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 2016
PERIOD = Short-term or Long-term, depending on number of years
lowF = Lower confidence limit (90%) of the estimated change in load, in 10^6 kilograms per year (kg/yr)
estF = Estimate of flow-normalized load change in Trend Period, in 10^6 kilograms per year (kg/yr)
upF = Upper confidence limit (90%) of the estimated change in load, in 10^6 kilograms per year (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 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 Association, v. 46, no. 5, p. 857-880

Hirsch, R.M. and De Cicco, Laura, 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.

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