DOI: 10.5061/dryad.gmsbcc2xh
title: Hydrological connectivity and local environment alternately drive spatial structure of floodplain aquatic community across season

description: Seasonal changes in the environment often strongly influence biological
 communities. In environmental transition zones, or ecotone, the
 environment fluctuates over time between two different types of
 environments, and the seasonal change is more pronounced. Although
 emphasis has been placed on the spatial variation of biota along
 environmental gradients, seasonal change has not been well studied despite
 the seasonal nature of many ecotones. In this study, we investigated
 seasonal shift in aquatic community structures of floodplain waterbodies
 characterized as transitions between lotic and lentic environments, and
 further investigated the biological processes behind the shift. We
 observed a clear seasonal shift of community structure in floodplain
 waterbodies. From the spring snowmelt season to the summer low flow
 season, the aquatic community structure was largely driven by the
 hydrological connectivity to the river, represented as the timing of the
 lotic-lentic transition during the seasonal flood recession. In contrast,
 after a few months of summer low flow period, the effect weakened over
 time, and the communities were structured based more on the basis of the
 local environment. The seasonal shift was largely explained by the change
 in amphibian and aquatic insect larvae, the main members of the floodplain
 aquatic assemblage, which metamorphose and emerge from the water during
 the summer period and then re-distribute in different ways more strongly
 influenced by local environmental factors such as water body size,
 temperature, and dissolved oxygen levels. Given that biota in ecotones
 occupy the habitat for a limited time due to the severe environmental
 fluctuations, such seasonal changes as we observed in this study may be
 widespread in ecotones. Landscape and local environmental conditions could
 alternately shape community structures in different seasons. Further
 attention to the temporal aspects of community structure is needed for
 community studies as well as for conservation.
description: The survey targeted four faunal groups: plankton, benthos, nekton
 (fishes), and amphibians. Benthic invertebrates were sampled with Surber
 net samplers (25 cm ´ 25 cm). Three samples were collected at each site on
 each sampling date and combined. Benthic samples were immediately sieved
 through a 0.5 mm mesh and preserved in 99% ethanol for later sorting. Fish
 were captured with a backpack electrofishing unit (Model 12B, Smith-Root
 Inc., Vancouver, Washington, USA) using a pulsed direct current setting
 (300–400V, DC). A crew of two or three study participants sampled in an
 upstream direction. The entire area of small waterbodies or the first
 20–120 m of paleo-side channels at the site longer than 120 m were sampled
 by the two-pass method. All fish collected in the surveys were identified
 to species and released back to the same site alive. The fish catch per
 unit effort was calculated by dividing the fish count by the total habitat
 area sampled. The density of amphibian larvae was binomial (very high or
 zero), because their presence depend on whether their adults lay egg-mass,
 which contains many eggs. Therefore, for amphibians, we recorded
 presence/absence of their larvae rather than their density by visual
 investigation during the electrofishing survey. For plankton, 10 L of
 water was filtered through a 70-μm-mesh plankton net and preserved in 2%
 Glutaraldehyde for zooplankton analysis.
description: # Hydrological connectivity and local environment alternately drive
 spatial structure of floodplain aquatic community across season
 [https://doi.org/10.5061/dryad.gmsbcc2xh](https://doi.org/10.5061/dryad.gmsbcc2xh) ## Description of the data and file structure In this study, in a floodplain of Butokamabetsu-river, Horokanai, Hokkaido in Japan, we investigated aquatic biota in 25 waterbodies with different hydrological connectivity to a river in three seasons. The data is analyzed and published in the following paper. Hiromi Uno, Shunsuke Utsumi, Kentaro Morita, Osamu Kishida, Md. Khorshed Alam, Junjiro Negishi (*2025*) Hydrological connectivity and local environment alternately drive spatial structure of floodplain aquatic community across season. *Ecology and Evolution.*  "2021onlyseasonalUryu_comm_update2.csv" file includes all the community data described in this paper: Each column represents a taxon including amphibian, fish, benthic macroinvertebrate, and plankton, and each row represents a sampling event data from a site in one season. The number indicate the density of each taxa at each sampling event. The methods of the sampling is described in the paper. Unit is as follows; Fish: individuals m-2 Amphibian: presence=1, absence=0 Benthos: individuals m-2 Plankton: individuals L-1 "2021seasonalUryu_connectivityFINAL.csv" file includes surface hydrological connectivity of each site to the mainstem river. The methods of the sampling is described in the paper. Distance: river distance from the outlet of the river to the lake. (meter) organic_mm: thickness of the organic layer at the bottom (mm) Substrate: substrate at the bottom Grainsize: (mm) Juliandate_lastsnowflow: Julian date when the river water by the snowmelt flood stopped flowing into the site conn_order: order of the connectivity. "1" represents the site with the highest connectivity. conn_easy2: connectivity category used in the paper conn_easy2_num: connectivity category as number (1=none, 2=overflow2, 3=overflow1, 4=flowing) side_inflow: presence of flow input from side (tributuary) flow: presence of flow at the time of sampling "2021seasonalUryu_chemistryFINAL.csv" file includes environmental variable such as pH, DO, temperature etc, measured at each sampling event at each site. The methods of the sampling is described in the paper. PH: pH COND: conductivity (mS m-1) DO_mgL-1: dissolved oxygen (mg L-1) Temp: water temperature (degree C) Season: sampling season Year: year of sampling total_Area: estimated surface area of the waterbody each site is located (m2)  total_Volume: estimated water volume of the waterbody each site is located (m3) Flow_cmsec: average flow rate (cm sec-1) bottom_conn: surface water connectivity to the mainstream river at the downstream end of the waterbody.