Zhenpeng Ge - Academia.edu (original) (raw)

Papers by Zhenpeng Ge

Authorea (Authorea), Aug 22, 2022

A tipping point is a critical transition point where a system is impending to collapse under a sl... more A tipping point is a critical transition point where a system is impending to collapse under a slight disturbance. Based on sequential time-series data, such transition can be captured by early warning signals like critical slowing down. However, sequential time-series data is limited for most macro-ecosystems, which brings the challenge for practical application. Here we report that density fluctuation, a purely spatial metric, robustly indicates the tipping point of Ising-type ecosystems. Ricker model and an agroecosystem, both of which have been proved to fall in Ising universality class, are used as prototypes to illustrate how density fluctuation captures the tipping point from instantaneous spatial configurations. The agroecosystem demonstrates experimental evidence that the existence of an Ising-type tipping point depends on the dynamics properties of the system. In addition to detecting tipping points, early warning signals were able to infer ecological processes from spatial patterns of the agroecosystem. As spatially high-resolution data are becoming increasingly available, density fluctuation offers a novel perspective on anticipating tipping points and identifying ecological processes from spatial patterns.

Ecology Letters, 2021

Biological behaviour-driven self-organized patterns have recently been confirmed to play a key ro... more Biological behaviour-driven self-organized patterns have recently been confirmed to play a key role in ecosystem functioning. Here, we develop a theoretical phase-separation model to describe spatiotemporal self-similar dynamics, which is a consequence of behaviour-driven trophic interactions in short-time scales. Our framework integrates scale-dependent feedback and density-dependent movement into grazing ecosystems. This model derives six types of selective foraging behaviours that trigger pattern formation for top-down grazing ecosystems, and one of which is consistent with existing foraging theories. Self-organized patterns nucleate under moderate grazing intensity and are destroyed by overgrazing, which suggests ecosystem degradation. Theoretical results qualitatively agree with observed grazing ecosystems that display spatial heterogeneities under variable grazing intensity. Our findings potentially provide new insights into self-organized patterns as an indicator of ecosystem transitions under a stressful environment.

Proceedings of the National Academy of Sciences, 2021

Significance Self-organization is increasingly recognized as fundamental to pattern formation in ... more Significance Self-organization is increasingly recognized as fundamental to pattern formation in geomorphology. Relative to other fields, however, underlying mechanisms have received little attention from theoreticians. Here, we introduce phase separation theory to study the formation of sorted patterned ground in cold regions; “sorted” refers to the segregation of soil and stones due to feedbacks between stone concentration and recurring ice growth. Using detailed measurements of the concentration of stones in soil and their displacements, we demonstrate that phase separation accounts for the observed sorting and patterns. Our study highlights phase separation theory as a source of important insight into studying ground patterns in cold regions and their potential value in signaling important changes in ground conditions with the warming climate.

Biodiversity Science, 2020

Over the past 30 years, the self-organization theory has effectively explained the regular spatia... more Over the past 30 years, the self-organization theory has effectively explained the regular spatial patterning of ecosystems and has led to a proliferation of studies investigating spatial patterns in ecology and biology. Indeed, the emergent properties generated by this self-organization process are now recognized as critical to ecosystem functioning. Here, we review this important theoretical framework by assessing the definition and development of the concept of self-organization and by evaluating two fundamental theoretical principles of self-organization theory, the Turing principle and the phase separation principle. We further describe the mathematical models of each principle in the context of different, unique ecosystems, and explain the emergent properties of the Turing principle on ecosystem functioning and the phase separation principle on cell functions, respectively. Finally, we propose three promising future developments for ecological self-organization theory: multi-scale self-organization patterns, transient patterns, and individual behavioral self-organization. Our review provides an assessment of this fundamental ecological theory and offers exciting new research directions and applications.

Earth Surface Processes and Landforms, 2020

Within the context of a warming climate, there are wide and increasing concerns about the way bea... more Within the context of a warming climate, there are wide and increasing concerns about the way beaches respond to different wave energy environments. However, behavioural differences in changes in beach elevation contours (including shorelines) in different wave energy environments remain unknown. Thus, it is unilateral to evaluate the changes in beaches based on a single elevation contour (e.g. shoreline) in coastal engineering and management applications. In this study, based on the collected shoreline and wave energy data of two international beaches, as well as the measured beach elevation contour data from Yintan Beach and the corresponding wave energy data simulated by Xbeach, our results show that frequency distributions of beach elevation contour changes exhibit distinct features under different wave energy environments. Under high wave energy environments, the frequency distributions of beach elevation contour changes show a Gaussian distribution. However, frequency distributions of beach elevation contour changes present a power law, intermediate between the logarithmic and Gaussian distributions under low and moderate wave energy environments, respectively. Furthermore, the conceptual model of beach elevation contour changes constructed by this study indicates that the relative importance of the wave energy and sediment resistance determines this phenomenon.

Continental Shelf Research, 2019

Knowledge of sediment grain size characteristics is important for a better understanding of the m... more Knowledge of sediment grain size characteristics is important for a better understanding of the morphodynamic behavior of beaches worldwide. In this paper, dramatic changes in the grain size of sediments at Yintan Beach, South China in response to Typhoon Rammasun (tropical storm no. 1409) were analyzed on the basis of the collected sediments, beach elevation, and hydrological data from June 1 to July 31. Variations in beach geomorphology were interpreted using the digital elevation taken by LiDAR technology, while changes in sediment grain size were detected by sediment parameters and associated sediment components. The results show that the sediments of Yintan Beach were nearly pure sand before Rammasun and became coarser and slightly better sorted with a higher negative skew after Rammasun. The sediment grain size pattern shifted from a high content (39%) of very fine sand in the lower intertidal zone pre-Rammasun to a high content (76%) of fine sand in the swash zone post-Rammasun. During Rammasun, wave action was responsible for the main transition of grain size pattern in the lower intertidal and mid-tidal zones, and tidal level and beach morphology could affect the grain size distribution of the sandbar and trough in the swash zone. In addition, the increase in the coarse-grained fraction in the upper beach and berm was primarily due to wind action.

Marine Geology, 2018

Estuarine beaches near large rivers are dynamic systems constantly shaped by tides, waves, and fl... more Estuarine beaches near large rivers are dynamic systems constantly shaped by tides, waves, and fluvial sediment inputs. However, little research has been done on the intrinsic characteristics of these geomorphic systems. Using eleven high resolution bathymetries, our results show that human disturbance mingled with natural forcings have induced bathymetric changes in Nanhui beach in the Changjiang estuary, China. Isobaths display a fractal geometry, with a lower fractal dimension when tides smooth the bathymetry and a higher dimension when waves dominate. Rates of sediment accretion and erosion present a Gaussian distribution driven by tidal and wave action. Episodic extreme wave forcing or frequent land reclamation is responsible for the intermittent adjustment of the estuarine beach bathymetry. After these events the distribution of erosion and accretion becomes power-law, possibly indicating disequilibrium. The fractal dimension of isobaths and the distribution of erosion and deposition rates can therefore be used as metrics to determine the dominant processes in estuarine beaches and whether the system is close to equilibrium or not.

Coastal Engineering Proceedings, 2018

Beach profile change induced by storms is a common and complex process in coastal engineering. St... more Beach profile change induced by storms is a common and complex process in coastal engineering. Storms often bring high water levels and large waves, which erode the berm and dune, carrying large quantities of sand offshore, often causing severe damage to coastal properties. Thus, considerable research has been carried out to determine storm impact. Early studies mainly focused on laboratory investigations and analysis of field data. Since the 1980’s, many engineering numerical models of beach profile change have been developed. Kriebel and Dean (1985) proposed a model (EBEACH) to simulate the beach profile evolution with focus on dune erosion during storms, using the concept of an equilibrium beach profile (EBP). However, features such as bars and berms are not described in this model. Larson and Kraus (1989) developed an empirically based model (SBEACH) for describing the formation of bars and berms, also applying the EBP concept. Steetzel (1990) developed a model for cross-shore t...

Estuarine, Coastal and Shelf Science, 2019

Cross-shore suspended sediment transport (SST) over meso-macro tidal beaches is of great importan... more Cross-shore suspended sediment transport (SST) over meso-macro tidal beaches is of great importance to worldwide coastal erosion due to global sea-level rise. A continuous field experiment of about six tidal cycles measuring cross-shore SST near the seabed in different wave conditions was conducted over Yintan Beach, a meso-macro tidal beach to the north of Beibu Gulf, China. The surveyed data, including synchronous hydrodynamics and suspended sediment concentrations (SSC), were collected with three upward Acoustic Doppler Current Profilers (ADCPs), three Tide & Wave Recorders-2050 (RBRs) and three Optical Backscatter Sensors (OBSs). The results indicate that the SSCs in low and moderate wave heights were responsible for variations in cross-shore suspended sediment fluxes (SSF) at Yintan Beach. During moderate wave conditions, a greater average SSC of over 1.89 kg/m 3 and a longer flood tide duration occurred in rising tide compared with falling tide, accompanied by a maximum SSC of 2.67 kg/m 3 and offshore-directed flows due to cross-shore SST induced by tidal asymmetry. For the most landward measurement site at the surf zone, both net cross-shore SSF and maximum cross-shore SSF were larger than that in the offshore measurement sites over moderate wave conditions, which was ascribed to the strong offshore flows (undertow) induced by breaking waves and radiation stress S xx decay.

Scientific Reports, 2016

An increasing amount of anthropogenic marine debris is pervading the earth’s environmental system... more An increasing amount of anthropogenic marine debris is pervading the earth’s environmental systems, resulting in an enormous threat to living organisms. Additionally, the large amount of marine debris around the world has been investigated mostly through tedious manual methods. Therefore, we propose the use of a new technique, light detection and ranging (LIDAR), for the semi-automatic recognition of marine debris on a beach because of its substantially more efficient role in comparison with other more laborious methods. Our results revealed that LIDAR should be used for the classification of marine debris into plastic, paper, cloth and metal. Additionally, we reconstructed a 3-dimensional model of different types of debris on a beach with a high validity of debris revivification using LIDAR-based individual separation. These findings demonstrate that the availability of this new technique enables detailed observations to be made of debris on a large beach that was previously not po...

Ocean & Coastal Management, 2015

Tidal flat, is a critical natural resource for coastal ecosystem and plays a tremendous role in c... more Tidal flat, is a critical natural resource for coastal ecosystem and plays a tremendous role in coastal sustainable development. However, most tidal flats in the world are facing serious challenges from both natural change and anthropogenic activities. Based on the multi-year monitoring records of tidal flats in the Changjiang (Yangtze) Estuary, the temporal-spatial changes of tidal flats and possible driving factors were statistically examined. The results indicate that the increased rate of the majority of tidal flats in the Changjiang Estuary has become slow since 2000s. Tidal flats of both Hengsha and Jiuduan Shoal showed minor enlarged trends from 2004 to 2009. However, Tidal flat areas of Nanhui Shoal above 0 m had greatly decreased by 80.8% from 1958 to 2012. Even though estuarine hydraulic engineering structures can mitigate tidal flats decreased trends, the tidal flats of the Changjiang Estuary will still suffer significant losses due to the decreasing sediment flux from upstream, ground subsidence, sea level rise and recent intensive reclamation. Thereafter, the adaptive management strategies for sustainable tidal flat resources of the Changjiang Estuary are as follows: (1) Proceeding comprehensive adjustment involving watershed and estuary; (2) keeping balance between reclamation and rebirth of tidal flats; (3) coping with sea level rise; (4) scientifically promoting aggradation of tidal flats.

Quaternary International, 2015

Continental freshwater discharge is vital to global human development. Intensive studies have bee... more Continental freshwater discharge is vital to global human development. Intensive studies have been conducted on changes of river discharge around the world (Dai et al., 2009; Milliman and Farnsworth, 2011). However, little work has been carried out on the daily continental freshwater discharge of the Red River in response to influence of the natural and anthropogenic forcings. This paper presents results of change analysis of daily continental freshwater discharge over the period 1956e2009 in the Red River. The wavelet analysis results showed observable periodicities in the continental freshwater discharge series with 4e6 months, 8e12 months, 1.5e2 years, and 4e7 years (48e80 months), respectively. The results from ManneKendall test indicated insignificant trends in annual continental freshwater discharge during the study period, but there is clearly decrease in annual suspended particulate matter of the Red River. It is shown that the continental freshwater discharge from the Red River was dominated by precipitation over the catchments. Moreover, changes in the continental freshwater discharge are closely related to SASM (the South Asia Summer Monsoon) and ENSO (EI Niño Southern Oscillation). Variations in daily discharge are lagged behind SASM 13e29 days. It revealed that El Niño and La Niña events are likely to induce extreme low and extreme high continental freshwater discharge from the Red River into the Tokin Gulf, respectively. Meanwhile, continental freshwater discharge from the Red River into the Tonkin Gulf experienced abrupt changes with present characteristics as 'no flood in the flood season, no drought in the drought season' due to water regulation induced by dam.

Marine Geology, 2017

Because of global sea-level rising with frequent storm activities, most beaches in the world expe... more Because of global sea-level rising with frequent storm activities, most beaches in the world experience widespread erosion, which poses a significant hazard to beach management. The morphodynamic process of the evolution of a beach in response to storm activities is of increasing concern. Using a terrestrial laser scanner, the topography of Yintan beach was continuously observed for 33 days with a 25 cm spatial resolution digital elevation model (DEM) of that covered an area of 15 ha before and after typhoon Rammasun. The short-term beach recovery was explored using a comprehensive approach, which included grey relational analysis, terrain analysis, Gaussian fitting, Gamma fitting, and Delft3D wave simulation methods. The results show that the Yintan beach recovery process can be divided into three stages with two transition points. Stage one began at the end of Rammasun, which indicated a weakly stable state with an average daily net erosion of −588 m 3 , a mean beach slope that ranged from 0.96°to 1.28°, and a landform with no obvious alterations. After the vast accretion of 6874 m 3 of first transition, stage two, which was characterized by oscillations, occurred in the region with an average daily net erosion of −396 m 3 and a conspicuous beach slope reconstruction in the range of 0.94°-2.16°. During this stage, sandbar reconstruction played a key role. The second transition event arose at the end of stage two with a vast accretion of 5762 m 3. Afterwards, the daily net accretion of 200 m 3 and the beach slope range of 0.93°-1.74°dominated the region during stage three, and the beach surface became similar to that of the pre-Rammasun. Within the entire observation period, intense beach elevation changes that ranged from −15 cm to − 6 cm and 6 cm to 15 cm mainly occurred in the sandbar and foreshore zones, respectively. Additionally, slight elevation changes (ranging from −4 cm to 4 cm) were densely distributed in the backshore and dunes, and moderate elevation changes (ranging from −6 cm to −4 cm and 4 cm to 6 cm) emerged along the entire beachface. It was concluded that the spatial distribution of the bottom shear stress that was induced by wave action was responsible for the reconstruction of the foreshore and sandbar after Rammasun, whereas the shortterm beach recovery process was affected by the beach states in various wave breaking conditions.

Journal of Geographical Sciences, 2018

Sandbars are of vital ecological and environmental significance, which however, have been intensi... more Sandbars are of vital ecological and environmental significance, which however, have been intensively influenced by human activities. Morphodynamic processes of sandbars along the Yichang-Chenglingji Reach of the Changjiang River, the channel immediately downstream of the Three Gorges Dam (TGD), are assessed based on remote sensing images between 2000 and 2016. It can be found that the entire area of sandbars reduces drastically by 19.23% from 149.04 km 2 in 2003 to 120.38 km 2 in 2016, accompanied with an increase in water surface width. Owing to differences in sediment grain size and anti-erosion capacity, sandbar area in the upstream sandy gravel reach (Yichang-Dabujie) and downstream sandy reach (Dabujie-Chenglingji) respectively decreases by 45.94% (from 20.79 km 2 to 11.24 km 2) and 14.93% (from 128.30 km 2 to 109.14 km 2). Furtherly, morphological evolutions of sandbars are affected by channel type: in straight-microbend channel, mid-channel sandbars exhibit downstream moving while maintaining the basic profile; in meandering channel, point sandbars show erosion and deposition in convex and concave bank respectively, with mid-channel sandbars distributing sporadically; in bending-branching channel, point sandbars experience erosion and move downstream while mid-channel sandbars show erosion in the head part along with retreating outline. We document that the primary mechanism of sandbars shrinkages along the Yichang-Chenglingji Reach can be attributed to TGD induced suspended sediment concentration decreasing and increasing in unsaturation of sediment carrying capacity. Additionally, channel type can affect the morphological evolution of sandbars. Along the Yichang-Chenglingji Reach, sandbars in straight-microbend channel are more affected by water flow than that in bending-branching channel.