Last Saturday at 5:26 p.m. the United States Geological Survey (USGS) river monitor at Harrisburg recorded a water temperature of 33.5 degrees Celsius which equates to 92.3 degrees Fahrenheit. Sunday morning the same monitor recorded a dissolved oxygen level of 4.9 milligrams per liter (mg/L).
Studies done by the USGS in cooperation with the Fish and Boat Commission, the Department of Environmental Protection (DEP) and the Susquehanna River Basin Commission over the last several years have demonstrated that very warm water and associated low dissolved oxygen levels between May 1 and July 31 are sickening and killing bass born in the spring. The warmer the water, the less dissolved oxygen it can hold. The Environmental Protection Agency has determined that early life stage fish need a dissolved oxygen level of 5 mg/L to survive. Young bass hang out near the shore in shallow, slow-moving water. Those areas are warmer and have lower dissolved oxygen levels than the water in the main channel.
In 2008 at a monitoring station at Clemson Island, upstream from Harrisburg, dissolved oxygen levels dropped below 5 mg/L during 31 of the 92 days of the May 1 to July 31 – a critical period for the survival of newly-born bass. On one day in 2008, dissolved oxygen levels remained below 5 mg/L for more than eight hours. The young fish during that time were essentially like a puppy left in a car with the windows up on a 95 degree day.
The USGS study compared the Susquehanna’s water temperatures and dissolved oxygen levels to those in Pennsylvania’s other big warm water rivers – the Delaware and the Allegheny. It found that the Susquehanna was consistently warmer and had consistently lower dissolved oxygen levels than the other two rivers.
One key factor in dissolved oxygen levels is the amount of plant nutrients – nitrogen and phosphorus – present in the water. High levels of those nutrients causes growth surges in water plants and algae. During the daylight hours, those plants produce oxygen, but when the sun goes down, they suck oxygen out of the water. Over the last several years there have been big blooms of stringy algae in the Susquehanna.
Thanks to the Chesapeake Bay clean up, upgrades of sewage plants and better farming practices, total levels of nutrients have been coming down in the Susquehanna over the last decade. So, what’s causing big algae and plant blooms in the river? Another USGS study identified a potential culprit – dissolved inorganic phosphorus which has been rising dramatically in the river for more than a decade. The rise in levels of dissolved inorganic phosphorus has coincided with big algae blooms.
A likely source of the dissolved inorganic phosphorus is manure spread on fields. Farmers have been spreading manure on some fields for so long that they are becoming super-saturated with phosphorus. When farmers spread on more manure on phosphorus-saturated fields, it simply runs off into the nearest waterway.
The Chesapeake Bay clean up plan is designed to further bring down the levels of total phosphorus going into the river, but it does not address the new problem of dissolved inorganic phosphorus. That is why it is so important for Pennsylvania to develop a specific cleanup plan that specifically targets the Susquehanna’s pollution problems. The Pennsylvania Fish and Boat Commission and environmental organizations have asked DEP to officially declare the river polluted and begin the process to develop a plan to cut the pollution that’s making the river and the bass sick. DEP secretary Michael Krancer has refused the request saying we don’t know what’s killing the bass.
Well, yes we do - it's warming water and increasing levels of pollutants like dissolved inorganic phosphorus. The warming water is directly linked to climate change and that's a long-term problem in need of urgent action. That makes it all the more urgent to cut the amount of dissolved inorganic phosphorus getting into the river by seriously addressing the likely source - over application of manure on farmers' fields.
There is more than enough information for DEP to take the step of officially acknowledging the river is polluted and no longer can support the survival of young bass. This summer the sick Susquehanna is running a fever. We need to take action to bring the fever down and save the Susquehanna.