Use of leaf litter breakdown and macroinvertebrates to evaluate gradient of recovery in an acid mine impacted stream remediated with an active alkaline doser

Community recovery of benthic macroinvertebrates in a stream influenced by mining activity: Importance of microhabitat monitoring

The decrease in freshwater biodiversity owing to anthropogenic disturbances such as mining activity is a global challenge; hence, there is an urgent need for systematic approaches to continuously monitor such disturbances and/or the recovery of biodiversity in freshwater habitats. The Hwangjicheon Stream is the source of South Korea's longest river and has been subjected to runoff from coal mining. We investigated changes in the diversity of the benthic macroinvertebrate community in various microhabitats, including riffle, run, and pool, to monitor the recovery of biodiversity in the stream following the improvement of a mining water treatment plant in 2019. The dataset comprised 111 samples obtained from four types of microhabitats (riffle, run, pool, and riparian) over a four-year period from 2018 to 2021. The mining-affected sites had lower macroinvertebrate community complexities according to a network analysis, and grouped into the same cluster based on self-organizing map (SOM) analysis. Moreover, 51 taxa selected as indicator species represented each cluster obtained through the SOM analysis. Among them, only Limnodrilus gotoi and Radix auricularia were included as indicator species at the mining-affected sites. However, after 2020, the benthic macroinvertebrate community complexity increased, and some of the microhabitats at the mining-affected sites were included in the same cluster as the reference sites in the SOM analysis, indicating that the recovery of benthic macroinvertebrate communities had initiated in certain microhabitats (e.g., riparian). Further analysis confirmed that the macroinvertebrate community clearly differed according to the survey year, even in different microhabitats at the same sites. This suggests that more acute microhabitat monitoring may be necessary to quickly confirm biodiversity restoration when assessing the degree of the recovery in river biodiversity from anthropogenic disturbances.

The Combined Application of Surface Floating Wetlands and Bottom Anaerobic to Remediate AMD-Contaminated Lakes

Acid mine drainage (AMD) causes environmental pollution that affects many countries with historic or current mining industries. The eco-remediation system (RW) which combined surface floating wetlands and bottom anaerobic sediments (SFW-BAS) was selected for AMD-contaminated lakes (AMDW). Meanwhile, AMDW and nature aquatic ecosystems (NW) were set as the control groups, respectively. The parameters, including pH, Eh, Fe, Mn, SO42−, and the degradation rate of the native dominant plant litter were investigated to assess the effects of remediation. The results showed that the average of pH, Eh, and EC, was 2.73, 484.08 mv, and 2395.33 μs·cm−1, respectively. The average content of SO42−, Fe, Mn, Cu, Zn, and Pb was 2190 mg·L−1, 40.2 mg·L−1, 4.6 mg·L−1, 249.2 μg·L−1, 1563 μg·L−1, and 112.9 μg·L−1, respectively. The degradation rate of plant litters in AMDW ranged from 14.5% to 22.6%. However, RW ultimately improved the water quality and the degradation of litters. RW has a good effect on buffering the acidity, ranging from 3.96 to 7.41. The pH of RW (6.14) is close to that of NW (7.41). The average content of SO42−, Fe, Mn, Cu, Zn, and Pb was 2071 mg·L−1, 3.4 mg·L−1, 2.4 mg·L−1, 85.3 μg·L−1, 607.4 μg·L−1, and 47.8 μg·L−1, respectively, which showed good pollutant removal performance. The degradation rate of plant litters in RW ranged from 27.8% to 32.6%. Therefore, RW can be used to remediate AMDW.

Passive Treatment for Acid Mine Drainage Partially Restores Microbial Community Structure in Different Stream Habitats

The assessment of the degree to which biological communities in streams impaired by acid mine drainage (AMD) are restored by passive treatment has focused primarily on eukaryotic-cell organisms and microbial processes. The responses of microbial community structure to passive treatment have received much less attention, even though functional processes such as nutrient cycling and organic matter decomposition depend on taxonomic composition. Our objective was to determine the degree to which passive treatment restored microbial communities in three types of habitats: aqueous, leaf, and sediment. To assess their recovery, we compared the community composition in these habitats based on 16S rRNA gene sequencing at three different stream sites: an untreated AMD site (U), a remediated site below AMD passive treatment (T), and an unimpaired reference site (R). The acidity, conductivity, and soluble metal concentrations at T were found to be elevated compared to R, but generally 1–2 orders of magnitude less than at U. Microbial community composition was found to be synergistically affected by habitat type and AMD impact, with the similarity among communities in the three habitats increasing with the severity of the AMD. Sediment- and leaf-associated microbial communities at U were characterized by taxa that are tolerant to severe AMD. The absence of the nitrogen oxidizing bacterium Nitrospira in sediment communities at T and U was found to correspond to higher NH4+ concentrations compared to R, possibly because of the presence of iron oxyhydroxide precipitate. In contrast, the microbial composition was found to be similar between the T and R sites for both aqueous and leaf communities, indicating that passive treatment was more able to restore these communities to the reference condition than sediment communities. The remediation of AMD streams should consider the habitat-specific responses of microbial community composition and be guided by future studies that empirically couple changes in taxonomic composition to measured functional processes.

Organic Matter Decomposition and Ecosystem Metabolism as Tools to Assess the Functional Integrity of Streams and Rivers–A Systematic Review

Streams and rivers provide important services to humans, and therefore, their ecological integrity should be a societal goal. Although ecological integrity encompasses structural and functional integrity, stream bioassessment rarely considers ecosystem functioning. Organic matter decomposition and ecosystem metabolism are prime candidate indicators of stream functional integrity, and here we review each of these functions, the methods used for their determination, and their strengths and limitations for bioassessment. We also provide a systematic review of studies that have addressed organic matter decomposition (88 studies) and ecosystem metabolism (50 studies) for stream bioassessment since the year 2000. Most studies were conducted in temperate regions. Bioassessment based on organic matter decomposition mostly used leaf litter in coarse-mesh bags, but fine-mesh bags were also common, and cotton strips and wood were frequent in New Zealand. Ecosystem metabolism was most often based on the open-channel method and used a single-station approach. Organic matter decomposition and ecosystem metabolism performed well at detecting environmental change (≈75% studies), with performances varying between 50 and 100% depending on the type of environmental change; both functions were sensitive to restoration practices in 100% of the studies examined. Finally, we provide examples where functional tools are used to complement the assessments of stream ecological integrity. With this review, we hope to facilitate the widespread incorporation of ecosystem processes into bioassessment programs with the broader aim of more effectively managing stream and river ecosystems.

Biodiversity mediates the effects of stressors but not nutrients on litter decomposition

Understanding the consequences of ongoing biodiversity changes for ecosystems is a pressing challenge. Controlled biodiversity-ecosystem function experiments with random biodiversity loss scenarios have demonstrated that more diverse communities usually provide higher levels of ecosystem functioning. However, it is not clear if these results predict the ecosystem consequences of environmental changes that cause non-random alterations in biodiversity and community composition. We synthesized 69 independent studies reporting 660 observations of the impacts of two pervasive drivers of global change (chemical stressors and nutrient enrichment) on animal and microbial decomposer diversity and litter decomposition. Using meta-analysis and structural equation modeling, we show that declines in decomposer diversity and abundance explain reduced litter decomposition in response to stressors but not to nutrients. While chemical stressors generally reduced biodiversity and ecosystem functioning, detrimental effects of nutrients occurred only at high levels of nutrient inputs. Thus, more intense environmental change does not always result in stronger responses, illustrating the complexity of ecosystem consequences of biodiversity change. Overall, these findings provide strong evidence that the consequences of observed biodiversity change for ecosystems depend on the kind of environmental change, and are especially significant when human activities decrease biodiversity.

Assessment of Impacts of Coal Mining in the Region of Sydney, Australia on the Aquatic Environment Using Macroinvertebrates and Chlorophyll as Indicators

Coal and coal seam gas mining have impacts on the water and sediment quality in the proximity of the mining areas, increasing the concentrations of heavy metals downstream of the mine discharge points. The objective of this study was to assess the impact of coal mining on the environment in the Sydney region, by investigating macroinvertebrates and chlorophyll as indicators of industrial pollution and environmental impairment. The study revealed changes in abundance, taxonomic richness, and pollution sensitive macroinvertebrate groups. A statistical evaluation of the aquatic life was performed and a correlation of the contaminants with the presence of a community in the ecosystem were studied. The environmental sustainability of the investigated rivers and streams with water chemistry affecting the biological system was assessed. A non-uniformity in the changes were observed, indicating a difference in the tolerance level of different invertebrates.

Using fatty acids to fingerprint biofilm communities: a means to quickly and accurately assess stream quality

The assessment of lotic ecosystem quality plays an essential role to help determine the extent of environmental stress and the effectiveness of restoration activities. Methods that incorporate biological properties are considered ideal because they provide direct assessment of the end goal of a vigorous biological community. Our primary objective was to use biofilm lipids to develop an accurate biomonitoring tool that requires little expertise and time to facilitate assessment. A model was created of fatty acid biomarkers most associated with predetermined stream quality classification, exceptional warm water habitat (EWH), warm water habitat (WWH), and limited resource (LR-AMD), and validated along a gradient of known stream qualities. The fatty acid fingerprint of the biofilm community was statistically different (P = 0.03) and was generally unique to recognized stream quality. One striking difference was essential fatty acids (DHA, EPA, and ARA) were absent from LR-AMD and only recovered from WWH and EWH, 45 % more in EWH than WWH. Independently testing the model along a stream quality gradient, this model correctly categorized six of the seven sites, with no match due to low sample biomass. These results provide compelling evidence that biofilm fatty acid analysis can be a sensitive, accurate, and cost-effective biomonitoring tool. We conceive of future studies expanding this research to more in-depth studies of remediation efforts, determining the applicable geographic area for the method and the addition of multiple stressors with the possibility of distinguishing among stressors.