Alternative states occur in streams- assessing biofilm community changes along biogeochemical gradients

Andrew Scanlan

February 5, 2009 @ 12:20 pm to 01:15 pm

10 Tyson

Alterative stable states theory predicts biotic communities respond to strong disturbances through non-reversible shifts in species composition, thereby giving rise to relative fixed, new community identity._ Streams are considered relatively open ecosystems that are subject to high rates of species immigrations._ My research tests the hypothesis, that despite their open nature, stable states occur among stream ecosystems likely related to differences in nutrient loads._ A factorial transplant experiment was carried out in two sets of streams in Pennsylvania that reflect biogeochemical conditions through a range of conditions in the mid-Atlantic region. Duplicate artificial substrata (sandstone tiles) were allowed to incubate for about 14 days in three streams of varying production (low, moderate, and high) situated in both the Appalachian Plateau and Piedmont ecoregions (n=24 for each region)._ After the incubation period, the intact biofilms on the substrata were then transplanted (all combinations) to streams of various productivity within each ecoregion._ The transplanted substrata were incubated for an additional 28 days, following which they were retrieved and the biofilms were removed. Chlorophyll was analyzed and a subsample was preserved for further biotic community analysis. Samples were analyzed in order to determine the relative abundance of diatom present (species level determination). In all, 116 diatom species were identified among the 48 samples.__ Hierarchal cluster analysis and similarity indices were used to compare the species composition among experiments treatments._ Univariate Analysis of Variance was preformed on the biofilms chlorophyll and trends indicated that transplanted assemblages would be similar to their new stream._ My results show that diatom communities and biofilm chlorophyll appear to move to alternate stable states along a stream productivity gradient._ These results suggest that streams, behave like shallow lakes when exposed to strong ecological perturbations.