Nutrient and Chlorophyll Relations in Selected Streams of the New England Coastal Basins in Massachusetts and New Hampshire, June-September 2001
This study was designed to measure nutrient and chlorophyll a concentrations for a range of wadeable sites from reference to nutrient-impaired conditions and to compare data from open- and closed-canopy sites in the same stream. Samples for nutrients and chlorophyll a from phytoplankton and periphyton were collected at all 13 sites. Seven field-blank and 10 field-replicate samples were collected throughout the sampling period for nutrients and chlorophyll a. Total nitrogen, total phosphorus, and periphyton chlorophyll a are the primary constituents discussed in this report. Statistical analyses were completed on the nutrient and algal data.
Each of the 13 sites was sampled on 5 occasions between June through September 2001. Streams were sampled during the summer in an effort to capture changes in biomass throughout the “growing season.” The equal-width increment (EWI) technique was used to obtain a representative water sample at each site. The samples were then processed in the field according to standard surface-water-collection protocols (Shelton, 1994). Samples were packed on ice and sent to the USGS National Water-Quality Laboratory (NWQL) in Denver, Colo., for analysis. Inorganic constituents were analyzed using methods cited in Fishman (1993) and Fishman and Friedman (1989). Field measurements for each sample included water temperature, dissolved oxygen, pH, specific conductance, and stream discharge. Field measurements, nutrients, and major ion data are stored in the USGS National Water Information System (NWIS) and published in the USGS Annual Water Data Report (Coakley and others, 2001; and Socolow and others, 2001).
Chlorophyll a was measured in phytoplankton and periphyton samples to estimate the algal biomass at the sampling sites. Phytoplankton measurements were determined by filtering 500 mL of water through a glass-fiber filter. The filter was then wrapped in foil, placed in a petri dish, and immediately put on dry ice for shipment to the USGS NWQL for chlorophyll a determination (Porter and others, 1993). Chlorophyll a in phytoplankton was analyzed by methods in Arar and Collins (1997). Periphyton samples were collected from five representative rocks in riffle areas by scraping the algae from the rock surface. The scraped area was estimated by fitting an equivalent area of aluminum foil to the scraped section, using the foil-template method (Porter and others, 1993). Two subsamples of algal slurry were filtered, stored on dry ice, and sent to the USGS NWQL for chlorophyll a and ash-free dry-mass determinations (Arar and Collins, 1997).
At each site, the open-canopy angle was used to assess the amount of direct sunlight reaching the stream. The left and right canopy angles were measured with a handheld clinometer and the percentage of open canopy was calculated (Fitzpatrick and others, 1998).
Field blanks provide information on the potential for bias due to contamination of analytical results by sample collection, processing, shipping, and analysis. A field-blank sample is processed with water free of the analytes of interest. The blank water is passed through all the sampling equipment, processed as a regular water-quality sample, and analyzed for all water-quality constituents. Analytical results from the seven field-blank samples indicated that concentrations for constituents discussed in this report were less than the laboratory reporting level.
Replicate samples provide information on the variability of analytical results caused by sample collection, processing, shipping, and analysis. Differences in concentrations between environmental and replicate samples for nutrients were generally less than 0.01 mg/L. Differences in concentrations between environmental and replicate samples for periphyton chlorophyll a were less than 2 mg/m2.
A Spearman rho correlation test was used to determine relations between nutrient concentrations in the water column to chlorophyll a concentrations in phytoplankton and periphyton. Correlations were considered significant if the probability was less than 5 percent (p < 0.05). The Kruskal-Wallis statistical test (Helsel and Hirsch, 1992) with an alpha value of 0.05 was performed on nutrient concentrations and chlorophyll a concentrations to determine if there were significant differences among the groups of data for each of the three site types. If results from the Kruskal-Wallis test indicated significant differences, a Tukey's multiple comparison test (Helsel and Hirsch, 1992) was used to determine which site types differed significantly. Linear regression analysis was used to determine the relation between total nitrogen or total phosphorus and chlorophyll a concentrations. All statistical analyses were performed using Statview Statistical Software (SAS Institute, Inc., 1998).
Next: Characterization of Nutrients and Chlorophyll
Back: Introduction
| AccessibilityFOIAPrivacyPolicies and Notices | |
| |
|