High vertical resolution sampling in density interfaces of estuaries and river plumes

Abstract

[EN] One of the most common procedures for studying the physical and biochemical processes in highly stratified areas, such as estuaries or river plumes (which can be very thin surface layers), is to take water samples and analyze them in a laboratory. To acquire samples in these areas with enough vertical resolution to describe the major changes in the physical and biochemical parameters that can occur near the density interface is often difficult. This paper presents two devices designed to take samples with high vertical resolution in density interfaces. The first device is for sampling in plumes and regions of freshwater influence and is based on the ones presented in Naudin et al. (Journal of Marine Systems 28:203¿227, 2001) and Durand et al. (Continental Shelf Research 22:267¿284, 2002). This device was able to obtain an accurate description of the river plume's vertical structure, although the plume was extremely thin, <1m (Sierra et al., Continental Shelf Research 22:361¿378, 2002). The second device, designed by the authors, is for sampling in estuarine interfaces. Both devices are able to take water samples at selected depths with the desired level of resolution. In this paper, some of the water samples acquired in the Ebro estuary and plume using these sampling devices are presented. To show the potential of these devices, some phosphorous data, acquired using them are compared with data obtained during previous campaigns using sampling methods that did not allow this level of resolution. Phosphorous has been selected to show the comparison as it is the limiting nutrient in most Mediterranean areas. This comparison shows peaks in the estuarine interface (also detected for other chemical and biological properties), which indicate processes (e.g., trapping of settled particulate matter, nutrient mineralization, etc.) in the interface that could not be identified in the previous campaigns and that could be analyzed with accuracy with this sampling technology. Additional and significant advantages of these devices are their low cost, their simplicity of manufacture, and the swiftness of sample acquisition. This illustrates the utility of the devices presented herein.