Samuel Mutiti

The impact of storm events on a riverbed system and its hydraulic conductivity at a site of induced infiltration

The spatial and temporal variability of riverbed vertical hydraulic conductivity (K(v)) was investigated at a site of induced infiltration, associated with a municipal well field, to assess the impact of high-stage events on scour and subsequently the riverbed K(v). Such impacts are important when considering the potential loss of riverbank filtration capacity due to storm events. The study site, in and along the Great Miami River in southwest Ohio, overlaid a highly productive glacial-outwash aquifer. A three-layer model for this system was conceptualized: a top layer of transient sediment, a second layer comprising large sediment resistant to scour, but clogged with finer sediment (the armor/colmation layer), and a third layer that was transitional to the underlying higher-K(v) aquifer. One location was studied in detail to confirm and quantify the conceptual model. Methods included seepage meters, heat-flow modeling, grain-size analyses, laboratory permeameter tests, slug tests and the use of scour chains and pressure-load cells to directly measure the amount of sediment scour and re-deposition. Seepage meter measured riverbed K(v) ranged from 0.017 to 1.7 m/d with a geometric mean of 0.19 m/d. Heat-transport model-calibrated estimates were even lower, ranging from 0.0061 to 0.046 m/d with a mean of 0.017 m/d. The relatively low K(v) was indicative of the clogged armor layer. In contrast, slug tests in the underlying riverbed sediment yielded K(v) values an order of magnitude greater. There was a linear relationship between scour chain measured scour and event intensity with a maximum scour of only 0.098 m. Load-cell pressure sensor data over a 7-month period indicated a total sediment-height fluctuation of 0.42 m and a maximum storm-event scour of 0.28 m. Scour data indicated that the assumed armor/colmation layer almost always remained intact. Based on measured layer conductivities and thicknesses, the overall K(v) of this conceptualized system was 1.6 m/d. Sensitivity analyses indicated that even complete scour of the armor/colmation layer would likely increase the overall K(v) only by a factor of 1.5. Most scour events observed removed only the transient sediment, having very little effect on the entire system indicating low risk of losing filtration capacity during storms. The research, however, focused on the point bar, depositional side of the river. More research of the entire river profile is necessary.

Assessing ground water development potential using Landsat imagery.

Seven villages in southeastern Kenya surround Mt. Kasigau and depend on the mountains cloud forest for their water supply. Five of these villages have regularly experienced water shortages, and all village water supplies were contaminated with Escherichia coli bacteria. There is a need to economically find new sources of fresh ground water. Remote sensing offers a relatively quick and cost-effective way of identifying areas with high potential for ground water development. This study used spectral properties of features on Landsat remote sensing imagery to map linear features, soil types, surface moisture, and vegetation. Linear features represented geologic or geomorphologic features indicating either shallow ground water or areas of increased subsurface hydraulic conductivity. Regarding soil type, black soils were identified as potential indicators of shallow aquifers based on their relatively lower elevation and association with river valleys. A vegetation map was created using unsupervised classification, and three of the resulting vegetation classes were observed to be commonly associated with wet areas and/or ground water discharge. A wetness map, created using tasseled cap analysis, was used to identify all areas of high ground moisture, including those that corresponded to vegetated areas. The linear features, soil type, vegetation, and wetness maps were overlaid to produce a composite that highlighted areas with the highest potential for ground water development. Electrical resistivity surveys confirmed that areas highlighted by the composite image had relatively shallow depths to the water table. Some figures in this paper are available in color in the online version of the paper.

Drinking water quality in the Mount Kasigau region of Kenya: a source to point-of-use assessment

Drinking water quality was investigated in seven rural villages surrounding Mount Kasigau in southeastern Kenya, where water is piped from unprotected dammed streams and springs in the Kasigau cloud forest down to taps, kiosks, and tanks in the villages. Analyses were conducted for nutrients, trace metals, and pathogen indicators in water from community taps, water stored in homes, and collection points along the pipelines up to catchment dams on the mountain. Water was relatively free from nutrient and trace-metal contamination; however, all samples were contaminated with total coliforms and nearly all were contaminated with Escherichia coli. There was no discernable pattern in the extent of contamination from the catchment dams to the villages. In each of three villages chosen for further study, six residents were selected for a more in-depth investigation. Water quality was generally worse in water stored in those homes compared to water collected at the village taps. The quality of drinking water in homes where treatment was applied was no better than in homes with no water treatment. The Kasigau villages, as many other areas in the developing world, need inexpensive and effective water treatment, as well as an assessment of the effectiveness of sanitary and hygienic practices.

Application of hydrogeophysical techniques to study the distribution of a burrowing crayfish in a wetland

Crayfish are important in wetland systems because of their function in soil nutrient turnover. Since many crayfishes are imperiled by anthropogenic activities, it is important to understand factors that are associated with their distribution within and among wetlands. This study investigated the soil and hydrogeological characteristics of a wetland and related them to the spatial distribution of crayfish burrows found within it. The study utilized field-collected soil cores, electrical resistivity, and ground penetrating radar to map subsurface characteristics at Bartram Forest, Baldwin County, Georgia. Wetland delineation was also conducted in the field to establish the wetland boundaries. Both 2D and 3D geophysical profiles were created. Soils samples were analyzed for grain size distribution, porosity, and hydraulic conductivity in the lab. Hydraulic conductivity of the wetland soils was also determined in the field using slug tests. Results show subsurface physical differences between crayfish inhabited zones of the wetland and those that do not have crayfish burrows.The Ambiguous Crayfish, Cambarus striatus was found in soils with a hydraulic conductivity of 0.01–0.4 m/day where soils outside of their colony boundary had a hydraulic conductivity of 0.4–1.2 m/day. Areas where C. striatus were located had a higher porosity (0.36) than areas without crayfish (0.26). Subsurface stratigraphy varied between the areas with and without burrows. C. striatus was found to live in a subsurface with relatively gradual stratigraphical boundaries when compared to surrounding areas.

Applying the process of backward design in revising an environmental science program

The purpose of this article is to share our model of a successful curriculum reform process and provide an overview so that it can be replicated by other programs. The process of backward design is commonly used for course design, and here we apply this framework to a program-level revision of student learning outcomes, curriculum, and assessment. Graduates from our Environmental Science program are expected to demonstrate an understanding of the appropriate academic content, to be able to conduct research and develop professional behaviors and dispositions. Our revised program now has clear, assessable student learning outcomes, a set of coursework that is well aligned with these outcomes, and planned assessment that will allow us to evaluate our students and our program. This program revision has been a long, time-consuming process that has been facilitated by the cooperative nature and dedication of the individuals on the Environmental Science committee and by support structures at our institution. We will discuss the methods used by our program to bring about these changes and also the challenges we faced.

The Effects of Lead Species and Growth Time on Accumulation of Lead in Chinese Cabbage

A major pathway for heavy metal exposure in contaminated areas is via consumption of locally produced food. This study investigated the accumulation of lead in Chinese cabbage grown in contaminated soils and estimated the weekly dietary intake. Experiments were conducted to determine the effects of different growth times, concentrations, and lead species (carbonate, nitrate, and sulfide) on the uptake of lead in shoots. Results show that Chinese cabbage accumulated up to 38 mg kg−1 in the shoots. There was a significant difference in lead uptake by plants grown in soils with 400 mg kg−1 (Upper Critical Limit: UCL) and those grown in 600 mg kg−1 (Above Critical Limit: ACL) lead concentrations. However, there was no significant difference in the ACL shoots despite the different growth period. The cabbages grown for eight weeks (at UCL) had four times more lead than those grown for four weeks. The elemental form also affected lead uptake with the lead sulfide (mineral form) having the least uptake and lead carbonate (solution) having the highest. Calculated weekly dietary intake levels of lead were higher (above 0.28 mg kg−1 per human body weight) than the recommended levels for human consumption (0.025 mg kg−1 per human body weight).