Aquatic habitat use in a semi-aquatic mammal: the Eurasian beaver

Background Semi-aquatic mammals exploit resources both on land and in water and may require both to meet their habitat requirements including food- and building resources, refuges, and for social interactions with conspecifics. Within this, the specific availability of both terrestrial and aquatic resources is expected to impact individual fitness. Beavers are highly dependent on water for movement and protection from predators. They are central place foragers and mostly forage on woody vegetation near water although aquatic vegetation may also be an important food resource. However, little is known about their use of aquatic habitats. We aimed to address this knowledge gap by dead-reckoning fine-scale movement tracks and classifying fine-scale diving events, which we then related to the spatial distribution of aquatic vegetation and habitat components within the territory. Results Overall, there was a statistically clear decrease in probability that diving would occur at dawn and with increasing distance from territory borders. In addition, the distance from the lodge at which animals dived decreased through the night and during the spring/early summer. There was strong selection for diving habitats located closer to the riverbank, with stronger selection for these areas being observed in individuals with larger home ranges. We saw a higher selection for diving above clay sediment, and within 150 m from the lodge, presumably because mud and clay sediment tended to be located closer to the lodge than sand and rock sediment. Furthermore, we found a clear selection for diving in the presence of quillwort (Isoetes spp.), shoreweed (Littorella uniflora), and stonewort (Nitella spp.). Selection for these focal species was stronger among subordinate individuals. Individuals with lower body condition dived closer to the beaver lodge, and dives located further from the lodge were associated with high densities of aquatic vegetation. Conclusion We provide new knowledge on the aquatic habitat use in a semi-aquatic mammal and show how energetic constraints may shape how beavers spatially use the aquatic environment, whereby short and shallow dives appear most beneficial. We show how aquatic habitats may have great importance for both foraging, building materials and safety, and discuss to how they may affect the fitness of individuals.

Recycling and Reuse of Sediments in Agriculture: Where Is the Problem?

Though suggested by international conventions for a long time, there are still several technical and legislative limitations to a complete reuse and recycling of dredged sediments. In particular, reuse of unpolluted sediments can be practiced, whereas sediment recycling is still affected by several downsides, and a significant proportion of the recycled fine sediments has no practical use and must be landfilled. However, the silty clayey fraction of the recycled sediments is rich in organic matter and macro- and micronutrients useful for plant growth. Nevertheless, sediment recycling in agriculture is not possible, even in non-food agricultural sectors, due to the lack of a permissive legislation and of consolidated supply chains. In addition to plant nutrients, the silty-clay sediment fraction may also accumulate organic and inorganic pollutants, and while the organic pollutants can be effectively biodegraded, metals and metalloids may concentrate at concentrations higher than the limits set by the environmental and agricultural legislations. In this paper, I briefly summarize the scientific evidence on the potential reuse and recycling of sediments in agriculture, and I discuss the main reasons for hindrance of sediment recycling in agriculture. I also present evidence from a real industrial biodegradation process that produces bioremediated fine sediment fractions with suitable properties as a mineral ingredient for plant-growing media. I propose that nutrient-rich recycled sediments could be reconsidered as a component material category in the new EU regulation on fertilizers.

Study on the Rheological Behavior of a Model Clay Sediment

Clay sediments are the main component of seabed sediment. Interactions between the nano-sized, disk-shaped and charged clay particles are complicated, as they control the sediment’s rheology. In this study, we studied the rheological behavior of the clay sediment modeled by laponite and bentonite suspensions experimentally using a rotational rheometer. The yield stress decreased when water content increased. Meanwhile, the yield stress of the laponite suspension first increased and then decreased with increasing salinity. It is considered that the face-to-face repulsive electrostatic interaction between clay platelets dominated the yield behavior. A yield stress model was developed to describe the change of the yield stress with both the water content and the salinity. When the system started to flow, the viscosity decreased with increasing shear. A master curve of viscosity is was from the viscosity-stress curves at different water contents if the applied shear stress was normalized by the yield stress and the viscosity normalized by a characteristic viscosity. This study provides a preliminary understanding of the clay sediment rheology and its mechanism for the investigation on the flowing of the sediment systems with strong interparticle interaction.

Karakteristik Keteknikan Sedimen Kuarter Kaitannya dengan Potensi Bahaya Geologi di Kawasan DAS Cimanuk Bagian Hilir

ABSTRAKKabupaten Indramayu yang akan dikembangkan sebagai kawasan industri didominasi oleh endapan Kuarter yang terdiri atas endapan fluvial, dataran banjir, pematang pantai, dan delta. Daerah tersebut terletak pada area dekat sesar aktif, yakni segmen sesar Baribis-Subang dengan besaran magnitudo 6,5 Mw. Penelitian di wilayah DAS Cimanuk bagian hilir Kabupaten Indramayu, Provinsi Jawa Barat bertujuan untuk mengetahui karakteristik fisik dan mekanik serta kaitannya dengan potensi bahaya geologi yang bisa terjadi. Metode yang digunakan dalam penelitian ini adalah pengamatan 4 inti bor teknik dan pola kurva sondir (10 CPTu dan 13 CPT) serta analisis laboratorium yakni ukuran butir, hydrometer, batas-batas Atterberg, dan klasifikasi sedimen. Berdasarkan pengamatan inti bor, pola kurva sondir, dan analisis laboratorium, jenis sedimen yang berkembang di daerah penelitian adalah lempung, lanau, lanau pasiran, pasir lanauan dan pasir dengan karakteristik yang spesifik. Tingkat kepadatan sedimen pasir serta tingkat konsistensi sedimen lempung bagian utara penelitian menunjukkan karakteristik yang relatif lebih lepas dan lunak dibandingkan dengan bagian selatan. Berdasarkan karakteristik keteknikan menunjukkan bahwa nilai N-SPT < 10 atau CPT/CPTu < 6.000 kPa pada sedimen pasir dan pasiran berpotensi terhadap likuefaksi dan nilai N-SPT < 4 atau CPT/CPTu < 5.000 kPa pada sedimen lempung dan lanau berpotensi terhadap amblesan. Kata kunci: bahaya geologi, Cimanuk, sedimen kuarterABSTRACTAs a future industrial area, Indramayu Regency is dominated by Quaternary sediment of fluvial, flood plain, beach ridge and deltaic sediments. The area is close to active faults, The Baribis-Subang fault segment with 6.5 Mw. This research is conducted around the lower Cimanuk catchment of Indramayu. Its aims to determine mechanical and physical characteristics related to potential geological hazards. The methods used in this research are 4 core observation, cone penetration patterns (10 CPTu and 13 CPT) and laboratory analysis such as grain size, hydrometer, Atterberg limits and sediment classification. Based on its methods, sediments that develop at the research area are clay, silt, sandy silt, silty sand and sand with specific character. Level consistency and density of clay and sand at the northern area is relatively soft and loose than the southern one. Based on engineering characteristics, the results show that NSPT < 10 or CPT/CPTu < 6,000 kPa value of sandy and sand sediment are potential against liquefaction and N-SPT < 4 or CPT/CPTu < 5,000 kPa value of silt and clay sediment are potential against subsidence. Keywords: geological hazards, Cimanuk, quarternary sediment

Effect of Sintering Temperature on Properties of Setiu Clay Sediments

The effect of sintering temperature on physical properties of Setiu clay sediment was studied. The ceramic samples were prepared via slip casting method, and sintered at different temperatures ranging from 900 to 1100°C, with 2 hours soaking time. Morphologies of ceramic samples were characterized using Tabletop Microscope. Shrinkage was determined from measurement of samples before and after sintering process. A good ceramic sample without warping or cracks obtained after casting process and after sintered at different temperatures. The results show that sintering temperatures greatly influence morphology of samples. As sintering temperature increased the grain boundaries between particles become smoother and compacted while pores shrunk due to the densification behavior. A considerable increased in shrinkage from 5 to 20% were observed with increasing temperature from 900 to 1100°C. As conclusion, Setiu clay sediment are suitable for production ceramic products and 1000°C can be consider the best sintering temperature in terms of quality of products and production costs.

Experimental Study of Sand Production during Depressurization Exploitation in Hydrate Silty-Clay Sediments

Silty-clay reservoirs are a weak point in sand production and sand control studies due to their low economy. However, China’s marine natural gas hydrates (NGH) mostly exist in silty-clay sediments, which restrict the sustainable and efficient development of NGH. In order to study the sand production of hydrate silty-clay sediments, hydrate production experiments in vertical wells and horizontal wells were carried out using a self-developed hydrate sand production and sand control simulation device. The results showed a great difference between the hydrate silty-clay sediments and hydrate sand sediments. The significant differences in production pressure and production temperature between the different layers indicated the low permeability and low heterogeneity of the hydrate silty-clay sediments. The sliding settlement of the overall depression in the horizontal well and overall subsidence in the vertical well of the hydrate silty-clay reservoir would easily lead to silty-clay flow and large-scale sand production. When water rates decreased, the property of “silty-clay sediment filtration and wall building” was found, which formed a “mud cake” around the wellbore. The good strength of adhesion and fracture permeability of the “mud cake” provided ideas for reservoir reformation. This study further discusses sand production and sediment reformation in hydrate silty-clay sediments.

CLAY DETECTION IN LAKES OF LATGALE USING GROUND PENETRATING RADAR

The most common method to determine the presence of clay in lakebed is coring method. This method requires survey of the whole lake area using stratified sampling method which is time and physical labour consuming process. To lessen the amount of coring samples and narrow the area of clay survey thus making the whole process faster and more effective, research was made to determine the possibility to indentify clay and its sediments using georadar survey or ground penetrating radar (GPR) method. GPR data analysis and coring studies in lake Zeiļu were used to evaluate GPR as potential method in lake clay sediment research. GPR method was tested in summer and winter during ice-covered period.

A Spatial Scale Assessment of Depositional Areas in Mid-West Water Bodies: Implications for Ecological Risk of Hydrophobic Organic Compounds

This study was designed to summarize grain size data (% sand, % silt and % clay) from mid-west United States water bodies to determine the percent of sites where sediment samples are primarily depositional sediment (more than 50% silt/clay) or non-depositional (less than 50% silt/clay). Sediment sampling protocols were reviewed for all the grain size measurements to determine if non-random or random sampling was conducted. Based on four studies with a total of 269 sites, the mean percent of sites dominated by the silt/clay fraction was approximately 5%. This value is very low and certainly shows that depositional areas are spatially limited in mid-west water bodies. The ecological relevance of this result is that silt/clay areas where Hydrophobic Organic Compounds (HOCs) may be found are spatially limited for mid-west water bodies. Before judging HOC ecological risk it is critical to know how sites for sediment collection were selected, using either a non- random or random approach, and this information also needs to be carefully considered when assessing potential ecological risk of HOCs in ambient mid-west sediment. A random sampling design on a watershed scale that includes spatially extensive sediment mapping is recommended in areas where HOC ecological risk is suspected.