Sengco Mario R.

No Thumbnail Available
Last Name
First Name
Mario R.

Search Results

Now showing 1 - 4 of 4
  • Article
    The importance of human dimensions research in managing harmful algal blooms
    (Ecological Society of America, 2009-02-10) Bauer, Marybeth ; Hoagland, Porter ; Leschine, Thomas M. ; Blount, Benjamin G. ; Pomeroy, Caroline M. ; Lampl, Linda L. ; Scherer, Clifford W. ; Ayres, Dan L. ; Tester, Patricia A. ; Sengco, Mario R. ; Sellner, Kevin G. ; Schumacker, Joe
    Harmful algal blooms (HABs) are natural freshwater and marine hazards that impose substantial adverse impacts on the human use of coastal and marine resources. The socioeconomic and health impacts of HABs can be considerable, thereby making a case for “human dimensions” research to support HAB response. Human dimensions research is multidisciplinary, integrating social science, humanities, and other fields with natural science to enhance resource management by addressing human causes, consequences, and responses to coastal environmental problems. Case studies reported here illustrate the importance of human dimensions research. Incorporating such research into the scientific agenda – as well as into management decisions of public agencies concerned with natural resource management, environmental protection, and public health and welfare – requires the development of both strategic guidance and institutional capacity. The recent development of a multi-agency research strategy for HAB response and a strategic plan for human dimensions research represent two important steps in this direction.
  • Preprint
    Using clay to control harmful algal blooms : deposition and resuspension of clay/algal flocs
    ( 2003-12-21) Beaulieu, Stace E. ; Sengco, Mario R. ; Anderson, Donald M.
    Harmful algal blooms (HABs) may be legitimate targets for direct control or mitigation, due to their impacts on commercial fisheries and public health. One promising control strategy is the rapid sedimentation of HABs through flocculation with clay. The objective of this study was to evaluate flow environments in which such a control strategy might be effective in removing harmful algae from the water column and depositing a layer of clay/algal flocs on the sea floor. We simulated the natural environment in two laboratory flumes: a straight-channel “17-m flume” in which flocs settled in a still water column and a “racetrack flume” in which flocs settled in flow. The 17-m flume experiments were designed to estimate the critical bed shear stress for resuspension of flocs that had settled for different time periods. The racetrack flume experiments were designed to examine the deposition and repeated resuspension of flocs in a system with tidal increases in flow speed. All flume runs were conducted with the non-toxic dinoflagellate Heterocapsa triquetra and phosphatic clay (IMC-P4). We repeated the experiments with a coagulant, polyaluminum hydroxychloride (PAC), expected to enhance the removal efficiency of the clay. Our experiments indicated that at low flow speeds (≤ 10 cm s-1), phosphatic clay was effective at removing algal cells from the water column, even after repeated resuspension. Once a layer of flocs accumulated on the bed, the consolidation, or dewatering, of the layer over time increased the critical shear stress for resuspension (i.e. decreased erodibility). Resuspension of a 2-mm thick layer that settled for 3 hours in relatively low flow speeds (≤ 3 cm s-1) would be expected at bed shear stress of ~0.06-0.07 Pa, as compared to up to 0.09 Pa for a layer that was undisturbed for 9 or 24 hours. For the same experimental conditions, the addition of PAC decreased the removal efficiency of algal cells in flow and increased the erodibility of flocs from the bottom. By increasing the likelihood that flocs remain in suspension, the addition of PAC in field trials of clay dispersal might have greater impact on sensitive, filter-feeding organisms. Overall, our experiments suggest that the flow environment should be considered before using clay as a control strategy for HABs in coastal waters.
  • Preprint
    Sterols of the syndinian dinoflagellate Amoebophrya sp., a parasite of the dinoflagellate Alexandrium tamarense (Dinophyceae)
    ( 2006-02-01) Leblond, Jeffrey D. ; Sengco, Mario R. ; Sickman, James O. ; Dahmen, Jeremy L. ; Anderson, Donald M.
    Several harmful photosynthetic dinoflagellates have been examined over past decades for unique chemical biomarker sterols. Little emphasis has been placed on important heterotrophic genera, such as Amoebophrya, an obligate, intracellular parasite of other, often harmful, dinoflagellates with the ability to control host populations naturally. Therefore, the sterol composition of Amoebophrya was examined throughout the course of an infective cycle within its host dinoflagellate, Alexandrium tamarense, with the primary intent of identifying potential sterol biomarkers. Amoebophrya possessed two primary C27 sterols, cholesterol and cholesta-5,22Z-dien-3-ol (cis-22-dehydrocholesterol), which are not unique to this genus, but were found in high relative percentages that are uncommon to other genera of dinoflagellates. Because the host also possesses cholesterol as one of its major sterols, carbon stable isotope ratio characterization of cholesterol was performed in order to determine whether it was produced by Amoebophrya or derived intact from the host. Results indicated that cholesterol was not derived intact from the host. A comparison of the sterol profile of Amoebophrya to published sterol profiles of phylogenetic relatives revealed that its sterol profile most closely resembles that of the (proto)dinoflagellate Oxyrrhis marina rather than other extant genera.
  • Thesis
    The aggregation of clay minerals and marine microalgal cells : physicochemical theory and implications for controlling harmful algal blooms
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2001-09) Sengco, Mario R.
    In recent years, the use of clay minerals has emerged as one of the most promising strategies for directly controlling harmful algal blooms (HABs). Its principle is based on the mutual aggregation of algal cells and mineral particles, leading to the formation of large flocs that rapidly settle to the ocean floor. This work investigated the effectiveness of various domestic clays against a number of bloom-forming species from the United States. Twenty-five clays were tested against the dinoflagellate, Karenia brevis (formerly Gymnodinium breve), and the chrysophyte, Aureococcus anophagefferens. In general, the highest removal efficiencies (RE > 90% at 0.25 g rl of clay) against K. brevis were found using montmorillonite, bentonite and phosphatic clays (i.e. a product of phosphate mining containing large amounts of montmorillonite). The RE of phosphatic clays remained high (> 80%) even at 0.03 g rl. Kaolinite and zeolite were mostly ineffective against K. brevis. Removal with clay exceeded those for alum, polyaluminum chloride (PAC) and several other polymeric flocculants by a factor of two. However, the combination of phosphatic clay and PAC (at 5 mg rl) decreased the amount of clay needed to maintain 80% RE by one order of magnitude. Cell viability and recovery remained high when clay loading stayed below 0.03 g rl with or without resuspension of the sediment. However, cell mortality approached 100% with 0.50 g rl even with daily resuspension. Between 0.10 and 0.25 g rl, K. brevis survival and recovery depended on the interplay of clay loading, the frequency of resuspension, and duration of contact prior to the first resuspension event. For A. anophagefferens, the RE did not exceed 40% for any clay at 0.25 g rl even in combination with coagulants and flocculants. The highest removal was achieved by thoroughly mixing the clay slurry (e.g. phosphatic clay) into the cell culture. The RE by phosphatic clay varied significantly in a survey consisting of 17 different species from five algal classes. Moreover, the removal trends varied substantially with increasing cell concentration. For example, cell removal increased with increasing clay loading and cell concentration for K. brevis. However, RE dropped below 70% when cell concentration was < 1000 cell ml-1 for clay loadings up to 0.50 g rl. This suggested that a critical number of organisms should be present for clays to remain effective. Similarly, enhanced removal with increasing cell concentration was also found in Akashiwo sanguinea (formerly Gymnodinium sanguineum), Heterosigma akashiwo and Heterocapsa triquetra. In the six remaining species, RE initially increased then decreased, or RE remained constant as more cells were treated. The removal pattern among the species at comparable cell numbers did not correlate with the cross-sectional area (R2 = 0.23), swimming speed (R2 = 0.04), or a type of cell covering (i.e. theca, silica frustule). However, when the total collision frequency coefficients were calculated (including collisions due to cell motility) over the interval when clays were < 50 μm, these values correlated well with the empirical RB's for the flagellated species (R2 = 0.90). These results suggested that collisions due to cell motility may be important during the early stages of aggregation when clay sizes are relatively small (i.e. near the surface where the clay layer is initially added). The electrophoretic mobility (EPM) of marine microalgae displayed a small range of negative values. While the values were smaller that those reported from freshwater species, these results confirmed earlier assumptions that marine species carry a negative charge like their freshwater counterparts. In addition, these results also revealed that the stabilities of cell suspensions in seawater are not controlled by charge neutralization. However, these measurements did not provide direct information on why one species was more readily removed over another by a given clay mineral (e.g. phosphatic clay). The EPM of clays in freshwater also exhibited predictable negative values, with montmorillonites showing the highest stability and phosphatic clays the lowest. Kaolinite and zeolite displayed a range of intermediate values. These differences vanished when the clays were suspended in natural seawater (29.6 salinity), reducing the surface charge to a small range of negative values. This effect occurred even at 1116 of the final salinity (1.85 salinity). Viewed alone, these results did not provide direct information on why one clay mineral worked better than another against a given algal species (e.g. K. brevis). Kinetic and modelling experiments using K. brevis and three minerals revealed some distinct patterns in aggregation and settling among the clays, including how they removed the organisms. After dispersing on the surface, phosphatic clays aggregated quickly by virtue of low stability (low EPM). Cell removal coincided with the onset of settling. Also, kaolinite aggregated quickly and was controlled by size as well as stability. However, cell removal followed clay settling over 40 min, after which cell removal decreased yielding only 46% RE. Bentonite aggregated slowly over 90 min due to its high stability (high EPM), but produced a number of large voluminous flocs that steadily removed the algae. The sinking rate of flocs increased as cells became incorporated, but the onset of settling was delayed when cells were present in phosphatic clay and kaolinite due to a predicted reduction in aggregate density. The process of kinetics and sedimentation were modelled using first order equations for all mineral-algae combinations. Finally, phosphatic clays demonstrated the ability to selectively remove K. brevis in a mixed culture with the dinoflagellate, Prorocentrum micans, or the diatom, Skeletonema costatum. While the RE's were generally comparable to individual cultures, the RE of either species increased in the presence of the other, especially for K. brevis. Similar results were observed in mesocosm studies using a natural assemblage during a Karenia bloom. In fact, the RE of K. brevis were higher than would be predicted from single species laboratory studies given its low initial concentration. Overall, this research demonstrated the effectiveness of clay treatment against a number of HAB species in the U.S. This work also provided new insights into the aggregation phenomenon between minerals and living algal cells by focusing on the physical (cell size), chemical and behavioral (i.e. motility) properties of both particle types, the effect of particle concentration, and the aggregation kinetics of the clay-algae system.