Assessing age of groundwater to determine resource availability
Groundwater discharge that flows into the Upper Colorado River Basin varies in response to drought, which is likely due to aquifer systems that contain relatively young groundwater, according to a new U.S. Geological Survey study published in Hydrogeology Journal.
The Colorado River and its tributaries provide water to more than 40 million people in seven states, irrigate more than 5.5 million acres of land, and support hydropower facilities. More than half of the total streamflow in the UCRB originates from groundwater. Reductions in groundwater recharge associated with climate variability or increased water demand will likely reduce groundwater discharge to streams.
This is the first study that examines the short-term response of groundwater systems to climate stresses at a regional scale by assessing groundwater age. USGS scientists determined the age of groundwater by sampling the water flowing from nineteen springs in the UCRB. Age-tracing techniques can assess how long it takes groundwater to travel from the time it enters the aquifer system as precipitation to when the groundwater exits to springs and streams. Scientists compared eight of the springs with historical discharge and precipitation records with the groundwater age to better understand how aquifers have responded to drought. These findings helped scientists understand the variability and timing of groundwater discharge associated with drought.
“About half of the springs analyzed in the Upper Colorado River Basin contained young groundwater, which was surprising,” said USGS scientist and lead author of the study John Solder. “These findings suggest that shallow aquifers, which are more responsive to drought than deeper systems, may be significant contributors to streamflow in the region.”
Results show that if springs contain mostly older water, groundwater discharge is less variable over time and takes longer to respond to drought conditions. Springs that contain predominately young water, around 80 years old or less, are more likely to vary seasonally and respond rapidly to drought conditions. These results indicate that young groundwater resources are responsive to short-term climate variability.
“Sampling 19 springs in a very large basin is just the start, and further studies are needed to better understand the groundwater resources of this specific region,” said Solder. “Determining groundwater age has promise in predicting how these systems will respond in the future and allows us to assess resource vulnerability where no historical records are available.”
This study was funded by the USGS National Water Census, a research program focusing on national water availability and use at the regional and national scales. Research is designed to build decision support capacity for water management agencies and other natural resource managers.
Here’s the release from the USGS (Anne Berry Wade/Sarah Haymaker):
Researchers at the U.S. Geological Survey and the U.S. Department of Agriculture have published a new study that demonstrates that agricultural conservation practices in the upper Mississippi River watershed can reduce nitrogen inputs to area streams and rivers by as much as 34 percent.
The study combined USDA’s Conservation Effects Assessment Project (CEAP) data with the USGS SPARROW watershed model to measure the potential effects of voluntary conservation practices, which historically have been difficult to do in large river systems, because different nutrient sources can have overlapping influences on downstream water quality.
“These results provide new insights on the benefits of conservation practices in reducing nutrient inputs to local streams and rivers and ultimately to the Gulf of Mexico,” said Sarah Ryker, Interior’s acting assistant deputy for Water and Science. “The incorporation of agricultural conservation practice information into watershed models helps us better understand where water quality conditions are improving and prioritize where additional conservation actions are needed.”
Until this study, nutrient reductions have been difficult to detect in the streams because changes in multiple sources of nutrients (including non-agricultural sources) and natural processes (e.g., hydrological variability, channel erosion) can have confounding influences that conceal the effects of improved farming practices on downstream water quality. The models used in this study overcame these difficulties to help validate the downstream benefits of farmers’ conservation actions on the land.
“As the results of this valuable collaboration with the USGS indicate, voluntary conservation on agricultural lands is improving water quality. When multiple farmers, ranchers and working forest land managers in one region come together to apply the conservation science, the per acre conservation benefit is greatly enhanced,” said USDA Natural Resources and Environment Deputy Under Secretary Ann Mills. “While there are no short-term solutions to complex water quality issues, USDA is committed to continuing these accelerated voluntary conservation efforts, using collaborative science to target conservation in watersheds where the greatest benefits can be realized.”
Nutrient reductions attributable to agricultural conservation practices in the region ranged from five to 34 percent for nitrogen and from one to 10 percent for total phosphorus, according to the study published in the journal Environmental Science and Technology.
High levels of nutrients containing nitrogen and phosphorus from agricultural and urban areas contribute to hypoxic regions (low oxygen “dead zones”) in offshore marine waters.
The study underscored evidence that slowing the water and routing it into the ground can significantly reduce the nitrogen that is eventually transported to streams. Structural and erosion control practices, such as conservation tillage, in the Upper Mississippi River Basin have been shown to reduce runoff and peak flows, thereby increasing water infiltration into the soils and the subsurface geology. An added benefit of these conservation actions is that, in some areas, hydrological and biogeochemical conditions in the subsurface can promote the removal of nitrogen by natural biological processes.
Phosphorus reductions were lower than was seen for nitrogen, possibly because of long time lags between conservation actions and the time it may take for sediment-bound phosphorus to move downstream. In addition, some erosion control practices, such as no-till and reduced tillage, have been shown to increase soluble phosphorus levels in farm runoff, which can potentially offset some benefits from erosion control practices.
The innovative approach combined information from process-based models from USDA’s Agricultural Research Service and the Natural Resources Conservation Service (NRCS) with a USGS hybrid statistical and process-based model to quantify the environmental benefits of agricultural conservation practices at a regional scale.
The USGS watershed model was calibrated with data from over 700 water-quality monitoring stations operated by numerous local, state, and federal agencies throughout the Upper Mississippi River basin. The investigation used the most recently available farmer survey data from CEAP (2003-2006), together with stream water-quality data that are approximately coincident with the time period (1980s to 2004, with the average centered on 2002) over which farmer conservation practices, as measured in the survey, were adopted.
Additional information on the USGS SPARROW modeling approach and a nutrient mapper and an online decision support tool for the Mississippi River basin is available online.
Two projects to improve Fountain Creek will get underway soon after contracts were approved at Friday’s meeting of the Fountain Creek Watershed Flood Control and Greenway District.
A $67,000 contract with MWH Global was approved to evaluate flood control alternatives on Fountain Creek between Colorado Springs and Pueblo.
It’s the next phase of a project to determine the best type and placement of flood control structures on Fountain Creek, which could include a dam or several smaller detention ponds.
The planning started with a U.S. Geological Survey study in 2013 that identified the most effective concepts to protect Pueblo from severe floods and reduce harmful sedimentation. Last year, another study determined flood control projects could be built without harming water rights downstream.
The new study will use $41,800 in grants from the Colorado Water Conservation Board through the roundtable process. It is expected to be complete by Jan. 31, 2017.
A second project, totaling $60,000, was approved to continue a study of Fountain Creek stability and sediment loading by Matrix Design. The project was begun in 2010, and will identify the most critical areas for projects along Fountain Creek.
The district obtained matching funds for the projects through the payment of $125,000 from Colorado Springs Utilities to the district under terms of a recent intergovernmental agreement with Pueblo County that allowed Southern Delivery System to be put into service.
The district board also agreed on a formula to fund routine operation of the district among member governments in Pueblo and El Paso County. The district is looking at $200,000 in funding for next year’s budget. The funding is allocated by population, with Colorado Springs paying half; unincorporated El Paso County, 25 percent; small incorporated cities in El Paso County, 5 percent. The city of Pueblo would pay $26,000, or 13 percent; Pueblo County, $13,000, or 6.5 percent.
Those costs are still subject to approval by each governmental entity.
Here’s the release from the United States Geological Survey:
USGS scientists have documented that the carbon that moves through or accumulates in lakes, rivers, and streams has not been adequately incorporated into current models of carbon cycling used to track and project climate change. The research, conducted in partnership with the University of Washington, has been published this week in the Proceedings of the National Academy of Sciences.
The Earth’s carbon cycle is determined by physical, chemical, and biological processes that occur in and among the atmosphere (carbon dioxide and methane), the biosphere (living and dead things), and the geosphere (soil, rocks, and water). Understanding how these processes interact globally and projecting their future effects on climate requires complex computer models that track carbon at regional and continental scales, commonly known as Terrestrial Biosphere Models (TBMs).
Current estimates of the accumulation of carbon in natural environments indicate that forest and other terrestrial ecosystems have annual net gains in storing carbon — a beneficial effect for reducing greenhouse gases. However, even though all of life and most processes involving carbon movement or transformation require water, TBMs have not conventionally included aquatic ecosystems — lakes, reservoirs, streams, and rivers — in their calculations. Once inland waters are included in carbon cycle models, the nationwide importance of aquatic ecosystems in the carbon cycle is evident.
Speaking quantifiably, inland water ecosystems in the conterminous U.S. transport or store more than 220 billion pounds of carbon (100 Tg-C) annually to coastal regions, the atmosphere, and the sediments of lakes and reservoirs. Comparing the results of this study to the output of a suite of standard TBMs, the authors suggest that, within the current modelling framework, carbon storage by forests, other plants, and soils (in scientific terms: Net Ecosystem Production, when defined as terrestrial only) may be over-estimated by as much as 27 percent.
The study highlights the need for additional research to accurately determine the sources of aquatic carbon and to reconcile the exchange of carbon between terrestrial and aquatic environments.
Here’s the abstract:
Inland water ecosystems dynamically process, transport, and sequester carbon. However, the transport of carbon through aquatic environments has not been quantitatively integrated in the context of terrestrial ecosystems. Here, we present the first integrated assessment, to our knowledge, of freshwater carbon fluxes for the conterminous United States, where 106 (range: 71–149) teragrams of carbon per year (TgC⋅y−1) is exported downstream or emitted to the atmosphere and sedimentation stores 21 (range: 9–65) TgC⋅y−1 in lakes and reservoirs. We show that there is significant regional variation in aquatic carbon flux, but verify that emission across stream and river surfaces represents the dominant flux at 69 (range: 36–110) TgC⋅y−1 or 65% of the total aquatic carbon flux for the conterminous United States. Comparing our results with the output of a suite of terrestrial biosphere models (TBMs), we suggest that within the current modeling framework, calculations of net ecosystem production (NEP) defined as terrestrial only may be overestimated by as much as 27%. However, the internal production and mineralization of carbon in freshwaters remain to be quantified and would reduce the effect of including aquatic carbon fluxes within calculations of terrestrial NEP. Reconciliation of carbon mass–flux interactions between terrestrial and aquatic carbon sources and sinks will require significant additional research and modeling capacity.
Click here to read the fact sheet from the United States Geological Survey. Here’s the introduction:
The U.S. Geological Survey’s (USGS) concept of a national census (or accounting) of water resources has evolved over the last several decades as the Nation has experienced increasing concern over water availability for multiple competing uses. The implementation of a USGS National Water Census was described in the USGS 2007 science strategy document that identified the highest priority science topics for the decade 2007–17. In 2009, the SECURE Water Act (Public Law 111–11, subtitle F) authorized the USGS to create a Water Availability and Use Assessment Program for the Nation, and in 2012, the Department of the Interior WaterSMART initiative provided funding to begin implementation of the USGS National Water Census (NWC).
Generally, the USGS NWC approaches water-availability assessment in terms of a “water budget.” The water-budget approach seeks to better quantify the inflows and outflows of water, as well as the change in storage volume, both nationally and at a regional scale and, by doing so, provides critical information to managers and stakeholders responsible for making water-availability decisions. The NWC has two primary components: Topical Studies and Geographic Focus Area Studies. Topical Studies do research on methods that can provide nationwide estimates of particular water-budget components at the subwatershed scale. Some examples of NWC Topical Studies include estimation of streamflow at ungaged locations; periodic quantification of evapotranspiration; and water use related to development of unconventional oil and gas. These efforts are planned to include additional topics in the future. Geographic Focus Area Studies (FASs) assess water availability and use within a defined geographic area, typically a surface-water drainage basin, to increase the understanding of factors affecting water availability in the region. In the FASs, local stakeholder input helps the USGS identify what components of the water budget are in most need of additional understanding or quantification. Focus Area Studies are planned as 3-year efforts and, typically, three FASs are ongoing in different parts of the country at any given time.
The Colorado River Basin (CRB) and the Delaware and Apalachicola-Chattahoochee-Flint (ACF) River Basins were selected by the Department of the Interior for the first round of FASs because of the perceived water shortages in the basins and potential conflicts over water supply and allocations. After gathering input from numerous stakeholders in the CRB, the USGS determined that surface-water resources in the basin were already being closely monitored and that the most important scientific contribution could be made by helping to improve estimates of four water-budget components: evapotranspiration losses, snowpack hydrodynamics, water-use information, and the relative importance of groundwater discharge in supporting streamflow across the basin. The purpose of this fact sheet is to provide a brief summary of the CRB FAS results as the study nears completion. Although some project results are still in the later stages of review and publication, this fact sheet provides an overall description of the work completed and cites the publications in which additional information can be found.
From the United States Geological Survey (Curt Meine):
No time seems more fitting than now – with the epic drought in California and major flooding from a nor’easter and Hurricane Joaquin – to pay tribute to Luna B. Leopold, the first chief hydrologist at the USGS. More so than any other scientist, he set the course for the USGS approach to understanding river flows, groundwater and surface water interactions and the value of long-term data collection. Today, the USGS is the world’s largest provider of hydrologic information with a mission to collect and disseminate reliable, impartial, and timely information that is needed to understand the Nation’s water resources.
Born on Oct. 8, 1915 in Albuquerque, Luna Leopold lived a rich life. From his renowned father, the biologist and author Aldo Leopold, he inherited a passion for outdoor life, a respect of craftsmanship, a highly disciplined curiosity, and an appreciation of the complex interactions of human society and natural systems. From his mother Estella, he inherited a deep connection to the semi-arid landscapes and watersheds of the American Southwest, a rich Hispanic cultural tradition, and a keen aesthetic sense. These qualities would meld and develop over time, across an extraordinary career in the earth sciences.
According to the Virtual Luna Leopold Project, “He was trained as a civil engineer (B.S degree), meteorologist (M.S. degree) and geologist (Ph.D.) and his publications reflect that blending of fields. His first publication in 1937 was entitled Relation of Watershed Conditions to Flood Discharge: A Theoretical Analysis and his most recent publication in 2005 was Geomorphic Effects of Urbanization in Forty-one Years of Observations. Few have written papers spanning 68 years, and fewer still have had such an influence on a field or on society.”
Luna Leopold’s creative intellect compelled him to explore the territory where science, policy, ethics, and environmental stewardship come together. In discerning the complex physical processes of stream formation and development, climate, precipitation, erosion, sedimentation, and deposition, he made connections to our human capacity to alter, or adapt to, hydrological realities. He understood that water science could not be separated from the water management and stewardship, which could not be separated from water ethics. On this he has been widely quoted: “Water is the most critical resource issue of our lifetime and our children’s lifetime. The health of our waters is the principal measure of how we live on the land.”
“The stream has to have change”
What he was referring to, of course, was our dominant historic tendency to reduce the inherent flux in stream systems, to manage flowing waters by controlling their dynamic variability. It is a fundamental lesson that several generations now of river managers and stewards have taken to heart and employed in restoration practice.
I suspect I highlighted that line in my notes, in part, because of its rich metaphorical potential. Luna Leopold understood change. He saw the reality of change and the need for change. He was himself an agent of change. In his field work, in his policy work, in his teaching and writing and consulting, he came to a view of rivers, of water, and of our future, that called for change. Through Luna’s understanding of science, history, and aesthetics, he came to perceive a “harmony in natural systems,” and held that “the desire to preserve this harmony must… be incorporated into any philosophy of water management, and I will call this, as did Herodotus, a reverence for rivers. If this is environmental idealism, then let it be said that I am an idealist.”
Wisdom from the past shapes the USGS today
Leopold was best known for work on the geomorphology of rivers, the study of land features and the processes that create and change them. He initiated a new era in the study of rivers, one that involved quantitative approaches that spread to the broader field of geomorphology. His research related meteorology and climatology to landscape process, a concept that has become a central feature of geomorphology. One of his better known papers, The Hydraulic Geometry of Stream Channels, published in 1953, initiated a new era in the quantitative study of rivers and stimulated quantitative approaches in geomorphology generally. Revealing an orderly framework of river behavior, the paper provided a basis for observing rivers worldwide through objective measurements and data collection.
Leopold retired from the USGS in 1972, having had a distinguished 22-year career where his focus on research and interpretation of data made a profound impact on the earth sciences. His enthusiasm for rivers proved contagious, inspiring generations of colleagues and students to devote their talents to the pursuit of science and to its application for society. Following his USGS career, Leopold, became a professor in the Department of Geology and Geophysics and the Department of Landscape Architecture at the University of California, Berkeley. He passed away in 2006 at the age of 90.
Today, as our nation is faced with the challenge of balancing a finite freshwater supply among competing needs, including agriculture, drinking water, energy production, and ecosystem health, we can appreciate even more Luna Leopold’s combination of field knowledge, leadership, and wisdom. His reverence for rivers, his way of connecting head and heart, has continued to inform new generations of scientists, policy-makers, land stewards, and philosophers who are extending his insights, exploring new dimensions in water ethics, and putting that ethic into practice. The stream has to have change. The change that Leopold helped to initiate and inspire must come. It comes more predictably, perhaps, in natural systems than in human ones. But now, as we come to know how the human and natural inevitably flow together, we can perhaps allow reverence and knowledge to flow together as well—as they did through Luna’s life.