Toward the Development of Nutrient Criteria for Streams of Pennsylvania
Open Access
- Author:
- Clune, John
- Graduate Program:
- Forest Resources
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 15, 2021
- Committee Members:
- Elizabeth Weeks Boyer, Dissertation Advisor/Co-Advisor
Elizabeth Weeks Boyer, Committee Chair/Co-Chair
Jay Richard Stauffer, Jr., Committee Member
Allyson Muth, Committee Member
Anil Kumar Chaudhary, Outside Member
J. Kent Crawford, Special Member
Bradley Cardinale, Program Head/Chair - Keywords:
- water quality
streams
Pennsylvania
nitrogen
phosphorus
biota response - Abstract:
- Nutrient pollution of surface waters is a widespread problem, calling for regional assessments of water quality conditions. Nutrients are the fifth leading cause of impairment to streams in Pennsylvania. Large amounts of nutrients from point and non-point sources can cause excessive algal growth, low dissolved oxygen concentrations, and reduce water quality for downstream waterbodies like the Chesapeake Bay, for which Pennsylvania is the leading contributor by jurisdiction for nitrogen (44%) and provides the second largest proportion of phosphorus (24%) to the estuary. Currently, important sources of nitrogen and phosphorus in Pennsylvania include inputs from agriculture (manure, fertilizers, and crop fixation), atmospheric deposition, wastewater, and runoff from developed land. Nutrient criteria for streams are required to be developed for each state in the United States. Despite longstanding USEPA recommendations and state efforts, numeric nutrient criteria have not yet been formalized for Pennsylvania and many other states. This is due in large part to the complex biological responses that are difficult to relate directly to nutrient concentrations in streams. The research described in this dissertation builds upon previous state and national efforts toward developing statewide nutrient criteria for streams in Pennsylvania. The purpose of this study is to: 1) quantify the spatial and seasonal variability of nitrogen and phosphorus in relation to land-use; 2) estimate statewide regional threshold concentrations for nutrient criteria for streams and compare those values to USEPA’s recommended values; and 3) explore which variables may be the best predictors of nutrients and ecological health in Pennsylvania streams. The results serve the needs of resource managers by providing a comprehensive synthesis of available nutrient data across multiple settings for comparison to background levels and regional nutrient criteria. Land use is a dominant driver of nutrient concentrations for streams in Pennsylvania. Using a multiagency statewide dataset, nutrient concentrations were shown to substantially increase with the percent of agricultural and developed land. Concentrations of TN in agriculture and TP in developed areas are 11 and 5 times greater (respectively) compared to undeveloped settings. Agricultural land in permeable geological settings (e.g., carbonate) present higher TN concentrations. Background concentrations from minimally impacted watersheds had a concentration of 0.42 mg/L for TN and 0.011 mg/L for TP. Overall, the use of the percentile approach overestimates background conditions in some ecoregions of Pennsylvania and should be used as a guide, because if used as a criterion the percent of sites exceeding the 25th percentile (53% for TN and 60 % for TP) would provide a weak foundation for criteria development without additional results from more robust approaches. Analysis of a more refined dataset of nutrients and multiple response variables showed the amplitude of diel DO concentrations was a meaningful indicator of stream metabolism conditions, but the strength of these relationships can vary by site and season. Incorporating available benthic sunlight with monitoring could provide more accurate stream metabolism estimates and better relations with nutrients. Diatom species that are indicators of low/high phosphorus concentrations coupled with multiple response variables indicate TP > 0.05 mg/L could be a guide to eutrophic impairment for streams in Pennsylvania and the Mid-Atlantic. Using several response variables will be essential to providing multiple lines of evidence towards developing useful and defensible numeric criteria in Pennsylvania. We suggest incorporating the response variables and analysis used in this study into the states multilevel approach for eutrophic cause determination in streams. As a next step, we also recommend the use of contemporary predictive approaches such as regression tree analysis coupled with modified structural equation modeling (SEM) using data and analysis from this study as a tool to evaluate a framework of stressor models for variables that best relate nutrients and ecological health in Pennsylvania streams.