Andrew Sekellick
Andrew has worked for the USGS since 2008, providing GIS, cartographic, and statistical support to a wide variety of projects. Experience and interests include tracking nutrient and sediment sources, the impacts of management practices, and the integration of geospatial, monitored, and modeled data to inform water resource management.
Professional Experience
Physical Scientist - USGS MD-DE-DC Water Science Center, Catonsville, MD: 2008-present
Education and Certifications
M.P.S. Geographic Information Systems, University of Maryland, Baltimore County
B.S. Geography and Environmental Systems, University of Maryland, Baltimore County
Science and Products
Filter Total Items: 22
Biosolids Data Input Disaggregation from County to National Hydrography Dataset Plus Biosolids Data Input Disaggregation from County to National Hydrography Dataset Plus
This metadata record contains two tables with reported and calculated amounts of biosolids applied to agricultural land within the Chesapeake Bay watershed in 2023 at different scales. Included in the dataset are (1) mass of land-applied biosolids calculated for NHDPlus Version 2.1 (NHDPlusV2) reach catchments in 2023 and (2) actual amount of biosolids applied to land by county in 2023...
Compilation of multi-agency specific conductance observations for streams within the Chesapeake Bay watershed Compilation of multi-agency specific conductance observations for streams within the Chesapeake Bay watershed
Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the...
SPARROW Model Inputs and Estimated Effects of Agricultural Conservation Practices on Total Nitrogen in Streams of the Chesapeake Bay Watershed SPARROW Model Inputs and Estimated Effects of Agricultural Conservation Practices on Total Nitrogen in Streams of the Chesapeake Bay Watershed
This data release contains input and output data tables from a SPAtially Referenced Regression On Watershed attributes (SPARROW) model, which estimated total nitrogen loads in streams of the Chesapeake Bay watershed under varying better management practice implementation scenarios. Further documentation about the SPARROW modeling framework can be found here: https://pubs.er.usgs.gov...
SPARROW model input datasets and predictions for predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay SPARROW model input datasets and predictions for predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay
This data release includes 5 files containing model inputs and resulting model predictions. A previously-calibrated spatially referenced regression (SPARROW) model was used to estimate effects of climate change on in-stream nitrogen (TN) loads in the Chesapeake Bay watershed between 1995 and 2025. Model scenarios were run using data for nitrogen sources and landscape characteristics from...
Nitrogen sources to and export from the Chesapeake Bay watershed, 1950 to 2050 Nitrogen sources to and export from the Chesapeake Bay watershed, 1950 to 2050
This U.S. Geological Survey data release contains datasets that combine past data with future projections of nitrogen sources and nitrogen export to the Chesapeake Bay watershed for the years 1950-2050. To help understand the effect of human and environmental changes over this time period, data for nitrogen sources from wastewater, agricultural fertilizer and manure, and atmospheric...
Chesapeake Bay Watershed Non-Tidal Network Station Catchments Chesapeake Bay Watershed Non-Tidal Network Station Catchments
Drainage basins of the 123 Non-Tidal Monitoring Stations in the Chesapeake Bay Watershed.
Filter Total Items: 17
Nitrogen in the Chesapeake Bay watershed—A century of change, 1950–2050 Nitrogen in the Chesapeake Bay watershed—A century of change, 1950–2050
Foreword Sustaining the quality of the Nation’s water resources and the health of our diverse ecosystems depends on the availability of sound water-resources data and information to develop effective, science-based policies. Effective management of water resources also brings more certainty and efficiency to important economic sectors. Taken together, these actions lead to immediate and...
Authors
John W. Clune, Paul D. Capel, Matthew P. Miller, Douglas A. Burns, Andrew J. Sekellick, Peter R. Claggett, Richard H. Coupe, Rosemary M. Fanelli, Ana Maria Garcia, Jeff P. Raffensperger, Silvia Terziotti, Gopal Bhatt, Joel D. Blomquist, Kristina G. Hopkins, Jennifer L. Keisman, Lewis C. Linker, Gary W. Shenk, Richard A. Smith, Alexander M. Soroka, James S. Webber, David M. Wolock, Qian Zhang
High-frequency data reveal deicing salts drive elevated specific conductance and chloride along with pervasive and frequent exceedances of the U.S. Environmental Protection Agency aquatic life criteria for chloride in urban streams High-frequency data reveal deicing salts drive elevated specific conductance and chloride along with pervasive and frequent exceedances of the U.S. Environmental Protection Agency aquatic life criteria for chloride in urban streams
Increasing specific conductance (SC) and chloride concentrations [Cl] negatively affect many stream ecosystems. We characterized spatial variability in SC, [Cl], and exceedances of Environmental Protection Agency [Cl] criteria using nearly 30 million high-frequency observations (2–15 min intervals) for SC and modeled [Cl] from 93 sites across three regions in the eastern United States...
Authors
Joel Moore, Rosemary M. Fanelli, Andrew J. Sekellick
Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA
This review aims to synthesize the current knowledge of sediment dynamics using insights from long‐term research conducted in the watershed draining to the Chesapeake Bay, the largest estuary in the U.S., to inform management actions to restore the estuary and its watershed. The sediment dynamics of the Chesapeake are typical of many impaired watersheds and estuaries around the world...
Authors
Gregory E. Noe, Matthew J. Cashman, Katherine Skalak, Allen C. Gellis, Kristina G. Hopkins, Douglas L. Moyer, James S. Webber, Adam J. Benthem, Kelly O. Maloney, John Brakebill, Andrew J. Sekellick, Michael J. Langland, Qian Zhang, Gary W. Shenk, Jennifer L. D. Keisman, Cliff R. Hupp
Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012 Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially-referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary...
Authors
Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel D. Blomquist, Andrew J. Sekellick
Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014 Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014
Efforts to restore water quality in Chesapeake Bay and its tributaries often include extensive Best Management Practice (BMP) implementation on agricultural and developed lands. These BMPs include a variety of methods to reduce nutrient and sediment loads, such as cover crops, conservation tillage, urban filtering systems, and other practices. Estimates of BMP implementation throughout...
Authors
Andrew J. Sekellick, Olivia H. Devereux, Jennifer L. D. Keisman, Jeffrey S. Sweeney, Joel D. Blomquist
Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012 Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012
Understanding changing nutrient concentrations in surface waters requires quantitative information on changing nutrient sources in contributing watersheds. For example, the proportion of nutrient inputs reaching streams and rivers is directly affected by when and where those nutrients enter the landscape. The goal of this report is to contribute to the U.S. Geological Survey’s efforts to...
Authors
Jennifer L. Keisman, Olivia Devereux, Andrew E. LaMotte, Andrew J. Sekellick, Joel D. Blomquist
Science and Products
Filter Total Items: 22
Biosolids Data Input Disaggregation from County to National Hydrography Dataset Plus Biosolids Data Input Disaggregation from County to National Hydrography Dataset Plus
This metadata record contains two tables with reported and calculated amounts of biosolids applied to agricultural land within the Chesapeake Bay watershed in 2023 at different scales. Included in the dataset are (1) mass of land-applied biosolids calculated for NHDPlus Version 2.1 (NHDPlusV2) reach catchments in 2023 and (2) actual amount of biosolids applied to land by county in 2023...
Compilation of multi-agency specific conductance observations for streams within the Chesapeake Bay watershed Compilation of multi-agency specific conductance observations for streams within the Chesapeake Bay watershed
Freshwater salinization is an emerging issue for freshwater environments in the Chesapeake Bay, USA region. Salinization is often described by measurements of specific conductance (SC). This data release contains specific conductance observations collected by multiple regional agencies for streams within the Chesapeake Bay Watershed. This inventory compiles and harmonizes data from the...
SPARROW Model Inputs and Estimated Effects of Agricultural Conservation Practices on Total Nitrogen in Streams of the Chesapeake Bay Watershed SPARROW Model Inputs and Estimated Effects of Agricultural Conservation Practices on Total Nitrogen in Streams of the Chesapeake Bay Watershed
This data release contains input and output data tables from a SPAtially Referenced Regression On Watershed attributes (SPARROW) model, which estimated total nitrogen loads in streams of the Chesapeake Bay watershed under varying better management practice implementation scenarios. Further documentation about the SPARROW modeling framework can be found here: https://pubs.er.usgs.gov...
SPARROW model input datasets and predictions for predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay SPARROW model input datasets and predictions for predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay
This data release includes 5 files containing model inputs and resulting model predictions. A previously-calibrated spatially referenced regression (SPARROW) model was used to estimate effects of climate change on in-stream nitrogen (TN) loads in the Chesapeake Bay watershed between 1995 and 2025. Model scenarios were run using data for nitrogen sources and landscape characteristics from...
Nitrogen sources to and export from the Chesapeake Bay watershed, 1950 to 2050 Nitrogen sources to and export from the Chesapeake Bay watershed, 1950 to 2050
This U.S. Geological Survey data release contains datasets that combine past data with future projections of nitrogen sources and nitrogen export to the Chesapeake Bay watershed for the years 1950-2050. To help understand the effect of human and environmental changes over this time period, data for nitrogen sources from wastewater, agricultural fertilizer and manure, and atmospheric...
Chesapeake Bay Watershed Non-Tidal Network Station Catchments Chesapeake Bay Watershed Non-Tidal Network Station Catchments
Drainage basins of the 123 Non-Tidal Monitoring Stations in the Chesapeake Bay Watershed.
Filter Total Items: 17
Nitrogen in the Chesapeake Bay watershed—A century of change, 1950–2050 Nitrogen in the Chesapeake Bay watershed—A century of change, 1950–2050
Foreword Sustaining the quality of the Nation’s water resources and the health of our diverse ecosystems depends on the availability of sound water-resources data and information to develop effective, science-based policies. Effective management of water resources also brings more certainty and efficiency to important economic sectors. Taken together, these actions lead to immediate and...
Authors
John W. Clune, Paul D. Capel, Matthew P. Miller, Douglas A. Burns, Andrew J. Sekellick, Peter R. Claggett, Richard H. Coupe, Rosemary M. Fanelli, Ana Maria Garcia, Jeff P. Raffensperger, Silvia Terziotti, Gopal Bhatt, Joel D. Blomquist, Kristina G. Hopkins, Jennifer L. Keisman, Lewis C. Linker, Gary W. Shenk, Richard A. Smith, Alexander M. Soroka, James S. Webber, David M. Wolock, Qian Zhang
High-frequency data reveal deicing salts drive elevated specific conductance and chloride along with pervasive and frequent exceedances of the U.S. Environmental Protection Agency aquatic life criteria for chloride in urban streams High-frequency data reveal deicing salts drive elevated specific conductance and chloride along with pervasive and frequent exceedances of the U.S. Environmental Protection Agency aquatic life criteria for chloride in urban streams
Increasing specific conductance (SC) and chloride concentrations [Cl] negatively affect many stream ecosystems. We characterized spatial variability in SC, [Cl], and exceedances of Environmental Protection Agency [Cl] criteria using nearly 30 million high-frequency observations (2–15 min intervals) for SC and modeled [Cl] from 93 sites across three regions in the eastern United States...
Authors
Joel Moore, Rosemary M. Fanelli, Andrew J. Sekellick
Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA Sediment dynamics and implications for management: State of the science from long‐term research in the Chesapeake Bay watershed, USA
This review aims to synthesize the current knowledge of sediment dynamics using insights from long‐term research conducted in the watershed draining to the Chesapeake Bay, the largest estuary in the U.S., to inform management actions to restore the estuary and its watershed. The sediment dynamics of the Chesapeake are typical of many impaired watersheds and estuaries around the world...
Authors
Gregory E. Noe, Matthew J. Cashman, Katherine Skalak, Allen C. Gellis, Kristina G. Hopkins, Douglas L. Moyer, James S. Webber, Adam J. Benthem, Kelly O. Maloney, John Brakebill, Andrew J. Sekellick, Michael J. Langland, Qian Zhang, Gary W. Shenk, Jennifer L. D. Keisman, Cliff R. Hupp
Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012 Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially-referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary...
Authors
Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel D. Blomquist, Andrew J. Sekellick
Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014 Spatial and Temporal Patterns of Best Management Practice Implementation in the Chesapeake Bay Watershed, 1985–2014
Efforts to restore water quality in Chesapeake Bay and its tributaries often include extensive Best Management Practice (BMP) implementation on agricultural and developed lands. These BMPs include a variety of methods to reduce nutrient and sediment loads, such as cover crops, conservation tillage, urban filtering systems, and other practices. Estimates of BMP implementation throughout...
Authors
Andrew J. Sekellick, Olivia H. Devereux, Jennifer L. D. Keisman, Jeffrey S. Sweeney, Joel D. Blomquist
Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012 Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012
Understanding changing nutrient concentrations in surface waters requires quantitative information on changing nutrient sources in contributing watersheds. For example, the proportion of nutrient inputs reaching streams and rivers is directly affected by when and where those nutrients enter the landscape. The goal of this report is to contribute to the U.S. Geological Survey’s efforts to...
Authors
Jennifer L. Keisman, Olivia Devereux, Andrew E. LaMotte, Andrew J. Sekellick, Joel D. Blomquist