Article 1 by Heejung Kim and Kang-Kun Lee* Effect of vertical flow exchange on microbial community dis- tributions in hyporheic zones School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea; *Corresponding author, E-mail: [email protected] (Received: November 2, 2018; Revised accepted: January 6, 2019) https://doi.org/10.18814/epiiugs/2019/019001 The effect of the vertical flow direction of hyporheic flux advance of hydrodynamic modeling has improved research of hydro- on the bacterial community is examined. Vertical velocity logical exchange processes at the hyporheic zone (Cardenas and Wil- change of the hyporheic zone was examined by installing son, 2007; Fleckenstein et al., 2010; Endreny et al., 2011). Also, this a piezometer on the site, and a total of 20,242 reads were zone has plentiful micro-organisms. The hyporheic zone constituents analyzed using a pyrosequencing assay to investigate the a dynamic hotspot (ecotone) where groundwater and surface water diversity of bacterial communities. Proteobacteria (55.1%) mix (Smith et al., 2008). were dominant in the hyporheic zone, and Bacteroidetes This area constitutes a flow path along which surface water down wells into the streambed sediment and groundwater up wells in the (16.5%), Actinobacteria (7.1%) and other bacteria phylum stream, travels for some distance before eventually mixing with (Firmicutes, Cyanobacteria, Chloroflexi, Planctomycetesm groundwater returns to the stream channel (Hassan et al., 2015). Sur- and unclassified phylum OD1) were identified. Also, the face water enters the hyporheic zone when the vertical hydraulic head hyporheic zone was divided into 3 points – down welling of surface water is greater than the groundwater (down welling). On point, mixed welling point and up welling point – through the other hand, surface water with groundwater influence emerges from vertical hydraulic gradient, and the bacterial communi- hyporheic zone where upward direction pressure of subsurface water ties were compared and analyzed. When the species diversity is greater than that of the stream channel (up welling) (Kim et al., 2011). index was additionally analyzed based on the pyrose- The zone is composed of permeable gravels, sands and silts and quencing data, richness and diversity of species were allows significant mixing of surface water with groundwater at the observed to be highest in the order of mixed welling point zone. The area is a complicated region whose boundaries are not always >down welling point >up welling point. Hence, quantita- easy to define. The exchange of stream water and groundwater in the tive changes and characteristics of the hyporheic zone hyporheic zone is dynamic in space (Kim et al., 2014a) and creates a were analyzed to have an effect on the resident bacterial unique community of the endemic bacteria. The exchange and mix- communities. ing of groundwater and stream water plays an important role in deter- mining the structure of bacteria diversity by influencing hydraulic and chemical condition (Zimmer and Lautz, 2015). However, there have Introduction been only a few data researches reporting on the influence of hydro- logic exchange on composition and spatial distribution of the hypor- The hyporheic zone (Kim et al., 2018) is a part of the groundwater heos (Jones et al., 2015). This study examines the influence of hyporheic interface in streams where a mixture of surface water and groundwa- exchange on biological characteristics of the hyporheic zone. ter can be found. The word of hyporheic derived from Greek roots for flow (rheo) and under (hypo). This area is saturated sedimentsain which surface water and groundwater mix. There are studies of this region as Study site a dynamic and distinguishable interface between surface water and o groundwater. (Findlay, 1995; Boulton et al., 1998; Smith et al., 2008; The study area, Haean basin is located between longitude 128 5'- o o o Vogt et al., 2010; Kim et al., 2014a). Hydrologists and ecologists have 128 11'E and latitude 38 15'-38 20'N with a range in altitude from ca. approached this region with their particular perspectives. There are 339 m to 1,320 m (Fig. 1(a)). These streams leave the basin at the eastern various literatures to identify and quantify hyporheic exchange flow border of the study area, where it eventually converges with Soyang (Kasahara and Wondzell, 2003; Storey et al., 2003; Cardenas et al., 2004; River. The drainage system specifically shows a dendritic pattern. The Westhoff et al., 2011). This water exchange is important to the hypor- total length of streams is about 63 km and the streams flow down to heic zone health because of its connection with living organisms in the depression of the basin but only one stream flows out in the east of the zone (Boulton et al., 2010; Griebler and Avramov, 2015). The the basin. Therefore, the hydrographic system of the area is relatively Episodes Vol. 42, No. 1 2 Figure 1. Location of the study area and hyporheic water sampling points. March 2019 3 simple when it compares with other areas (Lee, 2009; Jeong et al., hydraulic gradient was determined by dividing by the piezometer 2012; Lee et al., 2013). Geology of the study area is characterized by insertion depth. Jurassic igneous rocks intruding into the composite metamorphic Δh rocks (Lee, 2009; Kim et al., 2018). The extreme region is mainly VHG = ------ Δl made up of alternating meta-sedimentary rocks of mica schist, biotite- feldspar gneiss and quartzite. It has peculiar and interesting topo- where Δh is the difference in water levels of the piezometers and graphic feature like a bowl. The features of the area have been formed stream water, Δl is the difference in depths between streambed and through prolonged differential erosion and the depressed bottom is the point where the piezometer is installed. However, head differences made up of granite only (Lee, 2009). The geological section and pro- were often very small in the coarse-grained streambeds and thus, three to file of the basin are shown in Fig. 1(b). five measurements were averaged. The positive and negative vertical The climate is characterized by distinct wet and dry seasons (Ket- hydraulic gradients indicate up welling and down welling conditions tering et al., 2012; Kim et al., 2015). From 2005 to 2014, the average of the hyporheic zone, respectively (Bartsch et al., 2014). annual precipitation is estimated at 1,278.5 mm with 50% falling Hyporheic zone, which is the mixed zone of surface water and during the summer monsoon (KMA, 2015). The maximum and mini- groundwater, is where quantitative changes occur dynamically. It was mum of annual precipitations were 1,557 mm in 2011 and 809.5 mm divided into 3 points for analysis through vertical hydraulic gradient in 2014, respectively (Fig. 2). Based on the precipitations for the decade in the hyporheic zone: Up welling point where the effect of ground- (from 2005 to 2014), the wet and dry seasons were considered to be water is greater, down welling point where the effect of surface water from July to September and from October to February, respectively. is greater, and mixed welling point where quantitative changes of the groundwater and surface water were evenly observed. Fig. 3(a) shows the installed piezometer and Fig. 3(b) shows the hyporheic water sam- Materials and Methods pling. Vertical hydraulic Gradient of the Hyporheic zone Analysis of Pyrosequencing Reads The vertical hydraulic gradient (direction and its magnitude) between The samples were filtered through 0.2 µm filter and returned to the groundwater and stream water was evaluated using a piezometer tran- laboratory and stored in a -70oC refrigerator until DNA extraction and sect. The ambient vertical hydraulic gradient between groundwater pyrosequencing of 16S rRNA analysis. The DNA of sampled was and stream water was recorded using piezometer. The direction and extracted using a FastDNA Spin Kit (Qbiogene, USA) as specified by magnitude of hydrologic interaction were evaluated using piezometer the manufacturer. The quality of extracted DNA was checked by stan- transects. Each piezometer was made up of 2 inch (internal diameter) dard agarose gel electrophoresis and stored at -20°C. The DNA con- PVC (polyvinyl chloride) pipe (Hyun et al., 2011; Kim et al., 2014b). centration was determined using a UV-VIS Spectrophotometer (Mechasys At each transect, a total of 20 piezometers were inserted at 0.1 m depth Co. Ltd., Korea). 16S rRNA genes were amplified using forward and (Kim et al., 2014a) beneath the streambed adjacent to each seepage inverse primers to distinguish each sample prior to sequencing at meter installation point with a regular interval (see, Fig. 1(c)). The Chun Laboratory (Kim et al., 2015). Amplification condition for PCR head was measured relative to the stream water surface and vertical was i) an initial denaturation step of 94°C or 5 min, ii) 30 cycles of Figure 2. Annual precipitation in the study area from 2005 to 2014. Episodes Vol. 42, No. 1 4 total of 20,242 reads (PMHS8 6,065 reads, PDHS4 7,603 reads and PUHS20 6,574 reads) were analyzed (Table 1). Total Bacterial Communities When the bacterial communities inhabiting the hyporheic zone were analyzed at the phylum-level, Proteobacteria phylum was domi- nant with 11,067 reads (55.1%), and Bacteroidetes phylum had 3,238 reads (16.5%), Actinobacteria phylum had 1,516 reads (7.1%), Aci- dobacteria phylum had 885 reads (3.9%), Firmicutes phylum had 685 reads (3.5%), Cyanobacteria phylum had 490 reads (2.3%), Chlorof- lexi phylum had 464 reads (2.2%), Planctomycetes phylum had 435 reads (2.1%), and unclassified phylum OD1 had 240 reads (1.2%). Other phylum [Gemmatimonadetes, Armatimonadetes, Verrucomi- crobia, Nitrospirae, Elusimicrobia, Chlorobi, Fibrobacteres, Lentis- phaerae, Fusobacteria, Deinococcus-Thermus and unclassified (TM7, GN02, TM6, OP11, OP3, MATCR, WS3, WS5, AD3 and SR1)] were identified to be lower than 1~0.05% (data below 0.05% not shown) (see, Table 1).