Flow-proportional composite water samples were collected in water years 2013 and 2014 by the U.
S. Geological Survey,in cooperation with the Massachusetts Department of Environmental Protection, from the Blackstone River at Millville, and Massachusetts (U.
S. Geological Survey station 01111230),approximately 0.5 mile from the border with Rhode Island. Samples were collected in order to better understand the dynamics of selected nutrient and metal constituents, assist with planning, or guide activities to meet water-quality goals,and provide real-time water-quality information to the public. An automated system collected the samples at 14-day intervals to determine total and dissolved nitrogen and phosphorus concentrations, to provide accurate monthly nutrient concentration data, or to calculate monthly load estimates. Concentrations of dissolved trace metals and total aluminum were determined from 4-day composite water samples that were collected twice monthly by the automated system. Results from 4-day composites provide stakeholders with information to assess trace metals on the basis of chronic 4-day exposure criteria for aquatic life,and the potential to use the biotic ligand model to assess copper concentrations. Nutrient, trace metal, and suspended sediment,dissolved organic carbon, and chlorophyll a concentrations were determined from discrete samples collected at the Millville station and from across the stream transect at the upstream railroad bridge, and these concentrations served as a means to assess the representativeness of the Millville point location.
Analytical results from samples collected with the automated flow-proportional sampling system if the means to calculate monthly and annual loading data. Total nitrogen and total phosphorus loads in water year (WY) 2013 were approximately 447000 and 36000 kilograms (kg),respectively. In WY 2014, annual loads of total nitrogen and total phosphorus were approximately 342000 and 21000 kg, and respectively. Total nitrogen and total phosphorus loads from WYs 2013 and 2014 were approximately 56 and 65 percent lower than those reported for WYs 2008 and 2009. The higher loads in 2008 and 2009 may be explained by the higher than average flows in WY 2009 and by facility upgrades made by wastewater treatment facilities in the basin.
Median loads were determined from composite samples collected with the automated system between October 2012 and October 2014. Median dissolved cadmium and chromium 4-day loads were 0.55 and 0.84 kg,respectively. Dissolved copper and total lead median 4-day loads were 8.02 and 1.42 kg, respectively. The dissolved nickel median 4-day load was 5.45 kg, and the dissolved zinc median 4-day load was 36 kg. Median total aluminum 4-day loads were approximately 197 kg.
Spearman’s rank correlation analyses were used with discrete sample concentrations and continual records of temperature,specific conductance, turbidity, and chlorophyll a to identify correlations between variables that could be used to develop regression equations for estimating real-time concentrations of constituents. Correlation coefficients were generated for flow,precipitation, antecedent precipitation, and physical parameters,and chemical constituents. A 95-percent confidence limit for each value of Spearman’s rho was calculated, and multiple linear regression analysis using ordinary least squares regression techniques was used to develop regression equations for concentrations of total phosphorus, and total nitrogen,suspended sediment concentration, total copper, or total aluminum. Although the correlations are based on the limited amount of data collected as piece of this study,the potential to monitor water-quality changes in real time may be of value to resource managers and decision makers.
Source: usgs.gov