Major ion geochemistry of the Nansihu Lake basin rivers, North China: chemical weathering and anthropogenic load under intensive industrialization

Abstract

To explore the chemical weathering processes and the anthropogenic disturbance of weathering, 20 water samples were collected from the tributaries in the Nansihu Lake basin, a growing industrial area. The major ions in river waters were analyzed to identify and quantify the contributions of the different reservoirs. Based on stoichiometric analyses and end-member determination, the contributions of individual reservoirs were calculated for each tributary. In the study region, the averaged contributions of atmospheric inputs, anthropogenic inputs, evaporite weathering, carbonate weathering and silicate weathering were 2, 37, 28, 25 and 8 %, respectively. Combined with information regarding runoff and drainage area, the annual average contribution of TDS to waters was estimated to be 1.90 ± 0.95 ton/km² from silicate weathering, 5.68 ± 2.84 ton/km² from carbonate weathering. Furthermore, the associated consumption of CO₂ was calculated to be approximately 7.50 × 10⁹ mol/a. The industrial and mining activities were the main sources for anthropogenic inputs, and they produced non-CO₂ acids (NCA). Of all protons involved in chemical weathering, 34 % was presumed to be originated from NCA, causing 2.74 × 10⁹ mol/a of CO₂ degassing. Moreover, industrial inputs could play a major role in the modification of the chemicals in the water system, and they could even change the carbonate weathering rate in such an intensively industrializing region. In North China, the chemical weathering associated with NCA was found to be significant for the first time.

Appendix: Calculation methods (Eqs. 1–21)

Calculation methods

Contributions of various reservoirs

Atmospheric inputs

$${\text{X}}_{\text{atm}} = {\text{ F}}^{ - }_{\text{atm}} \times \left[ {{\text{X}}/{\text{F}}^{ - } } \right]_{\text{rain}}$$

(1)

Anthropogenic inputs

$$\left[ {\left( {{\text{Cl}}^{ - } + {\text{SO}}_{4}^{2 - } } \right)/{\text{Na}}^{ + } } \right]_{\text{anth}} = {{\left[ {\left( {{\text{Cl}}^{ - } + {\text{SO}}_{4}^{2 - } } \right)_{\text{S01}} {-}\left( {{\text{Cl}}^{ - } + {\text{SO}}_{4}^{2 - } } \right)_{\text{S02}} } \right]} / {\left[ {{\text{Na}}_{\text{S01}}^{ + } {-}{\text{Na}}_{\text{S02}}^{ + } } \right]}}$$

(2)

$${\text{NO}}_{{3\,{\text{agr}}}}^{ - } = {\text{NO}}_{{3\,{\text{riv}}}}^{ - } - {\text{ NO}}_{{3\,{\text{atm}}}}^{ - } - {\text{ NO}}_{{3\,{\text{ind}}}}^{ - }$$

(3)

Silicates

$$K^{ + }_{\text{sil}} = \, K^{ + }_{\text{riv}} {-} \, K^{ + }_{\text{atm}}$$

(4)

$${\text{Ca}}^{2 + }_{\text{sil}} = {\text{ K}}^{ + }_{\text{sil}} \times \, \left[ {{\text{Ca}}^{2 + } /{\text{K}}^{ + } } \right]_{\text{gg}}$$

(5)

$${\text{Mg}}^{2 + }_{\text{sil}} = {\text{K}}^{ + }_{\text{sil}} \times \, \left[ {{\text{Mg}}^{2 + } /{\text{K}}^{ + } } \right]_{\text{gg}}$$

(6)

$${\text{Na}}^{ + }_{\text{sil}} = {\text{ K}}^{ + }_{\text{sil}} \times \left[ {{\text{Na}}^{ + } /{\text{K}}^{ + } } \right]_{\text{gg}}$$

(7)

Chemical budget and chemical weathering rate estimation

$${\text{X}}_{\text{riv}} = {\text{ X}}_{\text{atm}} + {\text{ X}}_{\text{anth}} + {\text{ X}}_{\text{eva}} + {\text{ X}}_{\text{carb}} + {\text{ X}}_{\text{sil}}$$

(8)

$${\text{F}}^{ - }_{\text{riv}} = {\text{ F}}^{ - }_{\text{atm}}$$

(9)

$${\text{K}}^{ + }_{\text{riv}} = {\text{ K}}^{ + }_{\text{atm}} + {\text{ K}}^{ + }_{\text{sil}}$$

(10)

$${\text{NO}}_{{3\,{\text{riv}}}}^{ - } = {\text{ NO}}_{{3\,{\text{atm}}}}^{ - } + {\text{ NO}}_{{3\,{\text{anth}}}}^{ - }$$

(11)

$${\text{Cl}}^{ - }_{\text{riv}} = {\text{ Cl}}^{ - }_{\text{atm}} + {\text{ Cl}}^{ - }_{\text{anth}} + {\text{ Cl}}^{ - }_{\text{eva}}$$

(12)

$${\text{SO}}_{{ 4\;{\text{riv}}}}^{2 - } = {\text{ SO}}_{{ 4\;{\text{atm}}}}^{2 - } + {\text{ SO}}_{{ 4\;{\text{anth}}}}^{2 - } + {\text{ SO}}_{{ 4\;{\text{eva}}}}^{2 - } + {\text{ SO}}_{{ 4\;{\text{pyr}}}}^{2 - }$$

(13)

$${\text{Na}}^{ + }_{\text{riv}} = {\text{ Na}}^{ + }_{\text{atm}} + {\text{ Na}}^{ + }_{\text{anth}} + {\text{ Na}}^{ + }_{\text{eva}} + {\text{Na}}^{ + }_{\text{sil}}$$

(14)

$${\text{Ca}}^{{ 2 { + }}}_{\text{riv}} = {\text{ Ca}}^{{ 2 { + }}}_{\text{atm}} + {\text{ Ca}}^{{ 2 { + }}}_{\text{eva}} + {\text{ Ca}}^{{ 2 { + }}}_{\text{carb}} + {\text{Ca}}^{{ 2 { + }}}_{\text{sil}}$$

(15)

$${\text{Mg}}^{{ 2 { + }}}_{\text{riv}} = {\text{ Mg}}^{{ 2 { + }}}_{\text{atm}} + {\text{ Mg}}^{{ 2 { + }}}_{\text{eva}} + {\text{ Mg}}^{{ 2 { + }}}_{\text{carb}} + {\text{ Mg}}^{{ 2 { + }}}_{\text{si}}$$

(16)

$${\text{Cationic TDS}}_{\text{sil}} = \, \left[ {23.0 \times {\text{Na}}^{ + } + \, 39.1 \times {\text{K}}^{ + } + \, 20.0 \times {\text{Ca}}^{2 + } + \, 12.1 \times {\text{Mg}}^{2 + } } \right]_{\text{sil}} + \, 60.1 \times {\text{SiO}}_{2}$$

(17)

$${\text{Cationic TDS}}_{\text{car}} = \, \left[ {20.0 \times {\text{Ca}}^{2 + } + \, 12.1 \times {\text{Mg}}^{2 + } } \right]_{\text{carb}}$$

(18)

$${\text{Cationic TDS}}_{\text{eva}} = \, \left[ {23.0 \times {\text{Na}}^{ + } + \, 20.0 \times {\text{Ca}}^{2 + } + \, 12.1 \times {\text{Mg}}^{2 + } } \right]_{\text{eva}}$$

(19)

$${\text{CO}}_{{ 2 {\text{sil}}}} = \, \left[ {{\text{Na}}^{ + } + {\text{ K}}^{ + } + {\text{ Ca}}^{2 + } + {\text{ Mg}}^{2 + } } \right]_{\text{sil}}$$

(20)

$${\text{CO}}_{{ 2 {\text{carb}}}} = \, 0.5 \times \left[ {{\text{Ca}}^{2 + } + {\text{ Mg}}^{2 + } } \right]_{\text{carb}}$$

(21)

where units in all equations are μeq/L; X = K⁺, Na⁺, Ca²⁺, Mg²⁺, HCO₃ ⁻, Cl-, SO₄ ²⁻, NO₃ ⁻; S01, S02 = the concentration of the analyzed sample S01, S02; riv river, representing the concentration in river water, rain rain water, representing the concentration in rain water, gg granite gneiss, representing the abundance in granite gneiss, atm atmosphere, representing the atmospheric contribution to river water, anth anthropogenic, representing the anthropogenic contribution to river water, including agricultural and industrial contributions, arg agricultural, representing the agricultural contribution to river water, ind industrial, representing the industrial contribution to river water, eva evaporites, representing the contribution of evaporites to river water, carb carbonates, representing the contribution of carbonates to river water, pyr pyrite, representing the contribution of pyrite oxidation to river water, sil silicates, representing the contribution of silicates to river water.