McDowell R W, Sharpley A N
AgResearch Ltd, Invermay Agricultural Research Centre, Private Bag 50034, Mosgiel, New Zealand.
J Environ Qual. 2003 May-Jun;32(3):937-48. doi: 10.2134/jeq2003.9370.
Phosphorus runoff from agricultural fields has been linked to fresh-water eutrophication. However, edge-of-field P losses can be modified by benthic sediments during stream flow by physiochemical processes associated with Al, Fe, and Ca, and by biological assimilation. We investigated fluvial P when exposed to stream-bed sediments (top 3 cm) collected from seven sites representing forested and agricultural areas (pasture and cultivated), in a mixed-land-use watershed. Sediment was placed in a 10-m-long, 0.2-m-wide fluvarium to a 3-cm depth and water was recirculated over the sediment at 2 L s(-1) and 5% slope. When overland flow (4 mg dissolved reactive phosphorus [DRP] and 9 mg total phosphorus [TP] L(-1)) from manured soils was first recirculated, P uptake was associated with Al and Fe hydrous oxides for sediments from forested areas (pH 5.2-5.4) and by Ca for sediments from agricultural areas (pH 6.5-7.2). A large increase (up to 200%) in readily available P NH4Cl fraction was noted. After 24 h, DRP concentration in channel flow was related to sediment solution P concentration at which no net sorption or desorption of P occurs (EPC0) (r2 = 0.77), indicating quasi-equilibrium. When fresh water (approximately 0.005 mg P L(-1) mean base flow DRP at seven sites) was recirculated over the sediments for 24 h, P release kinetics followed an exponential function. Microbial biomass P accounted for 34 to 43% of sediment P uptake from manure-rich overland flow. Although abiotic sediment processes played a dominant role in determining P uptake, biotic process are clearly important and both should be considered along with the location and management of landscape inputs for remedial strategies to be effective.
农田的磷径流与淡水富营养化有关。然而，在水流过程中，底栖沉积物可通过与铝、铁和钙相关的物理化学过程以及生物同化作用来改变农田边缘的磷流失。我们在一个混合土地利用流域中，研究了从代表森林和农业区域（牧场和耕地）的七个地点采集的河床沉积物（顶部3厘米）对河流磷的影响。将沉积物放置在一个10米长、0.2米宽的水槽中，深度为3厘米，水以2升/秒的流速和5%的坡度在沉积物上循环流动。当来自施肥土壤的地表径流（4毫克溶解态活性磷[DRP]和9毫克总磷[TP]/升）首次循环时，森林区域沉积物（pH 5.2 - 5.4）的磷吸收与铝和铁的水合氧化物有关，而农业区域沉积物（pH 6.5 - 7.2）的磷吸收与钙有关。注意到易利用磷的氯化铵部分大幅增加（高达200%）。24小时后，河道水流中的DRP浓度与沉积物溶液中磷浓度（此时磷没有净吸附或解吸，即EPC0）相关（r2 = 0.77），表明达到了准平衡状态。当淡水（七个地点平均基流DRP约为0.005毫克/升）在沉积物上循环24小时时，磷释放动力学遵循指数函数。微生物生物量磷占富含有机质地表径流沉积物磷吸收量的34%至43%。虽然非生物沉积物过程在决定磷吸收方面起主导作用，但生物过程显然也很重要，为使修复策略有效，应将两者与景观输入的位置和管理一并考虑。
