A subscription to JoVE is required to view this content. Sign in or start your free trial.
Presented here is a cost-effective and transportable method/facility for measuring the primary productivity of microbial mats under actual in situ environmental temperature and light conditions. The experimental setup is based on widely available materials and can be used under various conditions while offering the advantages of laboratory-based models.
Measuring the in situ primary productivity of periphyton during the growing season gradient can elucidate the quantitative effect of environmental drivers (mainly phosphorus concentration and light intensity) and species composition on primary productivity. Primary productivity is mainly driven by light intensity, temperature, availability of nutrients, and distribution of the ionic species of the carbonate system in the respective depths of the euphotic zone. It is a complex system that is very difficult to simulate in the laboratory. This cheap, transportable, and easy-to-build floating barge allows measuring the primary productivity accurately-directly under the actual natural conditions. The methodology is based on measuring the primary productivity in real time using noninvasive oxygen sensors integrated into tightly sealed glass jars, enabling online oxygen flux monitoring and providing new insights into metabolic activities. Detailed seasonal in situ measurements of gross primary productivity of microbial mats (or other benthic organisms) can improve current knowledge of the processes controlling primary productivity dynamics in lentic waters.
Primary productivity is the only entry of autochthonous carbon into the aquatic systems that form the entire system food web1. Hence, the accurate estimation of primary productivity is an essential step toward understanding the functioning of aquatic ecosystems. Littoral zones are areas of high primary productivity and biodiversity. In addition to phytoplankton, periphyton (hereafter referred to as microbial mats) and macroalgae are assumed to significantly contribute to primary productivity in littoral zones2. Due to their sessile lifestyle and significant spatial heterogeneity, quantification of primary productivity is not trivial.
Primary productivity is driven mainly by light intensity, temperature, availability of nutrients, and distribution of the ionic species of the carbonate system in the respective depths of euphotic zones3,4. The depth markedly influences the spatial distribution of microbial mats. Microbial communities must cope with the adverse effects of high irradiation and pronounced seasonal temperature variations in shallow depths and with lower light intensity at greater depths. In addition to the depth gradient, dynamic trophic interactions generate multiple and complex spatial patterns at different scales5. This complex system is complicated to simulate in the laboratory. The most accurate way to infer the metabolic activity of individual primary producers from littoral zones is to set up in situ experiments.
The methodology introduced in this paper is based on the traditional chamber method2,6,7, together with a transportable and easy-to-build low-cost floating barge. This allows the measurement of primary productivity at different depths under the natural light spectrum, temperature, and different distribution of the ionic species of the carbonate system with the depth. The method is based on the principle of light versus dark bottle oxygen, which was first employed to measure phytoplankton photosynthesis6 and is still commonly used6,7. It compares the rate of change in oxygen in bottles kept in the light (which includes the effects of primary productivity and respiration) with those held in the dark (respiration only)8. The method uses oxygen evolution (photosynthesis) as a proxy for primary productivity. The measured variables are net ecosystem productivity (NEP, as a change in O2 concentration over time in light conditions) and ecosystem respiration (RE, as a change in O2 concentration over time in the dark). Gross ecosystem productivity (GEP) is the calculation of the difference between the two (Table 1). The term "ecosystem" is used here to denote that the periphyton is composed of autotrophic and heterotrophic organisms. The most significant improvement of this traditional chamber method is using noninvasive oxygen optical sensors and optimization of this primarily planktonic method for measuring periphytic primary productivity.
The technique is described in the example of measuring microbial mats in the littoral zone of newly emerged post-mining lakes in the Czech Republic-Milada, Most, and Medar. The metabolic activity of microbial mats is determined using direct in situ measurement of O2 fluxes performed directly at specific depths, where the studied communities naturally occur. Heterotrophic and phototrophic activity is measured in closed glass bottles equipped with noninvasive optical oxygen sensors. These sensors detect the partial pressure of oxygen using the fluorescence of light-sensitive dyes. The bottles with microbial mats are suspended and incubated on a floating device at the appropriate depths. The oxygen concentration inside the bottles was continuously measured during the daylight period from the small boat.
Samples of intact microbial mats are collected and placed in gas-tight incubation bottles at designated depths by scuba divers. Each bottle is equipped with a noninvasive optical oxygen microsensor, which monitors the O2 productivity/consumption over time. All measurements are done in five replicate dark/light pairs in each depth. The temperature and photosynthetically active radiation (PHAR) intensities are measured at respective depths throughout the incubation. After 6 h of in situ incubation (daylight hours), the microbial mats are harvested from the bottles and dried. O2 fluxes are normalized to microbial biomass. As a control, fluxes are corrected for changes in O2 concentration in separate light and dark gas-tight bottles (blank controls) containing lake water without microbial mat biomass. Below are detailed instructions for building the floating barge and performing the whole experiment step-by-step. This paper also presents representative results from the measurements of microbial mats at two depths (1 m and 2 m), with five replicates at each depth. Actual temperature and light intensity were measured during the whole experiment using dataloggers.
NOTE: Before sampling, determine the degree of replications based on the overall project needs, statistical design, or expected amount of sample variability.Five replicate pairs of light and dark incubation bottles are suggested for precise statistical analysis and to account for potential sample loss or breakage. The described floating experimental barge is designed to carry five replicates plus one pair of blank controls; see Figure 1 for a technical drawing of the experimental barge.
Figure 1: Technical drawings of the experimental barge and the side float. (A) Top view: the frame of the barge consists of four Aluminum angle L profile pieces (blue) that are joined together by four Aluminum flat bars (grey). XPS floats (pink) are mounted to the frame at two points, each one on the parallel aluminum pieces. Chains for incubation bottles are attached to the frame on both sides using snap hooks in predrilled holes (red arrows) with 550 mm of separation between them. Chains were provided with snap-hooks at 1 m and 2 m distances for incubation bottle attachment (choose the snap-hooks position according to the experimental depth). The concrete anchor is secured to the barge's bow, where an overhang of 25 mm allows for two predrilled holes (yellow arrowheads) to serve as an attachment point for the anchor's chain and research vessel. The frame is assembled or disassembled easily via the parallel joints between the four aluminum angle pieces (green arrowheads). (B) The side view shows the suspended chains with hanging incubation bottles and concrete anchor (brown square). (C) The side XPS float: Parallelaluminum angle L pieces (blue) are joined by vertical aluminum flat bars (grey). Below the crossbar section, the XPS float (pink) is mounted with the necessary hole sizes indicated (4 mm). The suspended chains are attached with snap hooks in 8 mm holes (red arrowhead). At the barge's bow, two 8 mm holes are drilled into the overhanging aluminum, one for securing the anchor to the barge (yellow arrowhead) and another for mooring the research vessel to the barge (blue). Please click here to view a larger version of this figure.
1. Construction of the experimental barge
NOTE: The floating barge consists of two equal sections mounted together, allowing easy assembly/disassembly. All used parts can be purchased at any hobby market or store selling building materials.
Figure 2: Assembled experimental barge. Photograph of the assembled experimental barge. Red arrowheads show the holes for the attachment of chains with incubation bottles. The green arrowheads point to where the two halves of the float are joined together. Please click here to view a larger version of this figure.
Figure 3: Incubation bottles. Photo of two pairs of dark and light incubation bottles hanging at a depth of 1 m. One pair of bottles contains the sample of intact microbial mats still growing on the stone (red arrowhead). The second one is the blank bottle with the lake water from the respective depth. A yellow arrowhead points to the oxygen sensor spot attached to the inner wall of the incubation bottle. Please click here to view a larger version of this figure.
2. Installation in the field
3. Incubation bottle preparation
4. Sample collection and handling
NOTE: Divers carry out the manual collection of samples in deeper water. In shallow water, it can be done by snorkeling or wading.
5. Measuring the primary productivity
NOTE: The person sitting in the boat takes the box from the diver and performs the following steps.
Figure 4: Schema of the experimental setup in the field. Illustration of the anchored experimental barge on the lake surface. The incubation bottles (0.5 L) with microbial mat biomass are hung at two different depths (1 m and 2 m). The divers collected samples of microbial mats directly into the incubation bottles at the appropriate depths. Oxygen concentration in individual bottles is measured from the ship. The bottles are pulled out of the water. The oxygen concentration value is measured in a few seconds by attaching an optical cable to the oxygen sensor. The bottles are then carefully lowered back into the water. The whole procedure of measuring two pairs of incubation bottles from two depths takes ~2 min. Please click here to view a larger version of this figure.
6. Sample analyses
7. Data analyses
Figure 5: Net and gross ecosystem productivity of microbial mats during daylight. (A) Light bottle-net ecosystem productivity: time course data of net oxygen productivity of microbial mats from the light bottles. The oxygen concentration change in incubation bottles was measured after 1 h during daylight. Grey circles: bottles with samples of m...
The methodology described in this paper is based on the principle of the light and dark bottle oxygen technique in combination with the noninvasive technique of measuring O2 concentration using optical oxygen sensors. This system allows the parallel measurement of different incubation settings as the optical fiber for measuring O2 can be moved quickly from bottle to bottle. The benthic communities from various depths can differ in taxonomic composition and productivity; simultaneously measuring them...
The authors confirm that they have no conflicts of interest to disclose.
This study was supported by the Czech Science Foundation (GACR 19-05791S), RVO 67985939, and by the CAS within the program of the Strategy AV 21, Land save and recovery. Many thanks to Ondřej Sihelský for taking the shots in the field - without him, the filming would have been complete hell. The project would not be possible without tight cooperation with companies, Palivový Kombinát Ústí s.p. and Sokolovská Uhelná, who provided access to the studied localities.
Name | Company | Catalog Number | Comments |
Aluminum angle L profile 40 x 40 mm x 3 mm, length 2,000 mm | |||
Aluminum flat bar 40 x 3 x 350 mm | |||
Bucket 15 L with concrete infill | |||
Carabine hook with screw lock 50 x 5 mm | |||
electric tape black | |||
Extruded polystyrene (XPS) material 500 x 200 x 150 mm | |||
Fibox 3 LCD trace | PreSens Precision Sensing GmbH | stand-alone fiber optic oxygen meter | |
Hondex PS-7 Portable Depth Sounder | Hondex - Honda Electronics | to measures distances through water - to bottom depth measurement; https://www.honda-el.net/industry/ps-7e | |
KORKEN - glass tight-seal jar 0.5 L | IKEA | incubation bottles; https://www.ikea.com/cz/en/p/korken-jar-with-lid-clear-glass-70213545/ | |
metal hook | |||
Oxygen Sensor Spot SP-PSt3-NAU-D5 | PreSens Precision Sensing GmbH | non-invasive optical oxygen sensor for measurements under Real Conditions | |
SCOUT infantable canoe | GUMOTEX | https://www.gumotexboats.com/en/scout-standard#0000-044667-021-13/11C | |
Screw 10 x 170 mm with hexagonal nuts | |||
Screw 4 x 15 mm with hexagonal nuts | |||
Screw 4 x 15 mm with wing nuts | |||
Snap hooks 50 x 5 mm | |||
Steel Carabine hook 50 x 5 mm | |||
Steel chain with wire diameter 3 mm, inside link 5.5 x 26 mm | |||
Steel chain, 5 m | |||
toothbrush | |||
tweezer | |||
Washer 10 x 50 mm | |||
Washer 4 x 10 mm | |||
Washer 4 x 10 mm |
Request permission to reuse the text or figures of this JoVE article
Request PermissionThis article has been published
Video Coming Soon
Copyright © 2025 MyJoVE Corporation. All rights reserved