Water-Quality Trends

Featured Study: Changes in influences that affect water quality

Featured Study: Changes in influences that affect water quality

Some of the major human influences on water quality—the ways we use land, water, and chemicals—have undergone dramatic changes over the last five decades. Patterns of urbanization, chemical use, and agricultural production are profoundly altered.

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Featured Study: Changes in chloride in U.S. streams

Featured Study: Changes in chloride in U.S. streams

The choice of sampling approach affects our perception of whether water quality in streams and rivers has changed over time. Here, integrated designs provide new insights into how chloride is changing in U.S. streams and rivers.

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Science Center Objects

Is water quality getting better or worse?  Answering this deceptively simple question has been a fundamental objective of the USGS National Water-Quality Assessment Project’s research. Learn about trends in contaminants in the nation’s streams and rivers, trends in contaminants that collect in the bed sediment of streams and lakes, and changes in the quality of the nation’s groundwater.

In 1991, Congress established the National Water-Quality Assessment (NAWQA) Project to address where, when, why, and how the Nation's water quality has changed, or is likely to change in the future, in response to human activities and natural factors. In response, the NAWQA Project developed multi-pronged approaches to characterize trends in diverse contaminants in the Nation’s streams, rivers, bed sediment, and groundwater.

 

Trends in Contaminant Concentrations and Loads in the Nation’s Streams and Rivers

The  NAWQA Project, other USGS programs, and other Federal, State, and local agencies have collected years of water-quality data to support their assessments of changing water-quality conditions. For the first time, all of these data have been combined to support the most comprehensive assessment conducted to date of water-quality trends in the United States. Collectively, these data provide insight into how natural features and human activities have contributed to water-quality changes over time in Nation's streams and rivers. Data are updated annually. The online Water-Quality Trends mapping tool allows users to visualize trends in water chemistry (nutrients, pesticides, sediment, carbon, and salinity) and aquatic ecology (fish, invertebrates, and algae)

 

Unnamed tributary of the Arkansas River near Cleveland, Okla., 2013; photograph by Stan Paxton.

Tributaries contribute to water quality in the Arkansas River, one of hundreds of U.S. streams and rivers where water-quality trends are being monitored. (Credit: Stan Paxton)

Trends in Sediment-Associated Contaminants

Many contaminants adhere, or sorb, to sediment, so that standard water-quality sampling and analysis is often unable to detect changes in their concentrations over time.  Sediment-associated contaminants include legacy contaminants, such as DDT and PCBs, and contaminants currently released into the environment, such as the pesticide bifenthrin and polycyclic aromatic hydrocarbons (PAHs).  An alternative approach to determine trends in concentrations of these contaminants is the use of sediment cores collected from lakes and reservoirs.

 

Changes in Groundwater Quality

Collecting groundwater data

Monitoring groundwater quality at a public-supply well.

USGS scientists are characterizing groundwater quality in principal aquifers, the primary source of the Nation's groundwater used for drinking.  Users can access an online tool to see how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation, and see in real time how chemical properties of groundwater at some sites are fluctuating.