Tracing nutrient and organic matter sources and biogeochemical processes in the Sacramento River and Northern Delta: proof of concept using stable isotope data

Isotope and chemical data for samples collected during several overlapping studies in the Sacramento River and Delta conducted 2009-2011 is presented to evaluate the potential usefulness of stable isotope techniques for testing hypotheses about sources of nutrients and algae, and biogeochemical processes in section of the San Francisco Estuary. These data are used to provide an independent test of the hypothesis that ammonium derived primarily from waste-water treatment plants was inhibiting phytoplankton uptake of nitrate. These data represent approximately monthly samples from 15-20 sites along transects of the river and delta and were analyzed for the stable isotopic compositions of ammonium, nitrate, particulate organic matter, dissolved organic carbon, and water then used to demonstrate the viability of assessing the temporal and spatial variations in the sources, transport, and sinks of nutrients and organic matter in the Sacramento River and Delta Another main focus was to assess whether there were significant differences between the chemistry and isotopic compositions of mainstem Sacramento River samples and (1) samples from tributaries within the Cache/Yolo Slough Complex, and (2) samples from the main two distributaries of the Sacramento River downstream of the waste-water treatment plant: Miner Slough and Steamboat Slough.\r\n\r\nUsing these data we present (1) "proof of concept" of the usefulness of isotope techniques combined with water chemistry and hydrological modeling in this ecosystem, (2) key findings from some of the ongoing parts of the studies, and (3) downloadable Excel files of the relevant isotope and chemistry data with associated metadata to facilitate these data being used for other investigations. The rationale was that if isotope techniques showed promise in identifying sources and processes in this ecosystem, a comprehensive multi-isotope approach would later be used for quantifying nutrient and organic matter sources and biogeochemical processes relevant to questions about causes of environmental problems. These more quantitative assessments are in progress.

本数据集呈现了2009-2011年间在萨克拉门托河（Sacramento River）及其三角洲开展的多项重叠研究中采集的样品的同位素与化学数据，旨在评估稳定同位素技术（stable isotope techniques）在检验圣弗朗西斯科河口（San Francisco Estuary）部分区域内营养盐、藻类来源及生物地球化学过程相关假说方面的潜在应用价值。本数据集可用于独立验证一项假说，即主要源自污水处理厂的铵盐会抑制浮游植物对硝酸盐的摄取。本数据集包含沿萨克拉门托河及三角洲断面布设的15至20个采样点的约月度样品，对这些样品中的铵盐、硝酸盐、颗粒有机质、溶解有机碳及水体的稳定同位素组成进行了分析，以此论证评估萨克拉门托河及其三角洲内营养盐与有机质的来源、迁移及汇的时空变化特征的可行性。本研究的另一核心目标是评估萨克拉门托河干流样品与以下两类样品的化学及同位素组成是否存在显著差异：(1) 卡什-约洛泻湖综合体（Cache/Yolo Slough Complex）内支流的样品；(2) 污水处理厂下游萨克拉门托河两条主要分流河道——迈纳泻湖（Miner Slough）与汽船泻湖（Steamboat Slough）的样品。
基于本数据集，本研究完成了三项工作：(1) 验证了同位素技术结合水化学与水文模型在该生态系统中的应用有效性，即完成了概念验证（proof of concept）；(2) 呈现了部分正在进行的研究的关键发现；(3) 提供了包含相关同位素与化学数据及关联元数据的可下载Excel文件，以方便该数据集被应用于其他研究。本研究的基本逻辑为：若同位素技术在识别该生态系统的来源与过程方面展现出应用潜力，后续将采用全面的多同位素方法，量化与环境问题成因相关的营养盐与有机质来源及生物地球化学过程。目前这类更具定量性的评估工作正在推进中。