William W. Simpkins

Design and placement of a multi-species riparian buffer strip system

A multi-species riparian buffer strip (MSRBS) system was designed and placed along a Central Iowa stream in 1990. Bear Creek, is typical of many streams in Central Iowa where the primary land use along the streams length is row crop (corn and soybeans) production agriculture or intensive riparian zone grazing. The Bear Creek watershed is long (∼ 35 km), narrow (3–6 km), and drains 7,661 ha of farmland. The MSRBS system is a 20 m wide filter strip consisting of four or five rows of fast-growing trees planted closest to the stream, then two shrub rows, and finally a 7 m wide strip of switchgrass established next to the agricultural fields. The 1.0 km long system, is located on an operational farm and is laid out in a split block design on both sides of Bear Creek. An integral part of this system is a streambank stabilization soil bioengineering component and a constructed wetland to intercept NPS pollutants in field drainage tile water flow. It is hypothesized that this system will function effectively as a nutrient, pesticide, and sediment sink for NPS pollutants coming from the upslope agricultural fields. Prior to establishment of the MSRBS system, the riparian zone along Bear Creek was grazed and row cropped to the stream edge. Since 1990 there has been dramatic alteration in the appearance and functioning of this riparian zone. After four growing seasons, the fast-growing tree species (cottonwood, silver maple, willow, and green ash) range in height from 2.4 m to over 5.5 m. Mean (four-year) biomass production of silver maple was 8.4 dry Mg ha−1, more than twice to seven times the yield from other silver maple research plots in Central Iowa. The shrub species, selected because of desired wildlife benefits, have done well in terms of survival and growth with ninebark, Nannyberry viburnum and Nanking cherry doing the best. The switchgrass grass has developed into a dense stand that effectively stops concentrated flow from the agriculture fields and allows for infiltration rates well above the field rate. Early root biomass data indicate significantly more roots below the MSRBS than agricultural fields. This suggests better soil stabilization, absorption of infiltrated water, and soil-root-microbe-NPS pollutant interaction characteristics within the MSRBS system than the cropped fields. Nitrate-nitrogen concentrations in the MSRBS never exceed 2 mg l−1 whereas the levels in the adjacent agricultural fields exceed 12 mg l−1. The water quality data collected suggest that the MSRBS is effective in reducing NPS pollutants in the vadose and saturated zone below the system. The soil bioengineering revetments have stabilized the streambank and minimized bank collapse. Initial results (from 4 months of operation) from the constructed wetland (built in summer 1994) indicate nitrate-nitrogen concentrations of the tile inflow water >15 mg l−1 whereas, the outflow water had a nitrate-nitrogen concentration of <3 mg l−1. Over time this wetland should become more effective in removing excess nitrogen moving with the tile flow from the agricultural fields because of the accumulation of organic matter from the cattails. Overall the MSRBS system seems to be functioning as expected. This MSRBS system offers farmers a way to intercept eroding soil, trap and transform NPS pollution, stabilize streambanks, provide wildlife habitat, produce biomass for on-farm use, produce high-quality hardwood in the future, and enhance the aesthetics of the agroecosystem. As a streamside best management practice (BMP), the MSRBS system complements upland BMPs and provides many valuable private and public market and non-market benefits.

Riparian forest buffers in agroecosystems – lessons learned from the Bear Creek Watershed, central Iowa, USA

Intensive agriculture can result in increased runoff of sediment and agricultural chemicals that pollute streams. Consensus is emerging that, despite our best efforts, it is unlikely that significant reductions in nutrient loading to surface waters will be achieved through traditional, in-field management alone. Riparian forest buffers can play an important role in the movement of water and NPS (non-point source) pollutants to surface water bodies and ground water. Riparian buffers are linear in nature and because of their position in the landscape provide effective connections between the upland and aquatic ecosystems. Present designs tend to use one model with a zone of unmanaged trees nearest the stream followed by a zone of managed trees with a zone of grasses adjacent to the crop field. Numerous variations of that design using trees, shrubs, native grasses and forbs or nonnative cool-season grasses may provide better function for riparian forest buffers in specific settings. Properly designed riparian buffers have been shown to effectively reduce surface NPS pollutant movement to streams and under the right geological riparian setting can also remove them from the groundwater. Flexibility in design can also be used to produce various market and nonmarket goods. Design flexibility should become more widely practiced in the application of this agroforestry practice.

Isotopic composition of precipitation in central Iowa

Abstract The isotopes of hydrogen and oxygen have been used extensively as indicators of groundwater age (3H) and paleotemperature of groundwater recharge (18O/16O, 2H/1H); however, comparisons of values in groundwater with those in recent precipitation are few. This study describes and interprets the isotopic composition of precipitation in central Iowa for the year 1992. An unusually mild winter driven by south-westerly flow of the jet stream was followed by an unusually cool and predominantly dry summer that was caused by a persistent northwesterly flow in the upper atmosphere. Temperature was below normal (9.0°C); precipitation was above normal (868.4 mm) and was mostly derived from a Gulf of Mexico moisture source. Fifty-one precipitation samples were collected from 37 events and analyzed for hydrogen and oxygen isotopes. Tritium activities ranged from 0 to 44 tritium units (TU) and the weighted mean 3H activity was 11.02 TU, a value consistent with International Atomic Energy Agency (IAEA) data. Anomalously high 3H activities suggested input of technogenic 3H. Weighted mean values of δ18O and δ2H were −8.02‰ and −53.62‰, respectively, and the equation of the local Meteoric Water Line was δ2H=9.26δ18O + 4.65. Weighted mean δ18O and δ2H values from the Gulf-Pacific moisture source (−10.80‰, −74.82‰) were more depleted than those ascribed solely to a Gulf of Mexico moisture source (−7.24‰, −47.39‰). Seasonal differences in temperature primarily controlled these differences in isotopic composition.

Groundwater flow, velocity, and age in a thick, fine-grained till unit in southeastern Wisconsin

Abstract Piezometer nests were installed at study sites in each of five north-south-trending end moraines of the late Pleistocene Oak Creek Formation in southeastern Wisconsin. The formation is composed primarily of a fine-grained glacial diamicton (till) and laterally continuous and discontinuous, coarse-grained lake and meltwater stream sediment. It overlies the Silurian dolomite aquifer, which is a source of drinking water to rural areas. The average vertical linear velocity and age of ground water in the Oak Creek Formation were estimated by three methods: Darcys Law, environmental isotopes including 3 H, δ 2 H, δ 18 O, and 14 C (dissolved inorganic carbon), and solute transport modeling of 18 O. The F-1 and Metro sites in the Tinley moraine showed excellent agreement among the three estimates of vertical velocity and showed the lowest velocity values (0.3–0.5 cm year −1 downward), which suggests that diffusion controls vertical mass transport at these sites. Although the extrapolated maximum age of ground water is 35 000 years, ground water below 75 m at these sites is probably not older than 15 000 years, which is the maximum age of the formation. Estimates of velocity showed less agreement at study sites in the Lake Border moraine system to the east and ranged from about 0.2 to 20.7 cm year −1 ; maximum groundwater age could range from 213 to 6000 years. Higher and more variable velocities, perhaps owing to thinner and more heterogeneous sediment in these areas, suggest that diffusion may not dominate vertical mass transport. Heterogeneity and fractures may also promote the development of groundwater flow systems dominated by lateral flow. Because of the uncertainty about the nature of groundwater flow, velocity, and age in the formation east of the Tinley moraine, future waste-disposal activity in southeastern Wisconsin should be confined to the thickest parts of the Tinley moraine near the present F-1 and Metro sites.

Experimental Determination of Effective Diffusion Parameters in the Matrix of Fractured Till

Diffusion is often the dominant mode of solute transport in soils when advection is minimal. This paper describes the application of a radial diffusion cell method to estimate the effective diffusion coefficient ( D e ) and effective diffusive porosity (θDe ) for use in solute transport models for fractured-porous media. Twenty-four experiments were conducted for 28 d using three conservative solutes (Br, PFBA, and PIPES) on eight late Wisconsinan and Pre-Illinoian till samples from Iowa. The mean value of the total porosity (θT) of the till samples was 30.0%. Concentrations of the three tracers in the reservoir decreased with time and eventually approached equilibrium concentrations. A model simulated the observed concentration data and the modified goodness-of-fit ( d 1) values ranged from 0.878 to 0.950. Mean values of θDe from the model were 28.3 (Br−), 26.5 (PFBA), and 21.6% (PIPES) and there were significant differences in θDe among the three tracers ( p = 0.05). Mean values of D e were 5.6 × 10−10 m2 s−1 (Br−), 2.9 × 10−10 m2 s−1 (PFBA), and 1.3 × 10−10 m2 s−1 (PIPES). Values of D e differed significantly by compound and were significantly different ( p = 0.05) from the aqueous diffusion coefficient ( D ). Calculated mean values of the first-order mass exchange coefficient (α) were 8.4 × 10−7 (Br−), 4.1 × 10−7 (PFBA), and 1.6 × 10−7 s−1 (PIPES); they differed by compound ( p = 0.05) and generally decreased with increasing molecular weight of the tracer. This study confirmed that the radial diffusion cell method is an efficient method to estimate effective diffusion parameters necessary to accurately model solute transport in fractured till and soil.

Isotopic evidence for paleohydrologic evolution of ground-water flow paths, southern Great Plains, United States

A confined aquifer in Triassic Dockum Group sandstone beneath the southern Great Plains was isolated from hypothesized paleorecharge areas in eastern New Mexico by Pleistocene erosion of the Pecos and Canadian river valleys and formation of hydrologic divides. Truncation of the flow system left meteoric water in the confined aquifer with mean {delta}D and {delta}{sup 18}O values that are 17{per thousand} and 2.0{per thousand}, respectively, lighter than those in the overlying High Plains aquifer. Thick upper Dockum mudstone retards downward flow from the High Plains aquifer, which has been recharged by isotopically heavy precipitation during the Holocene. Recharge to the confined aquifer occurred at altitudes of 1600 to 2200 m in proximal Dockum sandstone facies since eroded in eastern New Mexico, at a mean temperature 3 C cooler than present temperature across the southern High Plains. Effect of Pleistocene climatic change on isotopic composition of Dockum ground water could be superposed over geomorphologic effects.

Town Meets Gown: Creating a Collaborative Process for Expanding a University's Recycling Program While Supporting a City's Waste Diversion Efforts

Recycling presents a unique challenge for Iowa State University. It diverts 83 percent of its campus waste with the help of a Resource Recovery Plant that produces Refuse-Derived Fuel for a municipal, coal-fired power plant, effectively obviat ing a need for campus-wide recycling. This study was conducted because the university community has consistently shown strong interest in expanding recycling. Results showed that: 1.) the university recycles fewer commodities compared to peer institutions; 2.) beverage containers showed the greatest opportunity to expand current campus recycling efforts; 3.) closer proximity of recycling bins to newspaper stands, vending machines, and cafes, along with recycling education, could increase recycling; and 4.) students are willing to pay additional funds to expand recycling. Changes implemented based on study recommendations included a pilot recycling program for redeemable beverage containers at the Memorial Union in 2010 and a volunteer-driven program for glass, metal, plastic, and mixed paper in six campus buildings in 2012. The Live Green! website was upgraded and linked to social media; recycling bins were located on the campus map; recycling educational and signage efforts increased; use of refillable coffee mugs expanded; a dialog on recycling and diversion began with the city; and the Government of the Student Body formed a sustainability committee. The university community learned about their im pact on the university environment and realized the importance of implementing a program of Reduce, Reuse, and Recycle. The expansion of the university’s recycling program supports the city’s in-place waste diversion efforts.