Interstate Commission on the Potomac River Basin

Rockville, MD, United States

Interstate Commission on the Potomac River Basin

Rockville, MD, United States
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Harding L.W.,University of California at Los Angeles | Adolf J.E.,University of Hawaii at Hilo | Mallonee M.E.,Interstate Commission on the Potomac River Basin | Miller W.D.,U.S. Navy | And 5 more authors.
Estuarine, Coastal and Shelf Science | Year: 2015

Long-term data on floral composition of phytoplankton are presented to document seasonal and inter-annual variability in Chesapeake Bay related to climate effects on hydrology. Source data consist of the abundances of major taxonomic groups of phytoplankton derived from algal photopigments (1995-2004) and cell counts (1985-2007). Algal photopigments were measured by high-performance liquid chromatography (HPLC) and analyzed using the software CHEMTAX to determine the proportions of chlorophyll-a (. chl-a) in major taxonomic groups. Cell counts determined microscopically provided species identifications, enumeration, and dimensions used to obtain proportions of cell volume (CV), plasma volume (PV), and carbon (C) in the same taxonomic groups. We drew upon these two independent data sets to take advantage of the unique strengths of each method, using comparable quantitative measures to express floral composition for the main stem bay. Spatial and temporal variability of floral composition was quantified using data aggregated by season, year, and salinity zone. Both time-series were sufficiently long to encompass the drought-flood cycle with commensurate effects on inputs of freshwater and solutes. Diatoms emerged as the predominant taxonomic group, with significant contributions by dinoflagellates, cryptophytes, and cyanobacteria, depending on salinity zone and season. Our analyses revealed increased abundance of diatoms in wet years compared to long-term average (LTA) or dry years. Results are presented in the context of long-term nutrient over-enrichment of the bay, punctuated by inter-annual variability of freshwater flow that strongly affects nutrient loading, chl-a, and floral composition. Statistical analyses generated flow-adjusted diatom abundance and showed significant trends late in the time series, suggesting current and future decreases of nutrient inputs may lead to a reduction of the proportion of biomass comprised by diatoms in an increasingly diverse flora. © 2015 Elsevier Ltd.

Devereux O.H.,Interstate Commission on the Potomac River Basin | Prestegaard K.L.,University of Maryland University College | Needelman B.A.,University of Maryland University College | Gellis A.C.,Md Of Dc Water Science Center
Hydrological Processes | Year: 2010

Fine sediment sources were characterized by chemical composition in an urban watershed, the Northeast Branch Anacostia River, which drains to the Chesapeake Bay. Concentrations of 63 elements and two radionuclides were measured in possible land-based sediment sources and suspended sediment collected from the water column at the watershed outlet during storm events. These tracer concentrations were used to determine the relative quantity of suspended sediment contributed by each source. Although this is an urbanized watershed, there was not a distinct urban signature that can be evaluated except for the contributions from road surfaces. We identified the sources of fine sediment by both physiographic province (Piedmont and Coastal Plain) and source locale (streambanks, upland and street residue) by using different sets of elemental tracers. The Piedmont contributed the majority of the fine sediment for seven of the eight measured storms. The streambanks contributed the greatest quantity of fine sediment when evaluated by source locale. Street residue contributed 13% of the total suspended sediment on average and was the source most concentrated in anthropogenically enriched elements. Combining results from the source locale and physiographic province analyses, most fine sediment in the Northeast Branch watershed is derived from streambanks that contain sediment eroded from the Piedmont physiographic province of the watershed. Sediment fingerprinting analyses are most useful when longer term evaluations of sediment erosion and storage are also available from streambankerosion measurements, sediment budget and other methods. Copyright © 2010 John Wiley & Sons, Ltd.

Moltz H.L.N.,Interstate Commission on the Potomac River Basin | Lopes V.L.,Texas State University | Rast W.,Texas State University | Ventura S.J.,University of Wisconsin - Madison
Journal of Hydrologic Engineering | Year: 2010

The Santa Fe River Watershed in Santa Fe County, New Mexico was identified as one of the top five high risk nonpoint source pollution areas out in the Rio Grande Basin. This watershed was selected to demonstrate the use of hydrologic modeling as a powerful tool for assessing the impacts of land management practices on erosion and sediment control at the watershed level. A method based on the Hydrologic Simulation Program-Fortran was used to address the local nonpoint sediment pollution concerns. The model was modified to reflect predicted future land uses related to expected urban expansion in the watershed. Six scenarios were created and the costs and benefits of each were weighed. The total estimated costs ranged from under $1 million to over $66 million. Total average annual sediment yields at the watershed outlet ranged from 3,441 to 4,111 tonnes/year, depending on management practices employed. These results indicate the magnitude of expected sediment reductions under various management strategies. Additionally, they provide an indication of the magnitude of expected sediment reductions in the Santa Fe Watershed and the estimated cost of each management practice. © 2010 ASCE.

Moltz H.L.N.,Texas State University | Moltz H.L.N.,Interstate Commission on the Potomac River Basin | Rast W.,Texas State University | Lopes V.L.,Texas State University | Ventura S.J.,University of Wisconsin - Madison
Lakes and Reservoirs: Research and Management | Year: 2011

Sediment represents a major non-point source pollutant throughout the world. In addition to reduced agricultural productivity as the result of the loss of fertile soil, soil erosion also can have significant water-quality impacts in downstream waterbodies, reducing water transparency, degrading aquatic habitats and reducing the operational life and water storage capacity of reservoirs producing hydroelectric power. Various other pollutants also can absorb to sediment particles, creating additional downstream water-quality concerns for humans and the natural environment. In view of its human and environmental significance, two indices (an erosion index and runoff index) were developed to identify areas within the US portion of the Rio Grande Basin exhibiting physical characteristics conducive to producing significant non-point source pollution loads, focusing on land erosion as a sediment source. The erosion index is an adaptation of the Universal Soil Loss Equation, being the product of rainfall erosivity (R factor), soil erodibility (K factor), and a topographic factor (LS factor). The erosion index correlated well with measurements of sediment yields from runoff plots. The Curve Number was used as the runoff index. In conjunction with identified pollutant-generating land uses, or source landscapes, these indices were used to identify sub-watersheds within the US portion of the Rio Grande Basin that merit further investigation for non-point source pollution prevention and control via the use of hydrologic modelling techniques. © 2011 The Authors. Journal compilation © 2011 Blackwell Publishing Asia Pty Ltd.

Johnson J.M.,Vistronix | Buchanan C.,Interstate Commission on the Potomac River Basin
Environmental Monitoring and Assessment | Year: 2014

In 2006, a phytoplankton index of biotic integrity (PIBI) was published for Chesapeake Bay Lacouture et al. (Estuaries 29(4):598-616, 2006). The PIBI was developed from data collected during the first 18 years (1985-2002) of the Chesapeake Bay Program long-term phytoplankton and water quality monitoring programs. Combinations of up to nine phytoplankton metrics were selected to characterize bay habitat health according to plankton community condition in spring and summer seasons across four salinity zones. The independent data available at the time for index validation was not sufficient to test the PIBI because they lacked critical index parameters (pheophytin and dissolved organic carbon) and reference samples for some seasons and salinity zones. An additional 8 years of monitoring data (2003-2010) are now available to validate the original index, reassess index performance and re-examine long-term trends in PIBI conditions in the Bay. The PIBI remains sensitive to changes in nutrient and light conditions. Evaluation of the PIBI results over the entire 1985-2010 time period shows no discernible trends in the overall health of Bay habitat based on phytoplankton community conditions. This lack of overall PIBI trend appears to be a combined response to declines in water clarity and improvements in dissolved inorganic nitrogen and dissolved phosphorus conditions in the bay. © 2013 Springer Science+Business Media.

Schultz C.L.,Interstate Commission on the Potomac River Basin | Ahmed S.N.,Interstate Commission on the Potomac River Basin | Mandel R.,Interstate Commission on the Potomac River Basin | Moltz H.L.N.,Interstate Commission on the Potomac River Basin
Journal of the American Water Resources Association | Year: 2014

We have enhanced the ability of a widely used watershed model, Hydrologic Simulation Program - FORTRAN (HSPF), to predict low flows by reconfiguring the algorithm that simulates groundwater discharge. During dry weather periods, flow in most streams consists primarily of base flow, that is, groundwater discharged from underlying aquifers. In this study, HSPF's groundwater storage-discharge relationship is changed from a linear to a more general nonlinear relationship which takes the form of a power law. The nonlinear algorithm is capable of simulating streamflow recession curves that have been found in some studies to better match observed dry weather hydrographs. The altered version of HSPF is implemented in the Chesapeake Bay Program's Phase 5 Model, an HSPF-based model that simulates nutrient and sediment loads to the Chesapeake Bay, and is tested in the upper Potomac River basin, a 29,950 km2 drainage area that is part of the Bay watershed. The nonlinear relationship improved median Nash-Sutcliffe efficiencies for log daily flows at the model's 45 calibration points. Mean absolute percent error on low-flow days dropped in five major Potomac River tributaries by up to 12 percentage points, and in the Potomac River itself by four percentage points, where low-flow days were defined as days when observed flows were in the lowest 5th percentile range. Percent bias on low-flow days improved by eight percentage points in the Potomac River, from -11 to -3%. © 2013 American Water Resources Association.

Buchanan C.,Interstate Commission on the Potomac River Basin | Moltz H.L.N.,Interstate Commission on the Potomac River Basin | Haywood H.C.,Interstate Commission on the Potomac River Basin | Palmer J.B.,Interstate Commission on the Potomac River Basin | Griggs A.N.,Interstate Commission on the Potomac River Basin
Freshwater Biology | Year: 2013

The Ecological Limits of Hydrologic Alteration (ELOHA) method described in Poff et al. (2010) was applied to streams and small rivers in a large central region of the Potomac River basin in the U.S.A. The area, which is topographically complex, has karst geology, is increasingly urban and has few flow-altering impoundments, allows a test of the flexibility and applicability of the ELOHA method's four steps: build a hydrological foundation, calculate flow alteration, classify streams and develop flow alteration-ecology (FA-E) relationships. A hydrological foundation of baseline (undisturbed) and current (existing) hydrographs was simulated for 747 catchments using the Chesapeake Bay Program Hydrologic Simulation Program-FORTRAN (HSPF) model and the Virginia Department of Environmental Quality Online Object Oriented Meta-Model (WOOOMM) routing module. The outlet of each catchment was associated with one, and sometimes two or more, stream macroinvertebrate sampling sites. Pairing each catchment's simulated current flow with its own simulated baseline flow produced estimates of flow alteration that reflect the combination of natural and anthropogenic factors controlling streamflow in individual catchments. Flow metrics from the baseline and current simulations were compared with observed values from gauged streams in undisturbed and disturbed catchments. The model may have failed to simulate streamflow well in small urbanised catchments on or near karst geology, but observed data were insufficient to fully evaluate model behaviour in these units. Elsewhere, simulated and observed values of 13 of the 15 tested flow metrics generally agreed well. A stream hydrological classification system to account for natural biological variability was not feasible in the study area for two reasons. First, the natural landscape features that most strongly govern undisturbed streamflows (catchment size and karst geology) do not greatly influence undisturbed macroinvertebrate communities. Second, the study area's complex topography ensures that many streams crossed physiographic boundaries or flowed through karst geology before reaching the macroinvertebrate sampling sites. Stream macroinvertebrates responded strongly to alteration in the duration and frequency of both high and low flow events, rise rate, flashiness and magnitude of high flow events. They did not respond to the alteration in middle- and low-magnitude flow metrics, fall rate or extreme low flow frequency. Flow alteration-ecological relationships were developed for combinations of six flow metrics and seven macroinvertebrate metrics using quantile regression and conditional probability methods. Of the seven macroinvertebrate metrics, % scrapers, % clingers and the Chessie BIBI were most affected by flow alteration. Degraded habitat and water quality conditions modify and, if strong enough, conceal the flow alteration-ecological relationships. Water quality and habitat improvements can potentially ameliorate the impacts of flow alteration. Resource managers need to view each stream system holistically and consider all anthropogenic stressors before the impact of existing or future flow alteration can be determined. Overall, the ELOHA approach appears to have worked well in a large river basin with complex topography, karst geology, few flow-altering dams, many urban areas and macroinvertebrates as the ecological response variables. © 2013 John Wiley & Sons Ltd.

Annis E.R.,University of Maryland Center for Environmental science | Annis E.R.,Hood College | Houde E.D.,University of Maryland Center for Environmental science | Harding Jr. L.W.,University of Cambridge | And 3 more authors.
Marine Ecology Progress Series | Year: 2011

Growth and potential productivity of young-of-the-year (YOY) Atlantic menhaden Brevoortia tyrannus, a key forage fish, were investigated in Chesapeake Bay. A coupled foraging and bioenergetics model was developed to predict the dependency of menhaden size on chlorophyll a (chl a) and water temperatures in the bay. Substantial improvements were made to functional responses previously developed to describe YOY menhaden filtering efficiency on phytoplankton and swimming speed while filter feeding. Model output was calibrated to correspond to observed lengths of field-collected menhaden over an 11 yr period (1995 to 2005) by adjusting the percentage of chl a available to menhaden in the model. The model effectively represents variability in menhaden length in response to changes in chl a and temperature, indicating that only 9.2% of available chl a was required for menhaden to grow to lengths observed in the bay. In simulations of growth potential by bay region, the oligohaline (upper) region had the highest growth potential with decreasing potential in the mesohaline (middle) and polyhaline (lower) regions of the bay. Our results represent the first rigorous calibration and evaluation of a coupled foraging-bioenergetics model for Atlantic menhaden and establish a quantitative link between chl a standing stock and menhaden growth potential. © Inter-Research 2011.

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