Bare Sand Research Articles

Freeze-thaw cycles aggravated the negative effects of moss-biocrusts on hydraulic conductivity in sandy land

Moss-biocrusts (BCs) play an essential role in soil stabilization, but it reduces soil hydraulic conductivity, hindering precipitation convert to soil water. Freeze-thaw cycles (FTCs) is a natural phenomenon, which can alter soil properties, causing widespread concern. However, few studies have focused on the effects of FTCs on hydraulic conductivity in BCs, which may alter the negative effects of BCs on hydraulic conductivity. We conducted an in-situ FTCs simulated experiment in BCs and bare sand (BS), to analyze the response of particle-size composition, water-stable aggregates and water repellency (WR) to FTCs, and their effects on saturated hydraulic conductivity (Ks). The results showed that the existence of BCs had affected water-stable aggregates, particle-size composition, WR and Ks. Compared with BS, the percentage of clay-size particle content increased by 44% and 60% in BCs layer and its underlying soil, respectively. The stability of water-stable aggregates was 19% higher in BCs than the measured stability in BS. Ks of BS was 2.4 times higher than that of BCs, and the increasing percentage of water-stable aggregates larger than 5 mm would reduce Ks in sandy land. FTCs had the significant effects on water-stable aggregates, WR and Ks. WR and Ks of BCs were decreased 57% and 25% after FTCs, respectively. Moreover, after FTCs, the percentage of soil water-stable aggregates > 5 mm reduced 19%, while 1–5 mm increased 18%. WR and sand content were significantly and negatively correlated with Ks, while clay content and the percentage of soil water-stable aggregates > 5 mm were significantly and positively correlated with Ks in BCs. Our results indicated that BCs and FTCs had a significant and negative effects on Ks. FTCs further decreased the hydraulic conductivity, which was not conductive to the supply of meltwater to soil water reservoir in the period of winter and early spring.

Impacts of soil disturbance on plant diversity in a dry grassland

Dry grasslands are not only amongst the most species-rich habitats in Europe but also amongst the most threatened. Threats include habitat destruction as well as modification to the historic disturbance regime under which native plants have evolved (e.g. too high or too low levels of disturbance). The aim of this study is to examine the effects of soil disturbance intensity on species composition and diversity in a dry grassland in Mols Bjerge National Park in Denmark. We recorded vascular plant species inside and just outside patches of bare sand and at the transition between bare sand and dense vegetation outside the patches. We found that species richness was highest in the dense vegetation, intermediate in the transition zone and lowest in bare sand areas. However, an analysis of plant traits showed that the number of small annual species was highest in the transition zone. High abundance of small annual species may therefore indicate intermediate disturbance regimes. Moreover, literature indicates that many threatened species are adapted to such habitats, which suggests that dry grasslands should be managed to maintain areas with intermediate disturbance intensities to improve conditions for many threatened species. High abundance of small annual species thus indicates that favourable management has been achieved.

The use of pumice amended with sand media for domestic wastewater treatment in vertical flow constructed wetlands planted with lemongrass (Cymbopogon citratus)

The performance efficiency in constructed wetlands (CWs) technology is primarily affected by the media material and the types of plants used. Recently, investigations into the usage of local materials and plants in CWs has increased. Pumice is a material which is potential used as a media. However, research on amendment of pumice with other media in CWs is still limited. Therefore, this study aims to evaluate the potential of pumice amended with sand media and planted with lemongrass (Cymbopogon citratus) in CWs to remove organic matter, suspended solids, nutrients, and coliform. The adsorbents were characterized using X-ray diffraction, FTIR and XRF followed by adsorption experiments for PO4–P. Furthermore, Six vertical flow (VF) mesocosms with a diameter of 10.2cm and 55cm depth were established over six months. The treatments were based on percentage of sand media amended with pumice and planted with lemongrass. Furthermore, the barren media were applied to investigate the effect of lemongrass. The loading rate of domestic wastewater into the VF mesocosms was 2 L/day while inflows and outflows were determined for nutrients, organic matter, suspended solids and coliform. The adsorption of PO4–P followed the Langmuir model with adsorption capacity was 0.089 and 0.067 mol/g for pumice and sand, respectively. The results also showed that the removal efficiency of TSS, COD, NO3–N, NO2–N, PO4–P and total coliforms were in the range of 93.7–97.3 %, 52–83 %, 63–86 %, 51–74%, 81–88 % and 92–97 %, respectively. Based on the results, the highest removal efficiency was observed in the sand media amended with 50 % pumice and planted with lemongrass, while the lowest was found in the barren sand media.

On the spatial variability and influencing factors of soil organic carbon and total nitrogen stocks in a desert oasis ecotone of northwestern China

Accurate assessments of soil organic carbon (SOC) and total nitrogen (TN) stocks and controlling factors are essential for understanding carbon and nitrogen sequestration in soil. In this study, we analyzed the spatial distribution and influencing factors of SOC and TN stocks to the depth of 3 m in a desert oasis ecotone of northwestern China. The study area has experienced large-scale transition of dunelands to irrigated croplands in the past 40–50 years. The results showed that the vertical distributions of SOC and TN stocks were well demonstrated by quadratic function forms. The SOC and TN stocks at 0–3 m depths in nabkha dunes were generally significantly higher than that in bare sand dunes. Additionally, after converting nabkha dunes to croplands, both SOC and TN stocks at the top 0.4 m depths increased with the extension of cultivation years, the mean SOC and TN stocks significantly increased from 0.396 to 0.992 kg·m−2 and from 0.053 to 0.096 kg·m−2, respectively. The strongest heterogeneity of SOC and TN generally appeared at top 0–0.4 m depths and decreased with the depth. The SOC and TN stocks in the nabkha dunes near the water areas were relatively higher, which may be suitable for croplands reclamation. It is noteworthy that land use brought a major influence of SOC and TN at top 0–0.4 m depths, whereas soil texture (clay and silt contents) was the main factor that controlled SOC and TN at deep soil depths (1–3 m). The results indicate that the nabkha dunes also increased carbon and nitrogen stocks throughout the entire 3 m soil profiles. While the demand for food is almost certain to increase in arid and semiarid China and other regions worldwide, the conversion from non-traditional croplands such as dunelands to croplands is likely going to continue.

Sequential overgrazing by green turtles causes archipelago-wide functional extinctions of seagrass meadows

After centuries of decline, green turtle (Chelonia mydas) populations are showing handsome localized recoveries due to dedicated conservation efforts. This calls into question how much herbivory can be sustained by seagrass meadows that these turtle populations feed on. In our study, we documented the long-term impacts of green turtle foraging on seagrass meadows in the Lakshadweep archipelago, Indian Ocean. We tracked green turtle densities and seagrass areal extent in five atolls across the archipelago since 2005. Turtle densities first grew to record levels in the seagrass meadow of the Agatti lagoon around 15 years ago. Within a few years of intense herbivory, the meadow underwent radical biomass reduction and compositional shifts, leading to functional extinction and ultimately, bare sand. This trajectory of decline wtas repeated in every atoll, with turtle aggregations persisting 2 to 6 years before meadows were depleted, depending on their initial size. By 2019, all large meadows had declined, and in 2020, green turtles were distributed at low densities in every meadow. The meadows were limited to small patches of early successional species, maintained in a state of protracted recovery by constant, low-level herbivory. We measured the impacts of turtles on two key ecosystem services, a habitat for fish communities and stored organic carbon. Turtle overgrazing resulted in massive declines in seagrass fish diversity, biomass, and abundance, and major reductions in sediment-stored carbon. Apart from being important conservation flagships, green turtles are strong ecosystem interactors, and can potentially cause trophic cascades or functional extinction of seagrass ecosystems.

Setting the evolutionary timeline: Tillandsia landbeckii in the Chilean Atacama Desert

The Chilean Atacama Desert is among the oldest deserts of the world. Here, Tillandsia landbeckii is forming a unique vegetation type known as Tillandsia lomas. This vegetation consists in its typical configuration of one single vascular plant species only and forms regular linear structures in a sloped landscape and is largely depending on fog occurrence as dominant source of water supply. Without developing a typical root system, there are only few other terrestrial Tillandsia species growing on bare sand in Chile and Peru such as T. marconae, T. virescens, T. purpureaor T. latifolia. Although phylogenetic evidence is limited, convergent evolution of this unique growth behavior is evident. The predominantly arid and hyper-arid climate exists since the Early Miocene, which raises the question about timing of T. landbeckii evolutionary history. Phylogenomic analyses using whole plastome sequence data highlight the onset of diversification in T. landbeckii approximately 500,000 years ago. We also demonstrate subsequent secondary genetic contact with T. purpurea during the Late Pleistocene using DNA sequence data and genome size estimates, which resulted into the formation of T. marconae.

Using High-Spatial Resolution UAV-Derived Data to Evaluate Vegetation and Geomorphological Changes on a Dune Field Involved in a Restoration Endeavour

Nowadays, the employment of high-resolution Digital Surface Models (DSMs) and RGB orthophotos has become fundamental in coastal system studies. This work aims to explore the potentiality of low-cost Unmanned Aerial Vehicle (UAV) surveys to monitor the geomorphic and vegetation state of coastal sand dunes by means of high-resolution (2–4 cm) RGB orthophotos and DSMs. The area of study (Punta Marina, Ravenna, Italy), in the North Adriatic Sea, was considered very suitable for these purposes because it involves a residual coastal dune system, damaged by decades of erosion, fragmentation and human intervention. Recently, part of the dune system has been involved in a restoration project aimed at limiting its deterioration. RGB orthophotos have been used to calculate the spectral information of vegetation and bare sand and therefore, to monitor changes in their relative cover area extension over time, through the using of semi-automatic classification algorithms in a GIS environment. Elevation data from high-resolution DSMs were used to identify the principal morphological features: (i) Dune Foot Line (DFL); (ii) Dune Crest Line (DCL); Dune seaward Crest Line (DsCL); Stable Vegetation line (SVL). The USGS tool DSAS was used to monitor dune dynamics, considering every source of error: a stable pattern was observed for the two crest lines (DCL and DsCL), and an advancing one for the others two features (DFL and SVL). Geomorphological data, as well as RGB data, confirmed the effectiveness of planting operations, since a constant and progressive increase of the vegetated cover area and consolidation of the dune system was observed, in a period with no energetic storms. The proposed methodology is rapid, low-cost and easily replicable by coastal managers to quantify the effectiveness of restoration projects.

Eastern Hog‐Nosed Snake Habitat Selection at Multiple Spatial Scales in Ontario, Canada

ABSTRACTHabitat loss is the greatest contributor to the decline of species globally. To prioritize protection of imperiled species, it is important to examine habitat use at multiple spatial scales because the availability of different resources and habitat features is scale dependent. We conducted a radio‐telemetry study in the Long Point region of Ontario, Canada, in 2009 and 2010 to examine habitat selection at multiple spatial scales by eastern hog‐nosed snakes (Heterodon platirhinos), a species at risk in Canada. We documented the habitat composition of home ranges compared to the surrounding landscape, the selection of locations within home ranges based on classified satellite imagery, and the use of microhabitat features based on site characterization in the field. At the scale of the home ranges, hog‐nosed snakes avoided areas of agriculture and selected sand barrens. Within home ranges, hog‐nosed snakes selectively used areas altered by humans (e.g., residential sites, openings in tree plantations). Microhabitats used by hog‐nosed snakes had more woody debris, logs, and lower vegetative coverage than adjoining random sites. Because hog‐nosed snakes prefer open areas and require sandy soils for nesting, management efforts should focus on the conservation and maintenance of sand barrens and patches of early successional forest. © 2021 The Wildlife Society.

Variable contributions of seafloor communities to ecosystem metabolism across a gradient of habitat-forming species

The contributions of habitat-forming species to the biodiversity and ecosystem processes of marine and terrestrial ecosystems are widely recognized. Aquatic plants are considered foundation species in shallow ecosystems, as they maintain biodiversity and sustain many ecosystem functions such as primary production and respiration. Despite the increasing amount of biodiversity-ecosystem functioning experiments in seagrass habitats, the effects of benthic variability on ecosystem functioning are rarely investigated across spatially variable aquatic plant habitats. Here, we quantitatively link seasonal variability in seafloor metabolism (i.e. gross primary production and community respiration) with major benthic community components (i.e. microphytobenthos, aquatic plants and macrofauna) across a structural complexity gradient of habitat-forming species (in terms of shoot density and biomass), ranging from bare sand, to a sparse mixture of plants to a dense monospecific seagrass meadow. The increasing complexity gradient enhanced the magnitude of the relationships between benthic community and seafloor metabolism. The daily average seafloor metabolism per season at the bare site was similar to the sparse site, highlighting the role of microphytobenthos for seafloor metabolism in shallow unvegetated sediments. The contribution of the associated macrofauna to the seafloor respiration was similar to the aquatic plant community contribution. Infauna was the main macrofaunal component significantly explaining the seasonal variability of seafloor respiration. However, benthic community-metabolism relationships were stronger within the plant community than within the macrofauna community (i.e. steepest slopes and lowest p-values). Understanding these relationships are a priority since climate change and biodiversity loss are reducing habitat complexity around the world, jeopardizing valuable ecosystem functions and services.

Carbon accumulation by Pinus sylvestris forest plantations after different periods of afforestation in a semiarid sandy ecosystem

AbstractThe carbon pool is changing in afforestation ecosystems, which vary in their duration since establishment, in many semiarid sand regions. Understanding this is important for the management of the planted forest. The present study explored the dynamics of afforested forest carbon pool in a semiarid sandy ecosystem, northwest China. We studied afforested forests of pine (Pinus sylvestris) of five afforestation ages (20, 30, 40, 50, and 60 years since planting, and bare sand as control), the carbon storage and carbon sequestration rate of the forest aboveground biomass layer, surface litter layer, and soil layer (0–50 cm) were calculated, and the soil water content and soil organic carbon of 0–400 cm soil depth were measured. The results showed that the carbon sequestration rate was highest after 20–30 years, with 0.58 Mg C ha−1 yr−1 in the soil layer (0–50 cm). We found a rate of 0.13 Mg C ha−1 yr−1 in the surface litter layer, and a rate of 20.79 Mg C ha−1 yr−1 in the forest aboveground biomass layer. The carbon storage of the forest aboveground biomass layer was highest after 30–40 years, and the carbon storage of the surface litter increased with time. In the soil layer, the carbon storage at 0–10 cm depth was highest after 60 years, the carbon storage at 20–50 cm depth increased soon after afforestation and then decreased afterward with increasing afforestation ages with the maximum for 20‐50 cm occurring after 30–40 years. The total carbon storage [the forest aboveground biomass layer, surface litter layer and soil layer (0‐50 cm)] was higher when afforestation ages reached around 30 years, after that it decreased with increasing afforestation age. Our research improves the understanding of the P. sylvestris forest ecosystem carbon sequestration in a semiarid sandy area.

Gill microbiome structure and function in the chemosymbiotic coastal lucinid Stewartia floridana.

Lucinid bivalves harbor environmentally acquired, chemosynthetic, gammaproteobacterial gill endosymbionts. Lucinid gill microbiomes, which may contain other gammaproteobacterial and/or spirochete taxa, remain under-sampled. To understand inter-host variability of the lucinid gill microbiome, specifically in the bacterial communities, we analyzed the microbiome content of Stewartia floridana collected from Florida. Sampled gills contained a monospecific gammaproteobacterial endosymbiont expressing lithoautotrophic, mixotrophic, diazotrophic and C1 compound oxidation-related functions previously characterized in similar lucinid species. Another low-abundance Spirochaeta-like species in ∼72% of the sampled gills was most closely related to Spirochaeta-like species in another lucinid Phacoides pectinatus and formed a clade with known marine Spirochaeta symbionts. The spirochete expressed genes were involved in heterotrophy and the transport of sugars, amino acids, peptides and other substrates. Few muscular and neurofilament genes from the host and none from the gammaproteobacterial and spirochete symbionts were differentially expressed among quadrats predominantly covered with seagrass species or 80% bare sand. Our results suggest that spirochetes are facultatively associated with S. floridana, with potential scavenging and nutrient cycling roles. Expressed stress- and defense-related functions in the host and symbionts also suggest species-species communications, which highlight the need for further study of the interactions among lucinid hosts, their microbiomes and their environment.

Fungal symbionts of endangeredCrocanthemum canadense(Cistaceae) in Nova Scotia

Crocanthemum canadense (L.) Britton (Cistaceae) is critically imperiled in Nova Scotia. The decline of Nova Scotian Crocanthemum canadense is largely due to the loss of the Annapolis Valley sand barrens habitat. Fungal symbionts may aid in nutrient and water acquisition as well as plant defenses. The role of fungal associations with Crocanthemum canadense is unknown; our goal was to identify fungal symbionts to inform ongoing conservation research. We isolated fungi from eighteen Crocanthemum canadense plants collected from Greenwood, Nova Scotia. Using internal transcribed spacer (ITS) rDNA barcoding of fungal cultures, we identified 58 fungal taxa. ITS2 meta-amplicon barcoding of roots and rhizosphere soil revealed 241 fungi with basidiomycetes accounting for 53.8% of reads. Chaetothyriales sp., Mycetinis scorodonius, Acidomelania panicicola, and Scleroderma citrinum were the most abundant root associates based on meta-amplicon data. We quantified percent root colonization of arbuscular mycorrhizal fungi (AMF) using root staining and microscopy. The average AMF colonization rate of the roots was 29.6% (n = 18). Our research provides a foundation for understanding the fungal community in this declining habitat and the first account of fungal symbionts in the above- and below-ground tissues and rhizosphere of Crocanthemum canadense. Identifying fungi influencing endangered Nova Scotian Crocanthemum canadense is valuable for developing conservation strategies.

Effects of solution chemistry and humic acid on the transport of polystyrene microplastics in manganese oxides coated sand

Microplastics as the emerging persistent pollutants have attracted more attention in the terrestrial environments. In this study, the transport behavior of polystyrene microplastics (PSMPs) in manganese oxides coated sand (MOCS) was examined under different pH, ionic strength (IS), cationic type and humic acid (HA) conditions. Compared with the transport behavior of PSMPs in the bare sand, the mobility of PSMPs in MOCS was significantly lower and less affected by pH, IS and cation type, which can be attributed to the existence of attractive electrostatic force and rougher collector surfaces of MOCS. Specifically, the transport of PSMPs was inhibited when cotransport with Cd2+. Furthermore, the HA significantly increased the transport of PSMPs in the MOCS, and the mobility increased with the increase of HA concentration ranged from 0 to 10 mg L−1. The results can contribute to the further understanding of the migration mechanism and fate of microplastics in the soil system.

Soil biocrusts reduce seed germination and contribute to the decline in Artemisia ordosica Krasch. shrub populations in the Mu Us Sandy Land of North China

The sand-stabilising, xeric shrub Artemisia ordosica Krasch. has experienced widespread decline decades after being widely distributed through seeding in the Mu Us Sandy Land in China. The role of biocrusts in the decline of A. ordosica populations has received attention but has not been directly confirmed. To clarify the effects of biocrusts on shrub decline, a field study was conducted with different biocrust treatments (bare sand, lichen biocrust, moss biocrust, biocrust removed) in August 2019 in the Mu Us Sandy Land in North China. In each biocrust treatment, the age structure, dynamic indices, and reproductive allocation patterns of the A. ordosica population were determined, in addition to soil characteristics. A separate laboratory study was conducted to determine the effects of soil moisture and nutrients on seed germination. With the development of biocrust, the age structure of A. ordosica populations began to decline, but when the biocrust was removed, A. ordosica seedlings re-established. Soil moisture and nutrient contents were higher under lichen biocrust (earlier stage of biocrust development) and biocrust removal than under moss biocrust (later stage of biocrust development). In response to the adverse conditions under biocrust, A. ordosica increased reproductive output while reducing vegetative growth, thereby increasing the possibility for offspring dispersal and colonisation of new habitats. By contrast, with biocrust removal, A. ordosica reduced reproductive allocation. In addition, with the development of biocrust, soil moisture was reduced, and seed germination was limited. Thus, biocrusts are important in the decline of A. ordosica in sandy lands because of reductions in seed germination, which further suggests that moderate removal of biocrusts to improve seed germination can be key in the sustainable development of sandy land vegetation.

The autotrophic community across developmental stages of biocrusts in the Gurbantunggut Desert

Autotrophs, such as cyanobacteria, algae, and prokaryotic non-cyanobacterial autotrophs, play fundamental roles in biocrust development by adhering to soil particles and fixing CO2. The variation in autotrophic community structure, in particular that of prokaryotic non-cyanobacterial autotrophs, and the factors driving this variation during biocrust succession have not been revealed. In this study, we investigated the autotrophic communities in bare sand and three biocrust successional stages in the Gurbantunggut Desert by assessing the cbbL gene, which encodes the form I ribulose1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large subunit. The cbbL gene profiles demonstrated that the abundance of cyanobacteria and algae (form IAB, 105–107 copies g−1 soil) and prokaryotic non-cyanobacterial autotrophs (form IC, ~107 copies g−1 soil) changed significantly as succession progressed. Stepwise multiple regression showed that soil water, organic carbon, total phosphorous, available potassium content and pH explained 95.7% of the variation in cyanobacterial and algal (form IAB) abundance. Soil water content explained 60.1% of the variation in prokaryotic non-cyanobacterial autotroph (form IC) abundance. Variation partitioning analysis showed that the variation in form IC community structure was related to soil nutrients (C, N, and P), ion content (Mg2+, Na+ and Ca2+) and physical soil properties (86.1% explained). The variation in form IAB community structure could be predictable by total potassium, total organic carbon and Na+ and Mg2+ content (37.1% explained). Our results showed significant shifts in both autotrophic abundance and community structure, and highlighted the combined effects of soil factors on autotrophic community variation during biocrust succession.

Near-shore distribution of alien Ponto-Caspian amphipods in a European dam reservoir in relation to substratum type and occurrence of macroinvertebrate taxa

Knowledge of habitat requirements and interspecific interactions of invasive species helps predict their impact and spread. We determined the relationships within the invasive freshwater Ponto-Caspian amphipod assemblage, and their associations with macroinvertebrates in the near-shore zone of a central European lowland dam reservoir. We sampled five habitat types: bare sand at the water line, bare sand (0.2 m depth), bare sand (0.5 m depth), macrophyte-overgrown sand (1 m depth), stones (0.3 m depth) on four dates (October 2015–October 2016).Pontogammarus robustoidesoccurred in all habitats,Dikerogammarus villosusandEchinogammarus ischnuswere limited to the stony bottom. Amphipod densities were positively associated with one another exceptDikerogammarusjuveniles, negatively correlated with adults. The occurrence ofD. villosus,juvenileDikerogammarusandE. ischnuswas positively related to the presence of the shelter-forming bivalveDreissena polymorpha.Pontogammarus robustoideswas positively associated with sphaeriid clams and gastropods (shelters), as well as oligochaetes and chironomids (potential prey items).DikerogammarusvillosusandE. ischnuswere positively related to chironomids and oligochaetes, respectively. Coexistence of various alien amphipods in the studied area, indicated by prevailing positive relationships in their assemblage, may be enabled by the abundance of shelters and rich food sources allowing habitat partitioning.

Bio-morphological features of salsola richteri kar in cultural conditions

The article is devoted to the study of the bio-morphological features of the Richter’s saltwort (salsola richteri kar.) in the conditions of culture. Good growth of cherkez on bare sands, high seed productivity, the ability to reproduce by seeds and cuttings and tolerate significant salinity, powerful growth of the root system contributed to its promotion as a promising plant when fixing the sands.

Псаммофитная растительность Баргузинской котловины (Республика Бурятия)

Псаммофитная растительность Баргузинской котловины (Республика Бурятия)

Saved by the shell: Oyster reefs can shield juvenile blue crabs Callinectes sapidus

Juvenile blue crabs Callinectes sapidus use seagrass and other structured habitats as refuges from predation. Oyster reef habitats provide structural complexity that may offer refuge, but the value of these habitats for juvenile blue crabs has not been examined. We quantified survival of juvenile C. sapidus in structured oyster reef habitat versus unstructured soft-bottom habitat. In a field tethering experiment in the York River, lower Chesapeake Bay (USA), juvenile C. sapidus (10-50 mm carapace width [CW]) were tethered in sand (n = 40) or oyster reef (n = 39) habitats at subtidal sites 1-2 m deep. An underwater camera system was used to record predation activity during 24 h trials. Juvenile crab survival was significantly higher on the oyster reef habitat (53.8%) than on bare sand (15.0%), and tended to increase with crab CW in both habitats. The main successful predators on juvenile blue crabs were northern pufferfish Sphoeroides maculatus in the oyster reef habitat and adult blue crabs in the sand habitat. The high survival rate of juvenile C. sapidus in oyster reef habitats suggests that oyster reefs include physical habitat complexity that may offer refuge from predators. Restored and natural oyster reefs could provide an alternative nursery habitat for juvenile blue crabs, expanding the ecosystem services provided by restored oyster reefs.

Matric suction effect on distribution of stresses caused by vehicle wheels on a bare silty sand

-Soil compaction in cropping systems, caused by the external pressure of machinery, creates impermeable layers that restrict water and nutrient cycles reducing agricultural production. To evaluate the matric suction effects on distribution with depth of stresses in a soil, caused by the use of agricultural machinery, Jet Fill tensiometers were installed at two different depths (i.e. 0.15 m, 0.30 m) in a soil profile constituted by silty sand with gravel (SM); to register the increments on subsoil vertical stresses, two miniaturized load cells (i.e. 16. 5 mm in diameter) were installed in a horizontal position under the centre line of the vehicle wheels’ path, at approximately 0.15 m and 0.30 m depth. Care was taken to calibrate the load cells in field conditions. A vehicle was made to pass over the soil surface, at a speed less than 5 km/h; the tyre inflation pressure applied on wheel was 380 kPa. Response of load cells to vehicle loading was evaluated at different average matric suction measured on soil profile. Finally, measured stresses have been compared with values obtained by applying well-known elastic theoretical methods used to assess stresses applied by tyres on bare soils. The corresponding results show that the increment of vertical stresses decreases as matric suction increases, and a good correlation between measurements and simulations of the increment on subsoil vertical stress.