Alternative Biogeochemical States of River Pools Mediated by Hippo Use and Flow Variability
Alternative Biogeochemical States of River Pools Mediated by Hippo Use and Flow Variability
复制标题
DOI：
10.1007/s10021-020-00518-3
复制
发表时间：
2020-06-08
期刊：
影响因子：
3.7
通讯作者：
Post, David M.
中科院分区：
文献类型：
--
作者：
Dutton, Christopher L.;Subalusky, Amanda L.;Post, David M.
河马（Hippopotami）是生态系统工程师，通过从陆地放牧中转移有机物质和营养物质来补贴水生生态系统，对水生生态地球化学产生潜在的深远影响。我们研究了河马补贴对肯尼亚马拉河中不同水文条件和河马使用强度的水池中生态地球化学循环的影响。我们采样的上游，下游，并在不同的体积，流量和河马数量的水池的表面和底部，无论是之前和之后冲洗流。河马数量与水体停留时间的乘积作为河马补贴对水体生态地球化学影响的指标（河马补贴指数，HSI）。低HSI河马池之间的冲洗流仍然是好氧的，可能是一个源或汇的营养物质。高HSI河马池在冲洗水流之间迅速变得缺氧，并输出营养物质和厌氧微生物代谢的副产品，包括高浓度的总氨氮、硫化氢和甲烷。中等HSI河马池更类似于高HSI河马池，但还原物质的浓度较低。间歇性的高排放事件冲洗了水池，并将其重置为含氧状态。从好氧状态到缺氧状态的转变取决于水的停留时间，在冲洗流量较小的池中，向缺氧的转变速度更快。这些交替的好氧和缺氧状态之间的频繁转换在池中以及在下游接收沃茨中产生了空间和时间上的异质性。在河流系统中，河马对水质的影响是一个问题，保持自然的流动状态，包括冲洗流量，减轻河马的影响。
Hippopotami (hippos) are ecosystem engineers that subsidize aquatic ecosystems through the transfer of organic matter and nutrients from their terrestrial grazing, with potentially profound effects on aquatic biogeochemistry. We examined the influence of hippo subsidies on biogeochemical cycling in pools of varying hydrology and intensity of hippo use in the Mara River of Kenya. We sampled upstream, downstream, and at the surface and bottom of pools of varying volume, discharge, and hippo numbers, both before and after flushing flows. The product of hippo number and water residence time served as an index of the influence of hippo subsidies (hippo subsidy index, HSI) on aquatic biogeochemistry. Low-HSI hippo pools remained oxic between flushing flows and could be a source or sink for nutrients. High-HSI hippo pools quickly became anoxic between flushing flows and exported nutrients and byproducts of anaerobic microbial metabolism, including high concentrations of total ammonia nitrogen, hydrogen sulfide, and methane. Medium-HSI hippo pools were more similar to high-HSI hippo pools but with lower concentrations of reduced substances. Episodic high discharge events flushed pools and reset them to the oxic state. Transitions from oxic to anoxic states depended on water residence time, with faster transitions to anoxia in pools experiencing smaller flushing flows. Frequent shifts between these alternative oxic and anoxic states create heterogeneity in space and time in pools as well as in downstream receiving waters. In river systems where the influence of hippos on water quality is a concern, maintaining the natural flow regime, including flushing flows, ameliorates impacts of hippos.