Native Earthworm Research Articles

Interactions between earthworm burrowing, growth of a leguminous shrub and nitrogen cycling in a former agricultural soil

Attempts to restore native biodiversity into agricultural landscapes in New Zealand appear to be compromised both by soil nitrogen enrichment from farming and N-leakage to the wider environment. We investigated whether interactions between native earthworms and a native rhizobium-inoculated leguminous shrub (Sophora microphylla) have a measurable effect on the mobility of nitrogen in an agricultural soil that has been nitrogen-enriched and colonised by exotic earthworms. Plants grew better in the presence of both native and exotic soil-burrowing earthworms. Rates of root nodulation were considerably enhanced in the presence of the native megascolecid anecic earthworm Maoridrilus transalpinus. This species consumed more organic matter in the presence of inoculated plants whilst marginally lowering soil pH and enhancing critical concentrations of nitrate, but also reducing nitrous oxide emissions. Earthworms raised dehydrogenase enzyme activity and microbial activity in soil, but this was not commensurate with rates of nodulation. Our results show that some combination of earthworm-mediated soil aeration, modification of moisture conditions in the rhizosphere and drilosphere, and comminution of organic matter, modify microbial communities and significantly impact the N cycle.

Oxidative stress responses and insights into the sensitivity of the earthworms Metaphire guillelmi and Eisenia fetida to soil cadmium

Soil toxicological tests are commonly performed using Eisenia fetida as the standard earthworm species, but it is tolerant to a wide range of pollutants. Therefore, the inclusion of susceptible species is crucial for the accurate estimation of soil contamination. In this study, we examined the sensitivity to soil cadmium (Cd) of anecic Metaphire guillelmi and epigeic E. fetida by measuring multiple indexes of oxidative stress. Using subcellular partitioning analysis, we further elucidated the inherent mechanism underlying the species-specific sensitivity of the two earthworm species. Among the battery of biochemical indexes, reactive oxygen species and protein carbonyl groups served as sensitive biomarkers. According to their respective response thresholds, M. guillelmi was more sensitive than E. fetida and they differed in their dose-response relationships. In E. fetida, the activities of three antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST), exhibited a hormesis-like U-shaped dose-response relationship, while in M. guillelmi SOD, glutathione peroxidase (an analogue of CAT) and GST showed an inverted U-shaped relationship. The concentrations of Cd in the subcellular fractions and whole body of the earthworms well fit (R2>0.9) a saturation model versus bioavailable Cd concentrations determined by the diffusive gradients in thin films technique. Despite the lower accumulation capacity of M. guillelmi, the Cd-binding capacity (Cmax) of its subcellular heat-stable protein fraction, the so-called biologically detoxified metal pool, was 2.7 times lower than that of E. fetida, whereas the Cd binding affinity (logK) of its heat-denatured protein fraction, i.e. the metal-sensitive fraction, was 3.0 times higher, which accounted for the high susceptibility of M. guillelmi to soil Cd. Our results suggest that because of their sensitivity, as exemplified by M. guillelmi, native earthworm species should be taken into account in soil risk assessments to avoid underestimation of the toxicity of various pollutants.

Evidence for ongoing introduction of non-native earthworms in the Washington, DC metropolitan area

Earthworm introductions and invasions are ongoing, with significant consequences for ecological characteristics and function where populations of invasive species reach high densities. In North America the influx of people, goods and materials to coastal cities has long been recognized to be related to introduction and establishment of many different invasive organisms. We conducted surveys for soil invertebrates in the Washington, DC area along the Potomac River corridor to examine the influence of historic soil profile disrupting disturbances on the composition of soil invertebrate communities. Here we report three earthworm taxa that either (1) had never been previously reported in North America (Lumbricidae: Helodrilus oculatus), (2) had never been reported from “wild” caught samples in forested soils (Lumbricidae: Eisenia fetida), or (3) represented a notable range expansion for an introduced species (Lumbricidae: Murchieona muldali). All three species reported here have attributes that give reason for concern over their expansion into North American soils, not least of which is their potential for competitive interactions with the remaining native earthworm species.

Application of leaves to induce earthworms to reduce phenolic compounds released by decomposing plants

The negative impacts (allelopathic effects) of phenolic compounds (PCs) in soil on plant growth and microbial communities have recently received considerable attention. Similarly, there have been several recent studies on the effects of microbes on the degradation of PCs. Because of the profound effects of their feeding and burrowing activity, earthworms should have significant effects on PCs degradation; however, few studies have examined this potential effect, and particularly, factors that may affect the course of degradation. We tested different earthworm species and density, different conditions (sterilization or not) of mixture of soil and plant residual, and different source of PCs to evaluate the capacity of earthworms to accelerate PCs degradation. In addition, earthworm behavior experiments were set up to test whether adding plant leaves can stimulate earthworm feeding activity. The results showed that native earthworms exhibited a higher capacity than compost earthworms for degrading PCs; furthermore, when the number of Metaphire guillemi reached 300 individuals m−2 in our experimental units, the PCs decreased most quickly, and the residual PCs concentration was 105 μg (p-coumaric acid)g−1 (dry soil) less than that of control group. The source of PCs also affected their degradation rate, as PCs derived from leaves seemed to degrade more quickly. The results of our experiment suggested that earthworms avoid feeding on phenolic acids, but can be induced to do so by adding leaves to the substrate. These results indicate that earthworm activity can accelerate the degradation of total PCs, and that this may be further facilitated by incorporation of organic matter, which may be used to alleviate allelopathic effects of PCs in soil.

Earthworm and organic amendment effects on microbial activities and metal availability in a contaminated soil from China

We tested the effect of an addition of organic matter (OM: 10% of a mixture of coconut bran and cattle dung) and/or earthworm inoculation (15g fresh weight kg−1 soil) in a soil polluted by metals on microbial activities and concentrations of metal DTPA extractable fractions. The experiment, conducted under laboratory conditions, lasted for 60days. Soil organic C and total N in control were 15.3and 1.47mgkg−1, and total Zn, Cd, Pb and Cu contents, 405, 0.639, 439 and 394mgkg−1, respectively. The native earthworm species Amynthas morrisi exhibited 91.5% mortality in the un-amended polluted soil, whereas only 20% of Eisenia fetida individuals died. In the OM treatment the native species performed much better showing reproduction and a higher soil ingestion rate than E. fetida. In both amended and non-amended soils, casts exhibited higher concentrations of total organic C (+15.7 to 46.5%) and N(+13.3 to 59.3%) and alkali hydrolysable N (+78.0 to 133%), but not dissolved organic C. Microbial enzymatic activities were significantly increased when OM was added to the soil (+142 to 456%), with the sole exception of acid phosphatase activity. The addition of earthworms had contrasting effects on microbial activities: N-acetyl glucosamine activity was enhanced (+559 to 829%) while no significant difference was noted for other measured enzymatic activities. Introduction of earthworms in OM amended treatments tended to decrease all activities (−30.6 to −59.3%) although they were still higher than in the non- amended soil, especially for β-glucosidase (+182 to 230%). We noted no significant differences between the effects of the two earthworm species. Increased microbial activities resulting from the addition of organic matter did not substantially alter the availability of Zn, Cd, Pb and Cu assessed by their association with DTPA. Earthworm increased the availability of Zn (up to +31%), Cd (+78 to 193%) and decreased Pb (down to −16.4%) in the non-amended treatment. In the amended treatment earthworms induced an increase in Cd (up to 18.8%), but a decrease in Zn availability. Total Cd available concentrations in the experimental units (in soil and casts when earthworms were present) increased from 36.2% in control soil to up to 46.1% after 60days depending on treatments, while no significant changes were observed for other metals. This rather important change obtained for Cd in such a short amount of time indicates a possible environmental risk.

New species of Pheretima, Amynthas, Polypheretima, and Pithemera (Clitellata: Megascolecidae) from Mindanao and Associated Islands, Philippines.

Nonillon M. Aspe and Samuel W. James (2016) Studies over the past decade have shown the Philippine native earthworm fauna to be highly diverse, with apparent high endemism among islands and localities. Here we describe 17 new species of pheretimoid earthworms collected from priority conservation sites on Mindanao and associated islands. Nine species of the subgenus Pheretima (Pheretima), distinguished by the absence of secretory diverticula on the coelomic surface of the copulatory bursae, were detected. Pheretima acia n. sp., P. dinagatensis n. sp., P. enormis n. sp., P. hamiguitanensis n. sp., P. lantapanensis n. sp. belong to the P. urceolata species group, with a pair of spermathecal pores in 5/6; P. timpoongensis n. sp., P. camiguinensis n. sp., P. sibucalensis n. sp., and P. apoensis n. sp. belong to the P. sangirensis group, with a pair of spermathecal pores in 7/8. Pheretima (Parapheretima) pandanensis n. sp. and P. (Parapheretima) boaensis n. sp., members of the subgenus Pheretima (Parapheretima), with secretory diverticula on the coelomic surface of the copulatory bursae, are the first Philippine records of Parapheretima. In the genus Amynthas, A. dinagatensis n. sp. is athecate; A. cagdianaoensis n. sp. belongs to the belongs to the A. supuensis species group, with a pair of spermathecal pores at 8/9; and A. talaandigensis n. sp. belongs to A. rimosus group, with intrasegmental spermathecae in 6, 7, 8, and 9. In the genus Polypheretima, P. bukidnonensis n. sp. belongs to the Po. elongata species group, with paired genital markings on xix and successive segments, and paired spermathecal batteries in vi and/or vii; Po. zamboangensis n. sp., either has spermathecal pores in 5/6/7 or lacks them, and has a metandric male sexual system. Pithemera nolani n. sp. is unique among congeners in having only one pair of spermathecal pores in 5/6 and in having copulatory bursae. The geological history of Mindanao, which is a collision complex between three arc systems, may have contributed to the high diversity of the earthworm fauna on Mindanao. Future molecular studies can help elucidate the evolutionary relationships and geographical distribution of species and populations, and shed light on mechanisms of earthworm diversification in the Philippines.

Establishment of earthworms on reclaimed lignite mine soils in east Texas

Little is known about earthworm establishment after surface mining of lignite coal in continental climates such as the south central region of the United States. This study examined the abundance and species composition of earthworms in afforested lignite coal mine soils in east Texas. In a 3×3×2 factorial design, earthworms were sampled under two methods of land reclamation, haul-back (n=30) and mixed overburden (n=30). The study was conducted on a chronosequence of 2–28 years since afforestation under pine plantations and mixed pine and hardwood stands. The fieldwork was conducted from January 2012 through March 2014 using hand-sorting field methods. Forest cover type was significant at the mixed overburden sites (p=0.0128); mixed pine and hardwood forest soils (13.7±25.46ind.m−2) contained 43% more earthworms than pine plantation soils (7.6±17.06ind.m−2). The number of earthworm individuals was significantly lower in 2–8 year-old stands than in 12–18 and 22–28 year old stands (p<0.0001) at both haul-back and mixed overburden sites. Regression analysis found percentage of silt to positively influence earthworm abundance. Analysis of the species composition at both Beckville and Oak Hill mines revealed that 83% of earthworms were native earthworms species (from the genera Diplocardia and Bimastos) and 17% were exotic species (Aporrectodea trapezoides, Microscolex dubius, Lumbricus rubellus and Octolasion tytaeum).

Dominance of native earthworms in secondary tropical forests derived from slash-and-burn Mayan agricultural practices (Yucatán, Mexico)

In order to assess earthworm communities influenced by successional changes in tropical subdeciduous forest (TSF), we studied several secondary forests developed after annual crops in southern Yucatan (Mexico). All these secondary TSF were derived from slash-and-burn (S&B) Mayan shifting agricultural practices. Accordingly, four repetitions of four stages in the S&B shifting system were selected: currently cultivated annual maize crops, three-year-old fallow, and 20- to 30-year-old and 50-year-old secondary forests. Earthworm communities were characterized according to richness, abundance, and biomass values; some soil-related variables were also determined, both environmental (litter, moisture, and temperature) and physicochemical (texture, Cation exchange capacity-CEC, P, N, C). C and N content and CEC were lower in annual crops than in fallow and forests. Except for soil temperature (slightly lower in forests stages) and clay and sand content (respectively lower and higher in late stages), the other edaphic (pH, P content) and environmental variables (litter and soil moisture content) did not vary among successional stages. Five species of earthworms were found, one exotic (Dichogaster affinis) and four native (Balanteodrilus pearsei, Diplotrema oxcutzcabensis, Mayadrilus calakmulensis, and an unidentified ocnerodrilid). A higher number of species (4) was found in annual crops, whereas late successional stages contained only two species; conversely, higher values of abundance and biomass were found in 50-year-old forests than in annual maize crops. The native B. pearsei dominated all successional stages, with relative values of abundance and biomass over 80% in fallow and forested stages, reaching up to 99% in 50-year-old forests. The single exotic species was limited to annual crops with relatively low abundance and biomass values. We discuss the reasons for the prevalence of the native B. pearsei and the absence of exotic species in successional stages, especially regarding the kind of soils characteristic of the Yucatán peninsula, and the persistence of ancient Mayan agricultural practices.

Different impacts of native and exotic earthworms on rhizodeposit carbon sequestration in a subtropical soil

Earthworms are known to regulate the sequestration of soil and leaf litter carbon (C). However, their impacts on the more accessible rhizospheric C, which represents a major energy source for soil food webs and an essential factor for C sequestration, are still unclear. Previous studies indicate that earthworms regulate the dynamics of SOC and leaf litter-C by increasing C accessibility to microbiota. However, in the case of labile rhizodeposit-C, microbiota might not require any pre-conditioning by earthworms and may rapidly metabolize most of this root-derived C. Consequently, potential pathways by which earthworms may affect the fate of rhizodeposit-C would be to regulate the biomass and/or activity of rhizosphere microbiota and, further, to mineralize/stabilize microbial products. A 13CO2 labelling experiment was performed to determine the impacts of four different earthworm species on the fate of tree rhizodeposit-C in a subtropical soil. We hypothesized that endogeic earthworm species, representing primarily geophagous species, would closely interact with soil microbiota and sequester the microbially metabolized rhizodeposit-C more efficiently than epigeic and anecic earthworm species. We found that irrespective of ecological group affiliation, the three native earthworms did not affect rhizodeposit-C sequestration. In contrast, the exotic endogeic species stimulated the immobilization of rhizodeposit-C in the biomass of root-associated bacteria and/or arbuscular mycorrhizal fungi and, further, accessed the microbiota-metabolized rhizodeposit-C more efficiently. As a consequence, the exotic endogeic earthworm species transiently tripled rhizodeposit-C retention in soil. We propose that the weak linkages between native earthworms and rhizodeposits-related microbiota limit earthworm impacts on rhizodeposit-C sequestration. However, the exotic endogeic species Pontoscolex corethrurus may potentially alter rhizodeposit-C dynamics in invaded areas by shifting rhizosphere microbial community composition. This work highlights a distinct mechanism by which earthworms can regulate C dynamics and indicates a significant contribution of invasive earthworm species to belowground processes.

Interactions of native and introduced earthworms with soils and plant rhizospheres in production landscapes of New Zealand

Native and exotic earthworms and plants co-exist on the margins of agricultural land in New Zealand. Remnants of native vegetation support mixed assemblages of depleted populations of native Megascolecid earthworms together with apparently increasing invasive populations of introduced Lumbricidae. We question whether the survival and viability of these earthworm populations is a function of soil preference and whether there are significant differences in terms of how the two groups are influenced by and modify soil properties and plant growth. Choice chamber and mesocosm experiments, with and without plant rhizospheres, were used to study five species of native earthworms, two of which could be identified only by DNA barcoding, and four introduced exotic species. Both natives and exotics preferred agricultural soils to a plantation forest and a native forest soil. Earthworms also modified the physico-chemistry of soils and greenhouse gas emissions, with a marked interaction with root morphology of two native species of tea tree. Lesser differences were found between native and exotic earthworms than between functional groups. It is concluded that New Zealand’s production landscapes provide novel habitats with clear benefits both to threatened species conservation and to soil ecosystem services.

Differences in soil characteristics between field and forest may influence the distribution of an invasive earthworm

AbstractIn northern North America, invasive earthworms (including the nightcrawler Lumbricus terrestris) have been dispersing from points of introduction and dramatically affecting soil structure, soil food webs, and forest floor dynamics. However, little is known about the factors influencing the local distribution of invasive earthworms south of the Wisconsinan glaciation. Earthworms were sampled at suspected sites of introduction near Mountain Lake Biological Field Station, Virginia, USA. The density of invasive earthworms decreased as distance from suspected sites of introduction increased; native earthworms displayed the opposite relationship. However, the distance that L. terrestris was found into the forest was less than expected given dispersal rates calculated from more northern invasions. We also found correlations among population densities of L. terrestris and physical–chemical properties of the soil, and differences between field and forest soils in terms of temperature, moisture, and soil chemical properties. We conducted two experiments to analyze some factors possibly responsible for the observed distribution: (1) temperature and moisture, and (2) soil type (field vs. forest) and food resources. Our results suggest that L. terrestris may not disperse as far into forested habitats of the Southern Appalachians compared to northern forests due to local physical‐chemical soil characteristics.

Vermicomposting of Mucuna bracteata – a Fast Spreading Troublesome Weed in Kerala, India

Mucuna bracteata DC. is one among the common weeds spreading rapidly in Kerala. The spread of this weed becomes an environmental nuisance and a threat to the local biodiversity. Conversion of this troublesome weed into nutrient rich manure through vermicomposting with native earthworm species of Perionyx ceylanensis was attempted in this study. The phytomass of M. bracteata was subjected to precompost along with cattle dung in the ratio of 6:1 for a period of 15 days. The resulting precompost – partially decomposed phytomass – was fed into vermireactors. The vermireactors fed with 37.5 g (dry weight) precomposted weed mass and 10 adult earthworms were operated for 15 days. These experiments were repeated for six times. The vermireactors performed with 14–21.3% recovery of vermicast with a C/N ratio of 23.7, which is comparable with the reported values in the literature. The findings of this study indicate that the earthworm species P. ceylanensis is potential enough to convert the phytomass of M. bracteata into nutrient rich manure. Also, the worms multiplied and grew well by gaining weight. Hence, these reactors with precomposted phytomass of M. bracteata can be operated sustainably. DOI: http://dx.doi.org/10.5755/j01.erem.70.4.8552

Earthworm composition, diversity and biomass under three land use systems in south-eastern Australia

In south-eastern Australia, strips of planted native trees and shrubs (shelterbelts) are frequently established to restore ecosystem services altered by agriculture. Despite their wide use, little is known about the effects of establishing shelterbelts on soil macro invertebrates, especially earthworms, which are of major importance in soil processes. We assessed earthworm composition, diversity and biomass in three land use systems: native shelterbelts dominated by Acacia and Eucalyptus species, agricultural pastures and native remnant woodland fragments dominated by Eucalyptus blakelyi and/or Eucalyptus melliodora. Earthworm communities differed significantly among systems, with abundance, biomass and diversity greatest under pasture. Within shelterbelts we saw a shift from high earthworm biomass and density to low with increasing time after establishment. Soil edaphic variables did not correlate strongly with earthworm biomass or density, but were correlated with earthworm community composition. Overall the introduction of native woody vegetation was associated with a decline in density and biomass of earthworms, including a decrease in the relative abundance of exotic species. As such shelterbelts can be used to promote native earthworm relative abundance, which may be important for local diversity, soil function and landscape connectivity.

Earthworm Communities in Previously Glaciated and Unglaciated Eastern Deciduous Forests

Native earthworms were removed from forested ecosystems during the last glacial advance and have since been replaced with nonnative earthworm species. Nonnative earthworms can cause major changes in microbial and plant communities and nutrient cycling. In this study, we sought to compare the earthworm communities north and south of the last glacial terminus, and to examine correlations between plant communities and soil characteristics. In summer 2011, we measured the earthworm, herbaceous plant, and woody plant communities in 3 forests in southwestern Ohio and 3 forests in northern Kentucky. We also measured soil characteristics including moisture, pH, organic matter, and nitrate and ammonium content. We found no native earthworm species at any of our study sites; however, previously glaciated forests exhibited more diverse earthworm communities and included all ecological groups. Earthworm species richness increased with increased density of invasive woody plant species and decreased with increased soil ammonium. Scientists and managers should continue to survey the earthworm communities in forests to better understand the ranges of nonnative earthworms and the impacts they have on plant communities and nutrient dynamics.

Earthworm Invaders Have Huge Implications for Forest Health

Earthworm Invaders Have Huge Implications for Forest Health

Can the invasive earthworm, Amynthas agrestis, be controlled with prescribed fire?

Biological invasions are one of the most significant global-scale problems caused by human activities. Earthworms function as ecosystem engineers in soil ecosystems because their feeding and burrowing activities fundamentally change the physical and biological characteristics of the soils they inhabit. As a result of this “engineering,” earthworm invasions can have significant effects on soil physical, chemical and biological properties. The species Amynthas agrestis (family Megascolecidae) was introduced to the United States from Asia, and has expanded its distribution range to include relatively undisturbed forests. Here, to clarify life history traits, we reared individuals under seven different conditions of food provision using litter, fragmented litter and soil, and also analyzed the stable isotope ratios of field-collected specimens to investigate their food resources in the field. Second, we examined whether prescribed fire can be used to manage invasive earthworms. We constructed eight experimental plots, each with 100 individuals of A. agrestis each, and burned half of the plots. The feeding experiment showed that the earthworms in units containing soil and some form of organic matter (litter and/or fragmented litter) produced many cocoons, indicating that litter and fragmented litter are important food resources for them. Stable isotope analyses also supported this result. During the experimental fires, average soil temperature at 5 cm depth increased by only 7.7 °C (average maximum of 32.2 °C). Litter mass was significantly reduced by the fires. Although numbers of A. agrestis and cocoons recovered from burned and unburned plots were not different, the viability of cocoons was significantly lower in burned plots. Fire may also reduce the survival rate of juveniles in the next year by depriving them of their preferred food resource. Most native earthworms in the United States live in the soil, while many invasive ones live in the litter layer and soil surface. Therefore, prescribed fire could be a viable tool for control of invasive earthworms without negatively impacting native earthworm populations.

Impact of Exotic Earthworms on Organic Carbon Sorption on Mineral Surfaces and Soil Carbon Inventories in a Northern Hardwood Forest

Exotic earthworms are invading forests in North America where native earthworms have been absent since the last glaciation. These earthworms bioturbate soils and may enhance physical interactions between minerals and organic matter (OM), thus affecting mineral sorption of carbon (C) which may affect C cycling. We quantitatively show how OM-mineral sorption and soil C inventories respond to exotic earthworms along an earthworm invasion chronosequence in a sugar maple forest in northern Minnesota. We hypothesized that mineral surface area in A horizons would increase as burrowing earthworms incorporated clay minerals from the B horizons and that enhanced contacts between OM and minerals would increase the OM sorption on mineral surfaces and mineral-associated C inventories in A horizons. Contrary to our hypotheses, mineral surface areas within A horizons were lowered because earthworm burrows only extended into the silt-rich loess that separated the A and clay-rich B horizons. Furthermore, where endogeic earthworms were present, a smaller fraction of mineral surface area was covered with OM. OM sorption on minerals in the A horizons shifted from a limitation of mineral surface availability to a limitation of OM availability within a decade after the arrival of endogeic earthworms. C-mineral sorption depends on earthworm consumption of OM as well as the composition and vertical distribution of minerals. This finding may thus explain the contradictory results reported in earlier investigations. Our results highlight the rapid and drastic effects of exotic earthworms on key ecosystem processes in deciduous forests in post-glacial settings.

Removal of an invasive shrub (Chinese privet: Ligustrum sinense Lour) reduces exotic earthworm abundance and promotes recovery of native North American earthworms

This study investigated the possibility of a facilitative relationship between Chinese privet (Ligustrum sinense) and exotic earthworms, in the southeastern region of the USA. Earthworms and selected soil properties were sampled five years after experimental removal of privet from flood plain forests of the Georgia Piedmont region. The earthworm communities and soil properties were compared between sites with privet, privet removal sites, and reference sites where privet had never established. Results showed that introduced European earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion tyrtaeum) were more prevalent under privet cover, and privet removal reduced their relative abundance (from >90% to ∼70%) in the community. Conversely, the relative abundance of native species (Diplocardia michaelsenii) increased fourfold with privet removal and was highest in reference sites. Soils under privet were characterized by significantly higher pH relative to reference plots and privet removal facilitated a significant reduction in pH. These results suggest that privet-mediated effects on soil pH may confer a competitive advantage to European lumbricid earthworms. Furthermore, removal of the invasive shrub appears to reverse the changes in soil pH, and may allow for recovery of native earthworm fauna.

Triclocarban, triclosan and its transformation product methyl triclosan in native earthworm species four years after a commercial-scale biosolids application

Triclocarban (TCC), triclosan (TCS) and methyl triclosan (Me-TCS) were detected in soil and the native population of earthworms of an agricultural field in Ottawa, Canada, about four years after a commercial-scale application of biosolids. In soil that received biosolids, TCC and TCS were detected at median concentrations of 13.0 and 1.5ng/g soil (d.w.), respectively, while Me-TCS, the transformation product of triclosan, was detected at a six-fold higher median concentration than its precursor. In earthworms collected at the biosolids-amended field-plot about four years post application, Me-TCS was also detected at higher concentrations (26 to 114ng/g tissue d.w.) than TCS (16–51ng/g) and TCC (4–53ng/g). These data provide evidence that not only parent compounds but also their transformation products need to be considered in faunal bioaccumulation studies. Moreover, the preliminary results for pooled earthworm samples from different ecological groups suggest that the degree of bioaccumulation of biosolids-associated contaminants may depend on the habitat and feeding behavior of the organisms.

Earthworm density and biomass in relation to plant diversity and soil properties in a Palouse prairie remnant

Earthworms are important soil animals in grassland ecosystems and are considered to be important to soil quality. The overall impact of earthworms on soil properties and plant diversity, however, depends on earthworm species, functional group and the type of ecosystem. The primary purpose of this study was to document the relationship among earthworms, key soil properties and native and exotic plant diversity in the little studied, Palouse prairie grassland (Idaho, USA). A secondary objective was to determine the effectiveness of three methods commonly used to sample earthworms. A hillslope characterized by Palouse prairie vegetation, well-expressed, hummocky (mounded) topography and known to support both exotic and native earthworm species was selected for study. The hillslope was divided into three zones [annual-dominated (AD), mixed (MX) and perennial-dominated (PD)] based on characteristics of the inter-mound plant communities described in previous research. Total earthworm biomass in the MX zone (53.5gm−2) was significantly greater than in the PD zone (14.7gm−2) (P=0.0384), but did not differ from the AD zone. Earthworm density ranged from 52 to 81.1individualsm−2 but was not significantly different across zones. Total C and N at 0 to 10 and 30 to 50cm depths were significantly greater in the AD and PD zones as compared to the same depths in the MX zone. Soil textural class was silt loam within all zones and the soil silt fraction was positively correlated with total exotic earthworm density (R=0.783, P=0.0125) and biomass (R=0.816, P=0.0072). Native earthworms were only found in the zone with the greatest total and native plant diversity (PD). Total soil C and N were not correlated to earthworm density, but soil total C and N were significantly negatively correlated with exotic plant density, which indicates that invasive plants may be decreasing soil total C (R=−0.800) and N (R=−0.800). Calculated earthworm densities using data from the electroshocker were generally lower than those based on the hand-sorting method. Electroshocking, however, created lower disturbance and was the only method that resulted in the collection of the deep-burrowing, native species Driloleirus americanus.