Summary of Nitrogen, Phosphorus, and Suspended-Sediment Loads and Trends Measured at the Nine Chesapeake Bay River Input Monitoring Stations: Water Year 2018 Update

Prepared by Douglas L. Moyer and Joel D. Blomquist, U.S. Geological Survey, April 25, 2019

Changes in nitrogen, phosphorus, and suspended-sediment loads in rivers across the Chesapeake Bay watershed have been calculated using monitoring data from the nine Chesapeake Bay River Input Monitoring (RIM) stations during 1985 to 2018 (Moyer and Blomquist, 2019). These results for the nine RIM stations are used to help assess efforts to decrease nutrient and sediment loads delivered to the bay. Additional information for each monitoring station is available through the USGS Chesapeake Bay Nontidal Web site (https://cbrim.er.usgs.gov/) that provides State, Federal, and local partners, as well as the general public, ready access to a wide range of data for nutrient and sediment conditions across the Chesapeake Bay watershed. Results from two time periods are reported in this summary: a long-term time period (1985-2018), and short-term time period (2009-2018). All annual results are based on a water year which extends from October 1 to September 30.

The results are summarized for 1. loads delivered directly to the tidal waters for the most recent year (water year 2018); specifically, the

combined load from the nine River Input Monitoring (RIM) stations, 2. trends in loads at the RIM stations over the long- and short-time periods, and

What are the patterns in loads delivered to tidal waters from the RIM stations?

The USGS combined the load results from the nine RIM stations shown in figure 1 to quantify the total nitrogen, phosphorus, and suspended-sediment loads delivered from the watershed to tidal waters. Together, the nine RIM stations reflect loads delivered from 78 percent of its 64,000-square-mile watershed.

River flow and loads to tidal waters • Estimated annual-mean streamflow entering the Chesapeake Bay in 2018 was 109,000 cfs, about 38.3

percent (30,210 cfs) above the long-term (1937-2018) annual-mean streamflow of 78,790 cfs (fig. 2). How did this mean annual streamflow to the Bay rank? 2018 annual-mean streamflow was the 8th highest since 1937 and the 5th highest since 1985 (only exceeded by 1996, 2003, 2004, and 2011).

• In 2018, the combined loads from the nine RIM stations were as follows: o Total nitrogen (TN): 278 million pounds (Mlb), 72 Mlb more than the long-term average of 206

Mlb for 1985-2018 (fig. 3). The TN load for 2018 was the 7th highest since 1985.

o Total phosphorus (TP): 25.2 Mlb, 11.6 Mlb more than the long-term average of 13.6 Mlb for 1985-2018 (fig. 4). The TP load for 2018 was the 5th highest since 1985.

o Suspended sediment (SS): 7.84 million tons (Mton), 3.12 Mton more than the long-term average

of 4.72 (Mtons) for 1985-2018 (fig. 5). The SS load for 2018 was the 6th highest since 1985.

The Chesapeake Bay Program uses the RIM loads and estimates loads from the remaining unmonitored areas to compute a total nutrient and sediment load to the bay.

What are the trends in loads delivered to tidal waters from the RIM stations?

Trends in loads from the nine RIM stations are flow-normalized to remove the year-to-year variability in river flow; by doing so, changes in nitrogen, phosphorus, and suspended-sediment loads resulting from changing sources, delays associated with storage and transport of historical inputs, and (or) implemented management

actions are identified. Changes in loads for nitrogen, phosphorus, and suspended sediment are provided for two time periods: 1985-2018 (long term) and 2009-2018 (short term) (table 1). Loads that are lower in the end year than the start year are classified as improving conditions, while loads that are higher in the end year than the start year are classified as degrading conditions. Loads are classified as having no trend if there is not a discernable difference between start and end years.

Changes in total nitrogen loads • Long-term trends in total nitrogen loads indicate improving conditions at the majority of the stations,

including the four largest rivers (Susquehanna, Potomac, James, and Rappahannock). The Choptank and Pamunkey are the only stations where conditions are degrading.

• Short-term trends in total nitrogen loads indicate improving conditions at 3 stations and degrading conditions at 5 stations. Data from the Susquehanna station indicate no discernable short-term trends.

Changes in total phosphorus loads • Long-term trends in total phosphorus loads indicate improving conditions at only 3 stations (Potomac,

James, and Patuxent) and degrading conditions at the remaining 6 stations. • Short-term trends in total phosphorus loads indicate improving conditions at only the James and

Patuxent stations, degrading conditions at 4 stations, and no discernable change in conditions at the Susquehanna, Potomac, and Pamunkey stations.

Changes in suspended-sediment loads • Long-term trends in suspended-sediment loads indicate improving conditions at 3 stations (Potomac,

Patuxent, and Choptank), degrading conditions at 5 stations, and no discernable change in conditions at 1 station.

• Short-term trends in suspended-sediment loads indicate improving conditions at only the Susquehanna and James stations; degrading conditions at 5 stations, and no discernable change in conditions at the Potomac and Patuxent stations.

Table 1. Summary of long-term (1985-2018) and short-term (2009-2018) trends in nitrogen, phosphorus, and suspended-

sediment loads for the River Input Monitoring stations. [Improving or degrading trends classified as likelihood estimates greater than or equal to 66 percent]

Monitoring station Total nitrogen load Total phosphorus load Suspended-sediment

load Long term Short term Long term Short term Long term Short term

SUSQUEHANNA RIVER AT CONOWINGO, MD Improving No Trend Degrading No Trend Degrading Improving

POTOMAC RIVER AT WASHINGTON, DC Improving Improving Improving No Trend Improving No Trend

JAMES RIVER AT CARTERSVILLE, VA Improving Improving Improving Improving Degrading Improving

RAPPAHANNOCK RIVER NR FREDERICKSBURG, VA Improving Degrading Degrading Degrading Degrading Degrading

APPOMATTOX RIVER AT MATOACA, VA No Trend Degrading Degrading Degrading No Trend Degrading

PAMUNKEY RIVER NEAR HANOVER, VA Degrading Degrading Degrading No Trend Degrading Degrading

MATTAPONI RIVER NEAR BEULAHVILLE, VA No Trend Degrading Degrading Degrading Degrading Degrading

PATUXENT RIVER NEAR BOWIE, MD Improving Improving Improving Improving Improving No Trend

CHOPTANK RIVER NEAR GREENSBORO, MD Degrading Degrading Degrading Degrading Improving Degrading

Additional Information

• Tabular results for each station are available by going to the “Download” section of the following web page: https://cbrim.er.usgs.gov/

USGS Contacts

Web-page content Doug Moyer dlmoyer@usgs.gov Joel Blomquist jdblomqu@usgs.gov USGS Chesapeake Bay Studies: Scott Phillips, swphilli@usgs.gov or visit https://www.usgs.gov/centers/cba

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RIVER INPUT NONTIDAL BASINS

Figure 1. Location of the 9 River Input Monitoring (RIM) stations in the Chesapeake Bay watershed. Station numbers and names areprovided in table 2.

River Input Monitoring (RIM) station and identifier

1

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WATER YEAR (OCTOBER - SEPTEMBER)Figure 2. Estimated annual-mean streamflow entering Chesapeake Bay. Black line represents the average annual-mean streamflow of 78,790 cubic feet per second. (Source https://www.usgs.gov/centers/cba/science/chesapeake-bay-estimated-streamflow?qt-science_center_objects=0#qt-science_center_objects)

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Figure 3. Combined annual total nitrogen load delivered from the nine River Input Monitoring stations to the Chesapeake Bay. Black line represents the mean annual combined load of 206million pounds per year.

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WATER YEAR (OCTOBER - SEPTEMBER)Figure 4. Combined annual total phosphorus load delivered from the nine River Input Monitoring stations to the Chesapeake Bay. Black line represents the mean annual combined load of 13.6million pounds per year.

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Figure 5. Combined annual suspended-sediment load delivered from the nine River Input Monitoring stations to the Chesapeake Bay. Black line represents the mean annual combinedload of 4.72 million tons per year.