Topics








Preliminary Orientation to Lake Health

What follows is just a start at blocking out the basic information about lake health so that those concerned with the health of Prospect Lake can begin to orient themselves to the issues and challenges we face. It is by no means complete. We will continue to add to these pages.



Lake Structure





1. Littoral Zone - Shallows

2. Limnetic Zone - Open Lake

- Epilimnion - Warm surface layer

- Metalimnion - temperature changes with depth

- Hypolimnion - cold dark waters.  





Eutrophication

“Eutrophication, the gradual increase in the concentration of phosphorus, nitrogen, and other plant nutrients in an aging aquatic ecosystem such as a lake. The productivity or fertility of such an ecosystem naturally increases as the amount of organic material that can be broken down into nutrients increases. This material enters the ecosystem primarily by runoff from land that carries debris and products of the reproduction and death of terrestrial organisms. Water blooms, or great concentrations of algae and microscopic organisms, often develop on the surface, preventing the light penetration and oxygen absorption necessary for underwater life. Eutrophic waters are often murky and may support fewer large animals, such as fish and birds, than non-eutrophic waters.


Cultural eutrophication occurs when human water pollution speeds up the aging process by introducing sewage, detergents, fertilizers, and other nutrient sources into the ecosystem. Cultural eutrophication has had dramatic consequences on freshwater resources, fisheries, and recreational bodies of water and is one of the leading causes of aquatic ecosystem degradation.


Commonly, culturally eutrophic aquatic systems may exhibit extremely low oxygen concentrations in bottom waters, a condition known as hypoxia. This is particularly true of stratified systems such as, for instance, lakes during summer when concentrations of molecular oxygen may reach levels of less than about one milligram per litre—a threshold for various biological and chemical processes. Low oxygen levels can be further exacerbated by water blooms that often accompany nutrient loading of waters and may poison wildlife.


Much of the phosphorus in streams and lakes is delivered from agriculture, both through soil erosion and fertilizer runoff. Nitrogen from municipal sewage treatment plants and the direct runoff from animal feedlots are serious problems in many places. Pollution control and improved municipal, industrial, and agricultural practices could do much to curb the cultural eutrophication of inland and coastal waters.”

(Source: https://www.britannica.com/science/eutrophication)


Phosphorus, Nitrogen, and Dissolved Oxygen

Phosphorus (P), Nitrogen (N), and Dissolved Oxygen (DO) are the three primary variables that need to be considered for lake health. If you read the label on a bag of fertilizer you will note that P and N are the primary ingredients associated with plant growth. Aquatic plants including algae are no different.  In addition to being present in the water column P and N collect in the sediment at the bottom of the lake. 

In  lake health measures P is often referred to as Total Phosphorus  (TP). 

P in the water column feeds the algae while P in the sediment feeds the aquatic plants which, like terrestrial plants draw nutrients from the soil/sediment through their roots.


Dissolved Oxygen and Water

What is Dissolved Oxygen and How Does It Affect Aquatic Life?

Dissolved oxygen is the oxygen gas that is dissolved in water, typically in the form of O2 molecules. Aquatic organisms, such as fish, invertebrates, and plants, rely on this dissolved oxygen to carry out their life-sustaining metabolic processes, primarily respiration. Insufficient levels of dissolved oxygen can lead to a condition known as hypoxia, where oxygen deprivation occurs, leading to stress or death of aquatic life.

 (https://www.environmental-expert.com/articles/what-is-dissolved-oxygen-and-how-to-measure-1117414)


Importance of Dissolved Oxygen in Water Quality

Dissolved oxygen serves as a critical indicator of the overall health and quality of water bodies. It reflects the balance between oxygen consumption and replenishment through processes like photosynthesis and atmospheric diffusion. Here are some key points highlighting the importance of dissolved oxygen in water quality assessment:


  • Indicator of Ecosystem Health: High dissolved oxygen levels indicate a well-oxygenated environment, supporting diverse aquatic life. Conversely, low levels can signify pollution or excessive organic matter decomposition, threatening the ecosystem.
  • Effect on Fish Health: Fish and other aquatic organisms require adequate dissolved oxygen levels for their survival and growth. Low oxygen levels can lead to fish kills and disrupt the food chain.
  • Monitoring Pollution: Monitoring dissolved oxygen helps identify sources of pollution, such as nutrient runoff or wastewater discharges, which can deplete oxygen levels.
  • Wastewater Treatment: In wastewater treatment plants, dissolved oxygen is crucial for the growth of beneficial bacteria that help in breaking down organic matter.


Factors Affecting Dissolved Oxygen Levels

Several natural and human-induced factors influence dissolved oxygen levels in water bodies. Understanding these factors is vital for effective water quality management. Some of the key factors include:

  • Temperature: Warmer water holds less dissolved oxygen than colder water. Seasonal changes can significantly affect oxygen concentrations.
  • Photosynthesis: During daylight hours, plants and algae undergo photosynthesis, releasing oxygen into the water. At night, the opposite occurs, leading to fluctuations in oxygen levels.
  • Water Turbulence: Increased water turbulence, such as from waterfalls or strong currents, enhances oxygen exchange with the atmosphere, raising dissolved oxygen levels.
  • Pollution: Human activities like industrial discharge, agricultural runoff, and sewage can introduce pollutants that consume dissolved oxygen during decomposition.


Phosphorus Internal vs External Loading

Phosphorus is contained within the sediments in the lake. This is an Internal source of phosphorus. The External source of phosphorus is from the water running from the land into the lake including storm water, fertilizers, and septic system runoff.  Understanding the internal and external volumes of phosphorus allow us to determine what will be the most successful approaches to manage algal growth and in particular cyanobacterial growth in the lake. 

It should be clear that we will want to optimize our spending and efforts in addressing phosphorus and this requires we understand both the internal and external phosphorus load. If we develop a program to manage / reduce the internal load of phosphorus but the external load exceeds what we are reducing from the internal load our efforts are likely to fail.  This is why there is concern that individuals and organizations living and working within the areas that have runoff into Prospect Lake ensure minimal release of nutrient contaminated water.


Algae Blooms

Harmful algal blooms (HABs) are can be caused by many different types of algae in freshwater ecosystems, and can be triggered by nutrient enrichment. The most frequent and severe blooms typically are caused by cyanobacteria, the only known freshwater algae with the potential for production of toxins potent enough to harm human health. CyanoHABs can threaten human and aquatic ecosystem health.  Economic damages related to cyanoHABs include the loss of recreational revenue, decreased property values, and increased drinking-water treatment costs. 

Algal growth is usually limited by the available supply of either phosphate or nitrate, and we say that a water body is nitrogen limited if the ratio of nitrogen species to phosphorus species (N:P) is low, or is phosphorus limited if N:P is high.

 (Source: https://www.usgs.gov/mission-areas/water-resources/science/nutrients-and-eutrophication)


Seagulls

Seagulls Eat Garbage in Landfills and Then Poop Pollution Into Our Waters

What goes around comes around. Scientists say chemicals from trash in our landfills are making their way into our waters via the seagulls’ gastrointestinal tracts. A report on this delightful state of affairs was published in the journal Water Research.

We generally stop thinking about our trash the moment the garbage truck comes to collect it. But it doesn’t just disappear. No, our coffee filters and corn-chip bags head to the landfill, where they sit and sit and sit … unless they get eaten first. Then their nutrients, their nitrogen and phosphorus, disappear into an animal’s gullet and reappear on the other side, sometimes a few days later, sometimes miles away—and sometimes in our lakes, rivers, and streams.

Researchers wondered how much of an impact these trash-picking critters could have. They were especially interested in seagulls, whose poop has previously been shown to carry traces of toxic chemicals from our plastic-filled seas.

The first step was to figure out just how many landfill-mooching seagulls we have. Authors Scott Winton and Mark River of the Duke University Wetland Center used documented seagull sightings in the eBird citizen science database to estimate the number of landfill-living gulls across the entire United States. Their calculations came up with about 1.4 million birds.

"But the actual population is probably greater than 5 million,” Winton said in a statement. “That means the amount of nutrients deposited in the lakes, and the costs of preventing or remediating the problem, could be substantially higher."

The scientists then used that 1.4-million figure to calculate the amount of nitrogen and phosphorus the birds might collectively be dumping.

"The idea that gull feces can be a major water quality problem may sound comical—until you look at data from an individual lake," Winton said, noting the impact on North Carolina's Jordan Lake, home to a 14,000-acre state recreation area and more than 1000 campsites. "In Jordan Lake, for instance, we found that a local flock of 49,000 ring-billed gulls deposit landfill feces containing nearly 1.2 tons of phosphorus into the lake annually."

That phosphorus changes the water's chemical composition and could lead to more algae blooms, which can kill off other organisms in the lake’s ecosystem.

Winton and River suggest that rather than clean our waters after they're polluted, a better approach might be to stop the problem at the source: our trash. They recommend limiting landfill size and covering existing garbage heaps to keep the seagulls from ever finding it.

(Source:  https://www.mentalfloss.com/article/502282/seagulls-eat-garbage-landfills-and-then-poop-pollution-our-waters) 


Winton and River conclude that mega-flocks of landfill gulls are common and widespread, and that their capacity to transport nutrients may be contributing to the eutrophication of aquatic ecosystems and water supplies.

Source:  Winton RS, River M. The biogeochemical implications of massive gull flocks at landfills. Water Res. 2017 Oct 1;122:440-446. doi: 10.1016/j.watres.2017.05.076. Epub 2017 Jun 8. PMID: 28624727.


Other papers

Franklin AB, Ramey AM, Bentler KT, Barrett NL, McCurdy LM, Ahlstrom CA, Bonnedahl J, Shriner SA, Chandler JC. Gulls as Sources of Environmental Contamination by Colistin-resistant Bacteria. Sci Rep. 2020 Mar 10;10(1):4408. doi: 10.1038/s41598-020-61318-2. PMID: 32157139; PMCID: PMC7064522.