 Salinity: Salinity is the concentration of dissolved salts in the water and is an important element of a  habitat. Aquatic animals are adapted to living in a certain salinity range. Salinity is measured as a ratio  of salts to water and is expressed using the unit parts per thousand (ppt) which means the number of  parts of salts per thousand parts of water. There are 3 categories of salinity: 0 – 0.5 ppt = fresh water,  0.5 – 30 ppt = brackish water (partly salty), and >30 ppt = salt water. Salinity is affected by weather.  Dry seasons and evaporation cause the water, especially at the surface, to become saltier. Rains dilute  the salts creating fresher water. Saltier water also has less room for DO

 Dissolved Oxygen (DO): DO, the amount of oxygen dissolved in the water is expressed as a percentage  of parts per million (ppm). DO in the water comes from photosynthesis of algae and submerged plant.  DO also mixes in from the air with wind, waves, rain, and currents. The colder and fresher the water,  the more DO it will contain. Most animals need around 5ppm DO to survive. If the DO in the water  falls below 2 ppm the water is determined anoxic and does not sustain life well.

 Nitrates: Nitrates (NO3) are formed when bacteria combine the ammonia from animal waste or decay  with oxygen. Some nitrogen is needed in the water for plants. However, too much nitrogen can cause  algal blooms and eutrophication. Excess nutrients can come from waste water treatment plants, fertilizer  run-off, pet and livestock wastes. Nitrates are measured as a ratio in units of parts per million (ppm).

 Turbidity Turbidity is a measure of the amount of fine particles suspended in the water. As turbidity rises, light penetration, a key factor for aquatic plants and algae, diminishes. Particles can be the sites of intense microbial activity and can play a role in the transport of contaminants. In addition, areas of heavy runoff and erosion often have high particle concentration. In general, turbidity in the Hudson River increases in the lower estuary, reaches a maximum around upper Manhattan, and then falls as one goes further south.

 Phosphorus is usually present in natural water as phosphates  Phosphorus is a plant nutrient needed for growth and a fundamental element in the metabolic reactions of plants and animals (hence its use in fertilizers). Sources of phosphorus include human and animal wastes (i.e., sewage), industrial wastes, soil erosion, and fertilizers. Excess phosphorus causes extensive algal growth called "blooms," which are a classic symptom of cultural eutrophication and lead to decreased oxygen levels in creek water.

 pH: The percentage of hydrogen ions in a solution is called pH. The more hydrogen ions in a solution,  the more acidic the solution is. The pH scale is from 0, highly acidic to 14, highly basic. A pH of 7 is  neutral such as distilled water. Acidic solutions include lemon juice, vinegar, and soft drinks. Examples  of Basic chemicals are ammonia, baking soda, and Tums. Most plants and animals are adapted to  neutral or near neutral pHs (7.0 – 8.5)

 Salinity: Salinity is the concentration of dissolved salts in the water and is an important element of a  habitat. Aquatic animals are adapted to living in a certain salinity range. Salinity is measured as a ratio  of salts to water and is expressed using the unit parts per thousand (ppt) which means the number of  parts of salts per thousand parts of water. There are 3 categories of salinity: 0 – 0.5 ppt = fresh water,  0.5 – 30 ppt = brackish water (partly salty), and >30 ppt = salt water. Salinity is affected by weather.  Dry seasons and evaporation cause the water, especially at the surface, to become saltier. Rains dilute  the salts creating fresher water. Saltier water also has less room for DO

 Fecal Coliform Enterococcus is a bacteria used to determine sewage contamination  Enterococcus counts are useful as a water quality indicator due to their abundance in human sewage, correlation with many human pathogens and low abundance in sewage free environments.  The United State Environmental Protection Agency (EPA) reports Enterococcus counts as colonies (or cells) per 100 ml of water.

 Biochemical oxygen demand (BOD)- oxidation of an organic compound is carried out by microorganisms using the organic matter as a food source  BOD is measured by finding the change in dissolved oxygen concentration before and after bacteria is added to consume organic matter 