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G. M. Clark

Publications and source records attributed to G. M. Clark.

At least 19 recordsLinked to original sources
USGS2011

Old ice in rock glaciers may provide long-term climate records

Anyone who spends much time above the treeline has probably seen rock glaciers and paused to wonder about them. Their curious and occasionally spectacular forms (Figure 1) occur in alpine and polar regions throughout the world, yet much remains uncertain about how they develop. A core of ice recently recovered from a rock glacier in the Absaroka Mountains of northwestern Wyoming vividly illustrates several important aspects about rock glaciers. At least some rock glaciers are a form of debris-covered glacier, and original isotopic stratigraphy may be preserved within their ice. Perhaps most interesting of all, the core of some rock glaciers is composed of layered ice that can be drilled and recovered, and some of this ice is exceptionally old.

Eos, Transactions, American Geophysical Union↗
USGS2007

Springflow effects on chemical loads in the Snake River, south-central Idaho

The 150-kilometer middle reach of the Snake River (middle Snake) in south-central Idaho receives large quantities of water from springs discharging along the north side of the river from the regional Snake River Plain aquifer. Water-quality samples collected from nine north- side springs in April 1994 indicated that springs in the upstream part or the reach had larger concentrations of dissolved solids, dissolved nitrate, total nitrogen, tritium, and heavy isotopes of hydrogen and oxygen than to springs in the downstream part of the reach. Because the spring chemistry varies in the reach, discharge from the springs resulted in a degradation in water quality in some parts or the middle Snake and improvements in water quality in other parts. Depending on the annual discharge in the Snake River, the contribution from the north-side springs represented 32 to 66 percent of the discharge, 32 to 57 percent of the dissolved solids, 26 to 50 percent of the total nitrogen, and 7 to 14 percent of the total phosphorus transported annually from the middle Snake. Synoptic sampling showed that the north- side springs contributed 84 percent of the discharge and 35, 40, and 10 percent of the dissolved solids, total nitrogen, and total phosphorus lead, respectively, to the Snake River during the peak of the irrigation season in 1994.

Water Resources Bulletin↗
USGS2007

Nutrient concentrations and yields in undeveloped stream basins of the United States

Data from 85 sites across the United States were used to estimate concentrations and yields of selected nutrients in streams draining relatively undeveloped basins. Flow-weighted concentrations during 1990-1995 were generally low with median basin concentrations of 0.020, 0.087, 0.26, 0.010, and 0.022 milligrams per liter (mg/L) for ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus, respectively. The flow-weighted concentration of nitrate exceeded 0.6 mg/L in only three basins. Total nitrogen exceeded 1 mg/L in only four basins, and total phosphorus exceeded 0.1 mg/L in only four basins. The median annual basin yield of ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus was 8.1, 26, 86, 2.8, and 8.5 kilograms per square kilometer, respectively. Concentrations and yields of nitrate tended to be highest in northeastern and mid-Atlantic coastal states and correlated well with areas of high atmospheric nitrogen deposition. Concentrations and yields of total nitrogen were highest in the southeastern part of the nation and in parts of the upper Midwest. In the northeast, nitrate was generally the predominant form of nitrogen, and in the southeast and parts of the upper Midwest, organic nitrogen was the dominant form. Concentrations of total phosphorus were generally highest in the Rocky Mountain and Central Plain states.Data from 85 sites across the United States were used to estimate concentrations and yields of selected nutrients in streams draining relatively undeveloped basins. Flow-weighted concentrations during 1990-1995 were generally low with median basin concentrations of 0.020, 0.087, 0.26, 0.010, and 0.022 milligrams per liter (mg/L) for ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus, respectively. The flow-weighted concentration of nitrate exceeded 0.6 mg/L in only three basins, Total nitrogen exceeded 1 mg/L in only four basins, and total phosphorus exceeded 0.1 mg/L in only four basins. The median annual basin yield of ammonia as N, nitrate as N, total nitrogen, orthophosphate as P, and total phosphorus was 8.1, 26, 86, 2.8, and 8.5 kilograms per square kilometer, respectively. Concentrations and yields of nitrate tended to be highest in northeastern and mid-Atlantic coastal states and correlated well with areas of high atmospheric nitrogen deposition. Concentrations and yields of total nitrogen were highest in the southeastern part of the nation and in parts of the upper Midwest. In the northeast, nitrate was generally the predominant form of nitrogen, and in the southeast and parts of the upper Midwest, organic nitrogen was the dominant form. Concentrations of total phosphorus were generally highest in the Rocky Mountain and Central Plain states.Data collected across the US from 85 streams draining relatively undeveloped basins were used to identify broad regional and national patterns in nutrient concentrations and yields. The basins of interest were selected from three USGS programs: the Hydrologic Benchmark Network, the National Water-Quality Assessment, and the Research Program. Water samples from most basins were collected on a weekly to bimonthly schedule. While the flow-weighted concentrations of nutrients varied, concentrations were low in most basins. Median flow-weighted concentrations of ammonia, nitrate, total nitrogen, orthophosphate, and total phosphorus were 0.020, 0.087, 0.26, 0.010, and 0.022 mg/l, respectively. Nitrate concentrations tended to be highest in the northeastern US, while southeastern and north-central basins had some of the highest NH3 concentrations. Flow-weighted concentrations of total P were generally highest in the Rocky Mountain and Central Plain states and in parts of the southeast.

Journal of the American Water Resources Associatio↗
USGS2001

Simulation of stream discharge and transport of nitrate and selected herbicides in the Mississippi River Basin

Stream discharge and the transport of nitrate, atrazine, and metolachlor in the Mississippi River Basin were simulated using the DAFLOW/BLTM hydrologic model. The simulated domain for stream discharge included river reaches downstream from the following stations in the National Stream Quality Accounting Network: Mississippi River at Clinton, IA; Missouri River at Hermann, MO: Ohio River at Grand Chain, IL: And Arkansas River at Little Rock, AR. Coefficients of hydraulic geometry were calibrated using data from water year 1996; the model was validated by favourable simulation of observed discharges in water years 1992-1994. The transport of nitrate, atrazine, and metolachlor was simulated downstream from the Mississippi River at Thebes, IL, and the Ohio River at Grand Chain. Simulated concentrations compared favourably with observed concentrations at Baton Rouge, LA. Development of this model is a preliminary step in gaining a more quantitative understanding of the sources and fate of nutrients and pesticides delivered from the Mississippi River Basin to the Gulf of Mexico.

Hydrological Processes↗
USGS1999

Seasonal and annual load of herbicides from the Mississippi River Basin to the Gulf of Mexico

Water samples collected from rivers in the Mississippi River Basin were analyzed for selected herbicides to evaluate their discharge to the Gulf of Mexico and to identify their predominant source areas within the basin. Samples were collected from the Mississippi River at Baton Rouge, LA from 1991 to 1997 and from sites on the upper Mississippi, the Missouri, and the Ohio Rivers from 1996 to 1997. Atrazine, metolachlor, and alachlor ESA (an alachlor metabolite) were the most frequently detected herbicides in the Mississippi River at Baton Rouge, and, in general, were present in the largest concentrations. The peak annual herbicide load was in 1993 when about 640 metric tons of atrazine, 320 metric tons of cyanazine, 215 metric tons of metolachlor, 53 metric tons of simazine, and 50 metric tons of alachlor were discharged to the Gulf of Mexico. The annual load of atrazine and cyanazine was generally 1−3% of the amount annually applied in the Mississippi River drainage basin; the annual load of acetochlor, alachlor, and metolachlor was generally less than 1%. During 1996−1997 the Ohio River contributed about 50% of the discharge and 50% or more of the herbicide load to the Gulf of Mexico.

Environmental Science & Technology↗
USGS1999

Occurrence and transport of acetochlor in streams of the Mississippi River Basin

The herbicide acetochlor [2-chloro- N -(ethoxymethyl)- N -(2-ethyl-6-methylphenyl) acetamide] was first used on corn ( Zea mays L.) in the USA during the growing season of 1994. By 1996, it was the third most heavily used corn herbicide in the midwestern USA. During the growing season of 1997, 78% of 375 samples collected at 32 stream sites in the Mississippi River Basin contained detectable concentrations of acetochlor. However, concentrations in only 2% of the samples exceeded 2/µg/L, the maximum annual average concentration allowable in public water supplies derived primarily from surface water. The largest acetochlor concentrations were detected in streams draining basins in parts of Illinois, Indiana, and Iowa. The median concentration of acetochlor in streams was about 10% that of atrazine (6-chloro- N -ethyl- N -isopropyl-1,3,5-triazine-2,4-diamine), about 25% that of metolachlor [2-chloro- N -(2-ethyl-6-methylphenyl)- N -(2-methoxy-1-methylethyl) acetamide], about 50% that of cyanazine [2-[[4-chloro-6-(ethylamino)-l,3,5-triazin-2-yl]amino]-2-methylpropionitrile], and about threefold that of alachlor [2-chloro-2′,6′-diethyl- N -(methoxymethyl) acetanilide]. Load estimates indicate that, during the growing season of 1997, agricultural subbasins draining areas of Illinois, Indiana, and Iowa contributed about 37 000 kg, or 74%, of the 50 000 kg of acetochlor measured in streams of the Mississippi River Basin.

Journal of Environmental Quality↗
USGS1994

Hydrology and geochemistry of a surface coal mine in northwestern Colorado

The hydrology and geochemistry of a reclaimed coal mine in northwestern Colorado were monitored during water years 1988 and 1989. Some data also were collected in water years 1987 and 1990. This report describes (1) the sources of hydrologic recharge to and discharge from reclaimed spoil, (2) the relative contributions of recharge to the reclaimed spoil aquifer from identified source waters and the rate of water movement from those sources to the reclaimed spoil, and (3) the geochemical reactions that control water quality in reclaimed spoil. The study area was at a dip-slope coal mine encompassing about 7 square miles with land slopes of varying aspect. The area was instrumented and monitored at five sites; two sites had unmined and reclaimed- spoil areas adjacent to each other and three sites were unmined. The mined areas had been reclaimed. Instrumentation at the study sites included 1 climate station, 3 rain gages, 19 soil-water access tubes, 2 lysimeters, 18 wells completed in bedrock, 7 wells completed in reclaimed spoil, and 2 surface- water gaging stations. The results of the study indicate that the reclaimed spoil is recharged from surface recharge and underburden aquifers. Discharge, as measured by lysimeters, was about 3 inches per year and occurred during and after snowmelt. Hydraulic-head measurements indicated a potential for ground-water movement from deeper to shallower aquifers. Water levels rose in the reclaimed-spoil aquifer and spring discharge at the toe of the spoil slopes increased rapidly in response to snowmelt. Water chemistry, stable isotopes, geochemical models, and mass-balance calculations indicate that surface recharge and the underburden aquifers each contribute about 50 percent of the water to the reclaimed-spoil aquifers. Geochemical information indicates that pyrite oxidation and dissolution of carbonate and efflorescent sulfate minerals control the water chemistry of the reclaimed-spoil aquifer.

Water-Resources Investigations Report↗