plants was investigated by m a n ip u la tin g .th e composition o f the
bathing s o lu tio n in a system closed to the atmospliere. In Part H the p ro p e rtie s o f the carbonate system in natural waters w i l l be discussed along w ith the r e la t io n s h i p between plants and the carbonate
system open t o the atmos^liere, aiming towards a c l a s s i f i c a t i o n of lake types and the p la n t communities which c h a ra cte rize them.
i
Q rig in of a l k a l i n i t y in- lakes and i t s ro le in a f f e c t i n g t o t a l carbon concentratio ns.
In nature, ' water "î^cqu i res carbonate a l k a l i n i t y d i r e c t l y from the d i s s o lu ti o n of rocks by water with the a d d itio n a l aid of COg and SO^ picked up from the atmosphere. A whole range o f carbonaceous minerals occur which e x h i b i t considerable d iffe re n c e s
In s o l u b i l i t y . In a d d itio n these minerals w i l l determine the proportions of' metal cations present in the water fio'tably calcium and magnesium. The geology and hydrology of the draifiage basin and the flu s h in g rate determine the amount of inorganic carbon present in a lake. Frequently lakes near the sea receive consider able amounts of carbonate from wind-borne marine sands. N a tu ra lly
- i occu rrin g a l k a l i n i t y le vels range from about 5 m-equiv I in extremely hard-water lakes such as Lawrence Lake described by Wetzel (1975) t o zéro in acid waters. A l k a l i n i t y may be increased by the a d d itio n of OH from i n d u s t r i a l wastes, p a r t i c u l a r l y
some papermi I I e f f l u e n t s . More commonly acids are added t o waters and these destroy a l k a l i n i t y . Sources may be from mine wastewaters, and acid ra in produced by vo lc a n ic a c t i v i t y and by the burning of s u l p h u r - ri c h f u e ls .
In the open system where C0_ can be gained o r lo s t t o the atmospkgre, the t o t a l carbon w i l l tend to approximate the a l k a l i n i t y when the system is in e q u il ib r iu m with the a i r . A decrease in pH brought about by the a d d itio n o f acids increases the^COg] r e s u lt in g in the loss o f COg t o the atmoshere. Conversely Cy can be increased by the a d d itio n o f OH” . Water inflow s o r i g i n a t
ing from areas of a c i d i c rocks o r peat bogs would lower the t o t a l carbon concentration of the water In a lake even when i t s basin might l i e on calcareous rock.
Determination of a l k a l i n i t y , t o t a l carbon .and fre e C0_ in natural waters.
The ’ carbonate system’ has been described f o r s impie d i l u t e s o lu tio n s in Part I. Natural waters are considerably more complex In composition and t h i s w i l l a f f e c t a c t i v i t i e s and
io n iz a tio n constants as well as in trodu cing oth e r components c o n t r ib u ti n g t o a l k a l i n i t y , which under c o n d itio n s of high pH produce an over^estim ation of Cy ( T a i l i n g 1973). To define the carbonate system in a body of water at a given time, f i v e parameters must be measured; t o t a l a l k a l i n i t y , t o t a l inorganic carbon, pH,
* .. 2- temperature and c o n d u c t i v i t y . Concentrations of CO^, HCO^ and CO^ may be estimated from pH and Cy^using the io n iz a tio n fr a c t io n s corrected f o r temperature and the e f f e c t s of t o t a l so lu te concentra t i o n .
The sim plest determination is an a c id im é trie t i t r a t i o n of a water sample t o pH 8.3 ( phenolphthalein endpoint) followed by f u r t h e r t i t r a t i o n t o pH 4.6 (methyl red endpoint) which g iv e jc o ^ + OH ]and [hCO^ * CO^ + OH ] re s p e c tiv e ly . These t i t r a t i o n S ) u s u a l l y c a rrie d out w ith d i l u t e s o lu tio n s of strong acids, produce endpoints which are not very sharp and are s h i ft e d by
temperature and the presence of o th e r so lu te s. Some a n a ly t ic a l
techniques attempt to define the endpoints more p r e c is e ly by applying c o r re c tio n f a c to rs based on the o r i g i n a l pH of the sample and the c o n d u c t i v i t y ( a fu n c tio n o f t o t a l so lu te conce ntratio n) (Golterman 1969). The ’ methyl orange e n d p o in t’ may vary from about pH 5.3 t o 4.5 over the t o t a l carbon concentration range of 0,05 t o 2,0 mM. A l l a c id im é trie t i t r a t i o n s include t i t r a t a b l e bases such as H^SiO^, H^BO^^ H.S and, most im p o rta n tly, p a r t i c u l a t e CaCO^,
An evaluatio n of the r e l a t i v e e r ro rs in rne measurement of the parameters capable of d i r e c t a n a lysis Is given In Stumm and Morgan (1970 p ,142). None of the in d iv id u a l carbon species can be determined d i r e c t l y by a c id im é trie t i t r a t i o n . Free CO^ i t s e l f may be found by a l k a l i m e t r i c t i t r a t i o n ,
A method of determining the endpoints by means of a stepwise t i t r a t i o n has been described by Gran (1952) and has been tre a te d f u r t h e r by Dryssen (1965) and T a i l i n g (1973), The Gran t i t r a t i o n locates the endpoints a p p lica b le to the sample