Can fractal dimensions objectivize gastropod shell morphometrics? A case study from Lake Lugu (SW China)

1. Morphometrics are fundamental for the analysis of size and shape in fossils, particularly because soft parts or DNA are rarely preserved and hard parts such as shells are commonly the only source of information. Geometric morphometrics, that is, landmark analysis, is well established for the description of shape but it exhibits a couple of shortcomings resulting from subjective choices during landmarking (number and position of landmarks) and from difficulties in resolving shape at the level of micro-sculpture. 2. With the aid of high-resolution 3D scanning technology and analyses of fractal dimensions, we test whether such shortcomings of linear and landmark morphometrics can be overcome. As a model group, we selected a clade of modern viviparid gastropods from Lake Lugu, with shells that show a high degree of sculptural variation. Linear and landmark analyses were applied to the same shells in order to establish the fractal dimensions. The genetic diversity of the gastropod clade was assessed. 3. The genetic results suggest that the gastropod clade represents a single species. The results of all morphometric methods applied are in line with the genetic results, which is that no specific morphotype could be delimited. Apart from this overall agreement, landmark and fractal dimension analyses do not correspond to each other but represent data sets with different information. Generally, the fractal dimension values quantify the roughness of the shell surface, the resolution of the 3D scans determining the level. In our approach, we captured the micro-sculpture but not the first-order sculptural elements, which explains that fractal dimension and landmark data are not in phase. 4. We can show that analyzing fractal dimensions of gastropod shells opens a window to more detailed information that can be considered in evolutionary and ecological contexts. We propose that using low-resolution 3D scans may successfully substitute landmark analyses because it overcomes the subjective landmarking. Analyses of 3D scans with higher resolution than used in this study will provide surface roughness information at the mineralogical level. We suggest that fractal dimension analyses of a combination of differently resolved 3D models will significantly improve the quality of shell morphometrics

Data report: evaluation of shipboard magnetostratigraphy by alternating field demagnetization of discrete samples, Expedition 361, Site U1475

The paleomagnetic shipboard data of International Ocean Discovery Program Site U1475, with a record reaching back to approximately 7 Ma, allowed for the identification of major magnetic polarity chrons and subchrons back to ~3.5 Ma. However, the natural remanent magnetization (NRM) was very weak, and transitional intervals with unclear polarity were as thick as several meters. The midpoints of these transitional intervals were reported in the shipboard results without decimal places because of the poor data quality. To evaluate and possibly refine the shipboard magnetostratigraphy, subsampling was performed across the polarity transitions. Detailed alternating field (AF) demagnetization experiments were conducted on these discrete samples and were complemented by anhysteretic remanent magnetization acquisition measurements and subsequent demagnetization. AF demagnetization data of NRM were analyzed using anchored principal component analysis (PCA) to obtain the characteristic remanent magnetization. These PCA results generally confirm the smoothed signal across polarity transitions at Site U1475. However, the midpoint depths of the top of the Keana Subchron, the Gauss-Matuyama and Matuyama-Brunhes boundaries, and the base of the Olduvai Subchron were adjusted

Lake Management and Eutrophication Mitigation: Coming down to Earth—In Situ Monitoring, Scientific Management and Well-Organized Collaboration Are Still Crucial

Lakes, together with rivers and subterranean aquifers, are indispensable natural resources for humans and other organisms [...

Impact of surface albedo and vegetation on the response of the LLN climate model to the astranomical forcing

The main purpose and aim of this study is to simúlate the climate impacts of land surface albedo change induced by anthropogenic activity between 0 AD and pre-industrial Era, using LLN 2D climate model - MoBidiC. The reason why this topic was chosen is that first, human activities have changed the land surface significantly. Theoretically, by switching between different vegetation and land use forms, Earth’s surface radiation balance (land surface albedo) henee the energy received by the Earth can be altered significantly, which results Earth’s climate change. Second, the climatic effect of the vegetation has long been proposed, but its importance in climate formation and in climate change has not been fully understood (Otterman, 1977; Sagatí et al, 1979; Potter et al, 1981; Showstack, 2001). Third, vegetation clearing for agriculture practice is the only discemable anthropogenic impact on natural environment before Industrial Revolution.Doctorat en sciences (sciences géographiques) (GEOG 3)--UCL, 200

Plateau Lake Water Quality and Eutrophication: Status and Challenges

The continuous and widespread deterioration of lake water quality and eutrophication is not only a local problem, but also a global phenomenon [...

Plateau Lake Water Quality and Eutrophication: Status and Challenges

The continuous and widespread deterioration of lake water quality and eutrophication is not only a local problem, but also a global phenomenon [...

Seasonal Variation and Spatial Heterogeneity of Water Quality Parameters in Lake Chenghai in Southwestern China

Seasonal dynamics and the vertical stratification of multiple parameters, including water temperature (WT), dissolved oxygen (DO), pH, and chlorophyll-a (Chl-a), were analyzed in Lake Chenghai, Northern Yunnan, based on monitoring data collected in 2015 (October), 2016 (March, May, July), 2017 (March, June, October), 2018 (August), and 2020 (June, November). The results indicate that the lake water was well mixed in winter and spring when the water quality was stable. However, when WT becomes stratified in summer and autumn, the Chl-a content and pH value changed substantially, along with the vertical movement of the thermocline. With rising temperature, the position of the stratified DO layer became higher than the thermocline, leading to a thickening of the water body with a low DO content. This process induced the release of nutrients from lake sediments and promoted eutrophication and cyanobacteria bloom. The thermal stratification structure had some influence on changes in DO, pH, and Chl-a, resulting in the obvious stratification of DO and pH. In summer, with an increase in temperature, thermal stratification was significant. DO and pH achieved peak values in the thermocline, and exhibited a decreasing trend from this peak, both upward and downward. The thermocline was anoxic and the pH value was low. Although Chl-a maintained a low level below the thermocline and was not high, there was a sudden increase in the surface layer, which should be urgently monitored to prevent large-scale algae reproduction and even local outbreaks in Lake Chenghai. Moreover, Lake Chenghai is deeper in the north and shallower in the south: this fact, together with the stronger wind–wave disturbance in the south, results in surface WT in the south being lower than that in the north year-round. This situation results in a gradual diminution of aquatic plants from north to south. Water quality in the lake’s southern extent is better than that in the north, exhibiting obvious spatial heterogeneity. It is recommended that lake water quality monitoring should be strengthened to more fully understand lake water quality and take steps to prevent further deterioration

Monitoring natural and anthropogenic influences on an ancient Chinese lake

Among the most powerful influences on the state of our freshwater systems include global climate and human interference. We can measure the impact both natural and anthropogenic changes have on freshwater by studying deep sediment cores from ancient lakes. Lake Fuxian, China is one of the few ancient lakes in the world and serves as an important source of drinking water in China. This lake lies along the edge of the Indo-Pacific Warm Pool, home to the formation of El Nino and La Nina events. These events are major drivers of global climate, influencing temperature fluctuations, precipitation patterns, and natural disasters around the world. Recently, industrialization and urbanization in the Yunnan Provence is thought to have influenced the state of Lake Fuxian, increasing anthropogenic influences on the lake. We hypothesized that: (1) this lake could record changes caused by anthropogenic inputs and global climate; and (2) local anthropogenic inputs had a greater impact on the state of the lake than global climatic changes. We have measured the elemental composition of a 30-cm sediment core from this lake through spectroscopy at 1cm intervals, recording approximately 300 years of data. Results to date show cycling in conservative metals through the core, representing switches in global El Nino and La Nina events. An increase in heavy metal concentrations reveal changes caused by anthropogenic influences. Our results provide insight to the difference in severity that both natural and anthropogenic may cause to a freshwater system. The elemental changes of the highest magnitude were caused by global climatic variation, revealing how natural global phenomena can have a greater impact on lakes than local anthropogenic inputs, an important observation for lake management as the threat of the state of freshwater resources is globally on the rise