Reduction in the exchange of coastal dissolved organic matter and microgels by inputs of riverine organic matter
Rivers drive large amounts of terrestrial and riverine organic matter into oceans. These organic materials may alter the self-assembly of marine dissolved organic matter (DOM) polymers into microgels and can even affect the behavior of existing natural microgels. We used Suwannee River humic acid, fulvic acid, and natural organic matter as a model of riverine organic matter (ROM) to investigate the impacts of ROM input on DOM polymer and microgel conversion. Our results indicated that the release of extra ROM, even at low concentrations (0.1-10 mg L-1), into the marine organic matter pool decreased the size of self-assembled DOM polymers (from 4-5 μm to< 1 μm) and dispersed the existing natural microgels into smaller particles (from 4-5 μm to 2-3 μm). The particle size of the microgel phase was also less sensitive than that of the DOM polymers to external changes (addition of ROM). This size reduction in DOM aggregation and existing microgels may be closely tied to the surface chemistry of the organic matter, such as negative surface charge stabilization and Ca2+ cross-linking bridges. These findings reveal that ROM inputs may therefore impede the self-assembly of DOM polymers into particulate organic matter and reduce the sedimentation flux of organic carbon and other elements from surface water to the deep ocean, thereby disturbing the biological pump, the downward transportation of nutrients, and the marine organic carbon cycle.
該研究模擬氣候變遷造成極端氣候，暴雨帶入大量的陸緣性溶解碳有機質進入海洋環境對近岸海洋中有機碳聚合行為的影響。而研究指出陸緣性溶解碳有機質不僅能讓有機碳穩定的保持在溶解相，阻斷海洋微膠的形成，還能分散原本存在微膠態的有機碳顆粒，減少有機碳顆粒的粒徑，將改變海洋生物泵的循環。這結果提供河流排放或短期的極端暴雨可能對有機碳動態和海洋微系統產生長期的影響。於2017發表於頂尖期刊Water Research (IF=6.942, 1/88=1.14% in Water Resources)。