3. RESULTS AND DISCUSSION
3.1 water chemistry and nitrate concentration analysis
The field parameters and constituents of surface water and groundwater
were summarized in Table 2. The DO values in surface water ranged from
1.21 to 14.72 mg/L with an average of 8.01 mg/L, indicated the existence
of aerobic environment for surface water. The DO values in groundwater
varied from 0.82 to 8.97 mg/L with a mean of 4.44 mg/L, suggested that
both oxidizing and reducing environments were present in the
groundwater. The NH4+ concentration in
surface water ranged from 0.2 to 2.44 mg/L, with an average of 0.81
mg/L. The NH4+ concentration in
groundwater ranged from 0.13 to 4.61 mg/L, with an average of 1.18 mg/L.
21 water samples exceeded the environmental quality standard for
groundwater Class V (1.5 mg/L NH4+,
GB/T 14848-2017) set by the Ministry of Ecology and Environment of
China, and the higher NH4+concentration may be related to a large amount of turf cultivation and
ammonia nitrogen fertilizer applied in the study area in recent years.
The concentrations of DOC in surface water ranged from 2.2 to 30.72
mg/L, with an average of 11.98 mg/L; the concentrations of DOC in
groundwater ranged from 1.74 to 35.16 mg/L, with an average of 14.49
mg/L.
Table 2 Statistical
summary of chemical and isotopic parameters in SW and GW of the Huashan
basin
The spatial distribution of nitrate in surface water and groundwater in
the Huashan watershed are shown in Figure 2. The nitrate concentrations
in surface water were all less than 1 mg/L in spring, and the nitrate
concentrations in groundwater were all less than 2 mg/L. The
concentration of NO3- in surface water
in summer was less than 1 mg/L except at the basin outlet and upstream
of the Xiyuan subbasin; The average
NO3- concentration of groundwater was
2.26 mg/L, with four water samples having a concentration greater than 5
mg/L, located in the southeastern and southern regions of the watershed.
The NO3- concentration was relatively
low in the downstream area of the watershed.
NO3- in surface water is higher in the
downstream of the basin in autumn; the distribution of
NO3- in groundwater in autumn is
similar to that in summer, while the concentration is lower than that in
summer. The concentration of NO3- in
surface water further increased in winter, up to 5.1 mg/L in the upper
reaches of the Xiyuan subbasin; the
NO3- concentration in two groundwater
samples exceeded 10 mg/L in winter, distributed near the lower reaches
of the watershed.