Dynamics in Phosphorus Pools in Soils and Sediments along the Land-Freshwater Continuum of Agricultural Catchments

由于侵蚀和地表径流，大量宝贵的营养磷（P）从可耕地土壤中迁移出来，并转移到受纳沃茨。沿着其运输路径，保留和临时存储的P发生在土壤和沉积物的相互连接的植被缓冲带，排水渠道和河床。磷的截留和储存是重要的生态系统功能，但由于土壤地球化学过程的影响，磷可以从各自的储存库中重新释放，从而持续增加磷向下游水体的通量。这不仅增加了富营养化的风险，它也抵消了当代的保护措施，旨在减少磷输入到地表沃茨。如果我们要减轻磷转移从耕地土壤到地表沃茨，我们必须了解磷库动态不仅在耕地土壤本身，而且在相互关联的磷转移连续。在这里，水文状况和氧化还原条件发生动态变化，这反过来又对不同储存池（例如，吸附在铁矿物上的磷在还原条件下部分释放）。然而，由于研究方法的限制，土壤和沉积物中磷库的变化及其转化途径仍然知之甚少。因此，本研究的目的是（i）解开的机制，在不同的存储池之间的排水渠道，植被缓冲带，和侵蚀耕地土壤P的保留和动态转移;（ii）和阐明的意义，生物和非生物过程的变化，在P池。实验室培养实验将根据创新的同位素标记方法进行，该方法使用无机磷酸盐中稳定氧同位素比率（δ 18 OPi）的分析，以追踪动态氧化还原条件下土壤和沉积物中磷库的变化。总之，关键信息将获得关于农业集水区的磷循环，这将允许预测各自的存储池的稳定性，在长期依赖于其位置内的磷转移连续和当时的环境条件。

Pronounced amounts of the precious nutrient phosphorus (P) are mobilized from arable soil due to erosion and surface run-off and are transferred into the receiving waters. Along its transport path, retention and interim storage of P occurs in soils and sediments of interconnected vegetated buffer strips, drainage channels and stream beds. Retention and storage of P constitutes an important ecosystem function; however, P can be re-released from respective storage pools due to biogeochemical processes, thereby continuously increasing P fluxes to downstream water bodies for years and decades. This does not only increase the risk of eutrophication, it also counteracts contemporary conservation measures aiming to reduce P inputs into the surface waters.If we are to mitigate P transfer from arable soil to surface waters, we must understand P pool dynamics not only in arable soil itself, but also within the interlinked P transfer continuum. Here, dynamic changes in the hydrological regime and redox conditions occur, which have in turn a pronounced influence on the storage of P within the different storage pools (e.g., P sorbed to Fe-minerals is partially released under reducing conditions). However, due to methodological limitations, changes of P pools in soils and sediments and transformation pathways involved still remain barely understood. The objectives of this study are therefore (i) to unravel the mechanisms underlying the retention and dynamic transfer of P between the different storage pools in drainage channels, vegetated buffer strips, and eroded arable soil; (ii) and to elucidate the significance of biotic and abiotic processes underlying the changes in P pools. Laboratory incubation experiments will be conducted based on an innovative isotopic labelling approach that uses the analysis of stable oxygen isotope ratios in inorganic phosphate (δ18OPi) in order to trace changes in P pools of soil and sediments under dynamic redox conditions. In summary, crucial information will be obtained regarding the cycling of P in agricultural catchments, which will allow predicting the stability of respective storage pools in the long-term in dependence on their position within the P transfer continuum and the prevailing environmental conditions therein.