Environ. Sci. Technol. 2010, 44, 7193–7199
Uses and Biases of Volunteer Water Quality Data J . V . L O P E R F I D O , * ,†,‡,⊥ P I E T E R B E Y E R , § C R A I G L . J U S T , †,‡ A N D J E R A L D L . S C H N O O R †,‡ Department of Civil and Environmental Engineering, The University of Iowa, Iowa City, Iowa, IIHR-Hydroscience and Engineering, The University of Iowa, Iowa City, Iowa, and PG Environmental, LLC, Golden, Colorado
Received January 16, 2010. Revised manuscript received May 27, 2010. Accepted May 28, 2010.
State water quality monitoring has been augmented by volunteer monitoring programs throughout the United States. Although a significant effort has been put forth by volunteers, questions remain as to whether volunteer data are accurate and can be used by regulators. In this study, typical volunteer water quality measurements from laboratory and environmental samples in Iowa were analyzed for error and bias. Volunteer measurements of nitrate+nitrite were significantly lower (about 2-fold) than concentrations determined via standard methods in both laboratory-prepared and environmental samples. Total reactive phosphorus concentrations analyzed by volunteers were similar to measurements determined via standard methods in laboratory-prepared samples and environmental samples, but were statistically lower than the actual concentration in four of the five laboratory-prepared samples. Volunteer water quality measurements were successful in identifying and classifying most of the waters which violate United States Environmental Protection Agency recommended water quality criteria for total nitrogen (66%) and for total phosphorus (52%) with the accuracy improving when accounting for error and biases in the volunteer data. An understanding of the error and bias in volunteer water quality measurements can allow regulators to incorporate volunteer water quality data into total maximum daily load planning or state water quality reporting.
Introduction With nearly fifty percent of the rivers and streams in the United States not meeting their designated use requirements (1), marked decreases in funding for professional state and federal water quality monitoring programs (2, 3), and increases in volunteer water quality monitoring programs, it is important to consider how these monitoring programs can be better utilized to prioritize management actions. Water quality data traditionally generated by professional monitoring have been increasingly augmented by volunteer data as the number of volunteer monitoring programs has grown dramatically since the early 1990s. In 1994, the United States * Corresponding author e-mail:
[email protected]. † Department of Civil and Environmental Engineering, The University of Iowa. ‡ IIHR-Hydroscience and Engineering, The University of Iowa. § PG Environmental, LLC. ⊥ Current Address: Eastern Geographic Science Center, United States Geological Survey, Reston, VA. 10.1021/es100164c
2010 American Chemical Society
Published on Web 06/11/2010
Environmental Protection Agency (U.S. EPA) identified 517 volunteer monitoring programs (4), which have since grown to nearly 900 organizations in 2009 (5) with programs existing in nearly every state in the country (Figure 1). Volunteer monitoring has also grown worldwide as the number of countries participating in World Water Monitoring Day increased from 47 in 2005 to 81 in 2009 (6). In the U.S., due to the extensive number of samples analyzed by these monitoring programs, volunteer generated data sets have been used as a source for reports required by the Clean Water Act Section 305(b) (5, 7, 8) despite potential issues with data accuracy. While several studies have analyzed the accuracy of volunteer data, a majority of these studies have focused on benthic macroinvertebrates, and the accuracy of common nutrient pollutants such as nitrate and total reactive phosphorus have been largely ignored. A recent article in The Volunteer Monitor (9), the U.S. EPA national newsletter of volunteer water quality monitoring, reported a list of eleven peer-reviewed articles that investigated the validation of volunteer data sets by comparing them to results generated by professional water quality samplers. Eight of these articles investigated volunteer monitoring for benthic macroinvertebrates or other higher order organisms (10-17) and another investigated transparency measurements (18), but only two of the studies listed analyzed nutrient measurements (19, 20). No statistical differences between volunteer and professional total nitrogen measurements were found in the two studies with sample sizes of 125 and 29 (19, 20). Results from studies analyzing differences in total phosphorus measurements collected from lakes by volunteers and professionals have been mixed. Statistical differences were not found in one study with n ) 125 (19), but were found in a second study (20) as volunteers were reporting low total phosphorus measurements possibly due to their storage methods (average error ) -2.1 µg-P L-1 and -5.1 µg-P L-1 for concentrations 25 µg-P L-1, respectively; n ) 29). Other reports found that volunteer data from lakes showed a bias to overestimate total phosphorus concentrations as compared to professional measurements by 31% (n ) 104) (21) and averaged to be 50% higher in a study that analyzed data from 16 different sites (22) due to the accuracy of the different methods used by the volunteers and professionals. An area not addressed by any of these studies is the accuracy of volunteer measurements of dissolved nutrients in rivers and streams that cause eutrophication and hypoxic zones in places like the Gulf of Mexico and the Chesapeake Bay; problems that will be exacerbated with future climate and land use change (23-29). Currently, dissolved nutrients account for approximately 60% of the total nitrogen load and 30% of the total phosphorus load from the Mississippi and Atchafalaya Rivers to the Gulf of Mexico (30, 31). With Iowa contributing a disproportionately large amount of nitrogen and phosphorus to the Gulf of Mexico (23, 32), nitrate and total reactive phosphorus data generated by the Iowa Volunteer Water Quality Monitoring Program (IOWATER) could prove to be useful in identifying problematic watersheds or assisting in state 305(b) reporting. IOWATER is a citizen-based monitoring program that has been training Iowa citizens to assess chemical parameters including nitrate and total reactive phosphorus, physical parameters (i.e., temperature and transparency), and biological parameters (e.g., benthic macroinvertebrates) in the state’s rivers and lakes since 1999. The program is supported by the Iowa Department of Natural Resources, which supports VOL. 44, NO. 19, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Number of programs by state listed in the U.S. EPA National Directory of Volunteer Environmental Monitoring Programs, 5th edition (5). the cost of providing volunteers with training, sampling kits ($242), and sampling kit refills. Water quality measurements collected by IOWATER are stored in a publicly available online database (33) and contain data from sampling events where volunteers and professional measurements were taken concurrently. The goal of this study was to investigate the accuracy and bias of nitrate and total reactive phosphorus measurements collected by a volunteer monitoring organization, IOWATER, and determine whether these and similar data are suitable for use by regulators for 305(b) reporting or total maximum daily load (TMDL) planning processes. IOWATER was selected as a target program due to its proximity to hotspots of nutrient loading to the Gulf of Mexico (23, 32) and because the methods used to measure nitrate and total reactive phosphorus are commonly used methods of other monitoring programs (e.g., Fairfax County Stream Volunteer Stream Monitoring Program; Hoosier Riverwatch; Oklahoma Blue Thumb Program; San Diego Coastkeeper; Streamkeepers of Clallam County (WA)) and similar to methods used by other volunteer programs (e.g., Anchorage Waterways Council Monitoring Program; Nebraska Wildlife Federation’s Adopt a Stream Program, Waccamaw River Volunteer Monitoring Project (SC)). Results from this study provide a framework from which regulators can use data generated by IOWATER and other similar programs for regulatory purposes.
Materials and Methods Comparison of IOWATER and Standard Methods Measurements from Laboratory-Prepared Samples. Samples containing known concentrations of nitrate and total reactive phosphorus were prepared in the Environmental Engineering and Sciences (EES) Laboratory at the University of Iowa for measurement by IOWATER volunteers and staff using standard IOWATER sampling protocol (34). Briefly, nitrate is measured using test strips (Hach, 2745425) with sampling increments of 0, 1, 2, 5, 10, 20, and 50 mg-N L-1; nitrite is measured using test strips (Hach, 2745425) with sampling increments of 0, 0.15, 0.3, 1.0, 1.5, and 3.0 mg-N L-1; and total reactive phosphorus is measured colorimetrically (Chemetrics, K-8510) with sampling increments of 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, and 10 mg-PO43- L-1. Individual samples were analyzed by IOWATER volunteers (5 samples) and staff (4 samples) over a 6-month period and contained nitrate concentrations of 24.3, 10.3, 7.1, 4.9, and 2.5 mg-N L-1, and total reactive phosphorus concentrations of 0.12, 0.23, 0.45, 0.65, and 0.90 mg-PO43- L-1 in samples 1, 2, 3, 4, and 5, respectively. Laboratory-prepared samples were created by adding appropriate amounts of 1000 mg-N L-1 nitrate and 1000 mg-PO43- L-1 total reactive phosphorus stock 7194
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solution to 10 L of deionized water. Samples were buffered by a calcium carbonate system, which is described in more detail in the Supporting Information. The resulting pH of the buffered solution was approximately 7.2, which ensured that nitrate was the dominant form of nitrogen in the sample and which limited the dissolved orthophosphate species to HPO43- and H2PO42- (35). Nitrate concentrations of the prepared samples were measured via ion chromatography using a Dionex ICS 2000 ion chromatography system as per U.S. EPA method 300.00 (36); total reactive phosphorus was analyzed using the U.S. EPA ascorbic acid method 365.3 (36); and pH was measured using a Beckman Φ45 pH meter. Nitrite concentrations were minimized (
