滨海湿地水鸟传输下磷素反向迁移及累积通量研究

Phosphorus is one of the major ecosystems nutrients, with a kind of natural sedimentary cycle. There are various factors driving the redistribution of P in the ecosystem, which have received extensive attentions. But few researches focus on the reverse migration of P from aquatic to terrestrial ecosystems caused by waterfowls. This project studies on the P transport processes of aquatic to terrestrial ecosystems by waterfowl as biovector, which was driven by the reclamations and ecological restoration of coastal wetland creating a suitable habitat for waterfowls. The observation field includes high-tide roosting sites of Charadriiformes species and breeding habitat of Ardeidae birds and the control fields in the typical coastal wetlands of Hanzhou Bay. The distribution patterns of soil P under different landscape types are monitored seasonally and clarified by analyzing the nutrient content, biochemistry characteristics in soil, plant, aquatic and bird droppings. Phosphorus speciation, nitrogen and oxygen isotopes are also determined to trace soil P sources and evaluate the contribution of guano-derived P. Combined with P input and output analysis, the reverse migration flux of P from water to land system and the soil P cumulative flux are quantitatively evaluated. This work is helpful to clarify the process of P flow between water and land ecosystems, and provide a theoretical basis for understanding the biogeochemical cycle of P.

磷为沉积型循环，其从陆地向水体迁移的过程是关注的热点。以水域为食物来源且栖息于陆地的水鸟则对磷从水体向陆地反向迁移起着重要作用，但相关研究较少。本项目关注滨海地区由于滩涂围垦及其生态恢复创造了多样化水鸟适宜生境，强化了水鸟通过捕食将水体中磷以粪便、食物碎屑等形式返回陆地的过程。项目在杭州湾典型滨海湿地设置迁徙期鸻鹬类高潮停歇地和鹭类集中繁殖区及对照样地，分析土壤、植物和鸟粪中磷含量及其季节动态，阐明不同水鸟栖息生境类型下土壤磷分布规律；重点以有林湿地鹭类集中繁殖区为对象，监测大气干湿沉降输入及地表径流输出，借助磷形态、氮同位素及磷酸盐氧同位素测定，示踪湿地土壤磷素来源；结合系统磷素输入输出分析，定量评估水鸟传输下水陆系统磷素的反向迁移及土壤累积通量。研究结果有助于阐明水陆生态系统的磷素流动过程，为深入认识磷的生物地球化学循环过程提供理论基础。

水陆生态系统间营养物质流动过程及相互影响仍知之较少。滨海湿地是联系水、陆生态系统的主要通道。水鸟是滨海湿地重要的生物类群之一，位于食物链的顶端，具有集群取食和栖息等习性。水鸟可通过捕食将水体中磷以粪便、食物碎屑等形式返回陆地生态系统。但目前对磷从陆地向水体迁移的过程受到较多关注，而对磷从水体返回陆地的研究则较为欠缺。本项目系统开展杭州湾滨海湿地水鸟集群繁殖活动对土壤生态系统的影响、土壤累积磷来源及水陆系统磷素反向迁移转化通量评估。研究表明，鹭鸟栖息改变了栖息地的土壤理化性质、磷含量、碱性磷酸酶活性和细菌群落成。鹭鸟栖息区的土壤理化性质与对照区之间具有显著差异。鹭鸟栖息显著提高土壤中养分含量和电导率，但pH则相反。相比对照区，鹭鸟栖息改变了土壤TP及其组分的相对比例。鹭鸟栖息增强了土壤理化性质与磷形态之间的相关性，提高了栖息地表层土壤中的ALP活性。与对照相比，鹭鸟栖息导致表层土壤细菌群落也发生了显著变化。尽管鹭鸟栖息可以通过提高土壤磷素供给能力来缓解栖息地的缺磷现象，但也会导致栖息地土壤养分失衡和磷素流失。分析表明，采用草酸铵提取法得到的土壤磷饱和度和有效磷含量更适用于杭州湾鹭科鸟类集群栖息地土壤中磷的流失风险评估。基于生态化学计量学、磷形态分级、稳定同位素分析以及磷输入输出平衡分析等方法，分析并示踪了鹭鸟集群栖息地生态系统磷循环和来源。最后，通过鹭鸟栖息地土壤磷素输入输出分析，得到单位面积下以鸟粪形式、大气磷沉降输入的P通量分别为112134.75和129.4 kg/(km2a)，磷的径流输出量为91.8 kg/(km2a)，P输入的净通量为112172.4 kg/(km2a)。说明以鸟粪形式输入的磷对栖息地土壤养分的分配发挥了重要作用。在滨海湿地人为围垦活动这一特殊背景下，开展水鸟传输下磷素从水体向陆地的反向迁移研究，丰富了磷的生物地球化学循环过程理论。