A Phased Assessment of Restoration Alternatives to Achieve Phosphorus Water Quality Targets for Lake Okeechobee, Florida, USA

Complete Genome Sequence of Microcystis aeruginosa FD4, Isolated from a Subtropical River in Southwest Florida

We report the first complete genome of Microcystis aeruginosa from North America. A harmful bloom that occurred in the Caloosahatchee River in 2018 led to a state of emergency declaration in Florida. Although strain FD4 was isolated from this toxic bloom, the genome did not have a microcystin biosynthetic gene cluster.

Lake and River Restoration: Method, Evaluation and Management

Eutrophication has become one of the major environmental issues of global concern due to the adverse effects on water quality, public health and ecosystem sustainability. Fundamental research on the restoration of eutrophic freshwaters, i.e., lakes and rivers, is crucial to support further evidence-based practical implementations. This Special Issue successfully brings together recent research findings from scientists in this field and assembles contributions on lake and river restoration. The 12 published papers can be classified into, and contribute to, three major aspects of this topic. Firstly, a background investigation into the migration of nutrients, and the characteristics of submerged biota, will guide and assist the understanding of the mechanisms of future restoration. Secondly, various restoration strategies, including control of both external and internal nutrients loading, are studied and evaluated. Thirdly, an evaluation of the field sites after restoration treatment is reported in order to support the selection of appropriate restoration approaches. This paper focuses on the current environmental issues related to lake and river restoration and has conducted a comprehensive bibliometric analysis in order to emphasise the fast-growing attention being paid to the research topic. The research questions and main conclusions from all papers are summarised to focus the attention toward how the presented studies aid gains in scientific knowledge, engineering experience and support for policymakers.

Synergistic Recapturing of External and Internal Phosphorus for In Situ Eutrophication Mitigation

In eutrophication management, many phosphorus (P) adsorbents have been developed to capture P at the laboratory scale. Existing P removal practice in freshwaters is limited due to the lack of assessment of the possibility and feasibility of controlling P level towards a very low level (such as 10 μg/L) in order to prevent the harmful algal blooms. In this study, a combined external and internal P control approach was evaluated in a simulated pilot-scale river–lake system. In total, 0.8 m3 of simulated river water was continuously supplied to be initially treated by a P adsorption column filled with a granulated lanthanum/aluminium hydroxide composite (LAH) P adsorbent. At the outlet of the column (i.e., inlet of the receiving tanks), the P concentration decreased from 230 to 20 µg/L at a flow rate of 57 L/day with a hydraulic loading rate of 45 m/day. In the receiving tanks (simulated lake), 90 g of the same adsorbent material was added into 1 m3 water for further in situ treatment, which reduced and maintained the P concentration at 10 µg/L for 5 days. The synergy of external and internal P recapture was demonstrated to be an effective strategy for maintaining the P concentration below 10 µg/L under low levels of P water input. The P removal was not significantly affected by temperature (5–30 °C), and the treatment did not substantially alter the water pH. Along with the superior P adsorption capacity, less usage of LAH could lead to reduced cost for potation eutrophication control compared with other widely used P adsorbents.

Amphoteric starch-based bicomponent modified soil for mitigation of harmful algal blooms (HABs) with broad salinity tolerance: Flocculation, algal regrowth, and ecological safety

The treatment of harmful algal blooms (HABs) by in-situ flocculation is an emerging technology capable of efficiently removing HABs from natural waters. However, differences in salinity, pH and algal species in freshwaters and seawaters can influence the flocculation treatment. In this study, we developed a bicomponent modified soil using amphoteric starch (AS) and poly-aluminium chloride (PAC) in order to effectively flocculate microalgae under broad salinity conditions. Specifically, the impacts of water salinity (0-3.3%), pH (3-11), and algal species (Microcystis aeruginosa and marine Chlorella sp.) were investigated in order to evaluate efficiency, dosage and mechanisms of algae flocculation. The results showed that AS-PAC modified soils possessed excellent resistance to salinity change due to the anti-polyelectrolyte effect of AS, which contributed to 99.9% removal efficiency of M. aeruginosa in fresh and saline waters, and Chlorella sp. in marine water, respectively. The dosage of the flocculant modifier was only 10-20% of that of another proven modifier (i.e. Moringa oleifera), which substantially reduced the material cost. The high salinity tolerance of algal flocculation by the AS-PAC modified soil was attributed to the synergistic processes of charge neutralization and netting-bridging. Thus, this study has developed a universal flocculant and revealed fundamental mechanisms for the mitigation of HABs under broad salinity conditions.

Sorption Properties of the Bottom Sediment of a Lake Restored by Phosphorus Inactivation Method 15 Years after the Termination of Lake Restoration Procedures

Artificial mixing and phosphorus inactivation methods using aluminum compounds are among the most popular lake restoration methods. Długie Lake (Olsztyńskie Lakeland, Poland) was restored using these two methods. Primarily, P precipitation and inactivation methods significantly increased the sorption properties of Długie Lake bottom sediment. Fifteen years after the termination of the restoration procedure, the alum-modified “active” sediment layer still has higher P adsorption abilities, which can limit P internal loading. Relatively low amounts of phosphates in the near-bottom water of Długie Lake, even in anoxia, as well as the fact that the assessed maximum sediment P sorption capacity is still higher than NH4Cl–P (labile P) and BD–P (Fe-bound P) sum (“native exchangeable P”), confirm that hypothesis. Among the tested P adsorption models for the sediment, the double Langmuir model showed the best fit to the experimental data (the highest R2 values). This may indicate that phosphorus adsorption by the tested sediments most likely occurs through phosphate binding at two types of active sorption sites. P adsorption by the studied lake sediment during experiments was significantly connected to aluminum content in sediment. The research into the adsorption properties of sediment can be used as a tool for the evaluation of lake restoration effects.

The Latitudes, Attitudes, and Platitudes of Watershed Phosphorus Management in North America

Phosphorus (P) plays a crucial role in agriculture as a primary fertilizer nutrient-and as a cause of the eutrophication of surface waters. Despite decades of efforts to keep P on agricultural fields and reduce losses to waterways, frequent algal blooms persist, triggering not only ecological disruption but also economic, social, and political consequences. We investigate historical and persistent factors affecting agricultural P mitigation in a transect of major watersheds across North America: Lake Winnipeg, Lake Erie, the Chesapeake Bay, and Lake Okeechobee/Everglades. These water bodies span 26 degrees of latitude, from the cold climate of central Canada to the subtropics of the southeastern United States. These water bodies and their associated watersheds have tracked trajectories of P mitigation that manifest remarkable similarities, and all have faced challenges in the application of science to agricultural management that continue to this day. An evolution of knowledge and experience in watershed P mitigation calls into question uniform solutions as well as efforts to transfer strategies from other arenas. As a result, there is a need to admit to shortcomings of past approaches, plotting a future for watershed P mitigation that accepts the sometimes two-sided nature of Hennig Brandt's "Devil's Element."

Contribution of Internal Nutrients Loading on the Water Quality of a Reservoir

Sediment plays an important role in the water quality of a lake by acting as both a nutrient source and sink. The amount of phosphorus and nitrogen in the water depends on the internal load from the sediment as well as the external load. To estimate the effects of sediment load on the water quality of a reservoir, we applied a three-dimensional hydrodynamic and transport model based on the benthic chamber experimental results at Euiam Lake, South Korea. As shown in the sensitivity analysis results, the eutrophication period could be significantly extended by a change of phosphorus flux rates from the sediments. The increased phosphorus flux from the sediments intensifies the algal growth of Euiam Lake, which could cause serious algal bloom during spring and fall. This study provides information on nutrient concentrations in the sediment of Euiam Lake, verifies the role of the sediment as a source or sink of nutrients, and evaluates the effect of sediment release of nutrients and contaminants on water quality. This research is a useful tool in determining the effects of internal load in lakes and establishing the operation guideline for sediment management in order to maintain feasible water quality for beneficial use.

Modified Local Soil (MLS) Technology for Harmful Algal Bloom Control, Sediment Remediation, and Ecological Restoration

Harmful algal blooms (HABs), eutrophication, and internal pollutant sources from sediment, represent serious problems for public health, water quality, and ecological restoration worldwide. Previous studies have indicated that Modified Local Soil (MLS) technology is an efficient and cost-effective method to flocculate the HABs from water and settle them onto sediment. Additionally, MLS capping treatment can reduce the resuspension of algae flocs from the sediment, and convert the algal cells, along with any excessive nutrients in-situ into fertilisers for the restoration of submerged macrophytes in shallow water systems. Furthermore, the capping treatment using oxygen nanobubble-MLS materials can also mitigate sediment anoxia, causing a reduction in the release of internal pollutants, such as nutrients and greenhouse gases. This paper reviews and quantifies the main features of MLS by investigating the effect of MLS treatment in five pilot-scale whole-pond field experiments carried out in Lake Tai, South China, and in Cetian Reservoir in Datong city, North China. Data obtained from field monitoring showed that the algae-dominated waters transform into a macrophyte-dominated state within four months of MLS treatment in shallow water systems. The sediment-water nutrient fluxes were substantially reduced, whilst water quality (TN, TP, and transparency) and biodiversity were significantly improved in the treatment ponds, compared to the control ponds within a duration ranging from one day to three years. The sediment anoxia remediation effect by oxygen nanobubble-MLS treatment may further contribute to deep water hypoxia remediation and eutrophication control. Combined with the integrated management of external loads control, MLS technology can provide an environmentally friendly geo-engineering method to accelerate ecological restoration and control eutrophication.