R-WD-20-08 New Hampshire Lake Trend Report: Status and trends of water quality indicators Moores Pond, Tamworth, NH June 2020 R-WD-20-08 New Hampshire Lake Trend Report: Status and trends of water quality indicators New Hampshire Department of Environmental Services PO Box 95 Concord, NH 03302-3509 (603) 271-8865 Robert R. Scott Commissioner Clarke Freise Assistant Commissioner Thomas O’Donovan Water Division Director Ted Diers Watershed Bureau Administrator Prepared by Kirsten Nelson, Aquatic Ecologist and David Neils, Chief Water Pollution Biologist June 2020 Table of Contents EXECUTIVE SUMMARY ....................................................................................................................................... 9 1. INTRODUCTION ............................................................................................................................................ 11 1.1 The Volunteer Lake Assessment Program (VLAP)...................................................................................... 11 1.2 Indicators of condition ............................................................................................................................... 12 1.3 Lake Productivity ........................................................................................................................................ 14 1.4 Changing Landscapes ................................................................................................................................. 15 2.0 STUDY DETAILS AND ANALYSIS .................................................................................................................. 15 2.1 Data collection ........................................................................................................................................... 15 2.2 Data analysis .............................................................................................................................................. 15 3.0 RESULTS FOR PRIMARY INDICATORS ......................................................................................................... 17 3.1 Bacteria ...................................................................................................................................................... 17 3.1.1 Long-term trend in percentage of beach advisories............................................................................... 17 3.1.2 Long-term trend in beach advisory days ................................................................................................ 18 3.2 Chlorophyll-a .............................................................................................................................................. 18 3.2.1 Current Condition ................................................................................................................................... 19 3.2.2 Long-term trend ...................................................................................................................................... 20 3.2.3 Short-term change .................................................................................................................................. 23 3.2.4 Regional trends ....................................................................................................................................... 23 3.3 Cyanobacteria ............................................................................................................................................ 24 3.3.1 Long-term trend in cyanobacteria advisories ......................................................................................... 24 3.3.2 Long-term trend in cyanobacteria advisory days ................................................................................... 25 3.4 Invasive aquatic species ............................................................................................................................. 26 3.4.1 Long-term trend in infested waterbodies ............................................................................................... 26 3.4.2 Short-term change in acreage ................................................................................................................ 27 3.4.3 Short-term change in herbicide use ....................................................................................................... 27 3.4.4 Short-term change in alternative control methods ................................................................................ 28 3.5 pH ............................................................................................................................................................... 28 3.5.1 Current Condition ................................................................................................................................... 28 3.5.2 Long-term trend ...................................................................................................................................... 30 3.5.3 Short-term change .................................................................................................................................. 32 3.5.4 Regional trends ....................................................................................................................................... 33 3.6 Secchi Depth .............................................................................................................................................. 33 3.6.1 Current Condition ................................................................................................................................... 34 3.6.2 Long-term trend ...................................................................................................................................... 35 3.6.3 Short-term change .................................................................................................................................. 38 3.6.4 Regional trends ....................................................................................................................................... 38 3.7 Specific Conductance ................................................................................................................................. 39 3.7.1 Current Condition ................................................................................................................................... 39 3.7.2 Long-term trend ...................................................................................................................................... 41 3.7.3 Short-term change .................................................................................................................................. 44 3.7.4 Regional trends ....................................................................................................................................... 45 3.8 Total Phosphorus ....................................................................................................................................... 45 3.8.1 Current Condition ................................................................................................................................... 45 3.8.2 Long-term trend ...................................................................................................................................... 47 3.8.3 Short-term change .................................................................................................................................. 50 3.8.4 Regional trends ....................................................................................................................................... 51 4.0 RESULTS FOR ACCESSORY INDICATORS ..................................................................................................... 51 4.1 Alkalinity .................................................................................................................................................... 51 4.1.1 Current Condition ................................................................................................................................... 52 4.1.2 Long-term trend ...................................................................................................................................... 53 4.1.3 Short-term change .................................................................................................................................. 56 4.1.4 Regional trends ....................................................................................................................................... 56 4.2 Dissolved Oxygen ....................................................................................................................................... 57 4.2.1 Current Condition ................................................................................................................................... 57 4.2.2 Long-term trend ...................................................................................................................................... 59 4.2.3 Short-term change .................................................................................................................................. 62 4.2.4 Regional trends ....................................................................................................................................... 62 4.3 Ice in/ Ice out Records ..............................................................................................................................