environmental setting, water quality, and ecological indicators of

FIGURES
1-4. Maps showing:
1. Location of continuous-discharge surface-water sites and ground-water wells sampled in the
Mermentau River Basin, southwestern Louisiana, 1998-2001.......................................................... 4
2. Land use and location of surface-water data-collection sites in the Mermentau River Basin,
southwestern Louisiana, 1998-2001 .................................................................................................. 5
3. Land use and long-term water-quality data-collection sites in southwestern Louisiana,
1998-2001 .......................................................................................................................................... 7
4. Soils and location of surface-water data-collection sites in the Mermentau River Basin,
southwestern Louisiana, 1998-2001 .................................................................................................. 8
5. Bar chart showing sources and quantities of water used in the Mermentau River Basin, southwestern
Louisiana, 2000......................................................................................................................................... 10
6. Graph showing discharge for selected sites in the Mermentau River Basin, southwestern Louisiana,
1998-2001 ................................................................................................................................................. 11
7. Flowchart of statistical analysis of ecological data used in the study....................................................... 15
8. Boxplots showing concentrations of selected nutrients and major inorganic ions in ground water and
surface water from the Mermentau River Basin, southwestern Louisiana, 1998-2001 ............................ 21
9. Photograph showing grazing livestock near a surface-water data-collection site in the Mermentau
River Basin, southwestern Louisiana ........................................................................................................ 22
10-15. Graphs showing:
10. Concentrations of nitrite plus nitrate, potassium, and suspended sediment at the Mermentau datacollection
site in the Mermentau River Basin, southwestern Louisiana, 1998-2001......................... 23
11. Drinking-water and aquatic-life criteria, and maximum detected concentrations of selected
pesticides in ground water in the Mermentau River Basin, southwestern Louisiana, 2000-2001..... 25
12. Drinking-water and aquatic-life criteria, and maximum detected concentrations of selected
pesticides in surface water in the Mermentau River Basin, southwestern Louisiana, 1998-2001..... 27
13. Concentrations of selected pesticides at the Mermentau data-collection site in the Mermentau
River Basin, southwestern Louisiana, 1998-2001 ............................................................................. 28
14. Composition of predominant groups of aquatic invertebrates at basin and intensity site groups
in southwestern Louisiana, 2001........................................................................................................ 33
15. Median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini midges
at basin and intensity site groups in southwestern Louisiana, 2001 .................................................. 33
16. Canonical correspondence analysis (CCA) ordination biplot showing site (A) and species (B)
locations in relation to environmental variables of ecological data-collection sites in southwestern
Louisiana, 2001......................................................................................................................................... 35
17. Map showing land use and location of ecological data-collection sites and canonical
correspondence analysis (CCA) site groups in southwestern Louisiana, 2001 ........................................ 36
18. Graph showing composition of predominant groups of aquatic invertebrates at canonical
correspondence analysis (CCA) site groups in southwestern Louisiana, 2001 ........................................ 40
19. Graph showing median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini
midges at canonical correspondence analysis (CCA) site groups in southwestern Louisiana, 2001........ 40
20. Scatter plots showing relative abundances of Caenis sp. (mayfly) and Rheotanytarsus sp. (midge),
and significant habitat and water-quality variables identified by canonical correspondence
analysis (CCA) for ecological data-collection sites in southwestern Louisiana, 2001............................. 42
TABLES
1. Surface-water and ecological data-collection sites in the Mermentau River Basin and adjacent Calcasieu
River Basin, southwestern Louisiana, 1998-2001 .......................................................................................... 6
2. Annual mean flow for selected sites in the Mermentau River Basin, 1999-2001, and period of record........ 11
3. Drinking-water regulations, health advisory levels, and aquatic-life criteria for selected pesticides............. 16
4. Minimum, median, and maximum concentrations of selected nitrogen species for ground- and surfacewater
samples from the Mermentau River Basin, southwestern Louisiana, 1998-2001 ................................ 19
vi