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Aquatic Plant and Dissolved Oxygen Changes in a Reference‐Condition Prairie Stream Subjected to Experimental Nutrient Enrichments
Author(s) -
Suplee Michael W.,
Sada Rosie,
Feldman David L.
Publication year - 2019
Publication title -
jawra journal of the american water resources association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.957
H-Index - 105
eISSN - 1752-1688
pISSN - 1093-474X
DOI - 10.1111/1752-1688.12736
Subject(s) - nutrient , algae , macrophyte , environmental science , aquatic plant , nitrate , benthic zone , phosphorus , photosynthesis , environmental chemistry , diel vertical migration , growing season , aquatic ecosystem , zoology , chemistry , ecology , botany , biology , organic chemistry
Abstract Effects of controlled nutrient additions on a prairie stream were studied using a before‐after‐control‐impact paired design. The site is in a reference condition with low soluble nitrate (NO 3 ) and phosphate (soluble reactive phosphorus [SRP]) in summer (3 μg NO 3 ‐N/L, 4 μg SRP/L). Nutrients were added to two reaches over the growing season at two levels (Low Dose — 39 μg NO 3 ‐N/L and 4.4 SRP/L; High Dose — 119 μg NO 3 ‐N/L and 15.6 μg SRP/L). Continuously measured dissolved oxygen (DO) and changes in aquatic flora were compared to an upstream Control. Enrichment led microalgae and filamentous algae to increase in density, areal coverage, and thickness, and the magnitude of the changes were largely concordant with dosing (more in the High Dose); algal growth also suppressed macrophytes in the High Dose. Enrichment caused significant increases in diel DO swings whose magnitudes were consistent with dosing level. In the High Dose, benthic algae flourished in the growing season and then senesced en masse in fall. The decomposing algae led DO to crash (ca. 0 mg/L on the bottom), but DO impacts were out‐of‐sync with peak algal growth and photosynthesis, which occurred weeks earlier. This finding provides a plausible explanation as to why high DO delta in streams impacts aquatic life even when concurrently measured DO is not low. When DO crashed, DO was longitudinally patchy, some areas having low DO near the bottom, others near saturation. Geomorphology and exposure to wind may have caused this pattern.