Multi-proxy paleolimnological assessment of biogeochemical versus food web controls on the trophic states of two shallow,mesotrophic lakes |
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| Authors: | Bjorn A Lake Courtney R Wigdahl Kristin E Strock Jasmine E Saros Aria Amirbahman |
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| Institution: | (1) Department of Civil and Environmental Engineering, University of Maine, 5711 Boardman Hall, Orono, ME 04469, USA;(2) School of Biology and Ecology, University of Maine, Orono, ME 04469, USA; |
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| Abstract: | The frequency of nuisance algal blooms has been increasing during the last two decades in the shallow, headwater East Pond
(Smithfield, Maine, USA). Meanwhile, the hydrologically linked North Pond has not experienced an increase in algal blooms,
despite similar morphometry and higher external nutrient loads. Possible explanations for this difference include stronger
trophic cascade effects from planktivorous white perch (Morone americana) in East Pond as well as differences in phosphorus (P) release from the sediments of these two lakes. We conducted a paleolimnological
investigation of these two lakes to assess whether sedimentary evidence supported trophic cascade effects based on cladoceran
ephippia size, diatom fossils, and fossil pigments or biogeochemical controls based on potential sedimentary P release as
the primary driver of these increased algal blooms in East Pond. At the time of white perch introduction (~1930–1950), ephippia
size increases in East Pond, although no changes are observed in either diatom abundance or trends in the algal pigments.
Instead, algal pigments increase in recent decades (~1980 to present) along with an increase in diatom taxa with higher TP
optima These results suggest that predation by white perch is not resulting in top-down effects on algal abundance in East
Pond, as predicted by the trophic cascade hypothesis. While the P content of sediments from both lakes is relatively equal,
the releasable P in the top 10 cm of sediment in East Pond constitutes a greater percentage of the P extracted. Also, North
Pond sediments exhibit a greater capacity to permanently bury P via the mechanisms of sorption to Al(OH)3(s) and a slower mineralization of organic P compounds. The results of this investigation suggest that the ultimate driver of
the recent algal blooms in East Pond is internal P release from the sediments instead of trophic cascade effects. |
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