The evaluation of biological indices to assess the condition of hillslope seep wetlands in the Tsitsa River Catchment, South Africa.

The increase in the degradation of wetlands globally has highlighted the need to assess their ecological condition. Hillslope seep wetlands are among the least studied wetland types, yet they the most vulnerable because of their small size and steep slopes. Human pressure and the vulnerable nature of these wetlands requires wetland assessment tools to assess their condition. This study sought to evaluate the performance of the Floristic Quality Assessment Index for all species (FQAIall), the FQAI for dominant species (FQAIdom), and the Floristic Assessment Quotient for Wetlands (FAQWet) in response to the Anthropogenic Activity Index (AAI) and WET-Health in eleven hillslope seep wetlands and used these indices to assess the degree and intensity of disturbance. Vegetation samples were collected in summer 2016 and winter 2017. All assessment indices, FQAIall, FQAIdom, FAQWet and WET-Health, showed that hillslope seep wetlands were impacted by human activities. FQAIall showed the strongest response to AAI in winter, while FAQWet showed the strongest response to WET-Health. To the best of our knowledge, researchers in South Africa have used only WET-Health to assess wetland condition, and this is the first study to assess the condition of hillslope seep wetlands using a combination of indices (FQAIall, FQAIdom, FAQWet, and WET-Health). Overall, the findings of this study suggest that FQAIall and FAQWet are potentially better tools for assessing the biological condition of hillslope seep wetlands in South Africa.

Using a trait-based approach for assessing the vulnerability and resilience of hillslope seep wetland vegetation cover to disturbances in the Tsitsa River catchment, Eastern Cape, South Africa.

Hill slope seep wetlands are ecologically and economically important ecosystems as they supply a variety of ecosystem services to society. In South Africa, livestock grazing is recognized as one of the most important disturbance factors changing the structure and function of hill slope seep wetlands. This study sought to investigate the potential effect of livestock grazing on the resilience and vulnerability of hillslope seep wetland vegetation cover using a trait-based approach (TBA). Changes in vegetation cover were used as a surrogate for indicating grazing intensity. The degree of human disturbances was assessed using the Anthropogenic Activity Index. A TBA was developed using seven plant traits, resolved into 27 trait attributes. Based on the developed approach, plant species were grouped into vulnerable and resilient groups in relation to grazing pressure. It was then predicted that species belonging to the vulnerable group would be less dominant at the highly disturbed sites, as well as in the winter season when grazing pressure is at its peak. The approach developed enabled accurate predictions of the responses of hillslope plant species to grazing pressure seasonally, but spatially, only for the summer season. The predicted responses during the winter season across sites did not match the observed results, which could be attributed to the difficulty in species identification and accurate estimation of vegetation cover during winter. Overall, the approach developed here provides a general framework for applying the TBA and can thus be tested and applied elsewhere.

Development of a procedure for determining the mixing ratios in ecotoxicological experiments and its application in binary salt mixture experiments.

Although a plethora of models exist to describe the characteristics and risk assessment of chemical mixtures in ecotoxicology, there is no specific procedure to decide on the mixing ratios (i.e. proportions of the individual chemical substances that form the mixture) at any desired level of concentration in an ecotoxicological mixture experiment. In this study, an attempt was made to develop a procedure for determining the mixing ratios in ecotoxicological experiments. In brief, from a single salt exposure test, the relative toxic fractions, which represent the toxic effect exerted by the individual salts, are determined. Thereafter, the proportions of each individual salt at any level of concentration in the mixture are estimated by multiplying the desired concentration with the relative toxic fraction of that particular salt. The procedure was applied to ecotoxicological experiments involving four binary salt mixtures (MgCl2 + MgSO4, NaCl + Na2SO4, MgCl2 + Na2SO4 and NaCl + MgSO4) and Caridina nilotica, an indigenous South African freshwater shrimp. It is hoped that the application of this developed procedure will ensure administering the correct proportions of individual chemical substances in chemical mixtures in order to obtain the desired levels of concentration in aquatic ecotoxicological mixture experiments.

The mayfly nymph Austrophlebioides pusillus Harker defies common osmoregulatory assumptions.

Osmoregulation is a key physiological function, critical for homeostasis. The basic physiological mechanisms of osmoregulation are thought to be well established. However, through a series of experiments exposing the freshwater mayfly nymph Austrophlebioides pusillus (Ephemeroptera) to increasing salinities, we present research that challenges the extent of current understanding of the relationship between osmoregulation and mortality. A. pusillus had modelled 96 h LC10, LC50 and LC99 of 2.4, 4.8 and 10 g l-1 added synthetic marine salt (SMS), respectively. They were strong osmoregulators. At aquarium water osmolality of 256 ± 3.12 mmol kg-1 (±s.e.; equivalent to 10 g l-1 added SMS), the haemolymph osmolality of A. pusillus was a much higher 401 ± 4.18 mmol kg-1 (±s.e.). The osmoregulatory capacity of A. pusillus did not break down, even at the salinity corresponding to their LC99, thus their mortality at this concentration is due to factors other than increased internal osmotic pressure. No freshwater invertebrate has been previously reported as suffering mortality from rises in salinity that are well below the iso-osmotic point. Recently, studies have reported reduced abundance/richness of Ephemeroptera with slightly elevated salinity. Given that salinization is an increasing global threat to freshwaters, there is an urgent need for studies into the osmophysiology of the Ephemeroptera to determine if their loss at locations with slightly elevated salinity is a direct result of external salinity or other, possibly physiological, causes.

Defining an exposure-response relationship for suspended kaolin clay particulates and aquatic organisms: work toward defining a water quality guideline for suspended solids.

Water quality guidelines for suspended solids generally rely on the percentage departure from reference condition, an approach that has been criticized. Attempts to develop a biological effects-base guideline have, however, been confounded by low data availability. Furthermore, the high biological response variability to suspended solids exposure suggests that organisms are responding not only to exposure concentration and duration but also to other mechanisms of effect associated with suspended particles (e.g., size, shape, and geochemical composition). An alternative option is to develop more situation and site specific guidelines by generating biological effects data to suspended particles of a particular geochemistry and restricted size range. With this in mind, aquatic organism responses to kaolin clay particle exposure were collated from the literature and incorporated into 2 exposure-response relationship approaches. The species sensitivity distribution approach produced a hazardous concentration affecting 5% of species estimate of 58 mg/L for mortality responses, and 36 mg/L for sublethal data. The severity-of-ill-effect approach produced similar estimates for lethal and sublethal data. These results suggest that aquatic organisms are slightly more tolerant of kaolin clay particles than particles from barite or bentonite clays, based on results from previous studies on these clay types. This type of information can enable better estimates of the risk faced by aquatic organisms exposed to suspended solids. For example, when the sediments of a particular water body are dominated by a particular type of clay particle, then the most appropriate exposure-response relationship can be applied.

Risk assessment using the species sensitivity distribution method: data quality versus data quantity.

Species sensitivity distributions (SSDs) are cumulative distributions of measures of species sensitivity to a stressor or toxicant, and are used to estimate concentrations that will protect p% of a community (PCp ). There is conflict between the desire to use high-quality sensitivity data in SSDs, and to construct them with a large number of species forming a representative sample. Trade-offs between data quality and quantity were investigated using the effects of increasing salinity on the macroinvertebrate community from the Hunter River catchment, in eastern Australia. Five SSDs were constructed, representing five points along a continuum of data quality versus data quantity and representativeness. This continuum was achieved by the various inclusion/exclusion of censored data, nonmodeled data, and extrapolation from related species. Protective concentrations were estimated using the Burr type III distribution, Kaplan-Meier survival function, and two Bayesian statistical models. The dominant taxonomic group was the prime determinant of protective concentrations, with an increase in PC95 values resulting from a decrease in the proportion of Ephemeropteran species included in the SSD. In addition, decreases in data quantity in a SSD decreased community representativeness. The authors suggest, at least for salinity, that the inclusion of right censored data provides a more representative sample of species that reflects the natural biotic assemblage of an area to be protected, and will therefore improve risk assessment.

Global scale variation in the salinity sensitivity of riverine macroinvertebrates: eastern Australia, France, Israel and South Africa.

Salinity is a key abiotic property of inland waters; it has a major influence on biotic communities and is affected by many natural and anthropogenic processes. Salinity of inland waters tends to increase with aridity, and biota of inland waters may have evolved greater salt tolerance in more arid regions. Here we compare the sensitivity of stream macroinvertebrate species to salinity from a relatively wet region in France (Lorraine and Brittany) to that in three relatively arid regions eastern Australia (Victoria, Queensland and Tasmania), South Africa (south-east of the Eastern Cape Province) and Israel using the identical experimental method in all locations. The species whose salinity tolerance was tested, were somewhat more salt tolerant in eastern Australia and South Africa than France, with those in Israel being intermediate. However, by far the greatest source of variation in species sensitivity was between taxonomic groups (Order and Class) and not between the regions. We used a bayesian statistical model to estimate the species sensitivity distributions (SSDs) for salinity in eastern Australia and France adjusting for the assemblages of species in these regions. The assemblage in France was slightly more salinity sensitive than that in eastern Australia. We therefore suggest that regional salinity sensitivity is therefore likely to depend most on the taxonomic composition of respective macroinvertebrate assemblages. On this basis it would be possible to screen rivers globally for risk from salinisation.

Morphological abnormalities in frogs from a rice-growing region in NSW, Australia, with investigations into pesticide exposure.

Three frog species (Limnodynastes tasmaniensis, Limnodynastes fletcheri and Litoria raniformis) were surveyed in rice bays of the Coleambally Irrigation Area (CIA), NSW, Australia, during the rice-growing seasons of 2005/2006 and 2006/2007. A total external morphological abnormality index of 7.0% was observed in frogs of the CIA (n=1,209). The types and frequencies of abnormalities were typical of reports from agricultural areas with ectrodactyly being the most common aberration. A relatively low abnormality index of 1.2% was observed in L. raniformis (n=87) compared to indices of 7.1% and 8.2% observed in L. fletcheri (n=694) and L. tasmaniensis (n=428), respectively. No conclusive evidence was found of unnaturally high rates of intersex, gonadal maldevelopment or unbalanced sex ratios in any species. Rice bay surface waters differed significantly in mean pesticide concentrations of atrazine and metolachlor on farms growing rice and corn compared to farms with rice as the sole crop. However, the similar abnormality indices observed in recent metamorphs emerging from these two farm types provided no evidence to suggest a link between larval exposure to the measured pesticides and developmental malformations.

Distribution of frogs in rice bays within an irrigated agricultural area: links to pesticide usage and farm practices.

In the Coleambally irrigation area (NSW, Australia), the occurrence of four tadpole and frog species in rice bays on farms growing either rice only or both rice and corn was studied over two seasons. In addition to analysis of species occurrence, both gonadal histology and assessment of Batrachochytrium dendrobatidis infection rates were performed. The rice acreage available as potential tadpole habitat was extensively distributed throughout the irrigation area, but more corn was grown in the northern region compared with the southern region. The mean abundance of Litoria raniformis tadpoles was significantly lower in the northern sites compared with the southern sites. In contrast, tadpoles of Limnodynastes fletcheri, Limnodynastes tasmaniensis, and Crinia parinsignifera had a uniform distribution across all study sites. A principal components analysis showed a relationship between farm type and the rice herbicide applied when the crops were initially sown, with sites occupied by Litoria raniformis in the beginning being predominantly rice-only farms. A discriminant analysis showed that low concentrations of the corn herbicide metolachlor and increased pH were the main variables studied that determined site occupation by L. raniformis. This suggested that farms growing only rice (and not corn) with high algal production were the preferred sites. The rates of chytrid infection and gonadal malformations were low across both regions. Histology of the gonads of metamorphs showed that L. raniformis gonadal differentiation is slow compared to that of the two Limnodynastes species. We concluded that farm practices associated with increased corn cropping in the northern region, rather than any direct effect of corn herbicides, determine the reduced presence of Litoria raniformis in the northern region.

An assessment of two-step linear regression and a multifactor probit analysis as alternatives to acute to chronic ratios in the estimation of chronic response from acute toxicity data to derive water quality guidelines.

In aquatic ecotoxicology, acute to chronic ratios (ACRs) are often used to predict chronic responses from available acute data to derive water quality guidelines, despite many problems associated with this method. This paper explores the comparative protectiveness and accuracy of predicted guideline values derived from the ACR, linear regression analysis (LRA), and multifactor probit analysis (MPA) extrapolation methods applied to acute toxicity data for aquatic macroinvertebrates. Although the authors of the LRA and MPA methods advocate the use of extrapolated lethal effects in the 0.01% to 10% lethal concentration (LC0.01-LC10) range to predict safe chronic exposure levels to toxicants, the use of an extrapolated LC50 value divided by a safety factor of 5 was in addition explored here because of higher statistical confidence surrounding the LC50 value. The LRA LC50/5 method was found to compare most favorably with available experimental chronic toxicity data and was therefore most likely to be sufficiently protective, although further validation with the use of additional species is needed. Values derived by the ACR method were the least protective. It is suggested that there is an argument for the replacement of ACRs in developing water quality guidelines by the LRA LC50/5 method.