SBC LTER: OCEAN: Particulate Organic Matter Content and Composition of Stream, Estuarine, and Marine Sediments

An unprecedented five-year drought in California, coupled with
conditions of anomalously low ocean productivity and the prospect of
one of the strongest El Niño periods on record with above average
rainfall were the impetus for this RAPID award, which seeks to test
specific hypotheses pertaining to the origin, distribution,
processing, and bioavailability of terrestrial organic matter in
coastal marine sediments and their potential for serving as a
reservoir of nitrogen storage to fuel nearshore primary production
during periods when nitrate concentrations are low. The goals of the
research were to: (1) measure bulk properties and biomarker tracers
of particulate organic matter (POM) in stream water and in coastal
marine sediments at SBC LTER and other reef sites differing in
exposure to terrestrial runoff prior to and following large storm
events, (2) determine the bioavailability of dissolved organic
matter (DOM) released from POM in marine sediments following large
runoff events, and (3) measure changes in concentrations of
dissolved inorganic and organic nitrogen in pore water of marine
sediments near to and distant from stream mouths in the Santa
Barbara Channel. Samples were analyzed for organic matter content
using a loss-on-ignition combustion method, and samples were also
analyzed for organic carbon and nitrogen content and isotopes using
a stable isotope mass spectrometer interfaced with an elemental
analyzer. Subsamples were shipped to the laboratory of Marc Lucotte
at the University of Québec, Montréal for analysis of lignin content
using the cupric oxidation method.

加利福尼亚州前所未有的五年干旱，叠加异常偏低的海洋生产力状况，以及有望迎来有记录以来最强厄尔尼诺（El Niño）周期之一且降雨量高于平均水平的前景，成为本次RAPID项目立项的动因。本项目旨在验证一系列特定假说，内容涉及海岸海洋沉积物中陆源有机质的来源、分布、转化过程与生物标志物示踪剂，以及在硝酸盐浓度较低时期，这些沉积物作为氮储存库以支撑近岸初级生产的潜力。本研究的目标包括：(1) 在大型风暴事件前后，测量圣巴巴拉海岸长期生态研究站（SBC LTER）以及其他受陆源径流影响程度各异的礁区站点的溪流水体与海岸海洋沉积物中颗粒有机质（particulate organic matter, POM）的整体性质与生物标志物示踪剂；(2) 确定大型径流事件后海洋沉积物中颗粒有机质释放的溶解有机质（dissolved organic matter, DOM）的生物可利用性；(3) 监测圣巴巴拉海峡内靠近与远离河口的海洋沉积物孔隙水中溶解无机氮与溶解有机氮的浓度变化。研究采用灼烧减重燃烧法分析样品的有机质含量，并通过与元素分析仪联用的稳定同位素质谱仪，测定样品的有机碳、氮含量及其同位素组成。部分子样被送至魁北克大学蒙特利尔分校Marc Lucotte的实验室，采用铜氧化法分析木质素含量。