amounts and proportions of nutrients required to cause eutrophication in any 

 stream segment depends on local conditions. These include pattern and amount 

 of rainfall, size and shape of drainage basin, size and shape of stream 

 channel, current velocity, light penetration, and plant species present. 



Other inorganic ions . Inorganic materials also play important roles in 

 stream chemistry. The concentration of dissolved inorganic ions, particularly 

 of calcium (Ca), magnesium (Mg) , potassium (K) , sodium (Na), chloride (CI), 

 bicarbonate (HCO3), and silicon dioxide (SiOo ) determine the electrical 

 conductance of stream water (Golterman 1975). These materials are normally 

 derived from runoff or airborne dust particles and sea spray. Ionization of 

 calcium and magnesium carbonates (CaCO ^, MgCO 3; derived primarily from 

 sedimentary rock such as limestone) is the primary source of "hardness" in 

 natural waters (Reid 1961). Conductance and hardness have few known direct 

 effects on stream organisms. However, both of these factors may be indicative 

 of the amount of plant nutrients available and hence the potential 

 productivity of the stream system. Conductivity and hardness also may 

 determine the suitability of stream water for domestic and industrial uses. 



Carbonates in conjunction with carbon dioxide (CO2) are responsible for 

 buffering capacity (the ability to resist violent changes in levels of 

 acidity) in aquatic systems (Hynes 1970b). Well-buffered systems tend to be 

 more stable and frequently support more diverse biological communities than 

 those that are poorly buffered. 



Since most of the Maine coast is underlain by igneous and metamorphic rocks 

 the natural contribution of inorganic ions to stream water is probably minimal 

 (appendix B, tables 1, 5, 6, and 7; Golterman 1975). 



Organic matter . Organic matter is present in water in solution, and in 

 the form of organisms and organic debris. Most organic matter (other than 

 organisms) in streams is derived from external (allochthonous) sources, such 

 as fallen leaves. Dissolved portions of this material are consumed by some 

 bacteria (Reid 1961). Particulate organic material is a source of energy for 

 many invertebrate and some vertebrate detritivores (see "Energy Flow," below). 

 In addition, organic material leached from peat or other shallow water plant 

 debris is responsible for the yellowish-brown color common in the upper 

 reaches of many Maine streams (Reid 1961). 



Dissolved gases . Oxygen (0^) and carbon dioxide are the major dissolved 

 gases involved in the water chemistry and biological activity of streams. 

 Nitrogen (N 2) is also present in streams as a dissolved gas but has little 

 chemical or biological significance in this form. 



Oxygen, essential for plant and animal respiration, usually enters the stream 

 by diffusion from the atmosphere or as a byproduct of photosynthesis. In the 

 upper reaches (upper perennial) of a stream system aquatic plant growth is 

 usually limited, but turbulence enhances diffusion of oxygen to such an extent 

 that dissolved oxygen is maintained in the water at or slightly above 

 saturation levels (Golterman 1975). In autumn, when large amounts of leaf- 

 litter enters the stream and begins to decompose, oxygen levels may decline 

 due to microbial activity, but severe oxygen depletion is unlikely. In the 

 lower, deeper, and slower-moving sections of the stream (lower perennial, 

 tidal) aquatic vegetation plays a larger role in introducing oxygen into the 



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10-80 



