“Few if any turtle eggs hatch,” said Cramer, a state-licensed turtle rehabilitator, who looks after dozens of injured and sick turtles that park rangers bring to her Upper West Side apartment. Fertilizers in the water affect the turtles’ calcium intake, reducing the calcium content in their eggshells, she said.

But Matthew Brown, soil and water lab coordinator for the Central Park Conservancy, a public-private partnership that administers the park, said the use of fertilizers has “no effect on turtles” and pointed to “an abundance of turtles” in the park.

The conservancy’s woodland manager, Regina Alvarez, said the park had planted aquatic and wetland plants close to bodies of water that can filter runoff from lawns. Every month, Alvarez meets with naturalist groups to discuss wildlife needs. 

The conservancy tests for dissolved oxygen, pH levels, temperature and clarity in the park’s waterways, but not specifically for pesticides or fertilizers, said Brown, because of the expense associated with such tests.

In June 2004, the U.S. Environmental Protection Agency issued an award to New York City’s Department of Parks and Recreation for cutting down on the use of chemicals, including in Central Park.

The park reduced the use of active-ingredient herbicides from 70 pounds in 2000 to 7.5 pounds in 2003. More organic, non-toxic pest control products are now used. The park has also cut down on synthetic fertilizers, using organic versions that may have less of an impact on bodies of water, according to the EPA.

Apart from chemicals, changes in the turtle population have come about because of other factors too, said Cramer, who is also head of rehabilitation and education for the New York Turtle and Tortoise Society.

Snapping turtles, red-eared sliders and some painted turtles have replaced spotted, mud, musk box and wood turtles in the population. While snapping turtles have been beneficial because they help keep the water clean through bottom feeding, sliders are “pretty aggressive” and more likely to survive because they are faster eaters.

Turtles are generally found at Turtle Pond close to Belvedere Castle, the pond in the southern part of the park and Harlem Meer in the northern part.

The biggest source of non-native turtles in the park, Cramer explained, are Buddhist ceremonies in which worshippers will acquire turtles destined for the pot in Chinatown – sometimes a dozen at a time – and recite blessings before releasing them into the park.

One turtle in Cramer’s care – she is looking after 25 turtles in total and owns 15 more – is a 30-year-old spine-backed turtle named Princess.

Princess, who usually lives in a tank in Belvedere Castle, was moved to Cramer’s apartment while Christo’s “The Gates” were in the park because a stall was set up close to her tank.

Turtles are “personable,” said Kramer and interact in interesting ways. She likes watching her two diamond-backed terrapins, Click and Clack, wake each other up in the mornings.

Sediment samples taken from the bottom of the Central Park Lake are yielding a detailed and groundbreaking chronology of air pollution in New York City from the 1860s.

Geochemists, led by Steve Chillrud of Columbia University’s Lamont-Doherty Earth Observatory and Richard Bopp of Rennselaer Polytechnic Institute, found the concentration of metals in New York’s atmosphere coincided with peak years for solid waste incineration in the city. 

“Urban lakes act like big bucket collectors for atmospheric fallout,” said Chillrud.

The latest research, conducted by Beizhan Yan from the Idaho National Laboratory, found levels of harmful PAHs - polycyclic aromatic hydrocarbons – began declining in the 1970s. This was later than previously thought and linked mainly to the oil crisis of the 1970s and the introduction of catalytic converters, said Yan.

The researchers collected cores of up to 50 centimeters in depth from the bottom of the lake in January 1996. They chose the lake because it has never been entirely dredged and its layers of sediment are intact.

Check out the pop-ups below to view the scientists’ findings for lead, tin and zinc pollution over the decades.