4.1 水質調查結果
表 4.1 所示為台北縣二重疏洪道濕地水質，於九十二年二月份採樣之分析 調查結果。二沖疏洪道濕地基本上係屬於半鹹淡沼澤濕地地形，水生植物生長 行係已蘆葦及香蒲為主，此乃因由於該濕地係屬於受疏洪道出口之淡水河潮汐 影響。由於本研究計畫要以該濕地進行濕地水文及水理調查及濕地模式的建立 及模擬，因此共計採集水樣十點。由表 4.1 可知，該濕地十個測站之平均 pH 值接近中性，表示該濕地仍以受到淡水之影響為主。再由該十個測站之鹽度分 析結果可知，接近淡水河口採樣站(H1 及 H2)之鹽度皆超過 15‰，亦表示此部 分之濕地水質為半鹹淡水，應屬鹽沼之特性，至於其他測站之鹽度測値顯示，
該濕地係屬於淡水性濕地。在 DO 測值方面，十測站皆低於 3.0 mg/L，且第 H2 及 H5 測站(靠近疏洪道岸邊之濕地)之量測值甚至低於 2.0 mg/L，表示這些 地區濕地的水質受到兩旁道路、住宅及工商業的污染，至使濕地水中溶氧量降 低。雖然各個測站的 DO 值偏低，但是其生化需氧量(BOD)卻明顯分為二個不 同量級，H1 至 H5 靠近出水口淡水河部分的 BOD 測値較低，而從 L1 至 L5 靠 近五股工業區附近之濕地水質的 BOD 測値則較偏高。至於懸浮固體物(SS)測 值則十個測站的分析數據均接近，均不大於 50 mg/L，而平均值為 35.0 mg/L。
此一結果有可能是由於採樣的時間並非洪水期，至使上游溪流中泥沙含量較 低，但是有機污染物含量則較高，因而造成 BOD 偏高，而 SS 測值之則偏低的 現象發生；但也有可能是附近之各類污水之直接排入，抑或由附近污染之排水 獲悉流入滲所造成。至於濕地中營養鹽的濃度分佈亦可由各個測站中所分析之 氮及磷等營養鹽之數值可知。由表 4.1 中可知，十個測站不論是氨氮(NH3-N)
或總凱氏氮(TKN)，其測值如同 BOD 値一樣，亦可分為兩個量級，即 H1 至 SS(mg/l) 24.20 28.80 36.40 30.20 38.00 43.00 33.60 35.40 39.80 35.20 BOD(mg/l) 1.01 4.04 22.21 18.17 15.15 17.67 20.70 21.20 21.20 17.17 COD(mg/l) -- -- -- -- 49.02 -- -- -- -- 21.10 NO2 (mg/l) 0.051 0.073 0.240 0.243 0.284 0.195 0.243 0.267 0.284 0.266 NO3(mg/l) 0.163 0.041 0.496 0.528 0.528 0.415 0.453 0.593 0.684 0.634 TKN 總量
(mg/l) 6.17 20.70 36.94 35.17 27.13 17.81 19.42 23.27 14.27 10.67 TKN 溶解
(mg/l) 4.65 6.82 17.01 16.85 11.80 17.65 3.34 22.31 14.11 9.93 NH3 總量
(mg/l) 5.388 6.738 16.845 14.435 11.863 16.685 17.167 21.185 12.667 10.256 NH3 溶解
(mg/l) 4.591 4.880 12.797 12.154 6.689 13.440 2.863 18.261 7.332 6.881 有機氮
總量(mg/l) 0.784 13.965 20.090 20.733 15.269 1.125 2.250 2.089 1.607 0.417 有機氮
表 4.1 台北縣二重疏洪道濕地各個測站水質分析結果 (續)
採樣站
項目
H1 H2 H3 H4 H5 L1 L2 L3 L4 L5
TP 溶解
(mg/l) 0.479 0.617 1.960 1.927 2.229 1.818 1.641 1.893 1.969 2.308
PO4 總量
(mg/l) 0.414 0.625 1.860 2.036 2.070 1.641 1.700 1.616 1.910 2.137
PO4 溶解
(mg/l) 0.320 0.380 1.389 1.457 1.541 1.121 1.188 1.171 1.541 1.599 顆粒性 PO4
(mg/l) 0.094 0.245 0.470 0.579 0.529 0.521 0.512 0.445 0.370 0.538 有機磷
總量(mg/l) 0.084 0.260 0.126 0.017 0.420 0.269 0.042 0.336 0.314 0.188
有機磷
溶解(mg/l) 0.160 0.236 0.571 0.470 0.689 0.697 0.454 0.722 0.428 0.709 葉綠素 a
(mg/m3) 0.0019 0.0034 0.0136 0.0143 0.0131 0.0146 0.0134 0.0136 0.0117 0.0096
「--」表示受鹵素離子干擾，無法檢測
知整各濕地系統的水質係呈現厭氧的還原狀態。而各個不同型態磷的濃度，以 及葉綠素 a 之濃度，則於十個測站的測値均不高。因此二重疏洪道的濕地受到 人為污染的影響非常明顯。
4.2 台北縣二重疏洪道濕地質量傳輸模型的建立及模擬分析 4.2.1 模型分析所需之數據蒐集
The receiving water data used to support the model calibration were collected during a survey from November 8, 2002 to April 13, 2003. Salinity, suspended solids, and heavy metals including zinc, copper, and cadmium concentrations in the water column were measured at five locations in the Erh-Chung Flood Way wetland at a frequency of once a month. There values were used for comparison with the model results. Note that there data were tidally averaged. Measurements on the hydraulic geometry of Erh-Chung Flood Way wetland such as average velocity and water column depth were used to develop the model segmentation.
The time series of water surface elevation at the river mouth were measured from November 8, 2002 to April 13, 2003, which shows two high-low cycles in one day and tide elevation range from -0.55 to 0.86 m. The data was obtained from
gauging station G1 located at the downstream boundary. The average flow varied from 0.1 m3/sec to 1 m3/sec at station EC1.
The computational framework chosen to perform the numberical calculations is WASP (water quality analysis simulation program). WASP is a generalized modeling framework for modeling contaminant fate and transport in surface waters and is based on the finite-segment scheme. It is a very versatile program, capable of studying time-variable or steady-state, on, two, or three dimensional, linear or non-linear kinetic water quality programs. To date, WASP has been employed in many modeling applications that have included river, lake, estuarine, and ocean environments and have investigated dissolved oxygen, bacterial,
eutrophication and toxic substance problems.
WASP is the U.S. Environmental Protection Agency’s (EPA’s) latest version of the WASP and it is currently supported and distributed by Center for Exposure Assessment Modeling (CEAM) in Athens, Georgia, U.S.A. EUTRO5 is a
component of WASP5 that is applicable to modeling eutrophication, incorporating eight water quality variables [ammonium, nitrite/nitrate, orthophosphate,
phytoplankton biomass, carbonaceous biochemical oxygen oxygen demand (CBOD), dissolved oxygen, nonliving organic nitrogen, and nonliving organic phosphorus] in the water column and sediment bed. The kinetic structure and interactions between these systems. The reactions involved in EUTRO5 can be considered as due to four interacting systems: phytoplankton kinetics, the
phosphorus cycle, the nitrogen cycle, and the dissolved oxygen balance. Interest reader can refer to Ambrose et al. for details of each of these kinetic processes. In the present study, EUTRO5 was used to develop the mass transport model of the Erh-Chung Flood Way wetland.
The WASP model user manual lists four levels of application/configurations to address different complexities of water quality problems. Recent experience has shown that another levelof configuration is valuable in many modeling application.
For instance, the modeling framework can be used to calculate concentrations of conservative substances (salinity, chloride, specific conductivity, and total
dissolved solids) in mass transport modeling. Further, nonconservative substances can be modeled if they follow simple linear reaction kinetics. Examples of this type of application include total phosphorus or nitrogen (first-order decay from the water column) and total suspended solids (with a settling velocity).
In this study, a one-dimensional configuration of WASP is employed. The corresponding mass balance equation can be written as
d(AC)/dt = d[-U
xAC + E
xA(dC/dx)] + A(S
L + SB) + ASKwhere