'Nutrient Criteria to Protect Utah's Headwater Streams'
Plenary Speaker |
Abstract: |
Utah’s Division of Water Quality is proposing criteria to protect headwater streams from nutrient enrichment. To protect aquatic life uses in headwater streams where streams are placed into one of three enrichment tiers depending on whether or not ambient nutrient concentrations exceed two nutrient concentration thresholds. Lower criteria of 0.4 mg/L for total nitrogen (TN) and 0.035 mg/L for total phosphorus (TP) differentiate between low and moderate enrichment streams. A higher threshold of 0.80 mg/L for TN and 0.080 mg/L for TP differentiates between moderate and high enrichment streams. Moderately enriched streams require autotrophic and heterotrophic responses derived from empirical stressor-response models to assess biological degradation. Autotrophic responses include gross primary production (6 g O2/m2/day) and filamentous algae (1/3 aerial cover). Ecosystem respiration (5 g O2/m2/day) is used as a surrogate of heterotrophic responses. Recreational uses are also protected based on a statewide survey of algal cover that respondents considered to be desirable (125 mg chl-a/m2, or 49 g AFDM/m2). The underlying science behind these criteria and socioeconomic considerations will be discussed to better inform public comment on these proposed regulations. |
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