Temperature sensitivity and controlling factors of dissimilatory nitrate reduction processes in sediments of Qingcaosha reservoir, Yangtze Estuary

Slurry incubation experiments combinatedwith isotope-tracing techniques were conducted toexaminethe effectsof temperature on dissimilatory nitrate reductionprocesses and reveal associated environmental variables in Qingcaosha reservoir, the Yangtze Estuary.Results indicated that the potential rates of denitrification, anammox and DNRA in thereservoir sediments werein the range of 0.18 ~ 6.86, 0.26 ~ 3.16and 0.09 ~ 0.25μmol N/(kg·h), respectively, at in situ temperature (10℃). The denitrification rates ranged from 0.43to 6.22 and from 0.68to 6.56μmol N/(kg·h), increased by mean value of 15.7% at 20℃ and 21.6% 30℃, compared to that in 10℃. Anammox rates varied from 0.61 to 3.2μmol N/(kg·h) at 20℃ and from 0.77 to 3.54μmol N/(kg·h) at 30℃, increased by 27.8% and 42.6%. However, DNRA rates ranged between 0.09 and 0.23μmol N/(kg·h) at 20℃, and from 0.1 to 0.18μmol N/(kg·h) at 30℃, reduced by 4.2% compared to that in 10℃. Anammoxwas most sensitive to changes in the temperature, followed by denitrification, and increased with incrasedtemperature; the DNRA was least sensitive to temperature, decreased with the incrasedtemperature. OC, NH₄⁺, Fe²⁺ and S^2- werefound to have significant influence on these nitrate reduction processes. Denitrification and anammoxcontributed respectively 34% ~ 71% and 28% ~ 49% to the total nitrate reduction, while DNRA only contributed 2% ~ 17% in the Qingcaosha reservoir. Denitrificationand anammoxprocesses were estimated to remove 3.25×10³ t/a and 1.68×10³ t/a of nitrogen, accounting for 54.17% of the total external nitrogen transported into the reservoir.