Department of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria.
Department of Fisheries and Aquatic Sciences, University of Eldoret, Eldoret, Kenya.
PLoS One. 2021 Sep 8;16(9):e0257076. doi: 10.1371/journal.pone.0257076. eCollection 2021.
Populations of large wildlife have declined in many landscapes around the world, and have been replaced or displaced by livestock. The consequences of these changes on the transfer of organic matter (OM) and nutrients from terrestrial to aquatic ecosystems are not well understood. We used behavioural data, excretion and egestion rates and C: N: P stoichiometry of dung and urine of zebu cattle, to develop a metabolism-based estimate of loading rates of OM (dung), C, N and P into the Mara River, Kenya. We also directly measured the deposition of OM and urine by cattle into the river during watering. Per head, zebu cattle excrete and/or egest 25.6 g dry matter (DM, 99.6 g wet mass; metabolism) - 27.7 g DM (direct input) of OM, 16.0-21.8 g C, 5.9-9.6 g N, and 0.3-0.5 g P per day into the river. To replace loading rates OM of an individual hippopotamus by cattle, around 100 individuals will be needed, but much less for different elements. In parts of the investigated sub-catchments loading rates by cattle were equivalent to or higher than that of the hippopotamus. The patterns of increased suspended materials and nutrients as a result of livestock activity fit into historical findings on nutrients concentrations, dissolved organic carbon and other variables in agricultural and livestock areas in the Mara River basin. Changing these patterns of carbon and nutrient transport and cycling are having significant effects on the structure and functioning of both terrestrial and aquatic ecosystems.
在世界许多景观中，大型野生动物的数量已经减少，被牲畜所取代或排挤。这些变化对有机物质（OM）和养分从陆地向水生生态系统转移的影响尚未得到很好的理解。我们使用行为数据、排泄和排遗率以及粪便和尿液的 C:N:P 化学计量学，来开发一种基于代谢的方法，估算 OM（粪便）、C、N 和 P 进入肯尼亚马拉河的负载率。我们还直接测量了牛在饮水时向河流中沉积的 OM 和尿液。每头牛每天排泄和/或排遗 25.6 克干物质（DM，99.6 克湿质量；代谢）-27.7 克 DM（直接输入）的 OM、16.0-21.8 克 C、5.9-9.6 克 N 和 0.3-0.5 克 P 进入河流。为了用牛来替代单个河马的 OM 负载率，大约需要 100 头牛，但对于不同的元素则需要的数量要少得多。在调查的部分次流域，牛的负载率与河马相当或更高。由于牲畜活动导致的悬浮物质和养分增加的模式与马拉河流域农业和畜牧业地区的养分浓度、溶解有机碳和其他变量的历史发现相符。改变这些碳和养分运输和循环的模式正在对陆地和水生生态系统的结构和功能产生重大影响。
