Relationships Between the Surface Water Chemical and Soil Chemical Characteristics in Lake Hovsgol Steams
Tamir Puntsag, Myron J. Mitchell, Clyde E Goulden and Jeffrey S. Owen
Evaluating soil chemical and water chemical relationships in small watersheds provides important information about watershed impacts. We determined soil concentrations of calcium, magnesium, potassium, sodium, total phosphorus, total nitrogen and carbon and compared with each site’s water chemical conditions. Sixteen chemical parameters were studied monthly during the summer in six streams at four different locations. The chemical analysis followed standard methodologies. The data were analyzed by multiple regression methods.
Canonical Correlation analysis of the same chemical variables from soil and stream water was not significantly different from each other, only soil total N was correlated with water Total N (r2=0.56; p< 0.002). A strong negative correlation, using canonical correlation for the same compounds in water chemistry and soil is represented between a variety of elements, e.g., contrasting soil total N with water total N and between Ca and a soil total C with water total N and Ca. Sites with high total soil N and C have low concentrations of water N and C and Ca (r2= -0.54; p > 0.05) . These results suggest that in places with high soil total C and N concentration, there could be low erosion rates from the soil. These are the southern watersheds with low grazing pressure, where we measured low water major ions. Soil mineral content is high in Borsog, Sevsuul and Dalbay while total N and C concentrations were low, soil mineral content was low in Noyon and Shagnuul while total N and C concentrations were high.
It is depending on the compounds of parent rock and elevation (from 1615 to 1856m a.s.l) Bed rock of the upper sites except of Shagnuul River, mainly are granitoids and bed rock of the middle sites are basalts, thus having different ion concentrations.
On the other hand, low values of dissolved organic matter in the heavily grazed northern watersheds may be due to the greater thickness of the active layer above permafrost leading to a higher decomposition of organic compounds in situ. If this were true, one would also expect higher soil respiration in these soils and there is some indication that this is the case. There was a relationship between river DOC:DON ratio and C:N molar ratio (r2=0.44).
Lake Hovsgol and its tributary streams have ultra-oligotrophic condition because phosphorus is limiting factor of the lake and streams. Soil phosphorus values in bank soils in the Sevsuul upper and Shagnuul upper sites are higher than in the other sites. It suggests that, if these river shores become drier, intensively used as pasture, then phosphorus will be increased in stream and enters to the LakeHovsgol. No doubt, the higher levels of phosphorus are due in part to the concentrating effect of evaporation. To understand the hydro biogeochemistry of this watershed, attention needs to be focused on evaluating how various landscape components influence the temporal and spatial patterns of solute chemistry.