Opportunities to Improve the U.S. Geological Survey National Water Quality Assessment Program (2002) / Chapter Skim
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2 Transition from Cycle I to Cycle II: Representativeness of Study Units
2 Transition from Cycle I to Cycle II: Representativeness of Study Units
Pages 42-60
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From page 42... ...
. Despite cutbacks, a major effort during Cycle I was the compilation and synthesis of study unit data to make inferences about "regional" and "national" water quality (e.g., USGS, 1999~.
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From page 44... ...
In this regard, such inferences refer to the NAWQA study units, which are distributed across the nation but not clearly established to be "representative" of the nation. For the most part, recent written explanations of NAWQA results appear to be appropriately expressed; for example, Kolpin et
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From page 45... ...
Thus, NAWQA scientists should continue to endeavor to correctly state the geographic extent of scientific inferences. This chapter assesses the coverage and representativeness of NAWQA study units and provides recommendations designed to help ensure that Cycle II remains as effective as Cycle I in assessing water quality status, trends, and understanding.
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From page 46... ...
The Hydrologic Setting Regions Approach The representativeness of the Cycle II study units with respect to hydrologic characteristics is addressed through the identification and delineation of hydrologic landscapes (Winter, 1995, 2000, 2001) and hydrologic setting regions throughout the United States (Wolock et al., 2000~.
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From page 47... ...
These regions were mapped over the entire nation and combined with the map of NAWQA Cycle I study units to help select sites for Cycle II that correspond to the occurrence of the hydrologic setting regions across the nation. Thus, hydrologic setting regions can be used to help achieve representativeness for key natural hydrologic factors as long as the initial set of NAWQA study sites provides adequate coverage of the 17 region types.
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From page 48... ...
. Finally, those study units that had been selected for discontinuation were subsequently examined to ascertain if they possessed characteristics that would otherwise warrant their inclusion in the final 42.
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From page 49... ...
These watersheds represent 15 percent of the total number of eight-digit HCUs in the continental United States and include all known imperiled and vulnerable fish and mussel species. A value of O to 5 was assigned to each study unit based on the amount of coverage of critical watersheds (see Gilliom et al., 2000a, Appendix H)
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From page 50... ...
In addition, certain types of land use may not be represented adequately in the 42 Cycle II study units. For example, industries such as mining and forest products, whose operations can have a substantial influence on both surface water and groundwater quality, may not be well represented in either the original Cycle I or the reduced set of Cycle II study units, although several "mining indicator" lakes and reservoirs were sampled between 1992 and 2000 (Gilliom et al., 2000b)
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From page 51... ...
Although the NAWQA program does not have an extensive limnological component, it is sampling at the drinking water intakes in about a dozen lakes and reservoirs (Timothy Miller, USGS, personal communication, 2000~. If there are resources for sampling just a small or fixed number of lakes or reservoirs, LPA could be used to optimize the return on sampling perhaps by finding the combination of lakes or reservoirs supplying the most people or having the largest drainage basins or the most agricultural lands, etc.
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From page 52... ...
In particular, EMAP was based on a national probability sampling approach that was designed to permit statistical inference to a national or regional population. Probability sampling was not the basis for the selection of the NAWQA study units; rather, they were chosen to ensure that the most important national water quality issues in the nation's largest and most significant hydrologic systems were addressed (USGS, 1995~.
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From page 53... ...
Nevertheless, since lakes and reservoirs can often be important components of the local or regional hydrologic system, water quality studies, and public drinking water supplies, NAWQA activities in Cycle I study units that have "important" lakes and reservoirs basically were limited to sampling upstream and downstream. Thus, large reservoirs and lakes are essentially treated as "black boxes." Sampling in lakes and reservoirs was generally restricted to examining sedimentation and contaminant concentrations in cores (e.g., Callender and Van Metre, 1997~.
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From page 54... ...
, it is important to identify and understand water quality trends before they reach the crisis stage. Degradation of water resources used for drinking water, recreation, and wildlife habitat would constitute significant health, aesthetic, and financial losses.
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From page 55... ...
Watersheds with lakes and reservoirs in a variety of hydrologic settings still exist in the reduced Cycle II coverage, for example, Connecticut, Housatonic, and Thames River Basins (CONN) ; Mobile River Basin (MOBL)
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From page 56... ...
One could argue that since these two areas have quite unique systems that are not represented elsewhere and do not include much of the nation in terms of population and drinking water use, their exclusion does not compromise the objectives of the program. It is interesting to note that the planned Cycle II study units represent most of the different groundwater regions of the nation as defined by Heath (1982, 1984)
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From page 57... ...
However, the committee feels that the budgetary-imposed reduction in the number of study units will still maintain good coverage of the nation's water resources. The primary reason for maintaining good coverage and representativeness is the commendable and iterative use of hydrologic setting regions, coupled with the linear programming approach and expert judgment-based semiquantitative analyses to select the reduced number of study units.
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From page 58... ...
group of study units may be representative of certain types of land use that can heavily impact water quality such as mining, the forest products industry, or the petrochemical industry, for example. The following are the committee's recommendations: · Maintain sampling in lakes and reservoirs that are important public water supplies, collaborating with other organizations where feasible.
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From page 59... ...
1999. Emerging drinking water contaminants: Overview and role of the National Water Quality Assessment Program.
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From page 60... ...
2000. Delineation of hydrologic setting regions in the United States using geographic information system tools and multivariate statistical analyses.
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