## 3 Results and Discussion
### Association among Benthic Macroinvertebrates, Land-Use Coverage, and Ambient Water Quality
was more associated with ammonia concentration. Particularly, it was found that _Baetis_ spp. was less sensitive to ammonia toxicity than other mayflies [52]. We infer that the linkage between _Baetis_ spp. and ammonia concentration is highly associated with their tolerance. In this context, _Ephemera_ spp. and _Caenis_ spp. seem to inhabit in a similar water quality condition (Figure 5b). The spatial ordination of _Labiobaetis_ spp. was clearly distinct, which appears to be related to good water quality. The other Ephemeroptera, such as _Choropterpes_ spp., _Epeorus_ spp., and _Ecdyonurus_ spp., were placed on a mixture of wetland, cropland, and urban areas. However, there was little evidence to advocate their association with surrounding environmental conditions. The dominant Diptera groups were Chironomide and _Simulium_ spp. in the Seomijn River basin. These two groups were clearly separated in the data ordination induced by land-use coverage rather than water quality (Figure 5a). Chironomide were closely associated with wetland and cropland. Plenty of literature papers have reported that Chironomide are the most abundant insects in wetlands and play an important role in wetland food webs [53; 54]. In addition, it is clear that agricultural land use has influenced water quality, as evidenced by high nutrient concentrations [55]. Thus, the accumulation of organic matters subsequently fosters the colonization of Chironomide groups, particularly in lowland agricultural areas [55; 56]. In contrast, the same group of Diptera, _Simulium_ spp., was correlated with nitrogen rather than phosphorus in forest areas. The aforementioned _Hydrosyche_ spp. is known to prefer boulder microhabitats, which are commonly found in upstream areas (i.e., forest area in Seomijn River). It was remarkable to show a weak relationship between _Hydrosyche_ spp. and forest land cover. Given the interspecific competition between _Hydrosyche_ spp. and _Simulium_ spp., our result was plausible to make _Hydrosyche_ spp. separate in order to avoid excessive predation and competition [57]. Of the remaining benthic macroinvertebrates, _Asellus_ spp. and _Gammarus_ spp. were strongly identified in forest areas (Figure 5a). These two genera were clearly separated by components related to water quality, which we will discuss in relation to temporal water quality changes in the following sections. The Gastropoda groups _Radix_ spp. and _Semisulopsis_ spp. were similarly ordinated in the plot (Figure 5a). Although the former was more related to grassland (i.e., pasture) and the latter was more related to wetlands, it was difficult to characterize their habitat preferences. In this regard, further investigations are required. The Haplotaxida _Limmodrilus_ spp. were closely associated with ammonia concentration in agricultural areas, and are known to be tolerant of unfavorable condition such as hypoxic and eutrophic states [58]. Thus, we suppose that _Limmodrilus_ spp. is less sensitive to ammonia (NH\({}_{3}\)-N) toxicity, similar to the aforementioned _Baetis_ spp. and _Ephemera_ spp.