Cold and wet: Diatoms dominate the phytoplankton community during a year of anomalous weather in a Great Lakes estuary

As sentinels of climate change and other anthropogenic forces, freshwater lakes are experiencing ecosystem disruptions at every level of the food web, beginning with the phytoplankton, a highly responsive group of organisms. Most studies regarding the effects of climate change on phytoplankton focus on a potential scenario in which temperatures continuously increase and droughts intersperse heavy precipitation events. Like much of the conterminous United States in 2019, the Muskegon River watershed (Michigan, USA) experienced record-breaking rainfall accompanied by unusually cool temperatures, affording an opportunity to explore how an alternate potential climate scenario may affect phytoplankton. We conducted biweekly sampling of environmental variables and phytoplankton in Muskegon Lake, a Great Lakes Area of Concern that connects to Lake Michigan. We compared environmental variables in 2019 to the previous eight years using long-term data from the Muskegon Lake Observatory buoy, and annual monitoring excursions provided historical phytoplankton data. Under cold and wet conditions, diatoms were the single dominant division throughout the entire growth season – an unprecedented scenario in Muskegon Lake. In 10 of the 13 biweekly sampling days in 2019, diatoms comprised over 75% of the phytoplankton community in the lake by count, indicating that the spring diatom bloom persisted through the fall. Additionally, phytoplankton seasonal succession and abundance patterns typically seen in this lake were absent. In a world experiencing reduced predictability, increased variability, and regional climate anomalies, studying periods of extreme weather events may offer insight into how natural systems will be affected and respond under future climate scenarios.     

PARAFAC modeling of three-way hyperspectral images: Endogenous fluorophores as health biomarkers in aquatic species

Demand for a renewable liquid-phase fuel has reinvigorated interest in the development of novel biofuels from algae. The effects of fluctuating nutrients, temperature, and predation which arise in algal aquaculture necessitate novel analytical methods to assess and optimize the health of these cultures. In this article we describe the use of trilinear modeling to these ends, using imaging data of endogenous fluorescence from the marine diatom, Thalassiosira pseudonana, collected on a hyperspectral fluorescence confocal microscope (HSF-CM). By combining the spatial and spectral data with the additional physical parameter introduced by the varying photobleach rates of endogenous fluorophores, we obtain a means for employing trilinear analysis in this system. In this case, analysis was implemented using the method of parallel factors analysis (PARAFAC) which alleviates the rotational ambiguities involved in multivariate analysis of 2-way data. By imposing a nutrient limitation in our diatom culture, and collecting single cell microscopy data at various time points during the nutritional stress, PARAFAC results reveal evolution of the spectral emission characteristics of six components and a background as a result of incremental photobleaching. Although the underlying mechanisms for these observations are not addressed, the differences observed between nutritively normal and nutritively stressed cells provide signatures for early detection of health deterioration in the algal culture. Finally, the combination of hyperspectral fluorescence microscopy with PARAFAC is generally applicable for the study of complex biological systems with endogenous fluorescence.     

Natural, anthropogenic and fossil organic matter in river sediments and suspended particulate matter: a multi-molecular marker approach

Different classes of organic matter (OM) have been systematically investigated in sediments and suspended particulate matter (SPM) along the Danube River in order to understand causes of compositional changes. Analytical pyrolysis revealed the dominance of natural organic matter (NOM) in most of the samples. The predominance of aquatic biomass is evident mainly from the abundance of organonitrogen compounds and phenol distributions. As the river enters a forested gorge, the terrestrial component of the NOM in sediments is more significant. This is reflected in abundant methoxyphenols and a very high carbon preference index. SPM sample from a tributary shows a unique geochemical signature. It contains abundant carboxylic acids, amines, isoprenoids in the pyrolyzate, and is dominated by phytol and 24-methyl-cholesta-5,24(28)-dien-3β-ol in the extract, produced by a diatom bloom. Wax esters with a relatively high proportion of short, methyl-branched alkyl-chains appear together with abundant phytadienes and n-C₁₇ alkane in some samples, suggesting a microbial origin. Anthropogenic OM from runoff and atmospheric deposition was evident from a minor input of polycyclic aromatic hydrocarbons (PAHs) originating from mixed combustion sources. Multivariate analysis using PAH data led us to define simple molecular ratios to distinguish the PAH composition in sand and silty sediments. The newly defined ratios are the alkylated phenanthrenes and anthracenes ratio (APA; C₁-C₃/C₀-C₃ phenanthrenes and anthracenes) and the PAH ring number ratio (RN; 5-6 ring parent PAHs/all parent PAHs). This demonstrates that alkylated, as well as 5-6 ring PAHs are better preserved in the finer than in coarser grained sediments. A ubiquitous, but minor input of petroleum-related contamination with a uniform composition was evident in all samples as revealed by the analysis of petroleum biomarkers. This study demonstrates that the investigation of different classes of riverine OM requires a detailed molecular analysis, applying a series of analytical techniques and adequate statistical data treatment.     

Paleolimnological proxies reveal continued eutrophication issues in the St. Lawrence River Area of Concern

Recent surface-water surveys suggest that high nutrient concentrations and nuisance algae remain issues in the St. Lawrence River Area of Concern (AOC) at Cornwall, Ontario, specifically in the tributaries and nearshore zones of Lake St. Francis (LSF). In particular, it is unclear whether management actions designed to reduce nutrient inputs, first implemented in the 1990s as part of the Remedial Action Plan for the AOC, have reduced algal production or influenced assemblage composition. To address this issue, a paleolimnological approach was used to provide a historical context for the present-day nutrient concentrations and to quantify the extent of change in water quality in LSF since the early 1990s. A sediment core was collected near the north shore of LSF and was examined for changes in the concentrations and compositions of fossil diatoms and pigments, as well as stable isotope (δ¹⁵N and δ¹³C) values. Analyses of diatom and pigment concentrations indicated that overall algal abundance has risen in the last few decades, including trends of increasing occurrences of potentially toxic cyanobacteria, despite ongoing remediation efforts. Temporal patterns of stable isotope signatures in the core suggest a steady increase in nutrient influx since the mid-20th century, with the post-1990 increase in algal production likely attributable to recent inputs associated with land-use changes in local contributing watersheds. These patterns suggest that the AOC delisting goals for the LSF tributaries will not be reached without a drastic change in land management practices.     

Revision of the needle-shaped Fragilaria species (Fragilariaceae,Bacillariophyta) in the Laurentian Great Lakes (United States of America,Canada)

We investigated several common, needle-shaped diatoms to better characterize the taxonomy of the genus Fragilaria in the Laurentian Great Lakes. We conducted diatom morphometric analysis facilitated by SEM and LM imaging on samples collected as a part of the USEPA’s long-term biological monitoring program. We resolved several decades-long taxonomic problems in the Great Lakes. The results indicated that previous records of species formerly belonging to the genus Synedra, such as S. (Fragilaria) ostenfeldii, S. (Fragilaria) radians, and S. filiformis, should be corrected as these species likely do not occur in the Great Lakes. Valve morphology confirmed the presence of four previously undescribed species: Fragilaria andreseniana sp. nov., Fragilaria stoermeriana sp. nov., Fragilaria limnetica sp. nov., and Fragilaria michiganensis sp. nov. The morphology of several other Fragilaria taxa in the Great Lakes was examined, including a teratologic taxon (Fragilaria sp. 1), Fragilaria crotonensis, Fragilaria grunowii, and a taxon showing morphological affinity to Fragilaria lemanensis (reported here as Fragilaria cf. lemanensis). The spatial and seasonal distributions of these needle-shaped taxa were also analyzed and discussed.     

Silica Regeneration Processes in Nearshore Southern Lake Michigan

The seasonal depletion of dissolved silica to levels that limit diatom production is particularly critical in Lake Michigan's nearshore zone where diatom biomass is greatest, and where silica regeneration from sediments is not well-understood. In our study, intact, medium-fine sand cores, collected from an 11 m deep site in nearshore Lake Michigan during July-August 1980, released soluble reactive silica (SRS) at a mean rate of 2,707 ± 122 (SE) μg Si cm^?2 yr^?1 when incubated in darkness and at 12° C. This measured SRS release was greater than a diffusive flux (270 ± 49 (90% C.I.) μg Si cm^?2 yr^?1) estimated from SRS pore water profiles and physical sediment properties. SRS release from individual cores was not correlated with abundance of most macroinvertebrates (chironomids, pisidiid clams, or oligochaetes). However, a significant (P < 0.05) and inverse relationship between SRS release and Pontoporeia hoyi densities implied that amphipods suppressed SRS release through mixing and burial of a surficial floe layer, where most dissolution of biogenic silica occurs. Moreover, SRS release rates measured from our coarse-grained nearshore sediments were comparable to rates reported for fine-grained offshore material and further implicate dissolution of surficial biogenic silica as the source of remineralized SRS. Because nearshore areas of Lake Michigan undergo strong seasonal variations in temperature and diatom production, and because significant riverine silica inputs exist, we cannot extrapolate our results on a lakewide, or season-long basis. The data, however, strongly imply that nearshore sediments are an important participant in the Lake Michigan silica cycle.     

The engineering geological characteristics of lake sediments in the Yuanshan area, Ilan City, Taiwan

 The paper describes a study of the sedimentology and some engineering parameters related to the geological characteristics of the lake sediments which formed behind a barrier dam in a suburb of Ilan City, north east Taiwan. It is concluded that the variation in engineering parameters is strongly influenced by the proportion of diatoms present. Received: 14 November 1997 · Accepted: 20 January 1998     

Removal of freshwater diatoms (Synedra acus and Stephanodiscus sp.) by preozonation and addition of polyamine coagulant-aid

Pilot studies were conducted for the removal of two freshwater diatoms (Synedra acus andStephanodiscus sp.). Poly aluminum chloride (PAC), one of the coagulants commonly used in conventional potable water treatment, was found to be not effective in removing diatoms, especially forSynedra. In this work, preozonation and polyamine coagulant-aid in the presence of PAC were compared with each other and combined to investigate their performances on removing diatoms. It was found that the preozonation and polyamine coagulant-aid increased the removal rate significantly for both diatoms, better performance than PAC alone. When polyamine coagulant-aid and preozonation were combined with PAC, approximately 90% ofSynedra and 100% ofStephanodiscus were eliminated. It can be concluded that the combination of preozonation and polyamine coagulant-aid in the presence of PAC could be a promising solution for removing resistant diatoms in water treatment.     

Simulation of a mesotrophic reservoir (Lake Pareloup) over a long period (1983-1998) using ASTER2000 biological model

Lake Pareloup is studied since 1983. The model ASTER that simulated the ecosystem of the lake during the first phase of the study (1983-1987) has been modified. The new model, called ASTER2000 aims to improve the estimation of the trophic level and the water quality of different reservoirs. To this purpose, NH4, NO3 and O2 were added as state variables. Affluents and pumping inflow have also been considered in order to consider the evolution of the watershed inflow and the variation from year to year in rainfall and pumping inflow. We have a long data series (1983-1998) that allows testing the model under different hydro-climatic conditions. The model simulates the state variables for this period in a satisfactory way. The evolution of nutrient concentrations differences bound to year-to-year entries are well represented, which would have been impossible with the original model. The addition of variables permits to rely on a larger range of the water quality criteria. In combination with the thermal forcing (temperature and stratification) provided by the EOLE model, ASTER2000, represents a strong and easy tool which could be used on many other reservoirs. The main modification necessitated in such applications concerns the type of diatoms dominating: consumed or not by the zooplankton. It is also indispensable to have input data in line with the structure of the model.