Grantee Research Project Results
Final Report: Integrated Assessment of Estuarine Ecosystems
EPA Grant Number: R828684C001Subproject: this is subproject number 001 , established and managed by the Center Director under grant R828684
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: EAGLES - Atlantic Slope Consortium
Center Director: Brooks, Robert P.
Title: Integrated Assessment of Estuarine Ecosystems
Investigators: Whigham, Dennis F. , Gallegos, Charles L. , Hines, Anson , Marra, Peter P. , Hershner, Carl , King, Ryan , DeLuca, William , Bilkovic, Donna Marie
Institution: Smithsonian Environmental Research Center , East Carolina University , Virginia Institute of Marine Science
EPA Project Officer: Packard, Benjamin H
Project Period: March 1, 2001 through February 28, 2005 (Extended to February 26, 2006)
RFA: Environmental Indicators in the Estuarine Environment Research Program (2000) RFA Text | Recipients Lists
Research Category: Water , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
This research project was one of four projects under the Atlantic Slope Consortium (ASC) Center. The overall objective of the estuarine component of the ASC research project was to develop indicators for elements of hydrologically linked estuarine ecosystems, including aquatic animals, estuarine and coastal wetlands, and coastal waterbirds. The development and testing of biotic indicators was conducted in two types of sampling units: estuarine wetlands and nearshore shallows, which are units analogous to small watersheds being sampled to develop and test Indices of Biotic Integrity (IBIs) for aquatic fauna and Habitat Suitability Indices (HSIs) for species that use these habitats. Estuary segments, which are large units that include deep water habitats, were used for developing HSI models for highly mobile species, where direct sampling of organisms is difficult and data often are unreliable.
Summary/Accomplishments (Outputs/Outcomes):
This is a summary report for the Web. A more detailed report entitled “Integration of Ecological and Socioeconomic Indicators for Estuaries and Watersheds of the Atlantic Slope,” which also includes additional figures, is available on the Web at http://www.asc.psu.edu/public/pubs/_Final Report_AtlanticSlopeConsortium.pdf (PDF, 96pp., 2.88MB, about PDF) .
The Estuarine Segment Approach
Numerous studies have demonstrated that human activities on land can have negative impacts on estuarine ecosystems. Few studies, however, have quantified the direct linkages between particular land-use patterns and estuarine responses. One reason that it has been difficult to quantify linkages between specific land-use patterns and estuarine responses is that most monitoring studies have focused on large, open-water systems (e.g., the mainstream of Chesapeake Bay or the large rivers that flow into it). Large-scale monitoring studies of this type are useful in tracking temporal changes for indicators of estuarine health. The Chesapeake Bay Program, for example, has developed a diverse array of indicators for monitoring the Bay (http://www.chesapeakebay.net/indicators.htm ). The Chesapeake Bay Foundation uses a wide range of indicators to produce an annual scorecard of the health of Chesapeake Bay (http://www.cbf.org/site/PageServer?pagename=sotb_2004_index ).
Monitoring programs and large-scale models, such as those developed by the Chesapeake Bay Program (http://www.chesapeakebay.net/pubs/iannewsletter11.pdf (PDF, 4pp., 4.43MB, about PDF)), have been used to develop management plans, but they have limited use in guiding small-scale land-use decisions because they do not have the sensitivity to quantify the relationships between specific land-use patterns and estuarine indicators at a scale that is appropriate for making management decisions.
The objective of this part of the ASC project was to identify linkages between patterns of land-use and environmental indicators in shallow estuarine habitats. To accomplish this objective, we used existing data and sampled estuarine segments of the Chesapeake Bay that were linked to a watershed that was large enough to support at least one perennial stream but small enough for field teams to sample the several habitats within the subestuary in a reasonable period of time (i.e., 1 or 2 days).
Estuarine Segment Selection and Characterization
Smithsonian Environmental Research Center (SERC) and Virginia Institute of Marine Science (VIMS) scientists selected estuarine segments based primarily on land-use patterns, but they differed in the selection criteria.
SERC Estuarine Segments. SERC scientists selected estuarine segments independent of watershed size, except for the criteria (described in more detail below) that the watershed was large enough to support at least one perennial stream that flowed into the estuarine portion of the segment. They initially screened more than 75 potential estuarine segments based on salinity regime. An initial goal was to minimize the complicating effects of salinity on estuarine biota by selecting estuarine segments that were in the mesohaline portion (i.e., intermediate salinity between freshwater and seawater) of the Chesapeake Bay. To be included as an estuarine segment, the watershed portion had to: (1) be dominated by one of the land-use types described in Table 1; (2) discharge directly into the Chesapeake Bay or into the mesohaline portion of one of the large river systems; and (3) be large enough to have at least one perennial stream that flowed into the subestuary. In addition to shallow subtidal habitats, each estuarine segment included a small (< 2 ha or 5 ac), medium (2-7 ha or 5-18 ac) and large (> 7 ha or 18 ac) brackish tidal wetland. The 32 estuarine segments that were chosen for study were distributed along a north-south axis of the Chesapeake Bay (Figure 1) and, with the exceptions of portions of the Back River, Bird River, Gwynns Falls, and Jones Falls watersheds, were within the Coastal Plain province. Topography of the Coastal Plain varies from rolling hills on the western shore to flat terrain on the central and southern portions on the eastern shore. Land-use patterns on the watersheds of each segment were used as surrogates for human disturbance levels.
Table 1. Land-Use Categories Used to Characterize the Watershed Portions of Estuarine Segments
Land Use Category | Criteria |
Forested | Greater than 65% total forest covers (forest, mixed, forest wetland) and <10% urban |
Agricultural | Greater than 50% total agricultural covers (pasture, crop) |
Developed | Greater than 50% total urban covers (low and high residential and industrial areas) |
Mixed Developed | 20-50% total urban covers |
Mixed Agricultural | 20-50% total agricultural covers |
Figure 1. SERC (left) and VIMS (right) Estuarine Segment
VIMS Estuarine Segments. VIMS scientists selected 23 estuarine segments in the oligo-to-mesohaline (i.e., low-to-intermediate salinity) portions of the Chesapeake Bay based on: watershed land-use classification, salinity regime, and accessibility. United States Geological Survey (USGS)-designated 14-digit hydrologic unit codes (HUC) were used to select watershed sampling units, and watershed land-use classification was based on principal land-use percentages derived from the National Land Cover Database (30 m raster coverage). Because of the sizes of 14-digit HUCs, the number of available watersheds in each land-use category was limited, the VIMS estuarine segments, therefore, only included three land-use categories: forested, agricultural (including the mixed-agriculture category in the SERC classification), and developed (including the mixed-developed category in the SERC classification) (See Table 1). Similar to SERC estuarine segments, the VIMS watersheds were distributed along a north-south axis of the Chesapeake Bay (Figure 1) and, with the exceptions of portions of the Back, Patapsco, Severn, and Elk River Watersheds, were within the Coastal Plain province.
General Description of Sampling Methods
Data collection in each subestuary was tailored to each project (projects are described in more detail below).
In general, water quality parameters (e.g., temperature, salinity, dissolved oxygen, pH) were measured in the field at several sites in each subestuary. Field-collected water samples were returned to the laboratory for further analyses (e.g., total suspended solids, nitrate-nitrogen [NO3-N], total nitrogen [Total N], and total phosphorus [Total P]).
Subtidal habitats were sampled in several projects. Benthic samples were collected using coring devices (e.g., Ekman Grab) and habitat assessments (e.g., amount of woody debris, presence of submersed aquatic vegetation, characteristics of adjacent shoreline) were conducted. Fish and crabs were sampled using Fyke nets and nearshore seining, and samples of white perch (Morone americana) were retained and analyzed for polychlorinated biphenyl (PCB) concentration.
Foraging waterbirds and birds that nested in brackish wetlands were sampled in the field as was wetland vegetation. Samples of common reed (Phragmites australis), an invasive wetland plant species, were collected in the field and analyzed in the laboratory for nitrogen content.
Results
Table 2 provides a summary of the estuarine indicators that could be related to land-use patterns. In some instances, the indicators responded to land-use patterns only at the watershed scale. In other instances, the indicators responded to land-use patterns at the scale of the entire watershed and at the local scale, especially conditions close to the subestuary. One indicator (wetland breeding birds) only responded to local land-use patterns. In two instances (PCBs in white perch and abundance of common reed), we were able to determine that indicators responded to conditions at the watershed scale but more strongly to the relationship between land-use conditions and proximity to the estuary.
Table 2. Estuarine Indicators Identified for Estuarine Segments of the Chesapeake Bay
Indicator | Watershed | Local Land Use |
Macrobenthic Indices | X | X |
Fish Community Index | X | X |
Abundance and leaf nitrogen content of Common Reed (Phragmites australis) | X | X |
Blue crab and bivalve abundance | X | X |
PCBs in White Perch (Morone americana) | X | |
Waterbird Community Integrity | X | X |
Marsh Bird Community Integrity | | X |
Submerged aquatic vegetation abundance | X | |
Blue Crab and Bivalve Abundance
The goal of this project was to explore relationships between regional (e.g., salinity), watershed (e.g., land use), and local (e.g., land use, water quality, habitat) factors on the abundance of blue crabs and species of Macoma, common clams that are blue crab prey.
A number of socioeconomic and ecological attributes make blue crabs (Callinectes sapidus) potentially ideal indicators of environmental conditions in estuarine ecosystems. Blue crabs are distributed throughout the Chesapeake Bay and other estuaries of the East and Gulf Coasts of North America and disperse across a wide range of salinities following settlement in the relatively high salinity zone. Blue crabs are highly prized by humans for food and are the most important commercial fishery in the mid-Atlantic region. As the dominant benthic predator and as prey for some larger predators, they also play a critical role in energy transfer in estuaries. Blue crabs feed intensively on bottom organisms living in the sediment, particularly clams, suggesting that the spatial distribution of blue crabs might be tied to natural and anthropogenic factors that affect the distribution and abundance of bivalve prey. In addition, blue crabs may be sensitive to anthropogenic shoreline modifications because natural nearshore habitats, such as woody debris and marsh creeks, are important for both juveniles and molting crabs as refuge from predation. Finally, blue crabs are sensitive to hypoxia (low dissolved oxygen concentrations): thus, their distribution may be influenced directly by cultural eutrophication commonly associated with developed and agricultural land use in watersheds.
Classification and Regression Tree (CART) analysis, a type of statistical analysis, indicated that 46 percent of the variance in blue crab abundance was explained by salinity (9%), watershed land use (17%), and shoreline marsh habitat (19%). Crab abundance was greatest at intermediate and higher salinities (> 16 ppt) but in lower salinities crabs were most abundant along wetland shorelines in forested and mixed land-use watersheds. Juvenile crabs less than 85 mm (~3 in) were more strongly associated with wetland shorelines, particularly in estuarine segments with forested and mixed land-use watersheds.
Clams (Macoma) were similarly associated with wetland shorelines but mainly in muddy bottoms at moderate-to-high salinities; however, the best CART model only explained 25 percent of variance in bivalve abundance. These results were consistent with predictions that shoreline wetlands and watershed land use may have important effects on these taxa along the estuarine salinity gradient and are consistent with hypotheses based on previous descriptive and experimental research linking blue crabs and deposit-feeding clams to habitats rich in particles of plant leaf pods, broken stems, and other organic matter worked in from the watershed
Within habitat characteristics (salinity, shoreline condition, substrate type, abundance of wetlands) are important factors influencing the abundance of blue crabs and clams. Land use at the scale of the entire watershed also is important, and the lowest abundances of both organisms occur in estuarine segments that are downstream of watersheds dominated by development and agriculture. Land use, therefore, can be used as an indicator of estuarine conditions, but the target organisms (blue crabs and clams) also could be monitored to track conditions within subestuarine habitats.
Abundance and Leaf Nitrogen Content of Common Reed (Phragmites australis)
We hypothesized that the distribution and abundance of Phragmites might be linked to land use through pathways at both local scales (e.g., disturbance, nitrogen enrichment, and salinity reductions caused by adjacent land use) and watershed scales (e.g., enhanced nitrogen availability in surface water linked to agricultural and developed land uses in adjacent watersheds). To test this hypothesis, we examined the relationship between Phragmites distribution and abundance data collected from 90 tidal wetlands located within 30 estuarine segments spanning over 250 km of the Chesapeake Bay to digital land-cover data summarized at both local and watershed scales. We also explored the potential linkage between land use and increased nitrogen availability at the watershed scale and Phragmites leaf-tissue nitrogen, an indicator of enrichment.
Phragmites australis is an invasive species in North America, particularly in the mid-Atlantic region, and an introduced species appears to be responsible for the recent spread. Phragmites’ impacts on wetlands ecosystems are considered to be negative, so control or eradication management practices often are used. What factors are responsible for Phragmites invasion and spread? Development of nearshore areas and within-wetland disturbances and increased nitrogen are associated with an increased abundance, cover, and spread of Phragmites in New England tidal wetlands. Tidal wetlands of the Chesapeake Bay also have seen marked increases in the occurrence and abundance of Phragmites. Less is known, however, about the process of invasion and spread in the Chesapeake Bay compared to the more comprehensively studied New England salt marshes.
The Chesapeake Bay watershed is urbanizing rapidly and is the fastest growing and culturally enriched coastal region in North America. Cultural eutrophication has been related to point and nonpoint source nitrogen inputs from agricultural and urban (developed) lands. Thus, given the mechanistic relationships reported elsewhere, the increase in anthropogenic nitrogen and shoreline disturbances caused by agricultural and developed land uses may be responsible at least partially for the expansion of Phragmites in the Chesapeake Bay. No previous study has empirically examined such relationships in this estuarine ecosystem, however, and no study in any region has examined linkages between land use and Phragmites among many wetlands spanning a geographical extent as great as that of the Chesapeake Bay.
For wetlands that had Phragmites, abundance was best explained by the following factors, in order of importance, by percent inverse distance weighted (%IDW) development, %IDW forested land, and northing or longitude. If %IDW development was greater than 15 percent, Phragmites abundance increased dramatically. When %IDW development was less than or equal to 15 percent, wetlands in estuarine segments with less than or equal to 34 %IDW forested land tended to have higher Phragmites abundance. Wetlands in the middle and northern regions of the Chesapeake Bay also had more Phragmites.
Examination of data for all 90 sites showed that Phragmites almost always was present when the watershed associated with the subestuary had less than 39 percent forested land cover. When watershed forest cover was more than 39 percent, abundance was higher in estuarine segments that had higher percentages of development near the subestuary.
Nitrogen concentration in leaves also was highest when %IDW developed land exceeded 14 percent. In 2002, a drought year with lower runoff into the estuaries, %N in estuarine segments with agricultural watersheds were not consistently higher compared to forested systems and were much lower compared to developed watersheds. In 2003, a wet year with higher runoff from agricultural fields, we found the same relationship between %IDW and %N, but leaf nitrogen concentration tended to be higher at sites with agricultural watersheds (i.e., higher values for bold bubbles).
Land use, especially the amount of development at the watershed and local scale, are important factors contributing to the abundance of Phragmites and the nitrogen content of leaves. Land use, therefore, can be used as an indicator of estuarine conditions, but the target species (Phragmites) also could be monitored to track conditions within subestuarine habitats.
Macrobenthos Indices
Our objective was to examine the influence of shoreline alteration and watershed land use on nearshore macrobenthic (organisms, visible without magnification, living on or in the sediment) communities using established indices for related estuarine environments.
Human modification within watersheds arguably has the strongest impact on aquatic condition at the land-water interface. Biotic multimetric indices have been used extensively as measures of condition in a variety of systems, most recently estuaries. The characterization of ecosystem condition using integrative indices was developed initially for, and applied in, freshwater systems. Multimetric biological indices, such as benthic indices of integrity, however, have shown promise as methods for assessing condition in estuaries because of their predictable and integrative response to stressors.
Benthic macroinvertebrates have a long history as indicator organisms because of the ease of collection, their immediate and measurable response to impairment, and the fact that they are mostly sedentary, consequently reflecting local conditions. Macrobenthic community indices have been applied successfully in estuarine systems and may be useful as condition or diagnostic indicators in the critical nearshore ecosystem.
Shallow-water tidal habitats provide essential nursery and spawning areas, protection from predators, and foraging opportunities for numerous fish, shellfish, and crustacean species. This critical resource area is under intense and increasing pressure from a variety of uses and users, and the impact of shoreline and watershed land use on nearshore biotic communities is a fundamental ecosystem management question. Evaluation of the ability of macrobenthic community indices to characterize the influence of shoreline alteration and watershed land use in nearshore estuarine environments could lead to the development of viable management tools.
Biotic responses were correlated with habitat condition along the shoreline and in the watershed, with the highest scores (i.e., best condition) associated with forested watersheds. Nonparametric changepoint (statistical) analyses indicated that ecological thresholds existed in response to developed land use at the site and watershed scale. There was a significant reduction in Benthic Biotic Index scores at the site and watershed levels when the amount of developed shoreline exceeded 10 percent and developed watershed exceeded 12 percent, respectively.
The addition of shoreline land-use information enhanced the discriminatory ability of the indices in a given landscape. In particular, the site-scale Benthic Biotic Index shows promise for elucidating gradients of condition within landscapes with varying degrees of shoreline alterations. Because shoreline forests and wetlands may diminish the effects of urban land use in localized areas, the inclusion of detailed, site-specific information may be indispensable for defining condition.
Nearshore macrobenthic communities responded to land-use conditions at local (site) and watershed scales. Index scores decreased with anthropogenic alterations to the landscape (e.g., developed watersheds), and thresholds were identified for shoreline and watershed developed land use (10% to 12%), beyond which a negative response in macrobenthic communities occurred. Watershed and shoreline land use may be effective integrative measures of stress that are able to infer the state of degradation in a system. The integration of shoreline and watershed land-use measures with macrobenthos indices can lead to practical management tools with particular application on small watershed scales.
Ecosystem approaches to condition assessment should incorporate a variety of indicators that measure different scales or types of stressors. The measure of prey community (e.g., macrobenthic) responses to habitat condition adds a layer of information about the nearshore system that will aid managers in prioritizing and targeting sites or watersheds for restoration or protection.
Fish Community Index (FCI)
The goal of this subproject was to develop and test fish community metrics in the nearshore Chesapeake Bay and evaluate relationships among fish communities and habitat condition assessed at multiple spatial scales (subtidal habitat, shoreline condition and watershed land use).
Fish community characteristics have been used since the early 1900s to measure relative ecosystem health. Within the last 20 years, advances have stemmed from the development of integrative measures of ecological condition, such as the IBI, which relates fish communities to abiotic and biotic conditions of the ecosystem. Fish community IBIs were developed first for use in freshwater, Midwestern streams, and subsequently modified for application in Great Lakes bays, reservoirs, streams, and large rivers throughout the United States and other countries. The common thread that connects the various IBIs is a multimetric approach, which describes biotic community structure and function and relates it to the ecosystem or habitat. The use of fish community-level response as an indicator affords many advantages: (1) high public interest; (2) multitrophic response that integrates aquatic condition; (3) assessment of both habitat and biotic condition as well as cumulative effects; (4) assessment of large-scale regional effects because of their mobility; (5) ease of identification onsite; and (6) availability of long-term monitoring data.
Estuarine systems are arguably some of the most complex aquatic systems. Their natural variability compounds the problems of detecting anthropogenic impacts. Until now, use of fish community IBIs in estuarine systems has been limited, with varying degrees of success. With growing recognition that effective management of estuarine systems can occur only at ecosystem levels, the need for further development of these metrics is accepted widely.
Within estuaries, nearshore habitat provides essential nursery and spawning areas, protection from predators, and foraging opportunities for numerous fish species. This critical resource area is under intense and increasing pressure from a variety of uses and users and generally exists without an operative comprehensive management plan. For instance, the cumulative impact of shoreline armoring has been demonstrated to reduce drastically available shallow-water habitat structure and associated fish communities. Evaluation of nearshore habitat and shoreline condition in conjunction with descriptions of biological communities may establish links between landscape and the biota lending guidance to managers. This association may provide the basis for development of a diagnostic indicator of estuarine condition. Biotic responses were correlated with habitat condition in the nearshore, shoreline, and watershed. Fish Community Index (FCI) scores were significantly lower in developed and agriculture watersheds than in watersheds dominated by forests, and there also were negative impacts associated with local land-use patterns and nearshore habitat conditions. The lowest average FCI scores were found in areas with highly altered shoreline conditions and minimal subtidal habitat. This is intuitive, because the direct biotic response may be a result of changes in nearshore habitat, with indirect impacts caused by watershed land use. These results are supported by recent studies describing the relationship between shoreline alteration and nearshore/littoral habitat condition.
Links among habitat conditions were substantiated in the relationships between subtidal habitat and shoreline condition, as well as shoreline and adjacent watershed land use. Shoreline condition and subtidal habitat measures were significantly correlated, indicating a negative available subtidal structural habitat. Dominant watershed land use was reflected in shoreline land-use conditions for all three of the categories (developed, agricultural, forested).
Habitat conditions at multiple spatial scales (subtidal habitat, shoreline condition, and watershed land use) are correlated with the FCI scores. These measures may be used as indicators of estuarine condition in addition to the biological functional response as reflected in the FCI. For instance, because correlations between habitat and biota were noted, if mechanistic processes can be determined and thresholds of response established, then shoreline condition surveys become an essential diagnostic management tool.
Marsh Bird Community Integrity
Our objective was to construct a community index based on marsh birds designed to estimate the integrity of the marsh bird community as well as to provide insight into the integrity of the entire marsh ecosystem. We used basic ecological principles to develop the index of marsh bird community integrity (IMBCI) and subsequently tested the sensitivity of marsh bird community integrity to independently quantified land-use disturbances.
Birds are considered ideal for use in a community index because they are easy to survey and their life histories are relatively well defined. Previous research has shown that birds are linked to the overall ecological integrity of their respective ecosystem. This is true primarily because birds are sensitive to habitat fragmentation, landscape composition, and changes in habitat structure. Birds also may be particularly good indicators because species at higher trophic levels can be sensitive to disturbances at lower levels. Therefore, it is unlikely that a marsh with low ecological integrity can support a high-integrity marsh bird community.
Wetland size had a significant influence on IMBCI scores. Changepoint (statistical) analysis revealed a changepoint or threshold occurred when more than 14 percent of the area within 500 m of the marsh was developed. IMBCI scores decreased significantly as the percent of developed area increased beyond 14 percent. In fact, there was 95 percent probability that IMBCI scores would decline when more than 14 percent of the area was developed and a 60 percent probability of a change occurring when as little as 6 percent of the land within 500 m of a wetland was developed. Changepoints were not detected significantly, however, when agriculture or forest land use were tested against IMBCI scores at the 500 m scale.
Changepoint analysis also revealed a 95 percent probability of a changepoint occurring with greater than or equal to 25 percent development within 1,000 m, with a 60 percent chance of a changepoint occurring when 8.5 percent of the 1,000-m buffer was developed. Again, changepoints were not detected for agriculture or forest land use at the 1,000-m scale. In addition, changepoints in IMBCI scores were not detected for percent development, agriculture, or forest at the watershed scale.
Changepoints identified in this study represent ecological thresholds, beyond which the ecological integrity of the marsh bird community and potentially the entire marsh ecosystem becomes significantly compromised. These relationships were identified only at relatively local scales (500-m and 1000-m buffers), so it appears that local land cover is the best predictor of marsh ecosystem integrity. Furthermore, our results indicate that developed land use is the primary stressor to marsh bird communities of the Chesapeake Bay.
We demonstrated that the IMBCI is a reliable indicator of marsh bird community integrity that may assist in the assessment of the integrity of the entire marsh ecosystem. IMBCI scores, combined with the identification of a land-use threshold, are interpreted easily and provide rapid assessment approaches for communicating complex ecological data to natural resource managers and conservation planners. By helping to bridge the gap between scientists and regional conservation decisionmakers, the IMBCI could become a valuable tool in the ongoing efforts of restoring and maintaining the ecological integrity of coastal wetlands.
Waterbird Community Integrity
We developed an index of waterbird community integrity (IWCI) to provide insight into estuarine ecosystem integrity and used it as a tool to: (1) determine land-cover types that influence waterbird community integrity; (2) identify relevant geographic scales at which land cover influences IWCI scores; and (3) test if ecological thresholds exist in the amount of land-cover disturbance that causes significant declines in IWCI scores.
We modified the IMBCI to develop the index of waterbird community integrity (IWCI). We defined waterbirds as all species that forage exclusively or opportunistically on aquatic estuarine organisms (i.e., gulls, terns, waders, raptors, kingfishers, and waterfowl). Theoretically, the waterbird community is an ideal indicator because it is at the top of the estuarine food web. Therefore, this indicator is potentially sensitive to stressors influencing the system at multiple trophic levels. Furthermore, as a community that is closely tied to a functioning subestuarine ecosystem, it has high potential as an indicator to be sensitive to stressors at both the watershed and local scales.
In 2002 and 2003, one single-predictor model, which included developed land cover, was a significant predictor of IWCI scores. Depending on the year, this model was between 13 and 26 times more likely to describe variation in IWCI scores than any of the seven remaining candidate models. Because development was the only predictor with strong support in both years, we focused subsequent analyses on this land use.
As total development increased, IWCI scores decreased significantly at the watershed, IDW, and 500 m scales in 2002 and 2003. Suburban development also had a significant negative impact on IWCI scores at the watershed, IDW, and 500 m scales for both years. The relationship between total development and IWCI scores was consistently stronger than the relationship between suburban land cover and IWCI scores. In addition, more variation was explained in IWCI scores when the two geographic scales emphasizing local land cover (IDW and 500 m) were used as predictors. Increasing urban land cover also led to lower IWCI scores in 2002 and 2003 at the watershed scale; however, the relationship between IWCI scores and the IDW and 500 m scales were not linear.
Changepoint analysis indicated that in 2002, when as little as 4 percent of the IDW land cover within a watershed was urbanized, there was a 94 percent probability of a threshold response in waterbird community integrity. When testing the 500 m buffer scale in 2002, we found that when 4 percent of land cover was urbanized within 500 m of the subestuary, there was an 85 percent probability of a threshold response in waterbird community integrity. In 2003, when 5 percent of IDW land cover was urban, it led to a 99.9 percent probability of a threshold. Finally, in 2003 we found that when there was as little as 5 percent urbanization within 500 m of the shoreline, it resulted in a 99.9 percent probability of a threshold occurring.
The IWCI clearly identified developed land cover as the primary stressor influencing waterbird community integrity. The waterbird community is particularly sensitive to urban development, as it exhibits a threshold response to alarmingly low levels of disturbance near the shoreline. From a management perspective, the threshold response to urban development at the IDW and 500 m buffer scales, offers clear management guidelines of how much coastal development estuarine ecosystems can tolerate before a collapse in ecological integrity can be expected. A compromised waterbird community, at the top of the estuarine food web, may have significant implications for the entire ecosystem through altered top-down food web relationships and controls.
PCBs in White Perch (Morone Americana)
The goal of this project was to develop statistical models that predict total PCBs (t-PCBs) in an economically and ecologically valuable fish species in the Chesapeake Bay using different types of urban land use from estuarine watersheds.
PCBs are a group of organochlorine compounds that resist degradation in the environment and are widely distributed in aquatic ecosystems. PCBs accumulate in fat-rich tissues of biota. Because of their toxicity, PCBs present a health risk to both humans and a variety of other organisms. Although PCBs were banned in the United States in 1979, PCB levels in many aquatic ecosystems remain sufficiently high to contaminate food webs and cause consumption advisories for a wide range of valuable fish and shellfish species.
Major sources of PCBs in estuaries are thought to be legacy pools of past point-source releases by manufacturing and from nonpoint sources associated with the general use, storage, and disposal of these persistent compounds. The sources, spatial extent, and magnitude of PCB contamination are not well characterized, however, and have proven difficult to predict, presumably because estuaries are hydrologically open systems affected by long-distance transport of contaminants from upstream and downstream areas. Some recent studies have successfully linked land use data from small estuarine watersheds to various sediment contaminants. Given that PCBs are known to be associated with industrial or other urban land uses, these previous findings suggested to us that quantification of land-use patterns in watersheds might be useful for predicting PCB contamination in downstream estuarine ecosystems.
We tested the hypothesis that the amount and spatial proximity of urban land in watersheds would be linked significantly to concentrations of t-PCBs in biota from estuarine segments of the Chesapeake Bay. We examined: (1) the strength of correlations between different measures of developed (urban) land in the watershed and t-PCBs; and (2) the relative improvement in our predictions of t-PCBs afforded by weighting urban land by its inverse distance from the shoreline to account for proximity to the estuarine segments. We focused on t-PCBs in white perch (Morone americana), a widely distributed estuarine fish that supports a valuable commercial and recreational fishery throughout the Chesapeake Bay. White perch are an ideal indicator species for detecting watershed linkages to PCBs because they spend most of their lives within or near specific estuarine segments. White perch also prey upon small fish and bottom-dwelling invertebrates, which are consumers of fine organic particles running off of the land and accumulating in sediments. Moreover, white perch are semianadromous, moving into freshwater tributaries to spawn with the young moving back down into the estuarine segments to find a nursery and feeding habitat, so their life cycle spans a zone that continuously exposes them to runoff from the watershed. Finally, because PCB-related consumption advisories have been posted recently for several estuarine segments and many other locations have yet to be assessed, there is great interest in developing geographical indicators of PCBs in this region.
All unweighted developed land-use measures were significant predictors of t-PCBs in white perch, explaining 51 percent to 69 percent of the variance among the 14 estuarine segments. Percent high residential/commercial land was the best predictor of t-PCBs among the unweighted developed-land-use classes.
IDW markedly improved the linear fit of each land-use predictor and t-PCBs in white perch among the 14 estuarine segments, and %IDW commercial land was the best predictor of t-PCBs of any of the models considered and accounted for nearly all of the variance (r2 = 99%).
Two estuarine segments had distinctly higher levels of t-PCBs than the other estuarine segments and may have had disproportionately strong effects on the regressions; so the effect of removing these two observations from the analysis was evaluated. All land-use classes remained significant predictors of t-PCBs using the reduced (n = 12) set of observations. In particular, inverse-distance weighted models for percent high-residential/commercial and percent commercial land exhibited large improvements in explaining variance over unweighted models. Percent high-residential/commercial and percent commercial land explained 87 percent and 86 percent of the variance in white perch t-PCB concentrations, respectively, among all predictors in the reduced data set.
Our study is novel because we demonstrated a remarkably strong relationship between the amount of developed land in watersheds, weighted by its proximity to the water, and PCBs in white perch across many tributaries of the Chesapeake Bay. No previous study has demonstrated such a relationship between watershed land use and contaminants in fish, particularly among multiple watersheds. Perhaps more importantly, we also showed that very little watershed development, particularly near shorelines, corresponded to levels of PCBs that were unsafe for human consumption. Thus, these findings were not limited just to highly urban areas, where we already know the water is badly polluted. Although PCBs have been banned since 1979, new consumption advisories for several fish species have been posted across many Chesapeake Bay tributaries because of PCBs, and these advisories have been big news for communities previously unaware of this problem. Our study suggests that PCBs historically produced and used in this region are persisting in the environment at the scale of these watersheds, and urban runoff still may be acting as a source of legacy PCBs to downstream aquatic habitats.
The relationships we discovered will be very important to managers because they may be used as tools for predicting areas that have a high probability of PCB contamination. Moreover, because many other contaminants are associated with development, these models likely will be very useful for identifying other types of contamination in estuaries. Many new contaminants still are in production and use, including flame retardants (PBDEs), metals, and emerging contaminants, such as pharmaceuticals, and may be related in a similar way to the amount and spatial proximity of development in watersheds.
The study also helped confirm that white perch may be an ideal species for assessing bioaccumulation of estuarine contaminants associated with watershed runoff because of its small home range on an individual level but broad distribution across a wide range of salinities that span the length of the Chesapeake Bay.
On a broader front, this study points to the importance of better understanding the impacts of development on estuaries. Our study highlights the implications of development on the health of aquatic ecosystems. It links environmental and ecological conditions in estuaries to land use in their associated watersheds. There may be other contaminants at unsafe levels in estuaries that we have yet to discover that are related to urbanization.
Bio-Optical Indicators
Communities of submersed aquatic vegetation (SAV) are highly valued habitats because of the functions they perform in coastal systems. These functions include, among others, provision of refuge and nursery habitat for juvenile fish, shellfish, and crabs; sediment stabilization; and food for certain waterfowl. Loss of valuable SAV habitat has been one of the most deleterious effects of pollution in numerous coastal systems along the Atlantic slope. Presence or absence of SAV is, therefore, a powerful indicator of estuarine water quality. Efforts to preserve and restore seagrasses have focused mainly on factors affecting water clarity, because of the inherently high light requirement of seagrasses. The attenuation of light in water is controlled by the concentrations of three parameters: suspended particulate matter, phytoplankton chlorophyll, and colored dissolved organic matter (CDOM). The goal was to develop an optically based indicator of habitat suitability for SAV and explore its variation with land use in the local watershed.
Concentrations of chlorophyll were higher in estuarine segments with developed watersheds, whereas CDOM was higher in segments with developed and mixed agricultural watersheds. Concentrations of total suspended solids were remarkably independent of land use in the local watershed, including the reference site. Specific-absorption coefficients were significantly higher in segments with developed and mixed-developed watersheds. Specific-scattering coefficients also were elevated somewhat in these land uses. Using these specific-absorption and -scattering coefficients in bio-optical modeling routines, we determined water quality thresholds (Figure 2; diagonal lines) that delineate conditions that will support SAV (low concentrations, points near the origin) from those that will not (concentrations falling outside the thresholds).
Figure 2. Water Quality Thresholds for SAV Growth in Estuarine Segments of Chesapeake Bay With Differing Land Use in Their Watersheds. Differences as development increased were caused by higher concentrations of CDOM as well as higher specific-adsorption and -scattering coefficients of suspended particulate matter.
Not only did estuarine segments with developed watersheds have higher concentrations of optically significant water quality constituents (especially chlorophyll), but the water quality requirements for segments with developed watersheds were considerably more stringent than less developed watersheds. The results imply that greater management effort is expected to be required to restore SAV in developed watersheds. Optical properties of the particulate matter and bio-optical modeling offer improved insight into mechanisms responsible for loss of SAV.
Technical Report:
Full Final Technical Report (PDF, 96pp., 2.88MB, about PDF)
Journal Articles on this Report : 5 Displayed | Download in RIS Format
Other subproject views: | All 37 publications | 6 publications in selected types | All 5 journal articles |
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Other center views: | All 166 publications | 51 publications in selected types | All 44 journal articles |
Type | Citation | ||
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DeLuca WV, Studds CE, Rockwood LL, Marra PP. Influence of land use on the integrity of marsh bird communities of Chesapeake Bay, USA. Wetlands 2004;24(4):837-847. |
R828684C001 (2004) R828684C001 (Final) |
not available |
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King RS, Richardson CJ. Integrating bioassessment and ecological risk assessment: an approach to developing numerical water-quality criteria. Environmental Management 2003;31(6):795-809. |
R828684 (2002) R828684C001 (2002) R828684C001 (Final) R828684C003 (2003) |
Exit Exit |
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King RS, Beaman JR, Whigham DF, Hines AH, et al. Watershed land use is strongly linked to PCBs in white perch in Chesapeake Bay subestuaries. Environmental Science & Technology 2004;38(24):6546-6552. |
R828684C001 (2004) R828684C001 (Final) |
Exit Exit |
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King RS, Baker ME, Whigham DF, Weller DE, Jordan TE, Kazyak PF, Hurd MK. Spatial considerations for linking watershed land cover to ecological indicators in streams. Ecological Applications 2005;15(1):137-153. |
R828684 (2002) R828684C001 (2004) R828684C001 (Final) R828684C003 (2003) |
Exit Exit |
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King RS, Hines AH, Craige FD, Grap S. Regional, watershed, and local correlates of blue crab and bivalve abundances in subestuaries of Chesapeake Bay, USA. Journal of Experimental Marine Biology and Ecology 2005;319(1-2):101-116. |
R828684C001 (2003) R828684C001 (2004) R828684C001 (Final) |
not available |
Supplemental Keywords:
indicators, integrated assessment, wetland, stream, estuary, watershed, biological integrity, decisionmaking, ecosystem, environmental exposure and risk, geographic area, ecology, ecosystem indicators, bioindicators, land use, mid-Atlantic, hydrology, estuarine ecosystems,, RFA, ENVIRONMENTAL MANAGEMENT, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, estuarine research, Water & Watershed, Ecosystem Protection, exploratory research environmental biology, Ecosystem/Assessment/Indicators, Ecological Effects - Environmental Exposure & Risk, Aquatic Ecosystems, Ecological Monitoring, Ecological Indicators, Risk Assessment, Watersheds, bioindicator, coastal ecosystem, degradation, water sheds, ecological risk assessment, biogeochemical study, estuaries, aquatic biota , ecosystem assessment, nutrients, integrated assessment, ecological assessment, ecosystem indicators, estuarine ecosystems, environmental indicators, environmental stress, coastal ecosystems, integrative indicators, water quality, ecology assessment models, watershed assessmentRelevant Websites:
Full Final Technical Report (PDF, 96pp., 2.88MB)
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828684 EAGLES - Atlantic Slope Consortium Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828684C001 Integrated Assessment of Estuarine Ecosystems
R828684C002 Development of an Optical Indicator of Habitat Suitability for Submersed Aquatic Vegetation
R828684C003 Integrated Assessment of Watersheds
R828684C004 Socioeconomic and Institutional Research
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
5 journal articles for this subproject
Main Center: R828684
166 publications for this center
44 journal articles for this center