## 3 Results and Discussion
### Association among Benthic Macroinvertebrates, Land-Use Coverage, and Ambient Water Quality  
The CCA simplified the relationships among the variables of our interest (Figure 5). The CCA results explicitly accounted for 61% of the relational variability with two primary ordination axes; the first axis (45.5%) was related to land-use factors, and the second axis (15.5%) appeared to be related to water quality. The first ordination axis characterized the gradient of land-use coverage (Figure 5). The land-cover gradient was mainly separated by forest and agricultural/cropland areas. Urban land is topographically placed in the middle between forest and cropland. Wetland is close to cropland, which is reasonable because extensive agricultural areas have been converted from riverine wetlands by constructing levees in South Korea [44; 45]. The second ordination axis depicted the gradient of water quality parameters. On the whole, the upper part of plot is closely associated with the parameters related to water quality deterioration, such as the higher concentration level of BOD, Chl-_a_, TP, and TN (Figure 5). It was notable that the ammonia (NH\({}_{3}\)-N) concentration showed an inverse pattern against the other water quality parameters. This pattern appears to be associated with agriculture and pasture. In contrast, the NO\({}_{3}\)-N concentration showed a weak relationship with agricultural activities including grassland/pasture, while the PO\({}_{4}\)-P concentration had close association (Figures 5 and 6a). As previous mentioned, higher PO\({}_{4}\)-P concentrations were apparently observed in the lower part of the river (Figure 3). Thus, the CCA ordination depicted the disparate responses of nitrogen and phosphorus dynamics in the lower part of the Seomijn River. In the ordination pattern of key benthic macroinvertebrates (e.g., EPTC taxa: E = Ephemeroptera, P = Piccoptera, T = Tricoptera, and C = Coleoptera), the major Coleoptera groups, _Elmidae_ spp. Figure 5: Results of data ordination based on canonical correspondence analysis (CCA). Comparison of land use and water quality with benthic macroinvertebrate communities; (**a**) 14 groups, and (**b**) eight Ephemeroptera groups. Figure 6: (**a**) CCA data ordination associated with data samples and ambient environmental factors. (**b**) Dissimilarity of data attributes between May and September. and _Eubrianax_ spp., were distinctly differentiated according to water quality. These two genera, especially the riffle beetles _Elmidae_, are typically known as a large group of aquatic Coleoptera that are generally indicators of good water quality, because of their sensitivity to changes in the surrounding environmental conditions [46; 47]. Nonetheless, the association of _Elmidae_ with several water quality signals to eutrophic conditions (PO\({}_{4}\)-P, Chl-_a_, and BOD) was unexpected (Figure 5a). This counterintuitive pattern may be a confounding effect stemming from the spatial migration of larvae. However, there have been some evidence that _Elmidae_ can be distributed in a wide range of nutrient conditions [48]. We speculate that _Elmidae_ can prevail to some extent, since the Seomijn River watershed is mainly dominated by forest (48% on average, see Figure 1). The Tripcoptera groups, _Hydrosyche_ spp. and _Cheumatopsyche_ spp., were separately characterized. It appears that _Hydrosyche_ is more related to Chl-_a_ than _Cheumatopsyche_. There have been several literatures on food preferences and niche partitioning among these species [49; 50]. We understand the separate pattern of these species, in the sense that Hydrosyche larvae prefer higher-velocity microhabitats and mainly digest detritus and benthic diatoms [51]. Another key benthic macroinvertebrate Ephemeroptera generally tended to inhabit good water quality conditions (Figure 5b). However, they seemed to be apart from mountainous areas (i.e., forest areas). Within the same family Baetidae, _Baetiella_ spp. was more associated with wetland habitat, while _Baetis_ spp.