專題討論四之二 24/05/2008 鄭旭涵

山坡地漥蓄區位水資源監測與保蓄效益 授課老師：林俐玲 鄭皆達 陳鴻烈 林德貴 The Sites, Quality Monitoring and Reserve Benefit of Slopeland Water Depressions 專題討論四之二 授課老師：林俐玲 鄭皆達 陳鴻烈 林德貴 鄭 旭 涵 Doctoral graduate student, Department of Soil and Water Conservation, National Chung-Hsing University, Taichung 402, Taiwan, R.O.C. 2008年5月24日

Foreword 1 前期摘要 -1 台灣是全世界第18位缺水國 台灣地區全年水文收支 坡地降雨需營造貯蓄空間 真實集水區有窪地地形 以大湖鄉三個集水區為例 分級統計各集水區漥蓄量體

Foreword 2 前期摘要 -2 推估降雨-逕流-蒸發-漥蓄間關係 推估漥蓄容量-承容降雨量上限 統計集水區內不同降雨量-場次 分別計算河道漥蓄與坡面漥蓄 結論： 河道漥蓄約坡地漥蓄量體之2倍。 大湖鄉80％以上的降雨場次可為漥蓄所承容。 漥蓄承容量受上游網格水量限制。 農業生產區及濱水區之漥蓄具水資源調配價值。

逕流係數C、入滲率f與NDVI值之動態模式 漥蓄設施形式、結合緩衝綠帶之效益 池式 溝式 （文獻） 效益：灌溉保蓄、泥砂阻滯、水質改善 待研究課題 漥蓄量體與DTM網格精度及形數 逕流係數C、入滲率f與NDVI值之動態模式 漥蓄設施形式、結合緩衝綠帶之效益 池式 溝式 （文獻） 效益：灌溉保蓄、泥砂阻滯、水質改善 沉砂、滯洪

In most of the previous studies, however, the focus was on the assessment of the effectiveness of single sink structures in the reduction of sediment and N load under controlled field-plot experiments. 多數文獻僅評估單一緩衝結構對點源污染的控制。 Relatively few studies about relationships between N fluxes and diversified sink landscape structures under real world conditions have been conducted。相對較少文獻評估現地環境的各種緩衝結構與水流中含氮的關係。

N Nitrogen (Smil, 1991; Vitousek and Howarth, 1991; Ma, 1997) ：Discharges abundant in N may accelerate the eutrophication of reservoirs and lakes. N的大量排放，會加速造成水庫及湖泊的優氧化。 Adverse effects may include the formation of nitrosoamines, toxicity in aquatic life and a dramatic increase in water treatment costs.會產生亞硝基鹽類及毒性物質危害水生值物，及增加水處理的成本。 (Leuet al., 1996) ：Controlling N losses has increasingly become an important objective in water quality management。控制N的流失，逐漸成為水質管理的重要目標。

水體中Ｎ的來源 One of the most important pathways by which N enters waterbodies is via the diffuse runoff from agricultural lands during rainfall events.水體中N的來源 ，多經由農耕地因降雨產生擴散逕流而進入。 (Howarth,1988; Puckett, 1995; Hessen et al., 1997; Carpenter et al., 1998; Downing et al., 1999 )

Ｎ輸出 Spatial patterns within the landscapes, such as the location, distribution and proportions of watershed areas can crucially affect N exports。陸地的空間形質，例如集水區的位置、分布、大小是決定Ｎ輸出的關鍵。 (Jordan et al., 1993; Hunsaker and Levine, 1995; Hill, 1996; Creed and Band, 1998; Hillbricht-Ilkowska et al., 2000)

Landscape elements modify movements of N discharge to waterbodies。地貌結構元素可以減緩N進入水體的速率。 （Forman and Gordon, 1986; Turner, 1987; Ryszkowski,1989）

溼地或緩衝帶 There is increasing interest in providing various traps or sink structures (wetlands, buffer zones, etc.) on water pathways to slow down transportation and cycling of nutrients within agricultural watersheds：於農業集水區的水流路逕上利用溼地或緩衝帶可降低營養源移動增加循環利用。 （Dickey and Vanderholm, 1981; Cooper et al., 1987; Pomogyi,1993; Fleischer et al., 1994; Leonardson et al., 1994; Kuusemets and Mander, 2002）

Agriculture, Ecosystems and Environment 107 (2005) 381–396 The role of diversified landscape buffer structures for water quality improvement in an agricultural watershed, North China 不同結構緩衝之水質改善-中國北部農業集水區 X.H. Wang, C.Q. Yin *, B.Q. Shan SKLEAC, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, PR China Agriculture, Ecosystems and Environment 107 (2005) 381–396

Abstract Experiments were conducted in a headwater agricultural watershed in North China to study the hydrological and ecological interactions between complex landscapes and nitrogen (N) flow. 該實驗透過複合地景與氮流研究農業水源總氮量變化，探討水文與生態的交互作用。 It was found that a series of artificial and natural buffer/detention landscape structures, which include試區有一系列的人工及天然緩衝構造 1. four stone dams (SDs),4個石壩、 2. a roadside grassed ditch (RGD),1個路側草溝、 3. a vegetated filter strip (VFS), 1個植生濾帶、 4. two dry ponds (DPs) , 2個乾式池、 5. a riparian buffer zone (RBZ), to study. 1個岸邊的緩衝綠帶。 distributed along the ephemeral stream, could effectively reduce the export load of sediment and N in surface runoff.水流只要暫時分散流入緩衝結構，就可減低表面逕流中的土砂及N。

The objectives of this study were to explicate the hydrological and ecological processes of N transportation in a typical agricultural landscape of North China and to compare the stability and efficiency of different types of landscape buffer structures. 　該研究以氮在水文及生態輸送過程，比較中國北方典型農業地景中不同緩衝結構的穩定性與效益。

一、The study area Yuqiao Reservoir is the source of drinking water for Tianjin, the third largest city of China. The Taohuasi watershed is located on the north bank of the reservoir with an area of 248.9 ha。於橋水庫是中國第三大城天津市的主要飲用水來源，面積248.9 ha的桃花寺集水區是水庫北部主要的水源。

集水區地形 The topography of the watershed shows a transition pattern of mountainous area to plain from north to south with an elevation from 310 to 17 m above Bohai Sea level and with a steep (>250) to gentle (<50) slope.集水區海拔由北到南310m到17m，陡坡>250 ，平緩地區則<50 。

海拔↓310 to 17 m

land use The main forms of land use in the Taohuasi watershed are hilly land and cropland occupying 49.3 and 29.6% of the total area, respectively. Other land uses make up about 21.1%。 桃花寺集水區主要土地使用： 坡地 49.3％ 農田 29.6％ 其他 21.1％

生物污染源 There are 288 residents in theTaohuasi village and they raise about 6000 chickens, 80 pigs, 100 goats,20 cows and 50 deer。桃花寺村居民約288人，養殖約6000隻雞、80隻豬、100隻羊、20頭母牛及50隻鹿。 Most of the waste produced by the poultry and livestock is typically piled openly on the ground before being applied to the orchard and farmland.大部分牲畜排泄物，在做為果園與農田的肥料之前，是直接暴露在陸地上。

生物污染源 The farmers use dry toilets and most solid wastes are used as manure after fermentation. There are no wastewater treatment facilities. Most waste is spread openly on the ground.農人使用乾式廁所，且無廢水處理，排泄的固體廢棄物直接暴露在地面。 When it rains, the polluted runoff formed as a result of drainage through the piled manure,the courtyards and the streets flows into an ephemeral stream near the village and is transported downstream.當降雨時，糞便污染物便藉由逕流從庭院流入村莊附近的蝕溝。

肥料污染源 Farmers apply compound fertilizer and urea to crops as the basic and supplement nutrients. The amount applied is 400 kgN/ ha by top-dressing. 農人應用化學肥料及尿素作為主要的農地營養源，表土使用量為400KgN/ha。 During rainfall events, the nutrients are picked up by surface runoff and transported to the stream channel nearby. 下雨時，這些營養源就從表面逕流，流入附近的水溝。

Watershed climate and flow characteristics The climate of the watershed is characterized by warm summers and cold winters.　The mean annual temperature is 11.5℃. Long-term average precipitation is 748.5 mm and 80% of the rainfall occurs from June to August.集水區氣候夏暖冬寒。年均溫為11.5℃，平均降雨量748.5 mm ，80%的降雨集中在1月到8月。

流況 Water only flows in the stream channel during rainfall events in which surface runoff is generated.只有在降雨，產生表面逕流時，溝渠才會有水。 This watershed responds rapidly to rainfall and surface flow occurs for less than 24 h.集水區反應下雨及表面逕流的時間，低於24小時。

Characteristics of rainfall events in this watershed are high intensity and short duration. The main runoff yield pattern is infiltration excess runoff pattern.降雨通常急促而短暫。主要流失的營養源是來自於滲入土地內部的。 Surface runoff initiates as long as the rainfall intensity exceeds the infiltration capacity of soil and mostly in the early stage during a rainfall event.地表逕流多在降雨初期發生。 In short time, the pollutants could be transported by the surface runoff to the waterbodies downstream在這短暫的地面逕流時間內，污染物就已經流入水體中了。

2002－2003 21場降雨：5場連續及16場短暫

Sampling method and sample analysis The investigation was conducted from autumn 2001 to autumn 2003. 研究期間為2001年秋天到2003年秋天。 In this research, we chose 選擇緩衝結構： 1. four stone dams (SDs),4個石壩、 2. a roadside grassed ditch (RGD),1個路側草溝、 3. a vegetated filter strip (VFS), 1個植生濾帶、 4. two dry ponds (DPs) , 2個乾式池、 5. a riparian buffer zone (RBZ), to study. 1個岸邊的緩衝綠帶。

These structures were selected and not any of others because of their well hydrological continuity from the south of the hilly land to the outlet of the watershed and being looked upon as a combined landscape structure system dealing with the polluted runoff from various land uses near the stream channel.選擇研究這些結構，主要係因為一串不同結構恰好連續分布在水流路徑上，且流經河道邊不同土地利用之陸地污染。

(roadside grassed ditch ) (four stone dams) (roadside grassed ditch ) (vegetated filter strip ) (two dry ponds ) (riparian buffer zone )

監測點 Four stone dams were close to the village and could receive the polluted runoff from village and orchard during the period of rainfall events.4個石壩靠近村莊，因此在降雨時，會接受到來自村莊的污染物。 A series of sampling sites was installed from inlet to outlet of each buffer structure to study detailed processes during N flow crossing.在各個緩衝結構的入口及出口處安置連續的採樣點，以便研究詳細的N流。 These sampling sites included 28 sites to monitor surface flow in the stream channel and 5 of tributary flow from different land uses along the stream channel.有28個監測點監測主要的表面水流，5個監測溝渠。

監測採樣 During a rainfall-runoff event, the sampling volunteers（farmers who had sampling experience ） were divided into groups of three to five, according to the event size. The time of sampling on the hydrograph was recorded.降雨時，由具有採樣經驗的農人協助採樣，並紀錄時間。 We tried our best to keep the same series of samples being taken at the same time.一連續的採樣點，盡量於相同時間採樣。

逕流量測量 The discharge of runoff was continuously measured through V-notch concrete flumes which were all of 1200 notches, while water velocity was measured in two ways.利用1200 V形堰及兩種方式測量逕流量。 (1) When there was low water depth or dense vegetation, the use of a kinemometer was restricted and the flow velocity estimation was accomplished by measuring the tracer velocity of small plastic buoys.若水不深且植物覆蓋密集，流速計無法使用，利用塑膠浮子測量流量。 (2) When the water depth was deep enough, a kinemometer could be used. 水深夠時，就可使用流速計測量流量。 There was a V-notch weir in the inlet and outlet of each structure. Flow-proportional samples (4–10 subsamples/runoff event) were taken at each site.每個緩衝結構的進口與出口都裝V形堰。大約10個逕流事件可採樣4個。

逕流水樣 Samples of runoff water were taken in plastic bottles and mid-depth of runoff water at the monitoring sites when surface runoff was generated in a rainfall event.降雨時，於監測點以塑膠瓶採取一半深度處的逕流水，採取水樣。 Water samples were taken at 10 min or longer intervals depending on the duration of the event。每個水樣採取以降雨延時為依據，約採取10min或更長。

sample analysis 1. After sampling, 250 mL aliquots were filtered by pre-weighed 0.45 mm Millipore filters. Filters were then dried and reweighed to quantify total suspended solid (TSS). 250 mL 水樣以秤過重的濾紙過濾，過濾後濾紙烘乾再度秤重，重量差為總懸浮固體(TSS) 。 2. The filtrate was reserved for measuring dissolved constituents of total dissolved nitrogen(TDN), NO3-, NH4+ and the unfiltered samples wereused for measuring total nitrogen (TN).濾液測總可溶性氮(TDN) ，包括硝酸鹽氮(NO3-)及氨氮(NH4+ )，未過濾的水樣則測總氮(TN).

3. The filtered and unfiltered water samples were stored in a refrigerator at 4 ℃ and analyzed at the State Key Laboratory of Environmental Aquatic Chemistry within 48 h after sampling. All analyses were oneaccording to Standard Methods。過濾與未過濾的水樣保存在4 ℃ 冰箱，在48小時內以標準分析方法檢驗。

Calculation of sediment and N retention The retention efficiency of sediment and N for each buffer structure and for the whole system was calculated from flow-weighted mean concentration and runoff volume when it entered and left the structure. 每個緩衝結構以及整個系統的泥砂與N的滯留效率，以重量加權平均濃度及進出結構的逕流量計算。 Pollutants carried by tributaries were incorporated into the total import load of the corresponding structure to calculate the retention efficiency.支流的污染物併入相對應的結構，計算滯留效率。

計算滯留效率 The retention rate of the structure (or the system) was calculated using the following formula:結構的滯留效率計算方式如下： QPIi 、 QPOi ： inflow and outflow volume of the structure (m3), CPIi 、 CPOi ： flow-weighted mean concentrations in inflow and outflow of the structure (kg/m3), MPIi 、 MPOi： total pollutants mass in inflow and outflow of the structure (kg), i ：landscape structure number (1, SDs; 2,RGD; 3, VFS; 4, DPs; 5, RBZ), R ：the retention rate

3.Results and discussion

3.1 Diversified landscape buffer structures

The surface pathway Between these structures, there are no other buffer structures in the stream channel. 整個流路無其他緩衝結構。

Stone dams and Roadside ditches 1. Stone dams are small dams made of rocks constructed across the stream channel. In the 1960s, these stone dams were built to reduce channel erosion.石壩是在1960年代為攔截河道侵蝕，而以石塊所建置的小壩。 2. Roadside ditches are a common feature of the road section, conveying water parallel to the driving lanes. The soil surface of these ditches is covered with annual vegetation from spring to autumn。路邊溝道用於輸送與道路平行的水流，溝道的表面在春天到秋天這期間，覆蓋著天然植生。

vegetated filter strip To the south of the road, the stream channel crosses a large area of cropland. Abundant vegetation growing in the channel forms a long natural vegetated filter strip. Vegetation is comprised of sage (Salvia officinalis L.) and wormwood(Artemisia absinthium L.).道路南面穿過大片農田，溝道長滿以鼠尾草和亞洲苦艾為主的植物，形成一段植生綠帶。 The vegetated filter strip located in a relatively gentle relief is in a natural condition, and is not subject to human disturbance. 植生綠帶是天然且無人為介入所形成的。

Dry ponds There are many dry ponds distributed over the village, cropland, stream channel and reservoir bank.集水區坡面及河道遍布很多乾水池。 These ponds were artificially made for different purposes, including fish farming, irrigation and washing etc. 多為因應不同用途建置，例如養魚、灌溉及洗滌等 They can temporarily store some of the runoff following a storm. The storage capacity depends on their volume. 這些水池可以暫時儲存暴雨時的逕流水，儲存量取決於水池的量體。

Riparian buffer zone Abundant grasses cover the water table fluctuation zones of reservoir and this area can be regarded as a kind of buffer zone or land-water ecotone.濱水區被草類大量覆蓋，形成一個濱溪生態緩衝帶。 When polluted runoff enters this zone, the pollutan ts can be retained through various biological and chemical reactions. These retention mechanisms include sedimentation, uptake by vegetation and denitrification.當污染物進入這個緩衝帶，會因為生物與化學反應而滯留，機制包括沉砂、植物吸收及去硝化。

The primary retention mechanism of nutrients is sedimentation which results from the stilling effect of detention, allowing heavier sediments to settle by gravity, leaving a suspension.營養物主要的滯留機制為沉澱，因靜置而滯留，使得較重的泥砂不再懸浮而沉澱。 The longer the detention time within the ponds, the greater the amount of nutrients that will be retained.靜置時間越長，越多的營養物被滯留下來。 The pond overflows only when the water volume is in excess of its storage capacity. 當水體積大於水池容量時，池水將會溢流。 The two ponds selected as part of our research project are located in the downstream area.監測的兩個水池位於樣區的下游。

3.2 N concentration variation in the flowpath The concentrations of sediments and N pollutants were greatly affected by the landscape buffer structures during the transportation of the polluted runoff in the flow pathway。土砂和N的濃度，受到逕流過程中的緩衝結構很大的影響。 In the Taohuasi watershed, there are two types of surface runoff during a rainfall-runoff event: continuous runoff and discontinuous runoff。桃花寺集水區的逕流，可分為連續逕流及間歇逕流。

Continuous flow is generated only during a heavy rainfall event, in which water flow is transported from the upstream to the outlet of the watershed.連續逕流發生於大雨時，水由上游流向集水區出口。 Discontinuous flow is usually generated during a gentle rainfall, in which water flow is divided into several segments with little or no outflow exported from the watershed.間歇逕流發生於緩和降雨時，水流為指狀流，甚少或完全未流出集水區。 In both types of events, the concentration of sediments and N pollutants in the flowpath increased with the input of tributaries from various agricultural land uses (especially in village area) and gradually decreased as the runoff passed through each structure.這兩種水流都因農業經營與村莊的支流匯入，增加了土砂及N的濃度；也都因經過各個緩衝結構而濃度下降。

N concentration variation in the flowpath four stone dams roadside grassed ditch vegetated filter strip riparian buffer zone two dry ponds

four stone dams After passing through the four stone dams, particulate materials were largely retained. But the proportion of dissolved N pollutants (TDN, NO3-, NH4+) retained was small.經過4個石壩的流體，微粒狀的汙染物濃度大量減低，可溶性N污染(如總可溶N、硝酸鹽、銨鹽)的滯留量小。 This perhaps attributed to the low uptake quantity of N and low infiltration.由數據得知，石壩對N的過濾效果低。 大 小

roadside grassed ditch TSS in the inflow and the outflow of roadside grassed ditch was 1.08 and 0.65 g/L, respectively. While for N, the concentration presented a fluctuation pattern in this section.總懸浮固體TSS的量在經過路邊草溝時，由1.08降至0.65g/L。N濃度則呈現波動的變化。 The lack of effective management measures, occasional destructive events and the accumulation of trash at the bottom of the ditch.滯留效率不足的因素可是因草溝的管理不良，偶而會有垃圾沉積造成破壞。

vegetated filter strip The concentration of sediment and N pollutants decreased gradually as the runoff was transported in the vegetated filter strip.經過綠帶後，逕流的土砂及N污染物的濃度減少。 This strip was in a natural, less disturbed state. 這個綠帶是天然與穩定的。 The vegetated filter strip effectively reduced the concentration of various forms of N.綠帶的效率取決於N的形式。(硝酸鹽效率大於銨鹽) 下降 多

Dry ponds During polluted runoff transportation through dry ponds and the riparian buffer zone, the concentration of sediment and N was reduced further. 經過乾水池，逕流的土砂及N污染物的濃度亦減少。 The reduction of dissolved N pollutants (TDN, NO3-, NH4+) was not as significant as that of TSS and TN in the ponds zone.可溶性N降低的量沒有總懸浮固體與總N明顯。 This meant that the dry ponds were more effective in the reduction of particulate pollutants than dissolved forms. 證明乾式池對微粒狀的汙染物效率高於可溶性污染物。 下 降 多 少

Discontinuous runoff The reduction of TSS and N concentration was more rapid.在間歇逕流中，總懸浮固體和N的濃度更快被攔截。

The reduction of TSS and N concentration was more rapid The reduction of TSS and N concentration was more rapid. Under both continuous and discontinuous hydrological conditions, the buffer structures system effectively the concentration of TSS and N in surface runoff. 無論是持續或間歇的逕流，緩衝結構都可以減少逕流中的總懸浮固體TSS與N濃度。

3.3 Sediment and N retention 3.3.1. Retention efficiency of the buffer structure.緩衝結構之滯留效率。 3.3.2. Retention efficiency of single structure.各單一緩衝結構之滯留效率。 3.3.3. Stability of retention performance by single structure.各單一緩衝結構之行穩定性。 3.4. Primary control mechanisms for sediment and N retention.土砂與氮的控制機制。

3.3.1. Retention efficiency of the buffer structure SH：surface runoff from hilly land; 坡地逕流 SV：surface runoff from village;村莊逕流 SO：surface runoff from orchard;果園逕流 SC： surface runoff from cropland.農田逕流

Retention efficiency of stone dams and ponds During the continuous runoff event，the retention rate of water by the whole system was 50.2%. The capacity of these buffer structures is well below the theoretical maximum.在持續逕流時，整個緩衝系統的滯留效率達到50.2％，效果低於理論值。 This is possibly because:

(i) Due to the problem of filling up by alluvial soil, the capacity of stone dams was decreased to a great extent compared with the design standards.因為沖積土淤積，使得石壩的容量比當初設計時減低。 (ii) The dams and ponds remain partly full between rainfall events.在兩次降雨之間，石壩與乾式池的攔截水流未消退。 (iii) Four stone dams studied in this research had some rifts in the constituting rocks resulting in penetrating of water and decrease of storage capacity.這個研究中的4個石壩有裂縫，使得水流流出，減低蓄水容量。

During the discontinuous runoff events on 4 August 2002, the buffer structures system was all capable of markedly reducing the export load of sediment and N from the watershed.2002年8月4日的間歇逕流，整體緩衝結構都能完全攔截從集水區流出的土砂及N。

is mainly in the early stage of a Although local soils are susceptible to erosion, the erosion (TSS) loss and the volume of surface runoff during a rainfall event was relatively low in the experimental watershed. This was possibly because:雖然局部的土壤敏感易流失，但降雨時流失的量(TSS) 與逕流量的關聯性低，可能原因為： (i) Under the infiltration excess runoff pattern in North China, runoff volume directly depends on rainfall intensity and does not occur at sufficiently low intensities. High intensity of rainfall rainfall event in North China and this period is short. Thus, most of rainwater infiltrates the soil during a rainfall event。 (i)逕流的發生取決於降雨強度，中國北部的降雨強度低。只有在降雨初期才發生短暫而強的降雨情形。所以大部分的降雨都入滲進入土壤。

(ii) Water content of soil usually is very low before a rainfall event in North China for the dry climate. During the rain, dry soil can absorb a large quantity of rainwater and decreases the runoff volume further. (ii)降雨前的土壤水分含量通常相當的低，所以逕流量低。 (iii) There had many other stone dams in the upstream of the ephemeral stream and several dry ponds in the watershed besides the stone dams and ponds we have studied. These stone dams and ponds could intercept a large quantity of eroding soil and surface runoff before their flows enter the monitoring sites. (iii)在樣區上游仍有一些石壩、蝕溝、水池，這些構造會截斷大量土砂及逕流進入樣區。

3.3.2. Retention efficiency of single structure Retention rate (mean±standard deviation, %) of water and pollutants of single structure during different types of rainfall-runoff events。各個緩衝結構的滯留效率 (1) (2) (4) (3) (5)

(1)During the continuous runoff event on 22 June 2003, due to the huge storage capacity and long detention time, dry ponds had the highest retention rate of water, TSS and TN. Their retention rates were 31.8, 42.7 and 32.7%,respectively.在持續逕流，乾式池具有很大的儲存量及滯留時間，因此乾式池對水、總懸浮固體和總N量為最大的滯留速率，其值各為31.8, 42.7 and 32.7%。 (2) The vegetated filter strip had the highest retention rates for dissolved forms of TDN, NO3-,NH4+ of 32.1, 23.0 and 28.1%, respectively。植生帶對溶解性污染物有最高的緩衝效率。

(3) The riparian buffer zone had a higher retention rate of NO3- possibly due to its high potential for denitrification。岸邊的緩衝帶對硝酸鹽NO3- 具最高滯留效率。 (4) The stone dams had a high retention rate of sediment and TN as they reduced the runoff velocity and led to the formation of better detention conditions for particulate matter.石壩對土砂及總N具有最高滯留效率。

(5)The retention rate of N pollutants by the roadside grassed ditch was low, possibly because of intensive disturbances by human activities.因為人為活動的干擾，路邊草溝對N污染物的滯留效率很低。 This result suggested that without proper management and maintenance, the performance of these structures would fall below expectations. 研究的結果指出 ，如果沒有適當的經營與維護，緩衝結構無法達到期望的效果。

Retention (mean standard deviation) of water and pollutants by single structure during 5 continuous runoff events (a)

Retention (mean standard deviation) of water and pollutants by single structure during 16 discontinuous runoff events(b)

3.3.3. Stability of retention performance by single structure A statistical analysis of rainfall-runoff events of all five continuous and sixteen discontinuous runoff events, revealed that the stability of the structures (based on the coefficient of variation (CV) values of the retention performance dataset) differed significantly。利用統計分析5個持續及16個間歇降雨逕流，得到展現結構穩定性的CV值。 The CV of retention rates in discontinuous events was lower than that of continuous events. This suggests that the retention performance of these structures was more stable in the discontinuous runoff condition. 間歇逕流的CV值比持續徑留低。這樣的結果指出這些結構的間歇逕流穩定性比持續逕流高。

Stability of retention performance by single structure 穩定度高 最高 最低

Under the continuous or dis continuous runoff conditions, the vegetated filter strip, dry ponds and the riparian buffer zone were more steady than the roadside grassed ditch and stone dams.無論是在持續或間歇逕流情況下，植生綠帶(VFS)、乾式池(DP)、岸邊緩衝帶(RBZ)的穩定性，比路邊草溝(RGD)及石壩(SD)高。

3.4. Primary control mechanisms for sediment and N retention All processes which occur in the watershed are closely connected with hydrological conditions.所有發生於集水區的過程都與水文密切相關。 As a system composed of many types of buffer/detention landscape structures, the latter can cause decline in conduit capacity and an increase in the retention of water and N pollutants through their hydrological control on flow velocity and runoff volume.因為系統中設置多種緩衝結構，藉由控制流速與逕流量，可增加水及N污染物的滯留時間。

During the continuous runoff event on 22 June 2003 In the ponds zone, the flow velocity of outlet is very low (4.4 cm/s) due to a sharp decrease in kinetic energy.由乾式池流出的流速非常小，因為流體的動能銳減。 支流匯入 流速突然增大 石壩 乾式池 路邊草溝 植生綠帶 岸邊緩衝帶 經過緩衝結構 流速減小

During the discontinuous runoff event on 4 August 2002 During this event, no runoff entered the last seven monitoring sites (the buffer zone) because no water was exported from the outlet of the dry ponds.間歇逕流時，未監測到緩衝帶末端流出逕流，因為沒有水流從乾式池流出。 支流匯入 流速突然增大 石壩 乾式池 路邊草溝 植生綠帶

Primary control mechanisms for sediment and N retention 出口流量降低最多 (乾式池) 沒有水從乾式池流出 (無逕流)

Runoff volume was reduced from the inlet to outlet of the system for infiltration or storing by each structure. The decrease in runoff volume further reduces the flow kinetic energy.逕流量會因為各緩衝結構內的入滲及儲存而減少，亦會因為流體動能的減少而減量。 In the continuous runoff event,the ponds zone, the volume of reduction was larger.在持續逕流情形下，乾式池的滯留量比其他多。 In the discontinuous runoff event, the decreased runoff volume was more notable as a result of the relatively small runoff volume.在間歇逕流中，乾式池並無逕流流出，乾式池的滯留效果更為顯著。

Hydrological control by these structures is the primary control mechanisms of this system which decreases the kinetic energy of the runoff, reduces channel erosion and, because of the prolonged detention time, provides favorable conditions for the retention and transformation of sediment and N.這些結構的水文控制是系統最基本的控制機制，因為可以減少逕流的動能、避免河道的侵蝕，以及因為延長滯留時間預防土砂與N的流失。 And the longer detention time created favorable conditions for biological, chemical and physical reactions that can lead to the removal of pollutants.長的滯留時間，提供生物、化學及物理反應以移除污染物。 The results of this research show that a landscape buffer structures system is effective in the reduction of the export load of sediment and N by surface flow on watershed scale , especially those areas with relatively dry climates. 緩衝結構可以有效的阻止土砂及N由表面逕流流出坡地集水區，尤其是乾燥氣候的地區。

N pollutants (especially for nitrate) also can be transported by underground flow under appropriate conditions. N污染物，尤其是硝酸鹽，有可能藉由地下水輸送。 Downward percolation from water held by buffer structures probably contributes a part to this flow, taking with it a proportion of dissolved N.由水流滲入緩衝結構的可溶性含氮化合物，可能會造成地下水污染。 For the buffer structures being covered by flourish vegetation, the fate of nutrients in the form of biomass is also important for the control effect of nutrients flow.如果緩衝結構覆蓋著茂密的植生，其生物量也能有效控制營養源。 Vegetation should be harvested in appropriate time and take part in the recycling process of nutrients in the watershed ecosystem so as to avoid being flushed downstream when stream flow is strong enough.植物會吸收營養源，進入生態系再循環，就可以避免過大的逕流將營養源流到下游。 For the longer-term improvement in downstream water quality, good management and maintenance of these structures is necessary.為改善下游水質，緩衝結構需要妥善的經營與維護。

1. During discontinuous events, these retention rates were higher 2. Dry ponds and stone dams are more effective for the retention of particulate N, while the vegetated filter strip and riparian buffer zone are more effective for dissolved N forms.乾式池對微粒氮化物的滯留效率佳，植生綠帶對可溶性氮化物滯留效率佳。 3. The dry pond was the reliable structure for controlling pollutants export in this watershed, while the roadside grassed ditch was highly unstable.乾式池是阻止污染物進入集水區的可靠緩衝裝置，而路邊草溝的穩定性相對較差。

4. Hydrological control by this system of flow velocity and runoff volume was the main mechanism in the reduction of sediment and N.系統的流速和逕流量之水文控制，是影響土砂與N的主要機制。 5. These landscape buffer structures decrease the kinetic energy of runoff and, as the result of the prolonged detention time, provide good conditions for the retention and transformation of sediment and N.整個緩衝結構藉著降低逕流動能，延長滯留時間，使土砂與N滯留。