Shade and flow effects on ammonia retention in macrophyte-rich streams: implications for water quality

• Published in: Environmental pollution (1987) Vol. 132; no. 1; pp. 95 - 100
• Main Authors: Wilcock, Robert J, Scarsbrook, Mike R, Cooke, James G, Costley, Kerry J, Nagels, John W
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.11.2004; Elsevier
• Subjects: Ammonia; Ammonia - analysis; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biomass; Ecosystem; Ecotoxicology, biological effects of pollution; Fresh water environment; Freshwater; Fundamental and applied biological sciences. Psychology; Lowland stream; Macrophytes; Nutrients; Nutritional Physiological Phenomena; Plants - metabolism; Retention rate; Rivers; Water Movements; Water Pollution - adverse effects; Water Supply; Retention rate; Ammonia; Nutrients; Macrophytes; Lowland stream; Environmental factor; Biomass; Water current; Retention; Freshwater environment; Water quality; Nutrient; Stream; Aquatic plant
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2004.03.020

Controlled releases of NH 4-N and conservative tracers (Br − and Cl −) to five reaches of four streams with contrasting macrophyte communities have shown differing retentions, largely as a result of the way plants interact with stream flow and velocity. First-order constants ( k) were 1.0–4.8 d −1 and retention of NH 4-N was 6–71% of amounts added to each reach. Distance travelled before a 50% reduction in concentration was achieved were 40–450 m in three streams under low-flow conditions, and 2400–3800 m at higher flows. Retention (%) of NH 4-N can be approximated by a simple function of travel time and k, highlighting the importance of the relationship between macrophytes and stream velocity on nutrient processing. This finding has significant management implications, particularly with respect to restoration of riparian shade. Small streams with predominantly marginal emergent plants are likely to have improved retention of NH 4-N as a result of shading or other means of reducing plant biomass. Streams dominated by submerged macrophytes will have impaired NH 4-N retention if plant biomass is reduced because of reduced contact times between NH 4-N molecules and reactive sites. In these conditions water resource managers should utilise riparian shading in concert with unshaded vegetated reaches to achieve a balance between enhanced in-stream habitat and nutrient processing capacity.