A new report from the New Hampshire Department of Environmental Services is raising concerns about how development and warming summer temperatures are impacting water quality in the state’s rivers and streams.
Researchers looked at over 30 years of data and 40 sampling sites to draw conclusions about short- and long-term water quality trends in the state. They reviewed different water quality indicators, including pH levels, specific conductance and water temperature — all factors in measuring the level of stress a particular water body is under.
The researchers found that pH levels — a measure of acidity that can be impacted by industrial processes — are improving at several sites. Of the 40 sites sampled for pH levels, 30 presented an improving trend compared to 10 years ago.
David Neils, administrator of the state Watershed Management Bureau, attributes the improvement to “a decades-long curtailment of atmospheric emissions of the compounds that contribute to acid rain,” he said in an email. Still, recovering water bodies is a slow process, he added.
The report also identified some potentially concerning trends.
Specific conductance measures water’s ability to conduct electricity, and higher levels of this indicator can point to the presence of harmful compounds such as road salts, fertilizers and stormwater discharge.
That measure was “high at over one-third of river and stream trend monitoring sites relative to statewide data . . . and is worsening at fourteen sites,” reads the report.
Joshua Buonpane, an aquatic biologist with the Department of Environmental Services who led the research, said the work found a direct link between higher specific conductance and development in an area. The levels of specific conductance at rivers and streams located in more developed areas were up to six times higher than levels at sites in low development areas.
While those levels still don’t exceed water quality standards, Buonpane said it’s worrying that a worsening trend was widely identified.
“It's not just the sites that are already at the high end of the range that are increasing even more. We have sites across the whole range,” he said.
The report also looked at water temperature at the sites. All of the 28 sites analyzed saw warmer seven-day rolling water temperature averages compared to an earlier 2019 report, which included data from 2012 to 2017. In that report, averages were right at or below temperature benchmarks.
Warmer waters can cause immediate impacts to ecosystems, including the migration or disappearance of animal and plant species.
But more data is needed to establish a warming trend because of high variability in temperatures recorded year to year, Buonpane said. He related that variability to New Hampshire’s weather.
“We're seeing a lot of variability with these really dry years and with these wet years, which I think is in some ways obscuring, perhaps, the trends,” he said.
“I think that's an interesting story that we're hoping to continue to disentangle in future publications,” Buonpane said.
