Data from: Tracking the history and ecological changes of rising double-crested cormorant populations using pond sediments from islands in eastern Lake Ontario

In the Laurentian Great Lakes region, the double-crested cormorant
(Phalacrocorax auritus) has seen a thousand-fold population increase in
recent decades. These large colonies of birds now often conflict with
socioeconomic interests, particularly due to perceived competition with
fisheries and the destruction of terrestrial vegetation in nesting
habitats. Here we use dated sediment cores from ponds on islands in
eastern Lake Ontario that receive waste inputs from dense colonies of
cormorants and ring-billed gulls (Larus delawarensis) to chronicle the
population rise of these species and assess their long-term ecological
impacts. Modern water chemistry sampling from these sites reveals
drastically elevated nutrient and major ion concentrations compared to
reference ponds not influenced by waterbirds. Geochemical tracers in dated
sediment cores, particularly δ15N and chlorophyll-a concentrations, track
waterbird influences over time. Fossil diatom assemblages were dominated
by species tolerant of hyper-eutrophic and polluted systems, which is in
marked contrast to assemblages in reference sites. In addition to
establishing long-term ecological impacts, this multi-proxy
paleoecological approach can be used to determine whether islands of
concern have been long-term nesting sites or were only recently colonized
by cormorant or ring-billed gull populations across the Great Lakes,
facilitating informed management decisions about controversial culling
programs.