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An investigation of nutrient inputs to Lake Pontchartrain via North Shore streams

Study Description

The North Shore Lake Pontchartrain study investigates nutrient loading in streams draining into Lake Pontchartrain. The North Shore is rapidly expanding in population and urban development. Nutrient inputs into the lake from this rapidly-expanding urban and suburban area have been implicated in contributing to eutrophication. However, estimates of nutrient loading remain highly speculative. Initial samples have focused on one-time, seasonal water-chemistry and algae surveys. However, seasonal, even monthly, collections of water are not sufficient to characterize nutrient levels in these urbanizing streams, which are subject to swift, flashy drainage during rainstorms.

As the Nation develops nutrient criteria for evaluating water quality in the next few years, real- or near-real-time nitrate data will be invaluable to researchers and those responsible for making water-resource management decisions. Nitrates are an important component of nutrient enrichment of waterbodies, encouraging the growth of algae and aquatic plants, leading to algae blooms and clogging of waterways with nuisance plant species. In order to better characterize nutrient levels, we are currently field-testing an instrument for the continuous measurement of nitrate concentrations on the Tchefuncte River near Covington. The instrument, installed on a bridge, is capable of continuously sensing and recording nitrate in the low concentrations commonly encountered in the environment. Our lead technician, Van Bergeron, and chief, Dennis Demcheck, completed the first series of tests comparing the monitor's data to samples collected manually during a rainstorm. It is planned that the monitor will be linked to a satellite, enabling direct transfer of data to the Louisiana District office. The goal of this project is to display real-time nitrate data through the Internet.

Sites

Sites for this study were selected from previously sampled sites from our Bed Sediment and Fish Tissue Study and our monthly-sampled Fixed Sites, as well as small urbanizing streams sampled by other USGS studies.

Methods and Analysis

Water was sampled twice in the winter of 1998-1999, according to methods published in the "Field Guide for Collecting and Processing Stream-water Samples for the National Water-Quality Assessment Program, Open File Report 94-455". We also sampled the algae community once that winter, characterizing both phytoplankton, and woody-debris periphyton. Methods are described in the "Methods for Collecting Algal Samples as Part of the National Water-Quality Asssessment Program, Open File Report 93-409".

• Dissolved Major Ions
• Dissolved Nutrients
• Phytoplankton, Chlorophyll a and b
• Dissolved and Suspended Organic Carbon

For questions about our North Shore Nutrient Study, please contact Dennis Demcheck [ddemchec@usgs.gov], 225-298-5481.