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

Abstract

1. Effects of the incremental annual incorporation of new water-quality observations on trends-Graphic results for the six watersheds subject to detailed study 2. Tabular WRTDS results for period-of-record and 10-year flow-normalized trends in concentration and flux 3. Tabular WRTDS results for all stations and constituents modeled through water year 2012 [Also available on CD-ROM] 4. Effects of variability in annual sampling effort on trends-Graphic results for the eight watersheds subject to detailed study 5. Effects of variability in storm sampling effort on trends-Graphic results for the eight watersheds subject to detailed study 1. Map showing locations of major drainage basins in the Chesapeake Bay watershed and locations of CBNTN stations for which flux and (or) trend estimates were published through water year 2012 .

Fish life history trends indicate increasing flow stochasticity in an unregulated river

“…Observed decreases in sediment and nutrient loads (Chanat et al. ) are expected to improve fish habitat by increasing spawning substrate quality and decreasing eutrophication and algal production (Abell et al. ), but our results show inconsistent patterns in this regard.…”

“…), yet we observed decreasing smallmouth bass abundance (Table ) despite water quality improvements (Chanat et al. ). In contrast, streamflows may explain differences in this regard because flows in Ohio River are more regulated by dams than in the Potomac River (Villarini et al.…”

“…Although some water quality parameters have shown improvements over time in the study area (e.g., 20% reduction in total phosphorus between 1985 and 2010; Chanat et al. ), others have not (i.e., increasing chloride concentrations; Kaushal et al. ) and water temperatures have increased since the early 1920s (Kaushal et al.…”

An improved method for interpretation of riverine concentration‐discharge relationships indicates long‐term shifts in reservoir sediment trapping

“…And although our case study data set does not contain any censored values-i.e., concentrations reported as less than detection limit (typically 0.5 mg/L for SS)-there are published approaches for handling such data [e.g., Tobin, 1958], and others have shown how WRTDS can be implemented in such cases [Chanat et al, 2016;Moyer et al, 2012;Zhang et al, 2015]. In fact, WRTDS has already been adopted by many investigators to estimate concentration and flux for a variety of constituents, including nitrogen, phosphorus, chloride, and dissolved organic carbon.…”

Exploring Drivers of Regional Water‐Quality Change Using Differential Spatially Referenced Regression—A Pilot Study in the Chesapeake Bay Watershed

“…Methods vary between programs but functionally the calculation for a single year amounts to (a) characterizing the concentration‐discharge relation most representative of that year, and (b) using that relation as the basis for daily flux computation but with daily discharge values representative of the period of the water‐quality record, rather than the actual series of daily values observed in that year. Hirsch et al () provide a detailed discussion of the process in the context of WRTDS, and Chanat et al () present a case study comparing the process as implemented in WRTDS and LOADEST. Because WRTDS results are used in the analyses described herein, Hirsch et al's () term flow normalization is hereby adopted.…”