PEAT SUSTAINABILITY UNDER MANAGED WATER REGIMES

摘要

Water-regime management options that mitigate the processes of subsidence, soil degradation, reduced water retention, changing soil ecology and greenhouse gas emissions that are inherent in organic soil drainage practices must be informed by an understanding of how the water-table position influences these processes. Water management trials undertaken on UK lowland peat soils at West Sedgemoor, Somerset, indicate that the water table in peat soils is readily manipulated by the use of sub-surface irrigation, though the extent of such a system has a significant bearing on the degree of control possible. Based on both historical data and recent soil surveys, it is believed that careful water-table management could enhance the future integrity of peat soils, stabilising the hydraulic conductivity and water-release characteristics of the soil. To assess the extent and rate of soil subsidence, degradation and loss, soil survey data from Methwold Fen, Norfolk, collected in 1983, have been compared against a recent soil survey (2004) of the same area. The results suggest that subsidence, degradation and loss under arable farming may account for an average 1-2-cm decrease in peat thickness each year over a 21-year period. Initial findings also indicate that poor management of sub-surface irrigation systems can further exacerbate the degradation of peat soils. At Methwold Fen, where the sub-surface system is also used for drainage, significant changes in soil pH were found to occur within a 3-month period of such soil aeration. Such drainage is likely to change the microbial community structure and hence alter the efflux of greenhouse gases (carbon dioxide and methane), due to microbial respiration, from the soil. Analysis of the CO_2 emissions from fields under different water management regimes at West Sedgemoor indicates significant differences in soil respiration do occur under different water regimes. Also, laboratory trials on soil cores from both research sites indicate important differences in CO_2 flux occurs under different land uses/peat types when the water management regime is kept the same. Given that the water management can significantly alter microbial population structure, density and rate of respiration, other factors are likely to be influenced in the soil ecosystem, such as nutrient cycling and altered macro-invertebrate population density and diversity.