Research Paper

Nitrogen loading increases both algal and non-algal turbidity in subtropical shallow mesocosms: Implication for nutrient management

¹ School of Civil Engineering and Architecture, Chuzhou University, Chuzhou, China
² Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, China
³ Department of Ecoscience and WATEC, Aarhus University, 8000, Aarhus, Denmark
⁴ Sino-Danish Centre for Education and Research (SDC), University of Chinese Academy of Sciences, Beijing 100190, China
⁵ Limnology Laboratory, Department of Biological Sciences and Centre for Ecosystem Research and implementation, Middle East Technical University, Ankara 06800, Türkiye
⁶ Institute of Marine Sciences, Middle East Technical University, 33731 Erdemli-Mersin, Türkiye
⁷ Institute for Ecological Research and Pollution Control of Plateau Lakes, School of Ecology and Environmental Science, Yunnan University, Kunming, China

^* Corresponding author: zgmao@niglas.ac.cn

Received: 17 May 2023
Accepted: 4 August 2023

Abstract

Excess nitrogen (N) loading in summer often boosts phytoplankton growth and increase algal turbidity. In eutrophic shallow lakes, the increased algal production may also augment the abundance of deposit-feeding tubificid worms and thereby sediment resuspension and non-algal turbidity. However, few studies have explored the effects of high N loading on this benthic process in eutrophic shallow lakes. Here, we conducted an outdoor mesocosm experiment in a summer-winter season (177 days) on the shore of subtropical Lake Taihu, China. Each mesocosm contained a 10 cm layer of lake sediment and 450 L of lake water. Nitrate was added weekly to three of the mesocosms, while another three functioned as controls. Our results showed that N addition significantly increased algal particles as water chlorophyll a (Chl-a) increased significantly following N addition. Moreover, significantly higher levels of inorganic suspended solids (ISS) were observed in the mesocosms with added N, indicating elevation of non-algal turbidity as well by the N addition. We attribute the latter to increased sediment resuspension as the abundance of tubificid worms was significantly higher in the N addition mesocosms. Accordingly, our study indicates that high N loading in subtropical shallow lakes may boost both algal and non-algal turbidity in part via benthic-pelagic coupling processes. Our results suggest that alleviation of eutrophication in shallow eutrophic lakes may require a strategic approach to adequately control both N and phosphorus.