Steppe Wetlands Research Articles

Effect of temperature variation on phosphorus flux at the sediment-water interface of the steppe wetlands.

Environmental factors are generally considered to be important factors affecting the release process of phosphorus (P) in sediments. However, little is known about the effect of temperature increased at first and then decreased with the season change on the P flux rate and flux amount at the sediment-water interface in the steppe wetlands. The effects of the temperature variation on P flux at the sediment-water interface in the steppe wetlands during the vegetation growing season under simulated wetland habitat were studied. The results showed that the release of P from sediments to overlying water was greatly affected by temperature changes. When the temperature rose, P was released from the sediment into the overlying water, while P was precipitated from the water into the sediment with the temperature dropped. During simulation period, the total P in water flux rates between sediment and overlying water (FP) was ranged from - 4.51 to 4.99mg·m-2·day-1, while the dissolved reactive P in water flux rates between sediment and overlying water (FDP) was changed from - 5.37 to 5.14mg·m-2·day-1. The FP and FDP were negatively correlated with the content of total P in water (WTP), dissolved reactive P in water (WDRP), pH of sediment (pH), and microbial biomass P (MBP), but increased with temperature (T), aluminum phosphate (Al.P), and occluded phosphate (Oc.P). The P flux rates were affected by temperature variation both directly and indirectly; the mechanism of how temperature influenced the fate of P in the wetland is still not clear. Therefore, the physicochemical properties and kinetic, thermodynamic, and microbiology characteristics should be combined together to clarify the mechanism in future research.

Anthropogenic impact on the Taldykol lake system in the city of Nur-Sultan

The article describes study of the hydrochemistry of Taldykol lake system, consisting of the Big and Small Taldykol lakes, in the city of Nur-Sultan. The aim of the work is to assess the anthropogenic impact on the ecosystem of steppe wetlands located in the center of the developing capital. Sampling was carried out from 8 sites of the lake system in autumn 2020. The results of hydrochemical analysis of water samples made it possible to assess the level of chemical pollution and anthropogenic impact on the ecosystem, which, due to rapid urbanization, the lakes have been exposed to for decades. Now, due to the artificial fragmentation of lakes, the surface communication between the sites is disrupted, as evidenced by the different composition of pollutants in water bodies. Nevertheless, to draw up a complete picture and assess the anthropogenic impact on the Taldykol lake ecosystem, it is necessary to consider the results of a comprehensive study of lakes, which includes a number of additional works.

Responses of phosphorus flux in the sediment–water interface to C:N:P stoichiometry of different sediment components following temperature warming in steppe wetland, China

Responses of phosphorus flux in the sediment–water interface to C:N:P stoichiometry of different sediment components following temperature warming in steppe wetland, China

Lack of conspicuous sex-biased dispersal patterns at different spatial scales in an Asian endemic goose species breeding in unpredictable steppe wetlands.

Dispersal affects the spatial distribution and population structure of species. Dispersal is often male‐biased in mammals while female‐biased in birds, with the notable exception of the Anatidae. In this study, we tested genetic evidence for sex‐biased dispersal (SBD) in the Swan Goose Anser cygnoides, an Asian endemic and IUCN vulnerable species, which has been increasingly restricted to breeding on Mongolian steppe wetlands. We analyzed the genotypes of 278 Swan Geese samples from 14 locations at 14 microsatellite loci. Results from assignment indices, analysis of molecular variance, and five other population descriptors all failed to support significant SBD signals for the Swan Goose at the landscape level. Although overall results showed significantly high relatedness within colonies (suggesting high levels of philopatry in both sexes), local male genetic structure at the 1,050 km distance indicated greater dispersal distance for females from the eastern sector of the breeding range. Hence, local dispersal is likely scale‐dependent and female‐biased within the eastern breeding range. These findings are intriguing considering the prevailing expectation for there to be female fidelity in most goose species. We suggest that while behavior‐related traits may have facilitated the local genetic structure for the Swan Goose, several extrinsic factors, including the decreasing availability of the nesting sites and the severe fragmentation of breeding habitats, could have contributed to the absence of SBD at the landscape level. The long‐distance molt migration that is typical of goose species such as the Swan Goose may also have hampered our ability to detect SBD. Hence, we urge further genetic sampling from other areas in summer to extend our results, complemented by field observations to confirm our DNA analysis conclusions about sex‐specific dispersal patterns at different spatial scales in this species.

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.

Laboratory investigation of phosphorus loss with snowmelt and rainfall runoff from a Steppe wetland catchment.

Phosphorus (P) losses from terrestrial soils contribute to eutrophication of surface waters. As priority non-point source pollution ways, rainfall runoff (RS1) and snowmelt runoff (RS2) are the main carrier of P loss from terrestrial ecosystem. The aim of this study was to investigate the similarities and differences between P loss with RS1 and RS2 of the same soil type. Six types of soil were used in this experiment. Results have shown that 1), Different types of soil have different P loss with RS1 and RS2 under different slope, and the changes ranged from 0.003 to 0.370 mg L-1. 2), The effects of soil type, slope and runoff type on P loss with surface runoff was not independent, both individual effects of all factors and their interaction with the other two factors effected the P loss with runoff. 3), In our experiment, some soils showed no significant difference between P content in RS1 and RS2. In some soils, P loss with RS1 was higher than that with RS2 while the opposite conclusion was showed in Bog soil (BS) which with higher soil water content. 4), The P loss with RS1 and RS2 of different soils were both mainly affected by soil water content (SW), Olsen-P content (OP) and soil organic matter content (OM). These results can help us understand the P loss with different patterns of surface runoff better and are expected to provide pertinent opinions on the analysis of P loss with runoff and its influencing factors of grassland soils.

Leaf Functional Traits and Biomass of Wetland Plants in Forest and Steppe Zones

Leaf traits, the rate of gas exchange, and biomass were examined in five plurizonal species (Alisma plantago-aquatica L., Carex acuta L., Eleocharis palustris (L.) Roem. et Schult., Phalaris arundinacea L., and Typha angustifolia L.) of emergent plants growing in wetlands of forest (Middle Urals) and steppe (South Urals) zones. It was found that changes in the leaf thickness, leaf mass per area (LMA), the transpiration rate, and characteristics of the pigment complex associated with a rise in aridity were species-specific. Structural reorganization of the leaves of wetland plants growing in conditions of steppe wetland showed a general pattern of an increase in leaf density (1.2–2 times) and a reduction in leaf area (by 42–54%). This trend was accompanied by a reduction in the photosynthesis rate per 1 m2 (1.2–3.4 times) or per 1 mg of chlorophyll (by 29–63%). In two species, P. arundinacea and T. angustifolia, we detected a decrease in stomatal conductance by 2 and 4.8 times, respectively, in more arid conditions. Analysis of interspecific relations between plant productivity and leaf parameters has shown that plant biomass positively correlated with leaf area (r = 0.84, P < 0.01) and with the photosynthesis rate per leaf area unit (r = 0.97, P < 0.001) both in the regions of the Middle and South Urals. On the whole, structural changes in the leaves associated with adaptation of plant water relations to semiarid climate lead to a decrease in photosynthetic activity of leaves and, therefore, a decline of plant height and productivity of emergent plants growing in steppe wetland.

Effects of Sediment Chemical Properties on Phosphorus Release Rates in the Sediment-Water Interface of the Steppe Wetlands.

Rising temperature causes a process of phosphorus release, which can be characterized well using phosphorus release rates (VP). The objective of the present study was to investigate the major factors affecting sediment phosphorus release rates through a wetland habitat simulation experiment. The results showed that the VP of different wetland sediments were different and changed with the order of W–R (river wetland) > W–L (lake wetland) > W–M (grassy marsh wetland) > W–A (reservoir wetland). The main driving factors which influenced sediment phosphorus flux velocity in the sediment–water interface were sediment B-SO42−, B-MBN and A-MBP content. Path analysis and determination coefficient analysis indicated the standard multiple regression equation for sediment phosphorus release rates in the sediment–water interface, and each main factor was Y = −0.105 + 0.096X1 + 0.275X2 − 0.010X3 (r = 0.416, p < 0.01, n = 144), where Y is sediment phosphorus release rates; X1 is sediment B-SO42− content; X2 is sediment B-MBN; and X3 is sediment A-MBP content. Sediment B-SO42−, B-MBN and A-MBP content and the interaction between them were the main factors affecting sediment phosphorus release rates in the sediment–water interface. Therefore, these results suggest that soil chemical properties and microbial activities likely play an important role in phosphorus release rates in the sediment–water interface. We hope to provide effective scientific management and control methods for relevant environmental protection departments.

Hydrologic fluctuations trigger structural changes in wetland—dry grassland ecotones but have no effect on ecotone position

Ecotones between plant communities have received considerable attention among ecologists in the context of fragmentation, climate change and the management of heterogeneous landscapes. However, the predictability of ecotone dynamics is low and the processes taking place within ecotones are still poorly understood. In this study we aimed to characterize the positional and structural dynamics of thirteen ecotones in an ecotone-rich steppe–wetland landscape of Hungary in relation to the inter-annual fluctuations of water regime and the gradients of elevation and of soil composition. According to our results, the ecotones between steppe and wetland communities were sharp and their positions coincided with those places in the landscape where the rate of change in elevation was the highest, confirming that microtopography is a major determinant of ecotone position. Soil boundaries were also detected, mostly downhill to the ecotones. Interestingly, the fluctuations of the water supply had no effect on the position of the ecotones but significantly influenced a structural ecotone parameter, the compositional contrast bridged by the ecotones. High water supply caused high contrast, while low supply went along with low contrast. We explain these changes by asymmetric sensitivities to edge effects. When the water supply was low, the wetland edges became similar to the steppe edges due to the decrease of wetland specialists and to the increase of steppe specialists, but steppe edges did not exhibit an opposite change in wet years, suggesting that steppe communities dominated over wetland communities. The asymmetry in the interaction between the two communities may have pushed the soil boundaries downhill to the ecotones but the currently steppe-like soil of wetland edges could also make wetland edges more sensitive to edge effects; thus, the cause-effect relationship is difficult to disentangle.

Comparison of fatty acid contents and composition in major lipid classes of larvae and adults of mosquitoes (Diptera: Culicidae) from a steppe region

Emerging aquatic insects, including mosquitoes, are known to transfer to terrestrial ecosystems specific essential biochemicals, such as polyunsaturated fatty acids (PUFA). We studied fatty acid (FA) composition and contents of dominant mosquito populations (Diptera: Culicidae), that is, Anopheles messeae, Ochlerotatus caspius, Oc. flavescens, Oc. euedes, Oc. subdiversus, Oc. cataphylla, and Aedes cinereus, inhabited a steppe wetland of a temperate climate zone to fill up the gap in their lipid knowledge. The polar lipid and triacylglycerol fractions of larvae and adults were compared. In most studied mosquito species, we first found and identified a number of short-chain PUFA, for example, prominent 14:2n-6 and 14:3n-3, which were not earlier documented in living organisms. These PUFA, although occurred in low levels in adult mosquitoes, can be potentially used as markers of mosquito biomass in terrestrial food webs. We hypothesize that these acids might be synthesized (or retroconverted) by the mosquitoes. Using FA trophic markers accumulated in triacylglycerols, trophic relations of the mosquitoes were accessed. The larval diet comprised green algae, cryptophytes, and dinoflagellates and provided the mosquitoes with essential n-3 PUFA, linolenic, and eicosapentaenoic acids. As a result, both larvae and adults of the studied mosquitoes had comparatively high content of the essential PUFA. Comparison of FA proportions in polar lipids versus storage lipids shown that during mosquito metamorphosis transfer of essential eicosapentaenoic and arachidonic acids from the reserve in storage lipids of larvae to functional polar lipids in adults occurred.

Toad Tadpole Responses to Predator Risk: Ontogenetic Change between Constitutive and Inducible Defenses

Rhinella spinulosa is a toad common in rivers, streams, and steppe wetlands where they face a variety of insect predators. Rhinella spinulosa tadpoles are known to be unpalatable to dragonfly naiads at some developmental stages. In this paper, we studied susceptibility of R. spinulosa tadpoles to predation by two species of predators, water bugs (Belostoma bifoveolatum, Belostomidae) with piercing-sucking mouth parts and dragonfly larvae (Rhionaeschna variegata, Aeshnidae) with chewing mouth parts. We conducted feeding trials to test the effectiveness of tadpole chemical defenses against water bugs. We also performed behavioral and choice experiments to study whether tadpole behavior influences their vulnerability to predators, and whether R. variegata has the capacity of discern between palatable (stages 38-45) and unpalatable tadpoles (stages 24-26). Rhinella spinulosa tadpoles, when fully palatable, responded by reducing their activity levels in the presence of dragonfly larvae but did not alter their behavior at unpalatable-early stages. Chemical defenses were not effective against the sucking predator (B. bifoveolatum) and no changes in tadpole activity were observed. Selectivity experiments revealed the ability of dragonfly larvae to distinguish between unpalatable and palatable tadpoles. Inducible (behavior) and constitutive (toxins) defenses observed in R. spinulosa tadpoles and the transition between them could result in an important survival mechanism in response to variable predator risk in the habitats in which they co-occur.