Wetlands are valuable ecosystems because they are highly productive, support a wide range of wildlife, and serve as hotspots for biogeochemical cycling. Historically, vast areas of wetlands in the United States (US) were drained and converted to agriculture. Efforts are currently underway to restore wetland and floodplain functioning across the US and elsewhere. Re-wetting historically drained and farmed soils can potentially liberate legacy phosphorus (P) to surface waters as soluble reactive P (SRP), offsetting P retained by sedimentation during floods. A better understanding of the controls on SRP release is needed to estimate net P retention in these settings. Soil P saturation ratio (PSR) and soil P storage capacity (SPSC) are two proxies for SRP runoff risk that have shown promise for characterizing restored wetlands but require further testing. In this study, we examined soils at 42 riparian sites ranging from active farms to mature wetlands in the Vermont portion of the Lake Champlain Basin (USA), where phosphorus load reduction is a critical goal to achieve in-lake water quality targets. We additionally quantified potential SRP release to overlying water using intact soil cores from 20 plots spanning 14 sites. Final SRP concentrations in intact cores spanned two orders of magnitude and were predicted well by SPSC and PSR. SRP release was greatest at more recently and frequently farmed sites. Several soil properties, including PSR and SPSC, were correlated with farming frequency and time since farming, indicating that SRP release could be mapped using existing geodata for soils, hydrology and land use. Our findings confirm that soil SRP release during flooding needs to be considered in estimates of net P balance for restored riparian wetlands in agricultural landscapes.

湿地是宝贵的生态系统，因为它们生产力高，支持范围广泛的野生动物，并且是生物地球化学循环的热点。从历史上看，美国（US）的大片湿地被排干并转化为农业。目前正在努力恢复美国和其他地方的湿地和洪泛区功能。重新润湿历史上排水和耕作的土壤可能会将遗留的磷 (P) 作为可溶性活性磷 (SRP) 释放到地表水中，从而抵消洪水期间沉积物保留的磷。需要更好地了解 SRP 释放的控制，以估计这些设置中的净 P 保留。土壤 P 饱和比 (PSR) 和土壤 P 储存能力 (SPSC) 是 SRP 径流风险的两个指标，它们已显示出对恢复湿地特征的希望，但需要进一步测试。在这项研究中，我们检查了 42 个河岸地点的土壤，从活跃的农场到美国尚普兰湖盆地佛蒙特部分的成熟湿地，减少磷负荷是实现湖内水质目标的关键目标。我们还使用来自 14 个地点的 20 个地块的完整土壤芯，量化了潜在的 SRP 释放到上覆水。完整岩心中的最终 SRP 浓度跨越了两个数量级，并且由 SPSC 和 PSR 很好地预测。SRP 释放在最近和经常耕种的地点最大。几种土壤特性，包括 PSR 和 SPSC，与自耕作以来的耕作频率和时间相关，表明可以使用现有的土壤、水文和土地利用地理数据绘制 SRP 释放图。我们的研究结果证实，在估算农业景观中恢复的河岸湿地的净磷平衡时，需要考虑洪水期间土壤 SRP 的释放。