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Water-Quality Loads and Trends at Nontidal Monitoring Stations in the Chesapeake Bay Watershed


Bridge at river
James River at Richmond, Virginia

anthropogenic - resulting from human activity

atmospheric deposition - includes wet precipitation such as snow, rain, or hail, as well as dry deposition from airborne particles like smoke and dust.

base-flow conditions - normal streamflow conditions; that is, without recent input from precipitation.

censored data - data concentrations reported at less than a specified reporting limit or analytical limit.

concentration - the mass of a chemical per volume of water - commonly expressed as milligrams per liter (mg/L), or micrograms per liter (ug/L).

dissolved inorganic phosphate (DIP) - P00671 -- Dissolved inorganic phosphate (mg/L as P)

dissolved nitrite-plus-nitrate nitrogen (DNO23) - P00631 -- Dissolved nitrite-plus-nitrate nitrogen (mg/L as N)

ESTIMATOR - a multiple regression model used to quantify fluxes and determine trends in concentration.

Eutrophication - nutrient enrichment in a stream, lake, or other water body that stimulates excessive growth of algae and other aquatic plants and leads to reduced dissolved oxygen levels.

Fall Line - the boundary between the Piedmont and Coastal Plain Physiographic Provinces in the Eastern United States. In the area near this boundary, there is a relatively large change in elevation, resulting in waterfalls or rapids in streams or rivers flowing east; thus the name "Fall Line". This line roughly coincides with the area between the tidal and nontidal parts of each river.

flow-adjusted concentration trends - trends after streamflow has been removed as a factor affecting concentration; allows examination of the effects of management strategies.

high-flow conditions - above-normal streamflow conditions, as a result of stormflow or release of water.

homoscedastic - with constant variance throughout a dataset.

hydrogeologic setting - the geology and the resultant hydrologic conditions associated with an area.

inorganic - being or composed of matter other than plant or animal.

load - product of the concentration and streamflow, equivalent to the total amount of a constituent passing that point in the stream, at that time. Usually expressed as kilograms per time or pounds per time.

multivariate - more than one variable; for the regression model used in this project, variables of time, streamflow, and seasonality are used.

nonpoint source - a source of natural or man-made chemicals delivered to a stream; the source is distributed over an area and may include runoff from fields, groundwater discharge, and urban runoff.

nontidal - outside the area where the water level is influenced by tidal fluctuation. A nontidal stream reach may or may not be elevated in salinity.

nutrients - chemicals necessary for animal and plant life; includes phosphorus and nitrogen.

organic - of, relating to, or derived from living organisms.

physiographic provinces - geographic divisions based on landforms, geology, and geologic origin of an area.

point source - a source of natural or man-made chemicals that can be attributed to a single location, such as a pipe outflow.

p-value - the probability value, which is the estimated probability that a hypothesis is found to be true when it actually is not. In this study, it is the probability that a trend is found when there is in fact no true trend (that is, that random variation in concentration alone could produce the observed behavior). A lower p-value indicates greater confidence in a given conclusion.

regression - an examination of the relationship between a response (dependent) variable and the explanatory (independent) variable(s); a measure of the tendency for the expected value of one of these jointly correlated random variables to approach more closely the mean value of its own dataset than that of any of the other variables.

runoff - Overland flow to a stream that occurs when either (1) the precipitation rate exceeds the infiltration rate through the soil, (2) precipitation reaches soil that is already saturated, or (3) precipitation reaches a surface that is nearly impermeable, such as pavement or bedrock.

submerged aquatic vegetation (SAV) - a general term referring to the many species of plants that grow in the shallow water of the Chesapeake Bay and its tributaries; these plants provide an important habitat and food source for fish and wildlife.

suspended material - a general term indicating the concentration of either suspended sediment or suspended solids, depending on the analysis performed.

tidal - the area where the water level is influenced by tidal fluctuation. A tidal stream reach may or may not be elevated in salinity.

total nitrogen (TN) - P00600 -- Total nitrogen (mg/L as N).

total phosphorus (TP) - P00665 -- Total phosphorus (mg/L as P).

total suspended sediment (SSC) - the concentration of total suspended material carried by a stream as determined by an analysis of an entire collected water sample. P80154 -- SSC (mg/L) see also: total suspended solids.

trend - the measurable, statistically significant tendency for something (such as, chemical concentrations) to change over time.

unadjusted concentration trends - trends that account for all factors, including streamflow, that affect concentration; necessary when considering the health of aquatic organisms in the Chesapeake Bay and its tributaries.

wastewater discharge - water that has been treated to meet State and Federal standards for chemical levels.

WRTDS - Weighted Regressions on Time, Discharge, and Season a tool for the determination of nutrient and sediment fluxes and trends using multiple weighted regressions.

yield - a normalization of load by area, usually expressed as pounds per year per square mile, or kilograms per year per square mile.

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