Sampling sites were selected to represent major, large-scale contrasts in ecoregions, land use, and hydrogeology. Most of the data were collected in the predominantly agricultural San Joaquin Valley because factors likely to impact water quality are concentrated in this area. This focus was consistent with the first two topics selected for study at the national level by the NAWQA Program: pesticides and nutrients.
Studies were designed to provide multiple lines of evidence to describe water quality conditions (Gilliom and others, 1995). To this end, investigations of surface-water chemistry, contaminants in sediment and in tissues of aquatic organisms, and aquatic ecology took place at the same sites, if possible. The studies also were designed to provide information on water quality over a range of complementary temporal and geographic scales. The time scale of surface-water investigations varied from once-a-year, to once-a-month, to several times a day. The geographic scale of the ground-water investigations ranged from sampling 30 wells distributed over 2,000 square miles to sampling four wells within 200 feet. Each scale of study revealed relations between water quality and causal factors not apparent at larger or smaller scales.
At all levels of study, relevant ancillary information, such as land use, soil and aquifer properties, fertilizer-use rate, and locations of dairies, was collected to help explain the chemical and ecological data. Detailed information, such as change in streamflow during a winter storm or the timing of use of a particular pesticide, was also used for both design and interpretation of specialized studies. In general, the questions addressed by each study component became more focused during each of the 3 years of intensive data collection (September 1992 to August 1995).
Location of stream chemistry sites.
Location of stream ecology sites.
Location of ground-water chemistry sites.
|
Study
|
What data were collected and Why |
Types of sites sampled |
Number of sites |
Sampling frequency and period |
|---|---|---|---|---|
|
Stream Chemistry |
||||
|
Basic Fixed Sites
|
Streamflow, nutrients, major chemical constituents, organic carbon, suspended sediment, water temperature, specific conductance, pH, and dissolved oxygen to describe concentrations and seasonal variations. |
Representative of a variety of agricultural
land uses, and the basin outflow.
|
10
|
Monthly plus storms
Jan. 1993-Dec. 1994
|
|
Intensive Fixed Sites (IFS)
--pesticides
|
In addition to the above constituents, approximately
83 dissolved pesticides to describe concentrations and seasonal variations.
|
Subset of basic sites representing contrasting
physiographic areas, and the basin outflow.
|
4
|
twice weekly to monthly
Jan. 1993-Dec. 1993 |
|
Synoptic sites
--water chemistry
|
Streamflow, pesticides, water temperature,
specific conductance, pH, and dissolved oxygen to describe concentrations
and spatial distributions.
|
Basic sites and others representing agricultural
and urban land uses.
|
23
(low flow)
|
Once June 1994
|
|
Contaminants in
bed sediments
|
Total PCBs, 32 organochlorine pesticides,
63 semivolatile organic compounds, and 44 trace elements to determine occurrence
and spatial distribution.
|
Depositional zones of all basic and intensive
sites, plus additional synoptic sites.
|
17
|
Once Oct. 1992
|
|
Contaminants in
aquatic biota
|
Total PCBs, 30 organochlorine pesticides,
and 24 trace elements were analyzed to determine occurrence and spatial
distribution. Clams and whole fish for organic contaminants. Clams, fish
livers, or crayfish for trace elements.
|
Same sites as for contaminants in bed sediment
where tissue could be collected.
|
18
|
Once Oct.-Nov. 1992
|
|
Stream Ecology
|
||||
|
Intensive assessments
|
Assess communities of fish, macroinvertebrates,
and algae at each site; and quantitatively describe stream habitat for
these organisms.
|
Subset of BFS (9 of 10) plus a site in Yosemite
National Park.
|
3
4
6
|
3 reaches/site in 1995
1 reach/year, 1993-95 1 reach in 1993
|
|
Synoptic studies
|
Similar to the above, one reach per site,
for areal comparison of habitat and community composition, nutrient samples
collected.
|
Subset of BFS plus others.
|
32
|
Once in either 1993 or 1994
|
|
Ground-Water Chemistry
|
||||
|
Regional Aquifer Survey--eastern alluvial
fans
|
Major chemical constituents, nutrients, 83
pesticides, 60 volatile organic compounds, and radon to determine occurrence
of these constituents in this region.
|
Domestic wells in the eastern alluvial fans,
San Joaquin Valley.
|
30
|
Once in 1995
|
|
Land-use effects--corn, alfalfa, and vegetable
row crops
|
Major chemical constituents, nutrients, 83
pesticides, 60 volatile organic compounds, and radon to describe the effects
of agricultural land use on shallow ground water, eastern alluvial fans.
|
Shallow domestic wells;
Shallow monitoring wells;
>50 percent corn, alfalfa, and vegetables
grown in rotation within a 0.25-mile radius.
|
20
10
|
Once in 1995
|
|
Land-use effects--
almond orchards
|
Major chemical constituents, nutrients, 83
pesticides, 60 volatile organic compounds, and radon to describe the effects
of agricultural land use on shallow ground water, eastern alluvial fans.
|
Shallow domestic wells;
Shallow monitoring wells;
>50 percent almond orchards within 0.25 mile
radius.
|
20
10
|
Once in 1994
|
|
Land-use effects--vineyards
|
Major chemical constituents, nutrients, 83
pesticides, 60 volatile organic compounds, and radon to describe the effects
of agricultural land use on shallow ground water, eastern alluvial fans.
|
Shallow domestic wells;
Shallow monitoring wells;
>50 percent vineyards within 0.25-mile radius.
|
20
10
|
Once in 1993
|
|
Chemical and physical processes along ground-water
flow paths
|
Major chemical constituents, nutrients, 83
pesticides, 60 volatile organic compounds, radon, transformation products
of 1,2-dibromo-3-chloropropane, and constituents used to estimate date
when ground water was recharged.
|
20 wells at 6 sites along an approximate ground-water
flow path beneath vineyard land use in eastern alluvial fan, San Joaquin
Valley.
|
20
|
Once in 1994
Once in 1995
|
|
Special Studies
|
||||
|
Dissolved pesticide transport in winter storms
|
Dissolved pesticides and streamflow were measured
along with a dye traveltime study to assess the variability of concentrations
during storms and the impact on the basin outflow. Specific agricultural
and urban areas were assessed.
|
2 IFS, 3 western valley sites, and basin outflow.
5 eastern valley sites, 3 agricultural drains,
and basin outflow.
5 urban sites, 3 agricultural drains, 7 eastern
valley sites, and basin outflow.
|
6
9
16 |
Jan.-Feb. 1993
Jan.-Feb. 1994
Feb.-Mar. 1995 |
|
Transport of sediment-bound pesticides |
Sediment-bound pesticides, dissolved pesticide, suspended sediment, and streamflow to compare winter and irrigation season transport. |
2 Coast Ranges sites, 2 agricultural drains, 7 western valley sites, and basin outflow. |
8
12 |
June 1994 Jan. 1995 |
|
Aquatic ecology--Merced River, Yosemite National Park |
Assessment of algal community, chlorophyll-a and ash-free dry mass, and supporting data on nutrients, major constituents, trace elements, and organic contaminants in bed sediment and tissue. |
Synoptic sites. |
8 |
Sept. 1995 |