Applied Limnology Laboratory, Federal University of São João del-Rei, São João del-Rei, Brazil.
Applied Limnology Laboratory, Federal University of São João del-Rei, São João del-Rei, Brazil.
Sci Total Environ. 2016 Apr 15;550:785-792. doi: 10.1016/j.scitotenv.2016.01.158. Epub 2016 Feb 2.
Many tropical biomes are threatened by rapid land-use change, but its catchment-wide biogeochemical effects are poorly understood. The few previous studies on DOM in tropical catchments suggest that deforestation and subsequent land use increase stream water dissolved organic carbon (DOC) concentrations, but consistent effects on DOM elemental stoichiometry have not yet been reported. Here, we studied stream water DOC concentrations, catchment DOC exports, and DOM elemental stoichiometry in 20 tropical catchments at the Cerrado-Atlantic rainforest transition, dominated by natural vegetation, pasture, intensive agriculture, and urban land cover. Streams draining pasture could be distinguished from those draining natural catchments by their lower DOC concentrations, with lower DOM C:N and C:P ratios. Catchments with intensive agriculture had higher DOC exports and lower DOM C:P ratios than natural catchments. Finally, with the highest DOC concentrations and exports, as well as the highest DOM C:P and N:P ratios, but the lowest C:N ratios among all land-use types, urbanized catchments had the strongest effects on catchment DOM. Thus, urbanization may have alleviated N limitation of heterotrophic DOM decomposition, but increased P limitation. Land use-especially urbanization-also affected the seasonality of catchment biogeochemistry. While natural catchments exhibited high DOC exports and concentrations, with high DOM C:P ratios in the rainy season only, urbanized catchments had high values in these variables throughout the year. Our results suggest that urbanization and pastoral land use exerted the strongest impacts on DOM biogeochemistry in the investigated tropical catchments and should thus be important targets for management and mitigation efforts.
许多热带生物群落受到快速土地利用变化的威胁，但人们对其集水区范围内的生物地球化学效应知之甚少。之前关于热带集水区 DOM 的少数研究表明，森林砍伐和随后的土地利用增加了溪流水中溶解有机碳 (DOC) 的浓度，但尚未有关于 DOM 元素化学计量的一致影响的报道。在这里，我们在巴西塞拉多-大西洋雨林过渡带的 20 个热带集水区中研究了溪流水中的 DOC 浓度、集水区的 DOC 输出以及 DOM 元素化学计量，这些集水区主要由自然植被、牧场、集约农业和城市土地覆盖。牧场排水的溪流与自然集水区的溪流不同，其 DOC 浓度较低，DOM 的 C:N 和 C:P 比值也较低。与自然集水区相比，集约化农业集水区的 DOC 输出量更高，DOM 的 C:P 比值更低。最后，城市化集水区的 DOC 浓度和输出量最高，DOM 的 C:P 和 N:P 比值最高，但 C:N 比值最低，对集水区 DOM 的影响最大。因此，城市化可能缓解了异养 DOM 分解的氮限制，但增加了磷限制。土地利用——尤其是城市化——也影响了集水区生物地球化学的季节性。虽然自然集水区的 DOC 输出和浓度较高，且仅在雨季 DOM 的 C:P 比值较高，但城市化集水区在这些变量全年都具有较高的值。我们的研究结果表明，城市化和牧场土地利用对研究热带集水区的 DOM 生物地球化学产生了最强的影响，因此应成为管理和缓解工作的重要目标。
