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Salty freshwater streams?!

posted Dec 22, 2013, 6:11 AM by   [ updated Dec 22, 2013, 7:31 AM ]
Winter brings on the use of salty road treatments for safety. Recent research shows that rivers and streams are saltier as a result. This may explain why fewer River Herring now spawn in Mattawoman's upstream reaches.

A summary of the new research by the U.S. Geological Survey is here.

The scientists find that about 35 billion pounds of salt are applied annually in the United States. As a result, streams get saltier over the winter, and some never fully recover over the summer.

What might this mean for the Chesapeake Bay? Let's take a look at Mattawoman Creek. In the past, non-tidal Mattawoman river became less salty as you moved upstream, just like most other freshwater streams. But research by the Maryland Fisheries Service finds that non-tidal Mattawoman river becomes more salty as you head upstream!

The change the direction of the "salinity gradient" may explain why spawning River Herring have plummeted in the upstream reaches of the river, where before they were numerous.  River Herring (not to be confused with Atlantic Herring), live in the ocean but return to freshwater to spawn.  Mattawoman is famous as a spawning ground and nursery for these fish.

In our region, River Herring begin arriving in early March, when the accumulation of salt over the winter is expected to be high.

In the Mattawoman, the loss in upstream use by River Herring far exceeds the more modest decline near "head of tide" (where the tidal influence of the estuary ends).  We know this because of annual measurements of fish-egg densities conducted by MWS volunteers in collaboration with the Maryland Fisheries Service.

Road salt might explain why the River Herring decide to stop swimming upstream. Many tributaries to the Chesapeake Bay are also subject to increasing use of winter road-treatments as the amount of highway and parking-lot pavement increases. The Bay was once a breadbasket for Shad and River Herring, but numbers have sunk to just a few percent of the past.

Unless a change in where and how we grow, the outlook appears bleak to reverse the trend. The amount of pavement and rooftops is increasing five times faster than population, according to the Chesapeak Bay Program.  A just-released report by the Metropolitan Council of Governments projects that by 2040, vehicle miles traveled will increase by 24%. The miles of congestion will increase by a whopping 71%. So while the fish suffer, so do we.

A win-win would be for local governments to take seriously smart growth concepts in their growth plans. Unfortunately, Charles County, where most of the runoff to Mattawoman comes from, is doing just the opposite. Please check out and sign the petition to local elected officials.

More information on the USGS study is here.