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Hydrologic, Water-Quality, and Biological Assessment of Laguna de Las Salinas, Ponce, Puerto Rico, January 2003-September 2004

By Luis R. Soler-López, Fernando Gómez-Gómez, and Jesús Rodríguez-Martínez

 

In cooperation with the
MUNICIPIO AUTONOMO DE PONCE, PUERTO RICO, OFFICE OF THE MAYOR

 

Scientific Investigations Report 2005-5154

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ABSTRACT

The Laguna de Las Salinas is a shallow, 35-hectare, hypersaline lagoon (depth less than 1 meter) in the municipio of Ponce, located on the southern coastal plain of Puerto Rico. Hydrologic, water-quality, and biological data in the lagoon were collected between January 2003 and September 2004 to establish baseline conditions. During the study period, rainfall was about 1,130 millimeters, with much of the rain recorded during three distinct intense events. The lagoon is connected to the sea by a shallow, narrow channel. Subtle tidal changes, combined with low rainfall and high evaporation rates, kept the lagoon at salinities above that of the sea throughout most of the study. Water-quality properties measured on-site (temperature, pH, dissolved oxygen, specific conductance, and Secchi disk transparency) exhibited temporal rather than spatial variations and distribution. Although all physical parameters were in compliance with current regulatory standards for Puerto Rico, hyperthermic and hypoxic conditions were recorded during isolated occasions. Nutrient concentrations were relatively low and in compliance with current regulatory standards (less than 5.0 and 1.0 milligrams per liter for total nitrogen and total phosphorus, respectively). The average total nitrogen concentration was 1.9 milligrams per liter and the average total phosphorus concentration was 0.4 milligram per liter. Total organic carbon concentrations ranged from 12.0 to 19.0 milligrams per liter. Chlorophyll a was the predominant form of photosynthetic pigment in the water. The average chlorophyll a concentration was 13.4 micrograms per liter. Chlorophyll b was detected (detection limits 0.10 microgram per liter) only twice during the study. About 90 percent of the primary productivity in the Laguna de Las Salinas was generated by periphyton such as algal mats and macrophytes such as seagrasses. Of the average net productivity of 13.6 grams of oxygen per cubic meter per day derived from the diel study, the periphyton and macrophyes produced 12.3 grams per cubic meter per day; about 1.3 grams (about 10 percent) were produced by the phytoplankton (plant and algae component of plankton). The total respiration rate was 59.2 grams of oxygen per cubic meter per day. The respiration rate ascribed to the plankton (all organisms floating through the water column) averaged about 6.2 grams of oxygen per cubic meter per day (about 10 percent), whereas the respiration rate by all other organisms averaged 53.0 grams of oxygen per cubic meter per day (about 90 percent). Plankton gross productivity was 7.5 grams per cubic meter per day; the gross productivity of the entire community averaged 72.8 grams per cubic meter per day. Fecal coliform bacteria counts were generally less than 200 colonies per 100 milliliters; the highest concentration was 600 colonies per 100 milliliters.

TABLE OF CONTENTS

Abstract

Introduction

Description of Study Area

Purpose and Scope

Acknowledgments

Methods

Hydrologic Characteristics

Bathymetric Survey

Water Quality

Water Physical Properties

Temperature

pH

Dissolved Oxygen

Specific Conductance

Salinity

Secchi Disk Water Transparency

Water Chemical Properties

Nutrients

Organic Carbon

Chlorophyll a and b

Biological Characteristics

Primary Productivity

Light and Dark Bottle Primary Productivity, Community Respiration,

and Community Gross productivity

Diel Primary Productivity, Community Respiration, and Community Gross Productivity

Phytoplankton Biomass

Fecal Bacteria Concentration

Summary and Conclusions

References Cited

Appendix 1. On-site determination of pH, temperature, specific conductance, dissolved oxygen, salinity, and Secchi disk depth for water-quality sites sampled from February 2003 to March 2004 at the Laguna de Las Salinas, Ponce, Puerto Rico

Appendix 2. May 1, 2003, diel study physical properties

Appendix 3. October 16, 2003, diel study physical properties

Appendix 4. Fecal bacteria counts from February 2003 to March 2004

 

 


The citation for this report, in USGS format, is as follows:

 

Soler-López, Luis, Gómez-Gómez, Fernando, and Rodríguez-Martínez, Jesús, 2005, Hydrologic, water-quality, and biological assessment of Laguna de Las Salinas, Ponce, Puerto Rico, January 2003-September 2004: U.S. Geological Survey Scientific Investigations Report 2005-5154, 50 p.

 

Please visit http://pr.water.usgs.gov/ for more information about USGS activities in the Caribbean (Puerto Rico and the U.S. Virgin Islands).

 


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