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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 GW modeling, watershed level sediment studies, and QW modeling.

Current work focuses the effects of BMPs in the Chesapeake Bay and predicting water quality in baseflow and total flow using time sensitive modeling techniques.

Professional Experience

  • Geographer - 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

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Corn field in front of barn, silo, and houses

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...
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center
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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...
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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...
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Maryland-Delaware-D.C. Water Science Center
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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...
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Example layer-bottom altitudes from MODFLOW-NWT.

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...
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Maryland-Delaware-D.C. Water Science Center
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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...
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Filter Total Items: 13

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 Water Quali
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center, South Atlantic Water Science Center (SAWSC)

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/publication/tm
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Maryland-Delaware-D.C. Water Science Center

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 2012, cha
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Maryland-Delaware-D.C. Water Science Center

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 deposition are
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Water Resources Mission Area, Chesapeake Bay Activities, New Jersey Water Science Center

Chesapeake Bay Watershed Non-Tidal Network Station Catchments

Drainage basins of the 123 Non-Tidal Monitoring Stations in the Chesapeake Bay Watershed.
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Chesapeake Bay Activities, Lower Mississippi-Gulf Water Science Center

SPARROW model input datasets and predictions of nitrogen loads in streams of the Chesapeake Bay watershed

This data release contains mean-annual total nitrogen (TN) loads predicted by a SPARROW model for individual stream and shoreline reaches in the Chesapeake watershed as defined by NHDPlus, a 1:100,000 scale representation of stream hydrography built upon the National Hydrography Dataset (NHD) (Horizon Systems, 2010). Also included are the input variables required to execute the model, including la
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center

Discrete and high-frequency chloride (Cl) and specific conductance (SC) data sets and Cl-SC regression equations used for analysis of 93 USGS water quality monitoring stations in the eastern United States

High frequency estimated chloride (Cl) and observed specific conductance (SC) data sets, along with response variables derived from those data sets, were used in an analysis to quantify the extent to which deicer applications in winter affect water quality in 93 U.S. Geological Survey water quality monitoring stations across the eastern United States. The analysis was documented in the following p
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Maryland-Delaware-D.C. Water Science Center

Input and predictions from a suspended-sediment SPARROW model CBSS_V2 in the Chesapeake Bay watershed

These data represent input and estimates from a medium-resolution (1:100,000 scale) NHDPlus SPAtially Referenced Regression on Watershed attributes (SPARROW) model for the Chesapeake Bay watershed (CBSS_v2). The model spatially correlates long-term mean annual suspended-sediment flux in 113 non-tidal streams to likely upland and stream-corridor sources, landscape factors affecting upland sediment
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center

Inputs and Selected Predictions of the CBTN_v5 and CBTP_v5 SPARROW Models for the Chesapeake Bay Watershed

The CBTN_v5 and CBTP_v5 SPARROW models were developed to support inferences about causes of observed changes in nitrogen and phosphorus (respectively) fluxes in Chesapeake Bay tributaries between 1992 and 2012. Model inputs and outputs are included in three files, which are described below. Detailed documentation of the SPARROW modeling technique is available at https://pubs.er.usgs.gov/publicatio
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Water Resources Mission Area, National Water Quality Program, Chesapeake Bay Activities

Estimated effect of best management practice implementation in the Chesapeake Bay watershed from 1985 to 2014

This metadata record documents 3 sets of comma delimited tables representing the amount of reported best management practice (BMP) implementation within the Chesapeake Bay watershed as well as output data from scenarios of the Chesapeake Bay Program Phase 5.3.2 Watershed Model. The scenario data were used to estimate the effects of BMPs on water quality. The data are organized by three themes (chi
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center

Implementation of conservation tillage and cover crops in the Chesapeake Bay watershed, 1985 to 2012

Conservation tillage practices and cover crops are used throughout the Chesapeake Bay watershed to reduce soil loss and improve water quality. Implementation of these Best Management Practices (BMPs) were reported to the Chesapeake Bay Program (CBP) by each state in the watershed (New York, Pennsylvania, Maryland, Delaware, West Virginia, and Virginia). Estimates of acres of implementation per CBP
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center

itrogen and phosphorus from fertilizer and manure in the Chesapeake Bay watershed, 1950-2012

This dataset contains four tables of estimates of the yearly sum of nitrogen and phosphorus inputs from fertilizer applications and from manure applications in selected watersheds in Chesapeake Bay drainage basin from 1950 to 2012. For the fertilizer data, county-level loads were used from three published sources. Data from 1950 to 1985 are from Alexander and Smith (1990). Data for the year 1986 a
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center
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Filter Total Items: 13

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 “high-imp
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Andrew Sekellick, Scott Ator, Olivia H. Devereux, Jennifer L. Keisman
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Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center, Pennsylvania Water Science Center

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 inputs and
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Scott Ator, Gregory E. Schwarz, Andrew Sekellick, Gopal Bhatt
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Chesapeake Bay Activities

Nitrogen in the Chesapeake Bay watershed—A century of change, 1950–2050

ForewordSustaining 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 long-term e
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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, Alex Soroka, James S. Webber, David M. Wolock, Qian Zhang
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Water Resources Mission Area, Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center, New York Water Science Center, Pennsylvania Water Science Center, South Atlantic Water Science Center (SAWSC), Utah Water Science Center, Virginia and West Virginia Water Science Center

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: Southeast,
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Joel Moore, Rosemary M. Fanelli, Andrew Sekellick

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, and this syn
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Gregory B. Noe, Matt J. Cashman, Katherine Skalak, Allen Gellis, Kristina G. Hopkins, Doug L. Moyer, James S. Webber, Adam Benthem, Kelly O. Maloney, John Brakebill, Andrew Sekellick, Michael J. Langland, Qian Zhang, Gary W. Shenk, Jennifer L. D. Keisman, Cliff R. Hupp
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Climate Research and Development Program, Chesapeake Bay Activities, Florence Bascom Geoscience Center, Pennsylvania Water Science Center

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 inputs and
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Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel Blomquist, Andrew Sekellick
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Water Resources Mission Area, Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center, Pennsylvania Water Science Center

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 the Chesapea
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Andrew J. Sekellick, Olivia H. Devereux, Jennifer L. D. Keisman, Jeffrey S. Sweeney, Joel D. Blomquist
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Water Resources Mission Area, Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center, Pennsylvania Water Science Center

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 describe
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Jennifer L. Keisman, Olivia H. Devereux, Andrew E. LaMotte, Andrew J. Sekellick, Joel D. Blomquist
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Water Resources Mission Area, Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center

Modeling drivers of phosphorus loads in Chesapeake Bay tributaries and inferences about long-term change

Causal attribution of changes in water quality often consists of correlation, qualitative reasoning, listing references to the work of others, or speculation. To better support statements of attribution for water-quality trends, structural equation modeling was used to model the causal factors of total phosphorus loads in the Chesapeake Bay watershed. By transforming, scaling, and standardizing va
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Karen R. Ryberg, Joel D. Blomquist, Lori A. Sprague, Andrew J. Sekellick, Jennifer L. Keisman
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Water Resources Mission Area, Dakota Water Science Center

Water volume and sediment volume and density in Lake Linganore between Boyers Mill Road Bridge and Bens Branch, Frederick County, Maryland, 2012

To assist in understanding sediment loadings and the management of water resources, a bathymetric survey was conducted in the part of Lake Linganore between Boyers Mill Road Bridge and Bens Branch in Frederick County, Maryland. The bathymetric survey was performed in January 2012 by the U.S. Geological Survey, in cooperation with the City of Frederick and Frederick County. A separate, but related,
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Andrew J. Sekellick, William S.L. Banks, Michael K. Myers
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Water Resources Mission Area, Maryland-Delaware-D.C. Water Science Center

Statistical classification of hydrogeologic regions in the fractured rock area of Maryland and parts of the District of Columbia, Virginia, West Virginia, Pennsylvania, and Delaware

Hydrogeologic regions in the fractured rock area of Maryland were classified using geographic information system tools with principal components and cluster analyses. A study area consisting of the 8-digit Hydrologic Unit Code (HUC) watersheds with rivers that flow through the fractured rock area of Maryland and bounded by the Fall Line was further subdivided into 21,431 catchments from the Nation
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Brandon J. Fleming, Andrew E. LaMotte, Andrew J. Sekellick
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Water Resources Mission Area, Maryland-Delaware-D.C. Water Science Center

A regional classification of the effectiveness of depressional wetlands at mitigating nitrogen transport to surface waters in the Northern Atlantic Coastal Plain

Nitrogen from nonpoint sources contributes to eutrophication, hypoxia, and related ecological degradation in Atlantic Coastal Plain streams and adjacent coastal estuaries such as Chesapeake Bay and Pamlico Sound. Although denitrification in depressional (non-riparian) wetlands common to the Coastal Plain can be a significant landscape sink for nitrogen, the effectiveness of individual wetlands at
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Scott W. Ator, Judith M. Denver, Andrew E. LaMotte, Andrew J. Sekellick
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Water Resources Mission Area, Chesapeake Bay Activities, Maryland-Delaware-D.C. Water Science Center
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Manure and fertilizer inputs to land in the Chesapeake Bay watershed, 1950–2012 Scientific Investigations Report 2018-5022

Understanding changing nutrient concentrations in surface waters requires quantitative information on changing nutrient sources in contributing...

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