By Joe Zimmermann, science writer with the Maryland Department of Natural Resources
Temperatures and non-native fish species have increased, while acidity has lessened
Maryland Biological Stream Survey staff conduct electrofishing in Frederick County. DNR photo
Maryland 2024 - A Maryland Department of Natural Resources report found mixed results for the health of the state’s non-tidal streams, with some conditions getting better, others worse, and some remaining the same.
For this report on potential changes in stream conditions, the department’s Maryland Biological Stream Survey (MBSS) staff sampled hundreds of stream sites across the state, then compared what they found to data from those same sites 14 or 20 years earlier.
While the results highlight ongoing challenges for streams in the state, Scott Stranko, the department’s director of monitoring and nontidal assessment, said the report also demonstrates the importance and efficacy of work to protect Maryland’s streams.
“There are abundant efforts to protect and restore Maryland’s streams, so these results are encouraging to show that some things are improving and many healthy streams are staying healthy. It shows those efforts need to continue,” Stranko said. “As we continue to monitor, we hope to be able to see the results of those continued efforts to protect and restore streams.”
The report is the fourth round of a long-term MBSS sampling project, revisiting results from the first and second rounds of surveys in the mid-1990s and early 2000s. This round assessed four key metrics to determine how Maryland streams have changed over time: temperature, water chemistry, fish, and benthic macroinvertebrates (small aquatic animals including insects and crustaceans).
Overall, the report found that stream temperatures largely got warmer, aspects of water chemistry improved, and the ability for streams to support fish and benthic macroinvertebrates did not change significantly. But even within these categories, the results showed some variability and nuance.
Tracking temperature changes over 14 years (temperature data wasn’t sampled for the first round), randomly selected streams were found to be getting warmer in much of the state, consistent with rising global temperatures. Across Maryland, streams saw significant increases in average daily temperatures, minimum temperatures, and temperature readings above 68 degrees.
However, streams in western Maryland were not significantly warmer and even showed some signs of potential cooling, which is beneficial to stream life.
“We basically found that western Maryland streams might be the most resilient to changes in air temperature compared to the rest of the state,” said Kyle Hodgson, a DNR natural resource biologist and the lead author on the report.
This could be in part because of less development and more forested areas in that part of the state, said Lindsay Powers, a natural resource biologist and a report co-author who focused on temperature.
The report also found that “reference streams”—streams selected for the survey as high-quality sites—in central Maryland also didn’t demonstrate much warming, which Powers said was a surprising result, but could have something to do with the better quality of those streams.
Hodgson said the most promising results from the report were the findings on the water chemistry of the streams. Water chemistry sampling indicated that streams became less acidic and lower in sulfates over time, in addition to an increase in acid-neutralizing capacity, which makes streams more resistant to changes in acidity.
Amendments to the federal Clean Air Act and related efforts to limit atmospheric pollutants are possible reasons for that change, Hodgson said. Reductions in sulfates and acidity from abandoned coal mines may also have improved in western Maryland, leading to improved water quality in that region. These changes in chemistry affect everything down to the smallest fish and invertebrates in stream systems.
“We’re approaching more of a neutral pH, which is better for most stream life,” Hodgson said.
Still, the report also found that streams overall had more orthophosphate and chloride, as well as higher conductivity, which point to ongoing challenges in reducing pollution.
“These changes affect species living in streams in different ways,” said Mary Genovese, a biologist and report co-author who focused on benthic macroinvertebrates, including the larvae of several groups of insects. The report found that percentages of caddisflies increased, showing signs of improvement, however percentages of mayflies decreased, showing signs of degradation compared to 14 and 20 years earlier. No significant changes were found in dragonflies and damselflies, which, according to some other studies, appear to be in decline globally.
While overall biological integrity was stable over the time period, the report noted “more evidence of declines than improvements” for benthic macroinvertebrates, which are important indicators of stream health.
A giant stonefly larva such as this one is the type of macroinvertebrates that biologists look for to evaluate the health of a stream. Stoneflies are very sensitive to water quality conditions and their presence is typically indicative of good to excellent water quality. Photo by AJ Metcalf
Similarly, while fish biological integrity didn’t change significantly, smaller findings within that data were concerning to scientists. Non-native and invasive fish have become more abundant across streams, with ten species—including flathead catfish and Chesapeake Channa, or northern snakehead—collected during this round that hadn’t been observed 14 or 20 years earlier.
At the high-quality reference streams, all fish species declined in abundance, except for non-native fish. The report authors suggested this could be related to even minor stress in these streams being able to affect abundance, as similar declines were not noted at random stream sites.
At the same time, although the numbers of rare, threatened, and endangered fish found by the surveys did not decline significantly over the 14-year interval, they had declined over the 20-year interval. The report authors noted that such declines might be early warning signs that might eventually show up as declines in overall stream health indices.
“Increases in tolerant species and decreases in sensitive species may be early indicators of ecosystem alterations not yet reflected in more generalized biological indices,” the authors wrote in the report.
Biologists caught multiple white sucker fish like this one during the Patapsco stream survey. White sucker fish are among the most widespread fish in Maryland streams and rivers. Photo by AJ Metcalf
The researchers hope that this report inspires further study. Powers said the report gives an overview of streams across the state, but more research could be done on specific areas and on the effects of riparian forests on streams, for example. Hodgson said the report could also help other states assess if similar patterns are occurring in their streams.
Streams are fragile ecosystems, and freshwater animals are some of the most imperiled groups in the country. As stream health influences both the health of the Chesapeake Bay and the surrounding landscape, Stranko said he hoped that the report and further study could help to drive continued management, as well as restoration efforts and pollution reduction.
“Streams are really a place to see what’s going on in our environment,” he said. “The health of the stream reflects the condition of resources around it.”
Check the health of your local stream on the Maryland Biological Stream Survey’s Stream Health Index Map.
