A Field-based Macro Invertebrate Benchmark For Conductivity In The Hun-Tai River Basin, Northeast China

In recent years, many anthropogenic disturbances, such as coal mining and agricultural irrigation, have been caused conductivity at a higher level which led to serious effects to the water ecosystem and human in the Hun-Tai River Basin. It had been aroused wide concern of the department of environmental protection and management. Because of the complexity of composition of dissolved ions, it is difficult to establish the conductivity benchmark for aquatic organisms on the basis of experimental data. In this paper, the methods from U.S. EPA were used to establish the conductivity benchmark based on the field data. Moreover, we utilized epidemiology scoring method to explore the feasibility whether setting the relevant conductivity benchmark is feasible in China. Three research contents were conducted to test the feasibility, including (1) Are macroinvertebrate sensitive species affected strongly by conductivity. (2) Does the anthropogenic disturbance impose toxicity effect on aquatic ecosystems through conductivity and (3) Do some other environmental factors affect the accuracy of setting the benchmark? 95th percentile extirpation concentration values (XC95S) for all species was calculated by using the weighted cumulative function (CDF). Meanwhile, XC95S were used as endpoint to derive the conductivity benchmark of the Hun-Tai River Basin through species sensitivity distribution. The main results are as follows:(1) The sites where the concentration of conductivity is low, the diversity was high. Conductivity decreased the occurrence frequency of sensitive species significantly. The ration of agricultural and urban land use increased the conductivity level by analyzing the correlation between land use and conductivity. Conductivity was the main reason for dying out of sensitive species by analyzing the effects of other environmental factors which may cause the same influence. In summary, establishing conductivity benchmark based on field data is feasible, and moreover, some new ideas and methods should be applied for the future studies in relation to the water benchmark. (2) The dominant ions in the Hun-Tai River Basin were 15% to 80% Ca2+25% to 85%Mg2+.30%to 70%SO42- and 25% to 75% HCO3-. The total concentration of SO42- and HCO3- was higher than that of Cl- in almost all of the sampling sites. Extirpation concentration (XC95) of 57 species belonging to 35 families.16 orders and 5 phylums was calculated by using the weighted cumulative distribution function. The results of XC95S indicated that some species, such as Nephelopsis sp., were affected by increasing conductivity; by contrast, other species, such as Oyamia sp., were ot affected. Four typical distributions of observation probabilities, which were calculated by logistic regression observed in the Hun-Tai River Basin; this result revealed that different species, such as Eperus latifolium, Protohermes grundis. Cheumatopsyche sp. and Stenopsyche marmorata exhibit unique response to increasing conductivity. The following XC95 values were obtained according to the principles of a generalized additive model:approximately 760 p.S/cm for Epeorus latifolium, equal to 826 uS/cm for Protohermes grandis, equal to 624 uS/cm for Cheumatopsyche sp.. and greater than 816 u.S/cm for Stenopsyche marmorata. Monte Carlo method was used to generate species sensitivity distribution (SSD); the 5th percentile of SSD of XC95 of 57 species was 277.10 μS/cm.(3) The background conductivity which was estimated through Kohlrausch’s law is 142 μS/cm of the Hun-Tai River Basin. The value of background is approximately equal to the 25th percentile of conductivity (130.6μS/cm) and far less than macroinvertebrate conductivity benchmark (277.10 μS/cm). The correlation analyze between conductivity and water parameters showed that the correlation coefficients between conductivity and water temperature (r=0.59), habitat score (r=-0.59),NH3-N ((r=-0.62)) is high. Water temperature, habitat score and NH3-N maybe the potential factors in the process of deriving conductivity benchmark. To study the effects of water temperature, habitat score and NH3-N, sampling sites with higher temperatures [>22℃], poor habitat [habitat score<135], and high NH3-N [>1.0 mg/L] were removed. After removing sampling sites,56 species belonging to 34 families,16 orders and 5 phylumswere screened and only less one species than before removing sampling sites.The results of Independent-Samples T test showed that species of Trichoptera, Ephemeroptera, Diptera and other classes had no significant differences. Water tempreture, habitat score and NH3-N had a very slight effect on the conductivity benchmark.