Print PageGloeotrichia echinulata, a colonial, nitrogen-fixing cyanobacterium, has recently been noticed in oligotrophic and mesotrophic lakes in the northeastern United States, raising concerns about water quality and ecosystem function. Since it has a meroplanktonic life cycle, germinating on the sediments and then dividing in the water column, it has the capacity to transport sediment phosphorus into the water column where it can be released through leakage or when colonies are grazed. Hence, G. echinulata could be an autochthonous driver of eutrophication through both nitrogen fixation and phosphorus additions. Alternatively, the recent increase in G. echinulata could be largely driven by allochthonous nutrient loading due to changes in land use in the watershed. We used paleoecological analyses of algal pigments, dead parent colonies (akinete packages) of G. echinulata, and pollen from surface cores from three lakes in the northeastern United States—Long Pond (Maine), Pleasant Lake (Maine), and Lake Sunapee (New Hampshire)—to examine the evidence supporting hypotheses of autochthonous and allochthonous drivers of ecosystem change.
Results/Conclusions
Paleorecords revealed different histories of watershed disturbance, lake eutrophication, and the abundance of G. echinulata. The record from Long Pond supported the hypothesis that G. echinulata facilitates lake eutrophication. G. echinulata was present throughout the record, including prior to land clearance by European settlers, but it increased substantially beginning between 1925 and 1970. This coincided with increases in the abundance of cryptophytes, chlorophytes, and cyanobacteria but appeared, in recent decades of water quality monitoring, decoupled from lake phosphorus concentrations. In Pleasant Lake and Lake Sunapee, G. echinulata had its maximum abundance around the middle-1800s, a time of agricultural activity in these watersheds, while more recent sediment contained lower abundances of G. echinulata. In Lake Sunapee, the pigment record also suggested a late 20th century decrease in algal populations, but the timing was offset from the G. echinulata decrease. The timing of the maximum G. echinulata abundance and its decoupling from pigment records in Lake Sunapee provided more support for the hypothesis that G. echinulata was responsive to watershed disturbance than one of leading autochthonous change. Despite apparently coincident modern increases in G. echinulata in lakes regionally, no single driving mechanism explains the current abundance of G. echinulata in low-nutrient systems.
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