The role of organic nutrients in structuring freshwater phytoplankton communities in a rapidly changing world

Carbon, nitrogen, and phosphorus are critical macroelements in freshwater systems. Historically, researchers and managers have focused on inorganic forms, based on the premise that the organic pool was not available for direct uptake by phytoplankton. We now know that phytoplankton can tap the organic nutrient pool through a number of mechanisms including direct uptake, enzymatic hydrolysis, mixotrophy, and through symbiotic relationships with microbial communities. In this review, we explore these mechanisms considering current and projected future anthropogenically-driven changes to freshwater systems. In particular, we focus on how naturally- and anthropogenically- derived organic nutrients can influence phytoplankton community structure. We also synthesize knowledge gaps regarding phytoplankton physiology and the potential challenges of nutrient management in an organically dynamic and anthropogenically modified world. Our review provides a basis for exploring these topics and suggests several avenues for future work on the relation between organic nutrients and eutrophication and their ecological implications in freshwater systems

What makes a cyanobacterial bloom disappear? A review of the abiotic and biotic cyanobacterial bloom loss factors

Cyanobacterial blooms present substantial challenges to managers and threaten ecological and public health. Although the majority of cyanobacterial bloom research and management focuses on factors that control bloom initiation, duration, toxicity, and geographical extent, relatively little research focuses on the role of loss processes in blooms and how these processes are regulated. Here, we define a loss process in terms of population dynamics as any process that removes cells from a population, thereby decelerating or reducing the development and extent of blooms. We review abiotic (e.g., hydraulic flushing and oxidative stress/UV light) and biotic factors (e.g., allelopathic compounds, infections, grazing, and resting cells/programmed cell death) known to govern bloom loss. We found that the dominant loss processes depend on several system specific factors including cyanobacterial genera-specific traits, in situ physicochemical conditions, and the microbial, phytoplankton, and consumer community composition. We also address loss processes in the context of bloom management and discuss perspectives and challenges in predicting how a changing climate may directly and indirectly affect loss processes on blooms. A deeper understanding of bloom loss processes and their underlying mechanisms may help to mitigate the negative consequences of cyanobacterial blooms and improve current management strategies

Estuarine habitats in the St. Louis Estuary, Lake Superior, Wisconsin: past, present, and future

In the face of climate change, understanding trajectories of change is critical for coastal management, particularly for identifying future restoration and climate adaptation opportunities. The National Estuarine Research Reserves (NERRs), individually and as a system, therefore have an urgent need to identify the extent and spatial patterns of estuarine habitat loss. To meet this challenge, we studied habitat change across 30 U.S. estuaries to document coastal habitat loss, and identify key opportunities for future restoration and enhancement. At the St. Louis River Estuary, elevation-based mapping revealed 5,043 ha currently within the reach of high water levels and appeared to provide a fairly accurate estimate of current estuary extent. Within a focal area for historical mapping, emergent marsh underwent substantial (52%) loss between 1861 and the present. In order for the estuary to realize its full capacity to provide benefits to plants, animals, and humans, it is critical for the estuary to regain habitats that have seen the most losses. Active restoration, carefully planned to enhance future resilience, can help recover these lost habitats. The new information from this habitat change analysis thus helps us envision a more resilient coast as a legacy for future generations

Cyanobacterial blooms in oligotrophic lakes: Shifting the high-nutrient paradigm

1. Freshwater cyanobacterial blooms have become ubiquitous, posing major threats to ecological and public health. 2. Decades of research have focused on understanding drivers of these blooms with a primary focus on eutrophic systems; however, cyanobacterial blooms also occur in oligotrophic systems, but have received far less attention, resulting in a gap in our understanding of cyanobacterial blooms overall. 3. In this review, we explore evidence of cyanobacterial blooms in oligotrophic freshwater systems and provide explanations for those occurrences. 4. We show that through their unique physiological adaptations, cyanobacteria are able to thrive under a wide range of environmental conditions, including low-nutrient waterbodies. 5. We contend that to fully understand cyanobacterial blooms, and thereby mitigate and manage them, we must expand our inquiries to consider systems along the trophic gradient, and not solely focus on eutrophic systems, thus shifting the high-nutrient paradigm to a trophic-gradient paradigm

Cyanobacterial blooms in oligotrophic lakes : Shifting the high-nutrient paradigm

Freshwater cyanobacterial blooms have become ubiquitous, posing major threats to ecological and public health. Decades of research have focused on understanding drivers of these blooms with a primary focus on eutrophic systems; however, cyanobacterial blooms also occur in oligotrophic systems, but have received far less attention, resulting in a gap in our understanding of cyanobacterial blooms overall. In this review, we explore evidence of cyanobacterial blooms in oligotrophic freshwater systems and provide explanations for those occurrences. We show that through their unique physiological adaptations, cyanobacteria are able to thrive under a wide range of environmental conditions, including low-nutrient waterbodies. We contend that to fully understand cyanobacterial blooms, and thereby mitigate and manage them, we must expand our inquiries to consider systems along the trophic gradient, and not solely focus on eutrophic systems, thus shifting the high-nutrient paradigm to a trophic-gradient paradigm

Blooms also like it cold

Publication history: Accepted - 30 January 2023; Published - 17 February 2023.Cyanobacterial blooms have substantial direct and indirect negative impacts on freshwater ecosystems including releasing toxins, blocking light needed by other organisms, and depleting oxygen. There is growing concern over the potential for climate change to promote cyanobacterial blooms, as the positive effects of increasing lake surface temperature on cyanobacterial growth are well documented in the literature; however, there is increasing evidence that cyanobacterial blooms are also being initiated and persisting in relatively cold-water temperatures (< 15°C), including ice-covered conditions. In this work, we provide evidence of freshwater cold-water cyanobacterial blooms, review abiotic drivers and physiological adaptations leading to these blooms, offer a typology of these lesser-studied cold-water cyanobacterial blooms, and discuss their occurrence under changing climate conditions.Department of Agriculture, Environment and Rural Affairs, Northern Ireland ERDF/ESF Project Biomanipulation. Grant Number: CZ.02.1.01/0.0/0.0/16_025/0007417 MINECO. Grant Number: BES-2017-080558 US National Science Foundation (NSF). Grant Numbers: 1638554, 0639229, MSB 1137327, 1137353 Natural Sciences and Engineering Research Council of Canada. Grant Number: RGPIN-2018-06389 NOAA Office for Coastal Management. Grant Number: NA18NOS4200151 Projekt DEAL Spanish Agencia Estatal de Investigación. Grant Number: CTM2016-79741-R Swedish Research Council. Grant Numbers: 2020-01825, 2020-03222 Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning. Grant Number: 2020-01091 U.S. Geological Survey. Grant Number: G21AC1003

Blooms also like it cold

Abstract Cyanobacterial blooms have substantial direct and indirect negative impacts on freshwater ecosystems including releasing toxins, blocking light needed by other organisms, and depleting oxygen. There is growing concern over the potential for climate change to promote cyanobacterial blooms, as the positive effects of increasing lake surface temperature on cyanobacterial growth are well documented in the literature; however, there is increasing evidence that cyanobacterial blooms are also being initiated and persisting in relatively cold‐water temperatures (< 15°C), including ice‐covered conditions. In this work, we provide evidence of freshwater cold‐water cyanobacterial blooms, review abiotic drivers and physiological adaptations leading to these blooms, offer a typology of these lesser‐studied cold‐water cyanobacterial blooms, and discuss their occurrence under changing climate conditions