A new federal study shows less pollution in most New Jersey streams, but salt levels rising in some places.

The study by the U.S. Geological Survey found that levels of two key pollutants, nitrogen and phosphorus, either declined or stayed about the same over the last four decades in most of the 28 streams surveyed. But it also found salt levels rose, probably due to the increasing use of road salt during the winter that washes into waterways.

The New Jersey Department of Environmental Protection commissioned the federal agency to study long-term trends. The findings were consistent with other studies done in the Northeastern U.S.

Bob Martin, department commissioner, said the study was the largest ever done on nutrient trends in the state's streams. Contributing to the decline in pollutants, he said, were better management of stormwater at the local level and upgrades to wastewater treatment plants beginning in the 1980s and early 1990s, with regional plants replacing smaller local plants.

New Jersey has the strictest standards in the nation for phosphorus in fertilizer. Nitrogen and phosphorus are essential for plant and animal life, but high levels in water can cause algae blooms, drinking water concerns and low levels of dissolved oxygen, which harms marine life.

Tim Dillingham, executive director of the American Littoral Society who was not associated with the study, said two streams showed an increase in nitrogen levels where significant development is taking place: the Toms River in Ocean County, and the Cohansey River in Upper Deerfield Township in Cumberland County.

"While it is great news that there may be decreasing trends overall, the study reinforces earlier work pointing to increases in nitrogen into Barnegat Bay," he said. "The fact that pollution continues to increase near development shows we need to do more to control it and the overdevelopment of our watersheds that is the root cause. The work is not done."

Many environmentalists say the state needs to put a daily limit on how much pollution is allowed to wash into waterways, including Barnegat Bay.

Cindy Zipf, executive director of Clean Ocean Action, said the continued lack of control over run-off pollution is a serious problem.

"Sure there has been some improvement compared to the bad old days when small, outdated primary treatment plants were discharging into the waters throughout the state, but we should expect that given the investment of billions of dollars," she said. "Since then, however—especially post-2011— the trend is not looking good."

Her group cited federal figures showing that in 2008, designated public uses of waterway regions were fully attainable in 37 out of 480 areas, about 7.7 percent. By 2014, that figure had fallen to 14 of 958 areas, about 1.5 percent.

Bob Hirsch, a USGS scientist who co-authored the report, said researchers investigated salinity levels at four sites and found the levels of salt had nearly doubled over the last 30 years.

Pollution levels continued to improve throughout the study's 40-year span, but the greatest progress came in the first three decades. Salt levels, on the other hand, showed a steep climb from 2000 to 2011.

Department spokesman Larry Hajna said the agency has issued guidelines for municipalities to follow when it snows. They are directed to stockpile the snow plowed from the roads, which may contain road salt and dirt, in upland areas that are as far away as possible from waterways and storm basins.

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