Improvement of Hydraulic and Water Quality Renovation Functions by Intermittent Aeration of Soil Treatment Areas in Onsite Wastewater Treatment Systems

We tested intermittent aeration of the soil treatment area (STA) of onsite wastewater treatment systems (OWTS) for its ability to restore and maintain STA hydraulic flow and improve the water quality functions of conventional OWTS. Evaluation was conducted on hydraulically-failed conventional OWTS at three state-owned medical group homes in Washington County, RI, USA. Testing was conducted in two phases, with Phase I (before intermittent soil aeration (ISA)) comprising the first 6 months of the study, and Phase II (during ISA) the remaining 7 months. Intermittent soil aeration restored STA hydraulic function in all three systems despite a marked reduction in the STA total infiltrative surface. Soil pore water was collected from 30 and 90 cm below the STA during both phases and analyzed for standard wastewater parameters. Although the STA infiltrative surface was reduced—and the contaminant load per unit of area increased—after installation of the ISA system, no differences were observed between phases in concentration of total N, NO3, total P, or dissolved organic carbon (DOC). Apparent removal rates—which do not account for dilution or differences in infiltrative area—for total N, total P, and DOC remained the same or improved during Phase II relative to the pre-operation phase. Furthermore, intermittent soil aeration enhanced actual removal rates —which do account for dilution and differences in infiltrative area. The effects of ISA on actual removal of contaminants from STE increased with increasing hydraulic load—a counterintuitive phenomenon, but one that has been previously observed in laboratory studies. The results of our study suggest that intermittent soil aeration can restore and maintain hydraulic flow in the STA and enhance carbon and nutrient removal in conventional OWTS

Tools for monitoring and study of peregrine pheretimoid earthworms (Megascolecidae)

Peregrine pheretimoid earthworms, commonly known as jumping worms, are members of the family Megascolecidae that have become widely established outside of their native ranges. In many parts of the world this represents a second wave of earthworm invasions, following the introduction of peregrine European earthworms in the family Lumbricidae during the colonial era. Forest ecologists, turf managers, gardeners, and other land managers are concerned about the observed or presumed negative effects of jumping worms on invaded habitats. Although research on jumping worms has accelerated in recent decades, our understanding of their ecology remains limited. We compiled techniques useful to researchers working to fill voids in our understanding. Similar past efforts have focused on tools used to study common European species. Differences in life cycle, behavior, morphology, and physiology make it difficult to transfer experiences with European earthworms to pheretimoids. For example, the loss of reproductive features in many pheretimoid populations poses a challenge for identification, and techniques for individually tagging lumbricid earthworms have been less successful for megascolecids. The active and ongoing expansion of pheretimoid populations in many areas requires increased attention on distributed methods, such as citizen-science protocols, for detecting and tracking their expansion. Finally, the desire to limit populations of pheretimoids, including those invading gardens and other environments that might be successfully restored, has exposed the lack of options for targeted, effective control of unwanted earthworms. We identify opportunities to address these voids in our methodological tool kit and encourage the adaptation of techniques previously used in the study and management of other invasive animals

The soil fauna

Soil fauna includes earthworms, collembolans, mites, nematodes, and protozoa. These are eukaryotic, heterotrophic, motile organisms that require oxygen for metabolism. Their physical range, habitats, and food resources are constrained by their respective sizes and the availability of pores of appropriate size within the soil. This chapter describes both invertebrate animals that live in the soil and their habitat and additionally examines their activities in the context of the soil foodweb. We focus on the role of soil animals in controlling microbial pathogens, mineralizing nutrients, changing microbial community composition, and enhancing primary production. Like aboveground fauna, the physical structure of the ecosystem places constraints on the activities of the soil fauna, especially in relation to the microflora. As a result of their feeding, burrowing, and movement, the soil fauna also engineer the habitat for the soil microflora, transport beneficial and pathogenic microorganisms, and affect the production of detrital resources from plants

Role of the anecic earthworm Lumbricus terrestris L. in the distribution of plant residue nitrogen in a corn (Zea mays)-soil system

While the benefits of earthworms to crop production are widely acknowledged, the mechanisms involved are poorly understood. We examined the effects of an anecic earthworm (Lumbricus terrestris) on the distribution of plant residue N in a corn (Zea mays)/soil system. Soil (mixed Ap and B horizons) mesocosms (10 cm diameter, 39 cm deep) were amended with 15N-labeled corn litter, inoculated with one earthworm per mesocosm (WORM) or none (CTRL), and pre-incubated for 1, 2 or 3 weeks. Earthworms and remaining plant residues were removed and sweet corn grown in the mesocosms in a greenhouse for 3 weeks. Litter, earthworms, shoots, roots and bulk and burrow soil were analyzed for total N and 15N. Plant and earthworm biomass were also determined. Earthworms had no significant effect on the N content of shoots, roots or bulk soil. Recovery of 15N ranged from 92.6 to 101.9% in CTRL and 60.2 to 83.2% in the WORM treatment. The 15N content of bulk soil in the WORM treatment was significantly higher than in CTRL and increased with pre-incubation time. Excess at.% 15N of burrow soil was 10-100 times higher than in bulk soil. Incorporation of 15N by shoots and roots was significantly higher in the WORM treatment and increased significantly with pre-incubation time only in the WORM treatment. In WORM mesocosms pre-incubated for 3 weeks, the distribution of added 15N was 9.8% in litter, 6.5% in plant, 31.5% in soil, 12.0% in earthworms and 39.8% presumably lost as gas; in CTRL mesocosms, the values were 75.7% in litter, 3.2% in plant, 13.7% in soil and 7.4% in presumed gas losses. The activities of L. terrestris altered the distribution of plant residue N significantly, increasing the transfer of N to plants and soil and enhancing losses of N in the gas phase as pre-incubation time increased. © 2005 Elsevier B.V. All rights reserved

Microbiological characterization of the structures built by earthworms and ants in an agricultural field

The genesis and architecture of the structures built by ants and earthworms differ markedly, suggesting that-in addition to having different physical and chemical properties-the resident microbial community should also have unique properties. We characterized the inorganic N, biomass C, C mineralization rate, and functional diversity of the microbial communities of earthworm casts, earthworm burrow soil, ant mounds, and bulk soil from an agricultural field. Mound soil was most enriched in inorganic N and had the lowest pH, moisture content, and C mineralization rate. Functional diversity was evaluated by determining the ability of microorganisms to grow on 31 substrates using Biolog®EcoPlates in combination with a most probable number (MPN) approach. Casts had MPNs that were one to two orders of magnitude higher than burrow, mound and bulk soil for most substrates. Casts also had the highest MPNs for particular substrate guilds relative to bulk soil, followed by mound and burrow soil. Indices of substrate diversity and evenness were highest for casts, followed by burrow, mound, and bulk soil. Differences in the type of habitat provided by the structures built by ants and earthworms result in the differential distribution of nutrients, microbial activity, and metabolic diversity of soils within an agricultural field that affect soil fertility and quality. © 2007 Elsevier Ltd. All rights reserved

A Problem-Based Learning Approach to Teaching Introductory Soil Science

At most land-grant universities in the USA, Introduction to Soil Science is traditionally taught using a combination of lecture and laboratory formats. To promote engagement, improve comprehension, and enhance retention of content by students, we developed a problem-based learning (PBL) introductory soil science course. Students work in groups to solve five real-life problems during the semester for approximately five class periods each. Every problem is contained within a study unit that has learning objectives, relevant resources, as well as a description of the problem. As students work through problems, they go through a PBL cycle of: (i) understanding the question, (ii) identifying what they know and do not know, (iii) finding the information they need, (iv) sharing new information, and (v) identifying new questions. Each group produces a synthesis paper describing their approach and solution to the problem. Tests are based on the learning objectives and students can recapture points by explaining wrong answers. They can also revise synthesis papers. Most students reported improvement in verbal and written communication skills, ability to interact in groups, and problem solving skills. They identified writing and revising synthesis papers, and preparing for, taking, and revising exams as very helpful in learning course content. More than three quarters of students indicated a positive response to the PBL format for Introduction to Soil Science. Exam scores for students taught using PBL were 1 to 8 percentage points higher than those taught earlier by the same instructor using traditional methods

Phytoremediation of Heavy Metal-Contaminated Soil by Switchgrass: A Comparative Study Utilizing Different Composts and Coir Fiber on Pollution Remediation, Plant Productivity, and Nutrient Leaching

We investigated the effects of organic amendments (thermophilic compost, vermicompost, and coconut coir) on the bioavailability of trace heavy metals of Zn, Cd, Pb, Co, and Ni from heavy metal-spiked soils under laboratory conditions. To test switchgrass (Panicum virgatum) as a potential crop for phytoremediation of heavy metal from soil, we investigated whether the addition of organic amendments promoted switchgrass growth, and consequently, uptake of metals. Compost is a valuable soil amendment that supplies nutrients for plant establishment and growth, which is beneficial for phytoremediation. However, excess application of compost can result in nutrient leaching, which has adverse effects on water quality. We tested the nutrient leaching potential of the different organic amendments to identify trade-offs between phytoremediation and water quality. Results showed that the amendments decreased the amount of bioavailable metals in the soils. Organic amendments increased soil pH, electrical conductivity (EC), and soil nutrient status. Switchgrass shoot and root biomass was significantly greater in the amended soils compared to the non-amended control. Amended treatments showed detectable levels of heavy metal uptake in switchgrass shoots, while the control treatment did not produce enough switchgrass biomass to measure uptake. Switchgrass uptake of certain heavy metals, and concentrations of some leachate nutrients significantly differed among the amended treatments. By improving soil properties and plant productivity and reducing heavy metal solubility that can otherwise hamper plant survival, organic amendments can greatly enhance phytoremediation in heavy metal-contaminated soils

Soil micropore structure and carbon mineralization in burrows and casts of an anecic earthworm (Lumbricus terrestris)

Anecic earthworms (those that build semipermanent vertical burrows) are known to alter the biological activity and physical structure of soils through their burrowing and casting. Information on how earthworms change the physical structure of soil may provide clues about the mechanisms by which earthworms affect microbial processes such as nutrient mineralization. We evaluated the pore structure of bulk soil and of the soil in burrows and casts formed by an anecic species of earthworm (Lumbricus terrestris) in a fallow field. Differences in pore structure (specific pore volume, Vsp, and median pore neck dia., D) were assessed using mercury intrusion porosimetry. We also examined the relationship of these physical properties with mass water content at field capacity (θm), rate of C mineralization (Cmin) and specific C mineralization rate (Csp=Cmin/C content of soil). Mean values of Vsp (±SD) for bulk, cast and burrows were 242±35, 213±13, and 197±4 μl g-1, respectively. Values for D were (±SD) 10.8±2.5, 7.9±3.3, and 5.5±2.9 μm for bulk, burrow, and cast soil, respectively. A smaller proportion of the pore volume in cast and burrow soil was associated with pore diameters in the 3-30 and 30-100 μm range than in bulk soil. θm was higher in burrow and cast soil than in bulk soil and was inversely proportional to Vsp and D. Cmin and Csp followed the order: burrow \u3ecast\u3ebulk soil. Both Cmin and Csp decreased inversely with Vsp. By contrast, no consistent relationship was observed between either measure of C mineralization and D. Our results suggest that the changes in soil pore structure produced by anecic earthworms cause a shift towards smaller pore volume and smaller pore neck diameters. These changes in turn affect physical (e.g. water retention) and microbial (e.g. C mineralization) processes in soil. © 2001 Elsevier Science Ltd

Spatial and temporal variability of phosphorus retention in a riparian forest soil

Riparian zones remove P from surface runoff and can act as filters of nonpoint source (NPS) P pollution for surface waters. Riparian forest soils were investigated in spring and fall for their capacity to retain PO4/3-- P. Samples (300 on each date) were taken from a soil drainage catena from moderately well (MWD), somewhat poorly (SPD), and poorly drained (PD) soil in May and November of 1995 to examine spatial and temporal variability of P retention and its relationship to soil properties. The equilibrium P concentration at zero sorption (EPC0) was determined for each sampling point (lower EPC0, = higher P retention capacity). Mean (coefficient of variation, CV) EPC0 values were 3.8 (0.49) mg, P L-1 in May and no P sorption was apparent in November for SPD soil, 1.0 (1.34) and 1.5 (1.03) mg P L-1 in May and November, respectively for MWD soil, and 0.5 (1.87) and 1.3 (1.13) mg P L-1, respectively for PD soil. The EPC0 was significantly and positively correlated to organic matter (OM) for all drainage classes on both dates. Low EPC0 values-high P retention capacity-in MWD and PD soil corresponded with high Fe(ox) and Al(ox) values. For SPD soil, high mean EPC0 corresponded with low mean Fe(ox) and Al(ox) values. The relationship between EPC0 and Fe(ox) and Al(ox) was described by a hyperbolic function for MWD and PD soil, but not for SPD soil. The EPC0 did not exhibit spatial structure at the sampling scale used for any of the drainage classes, even though Fe(ox), Al(ox), and OM content showed spatial structure

Effects of Lumbricus terrestris L. on nitrogen dynamics beyond the burrow

The degree to which earthworms can affect the availability of plant nutrients depends on their distribution following formation in burrow soil. We conducted a mesocosm-scale laboratory experiment to test the hypothesis that anecic earthworms (those that build semi-permanent vertical burrows) can affect C and N dynamics beyond the confines of the soil immediately surrounding their burrows. Nitrate and ammonium concentrations and the rate of C mineralization were determined in burrow (defined as soil within 5 mm from the macropore wall, regardless of its origin) and bulk soil of treatments amended with Lumbricus terrestris (WORM) and in treatments containing artificial burrows (ARTF) and artificial burrows containing corn leaves (LEAF) periodically over the course of 16 weeks. Comparisons were made to soil in unamended treatments (CTRL) under two different moisture regimes, WET and DRY, during the course of the experiment. Nitrate concentration was significantly higher in WORM and LEAF bulk soil than in CTRL soil, but only under WET conditions. Differences in nitrate concentrations appeared after incubation for 5 weeks and persisted for 11 weeks. Ammonium concentration and C mineralization in bulk soil were not significantly different from CTRL soil for any of the treatments regardless of moisture regime, although values for both variables were significantly higher in burrow than in bulk soil in WORM and LEAF treatments. Anecic earthworms can enhance nitrate concentrations in soil beyond the confines of the burrow, a process that appears to be facilitated with increased soil moisture. © 2005 Elsevier B.V. All rights reserved