Opportunities to Improve the U.S. Geological Survey National Water Quality Assessment Program (2002) / Chapter Skim
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4 NAWQA Cycle II Goals - Trends and Statistical Support for Understanding
4 NAWQA Cycle II Goals - Trends and Statistical Support for Understanding
Pages 93-120
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From page 93... ...
The reliable and early detection of trends is of fundamental value because it can provide information on changes in water quality that might be useful for future decision making and scientific understanding relating to the management of water quality. If trends are successfully detected in a timely fashion, along with a scientific understanding of the reason for those trends, it may be possible to implement management strategies to help reduce future degradation in water quality (and/or to promote future improvements)
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From page 94... ...
A sensible approach to the design of water quality monitoring networks is essential to the detection and evaluation of water quality trends the topic of the third section of this chapter. Ideally, a water quality data series collected for trend analysis would include samples evenly spaced in time (e.g., monthly)
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From page 95... ...
(1999~. The design of water quality monitoring networks includes all activities involved in the planning and management of sampling activities to collect and process water quality data for the purpose of obtaining information about the physical, biological and chemical properties of water.
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From page 96... ...
in water quality to the major factors that affect observed water quality trends and conditions. In spite of very large expenditures on water quality monitoring networks, there still remains substantial uncertainty about many aspects of water quality regimes in lakes, rivers, and coastal waters in the United States and elsewhere.
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From page 97... ...
Further evidence of the integrated nature of NAWQA is provided by the dual use of both a temporal trends network and the space-for-time approach to assessing change, which is discussed earlier. The committee recommends that NAWQA continue emphasis on an integrated approach to water quality monitoring network design that attempts to coordinate efforts among various local, state, and federal agencies in an effort to make study unit designs as efficient and costeffective as possible.
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From page 98... ...
multivariate statistical water quality model for use in the design of water quality monitoring networks similar to the way in which regional multivariate statistical models of various streamflow statistics are used in the design of stream-gaging networks. The committee recommends that NAWQA attempt to extend the Network Analysis Using Generalized Least Squares (NAUGLS)
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From page 99... ...
Finally, comparatively little research has been performed relating to the frequency distribution of concentrations and/or loads. It is hoped that future NAWQA and other USGS research will address all relevant issues relating to the objective of designing water quality monitoring networks to ensure accurate estimates of long-term loads.
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From page 100... ...
Problems existed with water quality data assurance management and control programs during this period, particularly for constituents present in very low concentrations, such as dissolved trace elements. The NAWQA program was designed to help reduce these types of problems and produce more meaningful regional water quality assessments and trend detection and analysis studies (Hirsch et al., 1988~.
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From page 101... ...
There are also many statistical complications associated with testing trends in water quality data such as nonnormal distributions, seasonality, missing values, values below detection limit, changes in analytical detection methods, changes in sampling frequency and location, and serial correlation, among others. Fortunately, most of these problems have now been dealt with effectively through methodological improvements.
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From page 102... ...
Another common problem arises when the relationship between streamflow and concentration is weak and that relationship is then used to determine whether trends in water quality exist. Most water quality monitoring networks do not yield continuous measurements of concentration, yet continuous measurements of discharge are commonplace.
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From page 103... ...
The committee recommends that NAWQA place greater attention on the use of transfer function methods in its development of statistically based water quality models, because such methods properly account for the stochastic structure of time series of both water quality and its correlates. Simple bivariate and even more sophisticated multivariate statistical models are attractive because they are straightforward to estimate and employ in practice, and confidence intervals for resulting concentration and load estimates are available.
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From page 104... ...
One advantage of the space-for-time strategy is that the set of watersheds and aquifers involved in an analysis represents a population of watersheds and aquifers that is certainly greater in number than just the NAWQA study units. Crucial to the committee's charge (which addresses aggregation and presentation of information for regional and national inferences; see also Chapters 1 and 8)
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From page 105... ...
Combining Information to Improve Inference The commonality of design across NAWQA study units and the long-term nature of the NAWQA program provide opportunities for pooling data and model forecasts to improve analyses for a number of problems. Pooling data or "borrowing strength" from data-rich sites to infer behavior at data-poor sites is not new to USGS water resources investigations.
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From page 106... ...
Similarly, two streams with identical present-day land use in their watersheds may have vastly different ecological communities because of past land-use practices (e.g., Harding et al., 1998~. Dealing with these issues requires an attention to urban watershed management practices and historical land-use patterns during the site selection and data compilation phase of the research, something not currently addressed in the NAWQA site selection criteria.
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From page 107... ...
Streamwater quality characteristics to be sampled in Cycle II include conductance, temperature, pH, alkalinity, dissolved oxygen, nutrients, pesticides, and ions in the water column; trace elements in bed sediments; geomorphic and habitat characteristics; stage; chlorophyll a; benthic algae, invertebrate, and fish communities; and Escherichia cold near public water supply intakes (see Chapter 3 for further information) (Gilliom et al., 2000~.
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From page 108... ...
. The design guidelines will be based on pilot studies being conducted in the following study units (Gilliom et al., 2000~: Mobile River Basin (MOBL)
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From page 109... ...
of the ULUG data. In addition to the aforementioned three study units, the space-for-time urban gradient approach is being used in the New Jersey portion of the Long IslandNew Jersey Coastal Drainages Study Unit (LINJ; nj.usgs.gov/nawqa/linj.html)
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From page 110... ...
These changes have the potential for impacting the quality of surface water and groundwater resources. For example, agriculture has been identified as the major source of sediment, nutrient, and pesticide pollutants in surface water and groundwater resources and as the single largest source of water impairments (EPA, 2000~.
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From page 111... ...
Water quality monitoring is often incompatible with an agricultural conservation program' s time scale. A water quality baseline must be established before a project is started if impacts on water quality are to be determined.
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From page 112... ...
The NAWQA national trend networks for streams and groundwater will monitor trends by systematic sampling over time at carefully selected sites and study areas that represent key water resources and land uses. As pointed out in the NIT Cycle II design report, the trend networks only partially address issues related to changes in urban and agricultural areas, and are inadequate for assessing the effects of urban and agricultural land uses on aquatic biota and stream ecosystems.
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From page 113... ...
NAQWA has established water quality baselines and monitoring networks in the study units and is operating at a time scale sufficient to establish relationships between production practices and water quality at a watershed scale. This research will not be able to identify the water quality benefits of individual practices, but the USDA research can provide this information.
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From page 114... ...
The proposed HST is a national study team whose role will be the application and support of hydrologic and water quality models in NAWQA studies, including the use of models to aid in interpretive analysis of water quality. It seems logical that the HST will support research on the effects of changes in agricultural management on ground- and surface waters (Objectives TO and TV.
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From page 115... ...
Indeed, many of the techniques currently employed for the estimation of trends in hydrologic time series are based on work by USGS scientists. The reliable and early detection of trends is of fundamental value because it can provide information on changes in water quality (especially related to anthropogenic sources)
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From page 116... ...
should be extended to the design of water quality monitoring networks in Cycle II. This may be accomplished by extending the SPARROW multivariate statistical water quality model for use in the design of water quality monitoring networks similar to the way in which regional multivariate statistical models of various streamflow statistics have been used in the design of stream-gaging networks.
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From page 117... ...
U.S. Geological Survey Water-Resources Investigations Report 98-4245.
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From page 118... ...
1992. Water quality monitoring network design: A problem of multi-objective decision making.
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From page 119... ...
1997. Regional interpretation of water-quality monitoring data.
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From page 120... ...
B1sm^, N.D.: U.S. Geological Survey.
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