Capt. John Smith described the Chesapeake watershed as a “delightsome land with clear rivers and brookes running to a faire Bay.”
He didn’t do any scientific monitoring of those streams. But it’s a safe bet that today’s waterways have been dramatically altered from what the Bay’s first explorer saw.
In fact, the Department of Natural Resources’ Maryland Biological Stream Survey concluded in a report summarizing its comprehensive, three-year, stream review that “no truly pristine streams exist in Maryland today.”
Except for about 80 acres, Maryland’s entire landscape has been changed since Smith’s observation: The land has been logged, farmed and built upon; its rivers and streams dammed, straightened — even buried. Acid rain and other pollutants strike even the most remote areas from the air.
The survey grew out of the Department of Natural Resource’s acid rain monitoring program, which is funded by a surcharge on utility bills to assess environmental impacts of power generation. Under that program, scientists were able to document that streams in parts of the state were becoming more acidic because of air pollution.
But while they could observe changing stream chemistry, scientists had difficulty saying how acid rain was affecting stream biology: When they saw problems, they often couldn’t tell whether they stemmed from acid rain or something else.
That gave birth to the statewide stream survey. It gives scientists and officials a comprehensive baseline of what streams looked like in the mid-1990s. They can characterize what constitutes healthy — and degraded — streams for each region. Using that as a yardstick, future surveys can show whether streams are getting better or worse.
“We don’t have a lot of good historical data about where we’ve been. It’s a shame,” said Ray Morgan, professor at the Appalachian Laboratory of the University of Maryland’s Center for Environmental Science, who helped design the survey.
The sampling techniques used were field tested before the survey began, and peer reviewed by other scientists. So were the criteria used for development of the IBIs — Index of Biological Integrity — which measures the ability of a stream to support and maintain a balanced, integrated adaptive community of organisms which have a species composition, diversity and functional organization comparable to that of the natural habitat of the region.
To develop IBIs, the survey selected reference sites at minimally impacted sites in each geological region of the state to represent natural habitats. During the survey, sites were evaluated based on how they compared to the reference conditions
Rigorous sampling techniques led to scientifically defensible conclusions that can be used by decision makers. “It’s very, very defensible in court,” Morgan said.
Also, the random sampling technique allows scientists to extrapolate results to streams over the entire state, similar, in a sense, to the way a poll samples public opinion. For example, based on survey results, scientists could estimate the populations for each of the 83 fish species found in nontidal streams. Combining all species, the survey estimated there was an average of 10,325 fish per mile in wadeable Maryland streams.
“There are a lot of states looking at us, and they’re very envious,” Morgan said. But, he added, such a detailed survey was possible in Maryland because of its small size: It has only about 9,000 miles of freshwater nontidal streams. Pennsylvania, by contrast, has more than 80,000 miles, making such a program “a logistical nightmare,” he said.
Selected Survey Results
- Combined IBIs: A scale was established that rated all sites as good, fair, poor or very poor. Only 12 percent of all stream miles in the state are in good condition based on both the fish and benthic macroinvertebrate IBI. Another 42 percent were fair, and the rest were poor.
- For Benthos: 49 percent of stream miles fell into the range of good to fair, while 51 percent showed signs of degradation. The West Chesapeake had 70 percent of its stream miles rated very poor, while the Susquehanna had no sites rated very poor.
- For Fish: 45 percent of stream miles were considered good to fair, while 29 percent were poor or very poor. Another 26 percent of stream miles were too small to contain fish, and were not rated. Of the 17 basins, the Elk was the best, with 38 percent of stream miles rated as good.
Land use relationships
For all of the basins combined, fish and benthic IBI scores decreased with increasing urban land use. No stream with more than 15 percent impervious cover (low density development) was ever rated as good. All sites with more than 50 percent of the watershed in urban land use (high density development) had IBIs that were either poor or very poor. Sites with a good IBI score had an average of 4 percent urban land use, compared with a statewide average of 9 percent urban land use.
Fish IBI scores tended to increase in agricultural areas. No one is certain why. It could be that nutrients in the freshwater systems are increasing the food supply for fish. Or, it could reflect that many fish populations, unable to survive in nearby developed areas, are being displaced into agricultural areas. Benthos fared well in forested streams that were not impacted by acidity.
About 18 percent of Maryland’s stream miles are sensitive to acid rain. Natural acidification, mainly in blackwater streams on the Eastern Shore, affect about 3 percent of the state’s stream miles, while acid mine drainage affects another 3 percent. Fertilizer runoff acidifies another 4 percent of stream miles.
Acidity is measured on a pH scale of 1-14, with 1 being strongly acid, 14 being strongly alkaline and 7 neutral. Because pH is measured on a logarithmic scale, pH 5 is 10 times more acidic than pH 6, and 100 times more acidic than pH 7.
Except for those with natural acidity, streams with a pH below 5 had no fish, while streams with a pH higher than 6 averaged more than 9,000 fish per mile. Streams with a pH between 5 and 6 averaged 500 fish per mile.
Seventeen fish species were absent in acid-sensitive streams — those with low amounts of limestone and other natural buffers to acidity — and 44 other species were less abundant. On the average, acid-sensitive streams had 135 fewer fish per mile than well-buffered streams.
The blacknose dace, the most common species in Maryland streams, was among the most sensitive to acidity. Other species that are very sensitive to acidity are the mottled sculpin, rosyside dace, bluntnose minnow and creek chub.
The condition of biological communities is directly related to physical habitat quality. Sedimentation, impoundments, stream channelization, urban development timber harvesting, agriculture, livestock grazing and other activities degrade stream habitat. Statewide, a Physical Habitat Index developed for the survey rated conditions in 51 percent of stream miles as poor or very poor, while 49 percent were considered good or fair. Here are some major components of habitat quality:
- Buffers: Statewide, 58 percent of stream miles had forested buffers, while 14 percent had other kinds of vegetated buffers, such as wetlands, old fields, tall grass, or lawns. Another, 28 percent had either no buffer, or had discharge pipes directed into the stream, effectively bypassing streamside vegetation.
- Channelization: The survey estimated that about 17 percent of Maryland’s stream miles have been channelized — or straightened — mainly for agriculture but also for storm water drainage. The most channelization was in the Pocomoke with 81 percent of stream miles being channelized.
- Erosion: Based on criteria such as the height of the stream bank, the bank angle, the amount of bank protected by root cover, and other factors, the survey ranked erosion potential. Statewide, 35 percent of stream miles had a high potential for erosion, and 7 percent had a very high potential. Another 35 percent had low, and 22 percent very low, erosion potential. More than three-quarters of stream miles in the Patuxent and Gunpowder had poor bank stability. But two-thirds of streambanks in the Youghiogheny and the North Branch Potomac were considered good.
- Instream Conditions: Instream condition was assessed based on the substrate, quality of pools and eddies, quality of riffles and runs, and other features needed to support health communities. Statewide, 12 percent of stream miles were very poor, 38 percent poor, 28 percent fair and 22 percent good.
- Maryland has about 9,000 miles of nontidal streams, divided among 17 drainage basins.
- Statewide, there are more than 60 million fish in those streams of which about 1 million are game species.
- The blacknose dace is the most common fish in Maryland streams, with an average of 1,970 individuals per stream mile, and nearly 11.6 million individuals statewide.
- Statewide, 4 percent of stream miles had no fish, excluding watersheds which drain less than 300 acres and are considered too small for fish.
- All fish were examined for external anomalies. The occurrence of anomalies was lower among game fish (2 percent) than nongame fish (5 percent). Anomalies tended to increase with stream size. Most anomalies were related to parasites.
- Pathological anomalies were found in a fewer portion of fish, 0.8 percent of game fish and 0.5 percent of nongame fish. Numbers were highest in larger streams, perhaps indicating the cumulative impact of upstream pollution.
- The abundance of harvestable-size game fish was greatest in the Gunpowder basin, with an estimated 23,565 harvestable size game fish.
- The biggest stream stressor in the state was physical habitat degradation, which affected an estimated 52 percent of streams.
- Statewide, 79 percent of stream miles are on private land, only 17 percent are public. In some basins, the percent of private land can exceed 90 percent, as in the Choptank and Pocomoke.
- About 4 percent of stream miles had beaver ponds, with the highest occurrence in the lower Potomac basin.
- Only three fish species, largemouth bass, bluegill and pumpkinseed, were present in all 17 river basins.
- Only two amphibians, green frog and bullfrog, and one reptile, northern water snake, were present in all 17 basins.
Of more than 900 sites sampled, only 21 were rated as good by the fish IBI, the benthic IBI and the Physical Habitat Index.
A total of 38 sites were rated as good by both the fish and benthic IBIs.
They were distributed among 10 river basins, but nine were in the Youghiogheny and eight in the lower Potomac basins.
“These sites likely represent some of the most natural stream ecosystem conditions in Maryland,” a survey report said.
The temperature of runoff from urban areas is greater and more variable than runoff from forests. The highest temperature spikes can occur in streams during summer storms, as rainfall is heated on hot pavement. Also, impervious surface reduces infiltration and therefore the groundwater flows into stream which can help moderate temperatures.
The effect of land use on temperature is illustrated by survey results from two similar size streams in the Patuxent watershed. Dorsey Run is 73 percent forested, 10 percent urban and 17 percent agriculture. Nearby, Midway Run is 32 percent forest, 37 percent urban and 31 percent agriculture.
Monitoring in July 1997, showed Midway Run was warmer in the day and cooler at night than Dorsey Run. While temperatures often fluctuated only 5 degrees in Dorsey run, they sometimes fluctuated 14 degrees in Midway Run, subjecting stream dwellers to far more stress.
“The comparison between these two watersheds demonstrates how the loss of natural land cover can negatively affect water quality and potentially impair aquatic life, even though no regulatory criteria are exceeded,” the survey concluded.
Reptiles & Amphibians
The survey collected 45 species of reptiles and amphibians in and near streams. In many cases, especially for salamanders, results show that their populations are closely related to land use within a watershed.
Statewide, the number of aquatic salamander species decreased with increasing urban land use than 25 percent impervious surface — indicating a loss of biodiversity. A similar negative relationship was observed between aquatic salamanders and increasing agricultural land use statewide.
But aquatic salamander species diversity increased with forest land use statewide. In fact, four species were never found in watersheds with more than 3 percent impervious surface.
Aquatic salamanders appear to be an especially useful indicator for stream quality, especially for streams too small to contain fish populations.
The survey is considering the possibility of developing an IBI for reptiles and amphibians in the future.
The survey found that physical habitat quality was directly related to forest buffers: The wider the buffer, the better the physical habitat score. Also, the abundance of amphibians increased with forest buffer width.
Fish IBI scores increased with instream habitat structure and maximum depth while benthic IBI scores were strongly related to riffle quality. Both were correlated with riparian buffer width.
About 40 percent of stream miles had at least a 50 meter riparian buffer, while 32 percent had buffers of less than 50 meters. Areas with the least buffering were in the middle Potomac and the Patapsco, which include portions of the Baltimore-Washington corridor.
Nonnative Species & Biodiversity Loss
Of the 83 fish species found by the survey in freshwater streams, 19 were not native to Maryland. While they did not account for a large percentage of the total fish population, they were found in 46 percent of stream miles. Seven nonnative species are game fish, and some — largemouth bass, bluegill and pumpkinseed — are the most widespread, living in all 17 drainage basins. The presence of nonnative species is a concern because they can alter stream ecology and replace native fish.
The survey found that several fish species were very rare. Ten species were found in less than 0.5 percent of the state’s streams. The survey estimated that there were fewer than 600 individuals each of three species: the rainbow darter, banded darter and stripeback darter. The survey found that five species were more rare than previously thought, and are now being considered for listing under the state’s Heritage Program, which would offer them further protection.
Maryland Stream Video
The DNR has produced a 30-minute video that overviews the types of streams found in Maryland and major issues facing its waterways. “Maryland Streams: An Undiscovered Realm,” offers a closeup look at many dynamic and bizarre stream dwellers. Copies of the video are available for $10, (including shipping and handling) from the MD DNR Monitoring and Non-Tidal Assessment Division, Tawes State Office Building, C-2, Annapolis, MD 21401