Limnology and Oceanography: Methods最新文献

Sequential phosphorus (P) extraction (SPE) is a well-established and widely applied method for quantitatively and qualitatively determining the critical nutrient P in freshwater sediments. It allows the estimation of P bioavailability and facilitates the evaluation of the long-term effects of eutrophication mitigation measures. Most current protocols do not differentiate between redox-sensitive Fe(III)-P and more stable reduced Fe(II)-P minerals, such as vivianite. In this study, we tested a modified SPE protocol designed to quantify Fe(II)-P (vivianite-P) as a separate phase through the complexation of Fe(II) with 2,2′-bipyridine (Bipy). Seven lakes were selected as study sites with different sedimentary Fe and P contents and restoration histories. We validated the Bipy extraction step through direct comparison with results from the conventional protocol and the application of direct mineral detection methods, including x-ray absorption near-edge structure at the Fe and P K-edges, x-ray diffraction, optical microscopy, and scanning electron microscopy with energy dispersive x-ray spectroscopy. The Bipy fraction was primarily extracting P that was conventionally extracted in the bicarbonate-dithionite (redox-sensitive Fe/Mn-bound) and NaOH (metal-[Fe/Al-]bound) fractions. The results from the direct detection methods indicated that the extracted Fe(II)-P was predominantly vivianite. The efficiency of the Bipy extraction was decreased in samples with high crystallinity, but excessive Fe(II) or high organic content had minimal impact. Hence, it is highly recommended to use x-ray diffraction and x-ray absorption near edge structure in combination with the modified extraction protocol. Overall, the method tested with different freshwater sediments provides robust results when quantification of Fe(II)-P including vivianite is an important objective.

The concentration and size of particles in coastal oceans is of great ecological importance, for example for light penetration and thus primary production. A common tool to determine particle sizes and concentrations is the Laser In Situ Scattering and Transmissometry (LISST). Previous studies with LISST instruments have found large variations in particle sizes and a possible influence on the measurement by current shear. To determine the strength of this influence, we conducted a cruise in the German Bight. We determined particle sizes and concentrations using a Sequoia LISST-200X, as well as the encounter velocity and the direction with which the water hits the instrument frame using an Acoustic Doppler Velocimeter. The encounter velocity was modulated by drifting and steering of the ship, leading to minimal velocities of 0.1 m s⁻¹ during drift and maximum velocities of 0.6 m s⁻¹ during steering. We found that the determined particle size is strongly dependent on the encounter velocity and the orientation of the instrument. The determined particle size decreased by 17–56 μm per increase in 0.1 m s⁻¹ encounter velocity. Identifying and exploring two hypotheses, we assume that large particles are destroyed by the current shear at high velocities. We propose that for future LISST measurements, the encounter velocity with which the water hits the instrument be taken into account and reduced as far as possible. In addition, we propose measurements under controlled conditions that can accurately determine the extent of the influence of encounter velocity on particle size determination.

Dissolved organic matter (DOM) incubation experiments are an important method for disentangling the effects of dissolved organic carbon (DOC) characteristics and microbial community composition on carbon (C) bioreactivity. However, common quantification metrics (ΔDOC, biodegradability, C removal rate) measure different aspects of C degradation and can change through time, suggesting experimental conclusions may depend on the metric used and the time of measurement. We performed an incubation experiment crossing varying DOM sources and microbial communities and synthesized published experimental data to explore (1) whether the interpretation of C degradation activity changed with the metric used, (2) how incubation duration impacted measures of degradation, and (3) how these different metrics compared across studies. Through our incubation experiment, we found that all metrics agreed regarding which treatments were associated with the greatest amounts of C degradation, and in all cases we observed peak C removal rates within 24 h of incubation initiation. However, our literature synthesis found that just 10% of studies sampled within the first 24 h of incubation initiation, suggesting common measurement intervals may miss peak C removal rates. Using these findings, we propose combinations of C degradation metrics and sampling frequencies that may be especially effective for detecting differences in C bioavailability, microbial activity, or C degradation.

The response times of the Aanderaa 4330, Aanderaa 4330 WTW, RBRcoda T.ODO|slow, and PyroScience PICO-O2-SUB were evaluated in the laboratory over a range of profiling speeds at two temperatures. The PyroScience PICO-O2-SUB had the fastest response time (1–4 s), followed by the RBRcoda T.ODO|slow (~ 15–35 s), Aanderaa 4330 (~ 30–60 s), and Aanderaa 4330W (~ 50–100 s). This study provides recommendations on improving the quality of oxygen data from optodes in profiling applications by additionally assessing the impact of response time testing setups, thermal inertia effects, and foil types on sensor response times. This study provides a new response time function based on physical principles to predict response time for these four optode types.

Marine and coastal ecosystems have been undergoing dramatic shifts due to global environmental changes. The rise in seawater temperature, ocean acidification, hypoxia, eutrophication, and anthropogenic pollution severely affects marine organisms. There is an urgent need to better understand the influence of such disturbances on the physiology and life cycles of marine organisms. However, conducting controlled laboratory experiments often requires many replicates and information on individual origin, age, and genetic diversity. The availability of tropical model organisms is limited. Large-scale sampling efforts from wild communities may negatively impact local biodiversity, especially in coral-reef regions under threat. In this study, we present new methodologies for cultivating the tropical-origin ascidian (phylum: Chordata, class: Ascidiacea) Phallusia nigra in both closed and open water facilities, demonstrating feasibility to produce viable populations of juvenile P. nigra originating from the South China Sea (Singapore) and the Mediterranean and Red Sea coasts of Israel for research. In an open water system, P. nigra can be reared from eggs to adults for 11 months. Reproductive animals were obtained by the fourth month. As it is possible to rear individuals to maturity, long-term and cross-generational effect studies can also be explored. Finally, our work provides a method to produce a tropical model for biomedical research, which in regard to ascidians has so far been restricted to temperate cultivars. P. nigra offers fundamental opportunities for environmental research due to its wide global distribution, easy field sampling, and potential as a biological indicator species for anthropogenic pollution and global climate change.

The High-Pressure Plankton Observatory (HiPPO) is designed to quantify motions of zooplankton for behavioral study, including swimming and metabolic responses to environmental perturbations. It builds on prior chamber designs while filling gaps in capability for resolving orientation of small (< 1 mm) plankton, tracking their movements over ecologically relevant spatial scales, and recording in flow-through conditions on a vessel at sea. The HiPPO chamber has a direct light path for silhouette imaging of zooplankton as they move vertically and horizontally across a 3.56 cm diameter viewing area. Seawater forced by a high-performance liquid chromatography pump is exchanged continuously through the chamber, but flushing of zooplankton is prevented by fine mesh at the ports. A high-resolution camera/computer setup enables sustained imaging of plankton motions for quantitative analysis. Application of HiPPO to an investigation of larval behavior of deep-sea hydrothermal vent species revealed swimming behaviors similar to those of shallow-water species, including upward and downward helices, meandering, and short hovers. In conditions with microbial biofilm (a potential settlement cue) on a 2024 expedition, vent larvae unexpectedly swam rapidly upward in tight helices at velocities (0.15 cm s⁻¹) higher than those observed in prior experiments with no biofilm (0.03 cm s⁻¹). Many factors varied between the 2024 and earlier trials, so the difference cannot be attributed with certainty to a cue response. This study describes key new features of HiPPO and demonstrates the system's ability to document novel zooplankton behavior.

Human activities have significantly increased carbon dioxide emissions, leading to global warming and ocean acidification, which threaten marine ecosystems, including coral reefs with high biodiversity. Coral reef maintenance relies on a balance between calcium carbonate formation and dissolution. Among the processes, sandy sediments, covering vast areas and highly sensitive to ocean acidification, require urgent investigations to elucidate their dissolution mechanisms. However, conventional glass electrodes have limitations in continuous monitoring of the spatiotemporal distribution of pH within sediment. To address this, we developed a multichannel ion-sensitive field-effect transistor (ISFET)-pH sensor array with a tantalum oxide sensing membrane, which was embedded in the sediment to enable high-resolution and continuous pH monitoring. A 24-h pH monitoring experiment was conducted in coral reef sediments to validate the method. The performance of the sensor was evaluated through both laboratory and field observations, and a comparison with a conventional glass electrode confirmed that the ISFET-pH sensor provided stable pH measurements within the uncertainty range of the glass electrode. The developed sensor array is a low-cost and durable automatic measurement system, offering an alternative to conventional glass electrodes, which are expensive and fragile. However, optimizing sputtering conditions, annealing processes, and data processing techniques is necessary to reduce environmental influences and enhance measurement accuracy. The proposed array-based observation method enables the acquisition of high-resolution vertical pH profiles and is expected to contribute to the quantitative evaluation of the chemical role of sandy sediments and the elucidation of carbon cycling in coral reef ecosystems.

Measurements of chlorophyll concentration reported by fluorometers (fChl) are used in environmental research and monitoring, as inputs to models, and in the interpretation of remote sensing data. Researchers and managers benefit from understanding how to interpret and ensure the accuracy of fChl data collected by in situ fluorometers. Although fChl values produced by different manufacturers are often in agreement with discrete laboratory-derived Chlorophyll a (Chl a) concentration measurements, there are instances in which results significantly differ. Further, when measuring fChl side by side, different fluorometers may report values that differ significantly from each other, despite passing calibration checks prior to deployment. We compared environmental conditions and phytoplankton species composition associated with instances in which fChl measurements from three different fluorometers (EXO2 Total Algae Smart Sensor, YSI Inc./Xylem Inc., Yellow Springs, Ohio; FluoroProbe III, bbe Moldaenke GmbH, Kiel, Germany; WETStar, Sea-Bird Scientific, Bellevue, Washington) were significantly different from laboratory-derived Chl a concentrations. Results indicated that elevated primary productivity, as indicated by high pH, dissolved oxygen, and the ratio of Chl a to phaeophytin, were correlated with underestimated fChl values recorded by each sensor. After removing outliers, we determined unique correction guidance for each of the three sensors and demonstrated that after applying correction formulae, fChl measurements produced by each sensor became directly comparable.

Grottoli A. G., S. L. Dixon, A. M. Hulver, et al. 2025. “Underwater Zooplankton Enhancement Light Array (UZELA): A Technology Solution to Enhance Zooplankton Abundance and Coral Feeding in Bleached and Non-Bleached Corals.” Limnology and Oceanography, Methods 23: 201–211. https://doi.org/10.1002/lom3.10669.

In the first paragraph of the Materials and procedures, the text “… average of 700 lm through the acrylic lens …” was incorrect. This should have read: “… average of 700 μmol m⁻² s⁻¹ through the acrylic lens ….”

We apologize for this error.

Better characterization of biological N₂ fixation along with its controlling factors is needed for improved projections of the feedbacks between nitrogen cycling, ecosystems productivity, and climate dynamics. Building on an ongoing community effort to refine estimates of biological N₂ fixation, we outline several considerations aimed at improving ¹⁵N₂ incubation measurements. We first show based on a theoretical analysis that the bias associated with equilibrium isotopic fractionation is within the uncertainty of ¹⁵N₂ incubation experiments, even under conditions with a large headspace to aqueous ratio, such as in soil or sediment incubations. Second, we empirically determine the effects of temperature and agitation on the equilibration kinetics. Shaking intensity seems to be a dominant control on the kinetics of equilibration. Our results show that nearly complete equilibration of dissolved ¹⁵N₂ is achieved within 4 min of vigorous shaking at 20°C at atmospheric pressure, but significantly slower at lower temperatures. The equations presented in our study are adaptable to varying ¹⁵N₂ incubation conditions and other trace gas isotope addition experiments.