Response of lake water nutrient condition to anthropogenic activities from 1871 to 2013 in the Jiuzhaigou World Natural Heritage Site, China

Over the past century, lake degradation has increased around the world. Jiuzhaigou World Natural Heritage Site in southwestern China has been experiencing water nutrient enrichment, accelerated swamping, and algal biomass increases. These problems are likely associated with enhanced local anthropogenic activities over the past decades. In this study, radioactivities of 137 Cs and 210 Pb, diatoms, and nutrient accumulation rates in a lake sediment core from Tiger Lake in Jiuzhaigou World Natural Heritage Site were used as proxies to reconstruct a > 100-year record of environmental change to understand the extent and temporal variability of anthropogenic effects on lake water nutrients. Diatom communities reveal four distinct phases, relating to documented local human activities including (a) Primitive agriculture from 1871 to the mid-1930s, (b) Opium cultivation—logging from the mid-1930s to the mid-1970s, (c) Large-scale logging—the beginning of tourism from the mid-1970s to the early 1990s, and (d) Tourism development from the early 1990s to 2013. Nutrients in the lake (including total organic carbon, total nitrogen, and total phosphorus) steadily increased from 1871 until the late 1990s, declined from the late 1990s to the mid-2000s, and increased rapidly after the mid-2000s. Our data suggest that (a) Opium cultivation, deforestation, and tourism development led to the increase of lake nutrients and primary productivity, (b) Ecological protection measures taken from 1999 to 2004 effectively controlled water pollution, and (c) Post-2005 intensification of tourism further accelerated water quality deterioration. Additional monitoring and mitigation strategies are needed to further reduce nutrient input. Global studies suggest that while water quality of lakes in protected area is better than that of other lakes, care is still required to ensure that tourism activities do not inadvertently increase lake water nutrients.