Enhanced N input to Lake Dianchi Basin from 1980 to 2010: Drivers and consequences Wei Gao a , Robert W. Howarth b , Dennis P. Swaney b , Bongghi Hong b , Huai Cheng Guo a, ⁎ a College of Environmental Sciences and Engineering, The Key Laboratory of Water and Sediment Sciences, Ministry of Education, Peking University, 100871 Beijing, China b Department of Ecology and Evolutionary Biology, Cornell University, 14850 Ithaca, NY, USA HIGHLIGHTS • Net anthropogenic N inputs (NANIs) to Lake Dianchi drainage basin from 1980 to 2010 were estimated. • The rise of NANI was mainly due to fertilizer N application as well as human food and animal feed imports. • Human diet rather than human population is the single largest driver of NANI change. • Nitrogen level in the lake is able to respond significantly to N inputs to the drainage basin. abstract article info Article history: Received 29 May 2014 Received in revised form 2 October 2014 Accepted 5 October 2014 Available online 18 October 2014 Editor: Simon James Pollard Keywords: Human impact Nitrogen Nutrient Diet change Water quality Lake Due to a rapid increase in human population and development of neighborhood economy over the last few decades, nitrogen (N) and other nutrient inputs in Lake Dianchi drainage basin have increased dramatically, changing the lake's trophic classification from oligotrophic to eutrophic. Although human activities are consid- ered as main causes for the degradation of water quality in the lake, a numerical analysis of the share of the effect of different anthropogenic factors is still largely unexplored. We use the net anthropogenic N input (NANI) method to estimate human-induced N inputs to the drainage basin from 1980 to 2010, which covers the period of dramatic socioeconomic and environmental changes. For the last three decades, NANI increased linearly by a factor of three, from 4700 kg km -2 year -1 in 1980 to 12,600 kg km -2 year -1 in 2010. The main reason for the rise of NANI was due to fertilizer N application as well as human food and animal feed imports. From the pers- pective of direct effects of food consumption on N inputs, contributions of drivers were estimated in terms of human population and human diet using the Logarithmic Mean Divisia Index (LMDI) factor decomposition method. Although human population density is highly correlated to NANI with a linear correlation coefficient of 0.999, human diet rather than human population is found to be the single largest driver of NANI change, accounting for 47% of total alteration, which illustrates that the role of population density in the change of NANI may be overestimated through simple relational analysis. The strong linear relationships (p b 0.01) between NANI and total N concentrations in the lakes over time may indicate that N level in the lake is able to respond significantly to N inputs to the drainage basin. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Nitrogen (N) cycling on earth plays a vital role in regulating pro- ductivity, community structure, and biodiversity for many terrestrial and aquatic ecosystems (Vitousek and Howarth, 1991). During the last century, human activities have substantially altered the global N cycle by introducing new reactive N (Nr) from food and energy production (Galloway et al., 2004, 2008). By the mid-1970s, the amount of N input from human activities had matched natural inputs in terrestrial systems on Earth and since then it has become increasingly dominant (Howarth, 2004). Although the amount of Nr from anthropogenic activities is subject to significant uncertainty in calculations, evidence from the long-term record of the concentration of nitrous oxide in the atmosphere has provided clear information about anthropogenic influ- ence on the nitrogen cycle (Socolow, 1999). Furthermore, Nr input from human activities has led to various environmental and human health problems on regional, continental, and global scales (Erisman et al., 2013; Kaiser et al., 2013). The loss of biodiversity due to excessive N addition to the environment has been observed both in North America and Europe (Tilman, 1996; Sutton et al., 2011). In addition to direct effects such as loss of diversity in the ecosystem, other aspects of ecosystem characteristics, such as stability of the ecosystem, can also be affected (Vitousek et al., 1997). Howarth et al. (1996) estimated that riverine N export from most temperate Science of the Total Environment 505 (2015) 376–384 ⁎ Corresponding author. Tel.: +86 10 62751921. http://dx.doi.org/10.1016/j.scitotenv.2014.10.016 0048-9697/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv