Effects of nutrient enrichment on structure and function of detritus-based aquatic ecosystems
Nutrient enrichment of aquatic ecosystems is occurring worldwide as a result of human-induced changes to global nitrogen (N) and phosphorus (P) cycling. Fertilizer production and application, fossil fuel combustion, and suburban/urbanization have all contributed to increased mobilization of N and P and elevated concentrations of these elements in streams, lakes, and coastal marine environments. Such changes in nutrient availability can have strong indirect effects on aquatic community structure and function because many basal food resources (i.e., primary producers, detritus) undergo large changes in quantity and quality as a result of nutrient enrichment. Our general understanding of enrichment effects is limited, however, because most studies have focused on living plant- or algal-based food webs.
In many aquatic ecosystems, detritus (i.e., non-living organic matter) is a dominant basal resource and provides the energetic basis for diverse and productive detritus-based food webs. In these systems, enrichment may lead to changes that are fundamentally different than what we see in living plant-based systems. For example, enrichment stimulates productivity of microbes (i.e., bacteria and fungi) at the base of the food web, resulting in carbon mineralization - essentially loss of carbon at the base of the food web. In contrast, in living-plant based systems enrichment generally leads to gains in carbon at the base of the foood web (as living plant material.
At the University of Georgia, I was involved in a large-scale ecosystem manipulation in which we experimentally enriched a detritus-based headwater stream. We used a paired-catchment design to examine changes in the treatment stream as well as a reference stream for 2 years before and 2 years during our experimental enrichment.
My research focused on the following questions:
How does enrichment alter flows of carbon, nitrogen, and phosphorus into the food web? What are the ecosytem-level consequences in terms of carbon and nutrient storage?
How does nutrient enrichment alter patterns of consumer-resource stoichiometry in detritus-based food webs?
What are the consequences of nutrient enrichment on invertebrate community structure and secondary production?
Does enrichment alter elemental budgets of detritus-based ecosystems?
- J. Bruce Wallace, University of Georgia
- Amy D. Rosemond, University of Georgia
- Jennifer Greenwood, Tennessee State University
- Keller Suberkropp, University of Alabama
- Jonathan P. Benstead, University of Alabama
- Vlad Gulis, Coastal Carolina University
- Sue L. Eggert, USDA Forest Service, Minnesota