Australian Rivers Institute, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Australia.
Australian Rivers Institute, Griffith University, 170 Kessels Rd, Nathan, Brisbane, Australia.
Sci Total Environ. 2019 Mar 1;654:583-592. doi: 10.1016/j.scitotenv.2018.11.077. Epub 2018 Nov 8.
Erosion of soil from catchments during floods can deliver large quantities of sediment to the coastal zone. The transformations and processes of nutrient release from catchment soils during flooding are not well understood. To test the hypothesis that catchment soils supply nutrients to the coastal zone, we examined nutrient release and transformation following wetting of soils formed from three distinct rock types (basalt, granite and sandstone) with fresh and marine water. The soil samples were collected from eroding areas of a subtropical river catchment. We simulated runoff, transport and deposition by tumbling the fine fraction of the soils in freshwater for three days and settling in seawater for four weeks. We also collected and incubated cores from an adjacent coastal bay and added a layer of catchment soil to simulate deposition of new sediment following flood plume settling. Dissolved nutrients were measured in both simulations. Basalt soils were relatively nutrient rich and released substantial quantities of organic and inorganic dissolved nutrients, particularly phosphate. However when soils were added to estuarine sediment cores and incubated, there was a net influx of phosphate from the overlying water. All soils continually released ammonium in both experiments, indicating that catchment soils may be an important source of ammonium to fuel productivity within the coastal zone. This study provides new insights into increased nitrogen availability in a nitrogen-depauperate coastal zone and identifies catchment geology as an important influence in coastal productivity through delivery of soil nitrogen to downstream estuaries.
洪水期间集水区的土壤侵蚀会将大量泥沙输送到沿海地区。洪水期间集水区土壤中养分释放的转化和过程还不太清楚。为了验证集水区土壤向沿海地区供应养分的假设，我们研究了用淡水浸湿由三种不同岩石类型（玄武岩、花岗岩和砂岩）形成的土壤后，养分的释放和转化情况，以及用海水浸湿土壤后的释放和转化情况。这些土壤样本是从亚热带河流集水区的侵蚀区采集的。我们通过将土壤的细颗粒在淡水中翻滚三天并在海水中沉降四周来模拟径流、运输和沉积过程。我们还从相邻的沿海湾收集并培养了岩芯，并添加了一层集水区土壤以模拟洪水羽流沉降后新沉积物的沉积。在这两种模拟中都测量了溶解养分。玄武岩土壤相对富含有机物和无机溶解养分，特别是磷酸盐。然而，当将土壤添加到河口沉积物岩芯并进行培养时，来自上层水的磷酸盐净通量为正。在这两个实验中，所有土壤都持续释放铵，表明集水区土壤可能是为沿海地区提供生产力的铵的重要来源。本研究深入了解了在氮贫化的沿海地区氮素增加的情况，并确定了集水区地质通过向下游河口输送土壤氮素对沿海生产力的重要影响。
