Sediment Moisture Research Articles

Biomechanical Properties and Resistance to Uprooting of Laboratory‐Scale Wood Logs

AbstractWood dynamics affects riparian ecosystem functioning and river morphology. The spatial and temporal dynamics of wood pieces in river corridors, in particular of deposited rejuvenated wood logs, depend on their biomechanical properties and resistance to uprooting. The ability of stranded wood logs to withstand drag forces depends on how efficiently their roots have sprouted and on the interarrival time, magnitude, and duration of the moderate floods to which they are subjected. We performed static pullout tests on small‐scale wood logs (Salix species) of four different sizes, growth stages, and sediment moisture content. Statistics of root biomass growth rate and related spatial distribution along the trunk reveal important insights for upscaling dynamics. Similarly, force‐displacement curves indicate the maximum resistance and related energy for uprooting. Autocorrelation analysis of the sequence of force drops in the force‐displacement signal reveals the statistical nature of the mechanism of load redistribution among roots. These results are then used to advance a physically based mathematical model of the resistance of wood log roots to flow‐induced drag forces. Given that the magnitude, duration, and return period of hydrologic events are typically correlated, our model implies the existence of windows of opportunity for wood logs to either survive or remobilize.

Impacts of electrokinetic isolation of phosphorus through pore water drainage on sediment phosphorus storage dynamics

Pore water is a crucial storage medium and a key source of sediment phosphorus. A novel equipment based on electrokinetic geosynthetics (EKGs) was used for isolating phosphorus from eutrophic lake sediments through pore water drainage. Three mutually independent indoor group experiments (A, B, and C) were conducted to investigate the effects of voltage gradient (0.00, 0.25, and 0.50 V/cm) on pore water drainage capacity, phosphorus removal performance, sediment physicochemical properties, and phosphorus storage dynamics. The average reduction in the sediment moisture and total phosphorus content was 2.5%, 4.3%, and 4.6% and 28.15, 75.95, and 112.65 mg/kg after 6 days of treatment for A, B and C, respectively. Efficient pore water drainage through gravity and electroosmotic flow and electromigration of phosphate were the main drivers of sediment-dissolved and mobilized phosphorus separation. A high voltage gradient facilitated the migration of pore water and the phosphorus in it. The maximal effluent total phosphorous (TP) concentration was up to 27.9 times that in the initial pore water samples, and negligible effluent TP was detected when the pore water pH was less than 2.5. The TP concentration was exponentially and linearly related to the pH and electronic conductivity of the electroosmotic flow, respectively. The migration of H+ within the sediment matrix promoted the liberation of metals bounded to phosphorus, particularly of Ca–P and Fe–P. Pore water drainage through an EKG resulted in Ex–P separation of up to 87.50% and a 13.84 mg/kg decrease in Ca–P and 125.35 mg/kg accumulation of low mobile Fe–P in the weak acid anode zone.

Environmental and Spatial Influences on Biogeography and Community Structure of Saltmarsh Benthic Diatoms

Benthic microalgae play important roles in energy flow and biogeochemistry of coastal ecosystems; however, factors influencing community composition remain largely unknown. Our purpose was to identify and compare spatial and environmental influences on benthic diatom biogeography at regional scales. In summer 2018, we sampled sediment at various spatial scales (0.0001–180 km) from five saltmarshes in South Carolina, USA, and characterized diatom assemblages using DNA metabarcoding. Twenty-three environmental variables from marsh sediments, adjacent creeks, and atmosphere were recorded. Multivariate analyses revealed that the saltmarsh communities were clearly distinct. Community dissimilarity was compared to both geographic distance and environmental differences to determine influences on community structure. Mantel tests and redundancy analysis revealed that spatial influences, in addition to several environmental factors (phosphate, grain size, sediment sorting, sediment moisture, and creek salinity), were significant. Variation partitioning revealed that 26% of community variation was explained by geographic distance alone, whereas 60% could be explained by combined spatial/environmental factors. In contrast, the independent explanatory power of individual environmental factors was negligible. Our findings suggest that spatially structured environmental variation mainly conditioned the saltmarsh diatom biogeography in this region. Dispersal limitation, as evinced by the large pure spatial effect and distance-decay pattern, was also important. Spatial effects were stronger relative to that previously observed in other microbial groups (marine bacteria and phytoplankton) and detected at finer spatial scales. Results support prior studies that suggest body size and dispersal mode are important drivers of metacommunity structure and therefore must be considered when studying aquatic microbial biogeography.

Organic carbon storage and its influencing factors under climate warming of sediments in steppe wetland, China.

The effect of climate warming on soil organic carbon (SOC) of sediment in wetlands is important for accurately projecting SOC content. Thus, understanding the mechanism influencing SOC content under climate warming is necessary. Field investigation and a laboratory incubation experiment were conducted in Hulunbeier steppe wetland during 2016 and 2017. Four types of wetland were selected to incubate with ambient temperature and temperature increased by 2.5°C. The results showed that SOC content was negatively affected by temperature warming. The SOC content reduction in sediment caused by increasing temperature was ranged from - 2.34 to 39.52%. In addition, the content of sand, silt, total phosphorus (TP), calcium phosphate tribasic (Ca-P), total nitrogen (TN), and sediment moisture (MC) should be considered in models of SOC content in steppe wetland. However, it requires further validation, in particular how SOC content varies with warming temperatures, the duration of incubation, and other abiotic and biotic factors. These findings provide evidence that both climate warming and original characteristics of sediment can control the SOC storage dynamics in the steppe wetland. Graphical abstract.

Sub‐arctic river bank dynamics and driving processes during the open‐channel flow period

AbstractThere is growing concern that rapidly changing climate in high latitudes may generate significant geomorphological changes that could mobilise floodplain sediments and carbon; however detailed investigations into the bank erosion process regimes of high latitude rivers remain lacking. Here we employ a combination of thermal and RGB colour time‐lapse photos in concert with water level, flow characteristics, bank sediment moisture and temperature, and topographical data to analyse river bank dynamics during the open‐channel flow period (the period from the rise of the spring snowmelt flood until the autumn low flow period) for a subarctic river in northern Finland (Pulmanki River). We show how variations of bank sediment temperature and moisture affect bank erosion rates and locations, how bank collapses relate to fluvial processes, and elucidate the seasonal variations and interlinkages between the different driving processes.We find that areas with high levels of groundwater content and loose sand layers were the most prone areas for bank erosion. Groundwater seeping caused continuous erosion throughout the study period, whereas erosion by flowing river water occurred during the peak of snowmelt flood. However, erosion also occurred during the falling phase of the spring flood, mainly due to mass failures. The rising phase of the spring flood therefore did not affect the river bank as much as its peak or receding phases. This is explained because the bank is resistant to erosion due to the prevalence of still frozen and drier sediments at the beginning of the spring flood. Overall, most bank erosion and deposition occurrences were observed during the low flow period after the spring flood. This highlights that spring melt, while often delivering the highest discharges, may not be the main driver of bank erosion in sub‐arctic meandering rivers. © 2019 John Wiley & Sons, Ltd.

Microbial communities of upland peat swamps were no different 1 year after a hazard reduction burn

Fire in wetlands is poorly understood, yet hazard reduction burns are a common management practice and bushfires are becoming increasingly prevalent because of climate change. Fire may have long-lasting implications for the microbial component of these wetland ecosystems that regulate carbon and nutrient cycling. The extremely fire-prone Blue Mountains World Heritage Area in south-eastern Australia contains hundreds of endangered peat-forming upland swamps that regularly experience both bushfires and hazard reduction burns. In a before–after control–­impact study, we surveyed the sediment microbial community of these swamps to test the impact of a low-intensity hazard reduction burn. Along with sediment pH, moisture and organic content, we measured gene abundances including those relating to carbon cycling (quantitative PCR (qPCR) of pmoA, mcrA, bacterial 16S rRNA and archaeal 16S rRNA), and bacteria community fingerprint (terminal restriction fragment length polymorphism (T-RFLP)). One year after the hazard reduction burn, there were no significant differences in the gene abundances or microbial community fingerprint that could be attributed to the fire, suggesting that the hazard reduction burn did not have a long-term impact on these microbial communities.

Heavy metals in mangrove sediments along the Selangor River, Malaysia

Mangroves are woody plants that grow at the interface between land and sea in tropical and subtropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperature, and muddy anaerobic soils. The objectives of this study were to determine the selected heavy metals Copper (Cu), Zinc (Zn) and Lead (Pb) contamination in mangrove sediments at the Selangor River, Kampung Kuantan, Kuala Selangor, Selangor, Malaysia; and to compare heavy metals content in mangrove sediments between different plots and different sediment depths. Physical properties (sediment texture and sediment moisture) and chemical properties (pH water, electrical conductivity, and selected heavy metals) of sediments were determined by different plots and depths. The element of Pb was analyzed using the Inductively Coupled Plasma (ICP), whereas Cu and Zn using the Atomic Absorption Spectrometer (AAS). Data obtained were analyzed using the Statistical Analysis System (SAS) version 9.4 software. The results showed that the sediment texture was in the class of sandy clay, and soil moisture in all plots and at all depths were high. The contamination of sediment is affected by many factors, including soil pH and soil electrical conductivity. Cu, Zn and PB in sediment were determined around 1.00-10.60 mg/kg, 215.40-259.00 mg/kg and 18.83-28.59 mg/kg respectively, and were found to experience a significant difference between the plots, but not a significant difference between depths. The sediment in all plots and at all depths was contaminated with these heavy metals because of it being surrounded by residential and industrial areas, combined with particular recreational activities, agriculture and fishing along the Selangor River.

Experimental investigation on the decomposition characteristics of natural gas hydrates in South China Sea sediments by a micro-differential scanning calorimeter

Marine natural gas hydrate production has become a hot topic in recent years. There is still a long way to achieve the commercial production of marine hydrate reservoirs. The purpose of this work is to investigate the natural gas hydrate decomposition characteristics in the real marine sediments obtained from the South China Sea. A high-pressure micro-differential scanning calorimeter was employed to study the thermodynamic properties of natural gas hydrates. The results indicated that the increase in gas pressure or sediment salinity decreased the ice melting temperature by changing the vapor pressure of water. In addition, the decrease in sediment moisture from 40% to 30% increased the decomposition pressure of hydrates by 4.4 MPa at 278 K of sea bottom temperature, due to the water absorption capacity of the sediments increases the actual salinity furtherly. The influence of mixed gases on the decomposition pressure of hydrates was also investigated. The findings of this work on the effects of salinity and gas components on the decomposition pressure are significant to the spot safety production of marine natural gas hydrate reservoirs.

Influencing Factors of the Spatial–Temporal Variation of Layered Soils and Sediments Moistures and Infiltration Characteristics under Irrigation in a Desert Oasis by Deterministic Spatial Interpolation Methods

Soil moisture is the main limiting factor for crop growth and the sustainable development of oases in arid desert areas. Therefore, the temporal and spatial variation and infiltration laws of oasis soil moisture should be studied. The objective of this study is to reveal the influencing factors of the spatial–temporal variation of layered soil and sediment moisture and infiltration characteristics under irrigation in desert oases. Hydraulic conductivities were measured using the double-ring infiltrometer, while the regional and site soil moistures were measured and calibrated using weighted method and neutron moisture meter. Deterministic spatial interpolation methods, including multiquadric radial basis function, inverse distance weighted, and local polynomial regression isogram, were adopted to map the regional distribution of hydraulic conductivities, spatial soil moistures, and spatial–temporal isogram of the point site soil moistures in Yaoba Oasis, respectively. Results showed that the leading influencing factors of the (1) regional spatial soil moisture were soil and sediment permeability, stream link direction, microclimate, and dewfalls; (2) spatial layered soil and sediment moistures were microclimate and dew condensation; and (3) spatial–temporal variation at the point site profiles were soil texture, water requirement, and preferential flow. Under irrigation, soil moisture increased significantly, in which the maximum increase was 10.8 times the original state, while the recharging depth substantially increased up to 580 cm with the preferential flow. The spatial–temporal variation of the soil moisture under irrigation indicated that the best irrigation frequency should be 15 days per time. Moreover, the infiltration process can be divided into the preferential flow, piston flow, and balanced infiltration stages.

Salt Marsh Greenhouse Gas Fluxes and Microbial Communities Are Not Sensitive to the First Year of Precipitation Change

AbstractChanging precipitation patterns are predicted to alter ecosystem structure and function with potential carbon cycle feedbacks to climate change. Influenced by both land and sea, salt marshes are unique ecosystems and their productivity and respiration responses to precipitation change differ from those observed in terrestrial ecosystems. How salt marsh greenhouse gas fluxes and sediment microbial communities will respond to climate‐induced precipitation changes is largely unknown. We conducted 1‐year precipitation manipulation experiments in the Spartina patens (high marsh) zone of two salt marshes and quantified ecosystem functions at both and microbial community structure at one. Precipitation treatments (doubled rainfall, extreme drought, and seasonal intensification) had a significant, although transient, impact on porewater salinity following storms at both sites, but most site conditions (nutrient concentrations, sediment moisture, and temperature) were unaffected. Extreme drought led to a subtle change in microbial community structure, but most ecosystem functions (primary productivity, litter decomposition, and greenhouse gas fluxes) were not affected by precipitation changes. The absence of ecosystem function change indicates functional redundancy (under extreme drought) and resistance (under doubled precipitation and seasonal intensification) exist in the microbial community. Our findings demonstrate that salt marsh ecosystems can maintain function (including ecosystem services like carbon sequestration) under even the most extreme precipitation change scenarios, due to resistance, resilience, and functional redundancy in the underlying microbial community.

Subsurface Microbial Habitats in an Extreme Desert Mars-Analog Environment.

Sediments in the hyper-arid core of the Atacama Desert are a terrestrial analog to Mars regolith. Understanding the distribution and drivers of microbial life in the sediment may give critical clues on how to search for biosignatures on Mars. Here, we identify the spatial distribution of highly specialized bacterial communities in previously unexplored depth horizons of subsurface sediments to a depth of 800 mm. We deployed an autonomous rover in a mission-relevant Martian drilling scenario with manual sample validation. Subsurface communities were delineated by depth related to sediment moisture. Geochemical analysis indicated soluble salts and minerology that influenced water bio-availability, particularly in deeper sediments. Colonization was also patchy and uncolonized sediment was associated with indicators of extreme osmotic challenge. The study identifies linkage between biocomplexity, moisture and geochemistry in Mars-like sediments at the limit of habitability and demonstrates feasibility of the rover-mounted drill for future Mars sample recovery.

Grazers superimpose humidity effect on stream biofilm resistance and resilience to dry-rewet stress

Temperate low order streams increasingly experience intermittency and drying due to climate change. In comparison to well-studied Mediterranean streams, drying events in canopied temperate streams occur under higher ambient humidity which probably affects the metabolic response to drying. Previous work on drying sediments (in temperate streams) did not consider the interactions of trophic levels. We hypothesized that preservation of sediment moisture due to high humidity increases resistance to drying in temperate streambed biofilms and fast resilience of biofilm activity after flow resumption. We also expected the presence of macroinvertebrate grazers to modulate the biofilm response to dry-rewet stress. Following a two-level factorial design in 24 microcosms, we tested the effect of drying intensity (moderate and intense) and grazer presence and absence (P. antipodarum) on the activity of biofilm colonizing shallow hyporheic sediment. We measured the community respiration over a drying period of 27 days, a single rewetting event and a follow-up of three days. Grazer presence stimulated biofilm community respiration (CRmic) in the permanently wet control, but decreased biofilm resistance to desiccation (<0.2% of pre-disturbed activity), regardless of drying intensity. In the absence of grazers, higher atmospheric humidity in moderately drying microcosms resulted in maintaining a film of adhesive water and low CRmic (29% of pre-disturbed respiration) until the end of the drying period. After flow resumption, the CRmic increased within 8 h, achieving 79–83% of pre-disturbed respiration (no grazers) and 15–41% (with grazers), respectively. Results show that short dry periods in temperate streams, even under high humidity, impact the streambed biofilm community negatively. The complex response and strong effect of grazer presence indicates that experiments including interactions of trophic levels and settings mimicking environmental factors during dry-rewet stress are needed.

Key role of streambed moisture and flash storms for microbial resistance and resilience to long‐term drought

Abstract Spatial and temporal widening of drought periods together with occurrence of flash storm events are consequences of global change affecting temporary stream ecosystems. Streambed heterotrophic microbes and the key biogeochemical processes they carry on could be endangered by the strengthening of drought episodes. Here, we performed a 165‐day experiment through 12 streambed sediment columns to study heterotrophic microbial functional and structural responses to long‐term drought. Two sediment depths (surface and hyporheic) and leaf litter were monitored under three treatments: control (maintained in wet, pool‐like conditions), dry (5 months of drought), and dry–storm (5 months of drought including two flash storms). All treatments were then followed by rewetting. Surface sediment followed by leaf litter was the most affected by the long‐term drought as shown by the reduction of polysaccharidic enzyme activities and litter decomposition rate, although lignin decomposition was not affected. This resulted in a greater use of recalcitrant compounds which might be due to reduced labile organic matter sources and the greater resistance of fungi than bacteria to drought. Moreover, in surface sediment, bacterial viability and algal biomass were reduced while the production of extracellular polymeric substances was intensified with dryness, suggesting its potential role as survival strategy. Hyporheic sediments appeared more resistant to long‐term drought, and this might be linked to its slightly higher water content (2.5%) than the surface (0.5%) during drying together with a greater content of fine material that allowed fungi and bacteria to survive and extracellular enzyme activities to be maintained. Microbial resilience to long‐term drought in sediment and leaf litter was promoted by the flash storms as shown by the fast recovery of enzyme activities, bacterial viability and leaf litter decomposition rate in the dry–storm treatment, once rewetted. Storms might liberate previously occluded carbon sources that fuel the fast microbial reactivation as well as providing sediment moisture for microbial survival. Our results highlight that long‐term drought may compromise stream biogeochemical processes linked to organic matter decomposition and that microbes are highly sensitive to minimal water content changes. Thus, long‐term drought consequences could be mitigated by occasional precipitations or by natural streambed moisture.

The forgotten dimension in sandy beach ecology: Vertical distribution of the macrofauna and its environment

Spatial and temporal environmental heterogeneity influences biodiversity distribution patterns and dynamics on sandy beaches. In these ecosystems, the microscale vertical distribution adds a dimension to the analysis of biological and physical processes, whose ecological patterns have been rarely described. An intensive across-shore sampling in a dissipative beach was conducted, using a stratified corer to analyze small-scale vertical variations in macrofaunal and physical variables. Sediment temperature decreased towards the swash zone and at deeper sediments. Conversely, moisture, grain size and organic content increased seaward, concurrently with the highest vertical variability. Species richness and density increased from the dunes to the swash zone, being highest at the surface, whereas biomass was higher in sediments deeper than 15 cm as a consequence of larger individual sizes. Sediment moisture and temperature showed a consistent correlation with biological descriptors. Deconstructed by taxonomic group, a significant vertical segregation of body size was observed, suggesting different microhabitat preferences and burrowing abilities. Species spatial patterns varied according to life history traits and differential susceptibility to variations in environmental conditions. This study provides novel insights on vertical environmental and biological variations across the dune-shore axis in a dissipative beach. Expanding the findings of this research to larger spatio-temporal scales is a short-term need to decipher the processes underlying the community and population patterns outlined here.

Sedimentary profiles of pollution marker chemicals along a large tributary of Chesapeake Bay (mid-Atlantic USA)

Molecular markers in environmental geochemistry include natural product or pollutant chemicals in sediments that are indicative of discharge sources or emission pathways. Four classes of molecular marker compounds, including fatty acids, sterols, PCBs, and PAHs, in surficial sediments (top 2 cm) collected along a downstream transect of the Potomac River within the US mid-Atlantic region were analyzed and correlated with potential pollution discharge sources in close proximity to the sampling sites. Thirty-five surficial sediment samples were collected using a petite Ponar grab sampler along a 320-km longitudinal transect of the Potomac River (mid-Atlantic USA), a major tributary of Chesapeake Bay, ranging from the upland fluvial river to its confluence with the Bay. The sediments were collected along the transect at approximately equidistant points. The marker chemicals were extracted from sediments using microwave-assisted extraction and quantified on a dry weight basis by gas chromatography or gas chromatography-mass spectrometry. Sediment moisture, texture, and organic carbon and nitrogen content were also determined. Fatty acids and sterols were well correlated with ecological factors in the Potomac River, while the sterol ratio epi+brassicasterol/stigmasterol showed moderate spatial correlation with nearby waste treatment plants (WTPs) and city locations, especially in the upland and tidal freshwater river. The fecal sterol coprostanol also showed moderate spatial correlation with some WTPs in both the upland and tidal river. PCB and PAH concentrations were primarily correlated with urban and large military installations. PCBs in sediments appeared to be predominantly derived from Aroclors while PAHs showed a strong pyrogenic origin. Retene and perylene were unique markers for PAHs in sediment and were indicative of aged organic matter in sediments. The marker chemicals had utility in identifying pollution emission sources and pathways in the Potomac River. For PCB pollutants, sediment profiles reflected localized source emissions from industrial sites. PAHs showed a downstream plume effect derived from urban Washington, DC. Fatty acids and sterols were most useful for identifying ecological shifts (i.e., terrestrial versus aquatic origin), but showed spatial correlations with wastewater treatment plants and cities.

Does hydrological reconnection enhance nitrogen cycling rates in the lakeshore wetlands of a eutrophic lake?

Lakeshore wetlands are thought to be hot spots for biogeochemical processes. However, many lakeshore wetlands have been hydrologically disconnected from the associated lake by levees that have altered the ecosystem services they provide. Lakeshore restoration projects have been undertaken to recover the hydrological connection; however, the effects of the various restoration practices on biogeochemical cycling remain unclear. Here, we compared variation in sediment nitrogen (N) cycling rates to assess the restoration benefits of N removal in a series of recently hydrologically restored lakeshore wetlands, including ponds and bottomlands, of Lake Dianchi, China. The results showed that nitrification rates were generally higher in the ponds, while denitrification rates were higher in the bottomlands. Hydrological reconnection stimulated the development of several sediment properties critical for N cycling rates in the ponds, including increases in sediment carbon (C) and N contents; however, bottomland reconnection increased sediment moisture and decreased sediment C and N contents likely due to erosion by wind-induced wave action. Correspondingly, hydrological reconnection significantly increased the sediment N cycling rates in ponds but decreased the sediment N cycling rates in bottomlands over time. Path analyses revealed that substrate characteristics, including moisture and C and N availability, were the critical drivers regulating wetland N cycling rates. These results imply that the restoration targets could not be met simply by hydrological reconnection. Future wetland restoration requires further understanding of the relationship between changes in sediment properties and biogeochemical processes.

Has Submerged Vegetation Loss Altered Sediment Denitrification, N2O Production, and Denitrifying Microbial Communities in Subtropical Lakes?

AbstractLoss of submerged vegetation has become one of the most serious ecological issues in shallow lakes worldwide. However, there is limited understanding of the effect of vegetation loss on sediment nitrogen (N) cycling processes and microbial communities, which are closely linked to the N removal function of aquatic ecosystems. Here we investigated the sediment denitrification and N2O production rates of 10 macrophyte‐rich and 12 macrophyte‐free lakes in subtropical China. We determined the abundance of diversity of nirS‐ and nirK‐encoding denitrifiers in sediments using quantitative polymerase chain reaction and clone libraries. The results showed that denitrification and N2O production rates in vegetated lakes were slightly but not significantly lower than those in nonvegetated lakes. Sediment denitrification rates in vegetated lakes were positively correlated with water NO3− concentration but not significantly related to submerged vegetation and denitrifier communities. Similarly, the presence of submerged macrophytes had no significant effect on denitrifier diversity and abundance. Water N content and sediment moisture were the main factors affecting the composition of denitrifying communities. Moreover, no significant correlation was found between community similarity and geographical distance among lakes. Overall, our findings suggest that submerged vegetation degradation in Yangtze lakes has no significant effect on sediment denitrification rates and denitrifying community structure. Abiotic factors, especially water N level and sediment moisture, play a critical role in controlling N removal capacity of lake sediments.

Tourist Traffic Significantly Affects Microbial Communities of Sandstone Cave Sediments in the Protected Landscape Area “Labské Pískovce” (Czech Republic): Implications for Regulatory Measures

In the Protected Landscape Area “Labské pískovce” (Czech Republic), there are many sandstone caves accessible by permission only and where climbing equipment is commonly required. The tradition of visiting the caves dates back to turn of the 19th and 20th centuries, and visitors traditionally record their visits in log-books. We have gathered attendance data from 12 caves from log-books and via survey (2-year form collection period). The attendance varied from less than 10 to ~650 visitors annually. Signs of inadequate behavior of visitors were observed, especially waste disposal and smoking in the caves. Sediment step-compression increased significantly the ratios of fungi/bacteria and gram-positive to gram-negative (G+/G−) phospholipid fatty acids (PLFA) as well as PLFA of actinobacteria and activities of sediment phosphatases, glucosidases, and peroxidases. The number of visitors was correlated positively with the G+/G− ratio and sediment nutrients but negatively with sediment moisture and the activity of peroxidases. The results indicate a significant effect of attendance on sediment microbial communities, most likely caused by the import of nutrients into caves. Hence, reconsideration of the cave attendance policy is recommended.

Quality Assessment of Akinbo River Sediment around Lafarge Cement Wapco, Ewekoro, Nigeria

A study was conducted to assess the impact of industrial discharge on the quality of sediment obtained from River Akinbo around Lafarge Cement WAPCO, Ewekoro. Four locations were chosen along the water course (River Akinbo) to reflect a consideration of all industrial activities that are capable of changing the quality of sediments. Sediment samples were collected in three monthsbetween (October 2015 - June 2016) at the four sampling points. The physicochemical parameters determined were sediment pH, moisture content, sulphate (mg/l), nitrate (mg/l), phosphate (mg/l) and chloride (mg/L) using standard methods. Sequential Extraction Procedure (SEP) was used to determine the concentration of heavy metals to include (Pb, Cr, Cd, Mn, Ni, Fe) while XRF was used to determine the geo-chemical index of the sediment. Sediment pH is between slightly alkaline, the bioavailability of the metal followed a trend Ni &gt; Cr &gt;Mn&gt; Cd&gt;Pb&gt; Fe with a little interchange at some sampling point. Percentage by weight trend for the XRF were in the order of major metals Al &gt; Fe &gt;Ca&gt; K &gt; Na and in the order of minor metals Mn&gt; Cr &gt; Zn. The concentration of cadmium, chromium and iron were above the permissible limit WHO and FEPA. The high concentration of heavy metals in sediment is most likely as a result of the amount of effluents (dust and waste water) discharged into the river from the factory. To prevent mass extinction of aquatic organisms due to anoxic conditions, proper regulations should be implemented to reduce the organic load the river receives.

Phosphorus fraction and phosphate sorption-release characteristics of the wetland sediments in the Yellow River Delta

The aim of this study was to investigate phosphorus (P) fractions and phosphate sorption-release characteristics of the surface sediments regarding the wetland restoration in the Yellow River Delta (YRD). Sediments samples were collected from three typical sample plots: Phragmites australis community (p), Suaeda salsa community (s), and bare land (b) both in natural wetland (N) and restored wetland (R). The results showed that the mean content of TP was 541.58 mg/kg, and the rank order of P fractions were: inorganic phosphorus (IP) (65.6%) > residual phosphorus (RP) (24.9%) > organic phosphorus (OP) (9.5%). For sediments under the same land cover, TP and OP contents were significantly higher in natural wetlands than those in restored wetlands. This indicated that the restoration project really made a difference in TP content of sediments, and the decreased TP might result from decreased OP. For P kinetics sorption, a quick sorption mainly occurred within 0.5 h. The maximum phosphorus adsorption capacities (Qmax) ranging from 139.40 mg/kg to 224.06 mg/kg and the bonding energy constant (K) ranging from 0.33 mg/L to 1.37 mg/L were both obtained using a Langmuir model. In addition, Qmax, P release (Pr) and P release rates (Prr) were in the order of Nb > Np > Ns > Rb > Rp > Rs, Np > Rp > Ns > Rs = Nb > Rb and Rp > Ns > Rs > Rb > Np > Nb, respectively. This indicated that sediments from natural wetland could adsorb more P as well as release more P into overlying water, moreover, more content of P were left in sediments comparing to restored wetland. Sediments from bare land were more likely to retain P as a pool because of the highest sorption capacity while lowest release potential. Our study showed that P sorption-release and the quick sorption processes were mainly affected by sediment moisture, amorphous iron and aluminum oxides (Feox and Alox). Besides, Qmax was related to background value of sediments P. OP was the major P fraction adsorbed by sediments, and the P adsorbed by sediments was mainly adsorbed on Feox and Alox.