thalassionema, Thalassiothrix, Skeletonema, Asterionella, and Chaetoceros, was found in the gulf, plume, and Breton Sound. During any given season the relative concentrations of phytoplankton do not differ significantly from area to area. Significantly fewer phytoplankton were found in the river and plume at times of low water, but no significant difference in phytoplankton concentration in the gulf was found between May and the fall months.

You do not currently have access to this article.

Figures & Tables

Contents

AAPG Special Publication

Recent Sediments, Northwest Gulf of Mexico

Francis P. Shepard
Francis P. Shepard
Scripps Institution of OceanographyUniversity of CaliforniaLa Jolla
Search for other works by this author on:
Fred B Phleger
Fred B Phleger
Scripps Institution of OceanographyUniversity of CaliforniaLa Jolla
Search for other works by this author on:
Tjeerd H. Van Andel
Tjeerd H. Van Andel
Scripps Institution of OceanographyUniversity of CaliforniaLa Jolla
Search for other works by this author on:
American Association of Petroleum Geologists
ISBN electronic:
9781629812403
Publication date:
January 01, 1960

GeoRef

References

Related

Citing Books via

A comprehensive resource of eBooks for researchers in the Earth Sciences

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal