The use of large bottomless lysimeters in the determination of water balances for a raised mire

Large bottomless lysimeters were investigated for their suitability as a to ol in the study of water balances of treeless and tree-covered areas on a r aised mire. The lysimeters, large enough to contain a mature tree, were dev eloped to measure the liquid discharge from the peat monolith they enclosed . By determining the other, less elusive components of the water balance, t his approach enables evapotranspiration rates to be estimated and compariso ns between treeless and tree-covered areas to be made. The principal features of the design and operation of the lysimeters are de scribed. Discharge measured with the lysimeters was analysed for short-term periods as well as for a hydrological year, and was compared with expected amounts of discharge obtained from a simplified water balance (D-exp = P - 1.1 E-t for the winter, and D-exp = P - 08 E-t for the summer). Results in dicated that D was reliable for short intervals (10 days on average) with m oderate amounts of rainfall. Under more extreme weather conditions, leakage underneath the lysimeter walls could occur, resulting from the strong slop e-dependent water exchange across the lysimeter. Suggestions are made for i mprovements to the design of the lysimeter system, Copyright (C) 1999 John Wiley & Sons, Ltd.