Effects of eutrophication on sedimentary organic carbon cycling in five temperate lakes

Authors

Annika Fiskal, Longhui Deng, Anja Michel, Philip Eickenbusch, Xingguo Han, Lorenzo Lagostina, Rong Zhu, Michael Sander, Martin H. Schroth, Stefano M. Bernasconi, Nathalie Dubois, and Mark A. Lever

Even though human induced eutrophication has severely impacted temperate lake ecosystems over the last centuries, the effects on total organic carbon (TOC) burial and mineralization are not well understood. We study these effects based on sedimentary records from the last 180 years in five Swiss lakes that differ in trophic state. We compare changes in content of TOC and modeled TOC accumulation rates through time to historical data on algae blooms, water column anoxia, wastewater treatment, artificial lake ventilation, and water column phosphorus (P) concentrations. We furthermore investigate the effects of eutrophication on rates of microbial TOC remineralization and vertical distributions of microbial respiration reactions in sediments. Our results indicate that the history of eutrophication is well reflected in the sedimentary record. Subsurface peaks in sedimentary TOC coincide with past periods of elevated P concentrations in lake water. Sediments of eutrophic lakes show overall higher rates of microbial respiration, and a higher relative contribution of methanogenesis to total respiration. Yet, a clear impact of lake trophic state on the zonation of microbial respiration reactions is absent. Moreover, even though water column P concentrations have been reduced by ~ 80 % (range: ~ 50–90 %) since the period of peak eutrophication in the 1970s, TOC burial and accumulation rates have only decreased significantly (~ 20 and 25 %) in two of the five lakes. Hereby we found no clear relationship between the magnitude of the decrease in P concentrations and the change in TOC burial and accumulation rate. Instead, artificial lake ventilation, which is used to prevent water column anoxia in eutrophic lakes, may help sustain high rates of TOC burial and accumulation in sediments despite strongly reduced water column P concentrations. Our results provide novel insights into how eutrophication and eutrophication management practices affect organic carbon burial and the distribution of microbial respiration reactions in temperate lakes. These insights are important to understanding how anthropogenic activities affect the size of the carbon pool that is stored globally in lacustrine sediments.

Eutrophication will increase methane emissions from lakes and impoundments during the 21st century

Authors

Jake J. Beaulieu, Tonya DelSontro & John A. Downing

Lakes and impoundments are an important source of methane (CH₄), a potent greenhouse gas, to the atmosphere. A recent analysis shows aquatic productivity (i.e., eutrophication) is an important driver of CH₄emissions from lentic waters. Considering that aquatic productivity will increase over the next century due to climate change and a growing human population, a concomitant increase in aquatic CH₄ emissions may occur. We simulate the eutrophication of lentic waters under scenarios of future nutrient loading to inland waters and show that enhanced eutrophication of lakes and impoundments will substantially increase CH₄ emissions from these systems (+30–90%) over the next century. This increased CH₄ emission has an atmospheric impact of 1.7–2.6 Pg C-CO₂-eq y⁻¹, which is equivalent to 18–33% of annual CO₂emissions from burning fossil fuels. Thus, it is not only important to limit eutrophication to preserve fragile water supplies, but also to avoid acceleration of climate change.

Analysis of environmental drivers influencing interspecific variations and associations among bloom-forming cyanobacteria in large, shallow eutrophic lakes

Authors

Kun Shan, Lirong Song, Wei Chen, Lin Li, Liming Liu, Yanlong Wu, Yunlu Jia, Qichao Zhou, Liang Peng

Non-diazotrophic Microcystis and filamentous N₂-fixing Aphanizomenon and Dolichospermum (formerly Anabaena) co-occur or successively dominate freshwaters globally. Previous studies indicate that dual nitrogen (N) and phosphorus (P) reduction is needed to control cyanobacterial blooms; however, N limitation may cause replacement of non-N₂-fixing by N₂-fixing taxa. To evaluate potentially counterproductive scenarios, the effects of temperature, nutrients, and zooplankton on the spatio-temporal variations of cyanobacteria were investigated in three large, shallow eutrophic lakes in China. The results illustrate that the community composition of cyanobacteria is primarily driven by physical factors and the zooplankton community, and their interactions. Niche differentiation between Microcystis and two N₂-fixing taxa in Lake Taihu and Lake Chaohu was observed, whereas small temperature fluctuations in Lake Dianchi supported co-dominance. Through structural equation modelling, predictor variables were aggregated into ‘composites’ representing their combined effects on species-specific biomass. The model results showed that Microcystis biomass was affected by water temperature and P concentrations across the studied lakes. The biomass of two filamentous taxa, by contrast, exhibited lake-specific responses. Understanding of driving forces of the succession and competition among bloom-forming cyanobacteria will help to guide lake restoration in the context of climate warming and N:P stoichiometry imbalances.

Mitigating a global expansion of toxic cyanobacterial blooms: confounding effects and challenges posed by climate change

Authors

Hans W. Paerl, Karl. E. Havens, Nathan. S Hall, Timothy G. Otten, Mengyuan Zhu, Hai Xu, Guangwei Zhu and Boqiang Qin

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 reduce bloom occurrences. However, managers now face the additional challenge of having to address the effects of climate change on watershed hydrological and nutrient load dynamics, water temperature, mixing regime and internal nutrient cycling. Rising temperatures and increasing frequencies and magnitudes of extreme weather events, including tropical cyclones, extratropical storms, floods and droughts, all promote CyanoHABs and affect the efficacy of ecosystem remediation measures. These climatic changes will likely require setting stricter nutrient (including both nitrogen and phosphorus) reduction targets for bloom control in affected waters. In addition, the efficacy of currently used methods to reduce CyanoHABs will need to be re-evaluated in light of the synergistic effects of climate change with nutrient enrichment.

Postdoc (Fish genomics), University of Wisconsin-Stevens Point, WI, USA

The Larson Lab at UW-Stevens Point (https://larsonlab.wordpress.com/) is looking for a postdoctoral researcher to conduct genomics research on fish populations across the Great Lakes and beyond. The main focus of this position will be to develop genomic tools for whitefish in Lake Michigan to improve resolution of population structure and understand local adaptation. However, the successful applicant will have significant freedom to develop other projects, likely involving genome resequencing. Competitive applicants should have a strong background in bioinformatics and proficiency in one or more scripting languages such as Perl or Python. We will strongly consider applicants who have experience in population genetics regardless of past study organisms; previous experience in fish genetics is not required. Applicants must have a PhD. However, we are open to exceptional applicants that will be completing their PhD within the next six months. The position will be open until filled and start dates are negotiable. The salary is $50,000 per year plus benefits. Funding is available for two years with a possibility for renewal depending on job performance and funding situation. Applicants should submit a cover letter describing your previous research and research goals, a full CV, and names and contact information for three references to Wes Larson (Wes.Larson@uwsp.edu).

https://larsonlab.files.wordpress.com/2019/03/larson_postdoc_whitefish.pdf

Graduate studentship: Macquarie University, Sydney, Australia

1 PhD position in Behavioural Ecology

The Fish Lab, Department of Biological Sciences, Macquarie University, Sydney, Australia.

We are looking for a PhD student to join The Fish Lab for a 3 year project investigating the fitness consequences of laterality and personality in rainbowfish.

Start date: Semester 2 2019

Background:

We are looking for a student to be based at Macquarie University with a one year stint at Groningen as part of a Cotutelle agreement.  The project in Sydney, primarily supervised by Prof. Culum Brown, will focus on the cognitive consequences of laterality and personality. Our artificial streams and ponds lend themselves to the possibility of examining the long-term fitness consequences of behaviour under semi-natural conditions.

Macquarie has a 3 year PhD program thus the student can enrol any time from mid  2019. The student will join a large, collaborative lab (

http://www.thefishlab.com) which specialises in studying the behaviour, ecology and evolution of a range of marine and freshwater species.

MQ has strict PhD entry requirements (https://www.mq.edu.au/research/phd-and-research-degrees/how-to-apply) and the candidate must demonstrate English proficiency.

Contact: Prof. Culum Brown. Culum.Brown@mq.edu.au

Heterogeneity of Toxin-Producing Cyanobacteria and Cyanotoxins in Coastal Watersheds of Southern California

Authors

Avery O. Tatters, Meredith D. A. Howard, Carey Nagoda, A. Elizabeth Fetscher, Raphael M. Kudela, David A. Caron

Freshwater and marine harmful algal blooms are expanding on a global scale. Recent reports of toxic events have sparked a growing awareness of the importance of cyanobacteria and cyanotoxins at the land-sea interface and estuaries in general. A recent survey in the Southern California Bight documented a wealth of cyanobacteria-dominated communities at a variety of locations. To gain further insight into these assemblages, we repeatedly sampled several sites with different proximity and degrees of connectivity to the Pacific Ocean in four coastal watersheds along the coast of southern California. Our findings revealed temporal and spatial heterogeneity in the occurrence of potential toxin-producing cyanobacteria and associated toxins. Multiple toxins were measured in 45% of all samples (and 25% of shellfish examined), including samples testing positive for anatoxin-a, cylindrospermopsin, three congeners of microcystins, or the eukaryotic toxin domoic acid. The ecosystems are hydrologically connected to the Pacific Ocean and provide a source of cyanotoxins to marine and estuarine environments. Collectively, potential toxin-producing cyanobacteria were prevalent at all study sites and appeared to persist throughout the year in some locations. These findings indicate a need for implementation of coordinated monitoring programs across the land-sea interface.

The impacts of changing nutrient load and climate on a deep, eutrophic, monomictic lake

Authors

Alan D. Radbourne, J. Alex Elliott, Stephen C. Maberly, David B. Ryves, Nicholas John Anderson

1. Nutrient availability and climate have substantial effects on the structure and function of lakes. Predicted changes to climate (particularly temperature) over the 21st century are expected to adjust physical lake functions, changing thermal and nutrient use processes. Both increasing anthropogenic nutrient inputs and net reductions following remediation will also drive ecological change. Therefore, there is an increasing necessity to disentangle the effects of nutrient and temperature change on lakes to understand how they might act in additive and antagonistic ways.
2. This study quantified internal and external nutrient loads at Rostherne Mere, U.K., a deep (z_max = 30 m), monomictic eutrophic lake (average annual total phosphorus >100 μg/L) that has a long, stable period of stratification (c. 8.5 months). A lake biophysical model (PROTECH) was used to assess the effect of changes in these loads and climate change on lake productivity in a factorial modelling experiment.
3. During the summer, phosphorus released from the sediment is largely restricted to the hypolimnion and phytoplankton production is supported by the external load. On overturn, phosphorus at depth is distributed throughout the water column with the elevated concentration persisting to support algal productivity in the following spring.
4. Consequently, the model showed that internal nutrient loading was the main driver of current and future changes in the concentration of phosphorus (responsible for up to 86% P reduction), phytoplankton chlorophyll a and cyanobacterial blooms. However, although the external phosphorus load had a relatively small influence on annual mean phosphorus concentration, it had a statistically significant effect on chlorophyll a concentration, because it supported algal production during summer stratification.
5. Climate had minimal direct impact, but a substantial indirect impact by altering the timing, depth and length of lake stratification (c. 14 days longer by 2100), and therefore altered nutrient cycling and phosphorus availability.
6. In summary, the recovery trajectory at Rostherne Mere is limited by the annual internal soluble reactive phosphorus load replenishment that realistically is unlikely to change greatly on a shorter time‐scale. Therefore, the external soluble reactive phosphorus load has the potential to play an important role as it can be managed further, but is complicated by the indirect impact of climate changing stratification and flushing patterns.

PhD position MIO France: The effect of hydrodynamics in creating and redistributing diazotroph niches in the ocean (REDESIGN)

The effect of hydrodynamics in creating and redistributing diazotroph niches in the ocean (REDESIGN)

Dinitrogen (N2) fixation by diazotrophic plankton provides the greatest external source of nitrogen to the oceans. The energy and nutritional resources that limit N₂ fixation in are geographically distributed by global ocean circulation. Superimposed on this large scale, smaller flow instabilities such as submesoscale (0.1-10 km, hours/days) and mesoscale (10-100 km, weeks/months) structures mix seawater parcels altering natural resource gradients. While these structures can be depicted by satellite data, their effect on microbial community structure and their ecological interactions requires sampling in situ. Unfortunately, the usual spatiotemporal resolution of oceanographic cruises does not resolve the (sub)mesoscale. REDESIGN will use innovative high-resolution biomass and N₂ fixation and diazotroph diversity measurement devices to (i) explore how diazotroph niches are created and distributed by (sub)mesoscale structures, and (ii) quantify their effect on fixed nitrogen inputs to the ocean.

Diazotroph community structure at the (sub)mesoscale level will be investigated in oceanographic cruises in North Pacific and North Atlantic Oceans and the South China Sea.

The candidate will be based at the Mediterranean Institute of Oceanography (MIO, Marseille, France). The PhD scholarship will be covered by the Ministère de lʼEnseignement supérieur,

de la Recherche et de lʼInnovation.

 

We are looking for a highly motivated candidate with

·      A solid background in marine biogeochemistry and plankton dynamics

·      Availability to participate in oceanographic cruises

·      Matlab and/or R programming skills

·      Excellent English speaking/writing/reading skills

·      Molecular biology skills are desired but not obligatory

Interested candidates who are in hold of a Master degree in an adequate subject or envision finishing it before June 2019 may contact Mar Benavides (mar.benavides@ird.fr) with the following information:

·      Motivation letter

·      Contacts of 3 references

·      CV

·      Master’s degree qualifications (accompanied by an explanation of the country’s grading system if applicable)

Graduate studentship: Texas A&M University Corpus Christi, TX, USA

Position: MS Graduate Research Assistantship: Investigate Septic Nitrogen Pollution in Texas Coastal Bend.  

Location: Corpus Christi, Texas. 

Description:

We seek a highly motivated student to fill a MS assistantship at the Texas A&M University Corpus Christi to investigate nitrogen pollution from septic systems in Texas Coastal Bend. The successful applicant will conduct field work in several Texas Coastal Bend Bays and Estuaries. Potential septic pollutions will be identified using anthropogenic organic biomarkers and stable nitrogen isotopic ratios in dissolved inorganic nitrogen species. Nitrogen loads from septic systems will be quantified and compared with effluents from waste water treatment plants in the same region. The successful applicant will also help prepare manuscripts to disseminate results in peer-reviewed journals and conduct educational workshops with several state agencies.

The student will receive a MS in either Chemistry, Coastal and Marine System Science, Environmental Science, or Marine Biology. Marine Biology is a joint degree program with Texas A&M University Collage Station and Galveston (http://sci.tamucc.edu/LSCI/MARB/index.html).

Qualifications:

Applicants must hold a BS in Chemistry, Environmental Science, Oceanography, or a related field, have a GPA of 3.0 or greater, and competitive GRE scores.
Applicants must be highly motivated, have excellent written and oral communication skills, and be capable of working independently as well as managing a field team of several undergraduate students. The successful candidate must be willing to conduct sometimes strenuous physical activity under demanding field conditions (i.e., heat, high humidity, and insects). Experience with gas and liquid chromatography, discrete analyzer, and stable isotope biomarkers is a plus.   

To Apply:

Please email 1) cover letter describing research experience and interests, 2) CV, 3) transcripts, 4) GRE scores, and 5) contact information of three references to Dr. Lin Zhang (lin.zhang@tamucc.edu).

Salary:

Competitive stipend, plus tuition and benefits.

Start-Date:

As early as May 2019.