The Susquehanna is one of the oldest existing rivers in the world and the largest river on the East coast of the United States. Twenty thousand years ago during the last Ice Age, sea level was about 330 ft. lower than it is today. At that time, the Susquehanna flowed from the edge of the glacial ice cap in what is now Northern Central Pennsylvania down to the Atlantic Ocean. All of the waterways in what is now the Chesapeake bay watershed flowed into the Susquehanna and carved mountains in the process. As the Earth warmed and sea level rose, the Atlantic ocean filled in the Susquehanna’s valley floor, forming the Chesapeake Bay and the tidal rivers on its Western and Eastern shores. The Susquehanna’s large watershed brings the pollution that flows into Pennsylvania rivers and streams to Chesapeake Bay. On Sunday, September 29th, we paddled seven miles down the Mighty Susquehanna, and what we saw and learned proved to be very interesting.
Harrisburg, Pennsylvania is town situated nicely on the lower middle region of the Susquehanna. It is the section of the river where the Appalachian mountains begin, namely Blue Mountain. Since the town of Harrisburg is so close to the mountains, there is very little agriculture due to the sloping topography and increase in elevation. It is because of this that our canoe trip down the susquehanna starting north of Harrisburg was so great. The water clarity was surreal in comparison to the Chester river, as we could always see the bottom even when it was around eight feet deep. The current moved swiftly in the narrower stretches (~1/4-1/2 mile wide) and slower in the broader areas (~3/4-1 mile wide). Think of holding your thumb over a water hose to change the way water the water comes out. if your thumb is partially covering the spout, the water moves faster (narrow river) than if you take your thumb off completely (wide river). When water moves fast over portions of the river, minimal sediment is able to settle and the rocks on the bottom are very clean looking. In the wider, slower parts of the river, sediment can settle because it isn’t being pushed along by the same amount of force. Through a 500 ft. stretch of the river, we saw the bottom go from squeaky clean to layered with sediment and a film of algae. Why? Because in that 500 ft. span the river nearly doubled in width. The river got much wider because we were getting further away from the mountains and paddling into flatter areas where the waterway could expand over time.
I had the great fortune of having Dr. Doug Levin as a Canoe buddy this trip. As the Geologist of the group, Doug pointed out many changes in the landscape that would have otherwise been paddled past. For example, besides the changes in what was on the rocks, the rocks themselves also changed shape. When we paddled through Blue mountain, the rocks were very angular and Mafic (darkly colored, some with red/orange coloration from the presence of iron). The sharp edged, boxy looking rocks lay upon large masses of rock that were weathered through the process of lineation. In this case, lineation occurred through earthquakes caused by techtonic plate subduction several thousands of years ago. These earthquakes caused the rock to compress and form lines across the rock perpendicular to the river itself. We saw lineation along the course of the river very often, but as we got further away from the mountains the rocks became smaller and rounded and there was less lineation present. The majority of the rounded rocks were smaller than the angular rocks, and they laid on top of sandy, coarse grained sediment. The rounded rocks showed that they had been weather over time and had moved downstream from the mountain whereas the angular rocks indicated that they had more recently broken off from larger rocks and were early on in the weathering process. The sediment was a lighter color than further upstream, indicating that it was more mature and older than the darker sediment upstream. Moral of the story, having Dr. Levin in the canoe with you is a very educational experience. In this respect, the trip was more than a serene, casual float down a magnificent river, because I also gained more of a practical understanding of how the geology of the river has been shaped over time.
South of Harrisburg is Lancaster county, PA. In Lancaster, the local economy is heavily based in agriculture and is thus a major contributor of sedimentary pollution as well as nitrogen, phosphorus, and waste water treatment plant effluent, all of which settle into the 14 mile sediment pond behind the Conowingo Dam in Northern Maryland. This dam is very controversial for several reasons. It is located in Maryland but provides hydro electric power to Pennsylvania. Many people think the dam is a great thing because it provides renewable energy AND keeps tons of sediment from going into the bay. However, during major rain events, the dam gates are opened to avoid an overflow or catastrophic surge, and sediment pollution comes pouring into the lower Susquehanna through Maryland and eventually into the Chesapeake bay. It is also a problem for Marylanders in terms of policy because they have to comply with TMDL (total maximum daily load) allowances and water conservation plans made by the government. This is hard to do because when a major weather event occurs all the pollution that comes down from Conowingo makes their efforts all but obsolete.
The Susquehanna provides about half of the fresh water for Chesapeake bay, but is so polluted by runoff and other waste that it poses a threat to the health of the bay as a whole. Conowingo stops much of this pollution and sediment but only from the Susquehanna. Other rivers around the bay, especially on the Eastern shore where agriculture is a major part of the economy, runoff and sedimentation are having adverse effects on the body of the bay. Although waste going into the bay eventually makes it to the Atlantic, the rate of sedimentation is higher than the rate the sediment and waste is exiting the bay, which is mainly due to tidal influences. When the tide goes in and back out repeatedly, the pollutants in the water don’t make it very far, all the while more pollutants are being put into the system. What I learned from our paddle down the Susquehanna is that it’s not the fault of the river for the environmental crisis and polluted waters, the fault lies in the hands of the people around the waterways of Chesapeake bay. In the case of the Susquehanna river, agriculture and rainwater runoff among other waste influences are the reason for the immense water problems the area faces today.