Geology topics

Viviana Mazzei

Publications and source records attributed to Viviana Mazzei.

5 recordsLinked to original sources

USGS2026

Phytoplankton responses to experimental nitrogen and phosphorus loading in the eutrophic and colored Caloosahatchee River, Florida

The Caloosahatchee River, located in southwest Florida, is a eutrophic and colored river that flows from Lake Okeechobee westward into its estuary and the Gulf of America. Cyanobacterial harmful algal blooms (HABs) are a documented problem along this freshwater-to-marine waterway where nutrient enrichment has been identified as a key factor in bloom occurrence but has not been experimentally tested in the river. This study is the first to test the effects of inorganic nutrient loading on phytoplankton assemblages in the Caloosahatchee River and the effects of different nutrient sources on phytoplankton dynamics at different times of the year. Three independent, in situ experiments were conducted to test the effects of daily, incrementally increased ammonium, nitrate, and phosphate loading on phytoplankton at different times of the year (summer, fall, winter). Over the 72-hour enclosure period, phytoplankton abundance metrics (cell concentration, chlorophyll- a , and phycocyanin), dissolved oxygen, and pH increased, and fluorescent dissolved organic matter and turbidity decreased in all treatments and controls. Increased phytoplankton abundance metrics relative to controls were observed after 72 hours of exposure to elevated ammonium and nitrate in summer and only ammonium in winter, suggesting periodic nitrogen limitation; however, no treatment effects on phytoplankton assemblage structure in terms of resemblance and diversity metrics were found. Increases in total cell concentrations were driven by elevated growth rates of already dominant taxa but not sufficiently to form a visible bloom. Cyanobacteria consistently dominated the phytoplankton, particularly Aphanocapsa and Merismopedia , whereas the common HAB-forming Microcystis maintained consistently low abundance. This study provides new information on the ecology of phytoplankton assemblages in the Caloosahatchee River and could be used by water resources managers to evaluate strategies for controlling cyanobacterial HABs in the river.

Florida↗

USGS2025

Phytoplankton assemblage structure, drivers, and thresholds with a focus on harmful algal bloom ecology in the Lake Okeechobee system, Florida, USA

Untangling the complexities of harmful algal bloom (HAB) dynamics is an ongoing effort that requires a fundamental understanding of spatiotemporal phytoplankton patterns and the environmental filters through which assemblages are structured. To this aim, monthly field surveys were conducted from 2019 to 2021 at 21 sites in Lake Okeechobee, Florida – a large, shallow, eutrophic, and heavily managed lake with coastal connectivity that experiences intense and recurrent HABs. Phytoplankton assemblages were strongly spatially structured forming 7 distinct lake zones with significant dissimilarity in composition and total abundance. While successional patterns were not apparent across seasons or wet/dry periods, total phytoplankton abundance was significantly greater towards the end of the wet season. Distance-based linear models using 16 abiotic variables were used to identify significant explanatory variables of spatial and temporal patterns. The spatial model explained 93 % of the variability suggesting deterministic processes largely control spatial patterns. The temporal model explained only 48 % of the temporal variability suggesting stochasticity in lake-wide shifts in assemblages over time. However, the strong spatial structuring of assemblages may preclude lake-wide succession patterns. Total algal abundance metrics were inversely related to nitrate, orthophosphate, and total alkalinity, the strongest explanatory variables of assemblage patterns, suggesting a lag between peak resources and peak abundance as phytoplankton cycle “boom-to-bust” phases. Consistent with this inverse relationship, Threshold Indicator Taxa Analysis returned almost exclusively negative responder indicator taxa for all three explanatory variable gradients. The assemblage-level threshold defined the gradient boundary between boom- and bust-associated indicator taxa. These data contribute novel information about HABs ecology pertinent to management strategies.

Florida↗

USGS2024

Genome sequences of toxigenic cyanobacteria from a bloom in Lake Mattamuskeet, North Carolina (United States)

Lake Mattamuskeet, the largest lake in North Carolina, USA, has undergone decades-long eutrophication causing reduced water quality and promoting cyanobacterial blooms that may produce toxins. It is therefore necessary to evaluate the cyanobacterial diversity of the lake and their toxigenic potential. We present draft genomes of Microcystis , Pelatocladus , Raphidiopsis , and Umezakia strains isolated from Lake Mattamuskeet. The whole-genome shotgun projects for Umezakia ovalisporum BLCC-F208, Microcystis sp. BLCC-F209, Microcystis sp. BLCC-F210, Pelatocladus sp. BLCC-F211, U. ovalisporum BLCC-F215, and Raphidiopsis BLCC-F218 have been deposited in GenBank under accession numbers JBHFLK000000000, JBHFLL000000000, CP169647, JBHFLM000000000, JBHFLN000000000, and JBHFLO000000000, respectively. Based on the genomic analysis, several biosynthetic gene clusters (BCGs) with varying degrees of similarity to known toxic and bioactive compound gene clusters were identified across the different cyanobacterial strains.

North Carolina↗

USGS2024

Interdisciplinary science approach for harmful algal blooms (HABs) and algal toxins—A strategic science vision for the U.S. Geological Survey

Executive Summary Algal blooms in water, soils, dusts, and the environment have captured national attention because of concerns associated with exposure to algal toxins for humans and animals. Algal blooms naturally occur in all surface-water types and are important primary producers for aquatic ecosystems. However, excessive algae growth can be associated with many harmful effects ranging from aesthetic to toxicity concerns, so this excessive growth is commonly called a harmful algal bloom (HAB). Ecological imbalances that can lead to excessive algal growth, such as increased nutrient availability to waterbodies from natural and anthropogenic sources, are well documented in scientific literature. On the other hand, fundamental scientific understandings of environmental causes and controls leading to algal toxin production, environmental exposures, and adverse health outcomes for humans and animals could benefit from more attention by U.S. Geological Survey (USGS) scientists. Understanding when, why, and how the toxin is produced by individual algal cells or communities and why the toxin is released to the surrounding waterbody requires fundamental research to determine a toxin’s role, whether it provides competitive advantage or if other potential reasons exist for toxin production and release, such as secretions from otherwise benign biological processes. This research will require groundbreaking scientific discovery about underlying biologic and abiotic (non-living) processes commonly complicated by local variation in land use, microbial species composition, and ecosystem structure of the surrounding watershed. Although underlying processes by which HABs form may be similar from one waterbody to another, individual waterbodies may be controlled by local factors for HAB development and toxin production that are unique to the watershed. Consequently, many fundamental science gaps exist that prevent informed mitigation and prevention of toxic HAB events. There are also gaps in understanding local conditions that control algal growth unique to specific watersheds. Addressing these science gaps is needed to inform evidence-based decisions that protect human and animal health and that reduce recreational and socioeconomic losses.

Circular↗

USGS2024

Microbial diversity, genomics, and phage–host interactions of cyanobacterial harmful algal blooms

The occurrence of cyanobacterial harmful algal blooms (cyanoHABs) is related to their physical and chemical environment. However, less is known about their associated microbial interactions and processes. In this study, cyanoHABs were analyzed as a microbial ecosystem, using 1 year of 16S rRNA sequencing and 70 metagenomes collected during the bloom season from Lake Okeechobee (Florida, USA). Biogeographical patterns observed in microbial community composition and function reflected ecological zones distinct in their physical and chemical parameters that resulted in bloom “hotspots” near major lake inflows. Changes in relative abundances of taxa within multiple phyla followed increasing bloom severity. Functional pathways that correlated with increasing bloom severity encoded organic nitrogen and phosphorus utilization, storage of nutrients, exchange of genetic material, phage defense, and protection against oxidative stress, suggesting that microbial interactions may promote cyanoHAB resilience. Cyanobacterial communities were highly diverse, with picocyanobacteria ubiquitous and oftentimes most abundant, especially in the absence of blooms. The identification of novel bloom-forming cyanobacteria and genomic comparisons indicated a functionally diverse cyanobacterial community with differences in its capability to store nitrogen using cyanophycin and to defend against phage using CRISPR and restriction-modification systems. Considering blooms in the context of a microbial ecosystem and their interactions in nature, physiologies and interactions supporting the proliferation and stability of cyanoHABs are proposed, including a role for phage infection of picocyanobacteria. This study displayed the power of “-omics” to reveal important biological processes that could support the effective management and prediction of cyanoHABs.

Florida↗