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（Lienhuachi Experimental Forest）的两个森林流域，探究了其对3级台风下水化学响应特征：分别为24年生杉木人工林（WS4）与天然硬阔林（WS5）。26小时内累计降雨量达119毫米；尽管WS4的基流远低于WS5（WS4基流为0.012 L·s⁻¹·ha⁻¹，WS5为0.38 L·s⁻¹·ha⁻¹），但WS4的峰值溪流流量达80 L·s⁻¹·ha⁻¹，WS5则为11 L·s⁻¹·ha⁻¹。作为总离子强度表征指标的溪流水电导率（conductivity），在WS4中下降了约50%，WS5中下降约30%。泰利台风（Typhoon Talim）期间，杉木人工林的溪流流量与离子波动幅度均高于天然林，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物输出量较天然林高出两个数量级：人工林净悬浮物输出量为8.8 kg·ha⁻¹，天然林则为0.06 kg·ha⁻¹。在重现周期为6年的3级台风对溪流化学特征的影响中，人工林的抗干扰能力低于天然林。在所分析的11种离子中，氮、磷、钾是仅有的在天然林中浓度高于人工林的元素，这一模式与人工林的生物量积累及伴随的宏量必需元素高需求特征相符。将原生阔叶林转换为针叶人工林，会对水化学循环产生持久且显著的影响，这种变化在营林20年后仍可被观测到。