Forest Hydrology Laboratory, Department of Forest Sciences, Luiz de Queiroz College of Agriculture, University of São Paulo. Av. Pádua Dias 11, CEP 13418-900 Piracicaba, SP, Brazil.
Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, 20688 Solomons, MD, USA.
Sci Total Environ. 2017 Apr 15;584-585:339-347. doi: 10.1016/j.scitotenv.2016.12.150. Epub 2016 Dec 28.
In Brazil, the cultivation of bioenergy crops is expanding at an accelerated rate. Most of this expansion has occurred over low-intensity pasture and is considered sustainable because it does not involve deforestation of natural vegetation. However, the impacts on the water quality of headwater streams are poorly understood, especially with regard to the influence of land use patterns in the watershed. In this study, we investigated the effects of land-use conversion on the water quality of streams draining sugarcane fields and examined whether the preservation of forested areas at the top of the headwaters would help mitigate the negative impacts of intensive agriculture. Water samples were collected in two paired catchments in southeastern Brazil, which is one of the largest sugarcane production regions in the world. Our results show significant differences in the water quality of streams predominantly draining the pasture or the sugarcane field. Several parameters commonly used to indicate water quality, such as the concentrations of nitrate and suspended solids, were significantly higher in the sugarcane than in the pasture stream. Differences in water quality between the streams draining predominantly pasture or sugarcane fields were accentuated during the wet season. The preservation of forests surrounding the headwater streams was associated with overall better water quality conditions, such as lower nitrate concentrations and temperature of the stream water. We concluded that forest conservation in the headwater agricultural catchments is an important factor preventing water quality degradation in tropical streams. Therefore, we strongly recommend the preservation of robust riparian forests in the headwaters of tropical watersheds with intensive agriculture. More studies on the effects of best agricultural practices in bioenergy crops can greatly improve our capacity to prevent the degradation of water quality in the tropical waterways as intensive agriculture continues to expand in this region of the world.
在巴西，生物能源作物的种植正在加速扩张。这种扩张主要发生在低强度的牧场上，而且被认为是可持续的，因为它不涉及天然植被的砍伐。然而，人们对其对源头溪流水质的影响知之甚少，特别是流域土地利用模式的影响。在这项研究中，我们调查了土地利用方式的转变对甘蔗地溪流水质的影响，并探讨了在源头保持森林地区是否有助于减轻集约化农业的负面影响。我们在巴西东南部的两个配对流域采集了水样，该地区是世界上最大的甘蔗生产区之一。我们的研究结果表明，主要流经牧场或甘蔗地的溪流的水质存在显著差异。一些常用的水质指标，如硝酸盐和悬浮物浓度，在甘蔗地溪流中明显高于牧场溪流。在雨季，主要流经牧场或甘蔗地的溪流之间的水质差异更加明显。保护源头溪流周围的森林与整体更好的水质条件有关，例如硝酸盐浓度和溪流水温较低。我们得出的结论是，在农业流域的源头保护森林是防止热带溪流水质退化的一个重要因素。因此，我们强烈建议在热带流域的源头保护强健的河岸森林，这些流域有集约化农业。关于生物能源作物最佳农业实践的更多研究可以极大地提高我们在世界上这一地区防止水质退化的能力，因为集约化农业将继续在该地区扩张。
