De-La-Ossa-Carretero J.A.,University of Alicante |
Lane M.F.,Old Dominion University |
Llanso R.J.,Versar Inc. |
Dauer D.M.,Old Dominion University
Ecological Indicators | Year: 2016
The Benthic Index of Biotic Integrity (B-IBI) was developed and is currently employed for environmental assessment in Chesapeake Bay. The index consists of a variety of benthic community metrics (e.g. abundance, biomass, diversity, stress tolerance groups, etc.) scored by thresholds applied to seven benthic community habitats (tidal freshwater, oligohaline, low mesohaline, high mesohaline mud, high mesohaline sand, polyhaline mud, and polyhaline sand) This index was verified as being a sensitive and robust tool for summarizing the status of benthic communities. In our study we tested the classification efficiency of the index using new benthic data by characterizing each sample a priori as degraded or undegraded using criteria of sediment contaminant levels, bioassays and bottom dissolved oxygen levels. A primary objective of our study was to test the classification efficiency of the B-IBI in small water bodies connected to larger water bodies of the mainstems of the large rivers of Chesapeake Bay, as well as the efficiency of the index over time (1990 through 2009). The B-IBI was affected by the size of the water body, e.g., index accuracy was higher for water bodies in small watersheds in lower salinity habitats, whereas large water bodies of the mainstem of rivers were better classified by the B-IBI in habitats with higher salinities. Across the seven benthic habitat types overall correct classification was moderate to low and lower for correctly classifying undegraded sites. In general the index metrics showed some deficiencies that suggest improvements could be made by recalibrating existing metric thresholds or selecting new suitable metrics. © 2015 Elsevier Ltd. All rights reserved. Source
Voli M.T.,North Carolina State University |
Voli M.T.,Versar Inc. |
Wegmann K.W.,North Carolina State University |
Bohnenstiehl D.R.,North Carolina State University |
And 3 more authors.
Journal of Soils and Sediments | Year: 2013
Purpose: We employ a geochemical-fingerprinting approach to estimate the source of suspended sediments collected from tributaries entering Falls Lake, a 50-km2 drinking water reservoir on the Neuse River, North Carolina, USA. Many of the major tributaries to the lake are on North Carolina's 303(d) list for impaired streams, and in 2008, the lake was added to that list because of high values of turbidity, likely sourced from tributary streams. Materials and methods: Suspended sediments were collected from four streams with a time-integrated sampler during high-flow events. In addition, composite sediment samples representing potential sources were collected from stream banks, forests, pastures, construction sites, dirt and paved roads, and road cuts within tributary basins. Radiocarbon dating and magnetic susceptibility measurements were used to determine the origin of stream bank alluvial deposits. Sediment samples were analyzed for the concentrations of 55 elements and two radionuclides in order to identify tracers capable of distinguishing between potential sediment sources. The relative sediment source contributions were determined by applying a Monte Carlo simulation that parameterized the geochemical tracer data in a mixing model. Results and discussion: Radiocarbon and magnetic susceptibility measurements confirmed the presence of "legacy" sediment in the Ellerbe and New Light Creek valley bottoms. Mixing model results demonstrate that stream bank erosion is the largest contributor to the suspended sediment load in New Light Creek (62%), Ellerbe Creek (58%), and Little Lick Creek (33%), and is the second largest contributor in Lick Creek (27%) behind construction sites (43%). Conclusions: We find that stream bank erosion is the largest nonpoint source contributor to the suspended sediment load in three of the four catchments and is therefore a significant source of turbidity in Falls Lake. The presence of legacy sediment appears to coincide with increased contributions from stream bank erosion in Ellerbe and New Light creeks. Active construction sites and timber harvesting were also significant sources of suspended sediment. Water quality mitigation efforts need to consider nonpoint-source contributions from stream bank erosion of valley bottom sediments aggraded after European settlement. © 2013 Springer-Verlag Berlin Heidelberg. Source
Richkus W.A.,Versar Inc. |
Menzie C.A.,Exponent, Inc.
Human and Ecological Risk Assessment | Year: 2013
Oyster populations in Chesapeake Bay, USA, declined precipitously over the past three decades, and on-going efforts to restore the native oysters to former abundance were considered to be ineffective. Maryland and Virginia natural resource agencies proposed the introduction of a non-native Asian oyster (Crassostrea ariakensis) that is resistant to diseases affecting the native oyster and well adapted to the Chesapeake Bay environment. Numerous stakeholders raised concerns about potential adverse consequences of an introduction of a non-native species into a new environment. In response, state and federal agencies determined that an Environmental Impact Statement (EIS) should be prepared to address the environmental consequences of such an introduction as well as of seven other oyster restoration alternatives, including several involving only the native oyster. Preparation of an Ecological Risk Assessment (ERA) of the proposed action as well as all alternatives was an integral element of EIS preparation. This series of articles describes several different analyses that contributed to and collectively comprised the ERA conducted as input to the EIS. The final article of this series in HERA describes how the ERA and EIS findings were taken into account in the final decision on the preferred restoration alternative by state and federal agencies. © 2013 Copyright Taylor and Francis Group, LLC. Source
DeBerry J.W.,Versar Inc. |
Atkinson R.B.,Christopher Newport University
Southeastern Naturalist | Year: 2014
Ecosystems dominated by Chamaecyparis thyoides (Atlantic White Cedar) are critically endangered due to hydrologic alterations associated with ditching, logging, development, and agricultural conversion. Few studies have related structural and functional characteristics of this plant community to water tables, yet hydrologic management options may be critical to establish a peat-based seed refugium and allow Atlantic White Cedar self-maintenance in this ecosystem. In this study, we assessed aboveground forest biomass, litter production, and depth to water table at a mature (60-70 y) and an intermediate (20-35 y) age-class stand in two national wildlife refuges, Alligator River (AR) and Great Dismal Swamp (DS) in North Carolina. We calculated forest biomass from morphometric data gathered within randomized study plots. We made monthly litter collections at each study plot from November 1998 to April 2000; litter was sorted by species and type for the first 12 months. Wells installed at each study plot recorded water-table levels, which were at or near the surface at AR but >30 cm below the soil surface at DS throughout the study. Although Atlantic White Cedar was a dominant species at all sites, community structure differed between refuges. Total aboveground biomass was similar among age classes; however, Atlantic White Cedar stem density was greater and mean diameter at breast height was lower at AR. Mean annual litter production was higher at AR sites for each age class despite a persistently high water table. We conclude that the rates of primary production associated with high water tables at AR represent favorable conditions for Atlantic White Cedar self-maintenance. © 2014 Southeastern Naturalist. Source
Richkus W.A.,Versar Inc.
Human and Ecological Risk Assessment | Year: 2013
Failure of on-going management programs to restore oyster populations in Chesapeake Bay, USA, prompted state and federal agencies to consider the introduction of the non-native Asian oyster (Crassostrea ariakensis). An ecological risk assessment (ERA) of the proposed introduction was an essential element in preparation of a programmatic environmental impact statement (PEIS). The ERA had to assess risks of not only the proposed action (Asian oyster introduction) but also of the eight alternatives evaluated in the PEIS. The ERA suggested that the risk that the Asian oyster would not provide ecosystem services similar to those afforded by the native Eastern oyster was low, but there was moderate uncertainty associated with that conclusion. There was a non-zero risk of self-sustaining Asian oyster populations becoming established even if aquaculture with triploid, purportedly sterile Asian oysters were to be permitted. Nearly all of the risk conclusions had associated moderate to high uncertainty, not providing the level of proof that the agencies felt sufficient to justify proceeding with any action involving the Asian oyster. The irreversible nature of an introduction of the species bolstered that decision. Maryland and Virginia agencies have implemented numerous actions focused on the native oyster, but the outcome of these on-going actions is not yet known. © 2013 Copyright Taylor and Francis Group, LLC. Source