| The construction of large hydropower projects usually bring about extremely seriously damage to surrounding ecological environment. The construction takes up a lot of land, destroy forest plants, changes the method of water cycle and geological conditions. It further more causes soil erosion, decrease in biodiversity, geological disaster aggravating and unbalance of regional ecological system. Aimed at vegetation degradation, the status of nutrient loss and the sustainability of soil fertility in various types of slopes in disturbed area of Xiangjiaba, and the preliminary study of biological activity of artificially substrate did not make out.Taking Xiangjiaba Hydropower Project as a case, in this paper several various types of slopes in disturbed area were studied by sampling and analysis. Seven representative slopes were selected to study their soil fertility, which were framed beams soil covering (FBSC), vegetation-growing concrete gunning (VGCG), thick layer substrate (TLS), external-soil spray seeding (ESS), discarded residue (DS), natural forests (NF) and natural secondary forest (NSF), by four on-site sampling in November of each years since 2007 to 2010. The pH-value and the content of Organic matter (OM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), available phosphorus (AP) and available potassium (AK) was analyzed and evaluated. Soil enzyme activities of fourteen slopes were studied, which were two slopes of FBSC, five slopes of TLS, three slopes of ESS, one slope of VGCG, DS, NF and NSF, by two on-site sampling in June and November of 2010. The activity of Urease, invertase, neutral phosphatase, and catalase and polyphenol oxidase was analyzed and evaluated. This paper selected standard integrated grade method to estimate the fertility level of the seven representative slopes and chose calculation of membership function to evaluate soil enzyme index of the fourteen slopes, then integrated index of soil fertility level (G) and soil enzyme index (SEI) can be gained. Finally, the correlation between soil enzyme activities and chemical properties were analyzed. The results were as follow:(1) Natural forests and natural secondary forest is strongly acidic soils and acidic soils. Soil pH of framed beams soil covering, vegetation-growing concrete gunning substrate, and discarded residue was decreased from alkaline to neutral. Thick layer substrate and external-soil spray seeding substrate was neutral.(2) Overall, the content of OM, TN, AN, AK showed an upward trend except individual slopes. TP appeared a downward trend, the content of AP of the majority of slopes appeared change in the state of fluctuation. Nutrient content in TLS, VGCG and NF were in a higher level, while the nutrient content in FBSC and ESS was in the middle level. The content of TP and AK was higher in DS, but the other fertility indicators were the lowest levels.(3) Excepting DS, the G values of the other slopes showed a downward trend, that was, the promotion of fertility gradually increased over time. Overall, fertility level of VGCG was similar with TLS, followed by NF. The fertility level of FBSC, ESS and NSF was close to each other, and the fertility of DS was the worst.(4) After analyzing and comparing of the soil enzyme activity of various types of slopes, the results showed that the activity of urease, neutral phosphatase and catalase of all slopes in November was higher than June. Except some slopes, the other slopes'invertase activity and polyphenol oxidase activity also showed in November was higher than June. VGCG's urease activity was relatively higher, but was lower than some TLS slopes. June, November polyphenol oxidase activity of NF was the lowest, while the D slope, FBSC, DS were higher. Except polyphenol oxidase, the other four enzyme activities of DS were at the lowest level in June, November. There were some different changes in soil enzyme activity in June and November between the slopes that used the same remediation technology.(5) According to the result of soil enzymes Index (SEI), it showed that the SEI of NF, VGCG and the F, G slope of TLS were higher. DS soil enzyme index in June and November were the lowest. Overall, soil enzyme index of most of the slopes had little changes in June and November. There were some different changes in soil enzyme index in June and November between the slopes that used the same remediation technology.(6) According to analysis of correlation between soil enzyme activities and chemical properties, the result showed that they were significantly (p<0.05) or highly significantly (p<0.01) positive correlation between urease, neutral phosphatase, invertase and catalase, but the correlation between polyphenol oxidase and other enzyme factors and nutrients factors were negative of different degrees. The pH value and polyphenol oxidase were significantly (p <0.05) correlated with other factors and some enzymes showed varying degrees of negatively correlated with nutrient factors. Organic matter, available nitrogen, total nitrogen and five enzyme factors were all had good correlations. Total phosphorus, available phosphorus and potassium were not related to enzyme activity and were not reached a significant level associated with the main fertility.These results indicated that the G values of most of the slopes showed a downward trend, that was, the promotion of fertility gradually increased over time. Five soil enzyme activities affected each other in various types of slope soil, and had a certain correlation with soil fertility, suggested that integrated enzymatic activity could be used to indicate and estimate soil fertility of artificial remediation slopes in the disturbed area. |
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