Instituto de Investigaciones Marinas y Costeras, Consejo Nacional de Investigaciones Científicas y Técnicas (UNMdP-CONICET), FCEyN, CC1260, 7600 Mar del Plata, Argentina; Instituto de Geología de Costas y del Cuaternario, Universidad Nacional de Mar del Plata-CIC, 3350 Funes St., Level 1, 7600 Mar del Plata, Argentina.
Department of Earth and Environmental Sciences, KU Leuven, B-3001 Leuven, Belgium; UK Centre for Ecology and Hydrology, Lancaster Environment Centre, Lancaster LA1 4AP, UK.
Sci Total Environ. 2020 May 1;715:136909. doi: 10.1016/j.scitotenv.2020.136909. Epub 2020 Jan 24.
Eutrophication is a globally significant challenge facing aquatic ecosystems, mostly associated with human induced enrichment of these ecosystems with nitrogen and phosphorus. Given the complexity of assigning eutrophication issues to local primary N sources in field-based studies, this paper proposes a multi-stable isotope and biological framework to track nitrogen biogeochemical transformations, inputs and fate of nitrate in groundwater-dependent shallow lakes. Three representative freshwater ecosystems from the Pampa Plain (Argentina), with different land uses and topographic features were selected. Groundwater (N = 24), lake (N = 29) and stream (N = 20) samples were collected for isotope (δN-NO and δO-NO, δO-HO) and hydrogeochemical (major ions and nutrients) determinations, and in the case of surface water, also for biological determinations (chlorophyll-a, fecal coliforms and nitrifying bacteria abundance). Both chemical and isotopic characteristics clearly indicated that denitrification was limited in lakes and streams, while evidence of assimilation in shallow lakes was confirmed. The results suggested that groundwater denitrification plays a role in the nitrate concentration pattern observed in the Pampeano Aquifer. The proportional contribution of nitrate sources to the inflow streams for all years were estimated by using Bayesian isotope mixing models, being ammonium nitrified in the system from soil and fertilizers ~50 - 75 %, sewage/manure ~20 - 40 % and atmospheric deposition ~5 - 15 %. In this sense, agricultural practices seem to have a relevant role in the eutrophication and water quality deterioration for these watersheds. However, limnological, bacterial and algal variables, assessed simultaneously with isotopic tracers, indicated spatio-temporal differences within and between these aquatic ecosystems. In the case of Nahuel Rucá Lake, animal manure was a significant source of nitrogen pollution, in contrast to La Brava Lake. In Los Padres Lake, agricultural practices were considered the main sources of nitrate input to the ecosystem.
富营养化是水生生态系统面临的一个全球性重大挑战，主要与人类将氮和磷等营养物质人为地富集到这些生态系统有关。鉴于在基于实地的研究中确定富营养化问题与当地主要氮源之间的关系具有复杂性，本文提出了一个多稳定同位素和生物框架，以追踪地下水依赖型浅水湖中硝酸盐的氮生物地球化学转化、输入和归宿。从潘帕斯平原（阿根廷）选择了具有不同土地利用和地形特征的三个具有代表性的淡水生态系统。采集了地下水（N=24）、湖泊（N=29）和溪流（N=20）样本，用于同位素（δN-NO 和 δO-NO、δO-HO）和水文地球化学（主要离子和养分）测定，并且在地表水的情况下，还进行了生物测定（叶绿素-a、粪大肠菌群和硝化细菌丰度）。化学和同位素特征均清楚地表明，反硝化作用在湖泊和溪流中受到限制，而浅水湖中存在同化作用的证据得到了证实。结果表明，地下水反硝化作用在潘帕诺含水层中观察到的硝酸盐浓度模式中起作用。使用贝叶斯同位素混合模型估算了所有年份流入溪流的硝酸盐源的比例贡献，其中土壤和肥料中的铵硝化为系统提供的氮50-75%、污水/粪便20-40%和大气沉降~5-15%。从这个意义上说，农业实践似乎在这些流域的富营养化和水质恶化方面发挥了重要作用。然而，同时使用稳定同位素示踪剂评估的湖泊学、细菌和藻类变量表明这些水生生态系统之间和内部存在时空差异。在纳韦尔·鲁卡湖的情况下，动物粪便是氮污染的一个重要来源，而在拉布拉瓦湖则不是。在洛斯帕德雷斯湖，农业实践被认为是硝酸盐输入生态系统的主要来源。
