Survey on threshold detection methods of regime shift in shallow lake ecosystem

In the shallow lake ecosystems, the recovery of the aquatic macrophytes and the increase in the water transparency have been the main contents of the ecological restoration. Using the shallow lake ecological degradation and restoration model, CNOP method is adopted to discuss the instability and sensitivity of the ecosystem to the finite-amplitude perturbations related to the initial condition and the parameter condition. Results show that the linearly stable clear (turbid) water states can be nonlinearly unstable with the finite-amplitude perturbations, which represent the nature factors and the human activities such as the excessive harvest of the macrophytes and the sediment resuspension caused by artificially dynamic actions on the ecosystems. The results also support the viewpoint of Scheffer et al., whose emphasis is that the facilitation interactions between the submerged macrophytes and the water transparency are the main trigger for an occasional shift from a turbid to a clear state. Also, by the comparison with CNOP-I, CNOP-P, CNOP, and (CNOP-I, CNOP-P), results demonstrate that CNOP, which is not a simple combination of CNOP-I and CNOP-P, could induce the shallow lake ecosystem larger departure from the same ground state rather than CNOP-I, CNOP-P, and (CNOP-I, CNOP-P).

Download Full-text

High net CO<sub>2</sub> and CH<sub>4</sub> release at a eutrophic shallow lake on a formerly drained fen

Biogeosciences ◽

10.5194/bg-13-3051-2016 ◽

2016 ◽

Vol 13 (10) ◽

pp. 3051-3070 ◽

Cited By ~ 28

Author(s):

Daniela Franz ◽

Franziska Koebsch ◽

Eric Larmanou ◽

Jürgen Augustin ◽

Torsten Sachs

Keyword(s):

Global Warming ◽

Shallow Lake ◽

Typha Latifolia ◽

Open Water ◽

Emergent Vegetation ◽

Lake Ecosystem ◽

Co2 Uptake ◽

Mild Winter ◽

Ch4 Emissions ◽

Northeastern Germany

Abstract. Drained peatlands often act as carbon dioxide (CO2) hotspots. Raising the groundwater table is expected to reduce their CO2 contribution to the atmosphere and revitalise their function as carbon (C) sink in the long term. Without strict water management rewetting often results in partial flooding and the formation of spatially heterogeneous, nutrient-rich shallow lakes. Uncertainties remain as to when the intended effect of rewetting is achieved, as this specific ecosystem type has hardly been investigated in terms of greenhouse gas (GHG) exchange. In most cases of rewetting, methane (CH4) emissions increase under anoxic conditions due to a higher water table and in terms of global warming potential (GWP) outperform the shift towards CO2 uptake, at least in the short term.Based on eddy covariance measurements we studied the ecosystem–atmosphere exchange of CH4 and CO2 at a shallow lake situated on a former fen grassland in northeastern Germany. The lake evolved shortly after flooding, 9 years previous to our investigation period. The ecosystem consists of two main surface types: open water (inhabited by submerged and floating vegetation) and emergent vegetation (particularly including the eulittoral zone of the lake, dominated by Typha latifolia). To determine the individual contribution of the two main surface types to the net CO2 and CH4 exchange of the whole lake ecosystem, we combined footprint analysis with CH4 modelling and net ecosystem exchange partitioning.The CH4 and CO2 dynamics were strikingly different between open water and emergent vegetation. Net CH4 emissions from the open water area were around 4-fold higher than from emergent vegetation stands, accounting for 53 and 13 g CH4 m−2 a−1 respectively. In addition, both surface types were net CO2 sources with 158 and 750 g CO2 m−2 a−1 respectively. Unusual meteorological conditions in terms of a warm and dry summer and a mild winter might have facilitated high respiration rates. In sum, even after 9 years of rewetting the lake ecosystem exhibited a considerable C loss and global warming impact, the latter mainly driven by high CH4 emissions. We assume the eutrophic conditions in combination with permanent high inundation as major reasons for the unfavourable GHG balance.

Download Full-text

Detecting changes to the functioning of a lake ecosystem following a regime shift based on static food-web models

Ecological Modelling ◽

10.1016/j.ecolmodel.2015.08.026 ◽

2016 ◽

Vol 320 ◽

pp. 145-157 ◽

Cited By ~ 5

Author(s):

E. Ofir ◽

G. Gal ◽

M. Goren ◽

J. Shapiro ◽

E. Spanier

Keyword(s):

Food Web ◽

Regime Shift ◽

Lake Ecosystem

Download Full-text

Application of the CNOP Method in the Shallow Lake Ecosystem

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1010-1012.658 ◽

2014 ◽

Vol 1010-1012 ◽

pp. 658-661 ◽

Cited By ~ 1

Author(s):

Qian Qian Qi ◽

Bo Wang

Keyword(s):

Ecological Restoration ◽

Shallow Lake ◽

Submerged Macrophytes ◽

Finite Amplitude ◽

Water Transparency ◽

Lake Ecosystem ◽

Initial Condition ◽

Turbid Water ◽

Variable Model

It is serious on the degradation of the shallow lake ecosystem at present, while the recovery of the macrophytes vegetations and the increase in water transparency have been the main contents of the ecological restoration. Using a two-variable model, we discuss the instability and sensitivity of the ecosystem to the finite-amplitude perturbations related to the initial condition with CNOP-I method. Results show that the linearly stable clear (turbid) water states can be nonlinearly unstable with the finite-amplitude perturbations. The results also demonstrate that the facilitation interactions between the submerged macrophytes and the water transparency are the main trigger for a shift from the turbid to the clear state.

Download Full-text

Biodiversity changes in a shallow lake ecosystem: a multi‐proxy palaeolimnological analysis

Journal of Biogeography ◽

10.1111/j.1365-2699.1999.00298.x ◽

1999 ◽

Vol 26 (1) ◽

pp. 97-114 ◽

Cited By ~ 51

Author(s):

C. Sayer ◽

N. Roberts ◽

J. Sadler ◽

C. David ◽

P. M. Wade

Keyword(s):

Shallow Lake ◽

Lake Ecosystem ◽

Biodiversity Changes

Download Full-text

Effects of wind on a shallow lake ecosystem: Resuspension of particles in the Loosdrecht Lakes

Hydrobiological Bulletin ◽

10.1007/bf02291156 ◽

1986 ◽

Vol 20 (1-2) ◽

pp. 109-120 ◽

Cited By ~ 44

Author(s):

Herman J. Gons ◽

Roelof Veeningen ◽

Ronny Keulen

Keyword(s):

Shallow Lake ◽

Lake Ecosystem ◽

Loosdrecht Lakes

Download Full-text

End-to-End Airport Detection in Remote Sensing Images Combining Cascade Region Proposal Networks and Multi-Threshold Detection Networks

Remote Sensing ◽

10.3390/rs10101516 ◽

2018 ◽

Vol 10 (10) ◽

pp. 1516 ◽

Cited By ~ 17

Author(s):

Yuelei Xu ◽

Mingming Zhu ◽

Shuai Li ◽

Hongxiao Feng ◽

Shiping Ma ◽

...

Keyword(s):

Remote Sensing ◽

Neural Networks ◽

False Alarm ◽

Convolutional Neural Networks ◽

Detection Rate ◽

Detection Methods ◽

Detection Time ◽

Remote Sensing Images ◽

Threshold Detection ◽

Airport Detection

Fast and accurate airport detection in remote sensing images is important for many military and civilian applications. However, traditional airport detection methods have low detection rates, high false alarm rates and slow speeds. Due to the power convolutional neural networks in object-detection systems, an end-to-end airport detection method based on convolutional neural networks is proposed in this study. First, based on the common low-level visual features of natural images and airport remote sensing images, region-based convolutional neural networks are chosen to conduct transfer learning for airport images using a limited amount of data. Second, to further improve the detection rate and reduce the false alarm rate, the concepts of “divide and conquer” and “integral loss’’ are introduced to establish cascade region proposal networks and multi-threshold detection networks, respectively. Third, hard example mining is used to improve the object discrimination ability and the training efficiency of the network during sample training. Additionally, a cross-optimization strategy is employed to achieve convolution layer sharing between the cascade region proposal networks and the subsequent multi-threshold detection networks, and this approach significantly decreases the detection time. The results show that the method established in this study can accurately detect various types of airports in complex backgrounds with a higher detection rate, lower false alarm rate, and shorter detection time than existing airport detection methods.

Download Full-text