Executive Summary
This report presents results from “An Initial National Assessment of the Status of Fish Habitats,” an effort being conducted in support of the National Fish Habitat Action Plan (NFHAP). The impetus for this effort stems from one of the initial objectives of the NFHAP, which is to perform a comprehensive and objective condition assessment of all fish habitats within the United States by 2010 with periodic assessments thereafter. This report presents the results of the initial assessment of landscape condition in streams and rivers of the conterminous United States.
Two principal products have been generated as part of the Initial Assessment. The first is a spatial framework that allows for the organization and summary of information at multiple spatial levels. This spatial lanframework is based on stream reaches of the National Hydrography Dataset Plus (NHDPlus) and their associated local catchments as fundamental spatial units. By associating reaches and local catchments with the larger spatial units in which they are located (e.g., network catchments, hydrologic units, ecoregions, states, etc.), the spatial framework provides the flexibility to summarize information at any scale of potential use for different management purposes. The second product generated as part of this effort, and the main focus of this report, is an initial assessment of relative landscape disturbance levels in the catchments of rivers. For approximately 2.25 million stream reaches in the conterminous United States, assessment scores were calculated that estimate the relative degree of landscape impairment. In taking these initial steps, we have laid the groundwork for improved methods to be applied and results to be developed through 2010 and beyond.
Highlights of the Science behind the Assessment
The initial assessment is based on a landscape approach, which asserts that both natural catchment characteristics (i.e., climate, geology, topography, etc.) and anthropogenic landscape factors (i.e., land uses, roads, dams, etc.) control habitat characteristics of aquatic systems draining those catchments. The landscape approach has been well-supported by numerous scientific studies and has multiple advantages for this National assessment effort. First, landscape-level data are available nation-wide, providing continuous coverage that may be applied to every aquatic system in the study region, thus eliminating the need for sub-sampling or extrapolation. Second, using a landscape approach allows us to focus directly on the sources of impairment such as agricultural or urban land uses, water withdrawals, and high human population density, as opposed to symptoms that could originate from multiple causes. With information on the locations and severities of human activities known to degrade aquatic habitat and with the ability to summarize our results at multiple spatial scales, our assessment results can provide managers and decision makers with information for identifying protection, rehabilitation or enhancement opportunities.
Assessment Process and Results
We used a multivariate analytical approach to integrate a suite of variables into a single, cumulative measure of human disturbance for each stream reach in our study region. Using principal components analyses, we distilled a landscape disturbance data set with 17 human disturbance variables into a few composite disturbance axes that describe most of the variation in these variables within catchments of stream reaches. We then calculated integrated local and network measures of disturbance. This was accomplished by weighting the individual disturbance axes according to their influence on freshwater fishes, and then summing these into indices of local and network catchment disturbance. As a final step, we combined local and network disturbance indices into a single, cumulative landscape disturbance index for each reach in our study region. To do this, the two index values in each reach were weighted to reflect the influence that disturbances in local vs. network catchments have on fish communities in streams of different sizes.
Our cumulative disturbance index, scaled from 0 to 100 with high scores indicating greater disturbance, reflects the combined level of landscape disturbance in local and network catchments of the stream reaches in our study region. Eighty percent of reaches scored less than 38, with a mean cumulative disturbance score of 26. A national map of scores shows highest levels of disturbance near areas with extensive urban land and agriculture, and indicates a majority of highly disturbed habitats occur east of the Mississippi River with patches of disturbed habitat also occurring in Texas, Nebraska, Idaho, the California coast and central valley, and areas near Portland Oregon and Seattle Washington. We also show the utility of our spatial framework by summarizing cumulative landscape disturbance scores in 44 freshwater ecoregions defined by the World Wildlife Fund as well the 48 states in the conterminous USA, providing managers and decision makers working at smaller spatial scales with the ability to compare disturbance level in their region of interest to others nationally.
Future Directions
Through 2010, we will improve upon results of the initial assessment by incorporating additional existing landscape-level information describing disturbances and by evaluating the degree to which in-stream characteristics – including specific habitat measures and various biological metrics – respond to our cumulative human disturbance gradients. We will also attempt to enhance the way that connectivity loss and hydrologic alteration from dams is considered in the national assessment. This knowledge will allow us to refine assessment results and will provide greater insights into ways in which landscape factors may be affecting systems nationally. We will complete assessments for Alaska and Hawaii and will develop a plan that will allow us to incorporate lakes and reservoirs into our national assessment effort. We are also working with a team from NOAA to link their assessment of nearshore coastal regions with our inland work. Together, this information will provide the most comprehensive and integrated picture of the current condition of the Nation’s water bodies yet completed as it will examine from the mountain peaks to the marine pelagic zone.
Beyond 2010, we have identified a number of opportunities for improvement of the inland assessment and its utility for national prioritization of habitats for protection, rehabilitation, and enhancement. Information generated by Partnerships will provide higher resolution data in their regions than what may be available nationally, and the ability to link such information into the National assessment through the assessment framework will provide enhanced understanding of current conditions in Partnership regions. Also, with data and approaches for working at the national scale in place, we have the ability to better capture process-response relationships between landscape factors and detailed local habitat variables and fishes. Finally, while our assessment estimates current condition of catchments that influence aquatic systems, we see the potential value of integrating future threats, including projected changes in land use and climate, which would allow managers to consider system vulnerability along with current condition.
Dana Infante, Peter Esselman, and Lizhu Wang
July, 2009