水生大型無脊椎動物群集於人工溼地之時空變化及生物調控機制

Abstract

表面流人工溼地（SFCW）主要由數個相互連接，但擁有不同污水處理機制的單元（處理池）組成，不同處理池的建造亦配合了現地的形貌特徵。因為人工溼地內部不同處理單元漸進式的污水淨化及營養鹽去除機制，污水從最開始的處理單元到最後的處理池的淨化過程中，一個與整體溼地生物、環境因子變化相關的環境壓力梯度會隨之而產生。本研究之假說為底棲大型無脊椎動物群集結構會因應不同棲地條件的表面流人工溼地，以及溼地中不同處理池之環境壓力梯度而變化。因此，我們於2009-2010年於臺灣北部打鳥埤人工溼地(DN)及新海二期人工溼地(HS2)進行底棲大型無脊椎動物群集時空變化及其結構調控機制的研究。 研究結果顯示無脊椎動物群集的總豐度（總個數/m2）及生物多樣性（類群豐富度）在兩個人工溼地都會受到環境壓力梯度的影響，並且會隨著污水處理池子的漸進式處理而呈現顯著的上升（總豐度：五號池 > 四號池 > 三號池）。無脊椎生物群集之物種多樣性（類群豐富度，1/D及exp H’） 於DN顯著高於HS2。此外，本研究結果也顯示對無脊椎動物群集之總豐度最具影響力的環境因子為水溫、導電度、氧化還原電位、硝化/脫硝作用。本研究證實在生物多樣性及均勻度較低的新建表面流人工溼地中，無脊椎動物群集的總豐度可以有效的作為環境壓力梯度的監測指標。 探討人工溼地內生物之下行（捕食者與被捕食者之關係）與上行（消費者與生產者之關係）作用能作為了解溼地生態系統內生物群集結構之時空變化性與其構建機制之基礎，藉此了解如何促進溼地生態系統之穩定性。因此，本研究藉生物調控實驗（隔絕捕食者）探討相關機制以驗證水生無脊椎生物群集結構在人工溼地內同時受上行及下行調控影響之假說。本研究結果顯示魚類為下行調控之主要執行者因為無脊椎生物之群集結構在隔絕處理之樣本（無魚）之總豐度及生物多樣性（物種數）都顯著高於無隔絕處理之樣本（有魚），而鳥類之捕食效應對於無脊椎生物群集結構則不顯著，並只對特定之類群（如雙翅目）有著顯著的影響。典型相關分析（CCA）及逐步回顧分析（step-wise regression）之結果顯示無脊椎生物群集結構同時受上行（如：氨氮、總磷、溶氧、氧化還原電位；r2 = 11.51-55.69%）及下行（r2， 無魚 = 15.32-55.69%; 有魚 = 8.72-37.27%）所影響。綜合本研究之之結果，證實新SFCWs之生物群集結構主要受到上行調控所支配，而本實驗兩個研究溼地皆為資源控制之生態系統。 本研究提供了重要的人工溼地管理建議，即為主要捕食者（魚）之數量控制或維持人工溼地之無魚環境，以及透過適當的人為干擾事件（如定期的乾水/洪水淹沒期）作為減少少數環境高耐受性之優勢物種對於溼地水生無脊椎生物群集的長期支配，同時提高溼地內的生物多樣性。因此，本研究結果為未來溼地復育之永續管理策略提供了重要的導向性資料。

Surface-flow constructed wetland (SFCW) is established from interconnected ponds fitted into different local landscapes. As the consequence of all different removal mechanisms of progressive wastewater treatment stages in the SFCW, gradients of environmental stresses associated with the change of bio-physiochemical variables across wastewater treatment ponds could be resulted (bottom-up regulation). We hypothesized that the community structure of benthic macroinvertebrates not only changed in response to environmental stress gradients, i.e. across wastewater treatment ponds within our study SFCWs but also varied between our study SFCWs with different habitat conditions. We found significant increase in taxon richness (no. of taxa) and total abundance (indv/m2) of benthic macroinvertebrates from treatment pond 3 to pond 4 and 5 along wastewater treatment gradient in both DN and HS2 during the two study seasons. Benthic macroinvertebrate biodiversity (taxon richness, exp H’, 1/D) was significantly higher in DN than HS2. Our results also demonstrated that NO3-N, water temperature, conductivity, ORP, nitrification/denitrification were most influential environmental factors on benthic macroinvertebrate community in our study SFCWs. We suggested that total abundance of benthic macroinvertebrates could be used to indicate the environmental changes/stresses in the newly established SFCWs in particular when the the biodiversity and taxa evenness were low. As understanding the interactions between top-down (i.e. predator-prey relationship) and bottom-up (i.e. consumer-resource relationship) regulations are important for studying the spatiotemporal variation of biological community and useful for enhancing the ecological integrity of constructed wetland ecosystems, we carried out predator (fish/bird) manipulative experiment aiming to determine the relative importance of top-down and bottom-up regulations of the benthic macroinvertebrate community structure in SFCWs. Our results indicated that fish was the major top-down agent in our study SFCWs as bird predation only influenced the abundance of one particular taxa, i.e. Diptera, but the macroinvertebrate community structure and most of the dominant taxa were significantly higher in fish exclusion treatment than treatment control (non-excluded of fish) (P < 0.05). Both CCA and stepwise multiple regressions indicated that the benthic macroinvertebrate community structure were simultaneously influenced by both bottom-up (e.g. NH4-N, T-P, DO, ORP; r2 = 11.51-55.69%) and top-down regulations [r2: Nf = 15.32-55.69%; Nn = 8.72-37.27%)]. However, our results demonstrated that the bottom-up forces dominating benthic macroinvertebrate community in both DN and HS2, and this revealed that these two SFCWs were resource-control ecosystems. Results from the present study suggested that it would be important to (1) limit of the abundance of predatory fish abundance (or even maintain as fishless condition) and (2) maintain the environmental disturbance such as variation in water duration and periodic drying events in the newly established SFCWs to avoid over-dominance of tolerant taxa and enhance the wetland biodiversity. As we provided important information for understanding the structuring mechanisms of benthic macroinvertebrate community in newly established SFCWs, our results could be useful for the development of biodiversity management strategies based on biomanipulation approach for wetlands restoration.