Anthropogenic-induced acceleration of sediment and associated nutrients presents a serious challenge to water resource management across the globe. While wetlands are potential natural solutions, little is known of how well key wetland types attenuate downstream sediment fluxes and how these relate to local- and catchment-scale factors. This research aimed to develop an understanding of patterns and rates of sediment and phosphorus retention in valley-bottom wetlands in South Africa. The geomorphology, sedimentology and historical accretion rates of three wetlands which offered diversity in size, catchment position and degree of organic accumulation were compared to ascertain the impact of local- and catchment-scale factors. Estimates of sediment and associated phosphorus accumulation suggest higher rates in clastic sediment-dominated wetlands (1089–7655 g sediment m yr, 0.4–1.6 g-P m yr) compared to an organic sediment-dominated system (601–1308 g-sediment m yr, 0.2–0.3 g-P m yr). Sediment accretion rates generally increased longitudinally, indicating that distal wetland reaches act as sediment and phosphorus retention hotspots. Phosphorus distribution patterns were primarily attributed to variations in organic matter content and associated aluminium and iron complexing agents in fine-grained sediment deposits, while particle size distributions were less important. However, the relevance of individual complexing agents in phosphorus dynamics varied among wetlands with differing landscape conditions. Contrasts between these systems reflect variations in catchment lithology and hydroclimatic regime, which influence the relative magnitude of sediment supply and vegetation productivity. We postulate that intermediate-sized wetlands characterised by catchments around 900 ha in size, gentle longitudinal slopes (∼2 %), a high proportion of fine sediment deposition, limited organic matter breakdown, and a long vegetation growing season provide optimal conditions for sediment and phosphorus accumulation. This system-scale information is essential to guide management decisions to identify and prioritize within-catchment ‘hotspots’ of sediment and phosphorus retention.

中文翻译：

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南非旱地景观谷底湿地长期沉积物和磷积累的系统尺度动态

人为引起的沉积物和相关营养物质的加速对全球水资源管理提出了严峻的挑战。虽然湿地是潜在的自然解决方案，但人们对主要湿地类型如何减弱下游沉积物通量以及这些湿地与当地和流域规模因素的关系知之甚少。这项研究旨在了解南非谷底湿地沉积物和磷保留的模式和速率。对大小、流域位置和有机积累程度具有多样性的三个湿地的地貌、沉积学和历史沉积率进行了比较，以确定局部和流域规模因素的影响。对沉积物和相关磷积累的估计表明，与以有机沉积物为主的系统（601-1308 g 沉积物 m 年，1089-7655 g 沉积物 m 年，0.4-1.6 gP m 年）相比，以碎屑沉积物为主的湿地的沉积率更高（1089-7655 g 沉积物 m 年，0.4-1.6 gP m 年）。 0.2–0.3 gP m 年）。沉积物沉积率普遍纵向增加，表明远端湿地河段是沉积物和磷滞留热点。磷的分布模式主要归因于细粒沉积物中有机物含量和相关铝和铁络合剂的变化，而颗粒尺寸分布不太重要。然而，在不同景观条件的湿地中，各个络合剂在磷动态中的相关性有所不同。这些系统之间的对比反映了流域岩性和水文气候状况的变化，这影响了沉积物供应和植被生产力的相对大小。我们假设中等规模湿地的特征是流域面积约 900 公顷、缓和的纵向坡度（~2%）、高比例的细沉积物、有限的有机质分解以及较长的植被生长季节，为沉积物和沉积物提供了最佳条件。磷积累。这种系统规模的信息对于指导管理决策以确定流域内沉积物和磷滞留“热点”并确定优先顺序至关重要。