Spatial and temporal variability of water quality of the Patapsco River Estuary during 2013–2023: A report to Blue Water Baltimore

The Patapsco River Estuary (PRE), an urbanized tidal tributary of the Chesapeake Bay in the Mid-Atlantic Region of the United States, has long faced water quality concerns. However, a systematic analysis of the spatial and temporal variability in its water quality has been lacking. Utilizing surface data collected by Blue Water Baltimore from 2013 to 2023 at 20 stations throughout the PRE, we analyzed long-term averages and changes in ten water quality variables: temperature, salinity, dissolved oxygen, oxygen supersaturation, pH, total nitrogen (TN), total phosphorus (TP), Secchi depth, phycoerythrin, and enterococcus bacteria pass score (BPS). Long-term averages in the ten variables showed several distinct spatial patterns, with some variables (oxygen, pH, and BPS) increasing and other variables (TN, TP, and Secchi depth) decreasing down the estuary. The station at Jones Falls Outlet showed unique properties of low salinity, temperature, oxygen, pH, phycoerythrin and BPS and high TN, and Secchi depth. We hypothesized that given improvements in wastewater treatment, water quality has improved at all stations. Further, we hypothesized that stations with the poorest long-term average water quality conditions have shown the greatest improvement. Of the five water quality variables of greatest concern (BPS, Secchi depth, TN, TP, and phycoerythrin), the first three demonstrated general improvement, while the last two showed degradation, providing mixed support for our first hypothesis. The increases in TP were particularly large. Of the three variables showing improvement, the greatest improvements were observed at stations with the poorest long-term average water quality, consistent with our second hypothesis. Overall, our findings underscore the importance of comprehensive water quality monitoring in revealing spatial and temporal patterns that offer insights into the drivers of water quality variability in estuarine environments.