Dissimilatory nitrate reduction to ammonia (DNRA) is an important nitrate reduction pathway in lake sediments; however, little is known about the biotic factors driving the DNRA potential rates and contributions to the fate of nitrate. This study reports the first investigation of DNRA potential rates and contributions in lake sediments linked to DNRA community structures. The results of ¹⁵N isotope-tracing incubation experiments showed that 12 lakes had distinct DNRA potentials, which could be clustered into 2 groups, one with higher DNRA potentials (rates varied from 2.7 to 5.0 nmol N g⁻¹ h⁻¹ and contributions varied from 27.5% to 35.4%) and another with lower potentials (rates varied from 0.6 to 2.3 nmol N g⁻¹ h⁻¹ and contributions varied from 8.1% to 22.8%). Sediment C/N and the abundance of the nrfA gene were the key abiotic and biotic factors accounting for the distinct DNRA potential rates, respectively. A high-throughput sequencing analysis of the nrfA gene revealed that the sediment C/N could also affect the DNRA potential rates by altering the ecological patterns of the DNRA community composition. In addition, the interactions between the DNRA community and the denitrifying community were found to be obviously different in the two groups. In the higher DNRA potential group, the DNRA community mainly interacted with heterotrophic denitrifiers, while in the lower DNRA potential group, both heterotrophic and sulfur-driven autotrophic denitrifiers might cooperate with the DNRA community. The present study highlighted the role of the sulfur-driven nitrate reduction pathway in C-limited sediments, which has always been overlooked in freshwater environments, and gave new insights into the molecular mechanism influencing the fate of nitrate.

Estuarine wetlands are major contributors to mercury (Hg) transformation into its more toxic form, methylmercury (MeHg). Although these complex habitats are important, estuarine Hg bioaccumulation is not well understood. The longnose gar Lepisosteus osseus (L. 1758), an estuarine predator in the eastern United States, was selected to examine Hg processes due to its abundance, estuarine residence, and top predator status. This study examined variability in Hg concentrations within longnose gar muscle tissue spatially and temporally, the influence of biological factors, potential maternal transfer, and potential negative health effects on these fish. Smaller, immature fish had the highest Hg concentrations and were predominantly located in low salinity waters. Sex and diet were also important factors and Hg levels peaked in the spring. Although maternal transfer occurred in small amounts, the potential negative health effects to young gar remain unknown. Fish health as measured by fecundity and growth rate appeared to be relatively unaffected by Hg at concentrations in the present study (less than 1.3 ppm wet weight). The analysis of biotic and abiotic factors relative to tissue Hg concentrations in a single estuarine fish species provided valuable insight in Hg bioaccumulation, biomagnification, and elimination. Insights such as these can improve public health policy and environmental management decisions related to Hg pollution.

Integrated systems with appropriate bio-filters can be used to treat aquaculture effluents. However, the information on bio-filters that alters the ecological functions of the bacterioplankton community (BC) in biodegradation of the aquaculture effluents remains controversial. In this study, we implemented a comprehensive restoration technology combined with bio-filters [biofilm, clam (Tegillarca granosa), and macrophytes (Spartina anglica)] to investigate their influence on the stability of the BC and nutrient removal. We found that the diversity of BC was linked with biogeochemical factors in processing and upcycling nitrogen-rich effluents into high-value biomass. The BC exhibited significant distinct patterns in the bio-filter areas. Potential biomarkers for constrained harmfully algae-bacteria (Nitriliruptoraceae, Bacillales, and Rhodobacteraceae) and nutrient removal were significantly higher in the bio-filters areas. The bio-filters significantly promoted the restoration effects of N and P balance by reducing 82.34% of total nitrogen (TN) and 81.64% of total phosphorus (TP) loads at the water interface. The main mechanisms for TN and TP removal and nutrient transformation were achieved by assimilation and absorption by the emergent macrophytes (Spartina anglica). The bio-filters significantly influenced the biodegradability and resolvability of particulate organic matter through ammonification, nitrification, and denitrification of microbes, which meliorated the nutrient removal. Beside bio-filter effects, the BC was significantly controlled by abiotic factors [nitrate (NO₃⁻-N), dissolved oxygen (DO), total nitrogen (TN), and water temperature (WT)], and biotic factors (chlorophyll ɑ and green algae). Our study revealed that the co-existence system with bio-filters may greatly improve our understanding on the ecological functions of the BC in aquaculture systems. Overall, combined bio-filters provide an opportunity for the development of efficient and optimized aquaculture wastewater treatment technology.

The aim of the study was to investigate abiotic and biotic factors influencing the accumulation of endocrine disrupting compounds (EDCs) such as bisphenol A (BPA), 4-tert-octylphenol (OP) and 4-nonylphenol (NP) in mussels Mytilus trossulus from the Gulf of Gdansk (Southern Baltic). The key abiotic factor influencing BPA, OP and NP accumulation in mussels is their hydrophilicity/lipophilicity, which affects their main assimilation routes - by digestive tract for the more lipophilic OP and NP, and additionally by the gills for the less lipophilic BPA. As a result, high condition index (i.e. higher soft tissue weight) is more often correlated with high concentrations of OP and NP in mussels than with BPA. Furthermore, alkylphenols have 6–8 times greater accumulative potential than BPA. Concentration of the studied compounds was lower in females than in males following spawning, and the effect lasted longer for BPA than for alkylphenols. The influence of season and hydrological conditions on BPA, OP, NP in the mussel was more pronounced than the proximity of external sources of these compounds. An increase in water temperature in summer probably stimulated the solubility of BPA, the least lipophilic of the studied compounds, and led to increased assimilation of this compound from water (through gills). On the other hand, high OP and NP concentrations in mussels occurred in spring, which was caused by increased surface run-off and sediments resuspension.

Mediterranean Basin ecosystems, their unique biodiversity, and the key services they provide are currently at risk due to air pollution and climate change, yet only a limited number of isolated and geographically-restricted studies have addressed this topic, often with contrasting results. Particularities of air pollution in this region include high O3 levels due to high air temperatures and solar radiation, the stability of air masses, and dominance of dry over wet nitrogen deposition. Moreover, the unique abiotic and biotic factors (e.g., climate, vegetation type, relevance of Saharan dust inputs) modulating the response of Mediterranean ecosystems at various spatiotemporal scales make it difficult to understand, and thus predict, the consequences of human activities that cause air pollution in the Mediterranean Basin. Therefore, there is an urgent need to implement coordinated research and experimental platforms along with wider environmental monitoring networks in the region. In particular, a robust deposition monitoring network in conjunction with modelling estimates is crucial, possibly including a set of common biomonitors (ideally cryptogams, an important component of the Mediterranean vegetation), to help refine pollutant deposition maps. Additionally, increased attention must be paid to functional diversity measures in future air pollution and climate change studies to establish the necessary link between biodiversity and the provision of ecosystem services in Mediterranean ecosystems. Through a coordinated effort, the Mediterranean scientific community can fill the above-mentioned gaps and reach a greater understanding of the mechanisms underlying the combined effects of air pollution and climate change in the Mediterranean Basin.

Arsenic is the most toxic element for humans. Presenting naturally in aquatic ecosystems and due to anthropogenic action, this semi-metal transfers to shellfish through the food chain. This systematic review aims to explain the dynamic of arsenic in the marine aquatic system, investigating factors that affect its bioaccumulation. A total of 64 articles were considered from three databases. The key abiotic factor influencing the presence of arsenic in shellfish is anthropogenic contamination, followed by geographic location. The crucial biotic factor is the genetics of each species of shellfish, including their diet habits, habitat close to the sediment, metabolic abilities, physiological activities of organisms, and metal levels in their habitats and food. Finally, arsenic presents an affinity for specific tissues in shellfish. Despite containing mostly less toxic organic arsenic, shellfish are a relevant source of arsenic in the human diet.

In wetland ecosystems, vegetation can float freely on water surface, forming dense canopy which may play important ecological roles. This is especially true in many urban wetlands in which fluidity is low and nutrient level is high. So far, effects of free-floating vegetation on abiotic and biotic factors of wetlands have been known, while little on wetland ecosystem functions such as litter decomposition. To examine whether the canopy of free-floating vegetation on water surface will influence litter decomposition in wetlands or not, we conducted a 50-day in situ decomposition experiment in a subtropical urban pond wetland, in which litter bags of nine combinations of three mesh sizes and three litter species were put on the bottoms of total 22 ponds which were half with and half without free-floating vegetation canopy on the water surface. The ponds with and without the canopy had different water physicochemical properties. Overall, the canopy, the species identity, and the mesh size significantly decelerated mass loss and carbon loss of leaf litters while slightly on nitrogen loss. Effects of the canopy on leaf litter decomposition also showed species- and mesh size-dependent. Our results suggest that free-floating vegetation on water surface can alter water environmental factors and consequently change ecosystem functioning in wetlands.

Pinus gerardiana is considered an important species in dry temperate forests of North-Western Indian Himalaya because of its influence on ecological processes and economic dependence of local people in the region. But, large numbers of biotic and abiotic factors have affected P. gerardiana in these forests; hence, there is a crucial need to understand the regeneration dynamics of this tree species. The present investigation was conducted in P. gerardiana forests to understand vegetation pattern and regeneration processes on different sites in the region. Statistical analysis was performed to know variability in growing stock and regeneration on sample plots, while correlation coefficients and regression models were developed to find the relationship between regeneration and site factors. The vegetation study showed dominance of P. gerardiana, which is followed by Cedrus deodara, Pinus wallichiana and Quercus ilex in the region. The growing stock of P. gerardiana showed steep increasing and then steadily declining trend from lower to higher diameter class. The distribution of seedling, sapling, pole and trees was not uniform at different sites and less number of plots in each site were observed to have effective conditions for continuous regeneration, but mostly showed extremely limited regeneration. Regeneration success ranging from 8.44 to 15.93 % was recorded in different sites of the region, which suggests that in different sites regeneration success is influenced by collection of cone for extracting seed, grazing/browsing and physico-chemical properties of soil. Regeneration success showed significant correlation and relationship with most of abiotic and biotic factors. The regeneration success is lower than the requirement of sustainable forest, but varies widely among sites in dry temperate forests of Himalaya. More forest surveys are required to understand the conditions necessary for greater success of P. gerardiana in the region.

Pharmaceuticals in the aquatic environment may be decomposed by abiotic and biotic factors. Photodegradation is the most investigated abiotic process, as it occurs in the natural environment and may be applied in wastewater treatment technology. Although pharmaceuticals are detected in effluents and surface water in a mixture, the photodegradation process is mainly evaluated with single compounds. The photodegradation of fluoxetine (FLU) and fluvoxamine (FLX) in the presence of diclofenac (DCF) and triclosan (TCS) was investigated with HPLC and bioassay. FLU did not degrade under UV-Vis irradiation in SunTest CPS+ either with or without the tested additives, although small amounts of desmethyl fluoxetine and 4-(trifluoromethyl)phenol were formed. In contrast, during irradiation, FLX isomerized to cis-FLX. This process was enhanced by DCF and TCS, but to a lesser degree than by humic acids. Thus, the presence and composition of the matrix should be considered in the environmental risk assessment of pharmaceuticals. As the toxicity of the tested solutions depended only on the concentration of the tested drugs, it was suggested that the biological activity of the photodegradation products was lower than that of the parent compounds.

Ground-dwelling arthropod communities are influenced by numerous biotic and abiotic factors. Little is known, however, about the relative importance of vegetation structure and abiotic environmental factors on the patterns of ground-dwelling arthropod community across a wide range of soil salinities. Here, a field survey was conducted to assess the driving forces controlling ground-dwelling arthropod community in the salinized grasslands in the Hexi Corridor, Gansu Province, China. The data were analyzed by variance partitioning with canonical correspondence analysis (CCA). We found that vegetation structure and edaphic factors were at least of similar importance to the pattern of the whole ground-dwelling arthropod community. However, when all collected ground-dwelling arthropods were categorized into three trophic guilds (predators, herbivores, and decomposers), as these groups use different food sources, their populations were controlled by different driving forces. Predators and decomposers were mainly determined by biotic factors such as vegetation cover and aboveground plant biomass and herbivores by plant density and vegetation cover. Abiotic factors were also major determinants for the variation occurring in these guilds, with predators strongly affected by soil electrical conductivity (EC) and the content of fine particles (silt + clay, CS), herbivores by soil N:P, EC, and CS, and decomposers by soil EC and organic matter content (SOM). Since plant cover, density, and aboveground biomass can indicate resource availability, which are mainly constrained by soil N:P, EC, CS, and SOM, we consider that the ground-dwelling arthropod community in the salinized grasslands was mainly influenced by resource availability.