Use of the Species Sensitivity Distribution Approach to Derive Ecological Threshold of Toxicological Concern (eco-TTC) for Pesticides

The species sensitivity distribution (SSD) calculates the hazardous concentration at which 5% of species (HC5) will be potentially affected. For many compounds, HC5 values are unavailable impeding the derivation of SSD curves. Through a detailed bibliographic survey, we selected HC5 values (from acute toxicity tests) for freshwater aquatic species and 129 pesticides. The statistical distribution and variability of the HC5 values within the chemical classes were evaluated. Insecticides are the most toxic compounds in the aquatic communities (HC5 = 1.4x10−03 µmol L−1), followed by herbicides (HC5 = 3.3 x10−2 µmol L−1) and fungicides (HC5 = 7.8 µmol L−1). Subsequently, the specificity of the mode of action (MoA) of pesticides on freshwater aquatic communities was investigated by calculating the ratio between the estimated baseline toxicity for aquatic communities and the HC5 experimental values gathered from the literature. Moreover, we proposed and validated a scheme to derive the ecological thresholds of toxicological concern (eco-TTC) of pesticides for which data on their effects on aquatic communities are not available. We proposed eco-TTCs for different classes of insecticides, herbicides, and fungicides with a specific MoA, and three eco-TTCs for those chemicals with unavailable MoA. We consider the proposed approach and eco-TTC values useful for risk management purposes.

Study on Ecological Threshold of Groundwater in Typical Salinization Area of Qian’an County

A suitable groundwater level is an important condition to maintain the stability of the vegetation community, especially in arid and semi-arid areas. The surface of Qian’an County in Western Jilin Province is often accompanied by salinization due to the influence of natural and human factors. In order to maintain the healthy development of ecological vegetation and reduce the risk of soil salinization, the concept of an ecological threshold of groundwater level is proposed, and two methods are used to determine the reasonable ecological threshold of groundwater. (1) Based on field investigation and indoor experiment, the data layer of soil texture, land use type and groundwater mineralization degree in the research area was established by using remote sensing technology and GIS technology. According to the thickness of vegetation root layer and the height of capillary rise of different soil and water types, the influence of groundwater salinity is considered, and the sum of the two is taken as the ecological threshold of groundwater in the study area. The reasonable threshold value of suitable growth of various vegetation crops is 3.76~5.66 m. (2) According to the relationship between the normalized vegetation index (NDVI) and the groundwater buried depth and phreatic salt, the groundwater buried depth and the mineralization degree under the best vegetation cover are analyzed as follows: the buried depth of groundwater is between 4.8 m and 6.1 m, and the salinity of groundwater is between 0.37 and 1.25 g/L, which are reasonable groundwater properties in the study area of the ecological threshold. This result not only enriches and broadens the content of groundwater research, but also helps to predict the prospect of water resource development.

Ecological Thresholds of Toxicological Concern: A Review

The ecological threshold of toxicological concern (ecoTTC) is analogous to traditional human health-based TTCs but with derivation and application to ecological species. An ecoTTC is computed from the probability distribution of predicted no effect concentrations (PNECs) derived from either chronic or extrapolated acute toxicity data for toxicologically or chemically similar groups of chemicals. There has been increasing interest in using ecoTTCs in screening level environmental risk assessments and a computational platform has been developed for derivation with aquatic species toxicity data (https://envirotoxdatabase.org/). Current research and development areas include assessing mode of action-based chemical groupings, conservatism in estimated PNECs and ecoTTCs compared to existing regulatory values, and the influence of taxa (e.g., algae, invertebrates, and fish) composition in the distribution of PNEC values. The ecoTTC continues to develop as a valuable alternative strategy within the toolbox of traditional and new approach methods for ecological chemical assessment. This brief review article describes the ecoTTC concept and potential applications in ecological risk assessment, provides an overview of the ecoTTC workflow and how the values can be derived, and highlights recent developments and ongoing research. Future applications of ecoTTC concept in different disciplines are discussed along with opportunities for its use.

Calculation of the Ecological Thresholds of Normal Pressure of Machine Propulsion Drive in Working on Clay Soils

One of the conditions for achieving maximum land productivity is optimal soil density. In the Amur Region, ecological compaction thresholds for cereals are 1.0-1.24 grams per cubic centimeter, for soybeans – 1.09-1.25, which corresponds to a normal pressure of 80-120 kilopascals, depending on soil moisture. The authors showed that the tractors used in the Amur Region, acting on the soil, exceed the ecological compaction threshold. (Research purpose) To substantiate the ecological compatibility of mobile fi eld energy, primarily tractors engaged in fi eld work, in terms of the compacting eff ect from the normal load transmitted by their propulsion drive to the soil. (Materials and methods) The authors analyzed the experimental data on changes in density, hardness and resistance of soil to processing. An empirical dependence was obtained for calculating the increase in resistance to soil cultivation from the compaction load in a layer of 0-20 centimeters. (Results and discussion) The authors established an increase in plowing resistance of 12-25 percents at a normal load of 138-170 kilopascals, transmitted by the machine propulsion drive, which corresponded to a soil density of 1.25-1.30 grams per cubic centimeter; at a load of 180-250 kilopascals, the resistance increased by 43-50 percents which was equivalent to a soil density of 1.30-1.35 grams per cubic centimeter; at a pressure of 300-350 kilopascals, these indicators increased by 60-67 percents and up to 1.40-1.45 grams per cubic centimeter; and at 400 kilopascals, they showed an increase in resistance of 70-90 percents which is comparable to a density of 1.48 grams per cubic centimeter. (Conclusions) It was determined that the limit value of the normal pressure under the machine propulsion drive in fi eld work should be limited to 150-175 kilopascals. The ecological threshold of normal pressure was established – no more than 120-135 kilopascals with soil moisture of 20-23 percents which was comparable to the soil density of 1.2-1.25 grams per cubic centimeter. The limiting value of the normal pressure of the propulsion drive on the soil was calculated – 350 Pa, which corresponded to the critical soil compaction of 1.30 grams per cubic centimeter.

The structure and composition of macrozoobenthos community in varying water qualities in Kalibaru Waters, Bengkulu, Indonesia

Lilisti, Zamdial, Hartono D, Brata B, Simarmata M. 2021. The structure and composition of macrozoobenthos community in varying water qualities in Kalibaru Waters, Bengkulu, Indonesia. Biodiversitas 22: 106-112. Various human activities affect the quality of the aquatic ecosystem that can be assessed by measuring the physical, chemical, and biological parameters of the waters and sediments. This is the case of Kalibaru Waters, Bengkulu, Indonesia which shows changes in the estuary and marine ecosystems due to the cut-off of the main river around the area for the development of roads and bridges. The objective of this study was to analyze the quality of the waters and substrate, and the structure of the macrozoobenthos community as a bioindicator at the Kalibaru Waters. A survey was carried out in four stations, which was purposively selected based on human activities around the waters. Data collected included the physical and chemical parameters, and the diversity and density of macrozoobenthos species. The density of macrozoobenthos species was analyzed for summed dominance ratio (SDR), diversity (H'), homogeneity (E), and dominance (D) indices. The results showed that the physical and chemical parameters of Kalibaru Waters were acceptable for aquatic life, however, the oil contents at two stations exceeded the ecological threshold. Analysis of the macrozoobenthos community as a bioindicator for water quality found that the diversity and homogeneity indices were at a medium level indicating an unstable community, while the dominant index remained low indicating that none of the species was dominant in the Kalibaru Waters. This information is needed as a reference for the government of Bengkulu Province to make appropriate policies and management decisions to maintain the quality of the aquatic ecosystem in Kalibaru Waters.

Influence of Salinity Gradient Changes on Phytoplankton Growth Caused by Sluice Construction in Yongjiang River Estuary Area

Though the number of sluices and dams in coastal areas has increased rapidly in recent years, the influence of their construction on phytoplankton in estuary areas is hardly known. This paper aims to provide a reference for quantitative research on the ecological influence of sluice construction and give ecological justifications for the setting of environmental standards in the estuary areas. The survey data gained at the lower reach of the Yongjiang River and its estuarine areas in June 2015 were used in MIKE21 software (Danish Hydraulic Institute (DHI), Denmark)) for establishing a two-dimensional numerical model to simulate the salinity field distribution after sluice construction. Based on the simulation results, the salinity gradient changes caused by the construction were analyzed. The one-dimensional Gaussian model was applied to calculated the phytoplankton’s ecological threshold interval over the salinity changes, which helped predict the influence of salinity changes on phytoplankton cell density. The study shows that salinity in the Yongjiang estuary increases obviously, beyond the phytoplankton ecological threshold, after sluice construction without water discharge. Salinity will become a restriction factor to phytoplankton growth after sluice construction in the study area, which may cause a sharp decrease of certain phytoplankton species.

A unified typology for small European rivers

<p>A large number of chemicals such as pharmaceuticals, pesticides and industrial chemicals are in daily use. In Europe alone, an estimated 100,000 chemicals are in current use, of which 30,000 are produced in quantities larger than one ton per year. Chemicals can enter freshwater ecosystems as an intended (e.g. deliberate emission as in the case of pesticides) or unintended (e.g. wastewater discharge as in the case of pharmaceuticals) byproduct of their use. In the environment, many chemicals (hereafter called toxicants) can exert adverse toxic effects on freshwater organisms and in turn on ecosystem functions. The potential toxic effects of chemicals are often examined within the context of Ecological Risk Assessment (ERA). ERA consists of standardized procedures and methods to evaluate the environmental risks of ecological systems. An open question is to what extent ERA needs to account for differences between recipient ecosystems that are subject to chemical exposure. For example, in the European context, is a single ecological threshold concentration per substance sufficient or is the sensitivity of the organism’s dependent on water body size, geology or climate.</p><p>As previous studies have shown that the latter factors influence the community composition of algae and invertebrates, we aim to compare the sensitivity of communities across macroecological gradients. </p><p>We established a typology of small streams for eight European countries that captures the major macroecological gradients and identified typical ecological assemblages for each type. The typology is based on the Catchment & Characteristics Modelling 2 database and incorporates catchment properties such as climate, geology, and altitude as well as river attributes such as sinuosity and flow regime statistics. The latter are derived from modeled daily discharge values. Through CLARA-clustering of the resulting data, we obtained a classification into 14 stream classes. We focused on smaller rivers as they constitute the majority of river length, host a higher share of biodiversity than large rivers, and are more susceptible to pollution. The presented typology is built from the ground up with openly accessible data. All code will be made publicly available; thus, it will be easy to update, modify, and extend the typology. Beyond our application the typology can be used to regionalize ecological and hydrological models, to inventory the number and state of different river types or to develop individualized conservation programs.</p><p>Based on the identified typical assemblages we can also present preliminary relative sensitivities of stream types towards different toxicants.</p>

Delivering effective savanna fire management for defined biodiversity conservation outcomes: an Arnhem Land case study

Given the recent history of frequent and extensive late dry season wildfire in Australia’s fire-prone northern savannas, regional conservation-based fire management programs typically aim to mitigate wildfire through the use of strategic prescribed burning during the cooler early dry season. However, it remains unclear as to the extent such environmental management concerns are being addressed by these renewed fire management efforts. This study documents changes in fire regime in the western Arnhem Land region of northern Australia associated with the implementation of active fire management since 2006. Over a 12-year period, the regional fire regime has transitioned from late dry season, wildfire-dominated to being characterised by a majority of fires occurring as small early dry season prescribed burns. Although overall area burnt has not significantly decreased, most ecological threshold metrics have improved, with the exception of those describing the maintenance of longer-unburnt habitat. Challenges involved with defining, delivering, monitoring and evaluating heterogeneity targets are discussed.

A palaeolimnological perspective to understand regime-shift dynamics in two Yangtze-basin lakes

Natural and human disturbances have caused widespread regime shifts in shallow lakes of the lower Yangtze basin (LYB, China) resulting in a severe decline of ecosystem services. Improved understanding of the relationship between environmental forcing and ecosystem response, and the mechanisms behind regime shifts has significant implications for management. However, the patterns of these regime shifts and the underlying internal mechanisms are less known. In this study, two typical lakes (Chaohu and Zhangdu) from the LYB were selected to determine the trajectories of ecological regime shifts, both of which transitioned from vegetation- to plankton-dominated states several decades ago. Ecological trajectories since the 1900s in both lakes were reconstructed using palaeolimnological proxies, mainly diatom assemblages. Although results show that regime shifts occurred in both lakes in the 1970s and the 1950s, respectively, their inherent mechanisms were different. In Lake Zhangdu, altered hydrological conditions pushed the ecosystem across an ecological threshold, providing an example of a driver-mediated regime shift. In Lake Chaohu, ongoing nutrient loading influenced ecosystem processes and drove the lake to an alternative stable state, potentially presenting an example of a critical transition after a loss of resilience. This research indicates that palaeolimnological perspectives can provide insights into regime shift changes, as well as important information regarding which restoration methods should be tailored to individual lakes.