SGER: Phosphorus release and metal redox cycling associated with sediment reworking in the Colorado River Delta, Lake Powell, Utah

[0621371 .]美国科罗拉多河三角洲沉积物再加工过程中磷释放和金属氧化还原循环[j]。由于2000年开始的干旱和为科罗拉多河下游各州提供持续供水的水库工程，鲍威尔湖目前只有46%的容量。在这种情况下，河流的流入切断了以前沉积在科罗拉多河三角洲的沉积物。我们假设沉积物的再悬浮可能导致磷释放和金属氧化还原循环的增强。近年来，人们观察到在与三角洲沉积物相交的底水中出现缺氧，这也可能导致沉积物中氧化铁载体相的还原性溶解导致P释放。鲍威尔湖的初级生产是磷有限的，磷可利用性的变化可能会产生重大的生态后果。科罗拉多河带来的悬浮沉积物是鲍威尔湖磷的主要来源；大部分沉积物是在科罗拉多河流入湖中时沉积的（即河流-湖泊边界）。因此，先前沉积的三角洲沉积物代表了大量的磷储存库。知识价值。该项目将研究生物地球化学和物理过程的耦合及其对磷和微量金属动力学的影响。磷在固相（特别是悬浮沉积物和三角洲沉积物）中的形态将被确定，并与磷可能从这些沉积物中释放的条件有关。还将研究金属（如铁）氧化物的还原性溶解在磷释放中的作用。更广泛的影响。磷动态对鲍威尔湖初级生产起关键控制作用。我们预计，我们的研究结果将表明，在科罗拉多河流入穿过先前沉积的三角洲沉积物的当前条件下，磷和微量金属动力学是否发生了变化。如果磷的动态受到影响，干旱恢复期间初级生产模式和底水缺氧的发展可能与历史模式显著不同。该SGER项目还将支持加州理工学院环境科学与工程专业三年级研究生Richard Wildman先生的研究生培训。除了学术研究之外，他还积极参与加州Lawndale的Environmental Charter High School（一所位于洛杉矶县服务不足地区的公立学校）的拓展和课程开发。sg的理由。由于目前湖泊水位较低，因此有一个独特的机会来研究沉积物改造对营养动态的影响，特别是沉积物中磷的释放。目前，以前沉积的沉积物暴露在河流流入中。随着湖泊水位的上升，这些沉积物将被重新淹没。由于2000-2004年干旱的极端减少和2005年径流高于平均水平的流入，在沉积物三角洲创造了前所未有的物理条件，我们要求SGER资助来研究这个变化系统中的磷和微量金属动态。这项工作的时间安排也与垦务局计划的实地抽样相吻合，垦务局将为抽样提供后勤支持。

0621371HeringSGER: Phosphorus release and metal redox cycling associated with sediment reworking inthe Colorado River Delta, Lake Powell, UtahAbstract. As a result of the drought that began in 2000 and reservoir operations that provided aconstant water supply to the lower Colorado River basin states, Lake Powell is currently at only46% capacity. Under these conditions, the river inflows cut through sediments previouslydeposited in the Colorado River Delta. We hypothesize that the consequent resuspension ofsediments may result in enhanced phosphorus release and metal redox cycling. In recent years, ithas been observed that anoxia develops in bottom water intersecting the delta sediments, whichcould also result in P release due to reductive dissolution of iron oxide carrier phases in thesediments.Primary production in Lake Powell is phosphorus limited and changes in phosphorusavailability could have significant ecological consequences. Suspended sediment transported bythe Colorado River is the principal source of phosphorus to Lake Powell; much of this sedimentload is deposited as the Colorado River flows in to the lake (i.e., the river-lake boundary). Thuspreviously-deposited delta sediments represent a substantial reservoir of phosphorus.Intellectual Merit. The proposed project will examine the coupling of biogeochemical andphysical processes and their impacts on phosphorus and trace metal dynamics. Speciation ofphosphorus in solid phases (specifically the suspended sediment and delta sediments) will bedetermined and related to the conditions under which phosphorus may be released from thesediments. The role of reductive dissolution of metal (e.g., iron) oxides in phosphorus releasewill also be examined.Broader Impact. Phosphorus dynamics exert a key control on primary production inLake Powell. We anticipate that our results will show whether phosphorus and trace metaldynamics are altered under the current conditions where Colorado Rived inflows cut throughpreviously-deposited delta sediments. If phosphorus dynamics are affected, patterns of primaryproduction and the development of bottom water anoxia during the recovery from droughtconditions may be significantly different from historical patterns.This SGER project will also support the graduate training of Mr. Richard Wildman, athird year graduate student in Environmental Science & Engineering at Caltech. In addition tohis academic studies, Mr. Wildman has been actively engaged in outreach and curriculumdevelopment at the Environmental Charter High School in Lawndale, CA, a public schoollocated in an underserved area of Los Angeles County.SGER Justification. Because of the current low lake level, there is a unique opportunity toexamine the effects of sediment reworking on nutrient dynamics, specifically phosphorus releasefrom sediments. Currently, previously-deposited sediments are exposed to river inflows. As thelake levels rise, these sediments will be resubmerged. Since the extreme drawdown in the 2000-2004 drought and the above-average inflows of the 2005 run-off are creating unprecedentedphysical conditions in the sediment delta, we are requesting SGER funding to examine thephosphorus and trace metal dynamics in this changing system. This work is also timed tocoincide with planned field sampling by the Bureau of Reclamation, which will providelogistical support for sampling.