Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Taihu Laboratory for Lake Ecosystem Research, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China.
Sci Total Environ. 2020 Sep 20;736:139497. doi: 10.1016/j.scitotenv.2020.139497. Epub 2020 May 17.
Dissolved organic nitrogen (DON) accounts for a significant fraction of the dissolved nitrogen (N) pool in eutrophic lakes, and substantial components of DON are available for phytoplankton. However, long-term changes in DON concentrations in eutrophic lakes have been poorly documented, and the particulate-related internal cycling of DON at the molecular level remains unclear. In this study, changes in the concentration of DON during the past 14 years of Lake Taihu, China were analyzed. Algae and sediment suspensions were incubated under summer sunlight to examine transformations of DON (e.g., photodissolution) at the bulk concentration and molecular level. Concentrations of DON in Lake Taihu ranged from 0 to 4.59 mg L, with a mean of 0.82 ± 0.60 mg L (n = 3360). Although annual averages of the concentration of DON (n = 240) showed no significant linear variation from 2005 to 2018, the percentage of DON in total dissolved nitrogen (TDN) increased linearly (p < .05) and was maintained at >50% after 2015. Seasonally, DON concentrations were highest in spring (1.10 ± 0.56 mg L), followed by winter (0.87 ± 0.58 mg L) and summer (0.54 ± 0.37 mg L) concentrations, and lowest in autumn (0.44 ± 0.38 mg L). Outdoor incubation experiments suggest that both algae and sediment suspensions contribute to significant increases of DON concentrations but contribute to decreases of inorganic N concentrations at the end of incubations. Moreover, the production of DON by algae suspensions differed from that of sediment suspensions, with more labile components released from algae (e.g., proteins and amino acids), while more refractory components were released from sediment suspensions (e.g., lignin with low H/C and O/C). Taken together, these results emphasize the increasing percentage of DON in TDN during 2009-2018 and the different patterns of algae- and sediment-dominated internal DON transformations in Lake Taihu.
溶解有机氮（DON）在富营养化湖泊的溶解氮（N）库中占有相当大的比例，并且 DON 的大量成分可被浮游植物利用。然而，富营养化湖泊中 DON 浓度的长期变化记录很少，并且 DON 的颗粒相关内部循环在分子水平上仍然不清楚。在这项研究中，分析了过去 14 年中国太湖 DON 浓度的变化。在夏季阳光的照射下，培养藻类和沉积物悬浮液，以检查 DON（例如，光解）在总体浓度和分子水平上的转化。太湖 DON 的浓度范围为 0 至 4.59mg/L，平均值为 0.82±0.60mg/L（n=3360）。尽管 DON 浓度的年平均值（n=240）在 2005 年至 2018 年间没有明显的线性变化，但 DON 在总溶解氮（TDN）中的比例呈线性增加（p<0.05），并且在 2015 年之后保持在 50%以上。季节上，DON 浓度在春季最高（1.10±0.56mg/L），其次是冬季（0.87±0.58mg/L）和夏季（0.54±0.37mg/L），秋季最低（0.44±0.38mg/L）。户外培养实验表明，藻类和沉积物悬浮液都会导致 DON 浓度显著增加，但在培养结束时会导致无机 N 浓度降低。此外，藻类悬浮液产生的 DON 与沉积物悬浮液不同，藻类释放出更多的可利用成分（例如蛋白质和氨基酸），而沉积物悬浮液释放出更多的难降解成分（例如低 H/C 和 O/C 的木质素）。综上所述，这些结果强调了 2009-2018 年间 DON 在 TDN 中所占比例的增加，以及太湖中藻类和沉积物主导的内部 DON 转化模式的不同。
