柑橘園對東勢林場溪流水水質的影響

The effects of citrus orchard on river water quality in Tungshih forest station

本研究針對中興大學東勢林場內仙水坑溪進行溪流水化學檢測，探討栽植柑橘對溪流水質的影響。檢測分析項目計有：電導度（electrical conductivity, EC）、pH、陰陽離子濃度、總有機碳（dissolved organic carbon, DOC）等。結果獲知溪流水酸鹼值平均為8.03；電導度平均為478.41 μS cm-1；溶氧含量平均為 6.08 mg L-1；陽離子濃度以 Ca2+ 離子濃度最高，Mg2+ 及 Na+ 次之，K+ 較低，而NH4 + 因此區域森林覆蓋率高，土壤有旺盛的硝化作用而未偵測到；陰離子部分，以 HCO3 - 與SO4 2- 濃度較高，NO3 - 及 Cl- 次之，F- 、NO2 - 及 PO4 3- 較低；DOC濃度平均為 6.03 mg L-1。整體來看NO3 - 、 Cl- 、DOC及Ca2+ 含量偏高，特別是柑橘園附近的採樣點離子濃度均偏高，因此推論可能因農業施肥，導致NO3 - 等高於採樣點附近為森林之離子濃度，顯示仙水坑溪水質已受到周遭農業活動影響，其水質在各河段有明顯變化需要持續監測與關注。 This study was aimed to investigate the water chemistry of the Hsienshuikeng Creek in the Tungshih Forest Station, the Experimental Forest of the Chung Hsing University. We analyzed water chemistry, including electrical conductivity (EC), pH, concentration of inorganic cations (Na+ , NH4 + , K+ , Mg2+, Ca2+) and anions (F- , Cl- , NO3 - , NO2 - , SO4 2-, HCO3 - , PO4 3-), as well as dissolved organic carbon (DOC) to assess water quality. The results showed that the pH, EC and dissolved oxygen were 8.03, 478.41 μS cm-1 and 6.08 mg L-1, respectively. Ca2+ was, the highest concentration cation, followed by Na+ , Mg2+ and K+ ; however, NH4 + was not detected because of the strong nitrifi cation in the forest soil. The concentration of HCO3 - and SO4 2- were higher, followed by NO3 - and Cl- , whereas F- , NO2 - and PO4 - were among the lowest. The average concentration of DOC was 6.03 mg L-1. Overall concentration of NO3 - , Cl- , DOC and Ca2+ were high, especially, in sampling sites close to citrus orchard where the high NO3 - concentration might be due to agricultural activities. Our results indicated that the water chemistry characteristics of stream were affected by the surrounding agricultural activities. Therefore, continuing monitoring the water chemistry of the Hsienshuikeng creek is necessary in the future.