Enzyme Activity as an Indicator of the Ecological State of Alluvial Soils (Using the Example of the Zeya River)

摘要

The regulation of river flows by constructing hydroelectric power plants and dams leads to a significant transformation of the floodplain ecosystems downstream and their components. One way to assess the ecological state of natural landscapes is to determine enzymatic activity. However, the global literature has very little data on the enzymatic activity in floodplain landscapes, not only disturbed but also natural ones. This results mainly from the difficulties of studying floodplain areas, as they are highly dynamic natural objects with strong variations of properties and parameters, both in space and time. In this work, we partially fill in this gap by showing whether the activity of enzymes can be used to assess the ecological state of floodplain soils with the long-term regulation of the river flow. The Zeya River has been regulated by the Zeya Hydroelectric Power Station since 1975. We have determined the activity of enzymes (phosphatases, ureases, catalases, polyphenol oxidases, and peroxidases) in five types of floodplain landscapes: meadow on the riverine floodplain; meadow, arable land, and forest on the central floodplain; and a swamp in the backswamp depression. The high activity of phosphatase (max. up to 10 mg/g) and low activity of urease (max. up to 0.55 mg/g) and catalase (max. up to 0.55 g/cm(3)) have been determined. The activities of polyphenol oxidase (max. up to 85 mg/100 g) and peroxidase (max. up to 290 mg/100 g), expressed through the humus accumulation coefficient (max. 41%), indicate the average level of floodplain soil fertility. The diversity of enzymes has been evaluated using Pielou's index and geometric mean. Under the long-term regulation of the river flow, the highest levels of enzymatic activity have been determined for the soils under the floodplain forest and the lowest for arable soils. However, we have not identified a specific soil parameter that would reliably affect all enzymes. Phosphatase, urease, and catalase exhibit significant positive relationships with exchangeable acidity. Catalase has been characterized by strong positive relationships with organic matter and negative with pH. The data allow us to state that the long-term regulation of river flow leads to a decrease in the activity and diversity of enzymes.