Marine Derived Nutrients Plant and Invertebrate Stable Isotope Data, Kenai Penninsula, Alaska (2004-2006)

MDN and delivered by salmon and other anadromous fishes are considered important drivers in riverine ecosystems, providing nutrients and food to these land-based food webs. However, we know little about the relative value of MDN compared to other nutrient and carbon sources (e.g., watershed-derived) in the Gulf of Alaska region. The objectives of this study were to develop a water chemistry proxy for monitoring salmon returns, and to track and measure MDN effects in stream, riparian and nearshore environments, on the southern Kenai Peninsula. We show that stable isotopes and fatty acids were both effective indicators of MDN assimilation in stream resident fishes. Our water nutrient profiles suggest rapid nitrogen (N) uptake in Homer streams, which have underlying phosphorous (P) rich geology. Stable isotopes were most effective when the salmon-free end member was relatively depleted. Marine-derived nitrogen (deltaN15) was highly variable, likely due to spatial variation in N sources and cycling, and may not be a reliable predictor of MDN inputs at the watershed scale. Fatty acids were most effective when quantified as ω3:ω6. Based on our data the development of a nutrient proxy for estimating salmon escapement shows some promise in certain situations, but is unlikely in the majority of salmon streams in southcentral Alaska.

Walker, C.M., D. Rinella, M.S. Wipfli and C.S. Stricker. 2007. Presence and Effects of Marine Derived Nutrients (MDN) in Stream, Riparian and Nearshore Ecosystems on Southern Kenai Peninsula, Alaska: Developing Monitoring Tools for Tracking MDN in Alaska Watersheds. Exxon Valdex Oil Spill Trustee Council Gulf Ecosystem Monitoring Program Final Report (Project Number 040726).

海洋源氮（Marine-derived Nitrogen, MDN）经鲑鱼及其他溯河洄游鱼类输送，是河流生态系统的重要驱动因子，可为流域陆地食物网提供营养与食物来源。然而在阿拉斯加湾区域，相较于其他营养与碳源（如流域衍生源），海洋源氮的相对贡献占比仍鲜为人知。本研究的目标为构建水体化学替代指标以监测鲑鱼洄游量，并在基奈半岛南部的溪流、河岸带及近岸环境中追踪与量化海洋源氮的生态效应。
研究结果表明，稳定同位素与脂肪酸均可作为溪流定居性鱼类体内海洋源氮同化作用的有效指示物。本研究的水体营养特征分析显示，荷马（Homer）流域的底层地质富含磷（P），其溪流中的氮（N）吸收速率较快。当无鲑鱼端元的同位素值相对贫化时，稳定同位素的指示效果最佳。海洋源氮的δ¹⁵N值波动幅度较大，这可能源于氮源与循环过程的空间异质性，因此在流域尺度上，该指标或许无法可靠预测海洋源氮的输入量。当以ω3:ω6比值对脂肪酸进行定量分析时，其指示效果最为理想。基于本研究数据，构建用于估算鲑鱼逃逸量的营养替代指标在部分场景中具备应用潜力，但在阿拉斯加中南部的多数鲑鱼溪流中，该方法的实用性较为有限。
Walker, C.M.、D. Rinella、M.S. Wipfli 与 C.S. Stricker，2007年。《阿拉斯加州基奈半岛南部溪流、河岸带及近岸生态系统中海洋源氮的存在与效应：开发用于阿拉斯加流域海洋源氮追踪的监测工具》。埃克森瓦尔迪兹溢油理赔委员会海湾生态系统监测项目最终报告（项目编号：040726）。