Spatial and Temporal Evaluation of Hydrological Response to Climate and Land Use Change in Three South Dakota Watersheds

This study analyzed changes in hydrology between two recent decades (1980s and 2010s) with the Soil and Water Assessment Tool (SWAT) in three representative watersheds in South Dakota: Bad River, Skunk Creek, and Upper Big Sioux River watersheds. Two SWAT models were created over two discrete time periods (1981‐1990 and 2005‐2014) for each watershed. National Land Cover Datasets 1992 and 2011 were, respectively, ingested into 1981‐1990 and 2005‐2014 models, along with corresponding weather data, to enable comparison of annual and seasonal runoff, soil water content, evapotranspiration (ET), water yield, and percolation between these two decades. Simulation results based on the calibrated models showed that surface runoff, soil water content, water yield, and percolation increased in all three watersheds. Elevated ET was also apparent, except in Skunk Creek watershed. Differences in annual water balance components appeared to follow changes in land use more closely than variation in precipitation amounts, although seasonal variation in precipitation was reflected in seasonal surface runoff. Subbasin‐scale spatial analyses revealed noticeable increases in water balance components mostly in downstream parts of Bad River and Skunk Creek watersheds, and the western part of Upper Big Sioux River watershed. Results presented in this study provide some insight into recent changes in hydrological processes in South Dakota watersheds. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Water Use for Hydraulic Fracturing of Oil and Gas in the South Platte River Basin,Colorado

Water use for oil and gas development (i.e., hydraulic fracturing) is a concern in semiarid basins where water supply is often stressed to meet demands, and oil and gas production can exacerbate the situation. Understanding the impacts of water use for hydraulic fracturing (HF) on water availability in semiarid regions is critical for management and regulatory decisions. In the current work, we quantify water use for HF at several scales — from municipal to state‐wide — using the IHS Enerdeq database for the South Platte Basin. In addition, we estimate produced water (a by‐product of oil and gas production), using data from the Colorado Oil and Gas Conservation Commission to explore reuse scenarios. The South Platte River Basin, located in northeastern Colorado, encompasses the Denver‐Metro area. The basin has one of the most productive oil and gas shale formations in Colorado, with much of the production occurring in Weld County. The basin has experienced higher horizontal drilling rates coupled with an increasing population. Results show water use for horizontal and vertical wells averages 11,000 and 1,000 m³, respectively. Water use for HF in the South Platte Basin totaled 0.63% of the basin's 2014 total water demand. For Weld County, water use for HF was 2.4% of total demand, and for the city of Greeley, water use was 7% of total demand. Produced water totaled 9.4 Mm³ in the basin for 2014, which represents 42% of the total water used for HF.     

RED RIVER OF THE NORTH BASIN,MINNESOTA, NORTH DAKOTA,AND SOUTH DAKOTA1

ABSTRACT: The environmental setting of the Red River of the North basin within the United States is diverse in ways that could significantly control the areal distribution and flow of water and, therefore, the distribution and concentration of constituents that affect water quality. Continental glaciers shaped a landscape of very flat lake plains near the center of the basin, and gently rolling uplands, lakes, and wetlands along the basin margins. The fertile, black, fine-grained soils and landscape are conducive to agriculture. Productive cropland covers 66 percent of the land area. The principal crops are wheat, barley, soybeans, sunflowers, corn, and hay. Pasture, forests, open water, and wetlands comprise most of the remaining land area. About one-third of the 1990 population (511,000) lives in the cities of Fargo and Grand Forks, North Dakota and Moorhead, Minnesota. The climate of the Red River of the North basin is continental and ranges from dry subhumid in the western part of the basin to subhumid in the eastern part. From its origin, the Red River of the North meanders northward for 394 miles to the Canadian border, a path that is nearly double the straight-line distance. The Red River of the North normally receives over 75 percent of its annual flow from the eastern tributaries as a result of regional patterns of precipitation, evapotranspiration, soils, and topography. Most runoff occurs in spring and early summer as a result of rains falling on melting snow or heavy rains falling on saturated soils. Lakes, prairie potholes, and wetlands are abundant in most physiographic areas outside of the Red River Valley Lake Plain. Dams, drainage ditches, and wetlands alter the residence time of water, thereby affecting the amount of sediment, biota, and dissolved constituents carried by the water. Ground water available to wells, streams, and springs primarily comes from sand and gravel aquifers near land surface or buried within 100 to 300 feet of glacial drift that mantles the entire Red River of the North basin. Water moves through the system of bedrock and glacial-drift aquifers in a regional flow system generally toward the Red River of the North and in complex local flow systems controlled by local topography. Many of the bedrock and glacial-drift aquifers are hydraulically connected to streams in the region. The total water use in 1990, about 196 million gallons per day, was mostly for public supply and irrigation. Slightly more than one half of the water used comes from ground-water sources compared to surface-water sources. Most municipalities obtain their water from ground-water sources. However, the largest cities (Fargo, Grand Forks and Moorhead) obtain most of their water from the Red River of the North. The types and relative amounts of various habitats change among the five primary ecological regions within the Red River of the North basin. Headwater tributaries are more diverse and tend to be similar to middle-reach tributaries in character rather than the lower reaches of these tributaries for the Red River of the North. Concentrations of dissolved chemical constituents in surface waters are normally low during spring runoff and after thunderstorms. The Red River of the North generally has a dissolved-solids concentration less than 600 milligrams per liter with mean values ranging from 347 milligrams per liter near the headwaters to 406 milligrams per liter at the Canadian border near Emerson, Manitoba. Calcium and magnesium are the principal cations and bicarbonate is the principal anion along most of the reach of the Red River of the North. Dissolved-solids concentrations generally are lower in the eastern tributaries than in the tributaries draining the western part of the basin. At times of low flow, when water in streams is largely from ground-water seepage, the water quality more reflects the chemistry of the glacial-drift aquifer system. Ground water in the surficial aquifers commonly is a calcium bicarbonate type with dissolved-solids concentration generally between 300 and 700 milligrams per liter. As the ground water moves down gradient, dissolved-solids concentration increases, and magnesium and sulfate are predominant ions. Water in sedimentary bedrock aquifers is predominantly sodium and chloride and is characterized by dissolved-solids concentrations in excess of 1,000 milligrams per liter. Sediment erosion by wind and water can be increased by cultivation practices and by livestock that trample streambanks. Nitrate-nitrogen concentrations also can increase locally in surficial aquifers beneath cropland that is fertilized, particularly where irrigated. Nitrogen and phosphorous in surface runoff from cropland fertilizers and nitrogen from manure can contribute nutrients to lakes, reservoirs, and streams. Some of the more persistent pesticides, such as atrazine, have been detected in the Red River of the North. Few data are available to conclusively define the presence or absence of pesticides and their break-down products in Red River of the North basin aquifers or streams. Urban runoff and treated effluent from municipalities are discharged into streams. These point discharges contain some quantity of organic compounds from storm runoff, turf-applied pesticides, and trace metals. The largest releases of treated-municipal wastes are from the population centers along the Red River of the North and its larger tributaries. Sugar-beet refining, potato processing, poultry and meat packing, and milk, cheese, and cream processing are among the major food processes from which treated wastes are released to streams, mostly in or near the Red River of the North.     

Impacts of Multiple Stresses on Water Demand and Supply Across the Southeastern United States1

Abstract: Assessment of long‐term impacts of projected changes in climate, population, and land use and land cover on regional water resource is critical to the sustainable development of the southeastern United States. The objective of this study was to fully budget annual water availability for water supply (precipitation ? evapotranspiration + groundwater supply + return flow) and demand from commercial, domestic, industrial, irrigation, livestock, mining, and thermoelectric uses. The Water Supply Stress Index and Water Supply Stress Index Ratio were developed to evaluate water stress conditions over time and across the 666 eight‐digit Hydrologic Unit Code basins in the 13 southeastern states. Predictions from two Global Circulation Models (CGC1 and HadCM2Sul), one land use change model, and one human population model, were integrated to project future water supply stress in 2020. We found that population increase greatly stressed water supply in metropolitan areas located in the Piedmont region and Florida. Predicted land use and land cover changes will have little effect on water quantity and water supply‐water demand relationship. In contrast, climate changes had the most pronounced effects on regional water supply and demand, especially in western Texas where water stress was historically highest in the study region. The simulation system developed by this study is useful for water resource planners to address water shortage problems such as those experienced during 2007 in the study region. Future studies should focus on refining the water supply term to include flow exchanges between watersheds and constraints of water quality and environmental flows to water availability for human use.     

Modeling Water Quantity and Sulfate Concentrations in the Devils Lake Watershed Using Coupled SWAT and CE‐QUAL‐W2

Devils Lake is an endorheic lake in the Red River of the North basin in northeastern North Dakota. During the last two decades, the lake water level has risen by nearly 10 m, causing floods that have cost more than 1 billion USD in mitigation measures. Another increase of approximately 1.5 m in the lake water level would cause spillage into the Sheyenne River. To alleviate this potentially catastrophic spillage, two artificial outlets were constructed. However, the artificial drainage of water into the Sheyenne River raises water quality concerns because the Devils Lake water contains significantly higher concentrations of dissolved solids, particularly sulfate. In this study, the Soil and Water Assessment Tool (SWAT) was coupled with the CE‐QUAL‐W2 model to simulate both water balance and sulfate concentrations in the lake. The SWAT model performed well in simulating daily flow in tributaries with E_NS > 0.5 and |PBIAS| < 25%, and reproduced the lake water level with a root mean square error of 0.35 m for the study period from 1995 to 2014. The water temperature and sulfate concentrations simulated by CE‐QUAL‐W2 for the lake are in general agreement with the field observations. The model results show that the operation of the two outlets since August 2005 has lowered the lake level by 0.70 m. Furthermore, the models show pumping water from the two outlets raises sulfate concentrations in the Sheyenne River from ~100 to >500 mg/L. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.     

Impacts of Residential Development on Humid Subtropical Freshwater Resources: Southwest Florida Experience1

Abstract: The population of Collier and Lee Counties in southwestern Florida has increased 11‐fold from 1960 to 2004 with a concomitant increase in freshwater demand. Water levels and salinity within the water table aquifer over the past two to three decades have generally been stable, with more monitoring wells showing statistically significant temporal increases in water level than decreases. Residential development has had a neutral impact on the water table aquifer because the total annual evapotranspiration of residential communities is comparable to that of native vegetation and less than that of most agricultural land uses. Public water supply systems and private wells also result in net recharge to the water table aquifer with water produced from deeper aquifers. Confined freshwater aquifers have overall trends of decreasing water levels. However, with the exception of the mid‐Hawthorn aquifer, water levels in most areas recover to near background levels each summer wet season. Freshwater resources in humid subtropical areas, such as southwestern Florida, are relatively robust because of the great aquifer recharge potential from the excess of rainfall over ET during the wet season. Proper management can result in sustainable water resources.     

Spatial and Seasonal Response of Municipal Water Use to Weather across the Contiguous U.S.

Weather variability has the potential to influence municipal water use, particularly in dry regions such as the western United States (U.S.). Outdoor water use can account for more than half of annual household water use and may be particularly responsive to weather, but little is known about how the expected magnitude of these responses varies across the U.S. This nationwide study identified the response of municipal water use to monthly weather (i.e., temperature, precipitation, evapotranspiration [ET]) using monthly water deliveries for 229 cities in the contiguous U.S. Using city‐specific multiple regression and region‐specific models with city fixed effects, we investigated what portion of the variability in municipal water use was explained by weather across cities, and also estimated responses to weather across seasons and climate regions. Our findings indicated municipal water use was generally well‐explained by weather, with median adjusted R² ranging from 63% to 95% across climate regions. Weather was more predictive of water use in dry climates compared to wet, and temperature had more explanatory power than precipitation or ET. In response to a 1°C increase in monthly maximum temperature, municipal water use was shown to increase by 3.2% and 3.9% in dry cities in winter and summer, respectively, with smaller changes in wet cities. Quantifying these responses allows urban water managers to plan for weather‐driven variability in water use.     

Regional Blue and Green Water Balances and Use by Selected Crops in the U.S.

The availability of freshwater is a prerequisite for municipal development and agricultural production, especially in the arid and semiarid portions of the western United States (U.S.). Agriculture is the leading user of water in the U.S. Agricultural water use can be partitioned into green (derived from rainfall) and blue water (irrigation). Blue water can be further subdivided by source. In this research, we develop a hydrologic balance by 8‐Digit Hydrologic Unit Code using a combination of Soil and Water Assessment Tool simulations and available human water use estimates. These data are used to partition agricultural groundwater usage by sustainability and surface water usage by local source or importation. These predictions coupled with reported agricultural yield data are used to predict the virtual water contained in each ton of corn, wheat, sorghum, and soybeans produced and its source. We estimate that these four crops consume 480 km³ of green water annually and 23 km³ of blue water, 12 km³ of which is from groundwater withdrawal. Regional trends in blue water use from groundwater depletion highlight heavy usage in the High Plains, and small pockets throughout the western U.S. This information is presented to inform water resources debate by estimating the cost of agricultural production in terms of water regionally. This research illustrates the variable water content of the crops we consume and export, and the source of that water.     

Conditional Water Rights in the Western United States: Introducing Uncertainty to Prior Appropriation?

In the prior‐appropriation water rights regimes that prevail in the arid western United States, claims to annually variable surface water flows are fulfilled based on the order of their establishment. The two‐step process used to establish an appropriative water right in all 17 conterminous western states creates a temporary phase, or conditional water right, which has a priority date but no actual water use. We provide a review of the legal basis for these conditional water rights and demonstrate the potential uncertainty they introduce to current water users. We then present a complete census of conditional water rights in Colorado, including their amounts, ages, and uses. At the end of 2012 there were a large number of conditional water rights in Colorado (some over 90 years old) equal to 61% of the perfected water rights. Many of the controversial conditional water rights in Colorado have been associated with unconventional oil production in the northwestern portion of the state; however, conditional water rights are ubiquitous across the state and across many use types. In several basins, their existence can introduce uncertainty to some of the most senior water rights holders. Nevertheless, in most of the state, the effects of conditional water rights are restricted to a relatively junior class of water users. This work quantifies for the first time the result, in one state, of a peculiar aspect of water law common across all western prior‐appropriation states.     

Climate Trends but Little Net Water Supply Shift in One of Canada's Most Water‐Stressed Regions over the Last Century

The southern interior ecoprovince (SIE) of British Columbia, Canada represents the northernmost extent of the great western North American deserts, it is experiencing some of the nation's fastest economic and population growth making it one of Canada's most water‐stressed regions, and it includes two headwater basins of the transboundary (Canada‐US) Columbia River. Statistical trend analyses were performed on 90‐year regional indicator time series for annual conditions in observed temperature, precipitation, and streamflow reflecting the three major SIE river basins: the Thompson, and transboundary Okanagan and Similkameen. Results suggest that regional climate has grown warmer and wetter, but with little net impact on total water supply availability. The outcome might reflect mutual cancellation of increases in precipitation inputs vs. evapotranspiration losses. Conclusions appeared largely insensitive to low‐pass data filtering, Pacific Decadal Oscillation effects, or solar output variability. Ensemble historical global climate model runs over the same time interval support this absence of appreciable trend in regionally integrated annual runoff volume, but a possible mismatch in precipitation results suggests a direction for further study. Overall, while important changes in hydrologic timing and extremes are likely occurring here, there is limited evidence for a net change in overall water supply availability over the last century.     

Considering Climate Change in the Estimation of Long‐Term Flood Risks of Devils Lake in North Dakota

Terminal lakes are impacted by regional changes in climate. Devils Lake (DL), North Dakota, United States (U.S.), is a case in which a prolonged shift in the precipitation pattern resulted in a 10‐m water‐level rise over the past two decades, which cost over one billion U.S. dollars in mitigation. Currently, DL is 1.5 m from an uncontrolled overspill to the nearby Sheyenne River, which could lead to unprecedented environmental, social, and economic costs. Water outlets recently implemented in the lake to slow the water‐level rise and prevent an uncontrolled overspill are subject to significant concerns over the introduction of invasive species and downstream water quality. We developed a hydrological model of the DL basin using the soil and water assessment tool and analyzed DL's overspill probability using an ensemble of statistically downscaled General Circulation Model (GCM) projections of the future climate. The results indicate a significant likelihood (7.3‐20.0%) of overspill in the next few decades in the absence of outlets; some members of the GCM integration ensemble suggest an exceedance probability of over 85.0 and 95.0% for the 2020s and 2050s, respectively. Full‐capacity outlets radically reduce the probability of DL overspill and are able to partially mitigate the problem by decreasing the average lake level by approximately 1.9 and 1.5 m in the 2020s and 2050s, respectively.     

POTENTIAL CLIMATE CHANGE IMPACTS ON WATER RESOURCES IN THE GREAT PLAINS1

ABSTRACT: This paper reports on the current assessment of climate impacts on water resources, including aquatic ecosystems, agricultural demands, and water management, in the U.S. Great Plains. Climate change in the region may have profound effects on agricultural users, aquatic ecosystems, and urban and industrial users alike. In the central Great Plains Region, the potential impacts of climate changes include changes in winter snowfall and snow-melt, growing season rainfall amounts and intensities, minimum winter temperature, and summer time average temperature. Specifically, results from general circulation models indicate that both annual average temperatures and total annual precipitation will increase over the region. However, the seasonal patterns are not uniform. The combined effect of these changes in weather patterns and average seasonal climate will affect numerous sectors critical to the economic, social and ecological welfare of this region. Research is needed to better address the current competition among the water needs of agriculture, urban and industrial uses, and natural ecosystems, and then to look at potential changes. These diverse demands on water needs in this region compound the difficulty in managing water use and projecting the impact of climate changes among the various critical sectors in this region.     

Temporal and Spatial Variability of Water Supply Stress in the Haihe River Basin,Northern China1

Ji, Yuhe, Liding Chen, and Ranhao Sun, 2012. Temporal and Spatial Variability of Water Supply Stress in the Haihe River Basin, Northern China. Journal of the American Water Resources Association (JAWRA) 48(5): 999‐1007. DOI: 10.1111/j.1752‐1688.2012.00671.x Abstract: Water resources are becoming increasingly stressed under the influence of climate change and population growth in the Haihe River Basin, Northern China. Assessing the temporal and spatial variability of water supply stress is urgently needed to mitigate water crisis caused by water resource reallocation. Water supply and use data were compiled for the time period of 1998‐2003 in this synthesis study. The Water Supply Stress Index (WSSI) as defined as Water Demand/Water Supply was used to quantitate whether water supply could meet the demand of human activities across the study region. We found a large spatial gradient of water supply stress in the study region, being much higher in the eastern subbasins (ranging from 2.56 to 4.31) than the west subbasins (ranging from 0.56 to 1.92). The eastern plain region not only suffered more serious water supply stress but also had a much higher interannual variability than the western hilly region. The uneven spatial distribution of water supply stress might result from the distribution of land use, population, and climate. Future climate change and rapid economic development are likely to aggravate the existing water crisis in the study region.     

WATER USE RELATIONSHIPS AND PROJECTION CORRESPONDING WITH REGIONAL GROWTH,SEATTLE REGION1

ABSTRACT: The paper outlines both the methods used and the results obtained in a study of the demand for municipal and industrial water for the Seattle region. The study was made as part of a regional water management study program, one objective of which is to “… identify, quantify, and set priorities for all current and future water uses …”. A basic concept in the study of municipal and industrial water use is that the demand for water is derived from the demand for output and the direct services that water provides. Principal characteristics of the study are: (1) Water use is studied by type - residential, commercial, industrial and public -with identification of factors affecting each; (2) Water demands are studied by season as well as on an annual basis; (3) Projections of future water use are tied directly to projections of economic change in the service area; and (4) The effects of alternative policies on water use are estimated. Water use levels are projected under alternative regional growth assumptions provided by the Puget Sound Governmental Conference, a regional planning agency. Thus, the water use planning is consistent with other regional planning programs in this respect. The results can be varied according to changes in specific factors affecting water use. The factors considered in the present study include: single-family residential lot size, distribution of population between single- and multi-family units, per capita water use by multi-family unit residents, and industrial and commercial water use per employee. An income elasticity of demand was estimated for single-family residential water use.     

Spatial and Temporal Variations in Eastern U.S. Hydrology: Responses to Global Climate Variability

Coastal ecosystems are dependent on terrestrial freshwater export which is affected by both climate trends and natural climate variability. However, the relative role of these factors is not clear. Here, both climate trends and internal climate variabilities at different time scales are related to variations in terrestrial freshwater export into the eastern United States (U.S.) coastal region. For the recent 35‐year period, the intensified hydro‐meteorological processes (annual precipitation or evapotranspiration) may explain the observed streamflow variability in the northeast. However, in the southeast, streamflow is positively correlated with climate variability induced by the Pacific Ocean conditions (El Nino‐Southern Oscillation [ENSO] and Pacific Decadal Oscillation) rather than Atlantic Ocean conditions (Atlantic Multi‐decadal Oscillation and North Atlantic Oscillation). The centroid location for volume of terrestrial freshwater export integrated along the eastern U.S. has a positive temporal trend and is negatively correlated with ENSO conditions, suggesting the northward trend in freshwater export to U.S. eastern coast may be disturbed by the natural climate variability, especially ENSO conditions, i.e., the center of freshwater mass moves southward (northward) during El Nino (La Nina) years. The results indicate the spatial and temporal variations in freshwater export from the eastern U.S. are affected by both climate change and inter‐annual climate variability during the recent 35‐year period (1980‐2014).     

Assessment of Groundwater Depletion and Implications for Management in the Denver Basin Aquifer System

The Denver Basin Aquifer System (DBAS) is a critical groundwater resource along the Colorado Front Range. Groundwater depletion has been documented over the past few decades due to the increased water use among users, presenting long‐term sustainability challenges. A spatiotemporal geostatistical analysis is used to estimate potentiometric surfaces and evaluate groundwater storage changes between 1990 and 2016 in each of the four DBAS aquifers. Several key depletion patterns and spatial water‐level changes emerge in this work. Hydraulic head changes are the largest in the west‐central side of the DBAS and have decreased in some areas by up to 180 m since 1990, while areas to the northwest show increases in hydraulic head by over 30.5 m. The Denver and Arapahoe aquifers show the largest groundwater storage losses, with the highest rates occurring in the 2000s. The results highlight uncertainty in the volumetric predictions under various storage coefficient calculations and emphasize the importance of representative aquifer characterization. The observed groundwater storage depletions are due to a combination of factors, which include population growth increasing the demand for water, variable precipitation, and drought influencing recharge, and increased groundwater pumping. The methods applied in this study are transferable to other groundwater systems and provide a framework that can help assess groundwater depletion and inform management decisions at other locations.     

Conjunctive Water Use in Confined Basalt Aquifers: An Evaluation Using Geochemistry,a Numerical Model,and Historical Water Level

As withdrawals from deep compartmentalized aquifers increasingly exceed recharge throughout the western United States, conjunctive water use management alternatives have become an applied research priority. This study highlights both details and limitations of the role of irrigation canal seepage as groundwater recharge, revealing the regional limitations of canal seepage as a dependable source of recharge in overdrawn aquifers. A suite of geochemical indicators were used together with a numerical model to evaluate current and future management scenarios focused on recharge derived from seepage from a region‐wide irrigation canal system. Twenty‐five years of static groundwater level data were used to relate spatial trends determined using geochemistry and groundwater modeling with “on‐the‐ground” management practices, which vary based on acreage, crop, and irrigation scheduling. Increasing groundwater age determined using isotope analysis, and declines in potentiometric heads, each correlate with increasing distance from the canal reaches. Predictive modeling indicates that if pumping is gradually reduced, as has been suggested by management agencies, that recharge from canal seepage will be negligible by 2035 due to regional groundwater through‐flow and the pattern of potentiometric head recovery. Unfortunately, historic hydrographs suggest that under current groundwater development conditions most wells are not sustainable, irrespective of proximity to the canal.     

HERBICIDES AND DEGRADATES IN SHALLOW AQUIFERS OF ILLINOIS: SPATIAL AND TEMPORAL TRENDS1

ABSTRACT: During the fall of 2000, the occurrence was examined of 16 herbicides and 13 herbicide degradates in samples from 55 wells in shallow aquifers underlying grain producing regions of Illinois. Herbicide compounds with concentrations above 0.05 μg/L were detected in 56 percent of the samples. No concentrations exceeded regulatory drinking water standards. The six most frequently detected compounds were degradates. Water age was an important factor in determining vulnerability of ground water to transport of herbicide compounds. Unconsolidated aquifers, which were indicated to generally contain younger ground water than bedrock aquifers, had a higher occurrence of herbicides (73 percent of samples) than bedrock aquifers (22 percent). Temporal analysis to determine if changes in concentrations of selected herbicides and degradates could be observed over a near decadal period indicated a decrease in detection frequency (25 to 18 percent) between samplings in 1991 and 2000. Over this period, significant differences in concentrations were observed for atrazine (decrease) and total acetochlor (increase). The increase in acetochlor compound concentrations corresponds to an increase in acetochlor use during the study period, while the decrease in atrazine concentrations corresponds to relatively consistent use of atrazine. Changes in frequency of herbicide detection and concentration do not appear related to changes in land use near sampled wells.     

The South‐to‐North Water Transfer Project of China: Environmental Implications and Monitoring Strategy1

Abstract: In 2002, China launched the South‐to‐North Water Transfer Project after completing a 50‐year feasibility study. By 2050, the three‐route (i.e., East, Middle, and West) project will be capable of transferring 44.8 billion m³/year of water from the water rich Yangtze River to the arid north to alleviate water shortage and help secure a balanced social and economic development across the nation. However, diversion of such a large quantity of water could profoundly change the riverine environment of the upper Yellow River and the lower reach of the Han River, a tributary of the Yangtze River and the water supplying area of the project’s Middle Route, because of changes in the annual discharge. Secondary salinization seems inevitable in the water receiving areas of the North China Plain, and decrease in the discharge of the Yangtze River will result in seawater intrusion into the Yangtze Delta. This paper describes the project and discusses its environmental implications. Additionally, a long‐term monitoring strategy under the umbrella of the Chinese Ecological Research Network is proposed for environmental monitoring.