A recent study conducted by the Maryland Department of Natural Resources (DNR) indicates a mix of improving, deteriorating, and stable conditions in the state’s non-tidal streams. The findings, part of the Maryland Biological Stream Survey (MBSS), compare data collected from hundreds of stream sites across Maryland against benchmarks set 14 to 20 years ago.
Scott Stranko, DNR’s director of monitoring and nontidal assessment, commented on the survey’s implications, “These results are encouraging as they demonstrate the effectiveness of ongoing efforts to protect and restore Maryland’s streams. It’s crucial that these efforts continue.”
The fourth iteration of this long-term project revisited results from the first two rounds of surveys conducted in the mid-1990s and early 2000s. This latest report examined stream temperatures, water chemistry, fish populations, and benthic macroinvertebrates—key indicators of stream health.
Key findings include a general warming of stream temperatures across the state, likely tied to global climate trends, with average daily temperatures, minimum temperatures, and instances of temperatures above 68 degrees Fahrenheit all on the rise. Interestingly, streams in western Maryland displayed resilience, with some even showing signs of cooling, a positive sign for aquatic life.
Kyle Hodgson, a DNR natural resource biologist and the report’s lead author, noted, “Western Maryland streams might be the most resilient to changes in air temperature compared to the rest of the state, possibly due to less development and more forested areas.”
The study also found improvements in water chemistry, with streams becoming less acidic and showing reduced levels of sulfates alongside an increase in acid-neutralizing capacity—a shift likely influenced by amendments to the federal Clean Air Act and decreased pollution from abandoned coal mines.
Conversely, the presence of more orthophosphate and chloride and higher conductivity levels suggest ongoing pollution challenges. These changes in water quality have varied impacts on stream life, affecting everything from the smallest invertebrates to larger fish species.
Mary Genovese, a biologist who worked on the report, explained that while the biological integrity of benthic macroinvertebrates showed more signs of decline than improvement, the populations of caddisflies increased, indicating some positive changes. However, declines in mayflies pointed to ongoing degradation.
Despite the mixed results, the overall biological integrity of fish remained relatively unchanged. However, the survey noted increases in non-native and invasive fish species across Maryland streams, a concerning trend for ecosystem health.
The report calls for continued monitoring and further research, particularly into the specific impacts of riparian forests on stream health and localized studies of individual stream systems. “Streams are really a place to see what’s going on in our environment,” Stranko emphasized. “The health of the stream reflects the condition of resources around it.”
For Maryland residents interested in the health of local streams, the MBSS provides an online Stream Health Index Map.
