Trends Table

Trends are provided individually for each parameter and station in a simple table format. 
Not all constituents are available for all sites.

Key to column headings:
PCODE = Parameter code:
P00600 = Total nitrogen (as N)
P00631 = Nitrate (as N)
P00665 = Total phosphorus (as P)
P00671 = Orthophosphorus (as P)
P80154 = Suspended sediment
START_YEAR = First water year of modeling period used to estimate load
END_YEAR = Last water year of modeling period used to estimate load
NYEARS = Length of period over which trend is computed, in years, through 2018
PERIOD = Short-term or Long-term depending on number of years
lowF = Lower confidence limit (90 percent) of the estimated change in load, in millions of kilograms per year (10^6 kg/yr)
estF = Estimate of flow-normalized load change in Trend Period, in 10^6 kg/yr
upF = Upper confidence limit (90 percent) of the estimated change in load, in 10^6 kg/yr
FNT_PCT = Total change in flow-normalized load in percent
TrendDir = Trend direction, with 3 categories: No Trend, Degrading, Improving
Likelihood = Likelihood of trend direction, with 4 categories: as Likely as Not (likelihood coef, > 0.33 and < 0.67), Likely (likelihood coef, >= 0.67 and < 0.90), Very Likely (likelihood coef, >= 0.90 and < 0.95), Extremely Likely (likelihood coef, >= 0.95 and <= 1.0)
Nutrient and suspended-sediment concentrations and loads and flow-normalized concentrations and loads were estimated using a weighted regression approach called Weighted Regressions on Time, Discharge, and Season (WRTDS; Hirsch and others, 2010), which is included in the R (version 3.4.0) software package called EGRET - Exploration and Graphics for RivEr Trends (version 2.6.0; Hirsch and DeCicco, 2015). The uncertainty associated with the trends of nutrient and sediment loads was estimated using the R package called EGRETci (version 1.0.2; 'ci' stands for confidence intervals; Hirsch and others, 2015). The application of WRTDS to generate the results provided in this table is documented in Chanat and others (2016).

References Cited:

Hirsch, R.M., Moyer, D.L., and Archfield, S.A., 2010, Weighted regressions on time, discharge, and season (WRTDS), with an application to Chesapeake Bay river inputs: Journal of the American Water Resources Resources Association, v. 46, no. 5, p. 857-880. . (accessed May 24, 2016)

Hirsch, R.M. and De Cicco, L.A., 2015, User guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R packages for hydrologic data (version 2.0, February 2015): U.S. Geological Survey Techniques and Methods book 4, chap. A10, 93 p., . (accessed May 24, 2016)

Hirsch, R.M., Archfield, S.A., and De Cicco, L.A., 2015, A bootstrap method for estimating uncertainty of water quality trends: Environmental Modelling and Software, v. 73, p. 148-166., . (accessed May 24, 2016)

Chanat, J.G., Moyer, D.L., Blomquist, J.D., Hyer, K.E., and Langland, M.J., 2016, Application of a weighted regression model for reporting nutrient and sediment concentrations, fluxes, and trends in concentration and flux for the Chesapeake Bay Nontidal Water-Quality Monitoring Network, results through water year 2012: U.S. Geological Survey Scientific Investigations Report 2015-5133, 139 p. . (accessed May 24,2016)

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