What is NAWQA? What are they doing in southern Louisiana?
Studies and Surveys
Personnel and Links
Fixed Surface-water Sites
A monthly water-sampling study of southern Louisiana streams
The focus of the NAWQA Program in its first cycle has been the occurrence and distribution of various chemicals and compounds. A general survey of water-chemistry and ecological components gives a baseline against which NAWQA may compare future studies for the analysis of trends. For a national survey, NAWQA spreads its sampling across many study units, each contributing sampling of "fixed sites" for local and national assessment of water-quality status and trends. Our study unit has eight such fixed sites (called "fixed" because they will be sampled over many NAWQA cycles).
Site selection is determined from national priorities, optimally covering a range of physiographic settings, land uses, and stream types. The "Design of the National Water-Quality Assessment Program: Occurrence and Distribution of Water-Quality Conditions, Circular 1112" describes the objectives of the national study. "Indicator" sites are selected to focus on one main kind of land use, such as agriculture, urban, or forest. "Integrator" sites combine many land uses, and are used to monitor chemical inputs on a regional scale. In our study unit, we selected agriculture sites from our dominant crop types, rice and the combination of sugarcane, soybeans, and corn. We have an urban site in Baton Rouge. Guidelines for selecting urban stream sites can be found in "Study Plan for Urban Stream Indicator Sites of the National Water-Quality Assessment Program, Open-File Report 97-25". We have two Integrator sites, one of which has a significant component of industrial land use. We also have two "reference" sites, which have minimal land-use change from the potential natural vegetation.
To meet our local analysis needs, we attempted to pair sites based on stream size and land use. Members of a pair are separated into western and eastern. So we have a western reference site (Whiskey Chitto Creek), and an eastern one (Tchefuncte River), both in the piney upland areas. We have two medium-sized agricultural bayous (Bayou Grosse Tete and Bayou des Cannes) that have moderate amounts of channelization. We have two Integrator sites of similar size (Mermentau River and Bayou Boeuf). Matching stream sizes and types potentially reduces the variability that must be accounted for in analysis.
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Methods and Analysis
Surface water has been collected monthly throughout the high-intensity phase of the study, from August 1998 to September 2001. Additional semi-monthly samples were taken for a whole year in 1999, and the spring growing season of 2000. Methods for collecting and processing surface water are described in the "Field Guide for Collecting and Processing Stream-Water Samples for the National Water-Quality Assessment Program, Open-File Report 94-455". Additionally, we adhere to strict quality-control procedures to ensure the accuracy of our sampling, as described in "Quality-Control Design for Surface-Water Sampling in the National Water-Quality Assessment Program, Open-File Report 97-223".
Constituents assayed at these sites include major ions, nutrients, dissolved and organic carbon, chlorophyll, and a variety of soluble and less-soluble organic pesticides and volatile compounds. To ensure comparability of data between study units, there are specific methods for collecting and processing samples for inorganic constituents and for volatile organic compounds. These methods are described in the "U.S. Geological Survey Protocol for the Collection and Processing of Surface-Water Samples for the Subsequent Determination of Inorganic Constituents in Filtered Water, Open-File Report 94-539" and the "Field Guide for Collecting Samples for the Analysis of Volatile Organic Compounds in Stream Water for the National Water-Quality Assessment Program, Open-File Report 97-401".Constituents analyzed:
To further assess the quality of the selected waterbodies, we surveyed fish, invertebrate, and algae communities, and characterized stream habitats. This part of the fixed-site study is described in full on its own page.
Continuous discharge measurements are also taken at these sites as part of the Louisiana HydroWatch Program, and from this information, loads and transport of compounds can be estimated. The Hydrowatch Program provides real-time stage and discharge data on the Internet. The study unit is now conducting less frequent sampling at half the sites during its "Low Intensity Phase". The study unit will be "reactivated" to higher intensity sampling again in 2007, depending on the needs of national studies and public demand.
For questions about our Fixed Site water-quality surveys, please contact Dennis Demcheck [firstname.lastname@example.org], 225-298-5481.