David N. Steer

Efficiency of small constructed wetlands for subsurface treatment of single-family domestic effluent

Abstract Single-family constructed wetland systems in Ohio, USA, are studied to evaluate their effectiveness in improving water quality. Twenty-one, three-cell systems (septic tank with two wetlands) are found to meet US Environmental Protection Agency (EPA) effluent load guidelines in 68% of the quarterly water quality samples collected from 1994 to 2001. These wetlands most frequently meet EPA standards for mitigation of biochemical oxygen demand (89% below 30 mg/l); total suspended solids (79% below 30 mg/l); and fecal coliform (74% below 1000 counts/100 ml). Phosphorus and ammonia discharge meet the guidelines less often (50% at 1 mg/l and 16% at 1.5 mg/l, respectively). These data also indicate that domestic treatment wetlands can reduce output of fecal coliform 88±27%, total suspended solids 56±53%, biochemical oxygen demand 70±48%, ammonia 56±31% and phosphorus 80±20%. Analysis of variance for these systems indicates that biochemical oxygen demand reduction is ∼10% less efficiently reduced during winter and ammonia was reduced ∼20% more efficiently in fall when compared with the other seasons. Phosphorus reductions display complex seasonal variations that imply that the least efficient phosphorus reduction occurs in winter and the most efficient reduction occurs in fall.

Assessment and Active Learning Strategies for Introductory Geology Courses

Educational research findings suggest that instructors can foster the growth of thinking skills and promote science literacy by incorporating active learning strategies into the classroom. Active learning occurs when instructors build learner participation into classes. Learning in large, general education Earth Science classes was evaluated using formative assessment exercises conducted by students in groups. Blooms taxonomy of cognitive development was used as a guide to identify critical thinking skills (comprehension, application, analysis, synthesis, evaluation) that could be linked to specific assessment methods such as conceptests, Venn diagrams, image analysis, concept maps, open-ended questions, and evaluation rubrics. Two instructors conducted a series of analyses on sample classes taught with traditional lecture and inquiry-based learning methods. Qualitative and quantitative analyses show that such methods are preferred by students, improve student retention, produce no decrease in content knowledge, promote deeper understanding of course material, and increase logical thinking skills.

Using Conceptests to Assess and Improve Student Conceptual Understanding in Introductory Geoscience Courses

Conceptests are higher-order multiple-choice questions that focus on one key concept of an instructors major learning goals for a lesson. When coupled with student interaction through peer instruction, conceptests represent a rapid method of formative assessment of student understanding, require minimal changes to the instructional environment and introduce many of the recognized principles of effective teaching that enhance student learning. In this study, instructors from several different institutions developed over 300 conceptests for the geosciences. These instructors then used this suite of concept questions in a wide range of classroom settings, including large introductory general education Earth Science courses for non-majors at open enrollment institutions, smaller physical geology classes suitable for majors at private colleges, and in introductory geology laboratory settings. Results of pre- and post-class Geoscience Concept Inventory (GCI) testing and qualitative feedback from students and instructors showed that conceptests increased attendance, improved student satisfaction, and enhanced student achievement. Participating instructors found implementation of conceptests into their classes straightforward and required less than 30 minutes of preparation per class. The conceptest question database is available on-line for geoscience instructors.

How Students Think: Implications for Learning in Introductory Geoscience Courses

Non-major students in introductory geoscience classes exhibit a wide range of intellectual development. Approximately half of these students do not have the skills to understand the abstract scientific concepts traditionally discussed in introductory classes. Many geological concepts will remain unlearned without appropriate activities that build on a foundation of concrete examples. The good news is that these same students can improve their logical thinking skills when they participate in challenging in-class collaborative learning exercises with their more intellectually sophisticated peers. While the exercises themselves are important in promoting the development of higher-order thinking skills, the group interaction also appears to be a significant contributor to the improvement of reasoning.

Challenging Students Ideas About Earth's Interior Structure Using a Model-based, Conceptual Change Approach in a Large Class Setting

A model-based, conceptual change approach to teaching was found to improve student understanding of earth structure in a large (100+ student) inquiry-based, general education setting. Results from paired pre- and post-instruction sketches indicated that 19% (n = 18/97) of the students began the class with naïve preconceptions of the structure of the interior of the Earth. Many of the remaining students (95%; n = 75/79) began the lesson believing that the crust is several hundred kilometers thick. Peer discussion and instruction appeared to be effective in eliminating most naive preconceptions. Analyses of post-instruction sketches indicated that 3% (n = 3/97) of all students retained naïve preconceptions, 18% (n = 18/97) changed their views from naïve to the “thick crust” view, 58% (n = 58/97) began to recognize the relative scales of the boundaries with 30% (n = 28/97) drawing the sketch with scaled boundaries. Many of the students (65%; n = 76/117) could correctly answer formative earth structure conceptual questions that were asked five lessons after the earth structure lesson was taught. A comparison of pre- and post-course conceptual test question responses indicated that 13–20% more students could correctly answer similar questions two months after the model-based, conceptual change plate tectonics lessons were taught.

Life-cycle economic model of small treatment wetlands for domestic wastewater disposal

Abstract Total system life costs (capital cost and ecological based on released pathogens) were modeled for two-cell domestic treatment wetland systems and compared to costs of traditional and emerging technology systems. Small treatment wetlands that were operationally effective for 20-years had net present value (NPV) costs

Global supply of freshwater: the role of treatment wetlands

500–3000 less than those of sand filter systems. The same treatment wetlands were modeled as releasing ∼4 times pathogens, thus having a much higher ecological cost than sand filter systems. Wetland systems modeled using the highest possible pathogen treatment efficiencies still released ∼2 times the pathogens of sand filter systems. Treatment wetlands must function a minimum of 10 years before replacement in order to remain equivalent in cost to a sand filter lasting 20-years using a 6.25% discount rate. The maximum allowable installation costs for any alternative system (with no annual expenses) were

A test of four plant species to reduce total nitrogen and total phosphorus from soil leachate in subsurface wetland microcosms.

6675–7700 if required to be equal in total system NPV costs to wetlands. NPV costs were found to be particularly sensitive to uncertainties in installation and maintenance costs. Modeling indicated that the capital savings realized using wetland systems could be used to modify the simple 2-cell design such that both capital and ecological loads delivered to the environment could be minimized. Wetlands may provide a more sustainable option for communities if effluent is centralized and treated in an appropriately scaled wetland system.

The interacting effects of temperature and plant community type on nutrient removal in wetland microcosms

In 2000, humans used approximately 60% of run-off that is geographically and temporally accessible. With projected increases in population, humans may use between 72-99% (depending on whether per capita increases are factored) of accessible run-off by 2025, even accounting for new dam construction. Wetlands have the capability to filter polluted water and could therefore potentially affect access to freshwater. Based on an estimated 2507 km³/year of total wastewater produced in 2025 and a standard flow rate of wastewater at 5 cm/day, our model predicts that the construction of 171,114 km² of treatment wetlands can potentially reduce human appropriation of annual run-off to 64% by 2025, with additional freshwater returns of up to 23% of annual run-off.