Characteristics Of Secondary Salinization And Ecological Effects On Macroinvertebrates In The Hun-Tai River Basin

In recent years, some anthropogenic disturbances including urbanization, industrialization, coal mining and agricultural irrigation, have brought great changes in characteristics of water chemistry in Hun-Tai River Basin. All the disturbances have caused an increase of salinity and made a serious secondary salinization. The source of salinity and its influence on freshwater ecosystem have become a global hotspot issue. The purposes of the present study were listed below. Firstly, by using the historical data (1971-1983) and collected in the field sampling (2009-2010), methods of multivariate ranking analysis were performed to analyze the spatiotemporal distribution of major ions and investigate the drastic alteration of water chemistry over the past four decades. Secondly, the driving factors and source apportionment of secondary salinization were identified by multivariate statistics and positive matrix factorization (PMF) model. Finally, the community structure and physiological response of macroinvertebrates to salinization were identified and we explored the mechanism that caused the degradation of Hun-Tai River.The main results are as follows:(1) Except the bicarbonate (HCO3-) and alkalinity, major ions increased from 2.17 to 9.57-fold and hardness increased 2.64-fold during the last 40 years. Compared with other ions, the concentrations of chloridion (Cl-) and sulfate (SO42-) attained higher growth rates (0.017mmol/(L·y),0.016mmol/(L·y)). The dominant cation is calcium (Ca2+) in the historical and present periods, however, the dominant anion has shifted from HCO3- to SO42-. The current major water chemistry is typically characterized by the Ca-SO4 type instead of Ca-HCO3 type 40 years ago. The concentrations of water chemical ions in the mid-and downstream were higher compared with that in the upstream. The proportions of sodion (Na+) and Cl" increased significantly in the downstream. The current hardness (92.68mg/L) in the study area was much higher than the global average value (47.10mg/L). The affection of exogenous inputs and human activities were the major driving factors and made a drastic change for the natural hydrochemistry characteristics.(2) The results of Gibbs’ model and high ratio of (Ca2++Mg2+) to (K++Na+) (2.8-5.4) (in meq/L) showed that carbonate weathering was the main natural factor which influenced major ions in Hun-Tai River. The ratio of Cl" to Na+ increased with years and Cl- and Na+ were all positively related to the ration of farm and urban land use significantly, indicating agricultural irrigation and urbanization were the determinant to the concentrations of Cl" and Na+. Mining was the key cause which made the increase of conductivity, Ca2+, SO42- and HCO3-. Acid pollution was intensified and caused the hardness-alkalinity was far more upper on the 1:1 line, increased Ca2+ and Mg2+ and decreased HCO3-. Contribution rate of anthropogenic disturbances to the second salinization identified by PCA and PMF was 65.10% and 64.82%, respectively. All the analysis results indicated that the dominant factor for hydrochemical type in Hun-Tai River Basin has changed from its original rock dominance to anthropogenic dominance at present.(3) Conductivity and major ions increased significantly derived from heavy mining activities and agricultural irrigation in the upstream. Total species abundance of macroinvertebrates affected by conductivity responded as an inverted "U" shape. Owing to the salinization, caused by mining activities, the sensitive taxa, belonging to Ephemeroptera, Plecoptera, Trichoptera and Pulmonata, decreased in richness and abundance, while the tolerant taxa belonging to Oligochaeta and Chironomidae increased. The negative effects on macroinvertebrates were attributed to physiological stress implied by the research on the gastropod snail, Radix swinhoei. As conductivity rose, Na+K+-ATPase activity showed a rise first followed by a decline, probably being restrained at high level of salinity. The SOD and CAT activities would be induced by low salinity to adapt to environmental stress, but could be inhibited at high level of conductivity, leading to a lower level of antioxidant enzyme activity.