David Peck

Condition of stream ecosystems in the US: an overview of the first national assessment

Abstract The Wadeable Streams Assessment (WSA) provided the first statistically sound summary of the ecological condition of streams and small rivers in the US. Information provided in the assessment filled an important gap in meeting the requirements of the US Clean Water Act. The purpose of the WSA was to: 1) report on the ecological condition of all wadeable, perennial streams and rivers within the conterminous US, 2) describe the biological condition of these systems with direct measures of aquatic life, and 3) identify and rank the relative importance of chemical and physical stressors affecting stream and river condition. The assessment included perennial wadeable streams and rivers that accounted for 95% of the length of flowing waters in the US. The US Environmental Protection Agency, states, and tribes collected chemical, physical, and biological data at 1392 randomly selected sites. Nationally, 42% of the length of US streams was in poor condition compared to best available reference sites in their ecoregions, 25% was in fair condition, and 28% was in good condition. Results were reported for 3 major regions: Eastern Highlands, Plains and Lowlands, and West. In the West, 45% of the length of wadeable flowing waters was in good condition. In the Eastern Highlands, only 18% of the length of wadeable streams and rivers was in good condition and 52% was in poor condition. In the Plains and Lowlands, almost 30% of the length of wadeable streams and rivers was in good condition and 40% was in poor condition. The most widespread stressors observed nationally and in each of the 3 major regions were N, P, riparian disturbance, and streambed sediments. Excess nutrients and excess streambed sediments had the highest impact on biological condition; streams scoring poor for these stressors were at 2 to 3× higher risk of having poor biological condition than were streams that scored in the good range for the same stressors.

Acquiring data for large aquatic resource surveys: the art of compromise among science, logistics, and reality

Abstract The US Environmental Protection Agency (EPA) is revising its strategy to obtain the information needed to answer questions pertinent to water-quality management efficiently and rigorously at national scales. One tool of this revised strategy is use of statistically based surveys of aquatic resources such as lakes, wetlands, rivers, and streams. Implementing large-extent surveys involves decisions that reflect compromises between scientific rigor, consistent and practical implementation over large areas and many participants, and the realities of time and money. Primary constraints result from interactions among management objectives, time lines, funding, and institutional constraints of participants. Secondary constraints arise from the interaction between the survey design (geographic extent, sample size, use of existing data), logistics (sampling period, sample shipping, information management, crew expertise, field training), and the suite of ecological indicators selected (site-scale sampling design, field and laboratory protocols). We use our experience with the EPAs national Wadeable Stream Assessment and its Environmental Monitoring and Assessment Program Western Pilot Study to describe the key constraints and the resulting decisions made to implement those surveys successfully. The experiences from those surveys offer perspectives and information useful for effectively implementing future surveys of similar scope or spatial extent, including advanced planning, compatible survey designs, consistent methods, indicators, and cooperative research.

Survey design and extent estimates for the Wadeable Streams Assessment

Abstract The US Environmental Protection Agency (EPA) conducted a Wadeable Stream Assessment (WSA) of all wadeable streams and rivers in the conterminous US between 1999 and 2005. The assessment was led by the EPA Office of Water, in cooperation with EPA regions, states, tribal nations, and the EPA Office of Research and Development (ORD). The WSA was implemented as 2 large-scale regional surveys of streams and rivers. Both studies used EPAs River Reach File (RF3) as the basis for the sample frame. The Environmental Monitoring and Assessment Program (EMAP) Western Pilot Study, conducted by ORD in cooperation with EPA Regions 8, 9, and 10 and 12 western states, assessed all streams and rivers in the 12 western states (EMAP-West). A stratified, unequal probability survey design (50 sites/state and additional sites in 5 intensive study areas) was used to select sites from all streams and river segments coded as perennial in RF3. The unequal selection depended on Strahler order, aggregated Omernik level III ecoregion, and special study region. The WSA study used the EMAP-West wadeable streams (WSA-West) and implemented a new design for the remaining 36 eastern conterminous states (WSA-East). The WSA-East design was an unequal probability survey design with unequal selection depending on Strahler order, Omernik Level II ecoregion, and EPA region. RF3 includes 5.29 million km of rivers and streams, of which 39% (2.07 million km) are coded as perennial. The WSA sample frame included 2.84 million km of streams (54% of the total length in RF3), of which 2.24 million km were in WSA-East and 0.60 million km were in WSA-West. Each selected site was classified on the basis of wadeability and the presence of flowing water. The estimated length of wadeable streams and rivers in the 48 conterminous states was 1.30 ± 0.025 (SE) million km (45.7 ± 1.1% of the stream length in the sample frame). Of this wadeable stream length, 78.6 ± 1.0% (1.02 million km) was estimated to be appropriate for sampling. Nationally, 11.5 ± 0.8% and 5.2 ± 0.6% of this length could not be sampled because of access denial or physical inaccessibility, respectively. The proportion of length affected by access denial was higher in Southern Plains, Northern Plains, and Xeric West aggregated ecoregions, whereas stream length affected by physical inaccessibility was greatest in the Western Mountains aggregated ecoregion. Improvements in the sample frame (RF3 and its successors National Hydrography Database [NHD] and NHD-Plus) would reduce field costs for national surveys.

Continental-Scale Increase in Lake and Stream Phosphorus: Are Oligotrophic Systems Disappearing in the United States?

We describe continental-scale increases in lake and stream total phosphorus (TP) concentrations, identified through periodic probability surveys of thousands of water bodies in the conterminous U.S. The increases, observed over the period 2000-2014 were most notable in sites in relatively undisturbed catchments and where TP was initially low (e.g., less than 10 μg L(-1)). Nationally, the percentage of stream length in the U.S. with TP ≤ 10 μg L(-1) decreased from 24.5 to 10.4 to 1.6% from 2004 to 2009 to 2014; the percentage of lakes with TP ≤ 10 μg L(-1) decreased from 24.9 to 6.7% between 2007 and 2012. Increasing TP concentrations appear to be ubiquitous, but their presence in undeveloped catchments suggests that they cannot be entirely attributed to either point or common non-point sources of TP.

Twelve invasive plant taxa in US western riparian ecosystems

Abstract Assessments of stream ecosystems often include an evaluation of riparian condition; a key stressor in riparian ecosystems is the presence of invasive plants. We analyzed the distribution of 12 invasive taxa (common burdock [Arctium minus], giant reed [Arundo donax], cheatgrass [Bromus tectorum], musk thistle [Carduus nutans], Canada thistle [Cirsium arvense], teasel [Dipsacus fullonum], Russian olive [Elaeagnus angustifolia], leafy spurge [Euphorbia esula], English ivy [Hedera helix], reed canarygrass [Phalaris arundinacea], Himalayan blackberry [Rubus armeniacus], and saltcedar [Tamarix spp.]) to characterize a portion of that stressor. Observations from 961 probability survey reaches and 355 additional reaches distributed across 12 western US states provided a statistically defensible foundation for trend monitoring, risk assessments, or economic evaluation of these 12 taxa over a large area. We estimate that ≥1 of these taxa are present in riparian areas on 47 ± 3.6% of the perennial stream length in the western US. One or more of these taxa were present in >⅓ of the reaches identified as least-disturbed (reaches that define reference condition and are used to quantify instream biotic integrity). Association between target invasive presence and instream biotic integrity varied, particularly as a function of ecoregion. Relationships were often statistically significant in the Mountain climatic region, sometimes significant in the Xeric climatic region, and never significant in the Plains climatic region. Regional variations in associations and confounding relationships between multiple factors suggest that multiple variables should be examined to explain or predict the presence of invasive species or their associations. Our survey illustrates strengths and limitations of collecting information on a limited number of invasive plants in riparian vegetation as part of general probability surveys of aquatic ecosystems. Our survey of only 12 somewhat arbitrarily selected invasive plants provided much information for a limited cost. We recommend including similar efforts in future surveys.

Survey design and extent estimates for the National Lakes Assessment

Abstract.  The US Environmental Protection Agency (USEPA) conducted a National Lakes Assessment (NLA) in the conterminous USA in 2007 as part of a national assessment of aquatic resources. The EPA used the National Hydrography Dataset (NHD) as the basis for the sample frame for the NLA. The target population was all lakes >4 ha, excluding the Laurentian Great Lakes and the Great Salt Lake. An unequal probability survey design was used to select 4472 candidate lakes for potential sampling. The unequal selection depended on 5 lake area classes and 9 aggregated Omernik level III ecoregions. In all, 2034 candidate lakes were evaluated for inclusion in the target population, and 1309 lakes (representing ∼68,000 lakes in the sample frame) met the criteria. A total of 1028 lakes (of 1309) were sampled and represented ∼50,000 lakes. The remaining lakes (231, representing ∼18,000 lakes) could not be sampled because of access denial or physical inaccessibility. The target population included natural (41 ± 2% [SE]) and man-made lakes (59 ± 2%). All target lakes in the Southern Appalachian region and >90% of the target population in the Southern Plains and Xeric regions were man-made. In the Upper Midwest region, 97 ± 1% of the target population were natural lakes. Small lakes (4–10 ha) made up 47 ± 2% of the target population, and lakes >50 ha made up ∼15% of the target population. The results raise 2 issues that have implications for current and future NLA projects: 1) the cost and effort required to identify lake features in the sample frame that do not meet the criteria for inclusion in the target population (∼50% in NLA 2007), and 2) the potential for biased estimates of the size and condition of the target population caused by lakes that cannot be sampled. Future NLA efforts involve refining the survey design to include smaller lakes and resampling lakes from previous NLAs. We offer approaches for addressing both issues, including use of a high-resolution version of NHD as the basis for developing the NLA sample frame. Developing a master sample frame of lakes would provide a consistent basis of lake numbers (or surface area) from which to estimate extent or assess ecological condition.

Mapping watershed integrity for the conterminous United States

Watershed integrity is the capacity of a watershed to support and maintain the full range of ecological processes and functions essential to sustainability. Using information from EPAs StreamCat dataset, we calculated and mapped an Index of Watershed Integrity (IWI) for 2.6 million watersheds in the conterminous US with first-order approximations of relationships between stressors and six watershed functions: hydrologic regulation, regulation of water chemistry, sediment regulation, hydrologic connectivity, temperature regulation, and habitat provision. Results show high integrity in the western US, intermediate integrity in the southern and eastern US, and the lowest integrity in the temperate plains and lower Mississippi Valley. Correlation between the six functional components was high (r = 0.85-0.98). A related Index of Catchment Integrity (ICI) was developed using local drainages of individual stream segments (i.e., excluding upstream information). We evaluated the ability of the IWI and ICI to predict six continuous site-level indicators with regression analyses - three biological indicators and principal components derived from water quality, habitat, and combined water quality and habitat variables - using data from EPAs National Rivers and Streams Assessment. Relationships were highly significant, but the IWI only accounted for 1-12% of the variation in the four biological and habitat variables. The IWI accounted for over 25% of the variation in the water quality and combined principal components nationally, and 32-39% in the Northern and Southern Appalachians. We also used multinomial logistic regression to compare the IWI with the categorical forms of the three biological indicators. Results were consistent: we found positive associations but modest results. We compared how the IWI and ICI predicted the water quality PC relative to agricultural and urban land use. The IWI or ICI are the best predictors of the water quality PC for the CONUS and six of the nine ecoregions, but they only perform marginally better than agriculture in most instances. However, results suggest that agriculture would not be appropriate in all parts of the country, and the index is meant to be responsive to all stressors. The IWI in its present form (available through the StreamCat website; https://www.epa.gov/national-aquatic-resource-surveys/streamcat) could be useful for management efforts at multiple scales, especially when combined with information on site condition. The IWI could be improved by incorporating empirical or literature-derived relationships between functional components and stressors. However, limitations concerning the absence of data for certain stressors should be considered.