Abstract
The river–lake transition zone is affected by many environmental factors, leading to significant dynamics and complexity. This makes the boundary unclear, and not enough attention has been paid to this problem by scholars, even though it has great significance for research on water quantity, water quality, and the aquatic environment. In this paper, we define this transition zone, define its upper and lower boundaries, and develop the method for defining the hydrologic boundary. It includes a method for defining the upper boundary, based on the flow velocity mutation point, and a method for defining the lower boundary, based on the velocity gradient field. We then used this approach to examine the transition zones between the Fu River, Baigou Canal, and Baiyangdian Lake in China as a case study. We found that the upper boundary of the Fu River–Baiyangdian Lake transition zone was 2.35 km upstream of the lake’s inlet; the lower boundary was farthest from the lake’s inlet in July, and the maximum area of the transition zone was 2.603 km2. The lower boundary was closest to the lake’s inlet in March, when the minimum area was 1.598 km2. The upper boundary of the Baigou Canal–Baiyangdian Lake transition zone was 2.18 km upstream from the lake inlet, and the lower boundary was farthest from the lake’s inlet in August, when the maximum area was 2.762 km2. The lower boundary was closest to the lake’s inlet in April, when the minimum area was 0.901 km2.
Highlights
An ecotone represents the transition zone between adjacent ecological systems, and has characteristics that are uniquely defined by the spatial and temporal scales of the adjacent ecological systems, and by the strength of the interactions between them [1]
We concluded that the upper boundary of the Fu River–Baiyangdian Lake transition zone occurs at 2.35 km upstream from the lake inlet
Based on the results simulated by the coupled 1D and 2D hydrodynamic models, we extracted the monthly distribution of downstream flow velocities for the Fu River–Baiyangdian Lake and the the monthly distribution of downstream flow velocities for the Fu River–Baiyangdian Lake and the Baigou Canal–Baiyangdian Lake transition zones from March 2018 to February 2019
Summary
An ecotone represents the transition zone between adjacent ecological systems, and has characteristics that are uniquely defined by the spatial and temporal scales of the adjacent ecological systems, and by the strength of the interactions between them [1]. Water evolves from a lotic to a lentic environment, which represents a change from fast-flowing to slow-flowing water [9] This creates an obvious current velocity gradient [5]. The above research results demonstrate that the transition zone plays an important role in the ecological water supply and in maintenance of the biodiversity of aquatic ecosystems Despite this importance, little effort has been focused on transition zones [17], and in particular, insufficient attention has been paid to defining their boundaries. Hydrodynamic conditions, and especially flow velocity gradients, are obvious characteristics of such zones, and directly affect the transitions and changes of water quality, biological characteristics, and many other aspects of the transition zone. Development of a Hydrological Boundary Method for a River–Lake Transition Zone
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