Steven G. Paulsen

MONITORING FOR POLICY‐RELEVANT REGIONALTRENDS OVER TIME

The term trend describes the continuing directional change in the value of an indicator, generally upward or generally downward. Many policy questions concern trend across a number of sites, such as lakes in a region, rather than trend at a single site. Power to detect regional trend seldom is discussed, and monitoring designs suitable for detecting such trends rarely are explored. Components of variance and temporal sampling designs play central roles in characterizing trend detection. We present relative numerical values of important components of variance, developed from the Surface Waters component of U.S. EPA’s Environmental Monitoring and Assessment Program (EMAP) field data, and use them as a basis for further assumptions of values. We discuss power curves in general and present them in relation to temporal designs, years of field observation, components of variance, and the level of trend detected. Revisit designs give adequate power for moderate trend in 10–15 yr, even when revisits are less frequent than annually.

Designing a Spatially Balanced, Randomized Site Selection Process for Regional Stream Surveys: The EMAP Mid-Atlantic Pilot Study

In 1993, the U.S. Environmental Protection Agency (EPA), as part of the Environmental Monitoring and Assessment Program (EMAP), initiated a sample survey of streams in the mid-Atlantic. A major objective of the survey was to quantify ecological condition in wadeable streams across the region. To accomplish this goal, we selected 615 stream sites using a randomized sampling design with some restrictions. The design utilized the digitized stream network taken from 1:100,000-scale USGS topographic maps as the sample frame. Using a GIS, first- through third-order (wadeable) stream segments in the sample frame were randomly laid out in a line and sampled at fixed intervals after a random start. We used a variable probability approach so that roughly equal numbers of first-, second-, and third-order stream sites would appear in the sample. The sample design allows inference from the sample data to the status of the entire 230,400 km of wadeable stream length in the mid-Atlantic study area. Of this mapped stream length, 10% was not in the target population because no stream channel existed (4%), the stream channel was dry (5%), or the stream was not wadeable (1%). We were unable to collect field data from another 10% of the mapped stream length due to lack of access (mostly landowner denials). Thus, the field data we collected at 509 sites allows inference to the ecological condition for 184,600 km of the mapped stream length in the region.

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.

Striving for consistency in a national assessment: the challenges of applying a reference-condition approach at a continental scale

Abstract One of the biggest challenges when conducting a continental-scale assessment of streams is setting appropriate expectations for the assessed sites. The challenge occurs for 2 reasons: 1) tremendous natural environmental heterogeneity exists within a continental landscape and 2) reference sites vary in quality both across and within major regions of the continent. We describe the process used to set expectations for the multimetric index of biotic integrity (MIBI) and observed/expected (O/E) indices generated from predictive models used to assess stream condition for the US Wadeable Streams Assessment (WSA). The assessment was based on a reference-site approach, in which the least-disturbed sites in each region of the US were used to establish benchmarks for assessing the condition of macroinvertebrate assemblages at other sites. Reference sites were compiled by filtering WSA sample sites for disturbance using a series of abiotic variables. Additional reference sites were needed and were obtained from other state, university, and federal monitoring programs. This pool of potential reference sites was then assessed for uniformity in site quality and comparability of macroinvertebrate sample data. Ultimately, 1625 sites were used to set reference expectations for the WSA. Reference-site data were used to help define 9 large ecoregions that minimized the naturally occurring variation in macroinvertebrate assemblages associated with continental-wide differences in biogeography. These ecoregions were used as a basis for developing MIBI and O/E indices and for reporting results. A least-disturbed definition of reference condition was used nationally, but we suspect that the quality of the best extant sites in ecoregions, such as the Northern Plains and Temperate Plains, was lower than that of sites in other ecoregions. For the MIBI assessment, we used a simple modeling approach to adjust scores in ecoregions where gradients in reference-site quality could be demonstrated conclusively. The WSA provided an unparalleled opportunity to push the limits of our conceptual and technical understanding of how to best apply a reference-condition approach to a real-world need. Our hope is that we have learned enough from this exercise to improve the technical quality of the next round of national assessments.

The role of sample surveys for monitoring the condition of the nation's lakes

In order to meet a growing need to determine the condition of the nations ecosystems and how their condition is changing, the U.S. Environmental Protection Agency (EPA) developed EMAP, the Environmental Monitoring and Assessment Program. A common survey design serves as the foundation on which to base monitoring of status and trends among diverse ecosystem types. In this paper, we describe the need for a statistically based survey design, briefly summarize the basic EMAP design, describe how that design is tailored for the selection of a probability sample of lakes on which to make measurements of lake condition, and illustrate the process for selecting a sample of lakes in the northeastern United States. Finally, we illustrate how measurements taken on the sample of lakes can be summarized, with known uncertainty, to describe the condition of a population of lakes.

EMAP-Surface Waters: a multiassemblage, probability survey of ecological integrity in the U.S.A.

Data analyzed at national, multistate or state scales often reveal more serious deterioration of various biological assemblages than that suspected from site specific studies simply because the impacts are observed regionally rather than locally. Unfortunately many regional assessments are based on data collected with differing sampling designs and methods, making their representativeness, accuracy and precision questionable. In 1989, the United States Environmental Protection Agency (USEPA) began EMAP-Surface Waters (EMAP-SW), a program for developing methods to monitor and assess status and trends in the nations lakes and rivers in a statistically and ecologically rigorous manner. EMAP-SW has now conducted regional multistate pilots in streams and rivers throughout the U.S.A. in collaboration with State agencies, universities and EPA regional offices. We discuss EMAPs conceptual design, which focuses on biological integrity through use of multiple biological assemblages and includes physical and chemical habitat and landscape characteristics. When coupled with appropriate biological indicators, a probability-based design enabled us to provide accurate, precise and unbiased assessments of biological conditions, along with quantitative estimates of sampling uncertainty. Regional EMAP-SW surveys indicated the importance of assessing multiple biological assemblages because each assemblage was differentially sensitive to different stressors and at different spatial scales. Synthesizing multiple metrics from multiple assemblages allowed us to detect the effects of multiple anthropogenic disturbances. We also illustrate the value of using historical reconstruction and paleolimnological data for determining reference conditions where disturbance is extensive. We conclude that an EMAP approach to sampling design and indicators (recognizing natural ecoregional differences) has distinct advantages for monitoring and assessments that may be applicable to European Communities seeking to assess the ecological integrity of waters.

Indicators of Ecological Stress and Their Extent in the Population of Northeastern Lakes: A Regional-Scale Assessment

Article reporting findings from the Environmental Protection Agency (EPA)s Environmental Monitoring and Assessment Program (EMAP) conducted on a sample of lakes in the Northeastern United States from 1991 to 1996.

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.

Assessing the attributable risks, relative risks, and regional extents of aquatic stressors

Abstract A major goal of the national aquatic surveys being conducted by the Environmental Protection Agency in partnership with the states and tribes is to assess the relative importance, at a regional scale, of stressors that impact aquatic biota. The Wadeable Streams Assessment (WSA) was a prototype of these surveys, and it assessed 8 individual water-chemistry, physical-habitat, and landuse stressors in 2 ways. First, the WSA estimated the total length of streams in a region that was deemed to be in poor condition for each stressor considered separately. Estimates of stressor extent describe the prevalence and regional breadth of each stressors potential effects. Second, the WSA estimated each stressors relative risk, a measure widely used in human epidemiology. Relative risk estimates a stressors association with biota in terms of the likelihood that poor stressor conditions and poor biota conditions co-occur in a regions streams. We describe how the population attributable risk, also borrowed from epidemiology, combines extent and relative risk into a single, overall measure of a stressors regional effect. The attributable risk of a stressor is the % reduction in the regional extent of poor biological condition (measured here by the macroinvertebrate index of biotic integrity [MIBI]), that presumably would result from eliminating that stressor. Under the attributable risk assumptions, for example, the WSA data imply that the nationwide extent of poor MIBI conditions would be reduced by an estimated 26% if excess total P were eliminated as a stressor, but only by 3% if excess salinity were eliminated. We also illustrate the attributable risk for the combined effects of multiple, correlated stressors. Last, we discuss how best to interpret and apply attributable risk estimates.

The need to assess the condition of aquatic resources in the US

Abstract In 1972, the US Congress enacted the Clean Water Act (CWA) to protect US water resources. A critical section (305[b]) of the CWA calls for periodic accounting of the success or failure of efforts to protect and restore US waters. Over the years, several groups have reviewed the available data and concluded that they do not adequately describe the condition of US waters. The Wadeable Streams Assessment presents the first set of results from what will be a long-term partnership between the US Environmental Protection Agency, the individual states, tribal nations, and other federal agencies. The goal of this partnership is to fill critical information gaps that remain a deterrent to our ability to determine whether our policies and investments have resulted in improvement of US water resources.