USGS revises 2020 nontidal load and trend results
Issue: The USGS has revised loads and trends through 2020 from monitoring stations in the Chesapeake Bay Program (CBP) Nontidal Network (NTN). The original release of the results was in July 2022. During a process to implement a new software package for the next update of NTN data, the USGS discovered some questionable data values. Most of the questionable values were related to a coding transcription error that was occurring for selected values when data were pulled into files used to compute loads and trends for each NTN site, while others were related to data-reporting. The USGS has (1) corrected the data, (2) rerun all the loads and trends, and (3) updated the 2020 loads and trends.
Evaluation of Data Values
The USGS performed an examination of all the data used to compute loads and trends at 123 NTN sites: a total of 171,678 values of nutrient and sediment data. The review flagged 80 values that had data integrity issues, which represents 0.05 percent of the NTN data. The distribution of the flagged data was: 39 values for total nitrogen, 27 values for nitrate plus nitrite, 3 values for total phosphorous, 7 values for dissolved inorganic phosphorus, and 4 values for suspended sediment. The flagged values were associated with load computations at 16 sites, short-term trends at 17 sites, and long-term trends at 14 sites. USGS examined and corrected all the flagged values.
Updated Trend Results
Using the corrected data, the USGS reran both the short-term (2011-2020) and long-term trends (1985-2020) for the impacted sites. Ultimately, there were changes in trend direction at 2 sites for short-term trends, and 4 sites with long-term trends (figure 1).
For short-term trends, at the ~80 NTN sites, 2011-2020, 2 sites had a change in trend direction for nitrogen with no changes for phosphorus and sediment. The sites for changes in the nitrogen trends were:
- Rivanna River at Palmyra, VA, (02034000): no trend to improving; and
- Octoraro Creek near Richardsmere, MD (01578475): no trend to degrading
For the long-term trends: At the ~40 NTN sites, 1985-2020, 3 sites had a change in trend direction for nitrogen:
- South River near Waynesboro, VA (01626000): degrading to no trend
- Robinson River near Locust Dale, VA (01666500): degrading to no trend
- James River near Richmond, VA (02037500): no trend to improving
One site had a change in trend direction for sediment (Susquehanna River at Danville, PA (01540500): no trend to improving). There were no changes in phosphorous trends.
The nine River-Input Monitoring (RIM) Stations are not affected by these data issues.
The updated short-term trends for the NTN during 2011-2020 are:
Figure 2b. Updated short-term phosphorous trends. Click on image to enlarge.
- For nitrogen: 38 percent of the NTN stations are improving, whereas 42 percent are degrading, and the remaining 20 percent have no trend. (See figure 2a)
- For phosphorus: 44 percent of the NTN stations are improving, whereas 23 percent are degrading, and the remainder are showing no trend. (See figure 2b)
- For suspended sediment: 18 percent of the NTN stations are improving, whereas 46 percent are degrading, and the remainder are showing no trend.
The updated long-term trends are provided in the data release.
Management Implications
The CBP partnership uses the results to (1) help focus where nutrient and sediment reduction efforts can be most effective, and (2) track progress of water-quality improvements in the watershed.
The USGS collaborates with science partners to explain the factors affecting the nutrient and sediment changes. The USGS interacts with stakeholders to understand and apply the findings to inform water-quality restoration strategies.
For More Information
Issue: The USGS has revised loads and trends through 2020 from monitoring stations in the Chesapeake Bay Program (CBP) Nontidal Network (NTN). The original release of the results was in July 2022. During a process to implement a new software package for the next update of NTN data, the USGS discovered some questionable data values. Most of the questionable values were related to a coding transcription error that was occurring for selected values when data were pulled into files used to compute loads and trends for each NTN site, while others were related to data-reporting. The USGS has (1) corrected the data, (2) rerun all the loads and trends, and (3) updated the 2020 loads and trends.
Evaluation of Data Values
The USGS performed an examination of all the data used to compute loads and trends at 123 NTN sites: a total of 171,678 values of nutrient and sediment data. The review flagged 80 values that had data integrity issues, which represents 0.05 percent of the NTN data. The distribution of the flagged data was: 39 values for total nitrogen, 27 values for nitrate plus nitrite, 3 values for total phosphorous, 7 values for dissolved inorganic phosphorus, and 4 values for suspended sediment. The flagged values were associated with load computations at 16 sites, short-term trends at 17 sites, and long-term trends at 14 sites. USGS examined and corrected all the flagged values.
Updated Trend Results
Using the corrected data, the USGS reran both the short-term (2011-2020) and long-term trends (1985-2020) for the impacted sites. Ultimately, there were changes in trend direction at 2 sites for short-term trends, and 4 sites with long-term trends (figure 1).
For short-term trends, at the ~80 NTN sites, 2011-2020, 2 sites had a change in trend direction for nitrogen with no changes for phosphorus and sediment. The sites for changes in the nitrogen trends were:
- Rivanna River at Palmyra, VA, (02034000): no trend to improving; and
- Octoraro Creek near Richardsmere, MD (01578475): no trend to degrading
For the long-term trends: At the ~40 NTN sites, 1985-2020, 3 sites had a change in trend direction for nitrogen:
- South River near Waynesboro, VA (01626000): degrading to no trend
- Robinson River near Locust Dale, VA (01666500): degrading to no trend
- James River near Richmond, VA (02037500): no trend to improving
One site had a change in trend direction for sediment (Susquehanna River at Danville, PA (01540500): no trend to improving). There were no changes in phosphorous trends.
The nine River-Input Monitoring (RIM) Stations are not affected by these data issues.
The updated short-term trends for the NTN during 2011-2020 are:
Figure 2b. Updated short-term phosphorous trends. Click on image to enlarge.
- For nitrogen: 38 percent of the NTN stations are improving, whereas 42 percent are degrading, and the remaining 20 percent have no trend. (See figure 2a)
- For phosphorus: 44 percent of the NTN stations are improving, whereas 23 percent are degrading, and the remainder are showing no trend. (See figure 2b)
- For suspended sediment: 18 percent of the NTN stations are improving, whereas 46 percent are degrading, and the remainder are showing no trend.
The updated long-term trends are provided in the data release.
Management Implications
The CBP partnership uses the results to (1) help focus where nutrient and sediment reduction efforts can be most effective, and (2) track progress of water-quality improvements in the watershed.
The USGS collaborates with science partners to explain the factors affecting the nutrient and sediment changes. The USGS interacts with stakeholders to understand and apply the findings to inform water-quality restoration strategies.