PALEOECOLOGY 442
A long-term perspective on ecology and
environmental issues
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Tree
Rings | Lake
Sediments | Ancient
Environments | Mass
Extinctions
In Paleo 442 we spend a lot of time developing truly long-term perspectives on environmental changes. Few ecological studies last more than 3 years, which often makes it difficult to know what the "normal" state of a lake is, how it's changed, and what may be causing the changes. Fortunately, much longer ecological datasets can be obtained through paleoecological studies. In lab, we collect sediment cores from local waters and analyze the organic content and microfossils preserved in them to study if, how, and when factors such as acidification, sewage, fish stocking, rotenone treatment, fires, logging, or road salt have impacted Adirondack lakes.
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Click here for larger view of the picture Jason Fitzpatrick and Nate Reed practice gravity coring through the frozen surface of Lower Saint Regis Lake (winter, 2001); the Paul Smith's College campus lies a few hundred yards to the right. They later showshoed up into the High Peaks in their study of the relative impacts of acid rain and bog development on Avalanche Lake. |
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Click here for larger view of the picture Unsightly, potentially toxic phytoplankton "blooms" are increasingly common in many Adirondack lakes, but they get less media attention than acid rain does. Paul Smith's College students and faculty are among the very few who study the long-term history and causes of such blooms in the region. |
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Click here for larger view of the picture Black Pond, a few miles from campus, bloomed with toxic cyanobacteria (mostly Anabaena) in 1990. The cause was a mystery, because the watershed is virtually undeveloped. At the request of the Department of Environmental Conservation and Adirondack Park Agency, several sediment cores were collected from the lake by Curt and students. They yielded some important clues, outlined below. |
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Click here for larger view of the picture The tops of the sediment cores were black and highly organic, suggesting low-oxygen conditions typical of scummy eutrophic lakes, and were loaded with Asterionella formosa (shown here) a microscopic, silica-encased alga (diatom) that often appears in polluted lakes. The lower, older sediments, were brown and nearly free of Asterionella. Lead-210 and Cesium-137 dates placed the change in the 1950's. |
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Click here for larger view of the picture Discovering the date of onset of the blooms pointed to fisheries management practices as the most likely cause. One aspect of that management activity is "reclamation", in which rotenone is used to kill resident fish in order to make way for the stocking of more "desirable" fish. The DEC has reclaimed Black Pond five times since 1957 to kill off non-native perch and shiners that outcompete brook trout; this photo shows rotenone being applied in the latest reclamation, in 1997. |
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Click here for larger view of the picture The fish killed during reclamation rot in the lake; could this somehow fertilize the lake, perhaps causing algae blooms later on when weather or other conditions release the fishy nutrients stored in the bottom sediments? Most fishery biologists believe that's unlikely, but we are continuing to investigate the possibility. |
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Click here for larger view of the picture Another possible trigger for blooms may be "top-down" changes in the food chain caused by manipulating the fish community. If invasive fish or small, stocked trout fingerlings eat too many zooplankton (this is a photo of a tiny copepod) that graze on algae, the algae might become increasingly abundant. Perch were present in Black Pond by 1957 but we don't know when they arrived, and stocking began right after the first reclamation, so it's hard to tell which factor played the main role in changing Black Pond's water quality in the 1950's. |
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Click here for larger view of the picture Paleo studies by PSC faculty and students have revealed similar changes in other Adirondack lakes as well, suggesting that the plankton communities of many of our mid-elevation waters have become more productive in recent decades. Here is Asterionella ralfsii in sediments collected from Bear Pond by Nicole Cook and Jeff Dowd (Spring, 2001); it increased since the mid-1900's, perhaps due to the combined effects of acidification and fishery management. Could the proposed liming of Bear Pond free such algae from inhibiting acidity and thus trigger blooms in a lake once widely renowned for its unusual clarity? |
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