low flow. Riffles are reaches where flow is rapid and the channel gradient is 

 high. Depth of water during average flow is low and the channel is usually 

 covered with cobbles and boulders. Streams with smaller drainage areas (<77 

 sq miles; <200 sq km) may be composed of either or both upper or lower 

 perennial subsystems. The intermittent subsystem of a river or stream 

 consists of channel segments over which water flows only during portions of 

 the year, usually during spring freshets or just after periods of high 

 precipitation. Otherwise, the channel is dry or contains small pools of still 

 water. 



CHEMICAL CHARACTERISTICS 



The continuing compilation of water quality records by the USGS serves as a 

 valuable long-term record of general chemical variability in certain Maine 

 streams. Mairs (1968), Hutchinson (1968), and Taylor (1973) have provided 

 water quality data for certain streams in Maine. Recent data on chemical 

 characteristics are given in appendix B, tables 1 to 7 . The following is a 

 summary of water quality parameters. A discussion of the functions of water 

 chemistry parameters is presented in "Water Chemistry Parameters" below. 



In all riverine systems measured in coastal Maine, pH levels are highly 

 variable and no consistent trends are evident. Maine rivers rarely exceed pH 

 7.0 (see appendix B, tables 2 and 3). Frequently, pH levels in Maine streams 

 are at the lower end of the scale. Dissolved oxygen is variable in those 

 rivers where O2 has been measured (see appendix B, table 4). The 

 concentration of dissolved oxygen in measured Maine rivers ranged from 5.3 

 mg/1 (St. Croix River in summer) to 14.2 mg/1 (St. Croix River in spring). 

 Maine rivers show fluctuating, relatively low levels of alkalinity (appendix 

 B, table 5). Low alkalinity and extremely low levels of calcium and magnesium 

 are responsible for the "softness" of fresh waters. Maine streams show 

 variations in concentrations of phosphorus. Nitrate is one of the most 

 variable and unpredictable constituents measured. Natural levels of 

 phosphorus and nitrates are normally relatively low and highly susceptible to 

 influence by pollution. No sharp maximum or minimum specific conductance has 

 been seen in Maine rivers. Most tended toward a spring minimum under 

 conditions of heavy spring runoff (see appendix B, tables 6 and 7). 



Major cations in order of abundance are calcium, sodium, magnesium, and 

 potassium, while the order of abundance of anions is sulfate, bicarbonates , 

 chloride, and nitrate. Rather wide seasonal variability is found among trace 

 elements phosphorus, aluminum, iron, manganese, zinc, copper, and boron. No 

 high concentrations of heavy metals were detected in the water sampled in the 

 stream systems listed in appendix B table 1. 



ABIOTIC FACTORS AFFECTING THE RIVERINE SYSTEM 



Abiotic factors determine the composition of biota prevailing at a particular 

 site. Considered below are climatic, geologic, and physicochemical factors, 

 the effects of which usually cannot be separated. 



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