ABSTRACT Nutrient Enrichment Effects on Stream Periphyton Stoichiometry, Algal and Fish Assemblage Structure, and Grazing Fish-Periphyton Interactions Jason M. Taylor, Ph.D. Committee Chairperson: Ryan S. King, Ph.D. Anthropogenic inputs of nitrogen (N) and phosphorus (P) create novel environmental conditions that alter biological organization and ecosystem functioning in freshwaters. My research objectives were: 1) identify levels of nutrient enrichment thresholds for stream periphyton nutrient ratios, individual algal and fish species abundances, and overall assemblage composition; 2) experimentally investigate interactions between P enrichment, an important grazing fish, and periphyton biomass and elemental composition; and 3) examine the influence of nitrogen enrichment on fish- mediated nutrient recycling effects on downstream ecosystem structure and function. Analyses of field collected data indicated that sharp declines in periphyton elemental composition, a synchronous decline in several algal species, and sharp declines in at least two benthic specialist fishes (Etheostoma spectabile and Campostoma anomalum) occurred when surface-water TP exceeded approximately 20 µg L-1 and when TN was greater than 550 µg L-1. A stream mesocosm experiment demonstrated that grazing by C. amomalum decreased benthic C:Chlorophyll a ratios, disrupted the continuous deposition of detritus and inorganic sediment, and as a result, increased periphyton P and N content. Variation in grazer effects on periphyton C:P and C:N ratios across the P enrichment treatments resulted in N:P ratios that were greater on grazed substrates in control and low P streams but grazer effects diminished with increasing P enrichment. A second experiment that measured nutrient recycling effects showed that fish-mediated nutrient recycling decreased periphyton C:N and increased C:P and N:P longitudinally in N enriched streams. Additionally, chlorophyll a increased significantly downstream of cages with fish. Comparisons of bacterial biomass production (BBP) and photosynthesis (PS) rates downstream of enclosures indicated that aerial BBP and PS rates and coupling of algal and bacterial production (COVBBP-PS) were all higher downstream of enclosures with fish in high N:P streams. The combined results of these three studies suggest that there are serious biodiversity declines at low levels of nutrient enrichment, and loss of grazing fish species may have important consequences for stream ecosystem structure and function, as grazing fish plays an important role in modulating interactions between surface-water nutrients and benthic resources in streams. Nutrient Enrichment Effects on Stream Periphyton Stoichiometry, Algal and Fish Assemblage Structure, and Grazing Fish-Periphyton Interactions by Jason M. Taylor, B.A., M.S. A Dissertation Approved by the Department of Biology ___________________________________ Robert D. Doyle, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee ___________________________________ Ryan S. King, Ph.D., Chairperson ___________________________________ Robert D. Doyle, Ph.D. ___________________________________ Steven I. Dworkin, Ph.D. ___________________________________ Owen T. Lind, Ph.D. ___________________________________ Joseph D. White, Ph.D. Accepted by the Graduate School December 2011 ___________________________________ J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2011 by Jason M. Taylor All rights reserved h. TABLE OF CONTENTS LIST OF FIGURES .......................................................................................................... vii LIST OF TABLES ............................................................................................................. ix ACKNOWLEDGMENTS ................................................................................................. xi DEDICATION ................................................................................................................. xiii CHAPTER ONE ................................................................................................................. 1 Introduction ......................................................................................................................... 1 General Overview ......................................................................................................... 1 Response of Stream Assemblages to Nutrient Enrichment .................................... 2 Interactions between Nutrient Enrichment and Grazer Dynamics on Benthic Resources .......................................................................................................... 4 Nutrient Enrichment, Grazer Dynamics, and Downstream Nutrient Export .......... 6 Problem Statement ........................................................................................................ 7 Study Objectives ........................................................................................................... 8 Summary of Chapter Content ....................................................................................... 8 CHAPTER TWO .............................................................................................................. 10 Stream Biodiversity Thresholds in Response to Low-level Nutrient Enrichment have Important Implications for Numerical Criteria Development .................................... 10 Introduction ................................................................................................................. 10 Materials and Methods ................................................................................................ 13 Study Area and Field Sampling ............................................................................ 13 Environmental Variables ...................................................................................... 13 Species Assemblage Composition ........................................................................ 16 Data Analysis ........................................................................................................ 17 Ordination and Environmental Vector Fitting ................................................ 18 Generalized Additive Modeling (GAM) ......................................................... 19 iv Non-Parametric Changepoint Analysis ........................................................... 21 Threshold Indicator Taxa ANalysis (TITAN) ................................................ 22 Results ........................................................................................................................ 24 Environmental Variables and Assemblage Structure ........................................... 24 Periphyton Nutrient Content Thresholds .............................................................. 27 Species and Assemblage Thresholds .................................................................... 27 TITAN, Periphyton ......................................................................................... 27 TITAN, Fish .................................................................................................... 34 GAM, Fish ...................................................................................................... 37 Discussion ................................................................................................................... 40 What Landscape Factors Influence P Enrichment-Assemblage Structure Relationships? ................................................................................................. 44 Do Periphyton and Fish Assemblages Respond Differently to P Enrichment? .................................................................................................. 46 What are the Implications for Nutrient Management in Streams? ....................... 49 CHAPTER THREE .......................................................................................................... 53 Response of Periphyton Stoichiometry to Phosphorus Enrichment is Influenced by the Grazing Minnow Campostoma anomalum in Stream Mesocosms ............................. 53 Introduction ................................................................................................................. 53 Materials and Methods ................................................................................................ 56 Experimental Design ............................................................................................. 56 Data Collection ..................................................................................................... 59 Data Analysis ........................................................................................................ 60 Results ........................................................................................................................ 61 Water Column Nutrients ....................................................................................... 61 Biomass and Sediments ........................................................................................ 62 Elemental Composition ......................................................................................... 62 Nutrient Ratios ...................................................................................................... 67 v Discussion ..................................................................................................................