The Problem
Water quality in the South Platte River near the city of Denver, Colorado is of increasing importance and study in recent years. The Metro Wastewater Reclamation District (MWRD) and South Platte Water Renewal Partners (SPWRP), partnering with students at the University of Colorado Denver, have conducted yearly monitoring of chlorophyll-α at specific locations along the river. The goal of this monitoring is to assess whether the establishment of a new chlorophyll-α standard of 150 mg/m² by 2022 is plausible. Chlorophyll-α is a well-known indicator of phosphorus concentration in water bodies and may be measured from periphyton algae sampled from river sediment. High periphyton and chlorophyll-α levels indicate an algal bloom and eutrophic river conditions leading to elevated levels of phosphorus. This decreases dissolved oxygen in the river water, causing toxic conditions for aquatic life throughout the watershed and also negatively affecting human health throughout the city of Denver. Establishing a new daily limit for chlorophyll-α in the South Platte River will lead to more stringent monitoring and treatment in hopes of increasing river conditions and drinking water quality for Denver.
Site map of upstream and downstream sampling locations. Five transects were selected at each location.
The Goals
The Colorado Water Quality Control Division (CWQCD) is responsible for setting regulations to protect the designated uses of state waters. In recent years there has been a focus on regulation of both point and nonpoint sources of nutrient pollution. This includes addressing point and nonpoint sources of nitrogen, phosphorus, and chlorophyll-É‘. Point sources were largely addressed in Phase 1 of the nutrient reduction implementation plan, and the next phase consists of a 10-year plan to reduce nonpoint sources (CWQCD, 2018). A large part of this plan is the implementation of a new chlorophyll-α standard of 150 mg/m² by 2022 (CWQCD, 2018).
This new standard is of interest to MWRD and SPWRP because if violated point source emitters will have much stricter total maximum daily loads (TMDLs) imposed (Chlorophyll-α group, 2019). MWRD and SPWRP want to investigate whether the new standard is currently attainable in the South Platte River in the Denver Metro region. Additionally, they also want to assess the current “Standard Operating Procedures for the Collection of Stream Periphyton Samples” document (CWQCD, 2016). Further refining of these methods will be completed by validating the accuracy of the composite sampling method, refining a sieve method for determination of substrate type by size, and determination of the variability in chlorophyll-α measurements caused by substrate type and flow conditions.