The importance of nutrient co‐limitation in regulating algal community composition, productivity and algal‐derived DOC in an oligotrophic marsh in interior Alaska

• Published in: Freshwater Biology
• Main Authors: WYATT, KEVIN H., STEVENSON, R. JAN, TURETSKY, MERRITT R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2010
• Subjects: permafrost; Alaska
• Online Access: http://dx.doi.org/10.1111/j.1365-2427.2010.02419.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1365-2427.2010.02419.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2427.2010.02419.x

Summary 1. Compared to lakes and streams, we know relatively little about the factors that regulate algae in freshwater wetlands. This discrepancy is particularly acute in boreal regions, where wetlands are abundant and processes related to climate change (i.e. increased permafrost collapse and soil weathering) are expected to increase nutrient inputs into aquatic systems. To investigate how accelerated nutrient inputs might affect algal structure and function in northern boreal wetlands, we added nitrogen, phosphorus and silica to mesocosms in an oligotrophic marsh in interior Alaska. 2. We conducted two in situ mesocosm enrichment experiments during consecutive summer growing seasons, each lasting 24 days. In 2007, we investigated the effects of +N, +P, +Si and +N+P+Si enrichment on benthic algal biomass (chlorophyll‐ a , ash‐free dry mass, biovolume), chemistry (N : P ratio) and community composition. In 2008, we expanded our first experiment to investigate the effects +N+P, +N+Si, +P+Si and +N+P+Si on the same algal parameters as well as productivity (mg C m −2 h −1 ). 3. In both experiments, we measured water‐column dissolved organic carbon (DOC) inside treatment enclosures and related changes in DOC to standing algal biomass. 4. Benthic algal accrual did not increase following 24 days of enrichment with any nutrient alone or with P and Si together (+P+Si), but increased significantly with the addition of N in any combination with P and Si (+N+P, +N+Si, +N+P+Si). 5. Algal productivity (20 mg C m −2 h −1 ) increased between three‐ and seven‐fold (57–127 mg C m −2 h −1 ) with the addition of N in combination with any other nutrient (+N+P, +N+Si, +N+P+Si). Water‐column DOC concentration was significantly higher inside N‐combination treatments compared to the control during each season, and DOC increased linearly with benthic algal biomass in 2007 ( r 2 = 0.89, P < 0.0001) and 2008 ( r 2 = 0.74, P < 0.0001). 6. Taxonomic composition of the wetland algal community responded most strongly to N‐combination ...