Limnological comparison of pristine and impacted lakes from a tropical, high-altitude karst region in southern Mexico

Climatic conditions strongly influence tropical karst lake limnology, but more information is required to understand how human impacts can modify their ecological patterns. The “Lagunas de Montebello” lake district, a tropical, high-altitude karst landscape, contains 139 solution lakes surrounded by tropical rainforests. To investigate the limnological changes that have been taking place in the “Lagunas de Montebello” in the past 20 years, we selected fourteen lakes for a comparative study: four impacted and ten pristine. The impacted lakes are on the northwest (NW) plateau area fed by surface waters and underground, whereas the pristine ones are on the southeast (SE) intermontane zone fed underground. Impacted lakes receive nutrients and organic matter from agricultural and urban/domestic wastewater from point and nonpoint surface sources. Heavy tropical storms flood the plateau zone, interconnecting the lakes and facilitating pollutant dispersion among lakes. Pristine lakes remain isolated, and groundwater pollution is limited since most anthropogenic activities occur in the NW plateau zone. Most of the limnological variables measured differed between pristine and impacted lakes. Nutrients, chlorophyll-a, total suspended solids, and particulate organic carbon concentrations were higher in the impacted lakes. The hydraulic connection between the Montebello Lakes facilitates the rapid dispersion of pollutants from one lake to another, threatening lakes that are still pristine. Although aquatic karst environments promote phosphorus precipitation strongly P-limiting primary production, anthropogenic additions of N, P, and organic matter make this process impossible, stimulating ecosystem degradation and leading to eutrophication as evidenced in the “Lagunas de Montebello” lake district.

气候条件对热带喀斯特（karst）湖泊的湖沼学（limnology）特征具有显著影响，但目前仍需更多研究以阐明人类活动扰动如何改变其生态格局。蒙特贝洛湖群（Lagunas de Montebello）作为热带高海拔喀斯特地貌区，拥有139个被热带雨林环绕的溶蚀湖。为探究过去20年间蒙特贝洛湖群的湖沼学变化，本研究选取14个湖泊开展对比研究：其中4个为受人类扰动湖泊，10个为原生未受干扰（pristine）湖泊。受扰湖泊位于西北部（NW）高原区域，其补给水源包括地表水与地下水；而原生未受干扰湖泊则地处东南部（SE）山间盆地，仅由地下水补给。受扰湖泊的营养盐与有机质主要来自点源与面源地表排放的农业、城镇及生活污水。强热带风暴会淹没高原区域，使湖泊间相互连通，进而促进污染物在湖体间扩散。原生未受干扰湖泊彼此隔绝，且由于绝大多数人类活动均集中于西北部高原区域，其地下水污染程度较为有限。多数实测湖沼学变量在原生与受扰湖泊间存在显著差异。受扰湖泊的营养盐、叶绿素a（chlorophyll-a）、总悬浮颗粒物（total suspended solids）及颗粒有机碳（particulate organic carbon）浓度均更高。蒙特贝洛湖群的水力连通性可促进污染物在湖体间快速扩散，对仍处于原生未受干扰状态的湖泊构成威胁。尽管喀斯特水生环境会强烈促进磷沉淀，使得初级生产受磷元素强烈限制，但人类活动输入的氮、磷及有机质会打破这一自然调控过程，进而引发生态系统退化并最终导致富营养化，该现象在蒙特贝洛湖群中已得到证实。