A new study has shed light on the environmental history of Nahuel Huapi, the oldest national park in Argentina. The mountainous glacial region in northern Patagonia is vast, spanning two million acres, yet it has remained relatively unstudied, and little of its ecological history is understood. A study published on August 10 in ScienceDirect has revealed a window into the complex history of glacial Lake Perito Moreno Oeste in Nahuel Huapi, using lake sediments to look back through time.
The research team, led by the Argentinian scientist Natalia Williams, investigated the glacial lake’s history by digging deep into the lake’s sediment. Williams and her team hoped to better understand the environmental factors like temperature and human activities influencing the lake’s ecology over the past 700 years, and had the help of a small aquatic species known as Chironomidae. Also known as midges, Chironomidae are a type of insect found on every continent including Antarctica.
Across the globe, Chironomidae are abundant and can be used to understand the health and condition of water ecosystems. Unlike other species of their size, Chironomidae leave well-defined remains in lake sediments that allow researchers to study them like fossils. There are over 4,000 distinct Chironomidae species, which thrive in different environment conditions–some prefer warmer water while others prefer cold. By examining the number and species of past Chironomidae, the researchers can understand the health, composition, and temperature of the ecosystem through time.
The team collected the proxy data by dropping a 43 cm-long hollow pipe, known as an LL, into the bottom of the lake at Llao-Llao Bay—the deepest point of the lake at 20 meters. When the core was dropped, it filled with sediment and trapped preserved organisms. When the pipe was pulled to shore, it contained the layers of sediment which had built up over time, providing a chronological history of the lake. The researchers were then able to analyze the sediment through photographs, chemical tests, and observations of the sediment and individual midges once they cut the pipe in half.
Within the 43 cm-long core, a total of 1594 Chironomidae head remains were identified, and their depth within the core informed the researchers about the time of the deposition, with earlier organisms found deeper in the core.
There were higher numbers of warm water species found at the surface layers of the core, representing the more recent history around 1900. Their high abundance within the core corresponded to a period of time with higher temperatures and increasing human presence in Patagonia. The first buildings within the national park near Lake Perito Moreno were constructed in 1937, and the isolated glacier lake quickly became influenced by pollution, rising temperatures, the introduction of fish species, and the construction of roads.
Though the lake was free of human influence until the beginning of the 1900s, the ecology of the lake quickly changed in response to human presence in the park. As roads were built and new species were introduced, the lake’s oxygen levels increased beyond healthy levels and allowed the explosion of the Chironomidae population. When the sediment core showed high levels of the species’ remains, the researchers determined that the lake was less healthy than the period prior to human influence, experiencing an ecological imbalance that prevented other aquatic species from thriving.
In order to understand the full extent of human impacts on glacial environments, the history of a region must be taken into account. While it is not possible to go back in time to observe the past, species like those within the Chrionomidae give scientists the chance understand history more deeply.