Department of Biological Sciences, Dartmouth College, Hanover, NH, 03755, USA.
Department of Marine Sciences, University of Connecticut, Groton, CT, 06340, USA.
Environ Res. 2021 Mar;194:110629. doi: 10.1016/j.envres.2020.110629. Epub 2020 Dec 20.
Biogeochemical conditions and landscape can have strong influences on mercury bioaccumulation in fish, but these effects across regional scales and between sites with and without point sources of contamination are not well understood. Normal means clustering, a type of unsupervised machine learning, was used to analyze relationships between forage fish (Fundulus heteroclitus and Menidia menidia) mercury (Hg) concentrations and sediment and water column Hg and methylmercury (MeHg) concentrations, ancillary variables, and land classifications within the sub-watershed. The analysis utilized data from 38 sites in 8 estuarine systems in the Northeast US, collected over five years. A large range of mercury concentrations and land use proportions were observed across sites. The cluster correlations indicated that for Fundulus, benthic and pelagic Hg and MeHg concentrations were most related to tissue concentrations, while Menidia Hg was most related to water column MeHg, reflecting differing feeding modes between the species. For both species, dissolved MeHg was most related to tissue concentrations, with sediment Hg concentrations influential at contaminated sites. The models considering only uncontaminated sites showed reduced influence of bulk sediment MeHg for both species, but Fundulus retained sediment drivers at some sites, with dissolved MeHg still highly correlated for both. Dissolved organic carbon (DOC), chlorophyll, land use, and other ancillary variables were of lesser importance in driving bioaccumulation, though DOC was strongly related within some clusters, likely in relation to dissolved Hg. Land use, though not of primary importance, showed relationships opposite to those observed in freshwater, with development positively correlated and forests and agriculture negatively correlated with tissue concentrations across clusters and species. Clusters were composed of sites from geographically distinct systems, indicating the greater importance of small scale drivers of MeHg formation and uptake into the food web over system or region-wide influences.
生物地球化学条件和景观对鱼类体内汞的生物积累有很强的影响，但这些影响在区域尺度上以及在有和没有点源污染的地点之间的了解还很不清楚。正常均值聚类，一种无监督机器学习类型，被用于分析在东北美国的 8 个河口系统的 38 个地点内，鱼类（Fundulus heteroclitus 和 Menidia menidia）汞浓度与沉积物和水柱汞和甲基汞浓度、辅助变量以及土地分类之间的关系。该分析利用了 5 年来在这些地点采集的 38 个样本的数据。在这些地点观察到汞浓度和土地利用比例的范围很大。聚类相关性表明，对于 Fundulus，底栖和浮游生物汞和甲基汞浓度与组织浓度最相关，而 Menidia 汞与水柱甲基汞最相关，反映了两种物种不同的摄食模式。对于这两个物种，溶解甲基汞与组织浓度最相关，而污染地点的沉积物汞浓度则有影响。仅考虑无污染地点的模型显示，对于这两个物种，总体沉积物甲基汞的影响降低，但 Fundulus 在一些地点仍保留了沉积物驱动因素，对于这两个物种，溶解甲基汞仍然高度相关。溶解有机碳（DOC）、叶绿素、土地利用和其他辅助变量对驱动生物积累的重要性较小，尽管在一些聚类中 DOC 具有很强的相关性，可能与溶解汞有关。尽管土地利用不是主要因素，但与在淡水观察到的关系相反，在跨聚类和物种的组织浓度方面，发展与正相关，森林和农业与负相关。聚类由来自地理位置不同系统的地点组成，这表明在小尺度上形成和吸收甲基汞进入食物网的驱动力比系统或区域范围的影响更为重要。
