External nitrogen influxes hinder the efficacy of lanthanum-modified bentonite (LMB) on phosphorus and algae control in shallow lakes

Yanqing Han; You Zhang; Hu He; Xiaoyu Ning; Lei Zhang; Kuanyi Li

doi:10.1016/j.envres.2024.120364

External nitrogen influxes hinder the efficacy of lanthanum-modified bentonite (LMB) on phosphorus and algae control in shallow lakes

Environ Res. 2024 Nov 13;264(Pt 1):120364. doi: 10.1016/j.envres.2024.120364. Online ahead of print.

Authors

Yanqing Han¹, You Zhang², Hu He³, Xiaoyu Ning¹, Lei Zhang⁴, Kuanyi Li³

Affiliations

¹ School of Civil Engineering and Architecture, Chuzhou University, Chuzhou, 239000, China.
² Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China. Electronic address: yzhang@niglas.ac.cn.
³ Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China.
⁴ School of Civil Engineering and Architecture, Chuzhou University, Chuzhou, 239000, China. Electronic address: leizhang2014@163.com.

PMID: 39547570
DOI: 10.1016/j.envres.2024.120364

Abstract

Regulating internal and external phosphorus (P) holds a predominant position in eutrophication management of lakes and other water bodies, with less emphasis on controlling nitrogen (N) due to the presence of N₂-fixing cyanobacteria. Nonetheless, external N influxes may stimulate the proliferation of non-N₂-fixing cyanobacteria, thereby fostering cyanobacteria blooms during summer seasons. To elucidate the significance of N regulation, a two-factor orthogonal experiment was performed to study the influences of external N input on the efficacy of lanthanum-modified bentonite (LMB), a sediment capping material for P immobilization. At the experimentation ends, the total suspended solids (TSS), organic suspended solids (OSS) concentrations and optical attenuation coefficient (K_d) in the LMB + N treatment were 7.34, 8.65 and 5.20 times higher, respectively, compared to the LMB treatment. The total nitrogen (TN), total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations in the LMB + N treatment were 3.02, 1.30 and 0.60 times higher, respectively, than those in the LMB treatment. However, TP and SRP in the LMB + N treatment were 46.98% and 54.93% lower, respectively, compared to N treatment. The chlorophyll a (Chl a) concentration of algae in the LMB + N treatment was observed to be 2.86 times higher compared to the LMB treatment, and 17.13% lower compared to the N treatment. The biomass of cyanobacteria accounted for more than 95% of algae in the LMB + N treatment and N treatment. Furthermore, the photosynthetic performance of algae in the N treatment increased significantly, compared to the LMB + N treatment. Our results indicated that external N influxes significantly reduce the efficacy of LMB to control P and algae. Thus, the implementation of more stringent N control policies holds great significance in the eutrophication control.

Keywords: Algae; Eutrophication; Nitrogen; Phoslock®; Phosphorus.