CULTURAL EUTROPHICATION CAUSES MODIFICATION OF NUTRIENT CYCLES IN THE NEW YORK FINGER LAKES

We used a multi-proxy approach to identify the onset of increased anthropogenic eutrophication and its impacts on nutrient cycling in seven of the New York Finger Lakes over the last century. Historical and neolimnological records reveal significant shifts in land use, population, and lake water quality (e.g., nutrient composition, chlorophyll-a) since 1910. Today, these lakes span a size, nutrient, and trophic gradient: three small, shallow, meso- to eutrophic lakes (Conesus Lake, Canadice Lake, Honeoye Lake) and four large, deep, meso- to oligotrophic lakes (Canandaigua Lake, Seneca Lake, Cayuga Lake, Owasco Lake). One sediment core from the profundal zone of each lake was analyzed for their wt. % organic carbon (C_org), wt. % nitrogen (N), atomic ratio of organic carbon to nitrogen (C/N) abundance, wt. % biogenic silica (bSi), the stable carbon isotopic composition of bulk organic matter (δ¹³C_org), and the stable carbon isotopic composition of bulk organic matter (δ¹⁵N) to reconstruct shifts in nutrient availability and paleoproductivity.

Almost all of of the significant stratigraphic shifts in wt. % C_org, wt. % N, wt. % bSi, δ¹³C_org, and δ¹⁵N occur post-World War II. All seven lakes record atomic C/N ratios between 8 and 9, suggesting most organic matter preserved in the profundal sediment is algal. These lakes also record a decline in δ¹³C_org beginning during the 1940s followed by a rapid reversal during the 1990s. The decline in δ¹³C_org was coincident with a rapid rise in in wt. % C_org and wt. % N in all the lakes and wt. % bSi in the smaller, shallower lakes. The wt. % bSi records in the larger, deeper lakes are more complicated. For example, the wt. % bSi in Canandaigua Lake increased from the 1940s until the mid-1990s, but then declined while the wt. %C_org and wt. %N both increased upcore since 1990. In contrast, the wt. % bSi in Seneca Lake was nearly constant over the last century despite increases in wt. %C_org and wt. %N. These nutrient and paleoproductivity indicators suggest these lakes responded to a rise in nitrogen- and phosphorous-loading from sewage and agricultural runoff post-WWII. Biologically-induced silica depletion may have occurred in the larger lakes following the post-WWII peak in primary productivity.