contribute substantial quantities of dissolved organic material to stream 

 waters, causing yellow-brown water color. 



Water Chemistry Parameters 



Chemical constituents of freshwater systems are derived from material that 

 runs off, is eroded, leached, and/or dumped into the surrounding drainage 

 basin and material that is transported via the atmosphere and falls out with 

 precipitation. These constituents exist in the aquatic system as dissolved or 

 particulate inorganic matter, dissolved or particulate organic matter, or 

 dissolved gases. The chemical and biological interactions of these 

 constituents are similar in all freshwater systems (see "Water Chemistry," 

 above). However, because water is present in a given section of a stream for 

 only a short period of time, the chemical composition of flowing water tends 

 to vary more and be less affected by local conditions than that of standing 

 water over both time and distance. Chemical composition is particularly 

 sensitive to seasonal changes in flow rate and material input (Golterman 

 1975). 



Inorganic plant nutrients . Nitrogen (N) , a major plant nutrient that may 

 limit plant growth when in short supply (Reid 1961) is derived originally from 

 the atmosphere as molecular nitrogen (N2)- It may be fixed by bacterial or 

 algal oxidation into nitrite (NO2) and nitrate (NOo) within a body of water or 

 may be carried into the water as nitrate or amnonia (NH3) by precipitation or 

 runoff (Reid 1961). Decomposition of organisms, organic debris, and metabolic 

 wastes by bacteria and fungi helps to recycle nitrogen within the aquatic 

 system. Most nitrogenous compounds must be converted to nitrate (usually by 

 bacterial action) before they can effectively be used by plants. The world 

 average concentration of nitrate in fresh water is 0.3 ppm (Reid 1961). Some 

 values of nitrogen concentration in Maine rivers are presented in appendix B 

 table 1. Values of nitrogen in Maine rivers for which data are available are 

 somewhat higher than the world average, probably as a result of human imputs. 



Phosphorus (P) is a plant nutrient that is frequently in short supply in fresh 

 water aquatic systems and whose absence sometimes limits plant growth (Hynes 

 1970a). Phosphorus generally enters the water via runoff. Major storage 

 reservoirs are sedimentary bedrocks or soils derived from them (Golterman 

 1975). The forms of phosphorus that are most important to freshwater 

 organisms are soluble ionic phosphate (PO/), soluble organic phosphorus and 

 particulate organic phosphorus. Ionic phosphate is the form most available to 

 plants and is absorbed rapidly wherever plants are growing (Hynes 1970b). In 

 the particulate organic form, phosphorus is not easily available to plants. 

 This form may serve as a reservoir from which phosphorus is released 

 gradually. Concentrations of phosphates in rivers are normally higher than 

 those in lakes in similar areas, because less absorption by algae and emergent 

 vegetation takes place in rivers. Typical values of phosphorus in Maine 

 rivers range from about 0.01 to 0.27 ppm. 



Potassium, another major plant nutrient, is common in most bedrocks and soils, 

 and rarely limits plant growth in freshwater systems (Hynes 1970b) . 



High concentrations of plant nutrients in the proper proportions may lead to 

 rapid and dense plant growth (eutrophication) , which may have undesirable 

 effects. This is usually a problem in sluggish or still waters. The precise 



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