Lab 3: Aquatic Ecology and The Water Quality Index Flashcards
What is the Water Quality Index?
Used in quantifying and tracking the quality of water sources.
What are the nine parameters of WQI?
- Temperature
- pH
- Dissolved Oxygen
- Biochemical Oxygen Demand (BOD)
- Total Solids
- Total Phosphate
- Nitrates
- Turbidity
- Fecal Coliform
Quality Value (Q Value)
Each test parameter has a graph that represents the relationship between the measured parameter and its associated q-value. Q-values are converted and expressed on a scale from 0-100.
Each Q-value is multiplied by its weighting factor (based on its relative importance to overall water quality).
The nine weighted Q-values are then added together to arrive at an overall water quality index score. The highest score a body of water can receive is 100.
Weighting Factors
Change in Temperature= 0.11
pH= 0.11
Dissolved Oxygen (DO)= 0.17
BOD= 0.11
Total Solids= 0.07
Total Phosphate= 0.10
Nitrates= 0.10
Turbidity= 0.08
Fecal Coliform= 0.16
WQI score ranges and ratings
90-100 Excellent
70-90 Good
50-70 Medium
25-50 Poor
0-25 Very Poor
What is a lotic source?
Moving waters like a stream or river.
What is a lentic source?
Still water like a pond or lake.
What is point source pollution?
Any contaminant that enters the environment from an easily identified and confined place (Factory, sewage treatment plant)
What is nonpoint-source pollution?
Pollution resulting from many diffuse (general) sources such as runoff, precipitation (acid rain), and atmospheric deposition. Runoff can carry natural and human-made pollutants, eventually depositing them into bodies of water.
Effects of temperature on water quality
More gas can be dissolved in cold water than in warm water. Animals, such as salmon, that require a high level of dissolved oxygen will only thrive in cold water. Increased water temperature can also increase the photosynthetic rate of aquatic plants and algae leading to increased plant growth and algal blooms, which can harm the local ecosystem.
Thermal pollution caused by human activities can affect water temperature. Many industries use river water in their processes. The water is treated before it is returned to the river, but it is often warmer than it was before. Runoff entering a stream from parking lots and rooftops is often warmer than the stream and will increase its overall temperature. Shade is very important to the health of a stream because of the warming influences of direct sunlight. Some human activities may remove shaded trees from the area, which will allow more sunlight to reach the water, causing the water temperature to rise. Another factor that may affect water temperature is the temperature of the air above the water. The extent of its influence has a great deal to do with the depth of the water. A shallow stream is more susceptible to changes in air temperatures than a deep river. Water can be cooled by cold temperatures or from the introduction of colder water from a tributary or a spring. Problems generally occur when changes in water temp are seen along one stream on the same day. When you measure temperature for the water quality index, you are supposed to test the temperature of the water in one location and then test the temperature of the water in a location.a mile or two downstream from the original site.
Thermal stratification
In freshwater systems, such as lakes, the recycling of nutrients occurs in response to air temperature and wind changes, The nutrients at the bottom of lakes are recycled twice each year: in the spring and fall turnover, The spring and fall turnover are seasonal processes that recycle nutrients and oxygen from the bottom of a freshwater lake to the top of the lake.
During the summer months, thermal layering occurs in Lake George. The warm June sun heats the top layer of water to high temperatures. Diving into the deeper parts of the Lake during the summer can be a chilling reminder that the warm summer rays of the sun fail to reach the bottom. The cold, dense water remains separated from the warm upper layer by a thermocline: layers of water with temperatures that are significantly different from those above and below it. This thermocline is where temperatures change rapidly between the warm surface water and the colder deep water.
The thermal layers change as the cool winds of fall send a chill through the top water layer. The wind cools the water and the colder molecules sink. As the water sinks, it pushes the bottom water towards the surface and mixes the water into the lake. This process is the fall turnover. The bottom layer brings accumulated nutrients and oxygen upward as the cool upper water displaces it. Nutrients, minerals, and oxygen become mixed along the entire water column during this turnover. As fall gradually progresses into winter, the lake water remains at a fairly consistent temperature from top to bottom. The temperature range is very small, but important. The less dense water freezes on the surface, 0 degrees, forming ice. The water becomes warmer nearer the lake bottom. In a deep lake, the bottom water temperature is 4 degrees, the densest water. Ice and snow cover the lake during the winter forming an insulating blanket. In areas that don’t experience much temperature change through different seasons, lakes mix year round, or several times a year with varying weather conditions. Without this mixing, a lake can become stagnant, causing water quality to decline.
What is pH?
The measure of the relative concentrations of OH- and H+ ions in a solution.
Why is pH important to water quality?
Because of the sensitivity of aquatic organisms to the pH of their environment. If the pH of the waters in which they live is outside that range, they may not survive or reproduce.
What can cause changes in the pH of water?
Algal blooms (more basic), industrial processes resulting in a release of bases or acids (raising or lowering pH), or the oxidation of sulfide-containing sediments (more acidic). Rainfall can be slightly acidic.
pH ranges and the associated effects to the biotic community
3.0-3.5= Unlikely that fish can survive for more than a few hours in this range, although some plants and invertebrates can be found at pH levels this low.
3.5-4.0= Known to be lethal to salmonids.
4.0-4.5= All fish, most frogs, insects absent.
4.5-5.0= Mayfly and many other insects absent. Most fish eggs will not hatch.
5.0-5.5= Bottom-dwelling bacteria (decomposers) begin to die. Leaf litter and detritus begin to accumulate, locking up essential nutrients and interrupting chemical cycling. Plankton begin to disappear. Snails and clams absent. Mats of fungi begin to replace bacteria in the substrate. Metals (aluminum, lead) normally trapped in sediments are released into the acidified water in forms toxic to aquatic life.
6.0-6.5= Freshwater shrimp absent. Unlikely to be directly harmful to fish unless free carbon dioxide is high.
6.5-8.2= Optimal for most organisms
8-2-9.0= Unlikely to be directly harmful to fish, but indirect effects occur at this level due to chemical changes in the water.
9.0-10.5= Likely to be harmful to salmonids and perch if present for long periods.
10.5-11.0= Rapidly lethal to salmonids. Prolonged exposure is lethal to carp. perch.
11.0-11.5= Rapidly lethal to all species of fish.
