湖泊有机质降解过程生源要素活化行为研究进展与展望

Research Progress and Prospect on Regeneration Behavior of Biogenic Elements during Organic Matter Degradation in Lakes

水体富营养化是全球面临的最突出的生态环境问题之一。大量研究表明,碳(C)、氮(N)、磷(P)等生源要素是控制富营养化的关键因子。随着日益强化的流域污染治理工程的实施,流域外源氮磷输入通量显著减少,但很多湖泊水体的氮磷浓度并未如预期那样显著降低,藻类水华依然频发,湖泊内负荷被认为是罪魁祸首。湖泊内负荷聚焦的C、N、P等生源要素在湖泊生态系统中的生物地球化学循环往往以有机质为主要载体,藻类生长过程伴随着C、N、P的吸收和有机质形成,而有机质在水体沉降和沉积物早期成岩过程中的矿化降解则伴随着C、N、P的释放。虽然C、N、P等生源要素都伴随着颗粒有机质矿化而活化再生,但它们在此过程中并不是等比例活化释放。国内外有关有机质降解过程中生源要素活化行为的研究已取得重要进展,主要体现在:(1)水体颗粒物的C∶N和C∶P比值随水体深度增加而逐渐增大,表明水体颗粒态氮和颗粒态磷通常具有比颗粒态碳更快的矿化速率;(2)缺氧条件下有机质降解过程磷比碳优先释放且强度远高于富氧环境;(3)微生物及其驱动的聚磷酸盐循环和酶水解作用可能是导致有机质降解过程磷优先活化的重要原因。水体富营养化后,有机质降解过程磷优先活化可能加速了磷的再循环,易形成“藻类暴发→水体缺氧加剧→有机质降解磷优先活化”正反馈机制,加大了富营养化修复治理难度,未来研究应着重加强有机质降解过程生源要素活化行为差异的原因机制及生态环境效应研究。

Eutrophication is one of the most prominent ecological and environmental problems in the world. A large number of studies have shown that biogenic factors such as carbon(C), nitrogen(N) and phosphorus(P) are the key factors to control eutrophication. With the implementation of increasingly intensive watershed pollution control projects, the input flux of exogenous nitrogen and phosphorus decreased significantly, but the concentration of nitrogen and phosphorus in many lakes did not decrease significantly as expected, algae blooms were still frequent, and the high load of nutrients in lakes was considered to be the culprit. Organic matter is the main carrier of the biogeochemical cycles of biogenic elements such as carbon, nitrogen and phosphorus in the lake ecosystem. Algal growth is accompanied by the absorption of carbon, nitrogen and phosphorus and the formation of organic matter, while the mineralization and degradation of organic matter in the process of water sedimentation and early diagenesis of sediment are accompanied by the release of carbon, nitrogen and phosphorus. Although carbon, nitrogen and phosphorus are regenerated during the mineralization of particulate organic matter, they are not released in an equal proportion. Important progress has been made in the research on the regeneration behavior of biogenic elements during organic matter degradation, which is mainly reflected in the following aspects.(1) The C∶N ratio and C∶P ratio of particulate matter in water gradually increase with the increase of water depth, indicating that granular nitrogen and granular phosphorus in water usually have a faster mineralization rate than granular carbon.(2) The preferential release intensity of phosphorus than carbon during organic matter degradation under anoxic conditions was much higher than that in oxygen enriched environments.(3) The polyphosphate cycle and enzymatic hydrolysis driven by microorganisms may be the important factors leading to the preferential regeneration of phosphorus in the degradation process of organic matter. After eutrophication, the preferential regeneration of phosphorus may accelerate the recycling of phosphorus, which is easy to form a positive feedback mechanism of "algae blooms → water hypoxia intensification → preferential regeneration of phosphorus during organic matter degradation". This positive feedback mechanism has increased the difficulty of lake eutrophication restoration. The future research should focus on the mechanism and ecological environmental effects of the differences in regeneration behavior of biogenic elements during organic matter degradation.