Historic Mining and Agriculture as Indicators of Occurrence and Abundance of Widespread Invasive Plant Species

Elaboration of a Phytoremediation Strategy for Successful and Sustainable Rehabilitation of Disturbed and Degraded Land

Humans are dependent upon soil which supplies food, fuel, chemicals, medicine, sequesters pollutants, purifies and conveys water, and supports the built environment. In short, we need soil, but it has little or no need of us. Agriculture, mining, urbanization and other human activities result in temporary land-use and once complete, used and degraded land should be rehabilitated and restored to minimize loss of soil carbon. It is generally accepted that the most effective strategy is phyto-remediation. Typically, phytoremediation involves re-invigoration of soil fertility, physicochemical properties, and its microbiome to facilitate establishment of appropriate climax cover vegetation. A myco-phytoremediation technology called Fungcoal was developed in South Africa to achieve these outcomes for land disturbed by coal mining. Here we outline the contemporary and expanded rationale that underpins Fungcoal, which relies on in situ bio-conversion of carbonaceous waste coal or discard, in order to explore the probable origin of humic substances (HS) and soil organic matter (SOM). To achieve this, microbial processing of low-grade coal and discard, including bio-liquefaction and bio-conversion, is examined in some detail. The significance, origin, structure, and mode of action of coal-derived humics are recounted to emphasize the dynamic equilibrium, that is, humification and the derivation of soil organic matter (SOM). The contribution of plant exudate, extracellular vesicles (EV), extra polymeric substances (EPS), and other small molecules as components of the dynamic equilibrium that sustains SOM is highlighted. Arbuscular mycorrhizal fungi (AMF), saprophytic ectomycorrhizal fungi (EMF), and plant growth promoting rhizobacteria (PGPR) are considered essential microbial biocatalysts that provide mutualistic support to sustain plant growth following soil reclamation and restoration. Finally, we posit that de novo synthesis of SOM is by specialized microbial consortia (or ‘humifiers’) which use molecular components from the root metabolome; and, that combinations of functional biocatalyst act to re-establish and maintain the soil dynamic. It is concluded that a bio-scaffold is necessary for functional phytoremediation including maintenance of the SOM dynamic and overall biogeochemistry of organic carbon in the global ecosystem

Complex relationship between the diversity and stability of chironomid assemblages in the recent sediments of two large alpine lakes in SW China

There is no doubt that the diversity and stability of freshwater ecosystems have suffered dramatic changes as a result of intensified human activities. However, the relationship between community diversity and stability is still debated. In this study, we used biological and geochemical records from the recent sediments of two lakes to test the hypothesis that different aspects of the diversity of the chironomid community have different relationships with community stability. Yangzong Lake (YZ) and Chenghai Lake (CH) are large and deep alpine lakes in SW China. We conducted a multi-proxy study of the sedimentary records spanning the last 200 years from the two lakes. Our focus was on subfossil chironomid remains, but analyses of chemical elements, total organic carbon (TOC) and total nitrogen (TN) were also conducted. The principal results are as follows: 1) Both nutrient and chironomid assemblages underwent a critical transition in 1990 at YZ and in 1998 at CH. 2) The response of species richness varied between the two lakes, but the trends of their respective β diversity indices are consistent, despite the fact that the contributors to β diversity are different. 3) The stability of the chironomid communities has decreased in both lakes since the mid-20th century. 4) The relationship between diversity and stability varies in relation to the type of diversity. Overall, our results emphasize the importance of considering the complex nature of diversity and stability when studying community assemblages.

Failure and Collapse of Ancient Agricultural Stone Terraces: On-Site Effects on Soil and Vegetation

Ancient agricultural stone terraces, dated to the Roman and Byzantine ages, are prevalent across the Negev drylands of Southern Israel. The goal of these structures was to reduce hydrological connectivity by harvesting water runoff and controlling soil erosion, thus allowing cultivation of cereals. Land abandonment and the lack of maintenance have led to the failure and collapse of many of these stone terraces. The objective of this study was to assess the effect of failure and collapse of terraces on the on-site (on-field) geo-ecosystem functioning, as determined by vegetation cover and soil quality parameters. This was achieved by studying vegetal and soil properties in shrubby vegetation patches and inter-shrub spaces of intact-terrace plots and collapsed-terrace plots, as well as in the surrounding ‘natural’ lands. Mean cover of both shrubby and herbaceous vegetation was highest in intact terraces, intermediate in ‘natural’ lands, and lowest in collapsed terraces. The overall soil quality followed the same trend as the vegetation cover. Additionally, this study shows that the anthropogenic impact on geo-ecosystem functioning can be either beneficial or detrimental. While well maintained stone terraces benefit the soil and vegetation, abandoned and unmaintained terraces may result in accelerated soil erosion and land degradation.

Increasing agricultural land use is associated with the spread of an invasive fish (Gambusia affinis)

Land-use change and invasive species pose major threats to ecosystems globally. These stressors can act together, with disturbance due to changes in land-use facilitating invasion. We examined the potential for agricultural land use to facilitate the establishment and population growth (abundance) of a globally invasive fish (Gambusia affinis). To achieve this we examined Gambusia presence, abundance, and life history traits in 31 streams spanning an agricultural land use gradient in the North Island of New Zealand. We used regression models to quantify the relationship between agricultural land use and in-stream physiochemical and habitat variables, and zero-inflated models to explore the relationship among physiochemical, habitat and catchment-scale variables and Gambusia's distribution and abundance. The percentage of the catchment in agricultural land use was associated with changes to physiochemical and habitat conditions. Increasing agricultural land use was associated with increasing macrophyte cover and water temperature and decreasing velocity in streams. Catchment-scale variables (land use and site position in the network) and water temperature were the most important determinants of whether Gambusia occurred at a site. Local in-stream habitat (macrophyte cover and water velocity) and nutrient conditions were the most influential predictors of Gambusia abundance given Gambusia were present. Gambusia life-history traits, sex ratio and body length varied among sites but were not predicted by physiochemical gradients. The distribution of Gambusia in streams in New Zealand is partially controlled by catchment-scale conditions via a combination of dispersal limitation and environmental filtering, both of which are affected by agricultural land use. Agricultural land use alters local in-stream conditions, resulting in systems that are similar to those in Gambusia's natural range; these altered systems have the potential to support an increased abundance of Gambusia. This study provides preliminary quantitative evidence that agricultural land use is related to the spread of a globally invasive freshwater fish.