Megafire affects stream sediment flux and dissolved organic matter reactivity, but land use dominates nutrient dynamics in semiarid watersheds

Climate change is causing larger wildfires and more extreme precipitation events in many regions. As these ecological disturbances increasingly coincide, they alter lateral fluxes of sediment, organic matter, and nutrients. Here, we report the stream chemistry response of watersheds in a semiarid region of Utah (USA) that were affected by a megafire followed by an extreme precipitation event in October 2018. We analyzed daily to hourly water samples at 10 stream locations from before the storm event until three weeks after its conclusion for suspended sediment, solute and nutrient concentrations, water isotopes, and dissolved organic matter concentration, optical properties, and reactivity. The megafire caused a ~2,000-fold increase in sediment flux and a ~6,000-fold increase in particulate carbon and nitrogen flux over the course of the storm. Unexpectedly, dissolved organic carbon (DOC) concentration was 2.1-fold higher in burned watersheds, despite the decreased organic matter from the fire. DOC from burned watersheds was 1.3-fold more biodegradable and 2.0-fold more photodegradable than in unburned watersheds based on 28-day dark and light incubations. Regardless of burn status, nutrient concentrations were higher in watersheds with greater urban and agricultural land use. Likewise, human land use had a greater effect than megafire on apparent hydrological residence time, with rapid stormwater signals in urban and agricultural areas but a gradual stormwater pulse in areas without direct human influence. These findings highlight how megafires and intense rainfall increase short-term particulate flux and alter organic matter concentration and characteristics. However, in contrast with previous research, which has largely focused on burned-unburned comparisons in pristine watersheds, we found that direct human influence exerted a primary control on nutrient status. Reducing anthropogenic nutrient sources could therefore increase socioecological resilience of surface water networks to changing wildfire regimes.

Hydrophysical research in the Kruglaya Bay (Sevastopol)

On the basis of two hydrophysical surveys (August 28 and November 14, 2019), the spatial distribution was investigated of temperature, salinity, total suspended matter, dissolved organic matter features, and total suspended matter dynamic activity in the waters of the Kruglaya Bay. The horizontal and vertical distributions of these characteristics were considered. The hydrophysical parameters were measured from a small vessel at anchored stations using Kondor Sounding Complex. The analysis of obtained distributions showed that less saline and more turbid waters were observed in the apex of the bay. The highest content of suspended particles and dissolved organic matter were detected in this water area. An almost uniform stratification of hydrological parameters and total suspended matter concentration were observed in the vertical distribution over the entire water area of the bay. In the vertical dissolved organic matter distribution, an increase under the water surface layer of ~ 1–5 m was observed both in August and in November. This layer was more pronounced in November. The total suspended matter content in the surface water layer in August 2019 was on average twice as high as in November of the same year, and the dissolved organic matter concentration was lower.

Investigation of the field of colored dissolved organic matter concentration and its relationship to the salinity field in Dnieper-Bug estuary

Based on the data of the expedition carried out in August 2012, the features of the structure of the salinity and fDOM concentration fields, as well as the correlation between these values ​​in the Dnieper-Bug estuary, are analyzed. It is shown that the salinity field in the Dnieper-Bug estuary is characterized by all structural features typical of coastal sea areas freshened by river runoff, while the fDOM concentration field has anomalous properties due to the presence of an anthropogenic component of this value. The presence of fDOM of anthropogenic origin is most significant in the western part of the Dnieper estuary and is related to the influence of the city and port of Ochakov. The maximum content of fDOM was recorded here, which caused an anomalous horizontal distribution of this substance concentration, increasing from the mouth of the Dnieper to the open Black Sea waters. The contaminated areas of the studied water areas, which are adjacent to settlements and occupy the predominant part of the water surface of the Dnieper-Bug estuary, are characterized by an increased fDOM content and intrusive feature of the vertical structure of this substance concentration field of. It is revealed that in the Dnieper-Bug estuary there is no inverse correlation between the salinity fields and fDOM concentration, which is typical for unpolluted coastal waters, freshened by river runoff. A similar anomaly is an indicator of the pollution of coastal waters with organic matter.

Responses and Indicators of Composition, Diversity, and Productivity of Plant Communities at Different Levels of Disturbance in a Wetland Ecosystem

Grassland tourism is a very popular leisure activity in many parts of the world. However, the presence of people in these areas causes disturbance to the local environment and grassland resources. This study analyzes the composition, diversity, and productivity under different levels of disturbance of the plant communities in the Kangxi Grassland Tourist Area and the Yeyahu Wetland Nature Reserve of Beijing, China. It aims to identify indicators of plant communities and their responses to different levels of disturbance. Our analysis shows that the plant community density and coverage have a certain compensatory increase under disturbed conditions. With the increase in disturbances, more drought-tolerant species have appeared (increased by 5.7%), some of which have become the grazing-tolerance indicator species in the trampled grazed area (TGA). For plant community productivity, biomass and height are good indicators for distinguishing different disturbances (p < 0.05). In addition, several diversity indices reveal the change of plant communities from different perspectives (three of the four indices were significant at the p < 0.05 level). For soil parameters, soil water content and organic matter concentration help to indicate different disturbance levels (the former has a 64% change). Moreover, the standard deviation of the plant community and soil parameters is also a good indicator of their spatial variability and disturbance levels, especially for the TGA. Our analysis confirms that the indicators of productivity, diversity, and soil parameters can indicate the disturbance level in each subarea from different perspectives. However, under disturbed conditions, a comprehensive analysis of these indicators is needed before we can accurately understand the state of health of the plant community.

A general framework to model the fate of trace elements in anaerobic digestion environments

Due to the multiplicity of biogeochemical processes taking place in anaerobic digestion (AD) systems and limitations of the available analytical techniques, assessing the bioavailability of trace elements (TEs) is challenging. Determination of TE speciation can be facilitated by developing a mathematical model able to consider the physicochemical processes affecting TEs dynamics. A modeling framework based on anaerobic digestion model no 1 (ADM1) has been proposed to predict the biogeochemical fate TEs in AD environments. In particular, the model considers the TE adsorption–desorption reactions with biomass, inerts and mineral precipitates, as well as TE precipitation/dissolution, complexation reactions and biodegradation processes. The developed model was integrated numerically, and numerical simulations have been run to investigate the model behavior. The simulation scenarios predicted the effect of (i) organic matter concentration, (ii) initial TEs concentrations, (iii) initial Ca–Mg concentrations, (iv) initial EDTA concentration, and (v) change in TE binding site density, on cumulative methane production and TE speciation. Finally, experimental data from a real case continuous AD system have been compared to the model predictions. The results prove that this modelling framework can be applied to various AD operations and may also serve as a basis to develop a model-predictive TE dosing strategy.