Temperature-dependent effects of lanthanum-modified bentonite on sediment nitrogen removal processes and the...

Lanthanum-modified bentonite (LMB) is widely used for phosphorus control in eutrophic lakes, but its effects on sediment nitrogen removal remains unclear. This study investigated the effects of LMB on denitrification and anammox, and underlying microbial mechanisms, under different dissolved oxygen (DO) and temperature (T) conditions using isotope tracing and metagenomics. The results demonstrated that the influence of LMB on sediment nitrogen removal was highly temperature-dependent. At 15 °C, LMB significantly enhanced both processes: denitrification increased by an average of 67.75 % under aerobic conditions, while anammox increased by 163.52 % and 93.47 % under aerobic and anaerobic conditions, respectively. Conversely, at 30 °C, LMB inhibited both processes. The denitrification decreased by average reductions of 57.36 % and 79.46 %, and anammox decreased by 32.51 % and 54.46 % under aerobic and anaerobic conditions, respectively. Microbial results revealed that LMB regulated denitrification in a temperature-dependent manner by modulating the key functional gene nosZ. In contrast, LMB generally suppressed anammox genes (hzsA, hzsB, and hdh), particularly under anaerobic conditions. Redundancy analysis (RDA) and structural equation modeling (SEM) identified pH, moisture content (MC), electrical conductivity (EC), total carbon (TC), total nitrogen (TN), NO₃⁻-N, and NH₄⁺-N as the key environmental factors driving variations in functional gene abundances. Our findings reveal that the temperature-dependent effects are primarily driven by the regulation of the nosZ gene and synergistic interactions among key physicochemical factors. Therefore, for remediating of eutrophic lakes with severe nitrogen pollution, the addition of LMB should be strategically adjusted to low-temperature seasons to maximize its ecological benefits in promoting nitrogen removal.