parameter - A characteristic, or descriptive feature, such as odor, color, or temperature.
parasite - An organism that lives in or on another organism, causing it harm.
pathogen - A disease-producing agent, usually applied to a living organism. Generally, any virus, bacterium, or fungus that causes disease.
penetrate - To enter or force a way into; to spread or flow throughout an area.
periwinkle - Trailing evergreen plants of the genus Vinca. image
permeability - The ability of a material to allow a liquid to pass through it. Permeable materials, such as gravel and sand, allow water to move quickly through them.
pesticide - A chemical used to kill pests, especially insects and rodents.
pH - A scale from 0 to 14 used to measure relative acidity or alkalinity. A pH measurement less than 7 is acidic, 7 is neutral, and greater than 7 is basic or alkaline. image
phosphate - A form of phosphorous; an essential nutrient for plants and animals; usually present in natural waters as phosphate. Phosphate is an ion composed of one phosphorus atom and four oxygen atoms.
phosphorous - A non-metallic element designated with the chemical symbol P; an essential nutrient for plants and animals; usually present in natural waters as phosphate.
photosynthesis - A series of chemical reactions in producers, usually plants, in which light energy is used to make chemical energy in the form of food.
phytoplankton - Microscopic photosynthetic protists (i.e. bacteria and algae); form the basis of freshwater and marine food webs; the main producers in the open ocean. image
plankton - Microscopic organisms that drift freely with water currents; phytoplankton are producers; zooplankton are animals. image
pod - A seed vessel or fruit of a plant.
pollination - Sexual reproduction in plants in which pollen is transferred from anther to stigma of either the same plant or another plant.
pollution - Contamination of air, water, or soil by toxic organic or inorganic substances (e.g., industrial or agricultural waste by-products, engine exhausts, factory emissions, or human waste). Pollution can come from a single source (point-source) or be discharged over a wide area from many sources (non-point source).
point source pollution - Pollution coming from a single point (e.g., sewage-outflow pipe).
pond lily - An emergent vegetation; water lily of the genus Nymphaea; has floating leaves.
pond snails - Aquatic macroinvertebrate; phylum Mollusca, order Gastropda; organism is enclosed within one shell; tolerant of pollution. image
pool - A deeper area of water in a stream; usually quiet and often with no visible flow.
population - A group of organisms of the same species living in the same area.
porcelain-berry - Ampelopsis brevipedunculata; an exotic invasive plant that grows in intermittently flooded lowland forest. image
porosity - The percent of space or pores between sediment particles; indicates the amount of water the sediment can hold.
pouch snail - Aquatic macroinvertebrate; phylum Mollusca, order Gastropda; organism is enclosed within one shell; tolerant of pollution.
precipitation - Condensed water vapor that falls to or forms on the surface as rain, snow, hail, sleet, dew, and frost.
predator - An organism that kills and eats other organisms.
prey - A creature hunted or caught for food.
primary consumer - An organism that feeds on producers; an herbivore.
primary productivity - The amount of energy trapped by photosynthesis. This quantity determines how much life a region will support.
pristine environment - An environment remaining in a pure or uncorrupted state.
producer - An organism that makes its own food; a photosynthetic organism; an autotroph.
propagation - Increased or spread by natural reproduction.
purple dead nettle - Lamium purpureum; an exotic invasive plant that grows in a clearing (meadow or field). image
Q factor - A rating scale that translates water quality test results to a number from 0-100.