Changes in nitrogen, phosphorus, and suspended-sediment loads in rivers across the Chesapeake Bay watershed have been calculated using monitoring data from the Chesapeake Bay Nontidal Water-Quality Monitoring Network (NTN). These results are used to help assess efforts to decrease nutrient and sediment loads being delivered to the bay. Additional information for each monitoring station is available through this USGS Web site in order to provide the 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.

The results are summarized for

1. loads delivered directly to the tidal waters; specifically, the River Input Monitoring (RIM) stations,
2. trends in loads at the RIM stations, and
3. patterns in loads at each monitoring station in the bay watershed (that are part of the Chesapeake Bay Program [CBP] NTN).

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

The USGS combined the load results from the 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 2014 was 81,300 cfs, about 3 percent (2,738 cfs) above the long-term (1937-2015) annual-mean streamflow (fig. 2).
• In 2014, the combined loads from the nine RIM stations were as follows:
• Total nitrogen (TN): 189 million pounds (Mlb), 21 Mlb less than the long-term average for 1985-2014 (fig. 3).
• Total phosphorus (TP): 12.2 Mlb, 1.5 Mlb less than the long-term average for 1985-2014 (fig. 4).
• Suspended sediment: 3.58 million tons (Mton), 1.41 Mton less than the long-term average for 1985-2014 (fig. 5).

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 (see methods section of this Web site) to account for the changes in river flow to better understand changes related to land-use change activities in the watershed. Changes in loads for nitrogen, phosphorus, and suspended sediment are provided for two time periods: 1985-2014 (long term) and 2005-2014 (short term) (table 1). Decreasing loads are classified as improving conditions, while increasing loads are classified as degrading conditions.

Changes in total nitrogen loads

• Long-term trends in total nitrogen loads indicate improving conditions at the majority of the stations, including the five largest rivers. The Choptank River is the only station whose data indicate degrading conditions.
• Short-term trends in total nitrogen loads indicate improving conditions at only 3 stations and degrading conditions at 4 stations. Data from the Susquehanna and James stations indicate no discernable short-term trends.

Changes in total phosphorus loads

• Long-term trends in total phosphorus loads indicate improving conditions at 4 stations and degrading conditions at another 4 stations.
• Short-term trends in total phosphorus loads indicate improving conditions at only the Potomac and Patuxent stations, degrading conditions at 4 stations, and no discernable change in conditions at the 3 remaining stations.

Changes in suspended-sediment loads

• Long-term trends in suspended-sediment loads indicate improving conditions at 4 stations, degrading conditions at 3 stations, and no discernable change in conditions at 2 stations.
• Short-term trends in suspended-sediment loads are indicate improving conditions at 3 stations; degrading conditions at 5 stations, and no discernable change in conditions at the Susquehanna station.

What are the patterns in loads and trends across the nontidal monitoring network (2005-14)?

The USGS computes load and trend results from the NTN to display (1) the range in loads of nitrogen, phosphorus, and suspended sediment; and (2) the trends in these loads. The majority of the NTN sites whose data were used for the analysis had data collected since 2005 (fig. 6 and table 2). To facilitate the comparison of loads and trends between sites, load results from each NTN station are normalized by the respective drainage area to present the results as per-acre loads (also known as yield). The total number of NTN stations analyzed for total nitrogen, total phosphorus, and suspended-sediment load and trends varies because of the presence or absence of targeted water-quality samples collected during stormflow conditions (see Chanat and others, 2015).

Patterns in total nitrogen loads

• Total nitrogen loads range from 1.19 to 33.4 pounds per acre (lb/acre; fig. 7), and the average load is 7.33 lb/acre.
• Twice as many stations show improving trends as those showing degrading trends
• 44 of 81 (54 percent) stations have improving trends, with load reductions ranging from about 0.10 to 5.07 lb/acre.
• 22 of 81 (27 percent) stations have degrading trends, with load increases ranging from about 0.04 to 1.21 lb/acre.
• 15 of 81 (19 percent) show no discernable trends.

Patterns in total phosphorus loads

• Total phosphorus loads range from 0.13 to 2.31 lb/acre (fig. 8), and the average load is 0.52 lb/acre.
• Over three times as many stations showing improving trends as those showing degrading trends
• 41 of 60 (68 percent) stations have improving trends, with load reductions ranging from about 0.01 to 1.08 lb/acre.
• 12 of 60 (20 percent) stations have degrading trends, with load increases ranging from about 0.01 to 0.43 lb/acre.
• 7 of 60 (12 percent) have no discernable trends.

Patterns in suspended-sediment loads

• Suspended-sediment loads range from 18 to 2,206 lb/acre (fig. 9) and the average load is 482 lb/acre.
• There are ten more stations showing improving trends compared to the number of stations showing degrading trends
• 29 of 59 (50 percent) stations have improving trends, with load decreases ranging from 8.11 to 1,490 lb/acre.
• 19 of 59 (30 percent) stations have degrading trends, with load increases ranging from 4.75 to 341 lb/acre.
• 11 of 59 (20 percent) have no discernable trends.

The Chesapeake Nontidal Monitoring Network and Role of USGS

The Chesapeake Bay Nontidal Water-Quality Monitoring Network is a partnership implemented among the States in the watershed, the U.S. Environmental Protection Agency, the USGS, and the Susquehanna River Basin Commission. A network of monitoring stations has been established and is sampled using standardized protocols and quality-assurance procedures designed to measure pollutant loads and changes in pollutant loads over time. The initial network formed around 1985 with coordinated monitoring at the nine RIM stations. In 2004, the CBP formalized the network, and a period of expansion followed. In 2010 and 2011, the network was further expanded to address the needs of the Total Maximum Daily Load (TMDL). The network currently has 117 sites designed to measure changes in nitrogen, phosphorus, and suspended sediment in the Chesapeake Bay watershed. Through this partnership, nitrogen, phosphorus, and suspended-sediment loads and trends are determined based on (1) continuous streamflow monitoring, (2) extensive water-quality sampling, and (3) advanced statistical analysis. The USGS computes the loads and trends and present this information through this Web site.

Additional Information

• Maps of the load and trend in load results are available as
• Downloadable PDF Maps
• An Interactive Map
• Tabular results for each station are available in the Downloads section of the navigation menu on this Web site.

USGS Contacts:

Web-page content

Joel Blomquist, Baltimore MD,
Doug Moyer, Richmond, VA,
Mike Langland, New Cumberland, PA,

For more information on USGS Chesapeake Bay Studies