Breakpoint analysis and relations of nutrient and turbidity stressor variables to macroinvertebrate integrity in streams in the Crawford-Mammoth Cave Uplands Ecoregion, Kentucky, for the development of nutrient criteria

Abstract

To assist Kentucky in refining numeric nutrient criteria in the Pennyroyal Bioregion, the U.S. Geological Survey and the Kentucky Division of Water collected and analyzed water chemistry, turbidity, and biological-community data from 22 streams throughout the Crawford-Mammoth Cave Upland ecoregion (U.S. Environmental Protection Agency Level IV Ecoregion, 71a) within the Pennyroyal Bioregion from September 2007 to May 2008. Statistically significant and ecologically relevant relations among the stressor (total phosphorus, total nitrogen, and turbidity) variables and response (macroinvertebrate-community attributes) variables and the breakpoint values of biological-community attributes and metrics in response to changes in stressor variables were determined. Thirteen of 18 macroinvertebrate attributes were significantly and ecologically correlated (p-value < 0.10) with at least one nutrient measure. Total number of individuals, Ephemeroptera-Plecoptera-Trichoptera richness, and average tolerance value were macroinvertebrate measures that most strongly correlated with the concentrations of nutrients. Comparison of the average macroinvertebrate-breakpoint value for the median concentration of total phosphorus (TP, 0.033 mg/L) and for median concentration of total nitrogen (TN, 1.1 mg/L) to Dodds' trophic classification for TP and TN indicates streams in the Crawford-Mammoth Cave Uplands ecoregion within the Pennyroyal Bioregion would be classified as mesotrophiceutrophic. The biological breakpoint relations with median concentrations of TP in this study were similar to the U.S. Environmental Protection Agency proposed numeric TP criteria (0.037 mg/L), but were 1.5 times higher than the proposed numeric criteria for concentrations of TN (0.69 mg/L). No sites were impacted adversely using median turbidity values based on a 25 Formazin nephelometric turbidity unit biological threshold. The breakpoints determined in this study, in addition to Dodds' trophic classifications, were used as multiple lines of evidence to show changes in macroinvertebrate community and attributes based on exposure to nutrients.

Assessment of nutrient enrichment by use of algal-, invertebrate-, and fish-community attributes in wadeable streams in ecoregions surrounding the Great Lakes

“…However, Miltner and Rankin (1998) found fish IBI scores in wadeable streams of Ohio significantly decreased at concentrations greater than 0.61 mg/L of TN, and Wang and others (2007) found a similar breakpoint for TN of around 0.60 mg/L. Crain and Caskey (2010) found multiple significant breakpoints between TP and invertebrate attributes between 0.032 and 0.035 mg/L in Kentucky.…”

“…There tended to be a wide range of breakpoints in most of the biological communities. In previous studies in Wisconsin (Robertson and others, 2008), Indiana (Caskey and others, 2010), and Kentucky (Crain and Caskey, 2010) the mean or median of breakpoints from several relations were used to determine the appropriate breakpoint for a specific State or ecoregion. In our study, instead of averaging the significant breakpoints for attributes of each biological community, the breakpoints for each biological community were associated with either low nutrient concentrations indicative of lower trophic levels (oligotrophic) or high nutrient concentrations indicative of higher trophic (eutrophic) levels.…”

Linking Soil Erosion to Instream Dissolved Phosphorus Cycling and Periphyton Growth

“…(2013) in a review of stream nutrient criteria development in the U.S., which presented P threshold values of between 0.006 and 0.074 mg/L. This value was also greater than the biological breakpoint with median concentrations of TP (0.033 mg/L) observed by Crain and Caskey (2010). Bowes et al (2007) reported a threshold of 0.090 mg P/L on the River Frome in the UK.…”

Identifying nutrient reference sites in nutrient-enriched regions-Using algal, invertebrate, and fish-community measures to identify stressor-breakpoint thresholds in Indiana rivers and streams, 2005-9

“…Previous studies in nutrient enriched areas, such as the Central and Western Plains diatom ecoregion in the Midwest (Frey and others, 2011) and Wisconsin (Robertson and others, 2008), found low breakpoints for TP in the range of 0.075 to 0.088 mg/L. Several studies have identified low TP thresholds ranging from 0.025 to 0.040 mg/L based on modeled background concentrations (Robertson and others, 2006), the 33rd percentile of stream concentrations (Dodds and others, 1998), or breakpoint analysis in Kentucky (Crain and Caskey, 2010) and Wisconsin (Robertson and others, 2006). The mean low TP breakpoint threshold in this study was higher than those previously reported in the area.…”