Assessing Lake Health and Addressing Lake Pollution

     A new paper in Earth’s Future assesses the environmental health of lake ecosystems. The study compares and makes analogies of lake health to human health. The researchers introduced a global classification system modeled after the World Health Organization's human health classification system. The team used data from LakeATLAS for nearly 1.5 million lakes worldwide. According to Phys.org:

The team considered “maladies of the circulatory (such as flooding and drying out), metabolic (such as acidification and salinization), nutritional, and respiratory varieties—along with other types of disturbances. Researchers categorized lake health from excellent to critical. Around 115,000 lakes evaporate twice as much water as they receive, putting more than 153 million people who live near these lakes at risk.”

 

     The LakeATLAS dataset was introduced in 2022 and “forms part of the larger HydroATLAS data repository and expands the existing datasets of sub-basin and river reach descriptors by adding equivalent information for lakes and reservoirs in a compatible structure.”

The team concluded that the biggest broad threats are sewage, climate change, and damage caused by humans and non-native species. The map below shows the 7000 largest lakes and as can be seen, the vast majority are in the Northern Hemisphere.

 

      The researchers premise that the healthiest lakes produce the most ecosystem services. The health needs of lakes include adequate oxygen, clean water, and a balanced energy and nutrient supply. Lakes face stress from human activity. The health analogies consider thermal, circulatory, respiratory, nutritional and metabolic issues to infections and poisoning. As mentioned, lake drying, analogized as a circulatory malady, is one of the big dangers to lake health. Losing water means losing some of those ecosystem services. The team notes that the biggest risks of critical conditions occur in densely populated low-income countries. They note the challenges of assessing lake health. They note that in 1998 the U.S. EPA “described a healthy lake as a lake with clean water, balanced algal growth, adequate oxygen levels and abundance and diversity of fish, bottom-dwelling invertebrates and native plants.” This is a qualitative description. Quantitative analysis is more difficult.

     The first of the two figures below shows threats to human well-being as a result of degraded lake health. The second figure shows the health assessment range and criteria.

 

As will be noted, oxygen saturation, nutrient concentration, temperature, pH, and water clarity are key indicators of lake health.

 

 

NSERC Canadian Lake Pulse Network

 

     A Canadian study that sampled over 100 variables at 680 lakes in the country was published in 2019. This seems to be an important precursor study to the current study. The abstract describes the scope of the project and the development of the NSERC Canadian Lake Pulse Network:

 

“To provide Canada's first national assessment of lake health, the NSERC Canadian Lake Pulse Network was launched in 2016 as an academic-government research partnership. LakePulse uses traditional approaches for limnological monitoring as well as state-of-the-art methods in the fields of genomics, emerging contaminants, greenhouse gases, invasive pathogens, paleolimnology, spatial modelling, statistical analysis, and remote sensing. A coordinated sampling program of about 680 lakes together with historical archives and a geomatics analysis of over 80,000 lake watersheds are used to examine the extent to which lakes are being altered now and in the future, and how this impacts aquatic ecosystem services of societal importance. Herein we review the network context, objectives and methods.”

 

The main three stressors to lake health are land-use change, climatic change, and contaminants. The figure below gives the scope of the project and how these stressors will be evaluated.

 

 

     10% of Canada’s surface is covered by lakes. “Canada has about 20% of the world's freshwater stocks, many lakes, aquifers and glaciers are replenished very slowly, meaning that Canada has only about 7% of the world's renewable freshwater. This still ranks Canada fourth among all countries in terms of total renewable freshwater resources” In order to assess human impacts they developed a generalized human impact index. Canada is most populated in its southern, southwestern, and southeastern regions. Below are some figures from the paper showing the sample locations, Canadian ecozones, and the human impact index.

 

     The main theme of LakePulse is to determine how and why Canadian lakes have changed as a result of humans. The framework is divided into ten projects. Project 1 is to define the ‘pre-industrial’ state in order to get a baseline for a number of variables from which to measure the changes. Project 2 is making it easier to assess and study lake health through sedimentary DNA analysis. This approach uses paleolimnology to assess past lake events of the lake such as eutrophication, acidification, climate changes, and lake ontogeny including unraveling the lives of past organisms. Bottom sediment cores often contain pollen and spores which provide a pollen record. Pollen records can be a proxy for lake temperatures. Pollen records are read much like tree rings are read to unravel year-by-year climate changes. The goal is to unravel lake history. The main three stressors to lake health are land-use change, climatic change, and contaminants. Below from Wikipedia is a lake temperature history for a Canadian Lake reconstructed from pollen records.

 

Project 3 involves understanding characterizing the biogeochemistry of lakes through modeling carbon and nutrient cycles with emphasis on carbon sink, fluxes, and nutrient regeneration. Lake emit CO2 and methane in very significant quantities. They both emit and receive nitrous oxide and form an important part of the global N2O cycle. Carbon and nutrients can also be analyzed from sediments and sediment cores to understand past changes in these cycles. The researchers estimate that “the current “natural” GHG emissions {from Canada’s inland waters} are similar in magnitude to Canada's current anthropogenic GHG footprint of about 700 Mtons CO2eq yr−1.”

Project 3 also involves understanding and characterizing the nutrient fluxes in the lake ecosystem. Nutrient loading, or eutrophication, from natural or human activities reduces oxygen availability in the lake and often causes ‘blooms’ of microorganisms, or algae blooms, some of which are harmful to wildlife and humans. Agriculture is very often the major source of nutrients and the cause of the loading. Lakes also load nutrients from bottom sediments in a process known as internal nutrient loading. A better understanding of a lake’s internal nutrient loading can lead to a better understanding of its response to external anthropogenic nutrient loading.

     Project 4 is concerned with chemical contaminants entering lakes. The fate of these contaminants in lakes, how they break down, whether they stay in the water or get stored in sediment, and how they affect lake health are questions to be answered. Human pharmaceuticals and pesticides and their breakdown products during biotic and abiotic processes are of interest.  

     Theme 2 and Projects 5 and 6 address changes in planktonic and microbial communities. Project 5 addresses lake planktonic communities. Diatoms and cyanobacteria are often acknowledged as important indicators of lake health, but other plankton communities may be as well. One goal is to better understand how nitrogen and phosphorus drive cyanobacteria blooms in lakes. Project 6 considers the presence and effects of pathological organisms such as influenza virus, coliforms, and antimicrobial resistance. Fecal bacteria from sewage treatment plants, animal production operations, manure runoff, and manure slurry tanks is of most concern. Pathogenic E. coli, campylobacteria, and salmonella are specific microbes of concern. Keeping these contaminants out of drinking water or recreational water is a major goal.

     Theme 3 involves optical, morphometric, and watershed properties that can be assessed through remote sensing and spatial modeling. Project 7 involves remote sensing approaches and Project 8 involves geospatial modeling approaches. Remote sensing involves generating satellite data from sensors to remotely measure lake conditions such as water reflectance. This field is evolving fast with newer and better satellites, sensors, and algorithms to aid data interpretation. Spatial modeling integrates remote sensing data with geospatial analysis.

     Theme 4 concerns modeling lake ecosystem response to different environmental change scenarios. Project 9 models land use change and climate change in different scenarios. Contemporary analogs are utilized in this modeling. Project 10 assesses the impact of human activities on the delivery of aquatic ecosystem services.

     The Canadian Lake Pulse Network is an important framework and should be of great importance to the study of limnology.

 

 

More on the Lake Health/Human Health Analogy in the Earth’s Future Paper

 

     Getting back to the Earth’s Future paper on lake health, there are circulatory and thermal issues. Of much importance is heat accumulation, including prolonged and intensified thermal stratification. Heat distribution in the water column is important for lake health. Excess heat can result in loss of habitat, deoxygenation, growth of algae blooms, and growth of microorganisms, invasive species and toxin-producing cyanobacteria. Heat waves have been commonly associated with prolonged and intensified thermal stratification. This prolonged stratification can lead to harmful algal blooms and fish kills.

     Another way climate changes affects lakes is through the loss of ice cover. The authors note that the majority of lakes on Earth are still periodically covered by ice. There are impacts on humans in cold regions such as loss of ice roads and increased drownings. Loss of ice loss can also have some tentatively positive effects such as increasing lake productivity.

     Drying up of lakes is an issue that can have many negative impacts. However, that process is often natural, with geology sometimes leading to lakes being formed in arid areas that have inadequate recharge. Unfortunately, many of those drying lakes are in densely populated low-income countries. Understanding a lake’s water balance, mainly additions from precipitation and subtractions from evaporation is key to determining water loss and the rate of water loss.

     Flooding is another lake concern. It is most common in the tropics where there are strong tropical storms. Floods may be climate-driven but they can also be attributed to human activity as in the case of dam failures. Extreme flooding events can increase contaminant loads, macropollutants, and pathogenic microorganisms, especially when agricultural land is flooded. Overflows from sewers and industrial wastewater are of most concern.

     Nutritional issues include nutrient loading/eutrophication and the resulting problems mentioned above, such as algal blooms, and others such as increased methane output from those algal blooms, and importantly the death of many organisms from those algal blooms that produce deadly toxins.

     Respiratory issues include deoxygenation and low dissolved oxygen. Less dissolved oxygen in deeper waters affects benthic, or bottom-dwelling organisms. Fish kills are a common result.

 

"Fish kills are commonly related to the decay of massive algal blooms in highly eutrophic waters with low flushing rates (Zhou et al., 2015) and subsequent oxygen depletion (Rao et al., 2014). They have also been linked to cyanobacterial toxins (Carmichael & Boyer, 2016), infections (Scott & Bollinger, 2014), acidification episodes (Rosseland, 1986), exceptionally high organic carbon inputs related to browning (Brothers et al., 2014), high rainfall events (Kragh et al., 2020), pollutants, loss of habitat connectivity (Mendoza et al., 2022) or a combination of factors often related to heat waves.”

 

     Metabolic issues include acidification, salinization, and browning of lakes. These occur when pH/acidity, salinity and color/dissolved organic matter are outside of reference conditions. Acidification is caused by mining and industrial activities and acid-rain components like sulfur dioxide and nitrogen compounds. It can lead to fish kills. Acidification can be chronic or episodic.

Salinization is common in lakes that are drying out since when there is less water the concentration of salts and total dissolved and suspended solids increase. Agricultural activities and coastal saltwater encroachment can increase lake salinization. Increased inputs of human-derived dissolved organic matter and iron are the major causes of lake browning. Brown lakes often have higher growth and reproduction rates of microorganisms, including pathogenic ones, and emit higher levels of methane. Browning has a negative effect on drinking water. However, reference rates are not well-defined in lake browning, which mainly affects lakes in temperate or boreal areas.

     Lake ‘infections’ occur as a result of increased pathogenic microorganisms. These can be caused by sewage wastewater, waterfowl fecal matter, manure, or livestock runoff. I know of a small lake in Ohio that is surrounded by hilly areas with many homes built on the slopes with inadequate household septic systems, some directly discharging untreated or minimally treated wastewater, where the smell of sewage is common due to surface wastewater, and there is little doubt that this wastewater is ending up in the lake. Unfortunately, it is a problem that is not likely to get better any time soon.

     ‘Poisoning’ through accumulation of hazardous substances. Toxic substances like mercury and other heavy metals can enter the food chain. Sources include falling particles from combustion and industrial chemicals and also may include pharmaceutical residues, endocrine disrupters, personal care products, industrial chemicals, pesticides, and PFAS. Microplastics and other nano-pollution are also of concern. Macropollutants such as macroplastics and litter are a minor source of poisons. Overexploitation, including overfishing and excessive water removal for domestic, industrial, and agricultural use can also cause increased contamination. Another problem is hydrological modifications which may include dams, weirs, sluices, locks, channelization, decoupling of floodplains from active river channels, shoreline destruction, and many more human alterations. Hydropower plants are a major example of hydrological modification. They can lead to big increases in methane output, kill and disrupt fish and other aquatic species, and flood important habitats and cultural sites.

     Invasive species are of major concern regarding lake health. Like many land-based non-native species, many aquatic non-native species wreak havoc on local ecosystems. Invasive species like red swamp crayfish and zebra mussels can affect lake health and some can even possibly remove competitors to cyanobacteria, making harmful algae blooms more likely. I can still remember the horrible taste of the tapwater from Buffalo, New York which came from Lake Erie about 33 years ago when I lived there. The issue was caused by the proliferation of invasive zebra mussels that were carried into the lake, as are many invasive species, by ship ballast water.  

     As far as treatment strategies the authors return to the human health analogy and recommend:

 

“(a) intervention and preventative actions before health problems occur by, for example, nature conservation efforts, (b) regular screening and early identification of lake health issues and (c) remediation and mitigation efforts at an appropriate scale, spanning from local to global.”

 

These are summarized in the figure below. Preventative actions, interventions, early identification, and regular screening are emphasized as important treatment strategies.

 

 

     Remediation and mitigation efforts in the past included the development of wastewater and sewage treatment plants to reduce the amount of raw untreated pollutants entering water bodies. This resulted in “curing” many lakes of problems caused by that wastewater and the nutrients within it. This will need to continue and expand, especially in areas where sewage and industrial wastewater treatment remains inadequate. Stormwater and sewage treatment infrastructure investments have the potential to slow lake pollution where applicable. Decreasing agricultural runoff is another important strategy. The authors note some issues with treatment:

 

“The list of treatment options for lake health issues is long, ranging from nature-based solutions, physical, chemical and biological treatments to legislation. It is often a combination of treatments which is needed to cure lakes from health problems. Whenever treatments are chosen, there is an urgent need to move to watershed-oriented treatment strategies as practiced by, for example, the European Union. Such strategies can imply big challenges, in particular when watersheds cross jurisdictional or national boundaries. It is important to tackle these challenges, because globally only relatively few nations presently have laws that acknowledge the role of watershed hydrology and riparian buffers in the movement of pollutants from anthropogenic hotspots across watersheds into the adjacent water bodies (Owokotomo et al., 2020). Once treatments have been chosen and started, the progress of the treatments needs to be followed-up, a step which is commonly not yet done.”

 

They emphasize that many lake health issues are becoming chronic and can only be solved with adequate treatment and removing the sources of the contamination.

 

 

 

 

References:

Lakes worldwide are facing a slew of health issues that may become chronic. Sarah Derouin. Phys.org. April 23, 2024. Lakes worldwide are facing a slew of health issues that may become chronic (msn.com)

Global Lake Health in the Anthropocene: Societal Implications and Treatment Strategies. Gesa A. Weyhenmeyer, Azubuike V. Chukwuka, Orlane Anneville, Justin Brookes, Carolinne R. Carvalho, James B. Cotner, Hans-Peter Grossart, David P. Hamilton, Paul C. Hanson, Josef Hejzlar, Sabine Hilt, Matthew R. Hipsey, Bas W. Ibelings, Stéphan Jacquet, Külli Kangur, Theis Kragh, Bernhard Lehner, Fabio Lepori, Ben Lukubye, Rafael Marce, Yvonne McElarney, Ma. Cristina Paule-Mercado, Rebecca North, Keilor Rojas-Jimenez, James A. Rusak, Sapna Sharma, Facundo Scordo, Lisette N. de Senerpont Domis, Jonas Stage Sø, Susanna (Susie) A. Wood, Marguerite A. Xenopoulos, Yongqiang Zhou. Earth’s Future. April 17. 2024. Global Lake Health in the Anthropocene: Societal Implications and Treatment Strategies - Weyhenmeyer - 2024 - Earth's Future - Wiley Online Library

The NSERC Canadian Lake Pulse Network: A national assessment of lake health providing science for water management in a changing climate. Yannick Huot, Catherine A. Brown, Geneviève Potvin, Dermot Antoniades, Helen M. Baulch, Beatrix E. Beisner, Simon Bélange, Stéphanie Brazeau, Hubert Cabana, Jeffrey A. Cardille, Paul A. del Giorgio, Irene Gregory-Eaves, Marie-Josée Fortin. Andrew S. Lang, Isabelle Laurion, Roxane Maranger, Yves T. Prairie, James A. Rusak, Pedro A. Segura, Robert Siron, and David A. Walsh. Science of The Total Environment. Volume 695. December 10, 2019. The NSERC Canadian Lake Pulse Network: A national assessment of lake health providing science for water management in a changing climate - ScienceDirect

Paleolimnology. Wikipedia. Paleolimnology - Wikipedia

Eutrophication. Wikipedia. Eutrophication - Wikipedia

Global hydro-environmental lake characteristics at high spatial resolution. Bernhard Lehner, Mathis L. Messager, Maartje C. Korver & Simon Linke. Scientific Data volume 9, Article number: 351 (2022). Global hydro-environmental lake characteristics at high spatial resolution | Scientific Data (nature.com)