Defining and quantifying the resilience of responses to disturbance: a conceptual and modelling approach from soil science

There are several conceptual definitions of resilience pertaining to environmental systems and, even if resilience is clearly defined in a particular context, it is challenging to quantify. We identify four characteristics of the response of a system function to disturbance that relate to “resilience”: (1) degree of return of the function to a reference level; (2) time taken to reach a new quasi-stable state; (3) rate (i.e. gradient) at which the function reaches the new state; (4) cumulative magnitude of the function (i.e. area under the curve) before a new state is reached. We develop metrics to quantify these characteristics based on an analogy with a mechanical spring and damper system. Using the example of the response of a soil function (respiration) to disturbance, we demonstrate that these metrics effectively discriminate key features of the dynamic response. Although any one of these characteristics could define resilience, each may lead to different insights and conclusions. The salient properties of a resilient response must thus be identified for different contexts. Because the temporal resolution of data affects the accurate determination of these metrics, we recommend that at least twelve measurements are made over the temporal range for which the response is expected

Effect of Long-Term Zinc Pollution on Soil Microbial Community Resistance to Repeated Contamination

The aim of the study was to compare the effects of stress (contamination trials) on the microorganisms in zinc-polluted soil (5,018 mg Zn kg−1 soil dry weight) and unpolluted soil (141 mg Zn kg−1 soil dw), measured as soil respiration rate. In the laboratory, soils were subjected to copper contamination (0, 500, 1,500 and 4,500 mg kg−1 soil dw), and then a bactericide (oxytetracycline) combined with a fungicide (captan) along with glucose (10 mg g−1 soil dw each) were added. There was a highly significant effect of soil type, copper treatment and oxytetracycline/captan treatment. The initial respiration rate of chronically zinc-polluted soil was higher than that of unpolluted soil, but in the copper treatment it showed a greater decline. Microorganisms in copper-treated soil were more susceptible to oxytetracycline/captan contamination. After the successive soil contamination trials the decline of soil respiration was greater in zinc-polluted soil than in unpolluted soil

Metal Toxicity Affects Fungal and Bacterial Activities in Soil Differently

Although the toxic effect of heavy metals on soil microorganism activity is well known, little is known about the effects on different organism groups. The influence of heavy metal addition on total, bacterial, and fungal activities was therefore studied for up to 60 days in a laboratory experiment using forest soil contaminated with different concentrations of Zn or Cu. The effects of the metals differed between the different activity measurements. During the first week after metal addition, the total activity (respiration rate) decreased by 30% at the highest level of contamination and then remained stable during the 60 days of incubation. The bacterial activity (thymidine incorporation rate) decreased during the first days with the level of metal contamination, resulting in a 90% decrease at the highest level of contamination. Bacterial activity then slowly recovered to values similar to those of the control soil. The recovery was faster when soil pH, which had decreased due to metal addition, was restored to control values by liming. Fungal activity (acetate-in-ergosterol incorporation rate) initially increased with the level of metal contamination, being up to 3 and 7 times higher than that in the control samples during the first week at the highest levels of Zn and Cu addition, respectively. The positive effect of metal addition on fungal activity then decreased, but fungal activity was still higher in contaminated than in control soil after 35 days. This is the first direct evidence that fungal and bacterial activities in soil are differently affected by heavy metals. The different responses of bacteria and fungi to heavy metals were reflected in an increase in the relative fungal/bacterial ratio (estimated using phospholipid fatty acid analysis) with increased metal load

Role of microbial communities in conferring resistance and resilience of soil carbon and nitrogen cycling following contrasting stresses

Soils frequently experience environmental stresses that may have transient or persistent impact on important ecosystem services, such as carbon (C) and nitrogen (N) cycling. Microbial communities underpin resistance (the ability to withstand a stress) and resilience (the ability to recover from a stress) of these functions. Whilst functional stability and resilience have been studied extensively, the link to genetic stability is missing. In this study, the resistance and resilience of C mineralization, ammonia oxidation and denitrification, their associated gene abundances (16S rRNA, bacterial amoA, nirK, nirS, nosZ-I and nosZ-II) and bacterial community structures (T-RFLP 16S rRNA) were compared in two managed soils for 28 days after stressing the soils with either a persistent (1 mg Cu soil g−1) or a transient (heat at 40 °C for 16 h) stress. The average resistance of C mineralization to Cu was 60%, which was significantly greater than the resistance of ammonia oxidation (25%) and denitrification (31%) to Cu. Similarly, the average resilience of C mineralization to Cu was 52%, which was significantly greater than the resilience of ammonia oxidation (12%) and denitrification (18%) to Cu. However, this pattern was not significant after heat stress, indicating the critical role of different stressors. Changes in total bacterial community structure rather than abundance of 16S rRNA reflected the responses of C mineralization to Cu and heat. Both Cu and heat significantly decreased functional gene abundance (amoA, nirK, nirS, nosZ-I and nosZ-II), however, a significant recovery of denitrifying gene abundance was observed after 28 days following heat. There were lack of constant relationships between functional and genetic stability, highlighting that soil physiochemical properties, the nature of the stressor, and microbial life history traits combine to confer functional resistance and resilience. Genetic responses on their own are therefore inadequate in predicating changes to soil functions following stresses

A European perspective on alternatives to animal testing for environmental hazard identification and risk assessment

Tests with vertebrates are an integral part of environmental hazard identification and risk assessment of chemicals, plant protection products, pharmaceuticals, biocides, feed additives and effluents. These tests raise ethical and economic concerns and are considered as inappropriate for assessing all of the substances and effluents that require regulatory testing. Hence, there is a strong demand for replacement, reduction and refinement strategies and methods. However, until now alternative approaches have only rarely been used in regulatory settings. This review provides an overview on current regulations of chemicals and the requirements for animal tests in environmental hazard and risk assessment. It aims to highlight the potential areas for alternative approaches in environmental hazard identification and risk assessment. Perspectives and limitations of alternative approaches to animal tests using vertebrates in environmental toxicology, i.e., mainly fish and amphibians, are discussed. Free access to existing (proprietary) animal test data, availability of validated alternative methods and a practical implementation of conceptual approaches such as the Adverse Outcome Pathways and Integrated Testing Strategies were identified as major requirements towards the successful development and implementation of alternative approaches. Although the focus of the article is on European regulations, the considerations and conclusions are of global relevance.JRC.I.5-Systems Toxicolog