Smart and Sustainable Cities Program, University Nove de Julho (UNINOVE), São CEP SP, Brazil.
Smart and Sustainable Cities Program, University Nove de Julho (UNINOVE), São CEP SP, Brazil; Professional Masters in Environmental Management and Sustainability, University Nove de Julho (UNINOVE), São Paulo CEP 05001-100, SP, Brazil.
Environ Res. 2017 May;155:314-320. doi: 10.1016/j.envres.2017.02.023. Epub 2017 Mar 20.
Urban forests are usually affected by several types of atmospheric contaminants and by abnormal variations in weather conditions, thus facilitating the biotic homogenization and modification of ecosystem processes, such as nutrient cycling. Peri-urban forests and even natural forests that surround metropolitan areas are also subject to anthropogenic effects generated by cities, which may compromise the dynamics of these ecosystems. Hence, this study advances the hypothesis that the forests located at the margins of the Metropolitan Region of São Paulo (MRSP), Brazil, have high concentrations of atmospheric contaminants leading to adverse effects on litter fall stock.
The production, stock and decomposition of litter fall in two forests were quantified. The first, known as Guarapiranga forest, lies closer to the urban area and is located within the MRSP, approximately 20km from the city center. The second, Curucutu forest, is located 70km from the urban center. This forest is situated exactly on the border of the largest continuum of vegetation of the Atlantic Forest. To verify the reach of atmospheric pollutants from the urban area, levels of heavy metals (Cd, Pb, Ni, Cu) adsorbed on the litter fall deposited on the soil surface of the forests were also quantified.
The stock of litter fall and the levels of heavy metals were generally higher in the Guarapiranga forest in the samples collected during the lower rainfall season (dry season). Non-metric multidimensional scaling multivariate analysis showed a clear distinction of the sample units related to the concentrations of heavy metals in each forest. A subtle difference between the units related to the dry and rainy seasons in the Curucutu forest was also noted. Multivariate Analysis of Variance revealed that both site and season of the year (dry or rainy) were important to differentiate the quantity of heavy metals in litter fall stock, although the analysis did not show the interaction between these two factors. Precipitation appeared to be an important factor to disperse air pollutants; one method to better regulate this process is the development and integration of green infrastructure at city level, which might contribute to nature-based solutions.
Results suggest that although the Curucutu forest is not very far from the MRSP, which could result in heavy metal levels similar to those observed in the Guarapiranga forest, the weather conditions, geographic location and rainfall rates might act as efficient physical barriers against the dispersion of pollutants in the urban area. However, it is important to highlight that in the period studied (2012-2013), MRSP presented unusual features during the winter period marked by the highest levels of precipitation which was due to several numbers of frontal systems and also due to their permanence for a couple days in the region. Thus, it is recommended to continue this study in order to obtain a database for characterizing the seasonal variation of air pollution levels in the litter fall and their adverse effects on ecosystem processes in these remnants of the Atlantic Forest.
城市森林通常会受到多种类型的大气污染物以及天气条件异常变化的影响，从而促进生物同质化和生态系统过程（如养分循环）的改变。环绕大都市地区的城郊森林甚至天然森林也会受到城市产生的人为影响，这可能会影响这些生态系统的动态。因此，本研究提出了一个假设，即在巴西圣保罗大都市区（MRSP）边缘的森林大气污染物浓度较高，对凋落物储量产生不利影响。
对两片森林的凋落物产生、储量和分解进行了量化。第一片森林称为瓜拉皮兰加森林，更靠近城市区域，位于 MRSP 内，距离市中心约 20 公里。第二片森林称为库里楚图森林，距离城市中心 70 公里。该森林正好位于大西洋森林最大植被连续体的边界上。为了验证城市地区大气污染物的影响范围，还对森林地表土壤上沉积的凋落物所吸附的重金属（Cd、Pb、Ni、Cu）水平进行了量化。
在降雨量较低的旱季（旱季）收集的样本中，瓜拉皮兰加森林的凋落物储量和重金属水平普遍较高。非度量多维标度多元分析显示，每个森林中与重金属浓度相关的样本单元之间存在明显差异。库里楚图森林的干湿两季样本单元之间也存在细微差异。方差分析表明，无论是地点还是一年中的季节（旱季或雨季），对于区分凋落物储量中的重金属数量都很重要，尽管分析并未显示这两个因素之间的相互作用。降水似乎是分散空气污染物的重要因素；一种更好地调节这一过程的方法是在城市层面上开发和整合绿色基础设施，这可能有助于基于自然的解决方案。
结果表明，尽管库里楚图森林离 MRSP 不远，可能导致与瓜拉皮兰加森林相似的重金属水平，但天气条件、地理位置和降雨量可能会成为城市地区污染物扩散的有效物理屏障。然而，值得强调的是，在研究期间（2012-2013 年），MRSP 在冬季出现了异常特征，该季节的降雨量最高，这是由于多个锋面系统的存在以及它们在该地区停留了数天。因此，建议继续这项研究，以便为描述大西洋森林这些残余物凋落物中空气污染水平的季节性变化及其对生态系统过程的不利影响获得一个数据库。
