Center for Watershed Sciences-Davis, University of California, Davis, California, United States of America.
California Department of Water Resources-West Sacramento, West Sacramento, California, United States of America.
PLoS One. 2020 Sep 18;15(9):e0216019. doi: 10.1371/journal.pone.0216019. eCollection 2020.
Similar to many large river valleys globally, the Sacramento River Valley has been extensively drained and leveed, hydrologically divorcing river channels from most floodplains. Today, the former floodplain is extensively managed for agriculture. Lack of access to inundated floodplains is recognized as a significant contributing factor in the decline of native Chinook Salmon (Oncorhynchus tshawytscha). We observed differences in salmon growth rate, invertebrate density, and carbon source in food webs from three aquatic habitat types-leveed river channels, perennial drainage canals in the floodplain, and agricultural floodplain wetlands. Over 23 days (17 February to 11 March, 2016) food web structure and juvenile Chinook Salmon growth rates were studied within the three aquatic habitat types. Zooplankton densities on the floodplain wetland were 53x more abundant, on average, than in the river. Juvenile Chinook Salmon raised on the floodplain wetland grew at 0.92 mm/day, 5x faster than fish raised in the adjacent river habitat (0.18 mm/day). Two aquatic-ecosystem modeling methods were used to partition the sources of carbon (detrital or photosynthetic) within the different habitats. Both modeling approaches found that carbon in the floodplain wetland food web was sourced primarily from detrital sources through heterotrophic pathways, while carbon in the river was primarily photosynthetic and sourced from in situ autotrophic production. Hydrologic conditions typifying the ephemerally inundated floodplain-shallower depths, warmer water, longer water residence times and predominantly detrital carbon sources compared to deeper, colder, swifter water and a predominantly algal-based carbon source in the adjacent river channel-appear to facilitate the dramatically higher rates of food web production observed in the floodplain. These results suggest that hydrologic patterns associated with seasonal flooding facilitate river food webs to access floodplain carbon sources that contribute to highly productive heterotrophic energy pathways important to the production of fisheries resources.
与全球许多大河谷一样，萨克拉门托河谷已被广泛排水和筑堤，在水文学上将河道与大多数洪泛平原隔开。如今，以前的洪泛平原被广泛用于农业管理。缺乏对淹没洪泛平原的通道被认为是本地奇努克鲑鱼（Oncorhynchus tshawytscha）减少的一个重要促成因素。我们观察到三种水生栖息地类型（筑堤河道、洪泛平原的常年排水渠和农业洪泛湿地）中的鲑鱼生长率、无脊椎动物密度和食物网中的碳源存在差异。在 2016 年 2 月 17 日至 3 月 11 日的 23 天内，我们在三种水生栖息地类型内研究了食物网结构和幼年奇努克鲑鱼的生长率。洪泛湿地的浮游动物密度平均比河流高出 53 倍。在洪泛湿地饲养的幼年奇努克鲑鱼的生长速度为 0.92 毫米/天，比在相邻河道栖息地饲养的鱼类快 5 倍（0.18 毫米/天）。使用两种水生生态系统建模方法来划分不同栖息地中碳（碎屑或光合）的来源。这两种建模方法都发现，洪泛湿地食物网中的碳主要来自碎屑源，通过异养途径，而河流中的碳主要是光合作用的，来源于原地自养生产。具有暂时淹没洪泛平原特点的水文条件——较浅的水深、较暖的水、较长的水停留时间和主要是碎屑碳源，与相邻河道中较深、较冷、较快的水和主要是藻类为基础的碳源形成鲜明对比，似乎有利于在洪泛平原观察到的食物网生产的显著提高。这些结果表明，与季节性洪水相关的水文模式有助于河流食物网获取洪泛平原碳源，这些碳源有助于形成对渔业资源生产至关重要的高度多产的异养能源途径。
