Tracking Status and Trends in Seven Key Indicators of River and Stream Condition in the Chesapeake Bay Watershed

What are Status and Trend?

Status describes the condition of a particular indicator at one moment in time.

Trend describes change in an indicator over time. 

The status of an indicator often depends on its quantity or size defined as increase minus decrease over a previous time interval. 

Trend is a statistically meaningful departure from a previous condition measured over an interval of time between two or more previously documented states. 

In the Chesapeake Bay Watershed trends describing changes in stream health may span intervals ranging from five to 50+ years.

Streamflow Science Domain

Domain Lead – Samuel H. Austin

Definition – Freshwater flows from streams draining the Chesapeake Bay watershed. 

Key Indicators – Status and trends in streamflow described by means and moving average metrics integrating change over time, including eight annual values describing minimum, mean, median, and maximum flows (status), and smoothed lines identifying change over time (trend).

Data – USGS streamflow daily data collected at gaged basins throughout the Chesapeake Bay watershed and available from the USGS National Water Information System (NWIS).

Products – Monthly updated estimates of status and trends in freshwater flows into Chesapeake Bay with accompanying statistical metrics. Available online reports, newsfeeds, data stories, and interactive analysis and data retrieval tools.

Water Quality Science Domain

Domain Lead – Christopher Allen Mason

Definition – Nutrient and sediment loads, and trends in loads, delivered to the Chesapeake Bay across a 123-station non-tidal network (NTN) within the bay watershed. 

Key Indicators – Status and trends in water quality described by annual and monthly loads of nutrient and sediment constituents (status), and flow-normalized changes in loads (trend) at long- (30+ years) and short-term (most recent 10 years) periods. At least five years of data provide reliable annual and monthly load-only estimates.

Data – Data continuously compiled since 1985, at the earliest, from the NTN USGS monitoring stations across five states. Constituents collected include total nitrogen, nitrate/nitrite, total phosphorus, orthophosphate and suspended sediment.

Products – Estimated status of, and trends in, nutrient and sediment loads within the Chesapeake Bay watershed. Nine of the NTN sites representing ~78 percent of the watershed are analyzed each year. The entire 123-site network is analyzed every two years. Data is available online in data releases, newsfeeds, geonarratives, and websites.

Links to additional discussion of nutrient and sediment trends will be made available here when available.

Stream Temperature Science Domain

Domain Lead – John Clune, Ph.D.

Definition – Stream temperatures can fluctuate naturally due to atmospheric conditions, topography, stream discharge, streambed heat transfer, and anthropogenic perturbations such as land use, thermal pollution, impoundments, and climate change.

Key Indicators – Status of stream temperature is derived by aggregating representative sub-daily observations to monthly and annual metrics that describe minimum, mean, median, and maximum temperature.  Trends adjusted for season and flow show the rate of change over 20-year, 10-year, and 5-year intervals.

Data – Multi-agency datasets spanning the latitude, elevation and temperature ranges of the Chesapeake Bay watershed.

Products – Data release of multi-agency stream temperature observations across the Chesapeake Bay watershed.  Estimated monthly or annual status and trends available online in reports, science base, newsfeeds, geonarratives, videos, and interactive analysis and data retrieval tools.

Hydromorphology Science Domain

Domain Lead – Marina Metes

Definition – Hydromorphology is the complex interplay between flow, sediment, geomorphology, and vegetation that creates ecologically relevant physical habitat. 

Key Indicators – 

1. EPA Rapid Assessment metrics –  e.g., embeddedness, epifaunal substrate, bank stability, sediment deposition, riparian score, etc.
2. USGS Gage Analysis metrics – e.g., change in bed elevation, channel velocity, water depth, width, channel-driven flood risk.

Data –

1. Multi-jurisdictional Rapid Habitat Assessment Data (~25,000 obs.)
2. USGS surface water gage data, 10-125+ year history.

Products – 

• Multijurisdictional physical habitat data available internally (source agency restrictions on release).
• Code release for automated USGS gage analyses, metric calculations, and trend calculation.
• Data release of derived metrics.

Salinity Science Domain

Domain Lead – Rosemary Fanelli, Ph.D.

Definition – The increase in ionic concentrations in freshwater, also known as freshwater salinization. Increased ions originate from deicer applications, industrial discharges, weathering of infrastructure (buildings), enhanced weathering of natural material (karst), atmospheric deposition, mining leachate, and water softeners. 

Key Indicators – Specific conductance (SC) is used as a measure of total ionic concentrations. SC is measured at a variety of timescales (from minutes to years). Ecologically-relevant salinity metrics that capture seasonal variability are computed using SC data. 

Data – A multi-jurisdictional dataset has been compiled and screened from Water Quality Portal, which include measures of SC from 30+ monitoring organizations in the region from 1980 to present. 

Products – SC inventory data release.

Toxic Contaminants Science Domain

Domain Lead – Trevor P Needham, PhD; Emily H Majcher, PE

Definition – Chemical pollutants in streams.

Key Indicators –  Legacy: PCBs and organochloride pesticides, Current Use: Mercury, PAHs, agricultural pesticides, Emerging Contaminants: PFAS.

Data –  Fish tissue contaminant State datasets, localized data in other media. Data vary with respect to sample collection frequency and location. 

Products – Reports and data summaries.

Biological Aquatic Communities Science Domain

Domain Lead – Lindsey J. Boyle

Definition - aquatic communities (e.g., benthic macroinvertebrates and fish) inhabiting freshwater rivers and streams in the watershed that can be used to measure stream health and fish habitat. 

Key Indicators - metrics describing assemblage composition (e.g., life histories and tolerance classifications), taxonomic composition, multi-metric composite indices, and presence or abundance of specific species.

Data - benthic macroinvertebrate data compiled during the generation of the “Chessie BIBI” (Smith and others, 2017), and fish sampling data compiled for development of an assessment of fish habitat (Krause and Maloney, 2021). 

Products  – 

• Attribution of benthic macroinvertebrate and fish sampling data to NHDPlusV2 Catchments within the Chesapeake Bay Watershed (datarelease).
• Community metrics from inter-agency compilation of inland fish sampling data within the Chesapeake Bay Watershed (data release).

Status and Trends Tracking Techniques

Status and trends are identified using approaches suited to each science domain with a goal of harmonizing methods as much as possible.

Approaches include: 

• Weighted regressions on time, discharge, and season (WRTDS).
• Calculation of mean values over distinct time intervals.
• Moving average metrics that integrate change over time. 
• Generalized additive modeling (GAM). 
• Mann-Kendall and seasonal Kendall trend tests.

Data richness and computational intervals vary across science domains.  

When possible analyses employ common time periods or co-located sites among indicators to facilitate comparisons across space and time.

Accessing Status and Trend Results

Timely access to status and trends in key stream health indicators is available through this website, our Chesapeake Bay Watershed Stream Health Status and Trends web portal:

 https://www.usgs.gov/CB-status-trend

Information and interactive content are continuously updated and available via interactive tools, detailed interactive maps, news feeds, and reports.