基于DNDC模型评估水位变化对滨海湿地净生态系统CO_(2)交换的影响

Modeling Impacts of Changes in Water Level on Net Ecosystem CO_(2 ) Exchangein A Coastal Wetland of the Yellow River Delta Based on DNDC Model

水位是影响滨海湿地生态系统蓝碳功能的重要因素。气候变化引起的海平面上升以及极端气候事件的频发,可能加快水位的变化,从而改变生态系统碳交换的过程。然而,滨海湿地碳汇功能响应水位变化的机制尚不清楚。为了评估水位对滨海湿地净生态系统CO_(2)交换(NEE)特征的影响,以及验证DNDC(denitrification-decomposition)模型对模拟预测滨海湿地生态系统碳交换的适用性,该研究设计了野外水位控制试验(自然水位,地下20 cm水位、地表10 cm水位),并利用DNDC模型模拟和预测水位变化对滨海湿地NEE的影响。结果表明:(1)不同水位处理之间NEE差异显著,地表10 cm水位处理促进CO_(2)吸收,地下20 cm水位则抑制CO_(2)吸收;(2)经过校准和验证的DNDC模型可以准确模拟水位变化对黄河三角洲湿地NEE的影响,NEE模拟值的日动态与田间观测结果显著相关(R^(2)>0.6);(3)通过改变气候、土壤和田间管理等输入参数对DNDC模型进行灵敏度检验,生态系统碳交换过程对日均温、降雨和水位改变的响应最为显著,其中,水位对NEE的影响主要作用于土壤呼吸(Rs)。未来气候情境下,不同水位变化下的生态系统碳交换过程随年份增长呈现不同的规律,因此未来的模拟研究应关注DNDC中水文模块和植被演替过程的完善。该研究可为预测水文变化情境下滨海湿地碳汇功能的未来发展以及政策制定提供参考。

Water level is an essential driving factor affecting the blue carbon function of coastal wetland ecosystems.Climate change(such as seas level rise and extreme rainfall)have led to variation in water level,which may alter the carbon sink function of coastal wetlands.However,it is unclear how the ecosystem carbon exchange of coastal wetlands respond to changes in water level.To assess the effect of the water level on ecosystem CO_(2)exchange,a field manipulation experiment was conducted in a wetland in the Yellow River Delta.The experiment consisted of three water-level treatments,including natural water level(CK),20 cm groundwater table(B20),and 10 cm water level above the soil surface(A10).In addition,the process-based model(denitrification-decomposition model,i.e.DNDC)was used to simulate and predict changes in ecosystem carbon exchange of the coastal wetland in the future.The results showed that there was a significant difference in net ecosystem CO_(2)exchange(NEE)among different water level treatments during the growing season.The CO_(2)absorption rates under high water level treatment were much higher than those under low water level treatment,and its maximum value reached 655 kg·hm^(−2) in vigorous growing season.The NEE dynamics of different water levels simulated by DNDC model were significantly related to field observation results(R^(2)>0.6).According to the sensitivity test of DNDC model,daily temperature,rainfall and water level drove the variation of ecosystem carbon exchange.Water level significantly altered NEE mainly by changing soil respiration.Overall,the ecosystem carbon exchange of the wetland responded in different ways under the climate change scenarios.Therefore,future studies should focus on the improvement of hydrological modules and vegetation succession processes in DNDC to understand better the effect of hydrological processes on carbon exchange in coastal wetlands under climate change.This study can provide a reference for future development on predicting carbon sink function of coastal wetlands under changes in water level.