异龙湖草——藻型稳态转换的碳氮磷化学计量特征及埋藏量估算

Carbon, nitrogen, phosphorus stoichiometry and burial estimationof macrophyte- to algae-dominated stage of Yilong lake

了解湖泊沉积物中C、N、P化学计量特征对于加强陆地水域生态系统化学计量学研究和揭示草型、藻型不同湖泊生态系统生源要素响应轨迹具有重要意义。本文基于覆盖全湖的20根短钻岩芯,对云南浅水富营养湖泊异龙湖沉积物有机碳(TOC)、总氮(TN)、总磷(TP)进行测定与分析,结合前人对异龙湖稳态转换发生的对应沉积深度划分,探讨了水体富营养化驱动的草型、藻型湖泊演化阶段对沉积物化学计量特征的影响。结果表明,湖泊沉积物C、N、P化学计量特征存在明显的时空异质性,异龙湖藻型湖泊阶段TOC、TN和TP含量分别为(4.83±1.47)%、(0.42±0.09)%和(0.04±0.01)%,均显著高于草型湖泊阶段的(3.87±0.98)%、(0.31±0.08)%和(0.03±0.02)%。藻型湖泊阶段的C∶N∶P值为347∶26∶1,较草型湖泊阶段(519∶35∶1)显著下降,反映了水体富营养化驱动下草—藻型稳态转换过程的水生植物群落更替和水环境参数改变对低内稳态有机个体在生态化学计量学上的影响。在不同元素之间,受有机质来源组成、化学元素的功能及活性差异等多因素影响,异龙湖沉积物中C、N元素主要在河流入湖口及沿岸带富集而P元素在深水区富集,导致P元素与C、N元素间的耦合性较低。在表层0~15 cm,异龙湖沉积物TOC、TN和TP埋藏量分别为1829 t/km^(2)、160 t/km^(2)和16 t/km^(2),顶部0~5 cm(藻型湖泊阶段)的平均埋藏速率较10~15 cm(草型湖泊阶段)升高30%~36%,但受含水率影响,10~15 cm的储量是顶部0~5 cm的1.5倍。与其他富营养化湖泊对比发现,温度极大地影响着湖泊有机质的有效埋藏,对湖泊沉积物C、N、P的源、汇功能起到关键的调控作用。异龙湖较高的水温使得底泥营养盐容易释放到湖泊水体中形成二次污染,加剧了湖泊生态修复的难度。本文揭示的湖泊生态化学计量及储量特征可为深化高原湖泊C、N、P循环认识与评估营养盐埋藏提供重要的科学依据。

Understanding the stoichiometry of carbon(C),nitrogen(N)and phosphorus(P)in lake sediments is of great significance in enhancing the stoichiometric studies of terrestrial water ecosystems and revealing the response trajectory of biogenic elements between macrophyte-and algae-dominated lake ecosystems.Based on 20 sediment cores covering the whole lake,the total organic carbon(TOC),total nitrogen(TN)and total phosphorus(TP)in the sediments of shallow eutrophic Yilong lake were measured,and the influence of macrophyte-and algae-dominated lake on the carbon,nitrogen and phosphorus stoichiometry was discussed.The results showed that the stoichiometric characteristics of C,N and P in lake sediments presented spatial and temporal heterogeneity.The contents of TOC,TN and TP in the algae-dominated stage of Yilong lake were(4.83±1.47)%,(0.42±0.09)%and(0.04±0.01)%,respectively,which were significantly higher than those in the macrophyte-dominated stage((3.87±0.98)%,(0.31±0.08)%and(0.03±0.02)%,respectively).The C∶N∶P value of 347∶26∶1 for the algae-dominated lake stage was significantly lower than that of the macrophytedominated lake stage(519∶35∶1).This reflected the effect of aquatic plant community succession during the macrophyte-to algae-dominated stage transformation,and the impact of altered water environments on the ecological stoichiometry of low homeostasis organisms.Among different elements,due to the composition of organic matter sources,the function and activity of chemical elements,the C and N elements in sediments of Yilong lake were mainly enriched in the estuary and littoral zone,while the P element was enriched in the deep-water area,resulting in a low coupling between the P element and the C and N elements.In the surface 0~15 cm layer,the burial amounts of TOC,TN and TP in the sediments of Yilong lake were 1829 t/km^(2),160 t/km^(2) and 16 t/km^(2),respectively.The average burial rate in the top 0~5 cm(algae-dominated stage)was elevated by 30%-36%compared to the bottom 10~15 cm(macrophyte-dominated stage),but burial in the bottom 10-15 cm layer was 1.5 times higher than in the top 0-5 cm layer,as affected by water content.Comparison with other eutrophic lakes revealed that temperature greatly influenced the effective burial of organic matter in lakes and played a key role in regulating the source and sink functions of C,N and P in lake sediments.The high water temperature of Yilong lake made it easier for sediment nutrients to be released into the lake water,which aggravated the difficulty of lake ecological restoration.The ecological stoichiometry and burial characteristics of lake revealed in this study can provide an important scientific basis for deepening the understanding of C,N and P cycles in plateau lakes and evaluating nutrient burial.