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
New study evaluates effects of agricultural conservation practices on nitrogen in streams of the Chesapeake Bay
Issue: Adaptive management in support of Chesapeake Bay restoration is complicated by uncertainty about the effects of agricultural management practices on water quality. Despite increasing investment, effects of agricultural conservation practices on regional water quality remain difficult to quantify due to factors such as groundwater travel times, varying modes-of-action, and the general lack...
GIS & Dataset Capabilities @ MD-DE-DC
Spatial analysts at the MD-DE-DC WSC use Geographic Information Systems to interpret data collected through field reconnaissance and downloaded from internal USGS, other federal, state, and local agencies, academic institutions, industry, and other professional contracting organizations. GIS is used to analyze the data using shapefiles and geodatabased information to help prove or disprove...
Modeling Capabilities @ MD-DE-DC
USGS models are widely used to predict responses of hydrologic systems to changing stresses, such as increases in precipitation or ground-water pumping rates, as well as to predict the fate and movement of solutes and contaminants in water. The USGS is at the forefront of devising new techniques and computer software to solve practical problems in the study of water resources. Predictive models...
Filter Total Items: 22
Seasonal High Streamflow Generation Regions Model Inputs and Predictions for the Conterminous United States Seasonal High Streamflow Generation Regions Model Inputs and Predictions for the Conterminous United States
This data release contains input data tables and results from analysis to predict seasonal high streamflow generation regions of the conterminous United States. Input data consists of landscape characteristics, climate variables, and streamflow metrics at selected USGS streamflow gages as well as the same landscape characteristics and climate variables at ungaged locations. Results from...
Applied Biosolids Data Input Summed from Fields to National Hydrography Dataset Plus V2 in Virginia, 2024 Applied Biosolids Data Input Summed from Fields to National Hydrography Dataset Plus V2 in Virginia, 2024
This metadata record contains two tables with reported and calculated amounts of biosolids applied to agricultural land within Virginia in 2024 at different scales. Included in the dataset are (1) mass of land-applied biosolids calculated for NHDPlus Version 2.1 (NHDPlusV2) reach catchments in 2024 as a CSV and (2) reported amount of biosolids applied to land by county in 2024 as a CSV...
Illinois River basin seasonally dynamic total nitrogen and phosphorus SPARROW model inputs and outputs, 2000 through 2020 Illinois River basin seasonally dynamic total nitrogen and phosphorus SPARROW model inputs and outputs, 2000 through 2020
This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and...
Cropland Data Layer summaries for NHDPlus Version 2.1 Reach Catchments in the Conterminous United States, 2000-2022 Cropland Data Layer summaries for NHDPlus Version 2.1 Reach Catchments in the Conterminous United States, 2000-2022
This dataset contains summary tables of land cover from the Cropland Data Layer (CDL) for individual stream catchments of the conterminous United States from the National Hydrography Dataset Plus Version 2.1 (United States Department of Agriculture National Agricultural Statistics Service, 2024; McKay and others, 2012). These data were summarized from primarily 30 meter grid cell raster...
2014 Social Vulnerable Index factors compiled for CONUS at the NHDPlusV2 scale 2014 Social Vulnerable Index factors compiled for CONUS at the NHDPlusV2 scale
The released data contain both a csv and parquet file summarizing the Centers for Disease Control (CDC) Social Vulnerability Index (SVI), at the NHDPlus V2 stream catchment scale. Dasymetric mapping was utilized to bound 2014 populations to the 2013 National Land Cover Dataset and then trim them to NHDPlus V2 catchments. These produced data are summarized as numbers of people within each...
Nitrogen and phosphorus inputs from fertilizer and manure in the Continental United States, 2002-2017 Nitrogen and phosphorus inputs from fertilizer and manure in the Continental United States, 2002-2017
This dataset contains tables of estimated fertilizer and manure nutrient inputs in kilograms to individual stream catchments of the continental United States from the National Hydrography Dataset Plus Version 2.1 (McKay and others, 2012). These data were downscaled from county-level estimates of nitrogen and phosphorus inputs from Falcone (2021) by allocating mass of applied nutrients to
Filter Total Items: 17
Watershed Continuum Monitoring Approach: Combining multiple water quality patterns along stream and river flowpaths to track sources, pathways, and processing of pollutants Watershed Continuum Monitoring Approach: Combining multiple water quality patterns along stream and river flowpaths to track sources, pathways, and processing of pollutants
There is a growing need to improve and expand water quality monitoring approaches to more accurately track the sources, fate, and transport of multiple chemicals and pollutants holistically and quantify the effects of best management practices (BMPs) at the watershed scale. An overarching question raised by scientists, environmental managers, and the general public is: how far can water...
Authors
Sujay Kaushal, Ashley Mon, Stanley Grant, Paul M. Mayer, Aaron J. Porter, Andrew J. Sekellick, Jason Hamilton Chase, Shantanu Bhide, John D. Jastram, Tammy Newcomer-Johnson, Sydney A. Shelton, Alexis M. Yaculak, Joseph T. Malin, Carly Marcella Maas, Nicholas Salanitri, Daniel J. Silberstein, Steven P. Hohman, Ashley B. Dann, Weston M Slaughter, Megan A. Rippy, Ahmed Monofy, Ruth R. Shatkay, Jenna E. Reimer, Madeleine Seppi, Randi Noel, Julianna Mussa, Bennett Kellmayer, Gwendolyn Sivirichi, Melissa Grese, Walter L.M. Boger, Jeffrey G. Chanat, Shuiwang Duan, Kenneth T. Belt
Assessing streams in the Chesapeake Bay Watershed to guide conservation and restoration activities Assessing streams in the Chesapeake Bay Watershed to guide conservation and restoration activities
Freshwater streams in the Chesapeake Bay watershed are home to numerous aquatic organisms (like fish, amphibians, mussels, and insects) and provide drinking water and recreational opportunities to people living in or visiting the watershed. Land-use changes, such as urban development and increased activities in certain agricultural sectors, have degraded water quality and altered...
Authors
Kelly O. Maloney, Rosemary M. Fanelli, Matthew J. Cashman, Lindsey J. Boyle, Stephanie E. Gordon, Benjamin P. Gressler, Michelle P. Katoski, Alexander H. Kiser, Marina J. Metes, Gregory E. Noe, Andrew J. Sekellick, Allison Sussman, John A. Young
Predictive modeling reveals elevated conductivity relative to background levels in freshwater tributaries within the Chesapeake Bay watershed, USA Predictive modeling reveals elevated conductivity relative to background levels in freshwater tributaries within the Chesapeake Bay watershed, USA
Elevated conductivity (i.e., specific conductance or SC) causes osmotic stress in freshwater aquatic organisms and may increase the toxicity of some contaminants. Indices of benthic macroinvertebrate integrity have declined in urban areas across the Chesapeake Bay watershed (CBW), and more information is needed about whether these declines may be due to elevated conductivity. A...
Authors
Rosemary M. Fanelli, Joel Moore, Charles C. Stillwell, Andrew J. Sekellick, Richard Walker
Seasonally varying contributions of contemporaneous and lagged sources of instream total nitrogen and phosphorus load across the Illinois River basin Seasonally varying contributions of contemporaneous and lagged sources of instream total nitrogen and phosphorus load across the Illinois River basin
Quantifying nutrient sources in streams, their temporal and spatial variability, and drivers of that variability can support effective water resources management. Yet a lack of data and modeling capabilities has previously prevented comprehensive quantification across both space and time. Here a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model that...
Authors
Noah M. Schmadel, Olivia L. Miller, Scott Ator, Matthew P. Miller, Gregory E. Schwarz, Dale M. Robertson, Andrew J. Sekellick, Kenneth D. Skinner, David A. Saad
Estimated reduction of nitrogen in streams of the Chesapeake Bay in areas with agricultural conservation practices Estimated reduction of nitrogen in streams of the Chesapeake Bay in areas with agricultural conservation practices
Spatial data provided by the U.S. Department of Agriculture National Resource Conservation Service representing implementation at the field-level for a selection of agricultural conservation practices were incorporated within a spatially referenced regression model to estimate their effects on nitrogen loads in streams in the Chesapeake Bay watershed. Conservation practices classified as...
Authors
Andrew J. Sekellick, Scott Ator, Olivia Devereux, Jennifer L. Keisman
Predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay Predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay
Understanding effects of climate change on nitrogen fate and transport in the environment is critical to nutrient management. We used climate projections within a previously calibrated spatially referenced regression (SPARROW) model to predict effects of expected climate change over 1995 through 2025 on total nitrogen fluxes to Chesapeake Bay and in watershed streams. Assuming nitrogen...
Authors
Scott Ator, Gregory E. Schwarz, Andrew J. Sekellick, Gopal Bhatt
Science and Products
New study evaluates effects of agricultural conservation practices on nitrogen in streams of the Chesapeake Bay
Issue: Adaptive management in support of Chesapeake Bay restoration is complicated by uncertainty about the effects of agricultural management practices on water quality. Despite increasing investment, effects of agricultural conservation practices on regional water quality remain difficult to quantify due to factors such as groundwater travel times, varying modes-of-action, and the general lack...
GIS & Dataset Capabilities @ MD-DE-DC
Spatial analysts at the MD-DE-DC WSC use Geographic Information Systems to interpret data collected through field reconnaissance and downloaded from internal USGS, other federal, state, and local agencies, academic institutions, industry, and other professional contracting organizations. GIS is used to analyze the data using shapefiles and geodatabased information to help prove or disprove...
Modeling Capabilities @ MD-DE-DC
USGS models are widely used to predict responses of hydrologic systems to changing stresses, such as increases in precipitation or ground-water pumping rates, as well as to predict the fate and movement of solutes and contaminants in water. The USGS is at the forefront of devising new techniques and computer software to solve practical problems in the study of water resources. Predictive models...
Filter Total Items: 22
Seasonal High Streamflow Generation Regions Model Inputs and Predictions for the Conterminous United States Seasonal High Streamflow Generation Regions Model Inputs and Predictions for the Conterminous United States
This data release contains input data tables and results from analysis to predict seasonal high streamflow generation regions of the conterminous United States. Input data consists of landscape characteristics, climate variables, and streamflow metrics at selected USGS streamflow gages as well as the same landscape characteristics and climate variables at ungaged locations. Results from...
Applied Biosolids Data Input Summed from Fields to National Hydrography Dataset Plus V2 in Virginia, 2024 Applied Biosolids Data Input Summed from Fields to National Hydrography Dataset Plus V2 in Virginia, 2024
This metadata record contains two tables with reported and calculated amounts of biosolids applied to agricultural land within Virginia in 2024 at different scales. Included in the dataset are (1) mass of land-applied biosolids calculated for NHDPlus Version 2.1 (NHDPlusV2) reach catchments in 2024 as a CSV and (2) reported amount of biosolids applied to land by county in 2024 as a CSV...
Illinois River basin seasonally dynamic total nitrogen and phosphorus SPARROW model inputs and outputs, 2000 through 2020 Illinois River basin seasonally dynamic total nitrogen and phosphorus SPARROW model inputs and outputs, 2000 through 2020
This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and...
Cropland Data Layer summaries for NHDPlus Version 2.1 Reach Catchments in the Conterminous United States, 2000-2022 Cropland Data Layer summaries for NHDPlus Version 2.1 Reach Catchments in the Conterminous United States, 2000-2022
This dataset contains summary tables of land cover from the Cropland Data Layer (CDL) for individual stream catchments of the conterminous United States from the National Hydrography Dataset Plus Version 2.1 (United States Department of Agriculture National Agricultural Statistics Service, 2024; McKay and others, 2012). These data were summarized from primarily 30 meter grid cell raster...
2014 Social Vulnerable Index factors compiled for CONUS at the NHDPlusV2 scale 2014 Social Vulnerable Index factors compiled for CONUS at the NHDPlusV2 scale
The released data contain both a csv and parquet file summarizing the Centers for Disease Control (CDC) Social Vulnerability Index (SVI), at the NHDPlus V2 stream catchment scale. Dasymetric mapping was utilized to bound 2014 populations to the 2013 National Land Cover Dataset and then trim them to NHDPlus V2 catchments. These produced data are summarized as numbers of people within each...
Nitrogen and phosphorus inputs from fertilizer and manure in the Continental United States, 2002-2017 Nitrogen and phosphorus inputs from fertilizer and manure in the Continental United States, 2002-2017
This dataset contains tables of estimated fertilizer and manure nutrient inputs in kilograms to individual stream catchments of the continental United States from the National Hydrography Dataset Plus Version 2.1 (McKay and others, 2012). These data were downscaled from county-level estimates of nitrogen and phosphorus inputs from Falcone (2021) by allocating mass of applied nutrients to
Filter Total Items: 17
Watershed Continuum Monitoring Approach: Combining multiple water quality patterns along stream and river flowpaths to track sources, pathways, and processing of pollutants Watershed Continuum Monitoring Approach: Combining multiple water quality patterns along stream and river flowpaths to track sources, pathways, and processing of pollutants
There is a growing need to improve and expand water quality monitoring approaches to more accurately track the sources, fate, and transport of multiple chemicals and pollutants holistically and quantify the effects of best management practices (BMPs) at the watershed scale. An overarching question raised by scientists, environmental managers, and the general public is: how far can water...
Authors
Sujay Kaushal, Ashley Mon, Stanley Grant, Paul M. Mayer, Aaron J. Porter, Andrew J. Sekellick, Jason Hamilton Chase, Shantanu Bhide, John D. Jastram, Tammy Newcomer-Johnson, Sydney A. Shelton, Alexis M. Yaculak, Joseph T. Malin, Carly Marcella Maas, Nicholas Salanitri, Daniel J. Silberstein, Steven P. Hohman, Ashley B. Dann, Weston M Slaughter, Megan A. Rippy, Ahmed Monofy, Ruth R. Shatkay, Jenna E. Reimer, Madeleine Seppi, Randi Noel, Julianna Mussa, Bennett Kellmayer, Gwendolyn Sivirichi, Melissa Grese, Walter L.M. Boger, Jeffrey G. Chanat, Shuiwang Duan, Kenneth T. Belt
Assessing streams in the Chesapeake Bay Watershed to guide conservation and restoration activities Assessing streams in the Chesapeake Bay Watershed to guide conservation and restoration activities
Freshwater streams in the Chesapeake Bay watershed are home to numerous aquatic organisms (like fish, amphibians, mussels, and insects) and provide drinking water and recreational opportunities to people living in or visiting the watershed. Land-use changes, such as urban development and increased activities in certain agricultural sectors, have degraded water quality and altered...
Authors
Kelly O. Maloney, Rosemary M. Fanelli, Matthew J. Cashman, Lindsey J. Boyle, Stephanie E. Gordon, Benjamin P. Gressler, Michelle P. Katoski, Alexander H. Kiser, Marina J. Metes, Gregory E. Noe, Andrew J. Sekellick, Allison Sussman, John A. Young
Predictive modeling reveals elevated conductivity relative to background levels in freshwater tributaries within the Chesapeake Bay watershed, USA Predictive modeling reveals elevated conductivity relative to background levels in freshwater tributaries within the Chesapeake Bay watershed, USA
Elevated conductivity (i.e., specific conductance or SC) causes osmotic stress in freshwater aquatic organisms and may increase the toxicity of some contaminants. Indices of benthic macroinvertebrate integrity have declined in urban areas across the Chesapeake Bay watershed (CBW), and more information is needed about whether these declines may be due to elevated conductivity. A...
Authors
Rosemary M. Fanelli, Joel Moore, Charles C. Stillwell, Andrew J. Sekellick, Richard Walker
Seasonally varying contributions of contemporaneous and lagged sources of instream total nitrogen and phosphorus load across the Illinois River basin Seasonally varying contributions of contemporaneous and lagged sources of instream total nitrogen and phosphorus load across the Illinois River basin
Quantifying nutrient sources in streams, their temporal and spatial variability, and drivers of that variability can support effective water resources management. Yet a lack of data and modeling capabilities has previously prevented comprehensive quantification across both space and time. Here a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model that...
Authors
Noah M. Schmadel, Olivia L. Miller, Scott Ator, Matthew P. Miller, Gregory E. Schwarz, Dale M. Robertson, Andrew J. Sekellick, Kenneth D. Skinner, David A. Saad
Estimated reduction of nitrogen in streams of the Chesapeake Bay in areas with agricultural conservation practices Estimated reduction of nitrogen in streams of the Chesapeake Bay in areas with agricultural conservation practices
Spatial data provided by the U.S. Department of Agriculture National Resource Conservation Service representing implementation at the field-level for a selection of agricultural conservation practices were incorporated within a spatially referenced regression model to estimate their effects on nitrogen loads in streams in the Chesapeake Bay watershed. Conservation practices classified as...
Authors
Andrew J. Sekellick, Scott Ator, Olivia Devereux, Jennifer L. Keisman
Predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay Predicting near-term effects of climate change on nitrogen transport to Chesapeake Bay
Understanding effects of climate change on nitrogen fate and transport in the environment is critical to nutrient management. We used climate projections within a previously calibrated spatially referenced regression (SPARROW) model to predict effects of expected climate change over 1995 through 2025 on total nitrogen fluxes to Chesapeake Bay and in watershed streams. Assuming nitrogen...
Authors
Scott Ator, Gregory E. Schwarz, Andrew J. Sekellick, Gopal Bhatt