Hans W. Paerl's research while affiliated with University of North Carolina at Chapel Hill and other places

Publications (117)

Preprint
There is a need for a unified grazing method that can be used across the freshwater-to-marine continuum. To accomplish this, this research utilized dilution grazing assays across the freshwater-to-marine continuum and across the oligotrophic-to-hypereutrophic gradient by measuring size fractions of dilution-based mortality. This was investigated by...
Article
Excessive anthropogenic nutrient input has resulted in eutrophication and algal blooms which have severely impacted the function and sustainability of aquatic ecosystems, underscoring the need to implement nutrient management strategies. It was assumed that the increasing rainfall during flood season would affect the stoichiometric ratio of total n...
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Nutrient storage is considered a critical strategy for algal species to adapt to a fluctuating nutrient supply. Luxury phosphorus (P) uptake into storage of polyphosphate extends the duration of cyanobacterial dominance and their blooms under P deficiency. However, it is unclear whether nitrogen (N) storage in the form of cyanophycin supports persi...
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Algal blooms (ABs) in inland lakes have caused adverse ecological effects, and health impairment of animals and humans. We used archived Landsat images to examine ABs in lakes (>1 km²) around the globe over a 37-year time span (1982-2018). Out of the 176032 lakes with area > 1 km² detected globally, 863 were impacted by ABs, 708 had sufficiently-lo...
Article
Harmful cyanobacterial blooms (CyanoHABs) are expanding world-wide, adversely affecting aquatic food production, recreational and tourism activities and safe drinking water supplies. China's inland waters have been increasingly threatened by CyanoHABs during the past several decades. The environmental factors controlling CyanoHABs are highly variab...
Article
China has made a concerted effort to successfully improve water quality of rivers, but lake water quality has not improved. Lakes require controls on both catchment external nutrient loads and in-lake internal loads, where nature-based solutions are coupled with engineered systems to achieve the United Nations Sustainable Development Goals (SDGs).
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To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and tot...
Preprint
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The freshwater ecosystem characteristics in terms of nutrient inventory across seasons, spatial variations of chl- a biomass, and the phytoplankton community structure are prudent ecological assessment indices for a bloom management protocol. We evaluated the spatial and seasonal chl-a distribution under different nutrient conditions and phytoplank...
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Climate warming in combination with nutrient enrichment can greatly promote phytoplankton proliferation and blooms in eutrophic waters. Lake Taihu, China, is a large, shallow and eutrophic system. Since 2007, this lake has experienced extensive nutrient input reductions aimed at controlling cyanobacterial blooms. However, intense cyanobacterial blo...
Article
Estuaries function as important transporters, transformers, and producers of organic matter (OM). Along the freshwater to saltwater gradient, the composition of OM is influenced by physical and biogeochemical processes that change spatially and temporally, making it difficult to constrain OM in these ecosystems. In addition, many of the environment...
Article
The Neuse River Estuary (North Carolina, USA) is a valuable ecosystem that has been affected by the expansion of agricultural and urban watershed activities over the last several decades. Eutrophication, as a consequence of enhanced anthropogenic nutrient loadings, has promoted high phytoplankton biomass, hypoxia, and fish kills. This study compare...
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Trait‐based approaches provide a mechanistic framework crossing scales from cellular traits to community dynamics, while ecological stoichiometry applies first principles to understand how the balance of energy and elements shape ecological interactions. However, few studies have explicitly linked both frameworks. In this study, we tested the stoic...
Article
Harmful cyanobacterial blooms (CyanoHABs) are linked to increasing anthropogenic nitrogen (N) and phosphorus (P) inputs. However, CyanoHABs in many large lakes continue despite extensive abatement efforts, mostly focused on external P loading. Internal nutrient cycling can modify nutrient availability and limitation; thus, understanding the relativ...
Article
The global expansion of harmful cyanobacterial blooms (CyanoHABs) poses an increasing threat to public health. CyanoHABs are characterized by the production of toxic metabolites known as cyanotoxins. Human exposure to cyanotoxins is challenging to forecast, and perhaps the least understood exposure route is via inhalation. While the aerosolization...
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Picophytoplankton (PicoP) are increasingly recognized as significant contributors to primary productivity and phytoplankton biomass in coastal and estuarine systems. Remarkably though, PicoP composition is unknown or not well-resolved in several large estuaries including the semi-lagoonal Neuse River Estuary (NRE), a tributary of the second largest...
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Cyanobacterial harmful algal blooms (CyanoHABs) are an increasingly common feature of large, eutrophic lakes. Non-N2-fixing CyanoHABs (e.g., Microcystis) appear to be proliferating relative to N2-fixing CyanoHABs in systems receiving increasing nutrient loads. This shift reflects increasing external nitrogen (N) inputs, and a > 50-year legacy of ex...
Article
The Defense Coastal/Estuarine Research Program (DCERP) was a 10-year multi-investigator project funded by the Department of Defense to improve understanding of ecosystem processes and their interactions with natural and anthropogenic stressors at the Marine Corps Base Camp Lejeune (MCBCL) located in coastal North Carolina. The project was aimed at...
Article
The rational eutrophication management largely depends on the knowledge of the dynamics in the dissolved inorganic nutrients especially nitrogen forms which trigger exponential primary productivity in eutrophic systems. The present study investigated the phytoplankton interactions with the dissolved N forms, nitrate (NO3) and ammonium (NH4) in a su...
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Globally, many shallow lakes have shifted from a clear macrophyte-dominated state to a turbid phytoplankton-dominated state due to eutrophication. Such shifts are often accompanied by toxic cyanobacterial blooms, with specialized traits including buoyancy regulation and nitrogen fixation. Previous work has focused on how these traits contribute to...
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Coastal North Carolina experienced 36 tropical cyclones (TCs), including three floods of historical significance in the past two decades (Hurricanes Floyd-1999, Matthew-2016 and Florence-2018). These events caused catastrophic flooding and major alterations of water quality, fisheries habitat and ecological conditions of the Albemarle-Pamlico Sound...
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Estuaries regulate transport of dissolved organic carbon (DOC) from land to ocean. Export of terrestrial DOC from coastal watersheds is exacerbated by increasing major rainfall and storm events and human activities, leading to pulses of DOC that are shunted through rivers downstream to estuaries. Despite an upward trend of extreme events, the fate...
Article
To assess the comparability between taxonomic identification methods for phytoplankton, multiple approaches were used to characterize phytoplankton community composition within the Neuse River Estuary (NRE), North Carolina. Small subunit 18S rRNA gene (18S) sequencing and accessory pigment analysis displayed similar trends, indicating chlorophytes...
Article
Harmful cyanobacterial blooms (CyanoHABs) are a rapidly proliferating global problem, threatening the use and sustainability of our freshwater resources. In recent decades, the USA, China and other developed and developing countries threatened by CyanoHAB expansion have developed collaborative efforts aimed at mitigating and managing this environme...
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Hypoxia is common feature of eutrophic estuaries and semi-enclosed seas globally. One of the key factors driving hypoxia is nitrogen pollution. To gain more insight into the effects of hypoxia on estuarine nitrogen cycling, we measured potential nitrate reduction rates at different salinities and levels of hypoxia in a eutrophic temperate microtida...
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• Shallow lakes can shift between stable states as a result of anthropogenic or natural drivers. Four common stable states differ in dominant groups of primary producers: submerged, floating, or emergent macrophytes or phytoplankton. Shifts in primary producer dominance affect key supporting, provisioning, regulating, and cultural ecosystem service...
Article
Large-scale and rapid improvement in wastewater treatment is common practice in developing countries, yet this influence on nutrient regimes in receiving waterbodies is rarely examined at broad spatial and temporal scales. Here, we present a study linking decadal nutrient monitoring data in lakes with the corresponding estimates of five major anthr...
Article
The increasing freshwater ecosystem nutrient budget is a critical anthropogenic factor promoting freshwater eutrophication and episodic bloom of harmful algae which threaten water quality and public health. To understand how the eutrophic freshwater ecosystem responds in term of phytoplankton community structure dynamics to a sudden rise in nutrien...
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Hurricane Harvey (category four storm) made landfall along the coast of Texas (United States) and then stalled out over Texas and Louisiana, releasing 1.29 × 1011 m3 of precipitation over 5 days. This caused extensive flooding that elevated freshwater river discharge and land runoff into Galveston Bay and eventually into the Gulf of Mexico. The flo...
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Most aquatic systems show characteristic seasonal fluctuations in the total nutrient pool supporting primary productivity. The nutrient dynamics essentially exacerbate critical demand for the counterpart micronutrients towards achieving ecosystem equilibrium. Herein, the phytoplankton demand for iron (Fe) uptake under high concentration of nitrate-...
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Munitions compounds (i.e., 2,4,6-trinitrotoluene (TNT), octahy-dro-1,3,5,7-tetranitro-1,3,5,7-tetrazocin (HMX), and hexadydro-1,3,5-trinitro-1,3,5-triazin (RDX), also called energetics) were originally believed to be recalcitrant to microbial biodegradation based on historical groundwater chemical attenuation data and laboratory culture work. More...
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Flooding from extreme weather events (EWE), such as hurricanes, exports large amounts of dissolved organic matter (DOM) to both estuaries and coastal waters globally. Hydrologic connectivity of wetlands to adjacent river channels during flood events can potentially have a major control on the DOM exported to coastal waters after EWEs. In this study...
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Estuarine-coastal ecosystems are rich areas of the global ocean with elevated rates of organic matter production supporting major fisheries. Net and gross primary production (NPP, GPP) are essential properties of these ecosystems, characterized by high spatial, seasonal, and inter-annual variability associated with climatic effects on hydrology. Ov...
Article
Managing and mitigating the global expansion of toxic cyanobacterial harmful algal blooms (CyanoHABs) is a major challenge facing researchers and water resource managers. Various approaches, including nutrient load reduction, artificial mixing and flushing, omnivorous fish removal, algaecide applications and sediment dredging, have been used to red...
Article
Phosphorus (P) is a vital nutrient for algal growth. Aside from soluble reactive P (SRP), organic P (OP) is used by algae via alkaline phosphatase (AP) hydrolysis, which can play an important role in supplying P. Enzymatically-hydrolysable OP (EHP) can potentially be used as an indicator of bioavailability of P other than SRP in natural waters. We...
Chapter
Elevated atmospheric nitrogen (N) deposition has greatly influenced aquatic ecosystems, especially in N budget and phytoplankton structure. Compared with considerable studies for oligotrophic lakes, estuaries, and open ocean, few evidence for the importance of N deposition have been directly provided for eutrophic lakes. Our high-resolution systema...
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Bacteria play key roles in the function and diversity of aquatic systems, but aside from study of specific bloom systems, little is known about the diversity or biogeography of bacteria associated with harmful cyanobacterial blooms (cyanoHABs). CyanoHAB species are known to shape bacterial community composition and to rely on functions provided by...
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Background: Sharp increases in food production worldwide are attributable to agricultural intensification aided by heavy use of agrochemicals. This massive use of pesticides and fertilizers in combination with global climate change has led to collateral damage in freshwater systems, notably an increase in the frequency of harmful cyanobacterial bl...
Article
Agricultural, urban and industrial activities have dramatically increased aquatic nitrogen and phosphorus pollution (eutrophication), threatening water quality and biotic integrity from headwater streams to coastal areas world‐wide. Eutrophication creates multiple problems, including hypoxic “dead zones” that reduce fish and shellfish production; h...
Article
There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water col...
Article
We measured the microbial community composition and metabolic responses of Microcystis aeruginosa in a microcosm coculture system receiving dissolved inorganic nitrogen and phosphorus (DIP) close to the average concentrations in Lake Taihu. In the coculture system, DIP is depleted and the growth and production of aquatic microorganisms can be stres...
Article
Dissolved organic phosphorus (DOP) could be transformed to dissolved inorganic phosphorus (DIP) under phosphorus (P) deficient conditions by various enzymes, among which alkaline phosphatase activity (APA) is regarded as the most important one. To better understand the different response of phytoplankton to DOP and the role of alkaline phosphatase...
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Coastal North Carolina, USA, has experienced three extreme tropical cyclone-driven flood events since 1999, causing catastrophic human impacts from flooding and leading to major alterations of water quality, biogeochemistry, and ecological conditions. The apparent increased frequency and magnitudes of such events led us to question whether this is...
Article
Rising atmospheric carbon dioxide (CO2) may stimulate the proliferation of cyanobacteria. To investigate the possible physiological responses of cyanobacteria to elevated CO2 at different nutrient levels, Microcystis aeruginosa were exposed to different concentrations of CO2 (400, 1100, and 2200 ppm) under two nutrient regimes (i.e., in nutrient-ri...
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The concept of lakes “evolving” phosphorus (P) limitation has persisted in limnology despite limited direct evidence. Here, we developed a simple model to broadly characterize nitrogen (N) surpluses and deficits, relative to P, in lakes and compared the magnitude of this imbalance to estimates of N gains and losses through biological N transformati...
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Coincident climatic and human effects strongly influence water-quality properties in estuarine-coastal ecosystems around the world. Time-series data for a number of ecosystems reveal high spatio-temporal variability superimposed on secular trends traceable to nutrient over-enrichment. In this paper, we present new analyses of long-term data for Che...
Article
Harmful cyanobacterial blooms (=cyanoHABs) are an increasing feature of many waterbodies throughout the world. Many bloom-forming species produce toxins, making them of particular concern for drinking water supplies, recreation and fisheries in waterbodies along the freshwater to marine continuum. Global changes resulting from human impacts, such a...
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Plain Language Summary Recent hurricanes along the Southeastern and Gulf coasts of the United States have received much attention, because these extreme events have led to immense societal and economic impacts. Wetlands in coastal watersheds store large amounts of organic matter and upon flooding during extreme weather events are poised to release...
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In order to control nitrogen (N) pollution of Lake Taihu, China, we studied the spatial and temporal distribution characteristics of inorganic N in inflowing rivers polluted by industry, agriculture, and domestic sewage during low, moderate, and high flow periods. The results showed that dissolved total nitrogen (DTN) was the main fraction of total...
Article
River systems worldwide have become substantially influenced by human activities, including land use changes, river diversion operations, and flood control measures. Some of the unambiguous and best studied examples of effects of enhanced eutrophication on biotic resources can be found in Louisiana estuaries at the terminus of the Mississippi-Atcha...
Article
As the interface between riverine and coastal systems, estuaries play a key role in receiving, transporting, and processing terrestrial organic carbon prior to export to downstream coastal systems. Estuaries can switch from terrestrial organic carbon reactors under low river flow to pipelines under high flow, but it remains unclear how estuarine te...
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Flooding is a major disturbance that impacts aquatic ecosystems and the ecosystem services that they provide. Predicted increases in global flood risk due to land use change and water cycle intensification will likely only increase the frequency and severity of these impacts. Extreme flooding events can cause loss of life and significant destructio...
Article
Surface wind speed has declined significantly globally. However, the response of aquatic systems to decreasing wind speeds has received little attention.We examined the effects of a long-term decrease in wind speed on shallow, eutrophic Lake Taihu, China's third largest lake, by combining high-frequency monitoring, long-term meteorological and wate...
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Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on biogeochemical cycling and phytoplankton responses in a large est...
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Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent probl...
Data
Spring phytoplankton assemblage comparison among different years in Lake Taihu. The lower left corner shows the Bray & Curtis index (quantitative dissimilarity coefficient), and the top right corner shows the non-metric coefficients (Sørensen index) computed using mean spring MFGs biomass. Similarity/dissimilarity are shown with colors: green = Sør...
Data
Relationship between surface water temperature and air temperature in Lake Taihu. (TIF)
Data
Ordination results with wind speed. (a) RDA ordination of phytoplankton samples from 1997 to 2016. (b) Environment variables (p < 0.1) and MFGs in the first two axes RDA. (TIF)