|Scaling submersed plant community responses to experimental nutrient enrichment|
Murray, L.; Sturgis, R.B.; Bartleson, R.D.; Severn, W.; Kemp, W.M. (2000). Scaling submersed plant community responses to experimental nutrient enrichment, in: Bortone, S.A. (Ed.) Seagrasses: monitoring, ecology, physiology, and management. pp. 241-257
In: Bortone, S.A. (Ed.) (2000). Seagrasses: monitoring, ecology, physiology, and management. CRC Marine Science Series, 16. CRC Press: Boca Raton. ISBN 0-8493-2045-3. 318 pp., more
In: Kennish, M.J.; Lutz, P.L. (Ed.) CRC Marine Science Series., more
|Authors|| || Top |
- Murray, L.
- Sturgis, R.B.
- Bartleson, R.D.
Detailed mechanistic understanding of how nutrient enrichment leads to losses of seagrasses and related submerged aquatic vegetation (SAV) is still lacking, despite extensive research on the topic. In this study, we compare results from a series of three mesocosm experiments to address how physical and biotic scales influence responses of SAV communities to nutrient enrichment. These experiments, which involved the SAV species (Potamogeton peifoliatus) formerly abundant in Chesapeake Bay, considered the following specific ecosystem scales: (1) fiequency and timing of nutrient additions; (2) residence time of water within mesocosms; and (3) trophic complexity (food-chain length). Ecosystem model simulations were used to help guide experimental designs and interpretations. Time scales of response to nutrient enrichment differed for SAV (8-9 wk) and their attached epiphytes (2-6 wk). SAV growth responses to nutrients varied with season; in spring the above-ground plant tissues were most sensitive, while in fall responses were confined to below-ground biomass (roots and rhizomes). In the fall experiment, continuous nutrient input resulted in greater enhancement of epiphytes and inhibition of plant growth than did identical loading rates delivered as pulsed inputs. This may be explained by the higher biomass and kinetic saturation coefficients of the vascular plants, which favored their uptake of higher pulsed nutrient concentrations. In general, longer residence time of water over SAV beds improved the plant's ability to cope with nutrient enrichment, while faster water exchange rates favored epiphyte growth at the expense of SAV. Although herbivorous grazing on epiphytes partially relieved SAV growth inhibition at moderate nutrient loading, grazing did not significantly alter epiphyte or plant responses to enrichment at higher nutrient levels. A comparison of effects of the three scaling factors suggests that grazing exerted the largest relative influence on the SAV community under moderate nutrient enrichment. However, at high nutrient loading rates, changes from continuous to pulsed nutrient delivery and from high to low water exchange rates both resulted in stronger relative responses than did increased grazing. Results of these studies provide a basis for explaining variability in reported SAV community responses to nutrient enrichment and for extrapolating results from controlled experiments to conditions in nature.