Delimitation of domains in the external Río de la Plata estuary, involving phytoplanktonic and hydrographic variables

AbstractAutumn and spring hydrological (temperature and salinity) and biological (chlorophyll, phaeopigments and phytoplankton species) variables were analysed. Phytoplankton biomass, expressed as chlorophyll a reach a maximum of 6.1 µg L-1in autumn and 22.8 µg L-1 during spring. Maxima were found in the frontal zone and marine adjacent area. Four domains were identified through multivariate analysis: Riverine, Estuarine, Frontal and Oceanic; mainly due to salinity and depth in autumn and due to salinity and chlorophyll in spring. The Riverine and Oceanic domains (West and East boundaries) matched in location in both seasons, while in spring an additional domain was discerned in the Canal Oriental (Channel domain). Salinity and chlorophyll concentration increased from the Riverine to the Frontal domain, being positively correlated for salinities 14, indicating that chlorophyll concentration was modulated mainly by the oceanic influence that improved light availability. While salinity maintains an increasing trend toward the Oceanic domain, phytoplankton biomass decreases. Though in this zone the chlorophyll concentration must be regulated by a combination of light availability and grazing, further investigation is needed.

摘要：本研究对秋季与春季的水文（水温与盐度）及生物（叶绿素、脱镁叶绿素与浮游植物物种）变量进行了分析。以叶绿素a计的浮游植物生物量在秋季最高达6.1 µg L⁻¹，春季最高达22.8 µg L⁻¹。生物量峰值出现在锋面带及近海区域。通过多变量分析共识别出4类海域分区：河流域、河口域、锋面域与大洋域；秋季分区主要依据盐度与水深，春季则依据盐度与叶绿素。河流域与大洋域（分别对应西部与东部边界）在两个季节的空间位置保持一致，而春季在东方运河（海峡域）中额外识别出一类海域分区。盐度与叶绿素浓度从河流域向锋面域逐步升高，当盐度为14时二者呈正相关关系，表明叶绿素浓度主要受大洋影响调控——该影响提升了光照可及性。尽管盐度向大洋域呈持续升高趋势，浮游植物生物量却随之下降。尽管该区域的叶绿素浓度应由光照可及性与牧食作用共同调控，但仍需开展进一步研究。