Land Use Change Influences Ecosystem Function in Headwater Streams of the Lowland Amazon Basin
Land Use Change Influences Ecosystem Function in Headwater Streams of the Lowland Amazon Basin
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DOI：
10.3390/w13121667
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发表时间：
2021-06-01
期刊：
影响因子：
3.4
通讯作者：
Macedo, Marcia N.
中科院分区：
文献类型：
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作者：
Jankowski, Kathi Jo;Deegan, Linda A.;Macedo, Marcia N.
集约化农业改变了源头河流，但我们对其影响的了解仅限于目前农业扩张和集约化速度最快的热带地区。河岸森林保护是一个重要的保护工具，但他们是否提供足够的保护流功能，在这些地区的热带农业快速发展还没有得到很好的研究。为了解决这些差距，我们进行了一项研究，在低地巴西亚马逊，一个地区正在快速农田扩张，以评估土地利用变化对有机质动态（OM），生态系统代谢，营养物质的浓度和吸收（硝酸盐和磷酸盐）在11个一阶流排水森林（n = 4）或农田（n = 7）流域与完整的河岸森林。我们发现，流有类似的陆地凋落物输入，但OM生物量较低的农田流。总初级生产力低，土地利用之间没有差异，但生态系统呼吸和生态系统净生产表现出更大的季节性在农田流。虽然我们没有发现流浓度的溶解养分的差异，磷酸盐的吸收超过硝酸盐的吸收在所有流，是在农田比森林流。这表明河流对磷的保留性比氮更强，如果肥料氮到达河流，它将在河流网络中输出。总体而言，我们发现相对细微的差异流功能，表明河岸缓冲区迄今提供了保护，防止在其他系统中看到的重大功能转变。然而，我们确实观察到的变化与流域尺度的水文变化有关，水温，以及流域森林砍伐造成的光可用性。这对保护不断扩大的亚马逊农田地区数万公里的溪流具有重要意义。
Intensive agriculture alters headwater streams, but our understanding of its effects is limited in tropical regions where rates of agricultural expansion and intensification are currently greatest. Riparian forest protections are an important conservation tool, but whether they provide adequate protection of stream function in these areas of rapid tropical agricultural development has not been well studied. To address these gaps, we conducted a study in the lowland Brazilian Amazon, an area undergoing rapid cropland expansion, to assess the effects of land use change on organic matter dynamics (OM), ecosystem metabolism, and nutrient concentrations and uptake (nitrate and phosphate) in 11 first order streams draining forested (n = 4) or cropland (n = 7) watersheds with intact riparian forests. We found that streams had similar terrestrial litter inputs, but OM biomass was lower in cropland streams. Gross primary productivity was low and not different between land uses, but ecosystem respiration and net ecosystem production showed greater seasonality in cropland streams. Although we found no difference in stream concentrations of dissolved nutrients, phosphate uptake exceeded nitrate uptake in all streams and was higher in cropland than forested streams. This indicates that streams will be more retentive of phosphorus than nitrogen and that if fertilizer nitrogen reaches streams, it will be exported in stream networks. Overall, we found relatively subtle differences in stream function, indicating that riparian buffers have thus far provided protection against major functional shifts seen in other systems. However, the changes we did observe were linked to watershed scale shifts in hydrology, water temperature, and light availability resulting from watershed deforestation. This has implications for the conservation of tens of thousands of stream kilometers across the expanding Amazon cropland region.