The ASTERS Project
Alternate States, Thresholds, & Ecosystem Resilience in Streams
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Project Description

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Bob Hilderbrand Webpage

Welcome to the ASTERS project page. We will be adding to the page frequently, so check back periodically for updates on progress and results. 

Project Description:

The ASTERS project is an investigation into stressor thresholds, ecosystem resilience, and alternate states in stream ecosystems in Maryland.  It is a research program funded by the EPA STAR (Science To Achieve Results) program and the National Park Service and builds on several previous research and survey efforts funded by the National Park Service National Capital Region, the National Park Service Water Resources Program, the National Park Service Natural Resources Preservation Program, and the Maryland Biological Stream Survey (MBSS).  The project is a blend of theory and application and strives to better predict how, when, and where streams move from a desired condition into an undesired, degraded state.  These various states are idealized in our logo at the top of the page.  We have a number of goals that include:

  • Developing methods to predict the likelihood and identity of stressors that degrade streams
  • Predicting stressor levels within streams and watersheds given landscape-level information
  • Predicting stream condition and aquatic community structure given watershed and landscape variables
  • Develop a catalog of taxon-specific responses to potential stressors
  • Developing methods to quantify resilience of streams of varying types to stressors
  • Identify and characterize alternate states of stream ecosystem organization
  • Create stream vulnerability maps in relation to human actions
  • Predict changes in stream condition and aquatic community structure to changes in human population growth in Maryland and its neighbors.

Background:

Because water flows downhill, even actions far away from flowing streams have the potential to impact our waterways and possibly degrade our streams and the fish and other organisms that live in them.  The good news is that streams can be incredibly resilient to some stressors, and larger waters such as the North Branch of the Potomac River and the Youghiogheny River have made substantial recoveries compared to their condition in the middle of the 20th century.  However, the nature of the stressors has been changing, and we are in an age of deteriorating stream quality across the state and even across the country.  The Maryland Biological Stream Survey reports that nearly 50% of all wadeable streams are in poor to very poor condition and only around 20% are in good condition.  Stream assessments nationwide follow this general trend as well. As stream quality degrades, the animal communities (fish & invertebrates) can make dramatic and semi-premanent shifts in their structure.  As this happens, we lose recreational opportunites for fishing or general enjoyment.  In extreme examples, streams may lose all fishes and most of the invertebrates, essentially becoming little more than a pipe that connects the land with the Chesapeake Bay.

Approach:

Our approach is to use the long-term and extensive Maryland Biological Stream Survey (MBSS) dataset to identify patterns in community structure across the state of Maryland. Because the MBSS has 1400+ samples, we can use a space-for-time substitution across the land use gradient to model and predict how streams will change as the land use in the watershed changes.  The MBSS program collects quantitative information on fish, benthic invertebrates, and water chemistry as well as local habitat information.  More detailed information on the MBSS can be found here.  

We are analyzing responses of both organisms and entire communities to land use and landscape changes.  The main approach for organism-specific responses is to determine thresholds for presence/absence or abundance to specific stressors and land uses.  The approach for community responses and the identification of alternate states is to reduce the multitude of taxa to a few dimensions using nonmetric multidimensional scaling (NMDS) and derive confidence intervals within the NMDS axis scores for reference sites. Non-reference sites that fall within the bounds of the confidence envelope are  no different from the reference condition.  However, sites outside of the confidence envelope are organizationally different - we assume that non-member sites are degraded and have lost the self-organizing structures of reference state sites.  The figure to the right represents an idealized depiction of several alternate states.  The blue center represents the reference, intact system state in a multivariate context, whereas the red ellipses represent distinct alternate and degraded states. Of course the actual patterns are not nearly so clear or pretty.  Our initial results show a high correlation between a site's distance outside of the confidence envelope and the degree of impairment as assessed with an Index of Biotic Integrity.  Since NMDS typically orders sites along underlying environmental gradients, we expect that directionality in the non-member sites will provide insight into underlying stressors influencing community structure.  Our analyses are being carried out for both taxonomic structure and for function (trophic status).

By measuring the suite of site responses in the NMDS to various potential stressors, we can measure the resilience of different types of streams to varying potential stressors.  The natural extension will be to develop stream vulnerability maps for each type of stream.
Page Created by Bob Hilderbrand   Last updated 3/18/2006