新店溪流域大型無脊椎動物之時空變化: 在生物評估之應用

Abstract

本研究於對鄰近都會地區和農業開發活動之新店溪流域，根據不同時間季節及空間環境對其水棲生物之功能攝食群與各樣點之環境參數的相關性進行調查，以瞭解於當地溪流中無脊椎生物功能攝食群於不同環境與季節之群聚結構，並以其用於進行水質監測的指標生物；另外，河川之物理變量，包括海拔高度，河流寬度和與源頭之距離，並利用其和功能攝食群檢測河川連續概念。本研究供選擇7個樣區，自2010年12月至2012年12月，進行定期採樣 。 根據調查結果發現，共有8目46科87屬之水棲昆蟲，及另外3屬非昆蟲之底棲無脊椎生物被記錄；其中主要為脈翅目及雙翅目之幼蟲。其中無論根據Shannon, Simpson, and Pielou’s之指數分析，皆顯示於位於上游之樣區XD2、XD3及XD4 之物種密度與豐度皆高於位於下游之樣區XD5、XD6及XD7；而此結果亦與樣區受到之人為影響相符合。於樣區XD7中以能夠於底棲指標中，代表高度污染的搖蚊屬及貧毛綱為其主要物種。而在所有樣區，聚集者（collector-gatherers）不論時空變換皆為主要物種，亦符合本實驗之預期。 新店溪流域的水棲無脊椎生物之功能攝食群結構明顯受到其時空間變化影響，在不同月份及地點的群聚結構有明顯不同。聚集者（collector-gatherers）不論地點或季節皆為樣區之主要物種。物種豐度、碎食者 (shredders) 及捕食者 (predators) 從上游至下游漸漸減少，其結果符合河川連續概念 (River Continuum Concept)。研究結果顯示溶氧量、導電度、河床底質為卵石或礫石，為影響河流中功能攝食群組成的最主要因素。 而根據本研究之研究結果，根據不同之底棲生物指標，新店溪流域之水質由上游至下游漸漸劣化。簡言之 ，本研究認為以底棲生物作為水域之水質指標有其價值與重要性。

The effect of human impacts on river ecosystem is gaining attention, and concerns about the situation of freshwater natural resources are increasing globally, as are attempts to restore habitat that has been degraded by disturbance. Macroinvertebrates are most commonly used in bioassessment due to their ability of responses to alterations in water quality and provide a more localized assessment to the river condition. In the current study, we describe the spatial and temporal patterns of community structures and functional feeding groups (FFGs) of macroinvertebrates in relation to environmental variables, and assess the water quality using benthic metrics along a reach of the watershed with considerable economic importance at the Xindian watershed in Taiwan. The research was carried out at seven sampling sites (abbreviated as XD1-XD7) which have different human impacts from upstream tributaries to the downstream of the Xindian watershed from December 2010 to December 2012, once per month periodically. A total of eighty seven taxa belonging to forty six families within 8 insect orders, along with 3 other invertebrate taxa, were recorded, with most representative orders of Ephemeroptera and Diptera. In general, the mean values of density, abundance of macroinvertebrates, and diversity indices (Shannon, Simpson, and Pielou’s) were much higher in the upstream-undisturbed sites (XD1, XD2, XD3, and XD4) compared with midstream and downstream-impacted sites (XD5, XD6, and XD7). Collector-gatherers were the most dominant FFG at all sampling sites during the study period. Results of ordination showed that upstream sites were clustered closer which separate from the middle and downstream. The results of the canonical correspondence analysis (CCA) suggested that water quality measures, such as conductivity, ammonia, phosphate, and hardness were the most determinant factors in the downstream sites, while habitat measures, such as altitude, width, and canopy cover were the most important factors explaining the variability in macroinvertebrate assemblages in the upstream. The results of redundancy analysis (RDA) based on the relationships between environmental variables and FFGs showed that the altitude and substrate composition showed higher correlation with RDA axis 1 where a higher number of shredders and predators found at the upstream sites. The relative proportions of shredders and predators were decreased, while the collector-filterers were increased along the Xindian watershed. Moreover, a synthetic longitudinal gradient, including the altitude, canopy cover, river width, and distances from source showed a higher correlation with the taxon richness and shredders. Most of the benthic metrics were greater in the reference site compared to the impacted sites. As the result of assessment of different benthic metrics, water quality of Xindian watershed became gradually worse from upstream to downstream. The results of community structure, FFGs patterns of the macroinvertebrates and their relations with the environmental variables also clearly indicated that downstream sites impacted by human activities. Results of the univariate and multivariate analysis suggest that macroinvertebrate assemblages can be used for assessment of water quality.