Algal biomass accrual in relation to nutrient availability and limitation along a longitudinal gradient of a karst riverine system

Authors

• Mary D Penick ^{1, 2}
• Scott A Grubbs ²
• Albert J Meier ²

¹ USDA-NRCS Field Office, 820 William D. Jones Blvd, Fayetteville, TN 37334, USA.

² Department of Biology and Center for Biodiversity Studies, Western Kentucky University, Bowling Green, KY 42101, USA

10.1186/2008-6970-4-20

Abstract

Nutrient availability influences growth, productivity, and community structure of primary producers. Nutrient limitation, however, results from a deficiency mainly in nitrogen (N) or phosphorus (P) levels relative to cellular growth needs. Limitation is a function of biotic and abiotic factors, the latter including land-use activities (e.g., agriculture, septic systems) and underlying bedrock features. The purpose of this study was twofold: (1) to assess the relationship between algal biomass and ambient nutrient levels along the longitudinal course of a river through a transition from weak to well-developed underlying karst bedrock and (2) experimentally assess if periphyton was N- or P-limited between weak and well-developed karst reaches. Sestonic and Cladophora biomass (=chlorophyll-a) levels increased sharply along the longitudinal gradient. Cladophora biomass, in particular, was strongly correlated with nitrate levels. In contrast, periphyton biomass (=chlorophyll-a) levels were sporadic and did not display a longitudinal pattern. With the exception of ammonia, individual nutrient levels generally increased longitudinally and were higher in the downstream karst reaches. Total N/total P ratios also increased longitudinally and were >25 throughout the study region, suggesting P limitation. The results of the nutrient limitation studies, however, coupled with high concentrations of both N and P throughout the study reach in excess of eutrophication thresholds, suggest that total nutrients are not limiting within the study region. Overall, Kentucky's upper Green River appears to be a nutrient-enriched, eutrophic system and particularly in the downstream, well-developed karst reaches.

Keywords

• Algae
• Nutrients
• Phosphorous
• Nitrogen
• Nitrate
• Karst
• Cladophora

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