Typhoon impacts on stream water chemistry in a plantation and an adjacent natural forest in central Taiwan

We studied the hydro-chemical responses to a category 3 typhoon of two forested watersheds at Lienhuachi
Experimental Forest: a 24 year old China-fir plantation (WS4) and a natural hardwood forest (WS5).
One hundred and nineteen millimeters of precipitation fell in 26 h resulting in a peak stream flow of
80 l s1 ha1 in WS4 and 11 l s1 ha1 in WS5 despite a much lower base flow at WS4: 0.012 l s1 ha1
as compared to 0.38 l s1 ha1 at WS5. Stream water conductivity, an indicator of overall ionic strength,
decreased by approximately 50% in WS4 and 30% in WS5. The observation that the China-fir plantation
had a higher stream flow and ion fluctuation than the natural forest during typhoon Talim was the opposite
of that observed during non-storm periods. The output of suspended solids in stream water was two
orders of magnitudes higher in the plantation than in the natural forest during the storm period (8.8 vs.
0.06 kg ha1 net export of suspended solids). The plantation exhibited lower resistance than the natural
forest to the stream water chemistry impacts of a category 3 typhoon with a return interval of six years.
Among the 11 ions analyzed, nitrogen, phosphorus, and potassium were the only elements that had
higher concentrations in the natural forest than in the plantation, a pattern consistent with the aggradation
of biomass and the concomitantly high demand on the macro-essential elements in the plantation.
Conversion of a native broad leaf forest to a conifer plantation has persistent and large effects on hydrochemical
cycling, changes that are still evident after two decades of growth.

本研究针对莲华池实验林区（Lienhuachi Experimental Forest）内两处森林集水区，探究其对三级台风的水文化学响应（hydro-chemical responses）：分别为24年生杉木人工林（China-fir plantation，WS4）与天然硬阔叶林（natural hardwood forest，WS5）。26小时内累计降雨量达119毫米，使得WS4的溪流峰值径流量为80升每秒每公顷，WS5为11升每秒每公顷；尽管WS4的基流远低于WS5：WS4基流为0.012升每秒每公顷，而WS5基流为0.38升每秒每公顷。溪水电导率——作为整体离子强度的指示指标——在WS4中下降约50%，在WS5中下降约30%。本研究观测到，在台风泰利（Typhoon Talim）期间，杉木人工林的径流量与离子波动幅度均高于天然阔叶林，这与非风暴期的观测结果恰好相反。风暴期内，人工林溪流水中的悬浮固体输出量较天然阔叶林高出两个数量级（悬浮固体净输出量分别为8.8与0.06千克每公顷）。对于这场重现期为6年的三级台风，杉木人工林对溪流水文化学影响的抵抗力低于天然阔叶林。在所分析的11种离子中，氮、磷、钾是仅有的在天然阔叶林中浓度高于人工林的元素，这一规律与人工林的生物量累积及其对大量必需元素的高需求相吻合。将原生阔叶森林转换为针叶人工林，会对水文地球化学循环产生持久且显著的影响，这种变化在林木生长20年后仍可被观测到。