Topic 2.1:

https://youtu.be/JRKwxc3iQFY?list=PL9F61F8A6355EB3C5

Topic 2.2:

Marine ecosystems:

Salinity:

Any marine organisms tolerate a variety of salt concentration levels in the water, which can be checked with a few tools:

• Hydrometer - Measures specific gravity or density of a sample (relative weight of 1.0L salt water compared to 1.0L pure fresh water)
• Refractometer - Measures differences in light refraction between the saltwater sample and a freshwater control electrical conductivity can also indicate the amount of dissolved ions in solution
• pH - Use a pH meter. The pH of saltwater is naturally higher (i.e. more alkaline) than that of fresh water. According to several marine aquarium websites, a pH of 8.2 is ideal for saltwater fish.
• Temperature - Every organism has an optimal temperature range in which it thrives. An organism may be able to survive at warmer or cooler temperatures, but it will do so under stress, which requires more energy (and therefore food), and decreases its' ability to compete for other resources within the ecosystem. This is particularly important for ectothermic (cold-blooded) organisms, which are a majority of marine animals. A change in temperature can also influence the pH of water.
• Dissolved Oxygen (DO) - The amount of oxygen available for marine organisms, like terrestrial organisms, determines which organisms can survive in a particular location. DO levels fall with increased temperature and organic compounds from either sewage, agriculture, or industry. DO can range from 0-18 ppm, but most healthy ecosystems have a DO level of 5-6 ppm. Measuring DO can be tricky and labor-intensive, requiring either a complicated Winkler titration or oxygen-selective electrodes.
• Wave action - waves carry energy; thus, larger and prolonged waves can move larger particles, thereby 'mixing' water, oxygen, and sediment more. Areas with a lot of wave action tend to have higher DO levels. Waves can also increase the turbidity of the water and determine the nature of a coast line - i.e. sandy vs rocky.

Freshwater Ecosystems:

• Turbidity - "A cloudy condition in water due to suspended silt or organic matter." Cloudy = high turbidity and clear = low turbidity. "Turbidity in lakes, reservoirs, channels, and the ocean can be measured using a Secchi disk. This black and white disk is lowered into the water until it can no longer be seen; the depth (Secchi depth) is then recorded as a measure of the transparency of the water (inversely related to turbidity). The Secchi disk has the advantages of integrating turbidity over depth (where variable turbidity layers are present), being quick and easy to use, and inexpensive." Flow Velocity - the rate at which water moves through a specified area in a given amount of time. Some aquatic organisms prefer high flow velocity (fast water) while others thrive at lower flow velocities. The simplest way is to time how long a partially-submerged object takes to travel a certain distance. For an explanation of how to more precisely measure stream flow.
• pH - normal readings for freshwater ecosystems range from about 6.5 (acidic) to 8.5 (basic) depending on the underlying rock substrata, surrounding vegetation, and human activities within the watershed
• Temperature - see notes above
• Dissolved Oxygen - see notes above

Terrestrial ecosystems

• Temperature - depends on insolation (incoming sunlight), wind & ventilation, latitude, color and texture of the surface. Measure temperature with liquid thermometers or datalogging
• Light Intensity - influences photosynthesis rates as well as body temperature of ectotherms (cold-blooded animals). Light intensity is highly variable with weather conditions, season, time of day, and surrounding terrain & vegetation cover. It can be measured with light meters available from photography stores or the IST science department.