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Hydrology and Water Quality of the Levittown Lake, Toa Baja, Puerto Rico

Project Number: 2516-E5900
Project Chief: Luis R. Soler-López
Cooperators: Department of Natural and Environmental Resources
Period of Project: FY 2009-2011

Introduction

Figure 1. Location of the Levittown Lake in Toa Baja, Puerto Rico, about five miles west of the Bahía de San Juan

Levittown Lake is surrounded by dense populated areas to the north, east, and south, with an extensive vegetated buffer zone that extends by about 6 kilometers west of the lake (fig. 2). The lake is about 5 meters in depth and because of the man-made nature it has a presumably a flat bottom with little relief. The actual lacustrine system is composed of three basic identifiable components: the lake’s main water body, the inlet/outlet channel that connects with the sea, and a runoff channel that receives the majority of the urban runoff generated by rainfall.

The lake is connected to the Atlantic Ocean by a 1.6-kilometer channel and is surrounded by mangroves and tidal swamps (fig. 1). Although initially intended to be a draining system, the lake may have turned into a functional aquatic ecosystem with an effective trophic chain. With its inlet/outlet channel connecting the lake to the ocean, the Levittown Lake may be operating as a typical coastal lagoon exporting tons of organic matter to the sea supporting the food chain and removing tons of carbon dioxide from the atmosphere. Therefore, the Levittown Lake could have become an integral part of the nearby coastal resources and an important ecological oasis and carbon dioxide filter in the middle of a heavily developed and populated zone.

Problem

As designed, the Levittown Lake receives urban runoff from developed areas in order to contain the waters and drain them out of the system to avoid flooding of private property. This runoff however is suspected to be contaminated and affecting nearby housing units. Neighboring people have reported noxious conditions and foul odors that affect the quality of life of many families. In addition to the possible human hazard, noxious conditions could be negatively impacting the aquatic ecosystem since the Levittown Lake has become a habitat for many fish and bird species.

Runoff from the Levittown Lake basin is presumed to be contributing with sewage from possible sewer mains and septic tanks overflow, as well as contaminants like metals and oils derived from surrounding ground transportation infrastructure, and urban wastes dumped directly into the lake. During periods of high runoff events, high nutrient loads could enter the lake which can be deleterious to the lake’s ecological health and impair the homeostatic capacity of the semi-enclosed coastal resource. In addition, flood tides could be contributing pollutants derived from the nearby Río Hondo and Río Bayamón through the runoff channel (fig. 3).

Figure 3. Location of the Levittown’s inlet/outlet and runoff channels.

Although the Levittown Lake could be an important coastal resource in the middle of development, local and Federal authorities, there are no documented scientific data to characterize, manage, and regulate the resource. Therefore, the need to establish the water quality baseline data is necessary.

Objectives

The objective of this study is to obtain baseline data of the physical, chemical, biological, and bacteriological conditions of the Levittown Lake to define its present characteristics and provide to the stakeholders of the resource a holistic perspective of the area’s hydrology and ecological conditions.

Scope

The proposed study will encompass the Levittown Lake’s main water body, the inlet/outlet, and the runoff channels. Data collection will include monthly measurements of physical, chemical, biological, and bacteriological parameters to define seasonal variability during one year. The study will also include two diel studies to determine community productivity rates, diurnal variation of selected water-quality characteristics, water interchange of the lagoon with the ocean through the outlet channel. The study is proposed to be conducted between October 2009 and September 2011, for a total of two natural years.

Strategy and Approach

The study will include the following field activities:

1. Collection of selected physical properties of water at seven stations inside the lake and at the channels to define monthly and seasonal variations in Levittown Lake. The parameters will include temperature, pH, dissolved oxygen, specific conductance, salinity, and Secchi disk water transparency.
2. Collect surficial water samples at three stations inside the lake and at the channels to define monthly and seasonal variations in fecal indicator bacteria concentrations.
3. Collect surficial water samples for the determination of total and dissolved nutrients at two stations inside the lake.
4. Collect surficial water samples for the determination of dissolved metals at two stations within the lake.
5. Determination of plankton productivity at two stations inside the lake using the lightdark bottles method.
6. Conduct diel studies twice during the year to determine the community primary productivity, the community respiration, and the community gross productivity.
7. Conduct discharge measurements at the lake’s channel entrance during the diel studies to quantify the inflow and outflow of water to estimate the seawater exchange between the sea and the lake.
8. Conduct a bathymetric survey to define the lake’s bottom topography referenced to mean sea level and calculate its water volume.
9. Operate two tidal stations during one year, on inside the lake and the other on the seaward side of the outlet channel.

Table 1 summarizes the physical, biochemical, biological, and chemical parameters to be obtain at sampling stations in the lake. The proposed physical parameters, water quality, nutrients, primary productivity, phytoplankton, sediment, and tidal station locations at Levittown Lake are shown on fig. 4.

Benefits

This study will provide updated information on the hydrology, morphology, water quality, and biological characteristics of Levittown Lake, and how these interact and affect the aquatic ecosystem. The data will provide stakeholders with a broad overview and understanding of natural processes, which can be used to more effectively manage and monitor the Levittown Lake’s watershed and coastal surrounding areas, to protect the reserve and promote habitat utilization.