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Stephen J. Kalkhoff

Publications and source records attributed to Stephen J. Kalkhoff.

At least 37 records · Page 2Linked to original sources
USGS2007

Comparison of fate and transport of isoxaflutole to atrazine and metolachlor in 10 Iowa rivers

Isoxaflutole (IXF), a newer low application rate herbicide, was introduced for weed control in corn (Zea mays) to use as an alternative to widely applied herbicides such as atrazine. The transport of IXF in streamwater has not been well-studied. The fate and transport of IXF and two of its degradation products was studied in 10 Iowa rivers during 2004. IXF rapidly degrades to the herbicidally active diketonitrile (DKN), which degrades to a biologically inactive benzoic acid (BA) analogue. IXF was detected in only four, DKN in 56, and BA in 43 of 75 samples. The concentrations of DKN and BA were approximately 2 orders of magnitude less than those of the commonly detected triazine and acetamide herbicides and their degradation products. Concentrations of IXF, DKN, and BA were highest during the May through June postplanting period. The concentration ratio of BA/DKN was similar to the deethylatrazine/atrazine ratio with smaller ratios occurring during May and June. The relative temporal variation of DKN and BA was similar to that observed for atrazine and deethylatrazine. This study shows that low application rate herbicides can have similar temporal transport patterns in streamwater as compared to more widely applied herbicides but at lower concentrations.

Iowa↗
USGS2007

Using a Geographic Information System to determine the relation between stream quality and geology in the Roberts Creek watershed, Clayton County, Iowa

A geographic information system (GIS) was used to determine the relation between the stream-water quality and underlying geology in Roberts Creek watershed, Clayton County, Iowa, for base-flow conditions during the spring and summer of 1988–90. Geologic, stream, basin and subbasin boundaries, and water-quality sampling-site coverages were created by digitizing available maps. A contour coverage was created from digital line-graph data. The areal extent of geologic units subcropping in each subbasin was quantified with GIS, and the results then were output and joined with the discharge and water-quality data for statistical analyses. Illustrations showing the geology of the study area and the results of the study were prepared using GIS. By using GIS and a statistical software package, a weak but statistically significant relation was found between the water temperature, pH, and nitrogen concentrations in Roberts Creek and the underlying geology during base-flow conditions.

Iowa↗
USGS2007

Relation between stream-water quality and geohydrology during base-flow conditions, Roberts creek watershed, Clayton County, Iowa

An investigation to determine the relation between stream water quality and geohydrology in the Roberts Creek watershed, Clayton County, Iowa, was conducted during selected base-flow periods in 1988-90. Discharge measurements were made and water samples collected for analyses of nutrients and selected herbicides in 19 subbasins along the main stem and tributaries of Roberts Creek. The areal extent of unconsolidated and bedrock units subcropping in each subbasin was quantified. The hydrologic data were correlated statistically with the geologic data to determine relations. Roberts Creek generally gained water and had larger nitrogen concentrations in subbasins in which loess and alluvial material were underlain primarily by low-permeability till and shale units. Roberts Creek generally lost water and had lower nitrate concentrations in subbasins with subcropping karstic units. Nitrogen concentrations decreased in streams underlain by the karstic units because the nitrogen removed by biological processes was not replaced by ground-water inflow. Seepage from Roberts Creek to ground water in areas of subcropping karstic carbonate rocks reduced the flow, which reduced the velocity, causing increased residence time of water in the stream. The additional residence time may allow additional time for biological processes to remove nitrogen from solution. There was no significant relation between dissolved orthophosphate or atrazine and the underlying geology.

Iowa↗
USGS2006

Occurrence of isoxaflutole, acetamide, and triazine herbicides and their degradation products in 10 Iowa rivers draining to the Mississippi and Missouri Rivers, 2004

During 2004, a study to document the occurrence of herbicides and herbicide degradation products was conducted for 10 major Iowa rivers draining to the Missouri and Mississippi Rivers. Seventy-five water-quality samples were collected to measure isoxaflutole, acetamide, and triazine herbicides and their herbicide degradation products. An analytical method to measure isoxaflutole and its degradation products, diketonitrile and benzoic acid, was developed by the U.S. Geological Survey Organic Geochemistry Research Laboratory in Lawrence, Kansas, using vacuum manifold solid-phase extraction and liquid chromatography/mass spectrometry/mass spectrometry and is described in this report. Isoxaflutole, a low application rate preemergence herbicide for control of annual broadleaf weeds, is used extensively in Iowa. Findings from the study documented in this report indicate that isoxaflutole was designed to degrade quickly to diketonitrile, which appears to be more stable, and then to benzoic acid. Of the 75 samples collected to measure isoxaflutole, there were four detections of isoxaflutole, 53 detections of diketonitrile, and 41 detections of benzoic acid. Also, results of acetamide and triazine water-quality samples correlate with past studies, which indicate that herbicide degradation products are detected more frequently and often at higher concentrations in surface water than their parent compounds. In addition to analysis of isoxaflutole and its degradation products, samples were analyzed by the USGS National Water-Quality Laboratory schedule 2001 for about 52 pesticides and their degradation products.

Iowa↗
USGS2005

South Fork Iowa River watershed selected for a national water-quality study

The U.S. Geological Survey (USGS) is studying seven watersheds across the Nation to better understand how natural factors and agricultural management practices (AMPs) affect the transport of water and chemicals. Natural factors include climate and landscape (soil type, topography, geology), and AMPs include practices related to tillage, irrigation, and chemical application. The study approach is similar in each watershed so that we can compare and contrast the results and more accurately predict conditions in other agricultural settings. Study objectives Understand the links between the sources of water and agricultural chemicals (nutrients and pesticides) and their behavior and transport through the environment Predict the behavior and transport of water and agricultural chemicals in other agricultural areas not being studied Evaluate what the study results mean for management of water and water quality in a variety of agricultural settings We appreciate your help We are working with local growers and land owners to gain access to study sites. We also need information about the watershed and about current as well as historical agricultural management practices—past practices also affect concentrations of agricultural chemicals in ground and surface water. We will report the findings of the study in public meetings and in publications. These findings will provide information that will be useful for improving agricultural management locally and nationally, and will guide future studies in other watersheds. Why study the South Fork Iowa River watershed? The South Fork Iowa River and the other watersheds represent nationally important agricultural settings (chemical use, crops, and AMPs) and natural settings (climate, soils, topography, and geology). South Fork Iowa River, which is part of the Iowa River watershed, is representative of corn and soybean row cropping in the Midwest. Other features of the watershed that are relevant to this study: Use of agricultural chemicals: Commonly used chemicals include herbicides such as atrazine, acetochlor, metolachlor, and glyphosate; and fertilizers, both manure and chemical. Distinct natural setting: Low relief topography with common depressions that formerly formed ponds and wetlands and that are now drained by an extensive network of drainage tiles and ditches. Variety of agricultural management practices: AMPs include both tillage and no-tillage of fields used for corn and soybean production; production of large numbers of hogs in concentrated animal feeding facilities; small grassy riparian buffer zones commonly used to reduce overland runoff. Water-quality issues: Herbicides and nutrients have been frequently detected in Iowa surface and ground water, including in drinking-water wells (findings of USGS studies since the 1990s).

Iowa, Minnesota↗
USGS2003

Water-quality assessment of the eastern Iowa Basins: Selected pesticides and pesticide degradates in streams, 1996-98

Water samples were collected in streams of the Eastern Iowa Basins study unit from 1996 to 1998 as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. More than 350 samples were collected to document the occurrence, distribution, and transport of pesticides and pesticide degradates. The Eastern Iowa Basins study unit encompasses about 50,500 square kilometers (19,500 square miles) in eastern Iowa and southern Minnesota and is drained by four major rivers—the Wapsipinicon, Cedar, Iowa, and Skunk—which flow into the Mississippi River at the eastern border of Iowa. The most commonly detected pesticides— acetochlor, alachlor, atrazine, cyanazine, and metolachlor—were those most heavily used on crops during the study. Atrazine and metolachlor were detected in 100 percent, and acetochlor, alachlor and cyanazine were detected in more than 70 percent of all surface-water samples. Four pesticide degradates—metolachlor ethane sulfonic acid, alachlor ethane sulfonic acid, metolachlor oxanilic acid, and acetochlor ethane sulfonic acid were detected in more than 75 percent of the samples. Only one nonagricultural herbicide, prometon, was detected in more than 80 percent of the samples. Carbofuran, the most commonly detected insecticide, was found in 16 percent of all samples. Mixtures of pesticide compounds commonly occurred in the samples. Five or more parent pesticide compounds were detected in 50 percent of the samples. Four or more pesticide degradates were detected in 68 percent and seven or more pesticide degradates were detected in 17 percent of the samples. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor were generally present at low concentrations; median concentrations ranged from 0.01 to 0.22 microgram per liter. However, median concentrations for the pesticide degra-dates, 0.07 to 3.7 micrograms per liter, were larger than their parent compounds. Acetochlor, alachlor, atrazine, cyanazine, and metolachlor pesticide compounds were detected at an order of magnitude or higher in the late spring and summer than at other times of the year. Pesticide concentrations generally peak following application in May and June and decrease during the growing season. A small secondary peak of atrazine, acetochlor, alachlor, cyanazine, and metolachlor concentrations occurred in late winter at all sites. The seasonal patterns for the triazine (atrazine and cyanazine) degradates were similar to the parent compounds (increasing in the spring), but the triazine degra-dates often had higher median concentrations than their parent compounds in the fall and winter. The chloroacetanilide (acetochlor, alachlor, and metolachlor) degradates did not follow a strong seasonal pattern like their parent compounds. In general, the chloroacetanilide degradates had constant and higher median concentrations when compared to their parent compounds throughout the year. The median concentrations for the chloroacetanilide pesticide degradates were often an order of magnitude higher than their parent compounds. Concentrations of pesticides varied by land-form region. Atrazine and cyanazine and their degradates were present in significantly greater concentrations in streams of the Southern Iowa Drift Plain than streams of either the Des Moines Lobe or the Iowan Surface.

Iowa, Minnesota↗
USGS2001

Influence of natural factors on the quality of midwestern streams and rivers

Streams flowing through cropland in the Midwestern Corn Belt differ considerably in their chemical and ecological characteristics, even though agricultural land use is highly intensive throughout the entire region. These differences likely are attributable to differences in riparian vegetation, soil properties, and hydrology. This conclusion is based on results from a study of the upper Midwest region conducted during seasonally low-flow conditions in August 1997 by the U.S. Geological Survey (USGS) National Water Quality Assessment (NAWQA) Program. This report summarizes significant results from the study and presents some implications for the design and interpretation of water-quality monitoring and assessment studies based on these results.

Water-Resources Investigations Report↗
USGS2001

Water-quality assessment of the eastern Iowa basins– Nitrogen, phosphorus, suspended sediment, and organic carbon in surface water, 1996–98

Twelve sites on streams and rivers in the Eastern Iowa Basins study unit were sampled monthly and during selected storm events from March 1996 through September 1998 to assess the occurrence, distribution, and transport of nitrogen, phosphorus, suspended sediment, and organic carbon as part of the U.S. Geological Survey’s National Water-Quality Assessment Program. One site was dropped from monthly sampling after 1996. Dissolved nitrogen and phosphorus were detected in every water sample collected. Nitrate accounted for 92 percent of the total dissolved nitrogen. About 22 percent of the samples had nitrate concentrations that exceeded the U.S. Environmental Protection Agency’s maximum contaminant level of 10 milligrams per liter as nitrogen for drinking-water regulations. The median concentration of total dissolved nitrogen for surface water in the study unit was 7.2 milligrams per liter. The median total phosphorus concentration for the study unit was 0.22 milligram per liter. About 75 percent of the total phosphorus concentrations exceeded the U.S. Environmental Protection Agency recommended total phosphorus concentration of 0.10 milligram per liter or less to minimize algal growth. Median suspended sediment and dissolved organic-carbon concentrations for the study unit were 82 and 3.5 milligrams per liter, respectively. Median concentrations of nitrogen, phosphorus, and suspended sediment varied annually and seasonally. Nitrogen, phosphorus, and suspended-sediment concentrations increased each year of the study due to increased precipitation and runoff. Median concentrations of dissolved organic carbon were constant from 1996 to 1998. Nitrogen concentrations were typically higher in the spring after fertilizer application and runoff. During winter, nitrogen concentrations typically increased when there was little in-stream processing by biota. Nitrogen and phosphorus concentrations decreased in late summer when there was less runoff and in-stream processing of nitrogen and phosphorus was high. Dissolved organic carbon was highest in February and March when decaying vegetation and manure were transported during snowmelt. Suspendedsediment concentrations were highest in early summer (May–June) during runoff and lowest in January when there was ice cover with very little overland flow contributing to rivers and streams. Based on historical and study-unit data, eastern Iowa streams and rivers are impacted by both nonpoint and point-source pollution. Indicator sites that have homogeneous land use, and geology had samples with significantly higher concentrations of total dissolved nitrogen (median, 8.2 milligrams per liter) than did samples from integrator sites (median, 6.2 milligrams per liter) that were more heterogeneous in land use and geology. Samples from integrator sites typically had significantly higher total phosphorus and suspended-sediment concentrations than did samples from indicator sites. Typically, there was very little difference in median dissolved organic-carbon concentrations in samples from indicator and integrator sites. Concentrations of nitrogen and phosphorus varied across the study unit due to land use and physiography. Basins that are located in areas with a higher percentage of row-crop agriculture typically had samples with higher nitrogen concentrations. Basins that drain the Southern Iowa Drift Plain and the Des Moines Lobe typically had samples with higher total phosphorus and suspended-sediment concentrations. Total nitrogen loads increased each year from 1996 through 1998 in conjunction with increased concentrations and runoff. Total phosphorus loads in the Skunk River Basin decreased in 1997 due to less runoff and decreased sediment transport, but increased in 1998 due to higher runoff and increased sediment transport. Total nitrogen and total phosphorus loads varied seasonally. The highest loads typically occurred in early spring and summer after fertilizer application and runoff. Loads were lowest in January and September when there was typically very little runoff to transport nitrogen and phosphorus in the soil to the rivers and streams. Total nitrogen loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 97,600, 120,000, and 234,000 metric tons, respectively. Total phosphorus loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 6,860, 4,550, and 8,830 metric tons, respectively. Suspendedsediment loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 7,480,000, 4,450,000, and 8,690,000 metric tons, respectively. The highest total nitrogen and total phosphorus yields typically occurred in samples from indicator sites. Sampling sites located in drainage basins with higher row-crop percentage typically had higher nitrogen and phosphorus yields. Sites that were located in the Des Moines Lobe and the Southern Iowa Drift Plain typically had higher phosphorus yields, probably due to physiographic features (for example, erodible soils, steeper slopes). Synoptic samples collected during low and high base flow had nitrogen, phosphorus, and organic-carbon concentrations that varied spatially and seasonally. Comparisons of water-quality data from six basic-fixed sampling sites and 19 other synoptic sites suggest that the water-quality data from basic-fixed sampling sites were representative of the entire study unit during periods of low and high base flow when most streamflow originates from ground water.

Iowa, Minnesota↗
USGS2001

Water quality in the eastern Iowa basins

This article summarizes major findings about nutrients in surface and groundwater in the eastern Iowa basins (see map) between 1996 and 1998. The data were collected as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment Program (NAWQA). Water quality is discussed in terms of local and regional issues and compared with conditions found in all 36 National NAWQA study areas assessed to date. Findings are explained in the context of selected national U.S. Environmental Protection Agency (EPA) benchmarks, such as those for drinking water quality and the protection of aquatic organisms. The Eastern Iowa Basins Study Unit includes the Wapsipinicon, Cedar, Iowa, and Skunk River basins and covers approximately 19,500 square miles in eastern Iowa and southern Minnesota. More than 90 percent of the land in the study unit is used for agricultural purposes. Forested areas account for only 4 percent of the land area.

Iowa, Minnesota↗
USGS2001

It's not just how high; it's how clean: Sampling the spring 2001 flood in the Upper Mississippi River Basin

Floods can cause water-quality problems because of the large amounts of contaminants (sediment, nutrients, pesticides, and bacteria) that can be transported by floodwaters. during the flood on the Upper Mississippi River in 2001, water-quality and water-quality data were collected during near-record streamflow. This is the first time that samples for determining organic wastewater contaminants (pharmaceuticals, hormones, and industrial/household use compounds) and pesticide degradates have been collected during a flood of this magnitude.

Illinois, Iowa, Minnesota, Missouri, Wisconsin↗
USGS2001

Occurrence and distribution of pesticides in streams of the Eastern Iowa Basins, 1996-98

The U.S. Geological Survey began collection of water samples in streams of the Eastern Iowa Basins in 1996 for the analysis of pesticides and pesticide degradates as part of the National Water Quality Assessment Program (NAWQA). This study provides some of the first large scale monitoring data on pesticides and pesticide degradates in Eastern Iowa. Three hundred and forty-four samples were collected from 1996-98 to document the occurrence, distribution, and transport of pesticide compounds. Pesticide analysis included 80 pesticide compounds and 10 pesticide degradates. The Eastern Iowa Basins study encompasses about 50,500 square kilometers (19,500 square miles) and is drained by four major rivers--the Wapsipinicon, Cedar, Iowa, and Skunk. Agriculture accounts for approximately 93 percent of the land use in the study area. The most commonly detected pesticides were those most heavily used on crops. The triazine (atrazine and cyanazine) and chloroacetanilide (alachlor, acetochlor, and metolachlor) pesticides are some of the most heavily used (by weight) historically and during the period of data collection 1996-98. Atrazine and metolachlor were detected in all samples. Acetochlor, alachlor, and cyanazine were detected in more than 70 percent of all surface-water samples. Few non-agricultural herbicides were detected. One exception, prometon was detected in more than 80 percent of the samples at very low concentrations (less than 0.1 micrograms per liter). Pesticide degradates were some of the most frequently detected pesticide compounds in the study. Four pesticide degradates--metolachlor ethane sulfonic acid (metolachlor ESA), alachlor ethane sulfonic acid (alachlor ESA), metolachlor oxanilic acid (metolachlor OA), and acetochlor ethane sulfonic acid (acetochlor ESA) were detected in more than 75 percent of the samples. A few insecticides that may pose potential risk to aquatic invertebrates were detected in streams from May through September, the months when most application normally occurs. Carbofuran was the most commonly detected insecticide (16 percent of all samples). Although detected in less than 20 percent of all samples, carbofuran was detected in 68 percent of the samples in June. When present, carbofuran concentrations were generally less than 0.80 micrograms per liter. Chloropyrifos was detected in about seven percent of the samples. As with other insecticides, chlorpyrifos was detected most frequently in June (30 percent). The highest concentration was 0.06 micrograms per liter. Diazinon, a common urban insecticide found in other NAWQA studies throughout the Nation, was detected in only 2 percent of the samples in the Eastern Iowa Basins study. Pesticides were found to occur in mixtures with several compounds rather than individually. Four or more parent pesticide compounds were detected in 91 percent of the water samples and seven or more parent compounds were detected in 46 percent of the water samples. Four or more pesticide degradates were detected in 93 percent of the water samples and seven or more pesticide degradates were detected in 46 percent of the water samples. Commonly applied parent pesticide compounds (acetochlor, alachlor, atrazine, cyanazine, and metolachlor) were generally detected at low concentrations with median concentrations ranging from 0.01 to 0.22 micrograms per liter. The median concentrations for the pesticide degradates were larger than their parent compounds. Median concentrations for the pesticide degradates ranged from 0.07 to 3.7 micrograms per liter. Acetochlor, alachlor, atrazine, cyanazine and metolachlor pesticides compounds were present at least an order of magnitude or higher in the late spring and summer than at other times of the year. The maximum measured concentrations for acetochlor, atrazine, cyanazine and metolachor were approximately 11 to 48 micrograms per liter (the maximum for alachlor was 0.56 micrograms per liter). In contrast, maximum measured concentrations for the total pesticide degradates were lower than their parent compounds and ranged from approximately 0.7 to 12 micrograms per liter. The maximum measured concentration of a single pesticide compound was for atrazine at 48 micrograms per liter. Seasonal patterns of atrazine, acetochlor, alachlor, cyanazine, and metolachlor generally show peak concentrations following application in May and June and decreasing during remainder of the growing season. In addition, a small secondary peak in atrazine, acetochlor, alachlor, cyanazine, and metolachlor concentrations occurred at all sites in late winter. This secondary peak may be attributed to early "winter thaw" that can release pesticide residue from soil, making pesticides available to be transported to surface water by snowmelt and early spring rains. Pesticide degradates account for a significant portion of the total pesticide load at all sites. Eighty-one percent of the total pesticide load in samples from Iowa River near Rowan, Wolf Creek near Dysart, and the Iowa River at Wapello were as pesticide degradates. The pesticide degradates for the triazine compounds tended to follow the load pattern of the parent pesticide compounds closely throughout the year. In general, the degradate loads calculated for the triazine compounds were smaller than loads calculated for their parent pesticides. The loads for the chloroacetanilide degradate compounds were larger than those for the parent pesticides. The loads for alachlor were found to be small or nonexistent. Alachlor has been heavily used in the past, but since 1995 has been largely replaced by acetochlor or other herbicides. The loads for all degradates were higher than the parent compounds during the winter months. Overland flow may be diminished during the winter months, but shallow sub-soil drainage and ground-water flow may be a source of many pesticide degradates during the late fall and winter. Occurrence of pesticide compounds varied by landform region. The triazine herbicides, atrazine and cyanazine and their degradates were present in significantly greater concentrations in the Southern Iowa Drift Plain (predominantly loess soils) than either the Des Moines Lobe or the Iowan Surface (predominantly till soils). Less atrazine and cyanazine are applied to till soils because of pH and organic carbon content. Alachlor, metolachlor, and acetochlor have often been used to offset triazine pesticide reductions in area with till soils.

Iowa↗
USGS2000

Water quality in the eastern Iowa basins, Iowa and Minnesota, 1996-98

The water quality in rivers and streams and in selected aquifers in eastern Iowa and part of southern Minnesota is described and illustrated. Major ions, nitrogen and other nutrients, and pesticides and some of their breakdown compounds were analyzed in both surface and ground water. Biological communities that included fish, invertebrates, and algae, were described in relation to stream water quality. Volatile organic compounds that originate from fuels, solvent, and industry were analyzed from ground-water samples. Agricultural and urban land-use effects on shallow ground-water compared and contrasted.

Iowa, Minnesota↗
USGS2000

Summary of the major water-quality findings from the Eastern Iowa Basins study unit of the National Water-Quality Assessment Program

An integrated assessment of the water quality in streams and aquifers in the Wapsipinicon, Iowa, Cedar, and Skunk River basins was conducted in 1996 through 1998 as part of the Eastern Iowa Basins (EIWA) study unit of the U.S. Geological Survey's National Water-Quality Assessment Program (NAWQA). The EIWA study unit is one of 59 study units across the Nation designed to assess the status and trends in the quality of the Nation's ground- and surface-water resources and to link the status and trends with an understanding of the natural and human factors that affect the quality of water. Over 90 percent of the land in the EIWA study unit is used for agricultural purposes, while forested areas account for only 4 percent and urban areas about 2 percent of the land. Surface-water samples were collected monthly and during selected storm events from six sites in medium-sized basins (125 to about 400 mi2) and five sites in large river basins (2,300 to 12,500 mi2). The medium-sized basins were selected to be representative of various physical features, hydrogeology, and agricultural landuse (row crops and concentrated animal feeding operations) that may affect water quality. The large river sites were selected to determine the integrated effects of combinations of landuse and hydrogeology on river-water quality. Ground-water samples were collected primarily from the alluvial aquifers because of the aquifers' direct hydraulic connection with rivers and streams and because alluvial aquifers are one of the most important sources for domestic, municipal, and industrial water supplies in the study area. Monitoring wells were installed in agricultural and urban areas of the alluvial aquifers to assess the quality of the most recently recharged water in relation to land use. Existing domestic wells screened in alluvial aquifers and the Silurian/Devonian aquifer were sampled to assess deeper and older ground water. Surface- and ground-water samples were analyzed for a wide variety of chemical constituents (major ions, nutrients, and pesticides) commonly associated with agricultural and urban activities. Because they were not expected to occur in rivers and streams, volatile organic compounds (VOC's), commonly comprising fuels, solvents, and other industrial compounds were only analyzed in ground-water samples. The age of the ground water, important information needed to relate ground-water quality to land use, was determined using both tritium and chlorofluorocarbons (Freon?) age-dating methods. Results from the EIWA NAWQA study build on previous and ongoing research and water-quality monitoring programs in Iowa and provide new insights into the relation between the quality of the State's water resources and human activities. The major findings from the study are listed below.

Iowa↗
USGS1998

Degradation of chloroacetanilide herbicides: The prevalence of sulfonic and oxanilic acid metabolites in Iowa groundwaters and surface waters

Water samples were collected from 88 municipal wells throughout Iowa during the summer and were collected monthly at 12 stream sites in eastern Iowa from March to December 1996 to study the occurrence of the sulfonic and oxanilic metabolites of acetochlor, alachlor, and metolachlor. The sulfonic and oxanilic metabolites were present in almost 75% of the groundwater samples and were generally present from 3 to 45 times more frequently than their parent compounds. In groundwater, the median value of the summed concentrations of acetochlor, alachlor, and metolachlor was less than 0.05 μg/L, and the median value of the summed concentrations of the six metabolites was 1.2 μg/L. All surface water samples contained at least one detectable metabolite compound. Individual metabolites were detected from 2 to over 100 times more frequently than the parent compounds. In surface water, the median value of the summed concentrations of the three parent compounds was 0.13 μg/L, and the median value of the summed concentrations of the six metabolites was 6.4 μg/L. These data demonstrate the importance of analyzing both parent compounds and metabolites to more fully understand the environmental fate and transport of herbicides in the hydrologic system.

Iowa↗